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So i'm in the process of planning on rebuilding my engine for the spring. Currently I have Trickflow 215 heads, a ls6 intake, ARH headers and a qtp cut out. Current cam is a custom 235/239 .620/.623 on a 111 +2 built on lsl lobes and ls7 lifters.
Looking at going to a ported fast lsxr and jhonson 2116lsr lifters. Question is on the cam.
One of the guys at btr said i should go with the ls3 stage 3 or 4 but they both have less intake but a lot of exhaust duration. What do the. Cam guru's think?
A difference of 4 or 5 degrees is not at all a concern. LS engines, and specifically rectangular port heads, have relatively smaller exhaust ports and can use a bit more duration than the intakes need. For example, the LS9 supercharged engine has a 211/230 cam, and the LS7 NA engine is extremely close to that.
The reason for adding more is to improve "blowdown" of the cylinders so that when the int valve opens, the pressure in them has already bled off to as low as possible. Obviously this helps the atmosphere force mixture into them sooner and more as the pistons start to move downward at the beginning of the intake stroke. The poorer the exhaust system flows as a whole - head ports, headers/manifolds, and pipes - the greater this benefit will be.
There are a bunch of benefits from using less exh duration. Particularly when coupled with lower lobe separation angles. Remember, all of the valve timing numbers are based off of the intake's peak opening; butt, the exh valve opens before the int valve. This means that wide LSA makes the exh open potentially while the piston is still descending (being pushed down, i.e. producing power) toward the end of the power stroke. If the exh opens too early, cyl pressure is allowed to escape out the exhaust, instead of doing useful work. This might be beneficial especially in the case of a turbo, where you might get more effect out of having more vigorous exh flow spinning the turbo than the offsetting loss of cyl pressure. Butt for an engine other than turbo'ed, there is no such gain.
Both the exh duration and the LSA play into the exh opening point, which is then, in effect, the point in the cycle at which the piston ceases to produce power. So, in a N/A or blower application, it's a straight tradeoff between "thermal efficiency" (max conversion of heat energy to mechanical energy) produced by a low exh duration and low LSA #s, vs improved cyl fill and reduced contamination of the fresh incoming charge by unexhausted exhaust gases.
Another thing to consider is, when N/A, the int side of things has only the atmosphere pushing gases into the engine; but the exh side has potentially hundreds of psi behind expelling the gases from the cyl. Which in turn is why the valve opening can be lower for the exh; if the exh valve opening isn't The Bottleneck to the overall flow on that side, then all you get from increasing its opening, is stress on valve train parts. Lots of really good cams have less exh lift than int for this reason.
All of which is why there's no one "best" cam design. Even for otherwise identical engines. Too much depends on things external to the cam, or even external to the engine, as well as the usage of it.
You can have too much intake duration as well. Everything is a system that works together. One part out of sync can screw the whole system up and it operate inefficiently.
So now the question is do I stick with my old cam or do I go hunting for more power. Is there any more power to be found with a different cam in the 5000-7200 range Without going to A more extreme low profile? When I originally built this engine nobody is running ten twelve and even fifteen degree splits of the intake and exhaust duration Now They're suggesting huge splits like that even for Cathedral headed car such as mine.
So now the question is do I stick with my old cam or ... Is there any more power to be found with a different cam
At some level, that would depend on the cam you have, the surrounding parts (gears, converter, intake, exhaust, valve train setup, compression, ...), and whatever you want the engine to do for you. Coupled of course with your tolerance for the disadvantages of a "big" cam: driveability, need for tuning, fuel consumption, reliability, and so forth.
Fraid you're gonna have to be a bit more specific. Lots of variables here.
So now the question is do I stick with my old cam or do I go hunting for more power. Is there any more power to be found with a different cam in the 5000-7200 range Without going to A more extreme low profile? When I originally built this engine nobody is running ten twelve and even fifteen degree splits of the intake and exhaust duration Now They're suggesting huge splits like that even for Cathedral headed car such as mine.
Will the LS6 manifold support that kind of RPM with more cam and decent head flow from the TFS 215s? When I was looking at cams for my LS2, before it kicked the rods, BTR suggested the Stage 3 LS3 cam for me. They mentioned more exhaust duration to help with the "weak" exhaust port. I'll see if I still have the email.
At some level, that would depend on the cam you have, the surrounding parts (gears, converter, intake, exhaust, valve train setup, compression, ...), and whatever you want the engine to do for you. Coupled of course with your tolerance for the disadvantages of a "big" cam: driveability, need for tuning, fuel consumption, reliability, and so forth.
Fraid you're gonna have to be a bit more specific. Lots of variables here.
The car currently sit 3670 with me in it.moser 9" with 4.30 gears and a t56 , mcload rxt . Only exhaust side I have 1 ¾ arh Going into a cated y and a cut out. The new intake will be a mamofied fast lsxr. Currently the car is stock bottom and the trick flow 215 heads have 62 cc chambers.
As far as the current cam it is the cam card in my opening post.
Will the LS6 manifold support that kind of RPM with more cam and decent head flow from the TFS 215s? When I was looking at cams for my LS2, before it kicked the rods, BTR suggested the Stage 3 LS3 cam for me. They mentioned more exhaust duration to help with the "weak" exhaust port. I'll see if I still have the email.
Car is getting a ported fast 102 as i pull serious vacume on the top end.
The LS6 intake setup was holding up the potential of the Trickflow 215 heads. The tight split probably served that setup well. With the ported LSX you'll be putting in a lot more air that needs to be expelled, so a few more degrees of exhaust probably wouldn't hurt. That being said, I can't imagine you need as much exhaust duration as their rectangular-port designed cams offer. Their cathedral port should be more than sufficient.
The Stage 4 LS1/LS2 cathedral cam is very close to your current cam, with much more exhaust duration. Comparing the specs, that one along with the new intake setup and Johnson lifters should produce more power across the board.
The LS6 intake setup was holding up the potential of the Trickflow 215 heads. The tight split probably served that setup well. With the ported LSX you'll be putting in a lot more air that needs to be expelled, so a few more degrees of exhaust probably wouldn't hurt. That being said, I can't imagine you need as much exhaust duration as their rectangular-port designed cams offer. Their cathedral port should be more than sufficient.
The Stage 4 LS1/LS2 cathedral cam is very close to your current cam, with much more exhaust duration. Comparing the specs, that one along with the new intake setup and Johnson lifters should produce more power across the board.
Now the question is am I technically over cammed for the f a s t intake power band of 6800-7k max?
02-20-2023, 01:30 PM
Can you have too much exhaust duration? 
