Hank

Am currently running an iron head 502 torque monster setup in my 1966 roadster and I love it. But I want more HP without giving up the midrange or streetability.

Am planning to upgrade this engine over the winter. Any advice on heads and cam?

Current setup:
502/502 short block
1969 rectangular port closed chamber -840 iron heads
(though "hi perf" these have small valves -- 1.72 and 2.08)
GM hydraulic roller cam -- I believe it's the 502/502 item but not positive
Comp cams stainless roller rockers
Exhaust manifolds feeding factory style side exhaust
DP 750 holley on a single plane manifold
MSD 6AL ignition with pro billet distributor

FYI: this engine is starved for airflow --
Revs cleanly to 6500 (or more if I had the nerve)
Chassis dyno peak hp is 332 at 4500 RPM
Peak torque is 443 ft-lbs at 2800 RPM

and DD2000 program predicts peak HP at 4500 RPM of about 400 (which foots exactly with the chassis dyno run).

New setup (?)
1) Switch to GMPP aluminum rectangular port heads, #1236400, with 315cc intake ports and 2.25 intake / 1.88 exhaust valves
2) Switch to Crane hydraulic roller cam, either
139741 -- 234/242 duration, .610-.632 lift
139731 -- 226/236 duration, .587-.610 lift
note: if it now has 502/502 cam that's 224/234 duration, .527-.544 lift
3) Add headers that feed to sidepipes and switch to spiral core mufflers in the sidepipes. I just bought the Hedman corvette side exhaust small-primary headers (1 3/4" primaries) because I got them on Ebay and they were $900 cheaper than the 2 1/8 primary Sandersons would be.

What do you guys think of the heads and cam choices? DD2000 likes them a lot, predicting gobs of HP boost (like, 120+ including the headers).

I know the Gen VI has a "non adjustable" valvetrain -- I don't understand what I will need to change in the setup to make it all work. I assume I need new roller lifters with the new cam. Then I just swap over the pushrods, screw in studs, rockers, and guideplates to the GMPP assembled head? As Scoggin-Dickey sells the head it comes with a valve spring "good to .700 lift." I would be shocked if there are piston-valve clearance issues but I'm not so sure about valvetrain geometry.

I'd be open to other heads (Dart, Brodix, etc.) or cams -- I'd like to be close to the right setup though, without doing this more than once if possible.

Thanks for your input --
Gerry

Steve439

Outstanding vette - I run a 502 in my 66 too.

I'm surprised nobody wants to respond to this, but I'll throw
in my two cents...

The big GM heads will drop your compression and if you're running
the stock pistons you're pretty low already. The oval ports flow
almost as well and you'll save about a third of a point. Plus you
can buy the nice CNC ported GM manifold.

I think a 750 carb is a little small for a 502. I'm running the GM 850
vac sec on mine which seems pretty perfect.

I think Hedman says not to use the sidepipe headers with aluminum
heads. I have no idea why. It might be a good idea to give them a call
and see why.

If you buy the GM heads you'll be set in terms of studs and guideplates.
Those heads have adjustable setups. You should be able to use your
current lifters and rockers. Probably pushrods too, but I don't know
for sure.

The other aftermarket heads generally have raised exhaust ports
which can end up being a real PITA.

I'd go with the bigger of the cams you mentioned. I'm running
a 234/244 solid roller and I think I could go bigger.

69 N.O.X. RATT

I might consider leaving the heads on it you have and have them worked on. If you go to an after market head you can check the Edelbrocks 100 cc heads and have them worked on. They are ovals so If your intake is a rec port that would have to be delt with.

I would go with a much bigger cam at least 245 at .050 probably 250. I have 242 and 248 solid roller in a 460 and wish it were more.

I would also go with at least an 850 cfm carb

ZL1powr

I am a new member of the corvette forum and this is my first post even though I have been viewing for some time. Finally got the nerve to post.

My recommendation for heads would be Edelbrock's Victor Jr. CNC with rectangular ports. They are the best flowing heads I could find with exhaust ports at the stock location and with 112 cc chamber volume there impact on compression ratio should be negligible. They are a little pricy at $2600 for the pair, but no others compare with stock exhaust port location.

As for cam choice I would recommend a mild solid street roller such as Comp Cams 288A-R10 (244 deg at .050, .622 net lift). This combination in a 490 cu in ZL1 with 9.8:1 CR, a performer RPM intake, Holley 850 DP and Hooker header side pipes with restrictive mufflers produced 460 RWHP at 5600 RPM and 494 RWft. lbf at 4100 RPM on the chasis dyno at Carlisle this Aug. This is a vary streetable combination. I recommend the solid roller since you can use higher tension valve springs and avoid valve float at reasonable RPM's. I formerly used an Ultradyne hydraulic roller with similar specs and experience power robbing valve float above 5700 RPM. I also experienced multible valve spring failures dispite the use of premium springs.



[Modified by ZL1powr, 3:58 AM 10/6/2002]

350camaro

Years ago when GM came out with the oval and rectangular GM performance parts big block heads, around 1994 if I remenber correctly, there was a write up on the heads in chevy high performance. I am sure the article said that the heads were disigned and made by edelbrock. I would get either the GM or edelbrock, whatever is the better price.

69stingray

How interesting!