Head Flow question

**dude2000_22222** · 05-14-2010, 09:19 AM

Ok so I'm stumped. I have a SLP 402 with their 236/236 cam, ls6 intake, headers, and stock 98' heads ported with 2.02 intake valves.

The question I have is with this combo I only make 400rwhp and 420rwtq. And that is considerably lower than most setups I have seen. My tuner seems to think its the heads. So my heads, on the flow bench, are flowing 297cfm at .600 lift on the intake and 190 exhaust. These seem to be on par with most ported heads. Do I need to get better heads, is there a difference that I am not seeing because I don't see spending almost $1500 on heads for 10 cfms? Also could my flow chart be wrong or skewed intentionally?

Any information would be helpful.

**garygnu65** · 05-14-2010, 12:10 PM

the ls6 intake is holding you back a little.you need a different cam,need more exhaust duration.you gained a lot of intake flow,not much gained at exhaust flow.whats the ICL?

**dude2000_22222** · 05-14-2010, 02:47 PM

The centerline is 112 degrees. The power peaks at 5500 rpms. On other engines with the same cam I seen power around 480 to 500 rwhp. I dont think the intake is holding me back that much.

**garygnu65** · 05-15-2010, 06:30 AM

did you install the cam? was it degreed?whats the lsa?it sound like the cam is advanced a little.

**dude2000_22222** · 05-15-2010, 10:53 AM

The Lsa is 112 degrees also. And I installed it, just put it in back the way the other one was. I lined the teeth up exactly with the dots so I am pretty sure its not advanced.

**Firebirdjones** · 05-15-2010, 01:23 PM

Wow, if those numbers you posted are correct, the I/E ratio on those heads flat suck. They only have about a 65% I/E ratio.

With heads that flow like that, you would need a different camshaft that favors the exhaust side by 8-10 degrees to handicap those heads,,,,not that straight pattern 236/236 you currently have in there. There are other variables to that I can't comment on since you don't have the cam card listed, but from what I see already, it's what I'm leaning towards.

If you want to keep that camshaft I'd go for a better set of heads. Most of the aftermarket cathedral heads will flow as much as 320cfm on the intake side and have around 80-85% I/E ratio. With a percentage that high it would be more suited to the camshaft you currently have.

**dude2000_22222** · 05-15-2010, 04:09 PM

Intake

Lift Flow
.100.......81
.200.......142
.300.......223
.400.......262
.500.......285
.600.......290
.700.......294

Exhaust

Lift Flow
.078.......47.5
.155.......85.5
.232......115.6
.310......139.4
.388......178.5
.465......191.3
.543......197.6

I cant find the cam card but its the one from slp the 236/236 one.

So I def would benefit from better heads? And also is worth upgrading for just 30 cfm? I have a vast lack of knowledge in heads just throwing that out there.

**Firebirdjones** · 05-15-2010, 05:56 PM

Well, I know the 30 cfm of flow on the intake side doesn't sound like much, but it was the I/E ratio I was more concerned about.

With what you have posted, even the mid lift I/E ratio numbers are only around 68%. It appears to me the exhaust side of those heads need some more work.
Generally most head porters shoot for 75% or better. ~80% is considered just about optimum.