I was asked by q friend to spec him a cam for his 243 headed, full exhaust, ls6 intake ls1 trans am... He wants it to drive good and make very nice power to 6600-6700 rpm.... Specs I came up with was 231/238 .614/.585 112+3 using the lsl intake lobe and the extreme rpm exhaust lobe...

 

Is it a 6 speed car? I don't see a problem with that, its getting up there in duration but with a good tune I don't see much of a problem.

 

Yeah... 6 speed car...

 

Why the wide split, why not smaller on the exh. lobe like a 234(lxl) ?
Maybe even drop the lsa down to 111+2 and you'll still have 10.5* OL , and the same IVC..

 

been finding alittle more power and high rpm stability with the extreme rpm lobes.... and the wide exhaust split doesnt hurt... usually spread out the lsa 1 degree for every 4 degrees of increased exhaust duration

 

I like a bigger exhaust split on a M6 car.

A M6 car can get away with the torque curve hung out further into the RPM range than an automatic because the shift extension with a M6 is much greater rpm wise. Hanging the torque curve out further into the rpm range will allow the engine to recover a lot faster and keep it in its power band better than a smaller exhaust duration profile would.

I wouldn't be afraid to hit it with a 231/240 split in the duration to help build more torque later and keep it happy when he shifts gears. With a M6 a ton of torque down low is just going to blow the tires off anyways when he launches the car.

If it's strictly a street car or a cruiser then by all means keep some low end in it, but if it's going to see the track a good bit then don't be afraid of some more exhaust duration.

I also would like to see a LXL exhaust lobe or even a LSL/LSL combo unless he is trying to eek every bit of spring life out of his springs he can, but I agree it's not always needed or worth it to lift the exhaust valve that far open on a stock head deal.

 

With those specs, i would have just went with Speed Inc SI5 cam. 231/237.

You will see more results with that than your custom cam.

 

Well you could go with a lxl 230 lobe on the intake, then the intake valve springs would last longer, and I agree if spring wear isn't an issue then just go with LSL lobe on the intake and exhaust.

 

Why is that?

I'd like to hear your thoughts on this, Speed Inc has great cams, but the valve events and cam timing between the two are nill. A swing of 1-2 degree will make not a difference in the world.

A swing of 5-6 degrees will start to show a difference, but not as small as the difference between the two.

 

ill ask him what he wants but im still 95% on the 231/238 .614/.585 112+3 lsl/xe cam.. i have a lsl/lxl 239/246 in my car... so i might swing the lsl/lxl idea to him and see what he wants

 

Yeah the closing ramp rate on the LXL lobes are the same as the xe lobes, and like the xe lobes it'll keep valve train noise to a minimum.

 

Martin,

I agree with you with the bold. The only reason i said go with the SI5 is because its nearly the same size.

I seen TSP post a graph from a 224/224 vs. a 228/228 and it was a less than 5 hp difference.

I just dont buy into the whole custom cam stuff. I would only opt for a custom cam if my car was a straight up drag car or i spent the money for bigger cubes.



Highly doubt you will see as much results with that cam.

 

Looks very similar to my 230/238 EPS cam and I've been seeing more of them pop up. Geoff said mine with the 113+2 would be good to around 6800rpm but I've yet to see a graph of someone running the cam out fully so I can't be sure. I've been shifting mine at 6600rpm, afraid to go higher with stock 98 bottom end/rod bolts.

Set up with more advance should bring it down some. Anyone else have some thoughts on that?

 

XER is going to have a faster closing rate than the LXL due to the LXL having more total duration (290 vs. 287 for the same @.050 numbers).

Extreme RPM @.050 238* duration has a softer @.200 number than either the LXL or the XER and has more total duration (291*) so it will have more area than either the XER or the LXL, with a softer opening and close which is what you want on the exhaust lobe. That said the LXL is still a good lobe to use (application granted) on the exhaust side.

More ICL advance will bring the torque and hp peak rpm down some yes, but will also advance all the events.

 

The 231/238 .617/.615 112+3 Lsl/lxl cam made really good power and peaked at 6300 and held till around 6600 and drives great according to the owner... same cam tick sells except on a 112+3 instead of a 113+3

 

Fascinating. Could you please explain how a big exhaust split brings the torque curve up? I naively thought that was a matter of the LSA.

 

Good to know! It peaking at 6300 is from the 109 icl and carrying till 6600 is from the 238 exhaust and 112lsa giving him a 54.0 EVO event. I specified our Street Heat Stage 2 to peak at 6400rpm and carry to 6700-6800rpm. It has a 55 EVO event so it should do just that.
You've got it half figured out already.

LSA and exhaust duration in this aspect serve the same purpose of changing the torque curve and either sharpening/building it in the lower regions of the power band with less exhaust duration and a tighter LSA or raising it in the higher regions with more exhaust duration and a wider LSA.

Larger exhaust duration and a wider LSA open the exhaust valve earlier making the EVO event happen earlier. When you have an earlier EVO it will serve to build more torque after peak carrying the torque curve out further making more higher rpm horsepower.

Knowing how to manipulate the valve events to do the job is the secret to specifying the right profile for the application.

 

In my personal opinion I would only use a custom cam. But saying that I would not just let any dude design me a custom cam either.

 

Knowing how to manipulate the valve events to do the job is the secret to specifying the right profile for the application.[/QUOTE]

Very well put Martin.

 

Very true!! I am not totally against custom cams.. But i think for my car just being a fun, daily driveable car that never sees the track, i think its easier for me to go with a proven shelf cam rather than over think my setup and have a headache trying to figure out how is my cam gonna go work or react.

Now if i spent thousands of dollars on bigger cubes, or had a straight up drag car, i would look into a custom cam.