I'm seeing more and more reverse split duration cams coming out of R&D and into our motors. i cant see how this would benefit someone wanting to run nitrous or forced induction. Granted, i havent seen the cam spec cards for any of these types of cams, but, having the exhaust event shorter than the intake doesnt make sense. anyone?

 

I agree. Split patterns are designed to balance an imbalance between intake and exhaust capabilities. With all the help from blowers or nitrous I doubt the likelihood of stretching the intake lobe and shrinking the exhaust. Who knows, though. These motors seem to defy "normal" engine cam characteristics with their short duration, negative overlap (at .050), etc.

 

The theory as explained to me is: Increasing duration on the intake is done to compensate for the limit of 265cfm from the intake manifold. By not increasing the duration on the exhaust, overlap is not increased as much as if both durations were increased. Therefore more power without hurting the bottom end power. Sounds good, but as with any engine the results will tell.

 

I thought there would be a lot more interest in this. Any experiences?

 

Lots of hype, and no beef. The reverse split cams do not perform any better than single pattern cams.

The problem with the reverse split theory is that all of the reverse split duration cam packages DO NOT have very good totrque numbers. It is torque that you feel when you punch it. Only a drag racer with an A4 and a high stall can benefit from the 8 hp gain at 6500rpm seen on these reverse split cams.

I will post a graph of my G5 package with 438rwhp and 423rwtq and you all can plot it over any graph that you can find, and you can be the judge.

Just my 2 cents.

Lou Gigliotti LG Motorsports.

 

Lou, I'm not argueing for reverse splits. But if no reverse, no matter how small a difference from intake to exhaust, works, then what does that say about single patterns? Do they work as well as a standard split?

 

Jf

There have been plenty of discussions on other forums about the Dual patterns and split durations and reverse split cams. None of the reverse split cams are NOT making numbers so huge that they are the final answer. plus they lose torque.
On the contrary, our Split duration G5 cam makes more torque and hp up to the last 300 rpms . So that is my point. Using a larger duration on the intake, and leaving the exhaust shorter is just an experiment. Those who have tried it are just stuck defending it, rather than moving on to the next experiment.

Just my .02

Lou Gigliotti LGMotorsports.com





[Modified by LG Motorsports, 4:45 PM 7/26/2002]

 

Lou, I tend to agree with you about reverse splits, but that is a subjective opinion. I'm sure yours is based on lots more knowledge. What I was trying to determine is your opinion on single pattern vs split. For example if reverse patterns are never better do you feel a 216/220 is always better than a 218/218? Those are just cams pulled out of the air because they are familiar.

 

We developed our G5 cam based upon the head flow. In most cases the "Private" cams that individuals come up with on their own are guesses based upon other cams that are out there. Also the cam manufacturers will direct a person in the right direction. Our cam lobes were only proprietary for 1 year, then the cam manufacturer used it in their inventory.

The reverse split cams were a stab in the dark to just try and find something that would work. We have not tried one because our head design doesn't call for one. but anything is worth a try, but only after logic and physics fail. Or should I say that the laws of physics never fail, but that we fail in our caculations, or our assumptions. When formulas don't work, we have forgotten to include some variable.

There is plenty of hp left in the LS1 engine, but not much left in a cam and head package. There is no room left to put a real large cam in. The gains will now come from building the bottom end to accomidate the real hp cams.

We have a new engine package that will be done in September that should put everyone in shock. ( And we won't give out those cam specs either.)

As for your example using a 218/218 to equal a 216/220 it would depend on your head design. Reverse split cams are used in NASCAR winston Cup "Restrictor plate" engines, to make up for poor intake flow. On a stock LS1 engine the reverse split might work due to the poor intake flow. But on a properly ported and engineered cyl head, you would hurt power.

I don't know if I answered your question. I will think about it more, and get back to you.

Lou Gigliotti LGMotorsports

 

What I'm clumsily trying to ask is: Given a good set of heads(and at least 80% exhaust to intake) would a single pattern work better than a split since you can move the intake duration up and since the overlap is kept lower the bottom end shouldn't suffer. This of course leads to the question logically why wouldn't the reverse split be impacted in the some way? As you say we always miss something in our science. That's why trial and error moves us foward.

 

From everything that I have read if your exhaust flows 75% what what your intake flows you DO NOT need a split duration cam. Split duration cams are designed for bad flowing cylinder heads where the I/E efficiency is less than 75%. If your intake flows 300 cfm @ .050 and your exhaust flows > 225 @ .050 the general rules would say install a single pattern cam. If your intake flowed 325 @ .050 and your exhaust flowed 200 @ .050 you would install a longer duration cam (exhaust lobes) to make the exhaust valve stay open longer to compensate for the low flowing ports. I hope this makes sense.
Phillip :smash:

 

Phil, I used to live in Randallstown. Have to make my own crabcakes. Don't believe those menus outside your area that say "real Maryland crabcakes".
Back to the cams. Comp Cams uses 80% before they recommend a single pattern. At what point in that exhaust to intake does what pattern work well?
If heads flowed 1 to 1 would reverse split work?
Lou, do you think the intake is as good or close to as good as it can be?

 

For the stock cubic inch the manifold is sufficient. The fact that larger valves produce an increase bears this out. On a stroker, the manifold is a restriction.

Keep in mind that the C5R lemans engine has two 30mm restrictors. That is about the size of a couple of quarters. And that car makes over 650 hp.
(it is a stroker also, so more "suction" per revolution)

It would be interesting to try a 224/224 cam and then a 230/224 then a 224/230 then a 230/230 cam. That would answer the question about splits, then you would have to do the same test for each duration from 225 up to 229 to get some kind of scientific result.

That is why I get sceptical when someone comes on the board, and says that their NEW cam is the end all/be all.

Lou G

 

Thanks for the information. I would like to see the same tests.

 

since i am the author of this thread, i will divulge my decisions on cam choice. since i am going with a stroker motor (4.08" bore x 3.72" stroke) along with a somewhat aggressively ported set of ZO6 heads with bigger valves, i chose this custom grind: 236/236 .600/.600 112lca. I will post dyno results after i have this setup tuned properly (probably 4-6 weeks out).

 

Glad you started this subject. I will be going with a nice set of LS6 heads with 2.02/1.57 valves. Still haven't decided on a cam. It will not be a reverse.
They flow very well based on the porters bench. I will have my tuner flow them and put our heads together. I think advice from him is important based on what he has seen from his bench.