250 head porting ?

Geezerpleazer

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What kind of power increases can one expect from porting those heads with keeping the stock valves in a 472? Machine shop says they will do both heads for $500 is it worth spending the money to do it. Plan on running the Edelbrock intake, set of headers, Cad Company SS275 cam, and 10.25:1 pistons. Any other big bang mods that I should do now while the engine is apart?
 

5one9

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2007 Magnum SRT8, 1957 F100
Put the big valves in.
 

Roy Heisenberg

The 472 Crank is stronger due to overlap
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472 Caddy in a ‘75 Jeep J-20 TH-400 Dana-60 100LL
Add a set of roller rocker shafts, and prepare to melt tires. ;-)
 

Cadillac Kid 1

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Since you have a relatively mild cam I would assume this is not to be an all out street/strip car, but rather a "sleeper". As far as the "head porting" is concerned going to larger valves (contact MTS ((I still call them that)) that would be a natural at that time since the idea of porting is to increase flow and unless you are going to keep the revs below 4500 larger valves will be beneficial. Exhaust is going to be important and your engine room is tight, so a set of custom headers and exhaust will help.
One of the issues you have in front of you is a rear end both ratio and strength. What you have with a stock '82 r4ear end will be a one tire fire until in gives out from the added torque.
If this were me and I was starting a project I would do the motor mods discussed , the exhaust and rear end mods and see how close the performance is to what you want. I believe it will give you a l0w 14 second car if everything is done right (something like a 3.50 "positraction" rear end )
Greg Surfas
 

Geezerpleazer

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.538 lift with 274 duration is a mild cam? 3.5 gears behind a Turbo400 that going to be a bit stout won't it? Stock form didn't the 472/500 come with like 2.9something? I've got a rear end from a 73 CDV I was planning on using once I got limited slip put in.

I'll talk to the shop see what it would take to put the larger valves in. $275 doesn't seem to bad.
 

Cadillac Kid 1

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It's a very good street cam. You will see. Don't get hung up on the numbers. Cad Co seems to know what they are doing as far as cams is concerned. You are going to need something like a 2100 RPM stall converter. I think you are going to have a VERY hard time (read near impossible) getting a limited slip for the '73 cad rear end. On my (coincidentally 1973) coupe I went ahead and put in a Moser 9 inch with "all the goodies" and 3.50 gears. Later that has changed to 3.77 and I go through the lights at 110 MPH taching just about 5200 RPM.
Your power band should be between 2500 and 5000 RPM, so gear accordingly. Unfortunately you can't have your cake and eat it too meaning if you gear too tall for low highway revs your performance might be disappointing.
Greg Surfas
 

Geezerpleazer

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Looks like the stock converter for a TH400 is 1900 is that "good enough"?

I talked to the porter today he is going to flow everything after the port and will recommend if larger valves are needed based on the cam I have.
 

Heisenberg

Lube is important...
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1969 Caddy with back seat...
BF476E42-E9D5-427A-9982-A3F8298F44CC.png Have you thought about the CadCo 300 cam ? They make great power, and smoke the tires well !

CTA300-H is a torque monster ...
 

Geezerpleazer

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I'll be running 10:1 compression. I spoke with them at Cadco, they weren't completely sure if I could run the SS300-H without valve reliefs running stock peanut 68-69 pistons. They knew there shouldn't be any problem with the SS275, so I (we) decided on the SS275-H.
 

Big Cadoo!

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View attachment 24520 Have you thought about the CadCo 300 cam ? They make great power, and smoke the tires well !

CTA300-H is a torque monster ...
I had the Cadco 300ss cam years ago in 512 120 cc head kruzik parts engine in a 84 camaro. Oversize cadco valves RHS rockers Edlebrock intake 800 spread bore holley 1 7/8 headers 273 rear gear stock cadillac Seville th400 and 273 rear gears. It would smoke the tires through 3 speeds. Shifted it manually at 5000rpm. It would pull 5500rpm in 3rd gear. Had a metric speedometer and well I suppose it was going pretty fast too.
 
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