Here's one for the Ford purists. Fox mustang meets 500 Cadillac

[SuperBuickGuy]

did you swap on the 425 heads? (better compression - raises from 7.9:1 to 10.5:1)

[STINEY]

I have a couple of good 425 engines and a parts one, but no plans to do the 425 swap.

Supposedly the 425 heads do not flow as well as the open chamber 500 stuff, and comparing the ports side by side I can believe it.

If the need to get real hairy arises, do not despair, for I have a plan. Said plan might involve a pair of closed chamber heads that flow 320cfms and a block with a huge deck cut to work with a pair of Aries Olds 403 forged pistons.

[SuperBuickGuy]

right, 2.02 valves don't flow as well as 2.19 valves..... however, neither valve will be the limiting factor
That said, 425 heads do have some overheating issues that have to be addressed
If it were me, I'd clean up the ports and put the 500 valves in the 425 heads. Of course, that simple head swap nets something like 500 hp and 700 lb torque.... all from a basically stock 500

that said, it would be an interesting build with 403 pistons

[STINEY]

How does 2.25 sound to ya?

And the 320 is actually 316cfm, with a little creative shrink-porting.

The overheating 425 head swap thing if I remember rightly just needs a hole drilled in the 500/472 head gaskets and block decks, similar to the steam holes in a 400 sbc head.

[SuperBuickGuy]

2.25 is a very good number.... now to get that sunken intake problem solved

[Deaf Bob]

Isn't 472 heads on 500 lowers supposed to raise the CR?

[STINEY]

Isn't 472 heads on 500 lowers supposed to raise the CR?

Well, to answer your question, yes 472 heads CAN raise the compresssion ratio........if they are the closed chamber heads (as in my picture, those are shaved closed chambers)

The open chamber heads are more like a smogger SBC head chamber, like a 76cc chamber head.


Here's the gig on this family of cadillac engine heads. 4 types, early small chamber that came with dished pistons, later open chamber that came with basically flattop pistons, and then the 425 smaller open chamber with flattop pistons, and the 368 stuff that nobody cares about.

The 472 and 500 both came with the small chamber/dished piston setup, AND with the large chamber/flattop piston setup.

The 500 was Eldorado specific for a couple years, then was available in the other models. So both 472 and 500 were built in the same time periods, and had a similar Compression ratio, one was just more suckily low than the other. The difference between the 472 and 500 is all in the crank/rods, they even used the same pistons, whether they were dished or flattops.

So pistons and heads go together. Unless you mix-n-match them, small chamber heads with a flattop piston will put you in the 13-1 compression ratio range.

The 425 head is designed for a flattop piston. Putting open heads on a dished piston will net you 6-1 ratios.

The 425 chamber is slightly smaller than the open 472/500 head.

I think that's it...... might be forgetting something....

[SuperBuickGuy]

472/500 are the same head. Something like 120 cc combustion cambers. The 425 head has a smaller - like 96cc heads. The net Compression 425 heads on a 500 is 9:7-10:0.

[STINEY]

472/500 are the same head. Something like 120 cc combustion cambers. The 425 head has a smaller - like 96cc heads. The net Compression 425 heads on a 500 is 9:7-10:0.

Not all of them. The 902, 950 and 250 casting heads were 76cc small chambers

The 493 and 552 castings were 120cc large chambers, no smog rails.

[SuperBuickGuy]

I sit corrected, you're right the non-smog 472 had good heads.... 500 was all smog, all the time 7.9:1

[Scott Liggett]

I sit corrected, you're right the non-smog 472 had good heads.... 500 was all smog, all the time 7.9:1

Not so. The 70-71 500's were Eldo specific and had high compression. The 70's were 10.25:1.

[TheSilverBuick]

Funny you resurrect this thread. I was just thinking this last weekend that maybe I will build that Caddy 472/500 with the 4-6-8 rockers, and stick a big turbo on it and put it in my Centurion....

[Deaf Bob]

Funny you resurrect this thread. I was just thinking this last weekend that maybe I will build that Caddy 472/500 with the 4-6-8 rockers, and stick a big turbo on it and put it in my Centurion....

You WILL like the torque...especially if you raise the carb either with an adaptor or manifold... Dunno about this 4-6-8 thingy
But a 500 with a Holley 950 DP and adaptor made the 65 skylark lift it's l.front wheel...
If you look at the intake of the motors.. The charge has to go up into the heads...

[STINEY]

If you look at the intake of the motors.. The charge has to go up into the heads...

Already have a solution or two for that particular problem.

[milner351]

That MTS unit looks like serious business - I'm guessing that's for a later revision of the engine when you're running port injection, a full cage, and lexan windows.