Eliminated572

There isnt near enough cam talk happening but I can't find an answer here...
Commonly I noticed guys opt for the 525efi cam, I believe Whipple offers this cam in an upgraded package. My question is: When does it make sense to bump up the intake duration/lift to match the exhaust?? I've read articles and talked to people on here with no straight answer. I understand favoring the exhaust vs intake helps expend the charge. But what does just increasing the intake to match exhaust promote (not lowering the exhaust profile, but increasing the intake)? More low end torque at expense of top end? Wet exhaust play a role? This is a whippled 500 a builder spec'd. Peak power 5800-5900. Stock heads.

Example -

525 Cam (Common Upgrade)
Duration (advertised) - 298/306
Duration (@ 0.050) - 236/244
Lift - .610 Intake, .632 Exhaust
Lobe Center - 114*

Single pattern (I'm questioning from builder)
Duration (advertised) - 306/306
Duration (@ 0.050) - 245/245
Lift - .651 Intake, .651 Exhaust
Lobe Center - 114*

MILD THUNDER

I think generally, when it comes to cams and supercharging, there are simply a ton of fallacies out there. You'll hear things like " it needs to be a 114 LSA" , or it needs "10* min of split in duration" , and so on.

Theres lots of factors that play in. Cylinder head flow, RPM range of engine, amount of boost that will be run, and so on.

Speaking theoretically, you take a look at the crowd favorite, the "651" crane cam. It has a 244/256 duration, with a 114 LSA. That cam might might work better, with a build using stock GM iron heads, and a supercharger making 10-12lbs of boost. It might not work as well, with a build utilizing a very good exhaust port, and 5lbs of boost throughout the same rpm band.

The LSA itself, isn't what determines how much "boost" is blown out the exhaust during overlap. The overlap itself is. One might think the 114 LSA 651 cam is going to blow less boost out the exhaust, than another cam that is on a 112LSA, or 110LSA, but it isn't that simple. You may find, that going with a cam, that has say, 240/245 duration, on a 110 LSA, will have less overlap, or close to the same overlap, and generally perform better, in the application, making more average power from say, 3000-6000rpm.

Back to your original question though. The 245/245 vs 236/244 cam, both with 114 LSA. The power may actually be fairly similar up on plane, or on a dyno pull. There is something though, the 236/244 cam will probably do better. And thats idle quality. Having the intake valve close sooner, will have less intake reversion at low speeds, and more than likely, result in a better idling engine. The single pattern cam, might work better with a cylinder head that has mediocre intake port flow, but excellent exhaust flow. The 236/244 , might be better in a setup that has a good intake port, and poor exhaust port. Or, if say, a centrifugal vs a roots. The early closing intake, might work better off boost and low engine speed, where with a screw or roots, that just isn't a problem. The 236/244, will probably work better from idle to mid to upper rpm thanks to the early closing intake, and the 245/245, might start gaining ground in the mid to upper rpm, depending on the overall combo. just my thoughts on it.

MILD THUNDER

Often i believe many marine engines, are cammed incorrectly due to the LSA misunderstanding. Most assume 114 LSA is the ticket for marine engines. So they go pick a cam that has a 114 LSA , and ignore the camshafts actual overlap. While the 114 might work ok, the better choice, may have actually been a smaller duration cam, with a narrower LSA. Instead of making 600hp at 6000rpm, they may have made 600hp at 5600rpm.

If you look at the HP500 carb engine, it had a 110LSA. The 500EFI , and 525efi had a 114LSA. I dont have the cam specs in front of me, but the overlap on them, is probably not what you think.

Black Baja

Lsa determines the shape of the power curve. The important thing when determining LSA is the length of the rod and stroke of the crank. Trying to pick a cam based on .050 and LSA #'s is a poor way to pick a cam. The most important thing is where the duration occurs in relation to the crank.

MILD THUNDER

Heres an article comparing LSA's. However, that is comparing two similar cams duration wise, but changing LSA.

It gets deeper, when you now throw in, different duration cams, to different LSA's.

http://www.compcams.com/technical/FAQ/LSAproperties.asp

sutphen 30

you have a dyno sheet of this build?

MILD THUNDER

Another article explaining the importance if the proper timing events, and overlap.

http://www.compcams.com/Pages/416/va...-tutorial.aspx

Theres alot more to a cam than .050 numbers and lift. You can pick a cam thats 242/248 @ .050, with 630 lift on a 112 lsa, and another cam with the identical specs, but have completely different timing events, based on seat duration, ICL, etc.

MILD THUNDER

...

sutphen 30

must be a light dyno,,that thing would be into heavy knock retard w/ those lean afr's.

lets see the fuel lbs burned.

MILD THUNDER

Thats all i got for that dyno sheet. Eliminated sent it to me a while back.

Those afrs are certainly showing lean. Ive had supercharged engines on dyno that started there for afrs, and never shown any signs of knock. Of course they got fattened up from there.

I do believe these engines went into a 388 Hustler, and have ran great all season. The power numbers look clean , dont see anything weird going on?

I could show you my dyno pull, that started at 2900rpm to 6500rpm, at a sweep rate of 150rpm per second. Wanna talk about loading an engine down.....dyno pull was like 30 seconds long. I see some of the guys here do a 4k to 6k rpm pull at 800rpm per second and call the tune perfect. Dyno pull is over in blink of an eye.

What do you guys typically do for your dyno pulls?