XLR8NSS

iTrader: (4)

Well there are alot of camshaft discussions going on so why not have one for the heads.

Here are some things to discuss:

-Intake to Exhaust flow ratio for different setups(big cam, small cam, NOS, blowers, bolt ons)

-How much does valve size affect flow numbers?(at what rpm, affect on power, engine bore size)

-Porting?(broad topic, maybe it deserves its own thread)

I don't know alot about this so if you think of something you want to discuss throw it out here.

Lets get this thread fired up. <img src="images/icons/smile.gif" border="0">

[announcers_voice]Gentleman...Start your engines![/announcers_voice] <img src="images/icons/grin.gif" border="0">

Personally, I would like to know what type of flow I should be looking for out of the exhaust compared to the intake for a mild SC application.

XLR8NSS

[ November 16, 2001: Message edited by: XLR8NSS ]

[ November 16, 2001: Message edited by: XLR8NSS ]</p>

Brother J

OK, I'll throw out some input from what I've learned in preparation for porting my heads this winter.

My setup: hotcam, long tubes, ported maf/tb, lid, cut-out.

My goals: focus mainly on the exhaust side with mild work on the intake bowls and valve profiling; going to install N20, thus the emphasis on improving the exhaust side. This would apply to FI since the A/F mixture is going to get there under pressure.

Points I've learned: stock lift of the hotcam will not benefit very much from larger valves, radical reshaping of the bowls will negatively affect swirl/tumble, narrow LSA (112) of the hotcam reduces dynamic cylinder pressure compared to wider LSA's (good for nitrous use because will not promote detonation) but could benefit a bit with slight milling, say around .030", longer duration on the exhaust side will be a plus when using N20, intake/exhaust port matching is not really necessary, polished runners/bowls are a waste of time (air is blind), a really good 5-angle valve job and careful valve profiling will increase low-lift flow.

What I want: 10-15 hp increase and the satisfaction of having done it myself. I don't have the budget to spend on a professionally ported set of heads. To me the experience of doing it myself is worth more than the extra hp purchased from someone else.

CHRISPY

This isnt really a tech answer but I was at Nicks shop (ARE) and had a good look at a couple sets of heads there. Let me tell you, those S1 heads are a GREAT value and are equivalent to some other vendors S2 setups. Amazing work into those heads. The S2 heads are just awesome. I was very very impressed especially considering some of the heads I have seen from other vendors.
Also a S1 head properly ported with 2.02 ad 1.57 valves flow GREAT numbers and perform very well. Almost 295 cfm with GREAT flow numbers from 400-550 lift which aint shabby
Cheers,
Chris

Crazyquik

Lets talk exhuast flow vs intake flow.

You read in a lot of books that the exhaust should flow around 80% of the intake. From my numbers, the stock LS1 exhuast side flows about 80%, but the numbers I have for some Stage 2 heads flow like 72-74% of the intake. Pro Stock exhaust flow percentages are in the 60s.

J.

Brother J

[quote]Originally posted by Crazyquik:
<strong>Lets talk exhuast flow vs intake flow.

You read in a lot of books that the exhaust should flow around 80% of the intake. From my numbers, the stock LS1 exhuast side flows about 80%, but the numbers I have for some Stage 2 heads flow like 72-74% of the intake. Pro Stock exhaust flow percentages are in the 60s.

J.</strong><hr></blockquote>

That's interesting. I haven't researched the differences in in/ex flow rates between various stages of porting. Some other variables may be involved, such as dynamic cylinder pressure variances due to valve overlap, open headers/tuned headers for more scavaging, greater combustion efficiency and others, I'm sure, that might account for the differences. I'm just guessing out loud.

Crazyquik

I think the reason that the Pro Stock heads flow like that is b/c the intake flows soooo well. Not sure about the LS1 heads.

99 Black Bird T/A

iTrader: (4)

[quote]Originally posted by Chris ARE 360:
<strong>(ARE) and had a good look at a couple sets of heads there. Let me tell you, those S1 heads are a GREAT value and are equivalent to some other vendors S2 setups. Amazing work into those heads. The S2 heads are just awesome... a S1 head properly ported with 2.02 ad 1.57 valves flow GREAT numbers and perform very well. Almost 295 cfm with GREAT flow numbers from 400-550 lift which aint shabby
Cheers,
Chris</strong><hr></blockquote>

What's the flow at the lower lifts like 200 and 300 for the ARE Stage 1's?