calculate compression



calculate compression

Postby grumpyvette » May 13th, 2013, 12:59 pm

I picked up my 454 from the machine shop and want to make some changes. Originally a stock rebuild, 2 bolt main with stock rods. Machinist claims 9.1:1 compression, I don't believe this, and don't have the tools to verify it. The pistons are stock, cast 2 valve relief pistons,(flat top). I figure it to be closer to 8.1:1 maybe a smidge higher. Can I use a different head gasket to gain some more compression? Not much, just want to be closer to 9.1 or 9.5:1. If so, what do you recommend. The heads are cast iron 353049 with 2.19/1.88 valves and the cc's are about 122 for the chamber size.

two valve relief cut BBC pistons generally have 5cc-7cc in the valve notches, your uncut block will generally show a .023 deck height, your true compressions more likely near 7.96:1.
your 049 head are generally about 113-115cc

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heres a chart I found that I don,t fully agree with, I think its a bit conservative, by about 3%-5% on the required cam duration ,required to avoid detonation with todays crappy octane fuel, but it at least gives you a base to work from, but Id suggest selecting a bit more duration
detonation and rapid heat increases can ruin piston ring seal to the bore wall
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IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
grumpyvette

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Re: calculate compression

Postby grumpyvette » May 14th, 2013, 8:39 am

yes you might want to find a set of older closed chamber heads with smaller combustion chambers to boost compression, swapping from a 115cc open chamber head to a 97cc-98cc head would increase the compression ratio.but that option might depend on the price of the used heads and cost of machine work required, new pistons, rings,bearings and a balance job might also be an option, and considering that purchase of and a total rebuild of 45 year old heads might be required that might be the less expensive option


LOOK THRU THESE LINKS
viewtopic.php?f=52&t=3960&p=28588&hilit=closed+chamber#p28588

http://www.kb-silvolite.com/kb_car/perf ... dLen=6.135

viewtopic.php?f=38&t=3900&p=28672&hilit=balance#p28672

viewtopic.php?f=53&t=341&p=21051&hilit=balance#p21051

viewtopic.php?f=52&t=8460&hilit=seat+curtain+valve
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
grumpyvette

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Site Admin
Site Admin
 
Posts: 14105
Joined: September 14th, 2008, 1:40 pm
Location: florida


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