head to intake mismatch

Woodfin · 12-19-2023, 12:27 PM

Racers,

I have heard the stories of running a BBC rectangular manifold on an oval port head, which is a huge mismatch. The stories relate how such a mismatch ran well.

My situation is an LS3 head with a CDI intake that fits fine except the roof of the port. The port is about .080" smaller than the intake, at the top only. The engine is assembled except for the intake. If necessary, I can tape up and slightly the relive the top of the port.

My question: do I need to relive the top of the port, or is it wasted time?

Woodfin · 12-19-2023, 12:30 PM

By tha way, this is a 408 CI drag race engine, NA, carb., with expected output of around 725 horse on Methanol.

Mike Pearson · 12-19-2023, 01:01 PM

If I were in your shoes I would epoxy the intake to match the head.

Woodfin · 12-19-2023, 01:31 PM

Mike, that is a reasonable idea, thanks.

Another thought, the CID intake is very tall and has a very large plenum. I have considered selling it and using a super victor.

This engine is going in a 75 vette and the CID intake will require a sizable scoop to clear.

1320racer · 12-19-2023, 06:01 PM

Quote:

Originally Posted by Woodfin

Racers,

I have heard the stories of running a BBC rectangular manifold on an oval port head, which is a huge mismatch. The stories relate how such a mismatch ran well.

My question: do I need to relive the top of the port, or is it wasted time?

Larry, I say no. That said, I think you know I ran that mismatch for years, using an Edlebrock RPM dual plane manifold atop my then 650+HP 468 and it ran great. Rich Biebel aka scdiv1 over at DRR built the engine and did the fitment of the manifold. Ultimately a Brandywine aka Larry Woodward, fully ported Weiand single plane manifold ran .about 02 quicker. Best Et with the dual plane was 10.11 and single plane was 10.07 in better air.

prostockpete1 · 12-20-2023, 07:44 PM

I worked at a engine shop in the 70.s & we took a GM aluminum BBC Rectangular manifold & filled bottom of the runners with epoxy & then matched up to oval port heads .. made more power than any other existing oval port manifold avail at that time

12-19-2023, 12:27 PM	#1
Woodfin Senior Member Join Date: Sep 2006 Location: Kilgore TX Posts: 533 Likes: 8 Liked 263 Times in 103 Posts	head to intake mismatch Racers, I have heard the stories of running a BBC rectangular manifold on an oval port head, which is a huge mismatch. The stories relate how such a mismatch ran well. My situation is an LS3 head with a CDI intake that fits fine except the roof of the port. The port is about .080" smaller than the intake, at the top only. The engine is assembled except for the intake. If necessary, I can tape up and slightly the relive the top of the port. My question: do I need to relive the top of the port, or is it wasted time?

12-19-2023, 12:30 PM	#2
Woodfin Senior Member Join Date: Sep 2006 Location: Kilgore TX Posts: 533 Likes: 8 Liked 263 Times in 103 Posts	Re: head to intake mismatch By tha way, this is a 408 CI drag race engine, NA, carb., with expected output of around 725 horse on Methanol.

12-19-2023, 01:01 PM	#3
Mike Pearson VIP Member Join Date: Mar 2007 Posts: 2,444 Likes: 613 Liked 1,916 Times in 574 Posts	Re: head to intake mismatch If I were in your shoes I would epoxy the intake to match the head. __________________ Mike Pearson 2485 SS

12-19-2023, 01:31 PM	#4
Woodfin Senior Member Join Date: Sep 2006 Location: Kilgore TX Posts: 533 Likes: 8 Liked 263 Times in 103 Posts	Re: head to intake mismatch Mike, that is a reasonable idea, thanks. Another thought, the CID intake is very tall and has a very large plenum. I have considered selling it and using a super victor. This engine is going in a 75 vette and the CID intake will require a sizable scoop to clear.

12-20-2023, 07:44 PM	#6
prostockpete1 Member Join Date: Mar 2012 Posts: 254 Likes: 3 Liked 90 Times in 52 Posts	Re: head to intake mismatch I worked at a engine shop in the 70.s & we took a GM aluminum BBC Rectangular manifold & filled bottom of the runners with epoxy & then matched up to oval port heads .. made more power than any other existing oval port manifold avail at that time