fred

I am replacing cams in my 454/400 Cyclones....what is the best set up in cams, lifters and springs?..the motors are fairly fresh with 8.8:1 compression in a 40' Wellcraft Excalibur Hawk (heavy), max rpm's around 5,000, Edelbrock RPM air gap intakes with 750cfm Demon carbs, center-riser stock exhaust, what cam will work good with this combo and not give any reversion?......Fred

Dennis Moore

The stock marine camshaft used by GM has 224/224 intake/exhaust duration and .510/.510 intake/exhaust lift on 115.5 Lobe Sep. Angle. These camshaft lobes open and close the valves very slow. You need an aftermarket camshaft that has the same amount of duration but open and close the valves faster. Good for a 10-15 horsepower increase over the stock lobes.

With your stock exhaust system a camshaft with a little more exhaust duration will help scavenge the exhaust a little better. Don't go with to much, it needlessly increases valve overlap with no increase in power. Six degrees is plenty. An aftermarket camshaft with 224/230 intake/exhaust duration will work fine. Add 5 horsepower with a camshaft with more exhaust duration.

A large increase in power will come from a tighter lobe separation angle. A 110 degree LSA will increase the power by 10-15 horsepower over the stock 115.5 degrees.

The amount of lift is a touchy subject. The rocker arm geometry is designed to accommodate up to .550 lift without going to longer, aftermarket pushrods. Keeping the camshaft lift below this point also allows you to run moderate valve spring pressure. This is important to minimize lifter wear at idle speeds.

The performance difference between .510 lift and .610 lift is minimal but the durability difference is major, requiring regular valve train maintenance (checking spring tension, rocker arms, valve retainers, lifters, push rod ends and valve guides for wear).

When you install the camshaft you should take the time to degree it. Most automotive applications work better with the intake centerline at 105 - 108 degrees advance but marine engines like the intake lobe centerline at 109- 110 degrees advance. This would mean retarding the camshaft a few degrees from the way the camshaft manufacturer ground it. Good for a 5 horsepower increase over an advanced camshaft

I recommend a camshaft with 224/230 degrees intake/exhaust duration, .520 inches of valve lift. 110 degrees Lobe Separation Angle and installed with the Intake Lobe Centerline at 110 degrees. This cam will give you maximum power at 5200 rpm with excellent durability and no water ingestion at an idle.

Call the camshaft manufacturers and tell them what you need. They can help you with a custom ground camshaft for a little extra cost.

Sincerely
Dennis Moore

fred

Thanks for that information Dennis, I will look into cam suppliers for one of that grind....who do you recommend....Crane....Comp.....Ultradyne....Isky.. .....Crower???.....Thanks, Fred

Dennis Moore

Comp Cams Xtreme Energy XE268H

fred

Dennis, the cam that was in the motor is a Crane, the numbers on the end of it are H228/312 and 3-1383, I am going to contact Crane to get the specs on this cam as the online web page won't give the spec card for this cam, thanks for the comp cam recommendation, Fred

Ric232

Dennis,

From my calculations, the cam you are recommending has 7 degrees of overlap. Is that not too high for stock exhaust??

Incidentally, I spoke with Comp Cams regarding the best cam for a Gen VI, 454 Mag MPI (different motor from what is discussed here). They recommended XM270HR which is .510"/.510" lift, 218/224 duration, 112LSA. The only problem is, the Merc service manual shows the stock cam for this motor as .511"/.511" lift, 211/227 duration. Doesn't seem like there is anything to be gained vs stock. What do you suggest to keep stock valvetrain and reliability?

Biggus

From my personal experience, Comp Cams is very conservative with there cam recommendations.

Dennis Moore

Rick 232,

You are calculating 7 degrees overlap @ .050 check. Because overlap happens when the exhaust is almost closed and the intake is just starting to open, the overlap is more accurately checked with very low valve lift/duration numbers.

Comparing camshafts with similar duration at .050 may not always be a good indication of overlap. For example, the stock GM marine camshaft has 224 degrees duration at .050 but the duration at .004 is 296 degrees. Newer camshafts, such as the Comp Cams Xtreme Energy, have faster opening and closing lobes with 224 degrees of duration at .050 but 268 degrees duration at .004 lift.

If the camshaft delays the opening and then opens the valve quickly or delays the closing and then closes it quickly, the amount of time that the engine is in overlap can be quite different between camshafts with the same .050 duration specs.

New design, aftermarket camshafts can utilize more duration and a tighter Lobe Separation Angle than stock or older aftermarket camshafts and still have less valve overlap.
Dennis Moore

Crazyhorse

Fred, you know of the cams I've been using. If you're interested in the specs of any of them I'll be glad to post them or e-mail them to you. I don't sell them, but I'll be glad to give you the guy's phone number that does if you'd like to talk with him.
This time of year I like to coordinate a parts order with him so that I can pick the order up at Chevy Vettefest in Chicago, which is in late November. Gives me a great reason to visit Chicago.

dyno

Fred Daves combo works great, you here mine running all the time! Idles great no reversion problems.