I cooked my #4 cyl. Now I have to decide if I want 8.5 or 9.0 or 9.5 to 1 pistons . How much will low end power be hurt going with 8.5 pistons be compared with 9.5 ? I have a Vortech and with lower compression I can run my smallest pulley [2.87] and be close to 12lb's of boost at redline . So which pistons do you think would be best ?....Bill

 

If you're going to utilise 12 psi boost strategy on 91 octane fuel I would definitely go with the 8.5:1 comp ratio.............otherwise you will detonate the pistons to death unless you a retard the ignition timing by at least 10 to 15 degrees over stock timing.

Peter

APS

 

I hope I don't get to that point for a while, but comparing it to the 300ZX I would rather have lower boost but better low end power.

A question for Peter or anyone else, what would be the highest boost with 9.5 CR?

 

In my uneducated (relating to compression and boost) opinion, with the SC, I don't think I would go lower than 9.5 or 9.0.

With tt's, I think 8.5 would be great because you can just turn up the boost in the low end to compensate, but with the Vortech boost building from about 3k up, I would be worried that between 1k and 3k there wouldn't be any power with 8.5 to one compression.

That's funny you asked booger, 'cause I was pondering this exact dilemma on my way to work today.

 

What fuel octane do you have available in your state, it's not possible to answer this question accurately without knowing the fuel octane you use and what means you have to map the ignition timing.

Both items are critical to the positive pressure strategy you can utilise safely.

Peter

APS

 

with 91 octane

 

I would go 9.5:1 9.0 at the lowest. Like previous poster said, the SC power is more linear than the TT, so if you go too low, you'll have a gutless bottom end. You'll need to retard timing regardless....I think 15 degrees is a bit too much. Tuning with 91 octane fuel is always a bit tricky...but I dont think you'll be happy with 8.5:1 on an SC...you will loose about 25%-30% of your TRQ at the bottom end, and wont be able to compensate by raising boost, ala TT.

Even with my TT, I went with 9.0:1, since my goal is roughly 500-550whp max.

 

93 Octane and JS Safeguard

 

i went 9.0 to 1

 

Hey tig, is your engine build finished?

It would be nice to see a torque curve on some of these different compression ratios.

I'm not glad that people have blown their engines, but I'm glad that I'm not the first. Now I can see how well these different builds work so I no what to get when I finally blow mine.

 

no i think im gonna sell the parts

 

booger....you have PM

 

I'd aim for a static comp ratio of 9.5 to 1 for 93 octane fuel and you should be able to map turbo boost pressure to around 9 to 10 psi safely with a good/safe ignition timing map.

This will also depend on how efficient the air to air intercooler system performs.................the better the intercooling (colder charge air temperature) the easier it will be to achieve a safe and powerful state of engine tune.

Peter

APS

 

People have thrown rods or broken pistons with a supercharger? Was the supercharged aircooled or watercooled? You might want to save your money and just infest in some good tuning for 2 hours. Just get a water/methanol injection kit for $200-$300 that way you can run more timing by keeping the intake charge cooler.

 

Ok, Peter, gotta ask now. I understand that APS is beginning research on the built motor with more boost and different CR. Now, I can either mix my own (xylene) or buy (if I find a Sunoco) 100 Octane gas. With that, do you (APS) think that the turbo flow could still be maxxed out (17-18 psi) and avoid detonation with 9.0-9.5 CR?

Of course, I understand if the answers aren't here yet, but this is the real question I've been looking at since you annouced your kit.

 

tig488 and gq626 you both have PM's