Performer RPM or Airgap manifold
 

I have a perfectly good Performer RPM manifold on my Gen V 502. Would I see any gains by going to an AirGap or something else? I want to stick with a dual plane for driveabilty and idle quality. Just wondering if I will get $250 worth of improvement or should I save my money and just buy gas. I am changing the cam anyway so now would be the time to do the manifold.

Thanks, Doug

Depending on your HP and weight you are probally looking a 5-10hp. IF your close to stock and your manifolds are in good shape use the money elsewhere...The RPM Air Gap is a great manifold though...

BH

Hey Macdad, long time no see! Give me a call and let me know when you're going to be in Zeeland. I'll buy lunch and we'll talk boat big-blocks. 616-403-3962 is my cel.

Doug I doubt you will see any differance unless you spin the crap out of it....5700+++

But it'll sound really cool spinning that fast.

No. "Performer RPM AirGap" is just an updated "Performer RPM" with incrementally better runner design (not significant enough to warrant replacing) and a designed-in hollow underneath the plenum to isolate the runners from the heat transferred from the engine oil splashing from the cam and lifters onto it (which is noteworthy, but a valley splash guard will give much of the same benefit).

If I were buying new, of course I would pay the $60 premium for the newer airgap, but if I already had a P-Rpm, I would block off the heat crossover and stick a splash guard in it ($25 total in parts to do both) and rock on.

Mac, you already have a pretty good manifold, so no I don't think you'll have $250 in improvement.

Thanks for the replies guys. I think the consensus is to stick with the RPM. My motor already has the valley splash guard so I should be OK there. I kinda wondered if there really was much difference other than the "airgap" under the plenum. I have one of the Comp Extreme Energy cams with 224/230 duration that Dennis Moore is always talking about that I bought a few years ago when I was thinking of hopping up the old 7.4L. I have to pull the engine anyway this winter to install a bigger oil cooler so while it is out I am going to change the cam, too. I need about 1.5 to 2 more mph out of the old Baja to hit 65. With any luck the cam will get me a couple of hundred more RPM. :rolleyes:

See ya, Doug

MACDAD260, is the cam you are talking about the Comp Cams Grind# CB XE268H-10? if so I am trying one in one of my engines also.....just wondering about any reversion issues.....what exhaust are you running?.....Fred

I also am running the air gap intakes but as others said the change wouldn't be noticed especially for the $ it will cost to make the change....Fred

Fred, are you looking into different exhaust this year?

Crazy, I got a price on some stainless risers that dump the water farther away from the manifolds ( the guy makes them to my dimentions)......bought another new car so have to save some more cheese before that if I do it....Fred

I have to quit reading all of these tech posts. It makes me want to quit my job and start building engines again. I guess I will never grow up. ;)

Roby

Not to step on MACDAD260's thread, but what is anyone's opion on switching from a Dart intake from a 500HP currently on a 454mag motor with a HP cam and Stainless Exh. to an AirGap? Not wanting to run over 5200rpm, I'm not sure if the single plane intake is the best for my application, but I don't know if the change would be worth it.
Thanks, Brad

Fred, The cam I have has 224/230 duration, .515/.520 lift and lobe separation of 110*. I think it is the one you are referring to. I am running stock center riser exhaust. I have thought about this cam a lot and have decided to go with it per Dennis Moore's recommendation. The lobe separation of 110* is the only thing I am concerned about but, according to Dennis, the way this cam is ground, with fast opening and closing lobes, the LS should help power and not revert water. My motor has less than a 100 hrs on it since a total freshening so I am going to use the stock springs and rockers. If I go with a cam that has higher lift I feel I would at least need to change springs and probably switch to roller rockers. The cost difference is huge so I am going to go cheap and see how it works. I already have the cam and I am pulling the motor out anyway. The only thing I need to buy is a set of lifters and some gaskets. If I can get from 63.5mph to at least an honest 65 mph on GPS I will be a happy man. That is a full 10 mph faster than the stock 7.4L. I love the 502. It really wakes up the boat and makes it a lot more fun to drive. See ya. :cool:

BADINTN, No problem. I wanted to get some talk going about intake manifolds so you are welcome to post here. Good luck. :cool:

MACDAD260, The cam card say's to insall on 106 CL, Dennis said to set it up on 110 CL I have the cam now but haven't ran it on the hose to see if there is any reversion.....I'm hoping it will work fine with my exhaust which is also a center rise stock type system.....Fred

Wouldn't retarding the cam 4* move the torque curve up in the rpm range? Usually we are trying to meve it down. Maybe I am thinking about it backwards or maybe it is ground with 4* advance?

Dave

Dave,
A cam with a 110 LSA installed on a 106 ICL is ground 4* advanced. This cam installed on 110* ICL would be straight up. I don't have his reference available, but I would be surprised also at the suggestion to retard 4*
Bob

I guess if the plan is to spin it above 5500rpm straight up will be a good way to go. Thanks for the clarification Bob.

Dave

I will degree the cam in to see where its set at to get the 110* .....Fred

Hey Fred, Are you going to run your motor soon and check for reversion? If you are, I think I'll wait to hear what you find out before I install mine. Doug

Fred, I'll run it through desktop dyno to see what the IC change makes. Remember, you can't change the LSA, only the intake centerline.

ok, the XE268 cam makes 431@5000 degreed at 0 (106ICL), and makes 434@5000 -4 degrees (110 ICL). Take your pick but I'd put it in at zero.

Crazyhorse,

Can you run that cam on Desktop Dyno in a Gen V 502 Mag? I'd like to see how it compares to Fred's motors.

Oh, and I'd really like to get together for lunch someday but, lately my schedule in Zeeland is pretty tight. I'll give you a call someday, though.

Thanks, Doug

Funny you should mention that. I ran it through a 502, same specs as the 454, and it makes less power in the 502 than the 454 by about 10 horsepower. If you were to switch to 1.8:1 rockers you'd pick that back up plus a little more.

Crazy, why should I set it up at 106 ICL as opposed to 110 ICL.....is there any better of the two that would decrease the chance of reversion?...MACDAD260....I won't be running the motor until the spring....if it works well I will do the second motor....Fred

I'm just saying that if it was me installing the cam I'd put it in at zero. Low speed characteristics might be a little better but i really don't think you'd feel the difference.

I was told that marine apps. like between 109-110 ILC, that would mean retarding the cam a few degrees from the way the manufacturer ground it, good for a 5hp increase over an advanced camshaft....Fred

Fred,
I don’t mean to step on your thread, but there are some things to consider when you retard your cam. First, when you retard, you are not changing your LSA, duration, or overlap figures (the factors in reversion), you are altering the timing of your valve events. A retarded camshaft will delay the crossover point, and elevate HP and torque figures higher in your RPM curve. This will affect your low and midrange performance to some degree. It could be (depending on your SCR being high enough) compounded by a later intake closing point (by retarding valve events) bleeding off/lowering cylinder pressure making low and midrange lazy. It’s your call if the 5hp est. gains @ peak hp is an acceptable trade off for the possible loss of some low/midrange performance.
Bob

Thanks for the info Bob....I think I will set the cam at straight up "zero".....Fred

Why don't you guys call the Comp Cams cam help line? They always claim to have such great help, give them a try. They actually helped me out when I was selecting my cam. :)

I already have the cam in question, I was just gathering info from others experience on where to set it up at....which is info that others that haven't actually got a boat or have experienced characteristics of water injested exhaust have a informative information bank from past practices on....Fred

C'mon fred. Just knock it in with a big hammer and let's go boating, along with your twin cousin Tom. He fell down the other day too. It must be that GLM air is getting to all of us.

That GLM air can get pretty bad......along with the pull of gravity!....Fred

Crazyhorse,

Any idea why that cam would make less power in a 502 than a 454???

Yup. Wrong timing events and lift to support the 502. I'll be glad to run some numbers on other cams if you'd like.