version13

I have searched, just to let you know.

I've seen a lot of people running the NA rotors on a turbo. The compression for the NA ones are like 9.5:1 arent they? The turbo ones are something like 8.5:1, so obviously there would need to be lower boost, but what other advantages or disadvantages would there to be running NA rotors on the turbo?

Thanks.

Kim

Pro: Faster spool-up

Con: Less chamber volume
Con: Less power
Con: More likely to ping
Con: Wont handle high boost

Im no pro turbo guy but these are the basics of stuff I learned on the forum

White_FC

IMHO, there are no cons, unless you either:

1)Be dodgy and don't tune it correctly
2)Don't pay enough attention to the tune of the car
3)Don't follow either steps one through to 3
or
4)Want to run >20Psi of boost

high comp rotors in a turbo engine are great.

The series 4 (9.4:1) rotors would probably be the best for most people as its a good mid way between the 9.7 (or even 10:1) rotors and the low comp turbo rotors (either 8.5 or 9:1).

With the 9.7:1 and the 10:1 compression rotors you would need to spend alot of time on a dyno making sure everything was exactly right.......
And you'd probably want to make sure every tank of fuel wasn't bad... but you'd have to be pretty **** to do that..

ViperKillerWannabe

Where do you get 10:1 rotors from?

White_FC

An Rx-8......

Sponge Bob Square Pants

No cons?
How about the fact you can't run near as much boost and can't make as much power? I think that's at least one con.

White_FC

Im happy to accept your opinion on this....
However boost is not limited nearly as much as people think......
Especially if your using a stock S4/5 turbo, the boost would be limited by the efficieny of the turbo, not the motor first.

Like I said above 20psi it might become a slightly more contributing factor, but most, if not nearly all, people with FC's don't run that much boost..........

I don't have a whole lot of experience with high comp turbo rotaries, i've only built one so far.. :-)
but I do have a little bit of experience with high comp turbo piston engines.... The same basic principal applies though..

mcnannay

well running the same amount of boost on a higher compression rotor would put alot more stress on the seals, so thats definitly a con...you're gonna shorten the life of the engine

White_FC

Meh... running more boost on lower comp rotors puts more stress on the seals as well? Whats your point?
Making any power over what the engine comes with stock will most probably shorten the life of the engine.


High comp rotors _will_ make more power than low comp rotors at the same boost.
Simple fact.

NZConvertible

Wrong. The chamber volume at TDC is exactly the same, so the same amount of air is drawn in. The chamber volume is smaller an BDC, because that's what higher compression is...

Um, where did you learn that? The whole point of raising compression is to increase power. That's why it's done. By squeezing the air/fuel mix into a smaller volume, it's pressure and temperature are raised and so more nett energy can be extracted from the combustion.

If you increase compression, you get a similar effect to increasing engine volume: more torque (and hence power) right through the rev range. The downside is the increased combustion temp lowers the threshold of detonation. This is why (all things being equal) you can't run quite as much boost, so peak power potential is lower.

For a street car, higher compression makes much more sense than higher boost, because you spend so much of your time off boost. Effective intercooling and cold air intakes lower the chances of detonation.

Sponge Bob Square Pants

I definitely agree! When talking about performance, I just have the habit of talking about PERFORMANCE! hehe
So it may not be a con for 98% of owners out there, but it could be for some.

FDreaming

NZconvertable is entirely right. In a sort of round about way pressurized intake charge is alot like upping the compression. Because it ups the combustion chamber pressures. Combustion chamber pressure is what makes power, it's the force that spins the motor. For example it is becoming more and more popular with the Honda guys to run high compression turbo motors on the street, they spool much faster, and have a much more usable powerband. The Peak power is limited, but not by as much as you'd think. For example A friend of mine has a prelue running 10.2:1 compression and about 14psi. He is making 350hp and the thing spools just after three grand. It's fantastic! He has a little more room left for more boost, but anything after 400hp is pushing his luck. The highest horsepower Street prelude is making 493hp at 25psi on 8.8:1. So basically unless your power goals are astronomical, and not logical for a street car, the slightly higher comp. ratio may be for you.

note: I'll be standing behind these claims when I build my turbo motor. S4 NA rotors.