Bad to the bone

My cigarette has 502 mag motors i upgraded with full hydraulic
roller valve train 650 lift 308 dur. victor intake 830 holley, stellings
headers, GM rect. heads pocket ported and valve job.Crossovers
etc. How much horsepower would be gained by going with say a fully ported 310 set of aftermarket heads. Can heads be milled to boost up compression from current 8.75. Aluminum or cast. Please help.

Griff

Milling the heads .030 will get you about a .25 increase in compression. You could also try to use thinner head gaskets and maybe get another .1 increase.

Dennis Moore

Bad to the Bone
Do you realize that the stock rectangle port heads you have now have an intake port volume of aprox. 320 cc's? I don't think that you would get any performance increase by going with ported 310 cc heads.

With the huge camshaft that you installed the only performance increase you will get is from a compression increase and proping for higher engine rpm, around 6,000. I would shoot for at least 175 - 185 lbs. of cranking compression. With the big camshaft that could mean at least a 10:1 or 10.25:1 compression ratio. No you can't mill the heads that far, to keep the stock heads you will need to change the pistons.

Edelbrock makes some rectangle port aluminum cylinder heads with 110 cc combustion chambers and some oval port aluminum cylinder heads with 100 cc combustion chambers. Your stock chambers are 118 - 120 cc's. The Edelbrock heads would increase the compression ratio a fair amount.

Dennis Moore
FAMILY AND PERFORMANCE BOATING MAGAZINE

Tinkerer

Have Jim Valakeo put wedges in your stock heads and go to 2.3 intake valves. Also the numbers you gave for the cam -- is that duration at .050 or is that advertised duration? also the lift is it at .020? Cam is way too big if those are the #'s at the specs I asked about.

Bad to the bone

Thanks for the input the cam is 632/632 244/256 at .050
went with this cam expecting to stroke to 540 or upgrade
pistons. Engines run great just looking for more hp as usual.
If heads won't make a big difference what would you guys
suggest. Again thanks for the input.

Dennis Moore

With a low 8.75 :1 compression ratio and such a large camshaft you must have very low cranking compression. The intake valve is being held open way to long drastically shortening the compression cycle (the engine can't start building compression until the intake valve closes). I would guess that a compression check would show cranking compression well below 150 pounds.

To help correct the problem you can advance the camshaft with a multiple keyway timing chain set. Advancing the camshaft will close the intake valve sooner and build more compression in the cylinders. To do this correctly you should degree the camshaft to find where the valve is closing now. With your engine/camshaft combo the intake valve centerline should be at 105 degrees for best performance.

Low compression engines will respond to advancing the ignition timing as well. Because of your extremely low compression you can bump the timing up considerably without worying about detonation. About 20 degrees at an idle and 36 degrees by 3000 rpm would probably be optimum.

Hope this helps someone!

Sincerely
Dennis Moore
FAMILY AND PERFORMANCE BOATING MAGAZINE

Bad to the bone

Again thanks for the input as i mentioned i am building
these motors in stages. How much HP can i pick up
by going to ported aluminium heads and 10 to 1 compression
pistons.

Dennis Moore

I would say that increasing the compression and advancing the cam timing would make the engine feel totally different with a good increase in torque. Unfortunately you will never have a good combo with that big camshaft and single plane intake manifold on a 502 unless you increase rpm up past 6,200.
Sincerely
Dennis Moore

jdnca1

Bad;

How much power and Tq are you making now? What rpm are you running? How does the motor behave in the mid range? What centerline is your cam on? Answers to these q's will give a better read on your current set-up.

Bad to the bone

I do not know the numbers never been dynoed but enginge
runs strong. I went more for sound than top end love the
big cam sound but got spec from teague based on more
compression and 540 ci. Which i am willing to do both. Just trying
to get an idea how much alum heads and more compression will
help outside of more cubic inches. I have seen much wilder setups on members boats. I also understand the i will never run the 6000. Timing is set at 30 i do not know the cam degree.