Suburban 95 5.7 engine versions

eran tomer

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Hello
My truck is NA4 which means above 8500 gvw emissions. The manual says it has a lower compression ratio than trucks with emissions below 8500.
What’s the reason for decreasing the compression ratio?
My engine is probably not the original one, suppose it’s the lower emissions- can it run ok with the stock ecu?
 

Nick_R_23

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The decrease in compression ratio is to avoid detonation, common on heavier GVW trucks intended on carrying heavy loads more often. Either version of engine is close enough that stock ECU programming will work on both just fine.
 

Schurkey

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I'd expect so. But software in the ECU can make up for a modest drop in compression by being more-generous with timing, fuelling, or some other aspect of emission control. I'd also expect that emissions regulations may be less stringent on the higher GVW vehicles. It was at one time. I don't know about when these trucks were built, or now.
 
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