I tried calling summit and the pistons I know for sure that will work are only press pinned. I have bushed rods and want to do a floating pin setup because quite honestly, I don't trust the machine shops. Its bad enough I gotta take it to them to bore it and clean it. Both shops here in town have bad reputations. Anyways, back to my question. The only piston available in my price range is the sealed power forged piston:

.30 over piston (forged)
compression ratio with 64 CC heads : 10.46
Their -3.4cc flat heads with 2 reliefs.



Talked with the gentleman on summit's phone line he said with my 59-60 cc heads (ported and milled, stock is 58cc, so we'll assume I have 58cc heads just to be on the safe side) and a .042 thickness head gasket I will be at 11.5:1. I just don't see it being that high. Im looking for a 11:1 static ratio. Would these pistons not have enough relief's to meet my goal? If not, what size should I be looking at?

 

That's a fairly conservative assumption on the head milling and a high comp. ratio to boot. I bet it's a bit higher.

Hope that is an allum head and you won't be able to use anything but premium gas.

 

Yes aluminum heads, just purchased them. Stock CC on lt1 aluminum heads are 58cc. He said they were milled and the porting added 1-2 CC on the combustion chambers, he doesn't quite remember. These are ported LT1 castings with the following flow:

.100 72/54
.200 138/110
.300 195/144
.400 245/187
.500 262/202
.600 262/208

Their going on my new forged 383. Once again, their aluminum and im shooting for a 11:1 compression ratio considering factory lt4 engines cam with a 10.8:1, i'll be fine. I always run premium.

Anyone know what the CR would be with -3.4cc flat tops on a lt1 with a 58-60cc chamber?.

 

I think they are gonna be ok but it wouldn't hurt to assembele them and test a valve clearance in modeling clay. Then you know for sure.

 

Thanks for the help, would like to get some actual numbers here if possible. I will be measuring clearance and what not but its impossible for me to do until I have the pistons in hand =/.

 

You can't do anything like that without pistons in the hand, in the engine preferabilly.


Just use paydow, modeling clay, plumbers puitty ect. What ever you have around that will take an impression. It all works.

 

Not sure I understand what your saying. Im not speaking as far as piston to valve clearance, im talking the static compression ratio. If these -3.4cc flat tops will get me too high of a compression ratio, I do not want to order them only to have to return them after checking valve to piston clearance. Im still using stock sized valves and stock lengthed valves along with stock lengthed pushrods.

 

Bore 4.03 (inches)
Stroke 3.75 (inches)
Rod Length 6.0 (inches)
Cyl. Head Vol. 58 (cc)
Deck Height 0.025 (inches)
Head Gasket Bore 4.166 (inches)
Head Gasket Thickness 0.042 (inches)
Piston to Cyl. Wall Clearance 0.003 (inches)
Top Ring Land Height 0.25 (inches)
Piston Dome Vol. -3.4 (cc)


Compression Ratio:
11.306 : 1

Bore / Stroke Ratio:
1.075 : 1

Rod / Stroke Ratio:
1.6 : 1

Total volume:
860.064 cc's

Compressed volume:
76.075 cc's

Just a Rough estimate of what your cr will be around

 

Cool, see I tried using a calculator however, I don't know the deck height and head gasket bore. BTW, im running 5.7 rods, not sure how much that changes.