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New 355 with compression questions

1K views 12 replies 6 participants last post by  jaw22w 
#1 ·
Hey guys I just picked up a new 355 short block I couldn't pass up the deal. It's brand new and completely gone through the guy installed .30 Keith black hyper Pistons (unsure of the cc on the Pistons) but the guy said with 67cc heads it would be at 10.1 compression ratio, I'm assuming the guy new what he was talking about since he works at a machine shop but my question is can I run 64cc aluminum heads on it with the comp thumper cam (279/297 dur and 479/465 lift) and still run 93 octane and be streetable? I've read a bunch of threads but no clear yes or no answers. Thanks for the help in advance
 
#6 ·
your static compression ratio remains the same. Your dynamic cr varies with intake closing point. I have more compression and I use a bigger/better cam.
without knowing the parts list and goal you are attempting I can only guess if your cr matches your cam and heads.It all matters
 
#8 ·
If the engine is not installed roll the thing so one bank is level. You can get a graduated flask see here http://www.summitracing.com/parts/pow-pow351105

Use this to measure out the dish and valve relief in the pistons. Use some rubbing alcohol and food color or ATF. While you're there measure how much deck clearance there is from the piston crwon to the deck. You will need to invest is a degree wheel and positive stop to find true TDC for this measurement. Without these tools and performing tis process you're flying blind on someone elses' say so. Better to spend a few dollars and be sure than to risk high cost repairs to fix the engine. Once you know this then we can talk heads and cam, anything else is just peeing into the wind.

Think of it this way; "In God we trust, all others we audit".

Bogie
 
#9 · (Edited)
. Sounds like it will work fine to me with aluminum heads... would expect pinging with iron heads... are the pistons dished? flat top? 2 or 4 eyebrow? Sounds like flat top to me...


. Need to rotate crank and bring a piston to top and see how far it sits down in the bore... we're talking .025" or maybe -0-" to see how thick a head gasket to use for good engine quench effects:

https://www.google.com/?gws_rd=ssl#q=engine+quench


. Round off any razor sharp edges on piston tops and inside combustion chambers to greatly reduce chances of pinging... (rebuilding shops usually skip that step and their engines ping themselves to death)
.
 
#10 ·
They're flat top 2v relief Pistons, I found this set on jegs http://www.jegs.com/webapp/wcs/stor...0002&langId=-1&productId=380018&storeId=10001

If I had to guess based on the compression ratios given I would say these are the Pistons but still not sure, I was just worried if putting the 64cc heads on it if the compression would be to high to run 93 octane compared to the 67cc heads he had at 10:1 cr and I've read a lot where when you get up to 11:1 you don't wanna run pump gas
 
#13 ·
Like bogie said. You need the volume of the valve reliefs and where the piston is @TDC. Without these numbers SCR is just a guess. Not good enough. A mistake here at this point could be disasterous. You need these numbers to pick a combustion chamber volume and head gasket thickness and volume. Do yourself a favor. Get these measurements and post the results. It may cost a small amount $$$ now, but save a large amount $$$$$$$$ later.
As bogie also said. Think of it this way; "In God we trust, all others we audit".

I am running 11.34 SCR with alum. heads. Open motor, no hood or sides. .036" quench. Careful tuning. No detonation w/ 93.
 
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