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Low Compression after fresh rebuild


Kash

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Word! Completely OEM 280ZX will LIVE most of it's freeway like from 2500-3500 RPM AS DESIGNED!

 

My B16 crx would sit around 4000-4500 on the freeway, dipping in and out of vtec engagement. Sucker still get 35mpg being flogged on constantly and never once complained.

 

Hell, even a V8 designed for it can live at those RPMs too!

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No more complaints out of me, this thing is alive again…hit the gas pedal driving around town below 3000 rpm and it responds.  Now getting 160 +/- 2 psi across all after a 10-min warm up at first start...those numbers should only get better over the next few months, oh yeah!!:icon10:

 

The next investment will probably be a standalone to tune the most out this set-up...from what I read, this turbo runs best above 15 psi (current max).

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Good luck...Run your final compression ratio before you start upping the boost.

 

14.5:1 is about the max you can run on 93 octane no ethanol...add 10% ethanol to the mix and you can run 14.0:1. Adding the alcohol to the gas has reduced detonation resistance in any engine I've gotten to check back to back; even pulling timing.

 

Sooo....you stated you were going to increase the quench height, lowering detonation resistance, and increase the compression ratio to 8.7:1. Right, so you're starting with a less detonation resistant, more displacement, version of the flat-top L28e +t converted engines. Hmmm...They start seeing detonation problems around 10lbs of boost.

 

15PSI of boost would put your final compression ratio at 17.5:1....I figure about 9lbs of boost you'll be wondering why it spits back at you with any more boost, even when you pull timing.

Edited by Xnke
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So to answer your question, (and confirm what i read here) i think just break it in longer and recheck. use engine braking and rev the motor up near redline in gear then let off, do that a few times. My personal experience with rebuilds is it takes a few hundred miles for compression to go up. my l24 rebuild with cam and higher compression head read 160psi across the board at 200 miles. then at 1,000 miles it read 215 across the board. yay! my honda si rebuild got 20 mpg for a week or two, then after about 300-500 miles it got 30-32 mpg. crazy huh? 

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