What would my compression be?
What would my compression be? 408
-2cc diamond pistons
AFR 225 62cc
GM MLS gaskets
What would my compression be?
I didnt want to ask but I could not find the compression sticky!
-2cc diamond pistons
AFR 225 62cc
GM MLS gaskets
What would my compression be?
I didnt want to ask but I could not find the compression sticky!
Ok, I have an update to my parts list and want to check this compression/parts.
- -2cc Diamond Pistons
- 4.030 block bore
- 4.0 stroke
- 4.130 Gasket Bore (Cometic Gaskets with 0.40" Compressed thickness)
- AFR 225cc 72cc no mill
- as far as inches below deck, I dont have the engine yet but it will be a 408 LS1 iron 6.0 liter.
I calculated 11.1:1 Compression Ratio with the inches below deck at zero. If it goes to -0.015 the compression bumps up to 11.5:1
My goal for compression is somwhere between 11.3-11.5 and I need to know how to get there.
Also, what pushrods should I use if I leave the heads at 72cc and dont mill them.
THanks in advance for the input.
- -2cc Diamond Pistons
- 4.030 block bore
- 4.0 stroke
- 4.130 Gasket Bore (Cometic Gaskets with 0.40" Compressed thickness)
- AFR 225cc 72cc no mill
- as far as inches below deck, I dont have the engine yet but it will be a 408 LS1 iron 6.0 liter.
I calculated 11.1:1 Compression Ratio with the inches below deck at zero. If it goes to -0.015 the compression bumps up to 11.5:1
My goal for compression is somwhere between 11.3-11.5 and I need to know how to get there.
Also, what pushrods should I use if I leave the heads at 72cc and dont mill them.
THanks in advance for the input.
TECH Fanatic
Joined: Mar 2003
Posts: 1,946
Likes: 1
I get the same static numbers you do... What are all your cam specs???
BTW, if your pistons do end-up being .015 out of the hole that will put your quench at .025...
You might want to check the piston to deck height before you order the head gaskets...
Good Luck
BTW, if your pistons do end-up being .015 out of the hole that will put your quench at .025...
You might want to check the piston to deck height before you order the head gaskets...
Good Luck
Sad to say but I dont have a cam picked out yet. I was hoping to get one through Ed but he is not returning any of my PM or emails. Then I said I would get a custom through Futural but I am unable to get ahold of them as well. I would like a custom cam but it doesnt look very promising. I really dont want to buy an off the shelf cam but I just might have to. 
So then it sounds like I need to receive my shortblock and measure my piston height before I can order my gaskets or pushrods?
So then it sounds like I need to receive my shortblock and measure my piston height before I can order my gaskets or pushrods?
TECH Fanatic
Joined: Mar 2003
Posts: 1,946
Likes: 1
Originally Posted by 99whitews6
So then it sounds like I need to receive my shortblock and measure my piston height before I can order my gaskets or pushrods?
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Originally Posted by SideStep
Sure, that is what I would do. Most agree that a quench of .035 - .040 is best for street use and "little" tighter for strip only use... I am at .037-.038 ish.
Ok, engine builder measured and the piston sticks out of the block 0.005". So if I calculated correclty my compression ratio should be right at 11.3:1 with the cometic 0.040 compressed gaskets right?
- -2cc Diamond Pistons
- 4.030 block bore
- 4.0 stroke
- 4.130 Gasket Bore (Cometic Gaskets with 0.40" Compressed thickness)
- AFR 225cc 72cc no mill
- Pistons stick out 0.005"
So now what length pushrods do I need?
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Originally Posted by 99whitews6
Ok, engine builder measured and the piston sticks out of the block 0.005". So if I calculated correclty my compression ratio should be right at 11.3:1 with the cometic 0.040 compressed gaskets right?
- -2cc Diamond Pistons
- 4.030 block bore
- 4.0 stroke
- 4.130 Gasket Bore (Cometic Gaskets with 0.40" Compressed thickness)
- AFR 225cc 72cc no mill
- Pistons stick out 0.005"
So now what length pushrods do I need?
- -2cc Diamond Pistons
- 4.030 block bore
- 4.0 stroke
- 4.130 Gasket Bore (Cometic Gaskets with 0.40" Compressed thickness)
- AFR 225cc 72cc no mill
- Pistons stick out 0.005"
So now what length pushrods do I need?
I'm getting 11.1:1 also.
Maybe I miscalculated something(I am just using a spreadsheet that I was given). I guess I have 11.1:1 compression which is fine with me for now as I can always mill the heads down the road.
So will the standard 7.4 pushrods work for me?
So will the standard 7.4 pushrods work for me?
TECH Fanatic
Joined: Mar 2003
Posts: 1,946
Likes: 1
Originally Posted by 99whitews6
Ok, engine builder measured and the piston sticks out of the block 0.005". So if I calculated correclty my compression ratio should be right at 11.3:1 with the cometic 0.040 compressed gaskets right?
- -2cc Diamond Pistons
- 4.030 block bore
- 4.0 stroke
- 4.130 Gasket Bore (Cometic Gaskets with 0.40" Compressed thickness)
- AFR 225cc 72cc no mill
- Pistons stick out 0.005"
So now what length pushrods do I need?
- -2cc Diamond Pistons
- 4.030 block bore
- 4.0 stroke
- 4.130 Gasket Bore (Cometic Gaskets with 0.40" Compressed thickness)
- AFR 225cc 72cc no mill
- Pistons stick out 0.005"
So now what length pushrods do I need?
Push-Rods... I have no idea. If I was to guess, since you are not milling, 7.4s. You will also have to know how much smaller your base circle is on what-ever cam you get. TSP, Thunder, etc... should all know this and be able to give you a PR recommendation....
TECH Senior Member
Joined: Mar 2004
Posts: 14,620
Likes: 17
From: BFE
Dan, it looks like you got all of your answers answered 
I got the formula for CR from another website (First mistake )
It looks like the difference between the two was how volume was being calculated.
I was using their calculation which was
Bore x Bore x stroke x 12.87
The website above uses:
(Bore ÷ 2)2 x 3.14 x Stroke x 16.387064
(Bore ÷ 2)2 x 3.14 x Stroke x 16.387064
which is the same as
(radius)2 x 3.14 x Stroke x 16.387064
I've modified my Excel sheet, if you need an updated copy.
Oh and as for the pushrod length. I just order my tool from Byunspeed. When I'm all done with the heads, I'll just use them to determin the length.
I got the formula for CR from another website (First mistake
)It looks like the difference between the two was how volume was being calculated.
I was using their calculation which was
Bore x Bore x stroke x 12.87
The website above uses:
(Bore ÷ 2)2 x 3.14 x Stroke x 16.387064
(Bore ÷ 2)2 x 3.14 x Stroke x 16.387064
which is the same as
(radius)2 x 3.14 x Stroke x 16.387064
I've modified my Excel sheet, if you need an updated copy.
Oh and as for the pushrod length. I just order my tool from Byunspeed. When I'm all done with the heads, I'll just use them to determin the length.
