themick1414

Hey I just got my first FC it's an 89 GTU. It has a frankenstein rebuilt motor with just under 5k on it. according to the previous owner it has FD rotor housings, s4 rotors for the lower compression (I think the plan was to turbo the motor), s5 intake assembly, brand new seals and other minor parts all around. It also has Pacesetter exhaust manifold, ANSA cat back, and a cone filter on the intake, don't know if that matters.

My question is would it still be ok to rev the car to 8000, or should I stay @ 7000 because of the s4 rotors?? I guess I'm kind of wondering what the difference was that let the s5 rev a grand higher??

sorry if this sounds stupid, I'm a noob and a kid.

MmSadda

iTrader: (2)

Nah, dude. that's a valid question, not at all n00b-ish. That's one funny bastardization of an engine you're running; I always wondered how my s4 engine would hold up with s5 rotors and maybe e-shaft.

To address your question: If I'm not mistaken, the s4 rotors are heavier, probably making it riskier to rev beyond 7k. However, (and I could very well be wrong about this), it seems possible to me that the S5 uses a sturdier e-shaft, which was part of why it could rev higher. If that's the case, and you have an s5 e-shaft, maybe your redline will be somewhere between the two numbers.

Revving a little too high once or twice won't kill your engine; you could always dyno it, and see where your power drops off.

Also, maybe try to contact the previous owner, and/or engine builder. While what you're saying isn't inconceivable, it's a bit unlikely, especially for a car that was rebuilt like that to be sold so quickly. I'd find out as much as you can for sure about it, and see if the previous owner has receipts for any of the parts/work. Just a thought.

Good luck getting it figured out

RB_eater

iTrader: (1)

I'm pretty sure the higher redline on the S5 is due to lighter rotors and the improved intake.

However defining a redline isn't easy. Depends on weight, balancing, clearancing, durability of the materials, etc.

MmSadda

iTrader: (2)

RB Eater is right; both the lightweight rotors, as well as a better intake (manifold?) allow the s5 to rev higher. Are you still using the s5 Intake and manifolds?

Even if you are, though, 7k might be a safer bet

themick1414

Thanks a ton! hahaha, yeah that's what I thought when he told me about it, lol. The parts were all used for sturdiness though so I can't complain. I'll have to check all my info again to figure out the e-shaft, I'm pretty sure it's s5 though. I thought about dynoing the car but I don't have the money at the moment, thought there might be an objective way to tell from the parts put in. I heard that the apex seals have something to do with rev ability, is that true??

The car was going to be used for autocross but hasn't really seen much time out on the road. the previous owner bought it from the perosn that bought it from the builder, who had done the rebuild for himself. the guy I bought it from confirmed everything with the owner before it was too late for that. See, I would contact the buildler, but that's not really a possibility...

themick1414

yeah it's got all the s5 intake and exhaust on there with a K&N cone filter.

The Shaolin

iTrader: (5)

With the s4 intake manifold, your power will absolutely die at 7k. I guess I never thought twice about it, but I too have the S5 IM on the S4 shortblock and I plan on revving to 8k all day.

There are lots of people that did the IM swap and got it dyno-ed, you're fine.

themick1414

Awesome so I should be good to rev to 8 then huh? Thanks for your help guys the previous owner was wondering too.

Sideways7

iTrader: (7)

You are fine to run it to 8k. Both the s4 and s5 motors are rev limited to around 8.5k, so the rotors don't really make much of a difference. The reason the redline on the s4's was at 7k was because the power dies off much past 6.5k so theres no reason to rev past 7k. The s5 intake is what raises the power band about a grand, past 7.5k. Since it make power to 7.5+, they raised the redline to 8k.

Just so you know, this is all based on personal experience. I put an s5 intake on my s4 engine and I took it to 7.5-8k quite frequently. I still had the s4 ECU, and it hit fuel cut past the 8k that the tach displayed, I estimate it around 8.5k.

MmSadda

iTrader: (2)

Wow, this thread quickly became full of win. A lot of good **** in here that I wouldn't have thought to look up otherwise...

RB_eater

iTrader: (1)

Carbon apex seals are softer and so can allow the engine to rotate faster.

The fuel cut-off might be at 8.5k but that doesn't mean it's safe to go there often.

iSP33D-for-J3SUS

[semi-off-topic] You might want to consider dropping the pacesetter for a RB Header. I've heard bad things about pacesetter and not just on RX7s, either.

Cheers,
Cody