Remember, exhaust flow numbers are inflated in the range of 15% or so with a pipe. I would recommend using an exhaust number closer to 240 cfm for a ported LS6 head since Julio has gone on record with his heads flowing 205CFM without a pipe attached and I would imagine Jay's flow similarily.

 

Okay, we have real intake number, give me some exhaust numbers, flowed with a pipe or not.

Chris

 

From Jay's site.

http://www.absolutespeedls1.net/page5.html

LS1 FLOW NUMBERS
STAGE 1X STAGE 2 5.3l LS6 stg 2
LIFT- INT- EX LIFT- INT- EX LIFT-INT-EX
200- 147- 104 200- 151- 115 200-154-118
300- 200 144 300- 204- 163 300-208-171
400- 243- 183 400- 257- 198 400-258-204
450- 257- 201 450- 275- 209 450-278-212
500- 274- 212 500- 292- 218 500-296-221
550- 289- 215 550- 305- 222 550-310-227
600- 284- 219 600- 313- 227 600-320-229
650-326-230

 

stage 2.5 heads

 

Cstraub, we can use the Absolute numbers J-Rod posted from their site if you like rather than my guesses.

 

I pulled that from Jay's websight and it stated with a pipe but it was only at .400 lift since that was what Cstraub had asked for. It's in the post J-Rod shows above.

 

All right, Exhaust duration split lesson:
Now, this just comes from years of f#^%*&^ with engine builders and cam profiles. Proof to me it works is my happy customers.

For CID under 400, 75% exh ratio to intake dictates a single pattern cam, for over 400 CID, 80% dictates a single pattern. For every % point over you need to crutch the intake 1/2 degree of duration. . .GENERAL RULE OF THUMB. Now high RPM, over 8K will affect this somewhat. . .so I have to use an R&D guess.

Now with J-rods numbers supplied:
247 with intake on LS6 and 210 exhaust.
we have a 85% ratio of exhaust to intake.

Camshaft:
Stock 346 CID
Compression 11to1
Max RPM 6500
Max effort street car

Duration
233 Int.
229 Exh.
Max HP at 6100 will pull till 6500
Max Torque at 4300

Chris

 

And you guys thought you weren't going to get anything out of this...

On a serious note, the purpose of this thread was never to give you a hard and fast formula or tell you how to design the perfect camshaft. That takes more work, time, and effort than any of us care to contribute. On top of pure theory, years of experience are must be applied.

Before anyone goes out and buys a cam ground to those specs, keep in mind that Chris has effectively given you jack ****. You don't know the centerlines, the lift, the ramp rates or anything else about the lobe...no .100", .200" lift durations, etc.

It does serve as a wonderful example of how meaningless the "cam specs" everyone throws around are.

 

Yes, it sure does! Thanks to ALL for the Great info.
joel

 

Chris, let's say I have a set of heads that flow 280 cfm with LS6 intake in place and 270 cfm on exhaust with a pipe for a 96 percent ratio...

Would that suggest something like a 230/220 in your opinion or a 235/225 etc?

 

Yep. To back up what I have said here. Look at stock Honda cams.. . . exhaust on those things are in the 85 and 90% range. Duration favors those little bastards about 12 degrees on the intake over the exhaust.

Chris

 

Hmmmm.....

Street car???

What exhaust system and tubing size???

I "may" disagree somewhat Chris... but WTF do I know?????

I also noticed you left out a couple of "other" key numbers in your profile Chris. Getting the seeds planted???

Ed

 

Ed,
I don't have any seeds to plant. . .you know my rules about the public. . .I don't sell them. . . Hey, I am working on your new "valve lock" should have them in 6 to 8 weeks.

Chris

 

Calculations like this don't seem to favor for the larger CI motors. In my figuring, using this equation, a 383 with a head flow of 265 with the intake on will need a 255 duration camshaft to peak at 6800 rpm's. Seems rather big for a 383 and the numbers just keep getting bigger the more CI you add. Seems a bit out there to me, but seemed to work ok for a 346.

 

I think you guys need to start a new thread about how to match a cam to the heads

 

Rob
I think that is what we have done. Among the post in this thread is some good "basic" information for the LS1 enthusist to make a good decision on camshaft.

Chris

 

Ok, so lets summarize some of that.

Lets look at a couple of heads, and how you would select lobes.

Lets look at a couple of heads.

A LPE/GMPP CNC ported head with a 250CC runner
A AS CNC ported head with a 220 CC runner
A AFR head with a 205CC runner

Now, why did I select these three heads. Well, because flow is about the same on the heads, but runner volume (hence velocity is different).

Now, we all know that head porter do different things to get to the same end goal. With that in mind how do you select a lobe when you have a port that is fatter and lazier than a port that has better velocity.

My understanding from Chris' post is that he would use a slower opening port for a port with a more efficient port. So, would you use a port with a fast opening and closing in a port like the GMPP head where the port has a lot of volume, and velocity may be down over another head?

Would you look at something like the lobe that TR uses on its OMC cam 215 duration .600 lift which has nearly the same area under the curve as a TR230 lobe? (230/.575)



Hey Ed,

Since you might disagree with Chris a bit, what would you do on the little exercise above with the AS heads that Chris gave us .050 specs. I'm not asking for lift, LSA, etc... specs, but what you would do @ .050 and why.

 

Without all the low lift flow numbers... (.050" - .500")

"Disclaimer"

Using a 3600# C5 with real dual exhaust...
Long tube 1-3/4" headers...
LSX Intake - 80 MM TB

.585" Int - .575" Exh
232* Int - 234* Exh @ .050"
111* LSA - 110* ICL

Now...

I left out a few tidbits on ramp speeds and lift as well as rocker ratio... OK??

Ed

 

Chris that's for that info. That's the first case of a reverse split cam used OEM for a NA application I've heard of.

 

I think you make an excellent point. As I understand it that's the arguement for the top of the line port heads that can flow 280 cfm + thru an LS6 intake as a smaller cam can be used. The formula is more of a rule of thumb based on what the others are saying too.

I'll crunch a cam size based on Jay's LS6 2.75's thru the LS6 intake. I bet it will need a ~230 to 236 sized cam for a 383. Maybe a 240 at the max.