400 experts...I need your help...

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Jan 20, 2003 | 09:00 PM

zsir

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Senior User

Joined: Nov 2002

Posts: 375

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400 experts...I need your help...

I've been reading through these threads for a few weeks now, but I've yet to see this question nailed down....

I've decided to build a 400 for my 1971 f-100....

If this motor goes .030" over and the heads (1973 400) are milled .010" , I use a standard fel-pro head gasket...

What would the comp ratio(approx) be with standard 400 replacement pistons....?

What would the comp ratio be with flat top 351C pistons...???

Also how do you compute the volume of the piston to deck....is it actually measured or computed mathmatically....?

Fianlly....would it be beneficial to have 4bbl ex valves installed or a waste of money for a truck motor....

Thanks

Jan 20, 2003 | 10:54 PM

grclark351

Posting Guru

Joined: Dec 2002

Posts: 2,003

Likes: 2

From: chicago burbs

400 experts...I need your help...

here's a link to a guy's site w/rodding calculators
http://users.abilene.com/~dkelly/hot...mpression.html

Jan 21, 2003 | 09:14 AM

Bill_Beyer

Posting Guru

Joined: Aug 2000

Posts: 2,416

Likes: 4

From: PacNW

400 experts...I need your help...

Quote:

Originally posted by zsir

I've been reading through these threads for a few weeks now, but I've yet to see this question nailed down....

I've decided to build a 400 for my 1971 f-100....

If this motor goes .030" over and the heads (1973 400) are milled .010" , I use a standard fel-pro head gasket...

What would the comp ratio(approx) be with standard 400 replacement pistons....?

What would the comp ratio be with flat top 351C pistons...???

Also how do you compute the volume of the piston to deck....is it actually measured or computed mathmatically....?

Fianlly....would it be beneficial to have 4bbl ex valves installed or a waste of money for a truck motor....

The only way to accurately calculate the C.R. of an engine is to actually measure both the comb. chamber volume as well as the piston to deck volume. Comb. chamber volume can vary from 2-5 cc from the published specs and if the heads have been milled it's nothing more than a guess if you don't measure. Piston to deck volume will depend on the compression height of the pistons as well as the size of the dish and/or valve reliefs.

Anything you can do to an engine to help it breath more efficiently will help make better hp and torque. However you need to keep in mind the limitations of the port configuration when you go to improve the exhaust flow. You might be better off just cleaning up the pocket, removing the thermactor port bumps, removing material from around the valve guide, putting some decent headers on it and getting a dual pattern cam with a longer duraton/higher lift exhaust lobe.