compression help - Team Camaro Tech
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post #1 of 9 (permalink) Old Oct 8th, 03, 10:29 AM Thread Starter
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pulled the heads on the "crate" motor due to a valve problem,and to my horror i was looking at 31cc dished pistons!the heads are 58cc 305 heads and i am calculating an 8.56 static compression ratio with an embossed steel (.015 compressed)head gasket.
dont have the $ for a piston change right now and i was wondering about other options to bring the c/r up.the head #s are 14022601.anyone know what the minimum cc is that these heads can be taken to?any other ideas?
thanks
Eric

[ 10-08-2003, 01:09 PM: Message edited by: SLEEPER 86 ]

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post #2 of 9 (permalink) Old Oct 8th, 03, 08:49 PM
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The only pistons that I know of that have that much dish are from KB/silvolite. How did you determine these have 31cc dishes? You might also want to cc those heads...I have seen several sets of 601 castings closer to 54cc. You could mill them a bit if needed, but since they are a lightweight head you can't really go crazy. Pro-topline makes 50cc heads but a piston change would be cheaper.

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post #3 of 9 (permalink) Old Oct 8th, 03, 09:59 PM Thread Starter
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thanks for the reply travis!
i estimated the cc volume due to the fact that i have seen 21cc dish pistons and they are a d shape shallow dish,these are a full round dish with what appears to be brass tops and a moderate angle from about 1/4" in from the piston edge to an approximately 2" base circle.as for the heads 58 cc is just the standard for 305 heads,as soon as i get them cleaned up i'll cc them.the valves appear to be 1.94 and 1.50 but my mic. is at my dad's and i'll pick it up tomorrow.does this sound right?54 cc's would be better for sure!
thanks for giving me a bit of hope!i'll keep you posted
Eric

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post #4 of 9 (permalink) Old Oct 9th, 03, 01:55 AM
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Sounds like a stock 350 smog piston to me. I 'think' they are more like -13cc. You may have more compression than you thought [img]graemlins/thumbsup.gif[/img]

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post #5 of 9 (permalink) Old Oct 9th, 03, 02:10 AM
 
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And 1.84"/1.50" valves in your heads..

I bet you are right at 9 to 1 or so b/c didn't the dished four valve notch truck 350 pistons have like 7.9 to 8 to 1 CR. with 70 or so cc heads?? or maybe 76 cc ones???

So a 58 cc head should pick it up quite a bit....

Can you cc a cylinder in place by greasing her up with a little gun grease and putting the glass or plastic plate's hole right up top of the angle and then you would know for sure.. Just be sure and get her up on TDC and rock the piston a schosh flat with your hand!!

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post #6 of 9 (permalink) Old Oct 9th, 03, 10:30 AM Thread Starter
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yeah,that would work if i calculate quench volume.i wonder how many cc's in the area between the piston crown and the top ring?

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post #7 of 9 (permalink) Old Oct 9th, 03, 11:21 AM
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I wouldn't sweat it too much. While those 305 heads have small valves and small chambers they really don't run that bad unless you really want to spin your engine up a bit.

A typical small block has a deck height of about .025". When you use a steel shim head gasket that adds another .015-.018" so quench height is roughly .040-.045".

As long as there is at least .035" deck height you will be OK, but keep in mind though that those 350 smogger pistons only have a tiny quench area on the raised ring that goes around the outside diameter of the piston. So quench effect is pretty limited even if you get the desired .035-.045" deck height.

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post #8 of 9 (permalink) Old Oct 10th, 03, 12:15 AM Thread Starter
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i,d really like to see 6000 as a peak hp rpm for this motor,and i'm not sure the 1.84(measured them tonight)intakes will flow freely to that rpm with a 350+.040-.060.i'd think 1.94 would be about right with the higher lift cam,but geesh!machine shops are getting a fortune for enlarging valve bowls/seats these days!i'm seeing already done heads on evilbay for less than that job alone.
anyone know where there's a set available?
Eric
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86 camaro,383,topline vortecs,scat crank,wiseco forged 9.5:1,6"scat rods,comp xs282s,performer rpm,750 proform vac sec,msd in cap, hooker coated 1 5/8"headers,3"flowmaster,700r4,2800 stall,3.42 10 bolt posi,hotchkiss lca's,aje tube k member & a-arms
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post #9 of 9 (permalink) Old Oct 10th, 03, 02:56 AM
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With some porting I believe those heads will suprise you, even with teh stock valves. A buddy of mine ran a cast flat top 355 with those heads, stock valves and lightly ported (bowl blend, casting flash removal, and port matched), a performer intake, q-jet, cheapo summit 214/[email protected] cam, headers, 2 1/4" exhaust, and pretty much stock everything else in a '70 chevy 1/2 ton truck with 3.73's. It would pull 6K in every gear (about 120mph in 3rd), although peak power was probably closer to 5000. It still pulled well to 6K...I am sure the gentle ramps on that cam helped. To get a power peak around 6K, I don't think porting or bigger valves would help without a HUGE cam. But for low-midrange torque, those heads worked pretty darn good.

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