I can talk about this now.

Today was probably the biggest day this thread will have as far as junkyard finds go. For the unacquainted to the LSx world, you probably get lost in the land of acronyms and key words (Gen3, gen4, gen5, Iron block, aluminum block, cathedral port, rectangular port, etc.). It gets to be an undeniably long list of engine codes to sort through that I'll leave to the rest of the internet to provide fine detail on, but which one is best for me? How did I sort down the list?

Step #1
It all starts with the key understanding that you have 2 block materials, iron block or aluminum block. It is cheapest and easiest to find iron blocks because GM put them in a huge majority of their van/SUV/trucks from 1999 to 2014, but you get what you pay for. They carry a 50-ish pound weight increase over the aluminum block variants. For someone's already heavy street truck or non-competitively driven vehicle, you likely don't care about weight savings. In this lightweight car, I do... So... I REQUIRED aluminum block

Step #2
With block material selected, it's now down to a displacement decision. 4.8L, 5.3L, 5.7L, 6.0L, 6.2L, and 7.0L were all on the table as OEM displacements for the LSx engines. There is much truth to the "no replacement for displacement" slogan when focusing on naturally aspirated power. I wanted the biggest displacement that I could get to make the most n/a power that I could considering the external dimensions are all basically identical on all of these engines, so lets start at the top, the almighty 7.0L. The 7.0L is the oddball in the lineup that doesn't share a lot of commonality to the other smaller displacement variants and is only found in the LS7 for the C6 Z06. They make great n/a power, but due to some unique block differences that make fitment harder in a miata and the rarity (and therefore very high expense) of them I crossed that one off the list right away. Moving down to the next largest displacement, we land with the 6.2L. 6.2's are relatively straightforward to find either used or new so there's no shortage of supply and other than the aforementioned 7.0L, they are the highest performing n/a power option in the LSx lineup... so I REQUIRED the 6.2L

Step #3
So now that I'm filtered down to aluminum block 6.2L, you have some purchasing options to work through. GM put these in their "premium" lineup Truck/SUVs (...Escalade, Denali, etc) and their sports cars (C6 Vette, Camaro, etc) where the car variant is popularly known as the LS3. New LS3 crate engines are available to purchase, but there is no guarantee that they are of perfect quality AND they are the most expensive ($6.5k+ without accessories AT CHEAPEST). In the name of keeping cost from creeping up into very painful levels, I decided that I wanted a used longblock. You quickly realize that you aren't alone in this used aluminum 6.2L search once you start. LS3's hold a pretty strong premium in the used market, but what about the truck options I mentioned? Well, as it turns out there are 3 engine codes (L92, L9H, and L94) where they are basically known as the "poor man's LS3" put in select trucks. In short terms, GM took an LS3, tossed a long runner intake manifold on it and smaller lift cam in it tuned for low end torque (which trucks need), then they added displacement on demand, VVT, and/or Flex Fuel to them to further improve fuel economy and broaden the torque curve. The savings on a used (more common) L92/L9H/L94 over the relatively more uncommon LS3 is dramatic, well into the multiple thousands! Any perceived benefit that the LS3 had could be easily addressed with modifying a L92/L9H/L94 and still coming out money ahead... so... used L92, L9H, or L94 it is!

Step #4
Which of those 3 do I really want? This link on summit does a pretty good job of comparing/contrasting the differences in them. https://help.summitracing.com/knowle...SR-04851/en-us. That link basically boils down to this chart at the bottom, which I'll share here. All of them have VVT which gets removed with aftermarket cams, so no preferences there. The active fuel management (AFM) would be nice to NOT have if you intend to run the engine with factory valvetrain parts as the active lifters with AFM are known to be issue prone after prolonged mileage, but I'll be upgrading the valvetrain so that column also doesn't matter. For me, the only column that mattered was if it was flex fuel capable or not. If I can get larger injectors than an LS3 manifold has (as I pointed out in a previous post) then why not? Sooo that decision led to the L92 getting kicked out of the running and it put me on the search for a L9H or L94!


Step #5
Just go to car-part.com and start your search using a ~2010 Yukon Denali (or other premium SUV). The website will confirm the engine code as you search and all relevant models get pulled into the results. For my area, I had around 100 L9H or L94 within a 3hr radius of my house. Your mileage may vary (pun intended) on what you are comfortable with buying here, but prices in the greater Chicago region ranged from $1500-$4500 for these depending on condition, mileage, what's included, if they are willing to ship, etc. Mileage seemed to be the biggest factor affecting price, and honestly, I couldn't care less about it given I would be opening up the motor anyways and my experience with high mileage LS stuff has been very positive. I found what I felt was a solid deal on a barely broken in 198k mi L94 in the Northwoods of Wisconsin. They sent me videos of it running before it was removed and it was as good as any other LS I've heard so I was sold. It was fairly loaded as far as accessories go, including everything shown below. Electronics pigtails, sensors, coils, wires, etc can really creep up on you for costs with swap projects as I learned with the K24, so I was happy to find this as complete as it was.




Step #6
Go pick up your new-to-you engine! When I arrived, they had the engine all wrapped up and ready to go. One $2500 swipe of the card later and I now own a 403hp/417tq factory rated motor for the miata (with TONS of aftermarket n/a power headroom). While driving the cammed 5.3L SUV hauling the 6.2L intended for a vehicle close to a 1/3 of its weight, the realization started to hit me that this build thread is going to get very stupid in a great way. Compared to the $1100 that I spent for a 205hp/166tq factory rated K24 WITHOUT accessories, this engine deal seems like robbery.


Hoping to get the engine off the trailer and onto the engine stand next for the inevitable teardown and upgrades!

 

I am excited for this. And thank you for the LS education! They’re too rich for my blood, never knew that stuff. Except did I miss the square vs cathedral port?

 

I didn't get into that detail too hard, but as long as I'm on the LS education topic, here we go!

Square vs cathedral port refers to the intake port shape on the cylinder heads. 3rd generation GM small block (aka, Gen3) was released to the public with the C5 Vette in 1998 with the 5.7L LS1. They carried that Gen3 architecture into trucks in 1999 with the 4.8L and 5.3L and it basically snowballed into every v8 vehicle they made shortly thereafter. All Gen3's had cathedral port heads (as can be seen on the right by the image below). GM played around with 4.8L, 5.3L, and 6.0L displacements in the Gen3 architecture with various combinations of steel vs aluminum block, cam options, compression ratio options, etc but there was not a major update beyond those in car and truck v8 variants until the 4th generation small block (Gen4) was launched. With the Gen4, some service improvements were made. Knock sensors moved from valley cover to the sides of the block in easier to access spots. Cam sensor moved from the back to the front timing cover, and trigger wheel updated from 24x to 58x. Pistons and rods were strengthened. ECU capability was increased by addition of more closed loop controls, DBW throttles, VVT, flex fuel, displacement on demand (also known as active fuel management). Maybe most notably, the rectangular port on the heads was developed. GM launched the rectangular port heads with their most prestigious model first (the LS3 C6 Vette in 2008). This port is shown on the left and is a biggest reason why the 6.2L LS3 (Gen4 rectangular port) makes 430hp/425tq and the previously most powerful 6.0L LS2 (Gen3 cathedral port) only made 400hp/400tq. The best flowing cathedral heads flowed 250 CFM whereas rectangular heads flow 317 CFM. That flow difference is far more impactful to power than the 0.2L displacement difference.


Not to get too far into the weeds, but a Gen3 and Gen4 stuff was fairly interchangeable. GM took advantage of that and definitely got their money's worth out of their designs. GM had multiple years of overlap where certain engines had cathedral port and others had rectangular ports. Here is a nice breakdown I found of the full alphabet soup of engine models that got various heads. The easiest way to think of this is, anything 4.8L/5.3L/5.7L always got cathedrals. 6.0L depends on year/model, and then everything 6.2L whether it was n/a or boosted was rectangular.


Why the mix and match? Well, the answer is somewhat simple... On the smaller bore (<4") that those lower displacements had, the cathedral port heads made more torque. Trucks need intake velocity to make torque at low rpm, so the cathedral ports fit this well. Not flowing as much air in the higher RPM range was a fair trade off. The more powerful and expensive to build 6.0 and 6.2 truck variants that did get rectangular ports were saved for higher end / more premium models as a sell point (which is what I grabbed with my L94). In the sports car performance realm, moving to the rectangular ports is a no brainer. Shown below is a 6.2L with rectangular ports (red) vs cathedral (blue). After 4000rpm, it's game over for the cathedrals and party time for the rectangular heads all mods being equal in comparisons. It is worth noting, this graph is showcasing a 6.2L with an aftermarket cam and longtubes on an engine dyno with no accessories on it. Taking ~50hp/tq off for chassis dyno losses is quite reasonable, so it's not super uncommon to see full bolt-on N/A rectangular port 6.2's make 480-520whp depending on intake/cam selection and how you want your powerband shaped... If you want more than that while still N/A, you get into the point of diminishing returns for your dollar and a bit more exotic with head porting, compression increases, specifically tuned intakes, expensive valvetrain, and higher revs.


Now, I didn't touch on it anywhere in my last 2 posts, but GM did launch Gen5 architecture with the introduction of the 2014 C7 corvette. The 6.2L LT1 in the base C7 made 460hp/465tq, which is impressive numbers. How'd they do it? well.... there was yet another round of improvements made over Gen4. The biggest change made to provide that 30hp/40tq increase over the Gen4 LS3 was again in the heads. They changed from port fuel injection to direct fuel injection and further optimized the runner shape, valve sizes/angles, etc. Cooling the charge air directly in the cylinder via direct injection is much more volumetrically efficient, allows you to bump the compression up, and you also get better fuel economy / emissions overall. So what's the catch and why don't people swap LT1's in their cars because they are "better"?

well, this is my take on it.. Gen5 is deep into the point of diminishing returns for performance for the dollar. They are expensive to find given they are relatively new. Aftermarket parts are also more expensive on the order of nearly 2x compared to Gen3/4 parts in my experiences. Direct injection can be limiting on power potential, expensive/harder to control, and can lead to maintenance challenges like intake valve coking. It's a lot of people's opinion (including mine) that finding a used 6.2L Gen4 and tossing an aftermarket cam in it is simply a better HP/$ value while also generally being more simple and reliable.

 

Thanks for the education on the LS variants/engines and head differences. Very cool! I'm an LS noob so very much appreciate the education. That cammed rectangular port head doesn't even look like it's giving up too much low end.. 400 lb ft at 3k rpm.. whew..

 

Padlock, I'm not sure if you've seen the old Roadkill episode where they towed a boat to a lake, swapped the 350 from the truck into the boat in the parking lot, took the boat out for the day, swapped the engine back into the truck in the parking lot and then towed the boat home.

If we don't see a track day where the engine from the Suburban gets swapped into the Miata in the parking lot and then back I'm going to be disappointed

Exciting stuff! Can't wait to watch this one develop.

 

The history lesson I didn't know I needed! Thanks for sharing all that knowledge on the platform. And here I was thinking I was kinda cool for knowing the differences in BP specs over the years

Can confirm, that was a brilliant episode haha. Gonna have to put some of that show on later tonight.

 

I keep meaning to post I'm here, but have a habit of reading this forum on my phone and never jumping on a proper keyboard to reply. But a huge +1 on the thanks for the LS education. It was really helpful in general and definitely expanded my knowledge.

 

Keep in mind, the optimal head to use depends on the displacement you are running (and the torque curve you want). I can't seem to find a direct comparison online right now, but you'd see that cathedral port would notably outperform rectangular port under 4000rpm when used on a smaller 4.8L or 5.3L engine. When you are using the larger 6.2L displacement, there really isn't much of a downside to the rectangular port as the dyno chart above shows.

I'll be honest, the more likely scenario is the tow rig breaks down for some reason, so I'd need to pull the motor from the miata and put it in the Suburban (...which come to think of it, I wouldn't be opposed to ). It may prove quite helpful that the tow rig will be a functional parts vehicle for the car and vice versa.

 

I love to read your condensed knowledge posts. Thanks for another one!

It's disappointing to see what you got for your money when you can be flexible in your choice of engine, and it's readily available. I'm almost ashamed of what I paid for a VVT Miata engine in comparison.

Some time back I read an interesting article on modifying port vs direct injected engines made me consider it from another light - consider the total mass flow of the intake port. In a port injected engine, some of that mass flow has to go to fuel vapor and droplets. Not so in a direct injected engine, it only has to move air through the intake port and valve. When they ran the same engine in port injection vs direct injection, they found the power difference to roughly correlate to the percent of mass flow that was taken up by the fuel. And that trend continued when they tried different fuels that needed different air:fuel ratios. So if a fuel needed a lower air:fuel ratio (more fuel volume for the same amount of air) to achieve stoich combustion, the power gain for direct injection was proportional to how much extra fuel had to flow through the intake port and thus limit the amount of oxygen entering the cylinder. Neat stuff! Sadly I doubt I could find that article again.

 

I'll be real.... For having owned NA/NB miatas for well over a decade now, I feel like I should know more about BP's than I do. I never felt the need to deep dive into them as the N/A recipe for power just changed the car from being "slow with a heavy wallet in my pocket" to being "slow with a lighter wallet". I was content with my bone stock BP4W in this car for years as I developed the chassis/aero setup it has now. The higher power recipe (<350whp) is pretty straightforward with a turbo kitten helping out and key upgrades. Anything over 350whp I feel makes sense to consider other powertrains like I'm doing here.

Don't feel too bad. A VVT swap (while definitely a lower hp/$ gain than LSx) still pales in comparison to the total dollars that will be dumped here (or like were previously dumped on the Kswap). I'll have a full spreadsheet laying out the costs of this v8 transition that I'll share once completely populated. There's still missing pieces that I'm working to populate as I plan this all out.

There are a lot of really good SAE articles out there, but what you are describing here is EXACTLY what I was referring to as far as Gen5 VE improvements go with the direct injection change on the GM small blocks. Fuel not taking up "airflow space" in the port is a key part of that VE improvement. Having the cooling effect of fuel atomization right in the cylinder where combustion occurs does an awesome job of preventing knock as well. I had a 2.0L Cobalt SS Turbo (LNF engine) in college and with the DI that it had, I was running 20psi (34lb/min airflow) on its K04 turbo at a .87lambda (12.8:1) AFR on 91 octane without a knock ping in sight. Meanwhile, port injected BP's barely run that lean of an AFR at WOT when naturally aspirated. Pretty awesome on how lean you can run DI stuff without much for negative consequence. Having to clean intake valves as part of "standard maintenance" sucked though

 

+1 on what all the above guys said, thanks for the LS lessons! Why you ever went K-swap is a mystery we'll never solve...

 

9 years ago, I distinctly recall telling the guy I bought this car from that my plans were to LSx swap it, but I can tell you why I gave the K-swap a shot.

1. 5 years ago when the ZF trans upgrades were becoming the new drop-in hotness, it was VERY intriguing to do what I did in phase 1 of the build, enjoy it for a while n/a, then eventually build it into a turbo K24 in phases of driveline upgrades. Not having to dump all the money up front was interesting to me.
2. 5 years ago, the K-Swap didn't cost an eye watering $16k+ MSRP like it does now. I got deals on my parts over a 2 year span and my cost was not a whole lot more than very well sorted turbo BP cars. The small premium I paid seemed like a good tradeoff to not deal with cooling issues. Looking back, I still have zero regrets on that call.
3. The K-Swap is relatively drop-in and go. Zero chassis modifications needed to complete the swap. I didn't have much time to devote to the car as I was in the midst of early life milestones (home renovations, engagement, wedding, having kids, etc). I wanted to spend time that I did have driving the car, not wrenching.
4. I never owned a K24, but the idea of a higher revving inline 4 like my sport bikes in a nimble NB chassis was intriguing. You don't know if you like it unless you try it, right?

So what changed now? Well.... going back to the bulleted items:

1. The K-Swap driveline solutions are plagued with driveline vibration issues that I don't want to even think about. So glad I didn't try to be a guinea pig there to test unproven parts. Plenty of threads here on it and a few of you (ahem Zak) are reading this I'm sure with PTSD. If I'm spending thousands of dollars on a specifically designed solution that is tailored to exactly what I need, it better be flawless... it hasn't been... screw that.
2. Cost increases have inevitably occurred with KPI putting the K-swap now within the reach of what it costs to do a DIY LSx swap. Who would want to spend $16k+ for ~230whp when $20k can comfortably set you up in a 350-420whp LSx swap or $8k places you in a well sorted ~250whp BP? The value proposition that the K-swap had in the earlier years has began to all but evaporate in my eyes. Converting your N/A Kmiata to a Boosted Kmiata is an equally painful cost adder that was too hard for me to justify.... which wasn't the case when I first swapped the car.
3. Life keeps changing for the better. I have been lucky enough to be able to upgrade to a newer/bigger house recently (...no more renovations). The family is all happy/healthy and our careers are going well. I'm counting my blessings here. After kids go to bed, I now have late garage nights to myself to take my time and dive into the needed chassis modifications, which is "me time" that I didn't really have before. If this takes 1 or 2+ years I don't really mind as I'm enjoying the build process to create something that will make even seasoned v8 swap miata guys go "what the hell is he doing" [[foreshadowing....I have had A LOT of time to think about this...buckle up!]]
4. I can now say I've owned a K24 and got that out of my system.. I didn't have negative experiences with the setup, but the car triggered more of a mellow "this is how the car should have been built" reaction than I was expecting, which left me wanting more... and so here we are, installing "more" of what I feel the car needed.

 

Have a cat. That is a very persuasive analysis, and I will be interested to see if anyone challenges it.

FWIW I have gone the 'well sorted turbo BP' route, it cost me a whole lot more that $8k, even $8kusd, but I just paid someone to do it due to my life circumstances. So instead of having a workshop full of bits and pieces of turbo MX5, I am driving it. Just another permutation on the above choices.

 

Jumping to progress!

Made it the 3 hours home without a hiccup on Friday. Instead of wrestling the engine on a hoist by myself with all the accessories and wiring in the way, I decided to quickly strip off items while it was sitting on the trailer. Did you ever hear that LS engines are easy to work on? Well, I'm here to confirm to you that yes, they are brainlessly easy to work on. 30 mins with my M12 ratchet wrench, 10mm socket, and 15mm socket and I had the truck alternator/power strering bracket off, the AC compressor bracket off, the engine mounts, the full engine harness, the plug wires, coils, exhaust manifolds, and evap system all cleaned off.

The only issues that I ran across from disassembly were breaking off 4 of the 12 exhaust manifold bolts in the aluminum head. This is a relatively common thing to prepare yourself for on higher mileage motors as the OEM bolts get pretty crusty after so many heat cycles, so just be aware. My suburban had 2 broken bolts that I had to weld a nut onto in order to remove. Not a huge deal overall as new hardware will be installed with new headers, but plan on at least one breaking off. If the LS Gods bless you with all 12 manifold bolts coming out cleanly on a 150k+ mi motor, go buy yourself a lottery ticket and hope they bless you there too.


After much delicate solo hoisting, I managed to get it in the garage.


Jump to tonight, I figured now is as good of time as any to take advantage of child labor teach the 10yo on how to build things. I have vivid memories of working on farm equipment with my dad as a kid, and a lot of that carried into why I went into mechanical engineering as the curiosity on how/why things worked has never really died. sentiment of my own aside, we took the intake manifold off then figured out how engine hoists work


We then figured out how to transfer an engine from the hoist to the stand and quickly realized we didn't have bolts the right size to mount the stand to the engine. One quick hardware store run solved that (M10x1.5x70mm is the bolt you need for my Harbor Freight stand). He had questions on what things did, so I got to give the brief "suck, squeeze, bang, blow" theory of 4 stroke engine operation. In this photo you can see the knock sensor mounted to the side of the block yet. There is one just like it on the opposite side, which is one of the telltales that this is a Gen4 engine if you are paying attention to my LSx educational crash course the last few posts.


The water pump and crank pulley on this L94 truck motor are truck application specific, so they both gotta go to make space for car based accessories that are slightly lighter, lower profile, and offset closer to the block to save space. I'll be using the vette/camaro LS3 based stuff. This is all pretty simple.... so easy, a kid can quite literally do it.


Six 10mm bolts removed later then a few dead blow taps and the pump comes off, leaving us with nearly a bare L94 longblock. More education coming here soon, but with the water pump assembly removed you can now see the VVT solenoid built into the timing cover right above the crank pulley. The trucks had VVT, but the LS3 cars did not. You'll note that all GM v8 engines are single cam pushrod motors. VVT has the most benefit in dual overhead cam scenarios where you can phase the intake and exhaust cam separate from one another. A majority of the performance and fuel economy gains with VVT come by phasing the intake camshaft to optimize VE of incoming air to the combustion chamber. Exhaust cam phasing is not nearly as impactful as high pressure exhaust gases evacuate quite effectively. This is why the VVT BP motor has a phaser on intake-only and NOT exhaust. In single cam application, the performance gain by adding VVT is really quite minimal as when you are phasing the intake, the exhaust is also phasing the same direction when you'd prefer to have it stay fixed. In short, VVT is there on single cam motors more for a mild MPG improvement than any other reason (thanks EPA).


VVT on the LSx engine really limits you on performance camshaft options as the bolt pattern on the VVT cam gear (behind the timing cover) is unique. VVT (if kept) is also another solenoid to control via the ECM for not much benefit, so it's VERY common to just remove VVT, say screw the fraction of an MPG improvement I'm losing, and use camshafts developed for the performance cars (like the vette/camaro) that never had VVT to begin with. Remember, this L94 truck motor of mine was tuned for low end torque with a tiny cam and as much fuel economy as they could squeeze from it (hence the VVT). Giving up low end torque in exchange for more top end horsepower is all part of my plan and the VVT-delete and cam upgrade is part of that story. Before I can get the timing cover off, I need to remove the crank pulley. I don't have a crank pulley removal tool of my own, so that's in my Amazon cart to be ordered shortly as part of next steps.

 

Ya I figured as much, but didn't wanna clutter your thread up with too much banter. A more "low end cam" and smaller displacement probably benefit from the smaller port and result in a nice fat low end. I'm sure the dyno of the cammed rectangular port might be "weak" on the low end for a lot of LS guys, but us import guys are still drooling at 400lb ft at 3k rpm.

I totally get (and agree) with your assessment of the LS vs the turbo K. I started on the miata path because "miata is a cheap track car." A whole bunch of money later with additional expenses, it's definitely not "cheap." I think the moral of the story is it never is to do it right. With that said, I'm happy with the turbo BP and hopefully this car stays reliable on track for a while (low 200whp is fun and I'm gonna stay here a while). I'm intently watching your thread though as tossing an LS in down the road (5-10yrs from now) is definitely in the back of my mind.

Cool to see your son wrenching too! My son is 9, and I'm sure he'll be taking it to an auto-x one day. Definitely adds to the fun when the kiddos can join in on the activities. What's always interesting to me is how versatile these domestic V8 engines are. How the LS can be fitted to a truck and make good low end power with the same head casting as the corvette and the big difference is just "bolt ons" (cams, IM, exhaust, etc). The same goes for the Ford V8's as well. That's a big advantage as they're very plentiful and many parts are cheaper.

 

Someone's gotta take some of your KP vs Turbo BP vs LFX vs LS/etc post and sticky that information. Great analysis and it really drives the point home that there's a very specific cost/path of least resistance for achieving a certain power level with maximized reliability. Now if only we all knew exactly what power level we'd be happy with when we started our projects, lol. If I knew everything I know now (which still isn't a lot, I probably would've bought a slightly bigger turbo for my previous Miata, capped power in the low 300's, showed some more mechanical sympathy to my 6 speed in 4th gear, and grabbed five backup transmissions instead of spending the same money on the KP/BMW trans kit. Instead I ended dumping that car due to the headache/lack of ability to track it...

Love the continuum regarding LS motor operation and characterization. Those motors with the VVT cam also had a separate EGR system, right? Single cam VVT always intrigued me due to the fact that advancing timing for fuel economy eliminates the ability for the VVT system to create psuedo-EGR (which is done by retarding exhaust cam timing). We (Ford) currently have a 7.3L pushrod V8 for the F-super duty trucks that sports VVT, with no EGR system. Dunno how they're getting around that for emissions, but it always interested me.

Anyways, now that I've commented on the most boring part of your new badass engine...

 

Ain't this the truth... I'll admit that what I'm doing is probably a bit nuclear as I'm now at the point of just overkilling it knowing that I will have DBW to easily tame the beast down a bit if I deem that necessary.

No EGR on most Gen3 (early 98-00 LS1 is exception) or all Gen4 LS engines. You have to keep in mind that all EGR is really there for is to reduce NOx emissions. There are a lot of creative ways to reduce NOx and EGR is one them by simply introducing an inert gas into the cylinders. As combustion chamber designs (more efficient mixing of fuel/air), piston designs (pushing top ring land up for less residual), ECM capabilities (fuel/spark control), fuel injector design (better atomization), and exhaust catalysts (closer proximity to head for faster light-off) have developed for the better the need to use EGR as a NOx preventative measure has been reduced. I'm sure a combination of those things is what Ford did on the new 7.3L. As previously mentioned, GM moved to direct injection with the Gen5 V8. I feel a majority of the reason for that was performance targets, but improved NOx emissions from the previous Gen4 is likely a side benefit.

 

I'm deep into research on this topic, so as long as it's fresh on my mind, let's talk camshaft selection shall we?!

[[I warned you that I'd jump around on topics here....]]

As mentioned, the plan is going to be removing the VVT and transitioning to a fixed cam. 2 reasons why: To simplify and shift powerband from truck low-to-mid range efficiency zone to a performance mid-to-high range efficiency zone while maximizing performance and maintaining reliability in road course application <- this is important. LSx camshaft shopping opens pandoras freaking box of pain and misery as there are probably more cam/pushrod/rocker/spring combinations possible than total V8's GM has produced since its founding in 1908. Seriously, if you thought engine selection was bad, this is that x10

So let's get into it... Just to start conversation, it's worth understanding what GM has used for cam specs on their N/A 6.2L Gen4 V8's (which remember all have rectangular port heads). Power ratings are shown as reference. Specs are listed by duration (in degrees, with intake first / exhaust second), then lift (measured at the valve <- this is important, with intake first / exhaust second), then lobe separation angle (LSA) which basically influences valve overlap. Helpful diagram here...



Stock L94 cam specs are 198/209 0.500"/0.500" 115LSA (403hp/417tq)
Stock LS3 specs are 204/211 0.551"/0.525" 117LSA (430hp/425tq)
"Hot Cam" LS3 crate specs are 219/228 0.525"/0.525" 112LSA (495hp/473tq)
"525" LS3 crate specs are 226/236 0.525"/0.525" 110LSA (525hp/486tq)

From the 4 engines I somewhat randomly cherry picked, you can start to see 2 key trends. Duration the valves are open seems to dramatically affect HP/TQ and GM doesn't seem to push beyond 0.525" of valve lift on their 6.2L engines. Focusing on the duration topic first, holding valves open longer lets air in (and out) more effectively. I don't think that takes a ton of explaining here for why that is, but just realize there are limitations to this. GM must meet emissions targets (even with their crate engines!) so the amount of overlap (where intake and exhaust valves are both open) is minimal in order to achieve this. You can observe this by seeing that as durations increase, the LSA decreases. They are trying to keep overlap minimized to some extent, so you see most n/a cams with 220-23x duration in 110-113LSA ranges. Boosted applications can take advantage of more overlap, so you'll see turbo/sc cams as high as 117 LSA with similar 220-23x duration ranges. Adjustable cam gears used on DOHC engines (like the BP) basically allow for LSA tweaks between intake and exhaust, which is why they are popular. Single cam motors don't get that advantage as you get whatever LSA is ground into the single camshaft. The 0.525" valve lift limit I will get to shortly, but before I do, it is worth studying one of the more popular aftermarket cam companies for LS stuff (Brian Tooley Racing - BTR). Note, there are tens (if not hundreds) more aftermarket cam companies out there that offer what they think is the "best".

BTR has LS n/a stage cam kits, which are as follows:
Stage 1: 217/23x 0.619"/0.607" 114LSA
Stage 2: 221/24x 0.624"/0.636" 112LSA
Stage 3: 227/24x 0.636"/0.636" 111.5LSA (512whp/476wtq)
Stage 4: 233/25x 0.636"/0.636" 113LSA
Stage 5: 235/25x 0.646"/0.646" 111LSA (600+hp... max effort silliness)

Their stage 3 (S3) cam has very similar intake duration as the LS3 "525" cam, but the valve lift is 0.636" for In/Ex vs only 0.525" for the LS3 "525" cam. The extra lift allows more air in (or out) for the given duration the valve is open so it makes logical sense that the BTR S3 cam is making close to the same power TO THE TIRE that the LS3 "525" cam was rated for AT THE CRANK. It would be easy to say, "hell yeah, gimme the stage 3 bro. Don't overthink this Matt" but I must stay true to my nerdy engineering ways and overthink this. Why wouldn't GM have increased lift on the LS3 cam and gotten all this free power.... one word: reliability. As valve lift increases for any fixed duration the acceleration (and force) the components in your valvetrain must withstand also increases. There are a slurry of unintended consequences that can come with picking a camshaft that's too aggressive for your setup, but most of it boils back to reliability as a tradeoff. Many muscle car guys selecting these aftermarket camshafts are drag racers (or street cruisers). Time under load or high RPM is a small fraction of what road race application sees, and that application is what I'm building for. Quick math tells you that 100hrs of track time is close to 36,000 (yes, THOUSAND) 10 second passes!!! I do not want to be rebuilding this motor often, so sticking within limits that GM has deemed acceptable for engines that they warranty seems like a great place to stay within as I trust their judgement and validation much more than any aftermarket company. The 0.525" valve lift on the LS3 "525" cam is a nice reference, but did GM ever warranty anything more extreme that I could refer to to get more performance? You bet they did!!

So now we jump back to the almighty Gen4 7.0L LS7. It had larger (and therefore heavier) valves to control while also using more aggressive 1.8:1 ratio rockers (instead of 1.7:1 ratio rockers used nearly everywhere else, like on my L94). Stock LS7 cam specs are 211/230 0.591"/0.591" 121LSA (valve lift rated with 1.8:1 ratio OEM LS7 rockers). This engine was factory rated at 505hp/470tq

My above conclusion: GM warrantied the LS7 with nearly 0.600" lift while being "more aggressive" than the LS3 valvetrain layout. If they were comfortable doing that on that engine, then I can feel pretty comfortable that targeting for 0.600" of valve lift as my upper limit should be safe for what I'm doing. Soooooo... the search began... Find a cam that is somewhere around a 225-235 intake duration, 235-245 exhaust duration, and max 0.600" lift with 110-113LSA. This basically blends the LS3 "525" cam and BTR S3 cam duration and LSAs that know perform well, while also staying within the lift limits that should be relatively safe for reliability per LS7 design, being better than LS3 lift spec for performance that I know is left on the table with the LS3 "525" cam, but not being as extreme as BTR S3 lift spec where I was worried about failures from accelerating valves and lifters too quickly. This should nestle me in damn close to the illusive 500whp power goal of mine if you take the BTR S3 chassis dyno plots and de-rate it a bit for a bit less valve lift that I'm planning for.

I did run all this past the Harley Davidson valvetrain veteran at work whom I'm good friends with (perks of being in OEM powertrain job) and he mentioned this logical process of "reverse engineering" based on specs is likely the best that any DIY'er like us can do when reliability is in question. Cam profiles and how they affect valvetrain behavior get extremely complex and we spent a TON of money validating lobe shapes at work. Nobody that actually spends the time (and money) to do that publishes the information so at some point you are left make educated assumptions exactly like this...

[[so insert much Google usage here after many evenings]]

...and I found this cam!
https://www.texas-speed.com/p-8578-t...-camshaft.aspx

LS7 cams physically fit in the 6.2L blocks, but they are simply spec'd assuming different rocker ratios... remember when I said "spec'd at the valve" was important? Thats why... rocker ratio assumption affects valve lift
Published specs on this LS7 based cam are 234/246 0.635"/0.635" 112.5LSA (assumes LS7 1.8:1 ratio rockers).
When you convert it to the 1.7 ratio rockers that my L94 engine has, you simply take 1.7/1.8 (94%) of the lift value from before, leaving you with the following resultant cam spec 234/246 .596"/0.596" 112.5LSA.

So yeah... I found my cam that I want... Now I ONLY need to sort out pushrod, rocker, and spring upgrade options.

 

Nice writeup. I'd be doing a compression test on that motor before you go too much farther. That's just me.

I went with these for a trunion upgrade. The needle bearing based trunions on most stock LS engines is a weak point. https://www.texas-speed.com/p-5982-c...-bushings.aspx

The CHE guys even sent me new bushings free after I overheated on track. Sent them my old ones so they could analyze the wear.

 

The note on compression testing is a logical one, but that's where I'm going to draw the line in the sand and use my potentially unreasonable judgement. I need to remove heads to replace the lifters no matter what. If the bores on this engine look anything like the bores on my suburban with 232k on it, I'm just going to let it ride. I expect this 198k mi 6.2L to be more tired than something completely refreshed/new, but once you start digging into every fine detail on a used motor, you can quickly find yourself replacing everything, at which point buying a new motor to begin with can make more sense. I have zero desire to touch the bottom end (crank/rod/pistons/bores) or any of the main, rod, or cam bearings... so for right or wrong, that's where I'm drawing the line here in the name of staying on a junkyard engine budget... If a year or two down the road (after the swap is running) I want to build a bottom end, that seems like something fun to do on the empty engine stand while still enjoying the "tired" higher mileage motor in the car.

Shown below is one of my suburban bores immediately after removing the head.. cross hatching still visible in all 8 holes with nearly a quarter million miles and this story hasn't been uncommon for the higher mileage motors I've opened.. I have faith this 6.2L with 34k less miles will be similar.


Good call out on the trunnions. I will get to that detail in a future post, but be happy to know the CHE parts are already on the spreadsheet of parts to order!