Turboing N/a rebuild
 

A friend of mine has a very fresh rebuilt n/a engine, about 3000k on it. He has the following:

TII housings, 3mm seals (rx7 specialist's own seals) and supposedly "JDM light weight, high compression rotors" He says its 10:1 compression. Ive never heard of this. If this is so however, can he run about 4 lbs of boost with fmic and a few other goodies? I see ppl run turbo'd n/a motors, but i dont know about this 10:1 thing..



just want the advice, thanks in advance

I wouldn't feel safe with any boost on that high of compression.

:werd: 10:1 sounds kinda scary with boost..

Bah! You CAN do it. You just have to be extra careful tuning it. I WOULD NOT run on a scock ECU with that and get it tuned with a wideband 02 sensor. It CAN be done, but good luck on that!!

Yea I've been told that detonation will be alot easier to achieve (YOU DO NOT WANT THAT) with a higher compression ratio, thas why people are usually scared to turbo high compression engines.

But yea you will need something better than a stock ECU if you want to avoid detonation.

I think the N/A's are awesome to turbo or SC, just cause of the extra ports, its pretty sweet. But you just have to be carefull. If that compression is true, then you probably won't be able to get past 10psi... Im not discouraging you, im just saying go for it and tune it real well.

10 psi? Are you crazy? People running s4 n/a rotors run 10-13 psi max that I've seen. Not only that but I've heard that most of the people the turbo s5 n/a's end up blowing their engine because of the higher compression rotors, let alone 10:1 (if they even exist) rotors.

are you sure they are 10:1? Who makes them? I would suggest a S/C with 4psi rather than a turbo with 4psi.

...Er.. Why?

Yah... boost is boost, no matter if it's s/c or turbo.

it's not because of the higher compression rotors. 13psi on S5 rotors would be around 300+whp any motor running that much power on stock seals is a ticking timebomb. Not to mention the S5 N/A rotors are alot weaker(softer metal) so the seals can distort more = quicker to the boom. Think of running higher compression as lowering your threshold psi wise, but upping the amount of performance gained per psi. 13psi with a stock turbo on N/A motor made 300hp it'd take a bigger turbo to get that much power out of lower compression rotors. On "streetable" motors higher compression is usually a good idea, if you have modest goals you can get to them alot quicker and safer with higher compression than with pumping loads more boost into a low comp. motor. You guys really need to know more about what your talking about before spouting off about the high compression rotors blew up the motor. especially in a ported motor static compression means less than you think.

But higher compression + boost = more of a chance to detonate...

Why do you think tons of the import n/a piston cars require lower compression cylinders or rods or whatever (I know nothing about pistons) with their turbo kits?

Well number one, I really doubt he has 10:1 compression rotors. I've never heard of such a thing available at any cost lower then amazingly high...

Second, it would be appreciated if only those with turbo NA experience would reply to these kinds of threads. That means that at least you shoudl have actually seen a turbo-NA car.

Third, 4 PSI of boost is just a waste of time. :) If you're going to build a turbo-NA, make 10PSI your goal from the beginning.

Fourth, S5 rotors are not made of softer metal. The faces of the rotors are much thinner, which makes them prone to denting during detonation or through excessive boost...

Aren't RX-8 Rotors 10:1 compression?
they arn't amazingly expensive.. :)



But other than that 100% agree with you...

exactly. Good lord.

He said the compression ratio is that, i dont know if its true or not. what i do know is he spent near 4000$ canadian to get this motor built. Dont know what he has in it, just word of mouth. Im gonna be mounting my old s4 turbo on his block when i get my engine done and in my car. I do know his n/a has a sound like no other ive ever heard.


Thanks for the advice ppl. Good feedback.

:werd:

An intercooler is pretty much useless at 4psi and would probably cost a few hp. At that low boost the air doesn't heat up enough for an intercooler to be effective, and the pressure drop across the core costs more hp than the temp drop will gain.

I don't mean to be pedantic about this, but pressure losses are all relative.

Say you have a 1psi drop across the 'cooler at 14psi.

That doesn't mean you'd have a 1psi drop across it at 4psi. It would in fact be proportional to the ammount of boost your running. Not an absolute value.

And the more cooling you have the better really, it's an accumulative(sp?) thing.

Has anyone thought about if he can really hold the boost at 4psi? I mean it wasn't mentioned, but I'm sure he has some porting done if he's really spent that much on it, let alone intake and exhaust that I'm sure he has, boost will not just hold where you want it to (on turbo) so how are you going to make sure it stays there?

Boost may be boost, but with a S/C you're getting a much lmore usable powerband in the lower RPM's.

Forgot about that. But what are the chances he has RX-8 rotors? As far as I know, only Mazdatrix and a few individuals have tried, and apparently it was a major pain with very little gain... :)

My turbo-NA made full boost (8-10 PSI) from 1000 RPM up. 12 PSI over 3K.

Hey White_FC,

With the pressure drop, sure it might not be too much, and you can also increase boost to get the same boost at the manifold, but threre are other reasons not to have it. About the cooling, you'd get better cooling ditching the front mount as it blocks air going to the radiator, and induces turbulence in the air that gets through. From an engineering standpoint for optimum cooling you want the incoming air to have as little turbulence as possible. You'd also get much better throttle response going non-intercooled as the piping would be very short compared to the piping involved in a FMIC. I doubt that you'd see any kind of meaningful temperature decrease with an intercooler unless the turbo is horribly mismatched to the engine and is working past its efficiency range. A few months ago in SCC mag Dave Coleman the engineering editor talked about low boost turbos and superchargers and said that an intercooler usually isn't needed untill about 8psi. I'm also a mechanical engineering student, so I'm not just talking out my ass here.

I run high compression (9.4:1) rotors in my TII. it has a relatively aggresive street port. i useually see about 8 psi on the stock turbo. i have driven at 8 psi on 89 octane in 90-100 degree heat witht he stock IC with NO problems whatsoever. that was on the stock ECU.

I now have a microtech, although it is not fully tuned yet, and i am planning to upgrade to a T04 soon. my max boost goal will be about 12 psi. A this level i expect to make well over 300 whp.

people always worry about detonation...it is usually due more to something malfunctioning rather than too mcuh compression or not enough cooling.

pat

Absolutly, I agree, was just presenting a possibility.. :)

Theres a few racers here in Oz that have tried the rx-8 rotors, theres even a leading engineering/race shop that will mill the apex seal grooves to the right depth.

But apparently theres a big problem with side seals not sealing right..


Black91n/a, An intercooler is never really needed at all, even above 4psi, it´s just that they´re a damm good idea.
FC´s only ran around 5psi off the showroom floor, but they have an intercooler... So it must still be cooling the air down.

w.r.t the front mount debate on wether or not you loose more than you gain with the blockadge of air.. well.. if you have the money and the skills then theres always the H or V mount setups.. Really if your having overheating probs on the street even with a FMIC, i´d look for other cooling system probs first.. racing is a bit different I guess..

Sometimes you just have to compromise and stick it in a shit spot for the radiator though.. :)