John B

How much power can be gained by porting the stock 500 efi cylinder heads? I am thinking about also adding a 525 efi or equivalent cam.

Would it be advisable to increase the compression ratio at this time or not?

Would aftermarket cylinder heads be a better alternative?

Thanks, John B

PatriYacht

I have 2 great sets of Merlin 310cc rect. port heads for sale. Lots of HP improvements.

Dennis Moore

A carbureted engine needs intake ports sized perfectly for the rpm range that the engine will run in. This gives the intake port the maximum pull (vacuum) on the carburetor venturi for the given rpm. The higher the velocity of the intake port, the better the engine will run.
An MPI EFI engine (with individual port injectors) doesn't need high velocity intake ports because the injectors push the fuel into the combustion chamber. Vacuum in the intake manifold is almost a non issue with MPI.
The stock, large rectangle port heads, can be ported to your hearts content without affecting low speed performance. Install larger intake valves (2.25 inch) and pocket port the heads for a small increase in high rpm performance.
Dennis Moore

John B

Thanks Dennis,

Are we looking at 20 or 40 horsepower? What would you expect from good aftermarket heads?

Mr. Yacht,

My engine program shows your heads (stock) aren't any better than the stock GM square ports. Is this right?

Anybody have any test results? Dyno tests would be great!

Thanks, John B

Cord

iTrader: (2)

What about Valenko's wedges?

PatriYacht

I would expect them to be better. They have the 2.25 intakes and the exaust port looks much better, however I don't have any data to back that up. They have also been pocket ported and cleaned up to the gaskets.

JimV

iTrader: (1)

The exhaust ports are a problem on the stock heads. There is not enough short turn radius to make the ports flow. With extensive porting the flow can be increased dramatically, but not as good as ported aftermarket heads. A ported small block exhaust with a 1.6 valve will out flow a stock big block port by 5%.

Fully hand ported Dart exhaust ports will flow 300 cfm @ .700 lift where a stock head ported will flow about 270. The intakes 400 cfm vs. 360 for the gm heads. Less on the left hand port.

As far as hp increase it's depends on the combination. Our head/cam upgrade makes 650hp on a 502. No way with the stock EFI manifold.

John B

Jim V,
If the EFI is used with a modified program, what could be expected on your combination? I think the max desirable RPM range would be in the 5400-5700 range.
Do you do head work?
Why do you like Dart heads?
Thanks, John B

Tinkerer

BOY does Jim do head work.
he did my heads.
I am running stock heads with the wedges.
Real good workmanship.
I run 502's that are carbed, Dart intake, wedged heads,Lightning headers, Holley HP 950's ( a little too big - but plan on adding more cubes later ) and a solid ULTRADYNE cam.
Boat runs 77 gps at 5100 rpm with 28 pitch bravo 1's.
Estimate of HP - 600

John B

What are wedges? How much can be gained with work on the stock heads?