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Discussion Starter #1
Dodged a bullet... Motor needs a ring job. Zero damage to the bore.

Thinking of Mahle Pistons that fit the stock bore and 9.0.1 compression.

My question is this. Will lower compression pistons with a BWR SC give me less power than stock higher compression?

If the answer is yes can I not just up the boost given the added safety of lower compression?

10psi pulley? I guess I would have to get a custom tune or do you think the tune is conservative enough to run this kind of boost?
 

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you will lose power with just a compression drop but you will be able to up the boost quite a bit. probably gonna lose quite a bit of MPG too tho
 

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Discussion Starter #3
how large a loss do you think I will see with lower compression?

Can I compensate with a 3.1 pulley or is that going to be trouble with no IC.
 

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Will,

You will theoretically see a 4% drop in power per point of compression lost. I would recommend going with the stock compression because with a small displacement motor, the compression gives you a snappier response off-boost. You could lower compression and then spin the blower harder, but there are no guarantees that the current tune would suffice, it is likely close, but not perfect. Alternatively, you could send the car down to PES for a custom tune or go with a standalone.
 

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Will,
I would recommend going with the stock compression because with a small displacement motor, the compression gives you a snappier response off-boost. You could lower compression and then spin the blower harder, but there are no guarantees that the current tune would suffice, it is likely close, but not perfect. Alternatively, you could send the car down to PES for a custom tune or go with a standalone.


The stock compression on our cars is not ideal for boost to begin with so, In my opinion you have a great opportunity to lower CR to a safer level for extra boost and get a custom Tune from Charliex who knows the ECU inside and out and get you a SAFE TUNE WITH SAFE POWER! No offense Fzust but I know more than one PES tuned cars with your kit that are having problems even with your reflashes. I really don't think that is the best advice! -
 

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Mahle 9:1 > Stock Pistons. If you must have higher than 9:1, have Wisco custom make you 10:1 ratio pistons...but at that point you'd HAVE to sleeve, unlike the Mahles which are drop in if your engine is measured to be within spec. JesseIL, the newcelica.org forced induction moderator is running those custom spec pistons in his turbo'd GTS. As for lower compression pistons...

jlitman's engine build progress... - Page 9 - NewCelica.org Forum

Finally got around to datalogging boost today using my W/I software.

With the new pulley, boost climbs steadily to ~14.5 psi until lift, then drops to ~9.5, then climbs once again to a whopping >14.8 at 8400 RPM's.

I also think I've finally got the MAF sensor to stop maxing out when the temperature drops -- however, this means I'm running a bit less timing up top than I had (ECU adjusts fuel and timing according to measured air flow voltage), so the tune is probably no longer optimal.

Thus, it's back to the dyno for me after New Years. I'll also have synthetic oil and polydyn in place of the dino juice I've been using during break in.

Now here's what's really cool: With the 9:1 CR pistons and the 2.68" pulley, my effective compression is pretty much equivalent to what it had been with the OEM pistons (11.5:1) and the stock pulley (8.5 psi). With that in mind, I never made more than 175-185 whp with the stock set up, whereas with the current set up, I'm making 220 whp -- a difference of 35 - 45 hp!

Now that's pretty damn cool -- the same power-making potential in terms of effective compression, yet greater power is achieved with the alternate set-up. In short: Low comp pistons + more boost FTW! :thumbup:

More to come... :naughty:
That's jlitman's greddy supercharged, built block, automatic GTS.
 
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