Im going to start building an engine soon, and I have the opertunity to get some s4 t2 rotors. I know they have 8.5 compression vs the S5 t2s 9.0, but how much of a differnce will this make? I should be able to get them for about $100, so its a hell of a deal.

Also, what will I need to rev to 8500 safely and reliably without spending too much money? Im using FD stationary gears, will that be enough?

 

the lower comp rotors are good if you want to raise boost. if i were consistently running to 8,500 rpm i would build a transmission scattershield just in case. There will be very little difference between S4 and S5 rotors in a modified engine on the butt dyno though so I would go with what you can get the best deal on.

 

can anyone give me some detailed reasons why I should run the lower comp rotors?

 

It will give you more safty room with regards to detonation, but you loose off boost perfomance.

 

you can run higher boost with lower octane gasoline without pinging.

 

As far as high RPM's it has more to do with light rotors

 

It's not that big a difference for the average mildly modded streetcar. The difference between the 2 models stock was 15hp, and less than half that was due to the compression ratio...you also had changes in boost level and ecu programming as well as intake and turbo.

IN theory, the hicomp rotors will make a little more power at the same boost level and slightly better overall gas mileage and throttle response when off boost. Also in theory they will be slightly more likely to detonate at the edge because higher compression creates more pressure and more heat. They're slightly physically weaker than the older ones, *SEVERE* detonation can actually dent the face of one in.

Though they are 1lb lighter than the older ones, the stock redline was the same because a stock turbo can't continue to keep up near redline, thus there is no use in revving further if you're not continuing to make useful power. With a highly modded turbo/exhaust setup this could be overcome, and safely revving to 9krpm wouldnt be a problem. IN reality, the same could be said of the older versions too...occasional spurts to 8.5-9krpm wouldn't hurt anything.

 

https://www.rx7club.com/showthread.p...8&page=1&pp=15

check this ^ thread out it has some really good info about singel turbos dealing with the rotor compression ratio