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Lean burn is very much a thing to strive for thanks to emissions regulations, but can be challenging to successfully implement on a budget without making your emissions worse. The whole concept behind it is to use less fuel per combustion process = less hydrocarbons = better mpg. The burn rate (flame speed) of an A/F mixture is faster when running at leaner ratios (which is desirable as you ideally would like all of your A/F mixture to combust at once), but as a downside, a lean mixture burns hotter and has tendency to form more NOx, which then requires complex catalytic converter systems to reduce the NOx to acceptable levels before exiting the tail pipe. There are a lot of fueling strategies that OEM's are playing with to try to find that "ideal" balance point, but I'm not going to get into all of that.. it's very complex and we rely on computer models to help guide us along.

The ideal state would really be to have all of the A/F mixture combust at once where you don't have to worry about burn rate. This is called Homogeneous Charge Compression Ignition. Google it, it's neat tech, but still in the infant phases of development. To my knowledge, no OEM has gotten this to be a production viable option as its extremely sensitive to temperatures, A/F mixture, compression ratio, etc.

Curly pretty much nailed it. It comes down to costs and market availability for upgrade parts. Many of the DI systems rely on fuel pressure from the high pressure fuel pump (HPFP) to increase flow. The most efficient way of getting fuel pressure north of 2000+psi in the DI rails is to have a HPFP driven from an additional cam lobe. Depending on your engine, HPFP upgrades may not be available.

• Some companies have created larger lobes on the cam that drives the HPFP, but many times that comes at the expense of HPFP reliability long term.
• Larger HPFP's are becoming a more common thing in the Ecoboost community, but they can get pricey.
• Larger DI injectors are also quite hard to come by. Unless you get lucky and the engine you are talking about has a higher HP brother offered by the OEM (like LFX having the LF4), you probably won't find bigger injectors out there to help you.

So if you can't cost effectively upgrade your DI system, adding PI to a DI system is very much becoming an attractive option for enthusiasts. As curly mentioned, its pretty easy to tap a T into the low pressure fuel line to feed PI injectors. They could be controlled via piggyback or if you get a fancy enough ECU, you can control both PI and DI from the same unit. From an overall cost and complexity standpoint in a race environment, there is some level of attraction to swapping from DI to PI completely like Ryan is doing instead of running a hybrid DI/PI system. The "Keep It Simple Stupid" mindset is something that can't be ignored in the track environment in my opinion.

Extra injectors with piggyback controllers can and have been done successfully. One that comes to mind is the LNF engine found in the Turbocharged Chevy Cobalt.. You run out of fuel from your DI system around 400whp (depending on fuel type), so to get more they just toss an injector into a throttle body spacer which fogs the entire manifold with additional fuel over the top of the DI system. It also has proven to help keep intake valves cleaner, so it's got a side benefit to run from a maintenance standpoint.
https://zzperformance.com/products/l...tor-controller

ThePass

iTrader: (3)

Awesome info being shared here.

I considered several options when deciding which way to go on this. I quickly threw out the idea of a single auxiliary injector pre-throttle body for fear of uneven distribution between cylinders. I considered adding PI while retaining the DI, controlled by something like the split second system, and that would be an attractive option for a street car that wants to retain the factory ECU and systems, but it didn't make sense for this application - an added layer of complexity and still stuck with the limitations of the GM ECU.

I don't speculate on dyno numbers any more than I speculate on lap times (i.e. never ). But, the supercharger is currently off the motor, and I plan to get the Haltech up and running and work through setup on the majority of new systems before reintroducing boost. So there's a good chance I'll end up dynoing the car while NA as part of that process. However, it's unlikely that I'll be at the same dyno as I have been previously, and there will be some other variables that will have changed. For example, with the change to a universal ECU, it didn't make sense to retain the GM throttle pedal and TB and have to work out the calibration and quirks of those - far easier to convert to a well known TPS and DBW TB. So I now have a TPS on the Tilton throttle pedal and made an adapter to fit a Bosch throttle body from a Porsche 997 application to the LFX intake manifold:

cordycord

iTrader: (2)

LOVE all this extra information, and love this picture. Your idea of making things simpler may not resemble other people's thoughts on "simple."

Oh4One4

So. I have a slightly off topic question for you. Since you not using the OEM trans, or management, or anything anymore at this point, and since the car has been down for over two years, do you ever wish you just went with an LS?

ThePass

iTrader: (3)

Nope. For two very different reasons.

A) No way to avoid that the V8 is two cylinders longer. I can't move the engine through the firewall in Limited class, so those extra two cylinders would hang past the front wheels and be worse for weight balance. If I reach a point where I determine the juice isn't worth the squeeze to get the LFX to my power targets, I have a plan B in mind (always thinking several steps ahead), but an LS wouldn't be it.

B) Going the path less traveled has given me a ton of opportunity to face new challenges and learn and grow as I work through them. This car has been my university for the last 15 years. Wouldn't trade that for anything.

I've probably said it before, but to reiterate... the LFX is an amazing option for an out-of-the-box reliable and under stressed 300whp. If I were building a car for just driving enjoyment, I'd leave it as GM intended it and run it all day. There's more to an engine package than a power number, and the LFX has just the right amount of low end torque and smooth delivery to make the car really alive yet drivable. The only reason for all the extra hassle documented here is because this car's goal is to compete against big power TA cars and exotics at a FIA Grade 1 Formula One track (read: massive straights where nothing plays to the Miata's strengths).

Oh4One4

For some reason I forgot you were still in Limited. That's all fair, even if you're hanging hanging a super charger off the front of the engine and adding an intercooler. It should still weigh a bit less than those extra two cylinders. Fab experience is worth its weight too. Very excited to see it back out turning laps.

txbdan

Any new updates? Fantastic build.

I just finished an LFX swap in an RX8 and am loving the combo. The only slightly novel thing I did was fit a TR3160 to it since everyone seems to hate the AY6.

Derek1387

I remember seeing this thread when I was building an LFX Camaro 8 years ago.

Lola the V6 supercharged 15 Camaro. Think we chatted a few times actually.

super cool to see it still relevant.

txbdan

OP, what oil would you recommend for track use? Hard to find good LFX track experience out there.

ThePass

iTrader: (3)

Just did all the fluids in preparation of the first startup on the new config.

Motul 300V 5W-40 for the engine, Transmission and diff got Motul Gear300 75W-90 and the cooling system gets a mix of antifreeze, distilled water, and MoCool

txbdan

Thanks for the info. What diff are you running again? I'm running the Ford 8.8 and am running 75W140.

I'm VERRRRRY excited to hear about the latest build and how its going!

ThePass

iTrader: (3)

Getrag 3.42, currently with OE LSD, but OS Giken in development, so at that time will switch over to Giken's fluid.

Wingman703

Do you have any more information about this? I've been trying to decide between an 8.8 and Getrag, and the lack of a good diff to put in the Getrag has been it's major sticking point. Quaffe makes an LSD for them, but the results I've seen from the people that have tested them have been sub par, especially for the price. Being able to drop in something of OSG quality and reputation would be huge.

ThePass

iTrader: (3)

It's been quite a process. I sent OS Giken Japan a diff and axles back in 2019, and both they and we were all excited for the project.... and then covid happened, and as with so many things during that time, OSG reprioritized things and anything in the New R&D category got put on a back-burner that was so far back it was in a different kitchen. Our guys at OSG USA have been pushing to get the project going again for years, and I finally got the good news within the last 30 days that it's moving forward and we're now talking with Japan on design stuff, how many clutches they can fit, etc.
So I don't have a timeline yet on when we'll have them done, but it does finally look like it's happening.

txbdan

Why not use a Ford 8.8? It's pretty light weight, lighter than the stock RX8 diff at least. It'll hold up to anything and LSD options all day. Lots of shops tune OSGs, I'd talk to ShaftWorks. I'm running a Torsen T2R, but will prob do a tuned OSG at some point in the future. I haven't tracked the car yet so no idea how it'll work.

ThePass

iTrader: (3)

The Getrag is lighter, and has better exhaust clearance. The exhaust clearance doesn't matter for me now since it's side exhausts, but there are lots of guys running the Getrag option.

txbdan

That's true, it is a big ol' thang.