I am picking up a '90 tii next weekend and i was researching the specs on the car and one thing that struck my eye was the compression ratio. The s5 tii's have a compression ratio of 9.0:1 while the same s5 n/a motors have a compression ratio of 9.7:1 with the same rotor weight. i also know that changing rotors you may possibly need to change the flywheel for engine balanceno biggie.
so has anyone swapped the n/a rotors into thier tii's succesfully? was it worth it in terms of performance gains?

 

You can swap the rotors S5 to S5 without problems, but it will be very prone to blowing up with the extra compression. You will need a standalone and a really good tune.

 

by blowing up you mean detonation i take it. how about power numbers? anyone done this and have before and after numbers? i also take it that upgraded apex seals would be necessary too?

 

Blowing up because of detonation. As mentioned, it will require a good tune. Upgraded apex seals aren't required.

 

i did search and the closest i came up with was https://www.rx7club.com/showthread.p...ght=rotor+swap but this guy wanted to lower compression for some reason that is beyond me. i know you are able to turn the boost up on your turbo easier with lower compression rotors but why not use the same boost with the higher compression for even more power.... granted you have the standalone, uprgraded apex seals, and tune.

 

dyin for an answer here if anyone has done this or know someone who has!

 

It has been a common thing to do for a while. It is possible to get a nicer powerband with the higher CR rotors, but the tuning tolerances are tighter. The only reason I don't use them is that the castings are thinner, so the rotor face is actually weaker. I have seen pictures of 9.7 rotors that have the rotor face caved in.

If you want to make nice power and good response on low boost (ie under 350whp) then 9.7 rotors are a good idea. If you want any more than that, go for the 9.0 turbo rotors as they leave a wider margin for error on the tune.

FYI you do not have to interchange anything except the rotors when going from s5 to s5

 

check out rotary aviation apex seals. supposedly they cave in and dont damage your rotor housing upon detonation. im running them right now. im using a s5 keg with s4 electronics since my car is s4.... long story. but the compression ratio is a little more... slightly. .3 i believe? those apex seals are pretty inexpensive and seem promising since i've seen them used on lots of guys cars aroundhere.

plus the guy who built my motor has a s5 t2 motor with s5 na rotors in it. yeah just get a really safe tune and you'll be fine. my rule is just be safe... so when i go out drifting i just fully retard my timing, run some octane booster.

it really depends on what application you have for your motor. im going drifting so im doing alot of high rev heavy load driving. if you're going for drag, i'd recommend the 9.7:1 ratio rotors... but just get a good tune. ... and some water/methanol depending on your turbo choice

 

and are you just going to pull the motor apart in order to swap the rotors? . if that's the case and you're not going with a crazy port job and a huge turbo.... what's the point? unless you like spending large amounts of cash

 

^^ ha well yeah everybody likes to get sideways once in awhile but i don't think ill be building a drift car. i love the sport but cars get ruined way too easy for me to gamble it. im planning on just a street prowler but use it as a dd so i dont think i would be trying to push 350+ hp.
thanks for all the feedback though you answered all my questions thoroughly enough.

haha never said i wasn't gonna do any of that :P

 

i saw a back to back comparison of the 9.7's and 9.0's in a turbo car, and you have to tune so conservatively on the 9.7's that the 9.0's made about 50 more hp.

or basically that's what the turbo is for

 

your question was already answered. how many more times do you need to ask it?

 

was asking if anyone had done this or had numbers too, which wasn't answered.

 

you probably won't get a definitive answer. it's quite unlikely anyone went to the dyno and got figures then swapped rotors and did a dyno on the same EXACT setup. all you will hear is "the acceleration at lower RPMs increased" which is about all that is true of higher CR rotors.

the rotors are the same in all series 13B's but you do have to use the front and rear balancers for whatever series rotors you are going to use.