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I ran across a guy selling (2) BB Aluminum manifolds one was a Wieand the other a Edelbrock Performer.
Question how can I tell what Ports the original heads have?
Is there a Part number? on the heads or manifold?
I know i could take the manifold off but obviously don't want to if these are not right.
Weiand - WCPSQ 7505 - rectangular
Performer RPM - rectangular as well
If the heads are oval i'll pass on it.
Can't hurt to take some weight off the vette.
Vette is all original except for my modifications / repair.
Guess I should be looking for recommendations:
The Wieand Stealth oval port appears to be the best solution.
If anyone has comments please share - I can lose the carb spacer for the holley and it will fit under the hood.
Recommendations?
Street car and eventually ....Heads, Cam......but like a lot of gear heads i don't have unlimited funds.
Q's
Rectangular ports ?
Oval Ports?
Does it matter?
Ultimately like to get 375 - 400 hp out of this without breaking the bank. Yes I know changing the manifold won't do squat.....but I don't want to buy Oval then should have bought Rectangular.
Confused.
I'm want to start collecting the final build components as i go along...then next winter pull the motor and make small changes.
More Torque More HP.
Just an Idea.
Last edited by Dream Car C3; Feb 10, 2026 at 03:19 PM.
Reason: added info
Both of those manifolds are too tall to fit under your stock hood. Summit says the Wieand is 5.75 tall and the Edelbrock is 5.220 tall. Off the top of my head, stock is 3.56. I have a Performer RPM on my 73 big block, but with a L88 hood. Even that requires a drop base air cleaner.
On the Summit site, they call that Weiand manifold dual plane, but the picture shows it has the plenum opened up quite a bit. If you're after torque, that's probably not what you need.
There are repop copies of the L36 390hp manifolds available that are stock height and oval port. From what I remember, they're in the $500 range for a new one. You can look on Ebay for OEM and they're $400-700 depending on how many helicoils are in them and what numbers are cast into them.
DruMor,
Thanks - with the 3/4 inch Holley spacer, the Holley Street Demon Carb and the matching dropped Air cleaner with 2 inch filter I still have almost 1 inch clearance.
A 2 - 2.5 inch increase with those manifolds will not work as you mentioned.
OK not sure what Im going to do. One thing is for sure....not modifying the hood!
I love how clean the look is on the 74....no Chrome, no big Bumpers, no Scoops, no Wings. or Air Dams.
No way Im messing with the body.....ever.
I love all C3's - yes the Chromes are the best 71 in particular - but the 74 is a beauty is ins own right. Not to mention the split rear.
If what you're wanting is 375-400 HP and not break the bank, you should be able to do that with the heads you have. If you want an aluminum intake, either a repop L36 or an OEM L36 manifold. Have the heads gone thru and make sure everything is nice. Get the compression about 10:1 (which will still run pump gas), a mild cam and you should be at your goal and not spend a heck of a lot of money to get there.
If you end up with rec port heads, there is a repop version of the LS6 intake that is low profile and will fit under your hood as well.
I have a 1974 bb and am using an original ls6 alum intake with stock casting heads.
The factory heads are indeed 781 castings which have the large oval ports.
The original ls6 intakes are rectangle ports but the bb's dont mind so much if you are not going racing.
The LS6 intake casting # is 3963569 so search online for a repro with same.
As mentioned above, you can get a repro of the ls6 intake with matching larg oval ports to match the 781 head ports.
My factory cast iron heads were totaly rebuilt from scratch with oversize valves and some mild porting and bowl work.
I switched to a hyd roller cam with .510" lift and roller rockers, to avoid the break in problems people have with regular hyd cams these days.
The block was already .020 over so I had it opened another .010 to clean up cylinders.
Went with some Wiseco alum forged pop up pistons that increased my CR to 9.6/1.
HEI ignition and a Quick Fuel 750 carb.
I wanted an increase in power and torque too and boy did I get that.
Motor dynoed at 490HP and 547LB/FT of torque.
You don't need to do all the work I did to get the extra power you are wanting.
I went with the LS6 alum intake because it fits under the stock hood and it was available to me through a friend.
Good luck with however you choose to go.
The engine pics on the dyno show a 1" spacer under the carb.
That was only so the fuel lines used on the dyno would clear the intake.
That will not be in my car with my fuel lines.
My engine is parked on a stand right now but am sure the spacer is too much with the stock hood.
The motor actually dynoed over 500hp with the dyno operators 850 race carb.
I was looking more for the torque than the hp for a fun street car.
The engine pics on the dyno show a 1" spacer under the carb.
That was only so the fuel lines used on the dyno would clear the intake.
That will not be in my car with my fuel lines.
My engine is parked on a stand right now but am sure the spacer is too much with the stock hood.
The motor actually dynoed over 500hp with the dyno operators 850 race carb.
I was looking more for the torque than the hp for a fun street car.
The oval ports will easily support 500+ HP.
The R-ports are only preferred once you push it over ~5000rpm.
Under that ovals are preferred.
Your biggest HP & TQ issue is the really low compression ratio the stock 71 & up BBCs had. Like 8:1
Getting it over 9 to 9.5 really makes the throttle more crisp! And adds power too.
400 is sooo easy on a BB. Might as well shoot for 450-500.
Your factory rated ~270 HP is net, that is close to ~350HP already (gross HP).
See the 71 LS5 454 which was rated both ways by GM. It was only 15HP stronger.
For your goals, all you need is compression and a mild cam.
The LS6 is one of the only ones for a Holley. That fits well.
And you should get rid of your oem EGR intake anyway.
My LS6 clone dyno'd at 490HP / 550TQ. @ 5400 / 3500 rpm. It might have been even stronger with oval ports! 10.5 CR.
Your 74 hood is about as high as a 72 BB hood. You might have 1 inch more room?
The Torquer II is the height limit on a BB hood. With roughly 1/2" to spare.
Not sure a Performer is gonna make it.
Prop your carb or air cleaner up and check. Use some putty or crumpled al foil.
Last edited by leigh1322; Feb 17, 2026 at 09:34 PM.
with the 3/4 inch Holley spacer, the Holley Street Demon Carb and the matching dropped Air cleaner with 2 inch filter I still have almost 1 inch clearance.
This sounds like what’s choking a lot of power out of the engine.
Originally Posted by lars
I have made multiple posts about this. Here are the facts:
A few years ago, I did a bit of dyno testing on air cleaners. What we found to have the greatest effect on engine power and performance is the distance from the top of the carb's airhorn to the bottom of the air cleaner lid. Once this distance gets tight, as it does when people use the drop-base air cleaners with a low-profile air filter to gain hood clearance, power is dramatically affected. I found that the minimum distance from the carb's air cleaner gasket on the airhorn to the bottom of the air cleaner lid, to avoid serious upper-rpm performance problems, is 3 inches. Most air cleaners have a 1" "dome", which means that the minimum distance from the air cleaner gasket on the carb to the top surface of the air filter is 2 inches. Anything less than that and you will have issues. So, for instance, you cannot run a 2" tall air cleaner on a drop base - it puts you way below the 2" minimum height required above the carb. Check your heights and clearances - this can affect you more than the style of air cleaner you're using... Run the tallest filter you can, and get the air cleaner lid as far above the airhorn as you can without hitting the hood.
If you violate the minimum height (3") noted above, you will have serious power problems. If hood clearance is tight, you will gain power going to a lower profile intake manifold. Your other option is using a taller hood.
Lars
74 BB Auto Manifold
