HPJunkie

Good question. Im all ears. Greg

Thunderstruck

I just ordered two sets of the 305 cc CNC AFRs for 502 ci blocks also and am going to dyno after assembly, probably around Dec/Jan timeframe. After many hours of discussion and reading this board, the small cam (Crane 761 size) and bigger cam (Crane 741 size) opinions are running like the presidential election. Westech, Bullet cams and CMS Racing (CMS is on this board) recommended 236/242 or 244 duration with ~.6 lift on I and E give or take .020". Crane recommended the 761 cam and leads the small cam division along with some of the previous posts. As of right now, I am going to buy 1 cam with the bigger duration and dyno with that. If the peak Torque and HP is at too high rpm I will go back to the drawing board. The money invested in the heads makes switching cams a minor part of the overall package so I am game to try a couple if needed.

HPJunkie

Thunderstruck,
I cant wait to hear your dyno results. Are you running a blower of some type? My motor is a 502 also with Brodix ported 312's, 9:1 compression,Crane 741 ground on 114 (Crane recommended it) and a procharger at 7psi of boost. I wasnt able to complete dyno testing, after 10 hours on Tom Earharts dyno we couldnt find a miss. It just blubbered to a 680 horse number at like 4500rpm. Finally found the miss though...it wasnt a miss at all it was a loose blower belt! The motor does run good though as yours will Im sure. Please keep us posted. Greg

PatriYacht

People are having good results running the 741 cam in 540's with AFR heads. Even then the peak hp numbers are up around 5800 rpm. While it may work well with GM heads, it seems like the 741 is too big for a 502 with AFR heads. Unless you really like to wind it...

HPJunkie

Patri,
That could be why mine runs out at 6200 rpm or so. I need to change the prop to load the motor a bit more but I love the acceleration. Are you supposed to prop the boat to run at max torque at full throttle or higher or what? Greg

cstraub69@comcast

Wags,
I just did a project with a "marine guy" on a package deal for upgrading 502's. With the new cylinder heads out there, shorter duration and moderate lift will make more usable power under the curve the that of larger cams that make good dyno "Queens". Depending on your max rpm and a few other parameters, something in the high 220 range with a 4 degree split and around 600 lift on the intake will maxmize your combo for most power over a broad curve. Will something make more max HP, sure. Can you use . . .no. . .remember HP is a calculation.

TurboJax,
Playing around. . .backing the cams into my software about an average of 5% torque going out the pipes. If the cam is really "missed" you can loose as much as 15%. I have reduced duration by 20 degrees and lift by .75" on an engine that was way over headed and picked up 100HP and 70lbs of torque.. . .sprint engine.

Chris

PatriYacht

And then there's the reversion problem. My exhaust has a good drop and dumps the water 6 inches outside the transom. With Merlin heads and a Crane 651 cam (244 in. 256 exhaust) it was dry as a bone. Change to AFR heads and the water just poured in. Enough that it would stall the engine if you let it idle at 800. I had the tailpipes welded up and installed some water dumps but the damage was already done. In my end of the season leakdown test, 8 exhaust valves( out of 2 engines) are leaking. Probably got quenched a few times.

tomcat

Great discussion: How does all this change when you add a blower? Do you then need the extra exhaust duration to help get rid of the extra intake charge? Does that mean that a cam like the 741 with good heads that have 80% E/I is OK?

cstraub69@comcast

Tomcat,
The difference is no advance, straight up on the centerlines and base on the PSI and the engine combination will the duration figure be based. Rule of thumb the duration split is still based on the I/E ratio but due to cylinder pressure, duration at .100/.200/.300 changes drasticly.

Chris

aTX427

I would think that the 525 cam would be a safe bet considering. Is it true that the cam is a crane 741 on a 114 lobe separation? Just yesterday I spoke to AFR regarding head upgrades and they ecommended the 305 with the cnc option on the domes. He told me the 315 full cnc were too big for the 502ci engines. He also told me the 114cc domes would raise the compression to 9.7:1 and is safe with 87 octane, which is a must have for me. The only other thing is, would the more efficient AFR heads outweigh the gain from the longer runners of the 525HP headers?