IF you go with good flowing heads, you won't need a large cam. . .the heads will do the work.

Chris

Chris & Wags,
I agree. Those heads (with an 80% I/E ratio) and that displacement need approx 232*/236* on 112* LSA, a .60x"/.61x" lift. No more than 4* I/E split. Duration in excess of 236* will not increase peak torque #'s, just the RPM you reach them. RLW on this forum is making 706 HP, N/A, with a 540 CID motor, dead reliable, with AFR 305's and a cam(under 240* & .630" on both sides)
Bob

Bob,
I plan on using the Gil offshore exhaust that came original on the HP500 carb motors.I plan on max rpm of 5400-5500. What head would you use the 315 cnc or the 305 with only the chambers cnc'd ? I would love to stroke to 540" but the motors have low hours and I want to take the money that I saved on the bottom end and put in the heads. Jeff

FYI...

I also have 1997 HP500's (carb motors) that I was inquiring about raising the HP to around 600HP.

I was talking to Bob Teague this weekend at the Scope Poker Run. He gave me a few suggestions. He said get rid of the Gil exhaust (causes rversion) and get a good set like CMI. Get the MSD ignition. He also said to go with aluminum heads. He said the "new" oxegenated gas these days is destroying heads like crazy (I think he said the seats or valves??) It won't destroy the aluminum ones.

Teague was smoking crack. Or possibly he sells CMI's and not Gils.

My last motor had the standard low profile Gil HP500 exhaust risers with silent choice to boot. Cam was the Crane 741. No revesion what so ever.

I run with a buddy of mine who has the hp500 with the gils. I run the hp500efi CMI's, and we are dead even in speed. Both of us have 288 sunsations! The Gils are not a problem.

I'm watching this thread because he wants to produce 600 hp too.

So who has done it?

On another board we are waiting on some dyno problems to get fixed and then we will have a 509 with some figures. With a lean condition he is at around 560#/ft but with an A/F of 16/1 they haven't pulled it past 4900. The cam is under 230 duration on this one.

Bob, as you and I have talked with the cylinder heads today, cams don't have to be agressive to make power. Attention to duration at .100/.200/.300 is also an important factor. You may need an intake lobe that packs the cylinder and then shuts down quickly at .200 and on, where as the exhaust lobe may need to stay open longer under the curve.

Also the larger cams with these good heads make narrow power bands. Fine if you got a 5 speed and gears but we don't. By selecting a camshaft short on duration and moderate on lift you get good velocity into the chamber during boat cruising speed. . .3200 to 4000 and at max rpm of 4600 to 5600 for most the RAM effect occurs and packs the cylinder to make power. By doing this you have a broad power band to use and your happy at all speeds.

Chris

Thats why so many custom cams (especially marine) are being ground today. The majority of shelf grinds available are designed around cylinder head flow #'s from 10 yrs ago. These new heads and the flow #'s they make with either CNC or custom porters have vastly different cam requirements, especially low/mid-lift, splits, and duration. Then add in wet exhaust and peak power in by5400-5600 RPM, and it gets very specialized.
Bob

Jeff,

You are heading in the right direction. The exhaust is still o..k. but the tailpipes will have to be reowrked and if you have silent choice that will cause a reversion problem also. Give me a call, there is a local guy in Painesville who I will give you his number for the exhaust stuff. TOP SECRET.(440)796-8225

Andy Bloom

CIG 3, so are you saying that when this engine produces 600hp, useing the gils, there will be reversion problems?