Weird title to capture what I'm thinking - I've noticed there seems to be some curiosity/disappointment around modest horsepower on built motors. Seems like, if you're not making 300whp on your built motor, there is some let down. It's odd, because when I was working with my engine builder and tuner - guys who build/tune/run actual race cars/teams, there was a totally different attitude toward target horsepower/tuning. Why not bake in some cushion? Some reliability?

What am I missing? (I'm probably just old)

 

Speaking for myself, my full-fat race engine was built for area under the curve/grunt when picking up the next gear - it had nice numbers, but nothing to brag about. My turbo engine in the RGM is built (tuned) to protect the gearbox.

But then, I AM an old fart.

 

I'm not tuned for every last horsepower and yet I have the BMW ZF transmission to handle more. If I switched to larger injectors (which I own) and a 4 BAR MAP sensor instead of my 3 BAR, I could turn it up quite a bit.

I'm at 325whp and heat management on the track is my actual limiting factor. And it isn't just engine heat. I've had to duct air to Wilwood 11.75 brakes to try to keep pads from vaporizing in a single day because of the additional power.

The exhaust has required shielding to keep heat out of the transmission and differential as well.

The engine has a custom ordered triple pass stock car radiator and a large oil cooler, a giant Spal fan with custom shroud, and hood vents. The Spal required a larger alternator and bigger wiring. The bumper mouth is sealed to the radiator in every nook and cranny I could locate. And on hot days it occasionally asks for a cool down lap.

At this point it is reliable. That is the biggest goal. At 3 times stock power it makes 3 times stock heat. That's a lot to shed when the blacktop reads 135*F in the sun in Florida and this little car is scooping air right off that surface. And it catches C5Z06 cars on the straights just fine.

I'm tired of developing it and just want to drive it. So, yeah, I don't want to turn it up right now. I just wish I felt better and could drive it more.

 

My thoughts are very much in line with Gee Emm, target what the shitty OEM 6-speed Aisin can safely tolerate but also what's actually usable.
300hp seems to be the max for the NB's 6-speed Aisin gearbox but I'm happy with ~275hp, it SHOULD keep the gearbox "safe" (fingers and toes crossed).

I doubt that I'll ever need more than ~275hp (not a fan of "long straights") and more hp just requires more money to throw at ruggedising everything else to handle it.
I have a built engine with an EFR6258 so 275hp seems conservative but I'm confident I could thrash the car all day with this limit (probably need to change brake pads at least once).

Chasing high hp numbers without needing them is only for your ego and gets very expensive - when you start turning into "an old fart" you'll understand this more.

 

I use table switching along with flex fuel to have the best of both worlds. I.e. my track boost map is conservative, at 260whp or so at 12-13psi on e85, then I can flip a switch and boost targets allofit (18+psi) for fun on the streets and the occasional drag race where the car makes 300+.

Tuning wise we didn't target mbt, even on e85, we stopped adding timing when the HP gains got smaller (i.e. diminishing returns) and stopped there.

I'm on a rods only build and plan to stay on stock mazda gearboxes, and this is my track car, so conservative is a good idea. So much that I've embraced my ancient gt2860rs "disco potato" as part of the build, I see it as softening the powerband with slower spool and transient response so things don't blow up. So far so good.

 

A couple things. First, what makes you think we're not? I tuned mine for max power, and then I detuned it for safety. Sure, I posted the max power graph, but that doesn't mean that's what I was running on the track. If you're paying someone to tune the car, he's charging you by the hour. He's going to use his experience to skip intermediate steps, whereas I'm an amateur whose time is "free".

Second, the amount of cushion you needs depends on the intended use. A 24 hour endurance tune is different from a 20 minute sprint race tune is different from a street tune.

--Ian

 

For me, I can see arguments for both sides. If I paid for forged pistons then I want to make more power than stock pistons would handle, because otherwise it was money I didn't need to spend. Granted, I also appreciate knowing that those forged pistons are going to be more tolerant of a bad tune or leaky injector, lowering the chance that I need to rebuild the engine.

You're always going to be at the limit of some part, be it the rods, trans, injectors... Personally I figure overbuild so there's some reliability and then tune towards the upper limit of the weakest part.

Looking back now that I built my engine last winter I realize that I don't have a ton of desire to swap the drivetrain out to make as much power as the engine is capable of. In some ways that is disappointing, knowing that the engine could probably do 500, but most likely won't see over 300 (at least for a long while), but I also don't want to be popping 5/6 speeds every week.

I feel like it's disappointing in a similar way to driving a high performance car in traffic. You know that the car is capable of so much more, but there are other variables in your way.

 

I read a quote from Hustler on here at some point. It went something along the lines of "A 200whp Miata is fast on track, a 240whp Miata is a blast, a 280whp Miata on track is a lethal weapon."

My tuner capped the 91 octane tune on my built motor at 270whp for safety on track. I wouldn't have it any other way. We could've squeezed a little more power out of it but I'd rather not have to build another motor again. It's got 7 track days under its belt and has yet to skip a beat. It's as fast as any car needs to be. Sure, the car isn't catching GT500s or anything with over 500 horsepower on the straights, but it's still an absolute riot. I was still able to grenade 4th gear on a 6 speed transmission at that power level too.

On e85, my car makes around 300whp (turbo's maxed out at that point) and it's enough to make just about any passenger sh*t their pants. If I were smart, I'd just cap it at this power level.

In reality, I'm going to go bigger turbo eventually, but will probably only run 325whp max at the track like SixShooter, for survivability (both the engine and the driver).

 

Numbers are cool. But as the saying goes, you don't drive a spec sheet. Or dyno sheet.

That said I do like a fast car. In the past, I pushed the limits of OEM stuff a lot. Some of this was to understand where the limits are, so that they could be raised with new parts, or respected.

Now adays I'm a huge fan of having a factor of safety. For the most part, everything behind the engine in my car, has a FOS of 2. So twice as strong as it needs to be. Generally, a lot of the parts are rated this way. Way overkill for the expected power level. IMO, this is a big part of how to achieve reliability. I don't have the time/money/expertise to optimize everything, so sometimes I throw an overkill part so I don't have to worry about it moving forward. I'd say there's a 99% chance I have the "biggest" fuel system ever installed on a BP miata. But I did that because I've fought under-sized fuel systems parts (injectors, rail, fuel pumps, regulator, etc) and just tired of it. Not looking to optimize, looking to solve it and move on.

One could write an equation to describe how cars are built; the main variables that drive the output would be age and budget. The more of those you have, the less you tolerate nonsense.

 

What Pat said, we are all fixing or over building whatever cost us or others problems in the past so that we don't have them to deal with in the future. We just want to have fun and not worry about whatever has troubled us or our friends in the past. I don't see it as over building. I see it as addressing problems others have had or we have had so that we don't have them to worry about. We just want to have a good time. That's what this is all about.