Jantzer98SS

iTrader: (54)

Well everybody has their own opinion, but I think there is overwhelming evidence that suggests the exaust side is more important. Think about it, the intake manifolds are the limiting factor on the LS1. I believe that even ported heads only flow around 260cfm when the intake manifold is bolted on. Now I think around 85% e/i is a good place to be, so you want the exaust side to flow around 220-225 cfm, which is about what you get with a well ported exaust port. People talk about 300cfm intakes and etc., but it's pointless when the intake manifolds flow considerably less. Look at the size of the LS6 intake manifold runners and then the head runners, there is no reason the head intake ports need hogged out because they aren't the restriction. The key is to keep velocity up in the runner, while getting as much additional flow in other areas as you can. But it's all about head flow when the manifold is bolted on the head.

Now isn't it a coincidence that single pattern cams work so well especially on the ported heads? The split duration cams work better with stock heads because there is a need for more exaust flow. One more point, what yields more gains on an LS1, an LS6 intake or good set of headers?

My $.02

LS1derfull

JANTZER98SS, i did some checking around and ARE had a flow test article in GMHTP that stated 289cfm at.600" lift with LS6 intake bolted up that is alot more than 260 cfm. Also from what ive seen stock headed motors like single pattern cams and even ported seem to do well with single over dual.

Jantzer98SS

iTrader: (54)

LS1derfull:

You may be right about the GMHTP test, but wouldn't you make sure if you were going to be in a magazine that you had the best flowing port of the best flowing heads? I'm curious how much they flowed with the LS1 intake and without an intake at all. I KNOW there has to be a restriction with the intake, or why do the shops for 1 talk about what a restriction it is and 2, some are working on their own.

And I also think that the computer has something to do with the single vs. split pattern debate.

LS1derfull

JANTZER, i have the results of what your asking.
Same head W/out intake:314 cfm, with ls1 intake:268cfm. Yes there is a loss with intake, but thats even true with short runner carb. race intakes too.I agree with you about not making head port bigger than intake opening, and keeping velocity, but dont under estimate LS6 intake. The reason i think people are looking for alternatives has less to do with flow of intake, more to do with runner length not being correct for rpm of there targeted setup.The ls6 intake has made 700hp as far as i know.

LS1derfull

Jantzer i think your porting work looks very good, i might have flattened exhaust port floor slightly more than that, goes to show how good your pictures came out!

Damian

iTrader: (89)

I have been talking to quite a few local porters, and several of them seem to think that the intake side on an LS1 head doesn't really need to be worked. Just cleaned up. However most of them hog the hell out of the exhaust side. Porting the intake side will definately hurt bottom end if done excessively, but isn't there a safe zone where gains can be seen without compromising any loses? Say you were going to run a single pattern cam, I would think that more power could be made if there was a good median between sides.


Josh

ChrisB

On a NA car I would be most worried about the intake. If you just can't get the exhaust to work (which you should be able to) you can crutch the exhaust to some extent with cam selection - but it's quite a bit more difficult to get the intake crutch'd in the same way.

You shouln't have to choose though - have them both worked over - and this != hogging out It's all relative. They may say the intake flows "good" - where good is in respect to a set of camel hump heads, so they don't bother with it - but that doesn't mean it can't be made better - much better in fact. And the cars that are running fast aren't the ones that have heads that are just "okay".


Chris

Damian

iTrader: (89)

Thanks for the feedback Chris.

I was talking to a guy down down in southern GA that made 412 rwhp with a similar port job that I described, and a B1 cam. A local guy did his heads and just cleaned up the intake, and ported the hell out of the exhaust. It made some good power on the dyno, but I am wondering what was left on the table by not working the intake to match. Hmmmm