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!

 

I have an Excel file that I made up that I can send you. BUt you will need to know how much the piston comes out of block, compressed gasket thickness, Gasket bore.

 

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.

 

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

 

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?

 

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.

 

Thanks a bunch. Time to order everything else now!

 

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?

 

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?

 

Yupper.. looks like 11.28:1 to...

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....

 

So I have two different people with two different compression ratios! Which one if accurate, 11.1 or 11.28?

 

~ 11.28

http://www.rbracing-rsr.com/compstaticcalc.html

 

Thanks!

 

I get 11.28 CR as well. Use this calculator http://www.rbracing-rsr.com/compstaticcalc.html

Dan

 

Posted at the same time lol!

Dan

 

Contact Erik @ HPE, they have a great 408 cam. Its not super crazy, but if you wanted something larger I don't doubt they could crank out something equally wicked.

 

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.

 

http://www.diamondracing.net/cocalc.htm