383 compression ratio?

naasaa

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Jul 22, 2008
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Hi

Want to build a 383 to replace my tired 327.
Since this is for the street with decent performance, running pump gas, I have been looking at Scat's stroker kit.
However, the choice is either a 9.8 or 11.0 SCR with my 64CC Trickflow alu heads, where both seems to far from ideal. With piston volume of either 18CC or 5CC.

I have not found a proper DCR calculator (That I can use), but expect to be somewhere in between these two.
So I want to put a kit together myself, but have to decide on proper piston volume.

Anyone here with good experience?
Camshaft will be Crane 119701 with intake 0.05 closing at 38.0 ABDC

Thanks
Lars
 
Here's a good calculator:

http://www.race-cars.net/calculators/compression_calculator.html

My 383 is at 9.9:1 CR with -18cc dished pistons and 64cc heads and a thin .026" head gasket (blocked decked to 9.005"). Works really well for street use and pump gas.

If you want higher CR and can't find pistons you like, you can have the 5CC pistons machined to (example) 12cc volume - that of course is not cheap...

Your cam is milder than the one I use (222/230 vs 230/236) - it will probably not work with 11:1 CR but with 9.8:1 CR it will work well and I think it's a good choice for a street engine.

This Crane cam has more lift than my Comp cam, make sure you check piston to valve clearance especially if you deck the block.
 
Hi, and thanks for your reply.

I was just a bit concerned that my DCR would drop to far with said cam, hence loosing potential HP.
What is the quench distance with your setup?

Not sure if I'm too picky, but have learned the lessons a couple of time with too high DCR :blush:

Surely 18CC will be safe on pump gas, and maybe this should be it!

Lars
 
Hi

Want to build a 383 to replace my tired 327.
Since this is for the street with decent performance, running pump gas, I have been looking at Scat's stroker kit.
However, the choice is either a 9.8 or 11.0 SCR with my 64CC Trickflow alu heads, where both seems to far from ideal. With piston volume of either 18CC or 5CC.

I have not found a proper DCR calculator (That I can use), but expect to be somewhere in between these two.
So I want to put a kit together myself, but have to decide on proper piston volume.

Anyone here with good experience?
Camshaft will be Crane 119701 with intake 0.05 closing at 38.0 ABDC

Thanks
Lars

Before you make your mind on a set of heads you should pour the chamber to make sure its a true 64CC and we have seen AFR's that were advertised 65CC chamber actually pour 67.5

We have used all flat top pistonsc and zero deck in all our 383 builds with zero problems with 64CC heads as advertised.

Here are a couple of builds to look over

http://www.chevelles.com/forums/showthread.php?t=106715

http://www.chevelles.com/forums/showthread.php?t=236517
 
I agree, verifying the head cc is a good idea. If they turn out to be 68cc you can use a standard gasket (.040" thick) and get away with 93 octane gas with the -5cc pistons..... acc to the calculator the CR is only 10.06:1 if you don't deck the block and use a .040" thick gasket. Quench however is .065" ...
 
Hi

Right about checking the correct head volume. Overhauling the heads at the moment.
I think that I will pick parts my self for a stroker.
Being a Scat crank and rods, and a set of KB 12 or 13 CC pistons.
Want to get the quench spot on, and SCR higher than 10:1.

Mybad, have you dunoed your 383?
 
Mybad, couple of questions here;
If I use the compression calculator I end up with I guess the wrong numbers.
This is the rotating assembly that I have:
http://cgi.ebay.com/ebaymotors/SBC-...ptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories
According to them with 64 cc chambers it's 10.5-1
According to the calculator it's 11.14 with 4.030 3.75 stroke 5 cc combustion chamber -4 cc piston and 0.040 gasket.
What am I doing wrong?
 
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I don't see how they made it to 10,5-1 with these pistons!

On the other hand, I dont either see how these pistons has a negative chamber!

Lars

Mybad, couple of questions here;
If I use the compression calculator I end up with I guess the wrong numbers.
This is the rotating assembly that I have:
http://cgi.ebay.com/ebaymotors/SBC-...ptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories
According to them with 64 cc chambers it's 10.5-1
According to the calculator it's 11.14 with 4.030 3.75 stroke 5 cc combustion chamber -4 cc piston and 0.040 gasket.
What am I doing wrong?
 
Mybad, couple of questions here;
If I use the compression calculator I end up with I guess the wrong numbers.
This is the rotating assembly that I have:
http://cgi.ebay.com/ebaymotors/SBC-...ptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories
According to them with 64 cc chambers it's 10.5-1
According to the calculator it's 11.14 with 4.030 3.75 stroke 5 cc combustion chamber -4 cc piston and 0.040 gasket.
What am I doing wrong?

-5cc (negative for dished pistons) or do you have a 5cc dome ??

64 cc is the head chamber volume

.065 is the gasket thickness (many gaskets are .040") plus .025" for the deck height (if the block is not decked)
the deck height is 9.025" and the piston top is at 9.000" so there is an additional .025" from piston to deck surface. If the block is "zero" decked .025" are removed from the deck surface.

calculator says it's 10.49:1
 
I'm getting by with an effective 16:1 haha. ...Although I have melted two pistons... :crylol:
 
Thanks, it appears I had a blond moment and I forgot about the deck height.
My bad, no pun intended......
 
But the quench would be too high!

With correct quench it is about the said 11.14:1


Mybad, couple of questions here;
If I use the compression calculator I end up with I guess the wrong numbers.
This is the rotating assembly that I have:
http://cgi.ebay.com/ebaymotors/SBC-...ptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories
According to them with 64 cc chambers it's 10.5-1
According to the calculator it's 11.14 with 4.030 3.75 stroke 5 cc combustion chamber -4 cc piston and 0.040 gasket.
What am I doing wrong?

-5cc (negative for dished pistons) or do you have a 5cc dome ??

64 cc is the head chamber volume

.065 is the gasket thickness (many gaskets are .040") plus .025" for the deck height (if the block is not decked)
the deck height is 9.025" and the piston top is at 9.000" so there is an additional .025" from piston to deck surface. If the block is "zero" decked .025" are removed from the deck surface.

calculator says it's 10.49:1
 
But the quench would be too high!

With correct quench it is about the said 11.14:1


I agree, quench is too high. To get it down I'd deck the block to 9.015" and use a .028" gasket.

With these numbers and -5cc (negative) pistons it's at 11.19:1
 
OK, thread hijack, I'm missing something here.
As in is 10.4 correct or is it 11.14?
Why would the quench be too high?
Block should be 9.020.
I'm royally confused.....
 
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