SMOKINV8

iTrader: (6)

I've read through probably HUNDREDS of posts on here about various cams that people have had success with, or cams that someone wants to try out because they heard it works well. Funny thing is, RARELY do you ever read about a follow up from the people who tried out a cam. My gut feeling on this is because they basically didn't know how to match a camshaft to the rest of their combo.

My reason for posting this, is I'm wanting to learn a little bit about what goes into cam selection for the LS1. It doesn't seem like all the rules of old school small block chevy's apply here.

Any way that someone wants to break this down is fine with me. I'm just trying to learn a little about what makes a COMBINATION work, not just what effects each cam spec has on the projected performance.

Any insight is appreciated.

Vents

iTrader: (9)

about 15-20 mins worth of a phone call to comp would explain this better than i can, but all it basically comes down to is a I/E flow ratio of the cyllinder heads, where you want it to peak, and where the heads flow there best numbers. what Gear/ Tire you're using, ect, ect..

say you have a set of ported LS6 heads flowing say: 300/220 (a-typical i know)
if 300 is equal to 100% you'd have a I/E ratio of 73%

now take that number and apply it to your camshaft split. since the intake side has the emphasis on flow, and the exhaust side is mostly spent anyway, the cam grinders leaned towards the "reverse" split cams using this ratio, and another factor to account for the lesser volume of exhaust gasses. you end up with cams like the 230/224, 227/224 ect...

those are angles towards N/A applications, and FI as well as N20 are a diffrent ballgame all together, as well as dynamic CR, ect..ect... all fun little tricks you can incorperate if you know how to play the game.

most popular aftermarket cam designs operate on an upper 90 percentile i/e flow ratio, in the split, if not, true 100% numbers. the splits arent really that big a deal with these heads because of the flow carachteristics (sp?). LSA's are prectically indipendant variables that can be mooved up or down, depending on your powerband needs/wants, or idling characteristics, or whatever.

SBC technology isint even comparable here, because thats a totally diffrent ballpark in port technology, and flow carachteristics. thats why this technology cannot be used or assumed. diffrent heads have diffrent needs.

basically what i do is base it off of what i want to car to do overall, and go from there. lift ballparked in the peak flow numbers, duration where i want it to peak/ and where i want to gear it to cross the traps, based on the limitations i've got(intake, TB, ect ect..).

SMOKINV8

iTrader: (6)

Strange that you picked those flow numbers. That's not far off from one set of flow numbers I've got on my heads. The ratio for both is in the 74%-75% range.

This kind of contradicts what I'd read about this topic in the past in this forum. I was under the impression that the real reason for the reverse split was to make up for the lack of intake flow, not to make up for the lesser volume of exhaust gas. After all, I would think there would be more exhausted air compared to intake airflow due to the expansion from the heat? Thats getting more indepth than I'm wanting to make this though.

Also, if anyone has any proven combo's, including bolt-on's, I'd be interested in seeing those as well.

99 Black Bird T/A

iTrader: (4)

The reverse split 230/224 type cam is to make up for the intake flow under certain special conditions, Paul @ Thunder can explain better than almost anyone why specific reverese splits work well with these engines. In the end it sort of boils down to the intake isn't what it really needs to be.

Iv_z28

I don't think head flow numbers by itself explain everything... ..though it would be very nice ..on ls1 engines the intake is the bottleneck - hence the search for a better intake, swapped ls6 intakes on earlier ls1's and reverse-split cams. Likewise, if you swap mac-headers with cats for some top-of-the-line kooks or you name it with no backpressure, that will also change parameters of the optimal cam. You cannot just measure cam specs based on head-flow #'s.

...I'm actually always wondering why no sponsor ever publish flow data of the whole intake path and of the exhaust system.
It cannot be that difficult and it would cut off some of the tricks, which don't really work in head porting, not to mention give us realistic #'s to pick up a cam.

Vents

iTrader: (9)

well, sure. the intake is a obviously a bit of a bottleneck here, but, our primary focus, is mooving air. if you have a VERY good exhaust in a cyllinder head, which these do, you can pretty much force as much air in the intake as is possible for peak cyllinder pressure. reverse split cams do this, and work well with the intake limitations.

now, consider this:

the reason the SBC's used more exhaust bias standard splits is to moove the exhaust gasses out in a similar ratio as the intake side. the more air in and out, the better the thing works. the LS1 based motors, dont require as much exhaust bias here. think, you've got a 346ci motor, running N/A. the 220+ CFM exhaust runner is more than enough flow to support the INTAKE side to 300+ RWHP. thats as much flow as a Stock LT1 intake runnner. spent gasses will be less than intake charges. thats why the valves are sized diffrently.

as far as your specific combo goes, PM me later w/ specs if you want, i'd be happy to help if i can.