Hey guys. I get to see a lot of data working at Cam Motion, but this test surprised me a bit. I had a customer with a marine engine who recently tested a 237/237 duration camshaft vs a 237/252 duration camshaft in a 10.6:1 408" LS boat engine with stock LS3 heads and a TFS single plane intake. The engine with the split pattern cam picked up 36 horsepower over the single pattern. If you will not the 237/252 duration camshaft had 7.5 degrees more overlap and a 7 degree earlier IVO. Here is the dyno graph:

 

whats even better is, (If Im looking at the graph correctly) it picked up power EVERYWHWERE... except from 3800-4600 but didnt loose anything there

 

Just shows rectangular port heads LOVE a split pattern cam! Had they been cathedrals maybe not as much difference.
Good info!

 

I'm not sure this is a great comparison of a single vs split pattern cam. It is more of a comparison between one cam and a cam with much more exhaust duration.
It would have been interesting to see a single pattern cam with 242 or 244 durations vs a 237/252. Might've needed to rework the LSA and advance a little to get the intake events more evenly paired.

 

Thanks for posting Steve. This is my dyno run. Minor correction. Its a 408 with 10.6:1. I will get you some more overlays and updates as we build upon this as we discussed

 

The next test we will be doing is advancing the cam to 107icl and doing an on the water test. Then the engines come out end of october, heads get milled .030, hand ported and blended, 5 angle valve job, flow tested which they are telling me 365cfm @ 272cc, johnson 2126 lifters, and redyno with overlay. We are suspecting port noise on the flow above .550.

 

I like how it also made more power down low and up top. Interesting it matched the other cam in the middle.

The boat will appreciate that extra grunt down low though for sure.

 

They are in a twin engine daytona 28. I actually prefer a slightly softer bottom end, which the ls engine give compared to the stroked 496 blower motors they replaced. They would constantly blow the props out getting on plane. These work well and are easy on the outdrives. The added bottom end surprised me as well as I was expecting only more top end. Just an added bonus. Also keep in mind these were dyno with full accessories and a sea water pump so numbers are slightly skewed. Nothing amazing but skewed nonetheless.

 

Doesn't seem shocking given that its a square port. I'd love to see the same test on a cathedral...

 

Thank you for the correction Doug!

 

Makes sense. Opened exhaust valve earlier, made more power up top. Little to no change down low.

 

I agree with the above, but it is also generally accepted that rectangular port heads favor a decent duration split due to the port size disparity. Going from cathedral to rectangular gave BIG intake ports, but barely increased exhaust port volume.

 

I look at the individual valve events when evaluating these things. Here are the valve events at .050" lobe lift. The 3 significant differences are the EVO (exhaust valve open) EVC (exhaust valve close) and the resulting overlap (when both the intake and exhaust valves are open at the same time when the piston is near top dead center at the end of the exhaust stroke and the beginning of the intake stroke).

Since both the EVO and the EVC are both different between the two camshafts in this dyno session, we have to philosophize a bit about which valve event is responsible for what performance characteristic change.

In general, an earlier EVO can help reduce pumping loses on the exhaust stroke. This will typically show up as power improvements in the upper RPM ranges. The probable downside to an earlier EVO can be reduced torque at low engine speeds and a diminished throttle response at low speed. This could be experienced as poorer drivability.

In general a later EVC will contribute to increase overlap which can improve high RPM cylinder scavenging. This will typically show up as power improvements in the mid and upper RPM ranges. The downside to the later EVC is that the increased overlap will reduce engine vacuum, reduce idle efficiency, idle quality, low speed torque and drivability.

With all of this said, one of the surprises of this comparison is the improvement in low speed to torque from 3100-3900 RPM. It is possible that this is a dyno quirk that can happen when the dyno first couples up at the beginning of the pull. A repeat test that starts the pull at a lower RPM could clear that up if were motivated to optimize that part of the RPM range.

~Steven

 

Do you have any conclusive testing done with the cathedral style ports? Perhaps this concludes that the pushrod V8s are way undervalved?

 

To be fair, anytime someone has tested a wide split camshaft on both cathedral and rectangle, it also picked up power on the cathedral head.
http://www.cpgnation.com/rectangle-v...91;gallery]/1/
http://www.superchevy.com/how-to/ght...s-head-to-head

 

I'm confused as to why its surprising that more duration on the exhaust picked up power. I mean i'm no professional, but You'd think anytime you free up flow, there would be more power produced. Like going from manifolds to headers. I've never seen any engine make more power with choked up manifolds vs headers....to me this is pretty similar, just increasing flow a different way.

 

So this is using a carburetor? Excuse my ignorance but wouldn't that affect the results?

 

Yes. Pro systems 850 Venom VX. The only thing I would say it genuinely effect aside from side to side bank afr differential, is lack of surging/ idle instability. Carbs are much easier to tune when using a lopey cam especially on a boat where it is direct drive that drops rpm 350rpm when put in gear. The intake design has more effect than a well tune carb vs efi

 

this.

 

Those are great reads.