WAGS382

I have been reading alot on OSO about cams and heads, there are alot of people here who have more experience than me, so it would be foolish for me not to ask for help. I have read alot about the 540 with the 305 and 315 heads with very impressive results, but not as much info on the 502. I was originaly interested in the 741 cam but now I feel it is too much. I would like to keep the max rpm around 5500 and cruise between 3200-3600. Now I am leaning towards the 761 cam or a custom ground. Just when I was convinced the 741 was too big I find out the 525efi has the same specs ground on a 114* lobe sep.

168761 cam:
Lift in 598
lift ex 610
duraton at .050:
in 230*
ex 236*
lobe sep 112*

168741 cam:
lift in 610
lift ex 632
duration at .050
in 236*
ex 244*
lobe sep 112*

1998 HP 500 carb base engine
gen VI 502
800 Holley
dart 6200 single plane
AFR 305 with cnc chambers (114 cc)
9.2:1 compression
Gil wet offshore with HPI silencers
thunderbolt ignition
boat: 1998 382 Fastech Formula
10,450 lbs. dry

PatriYacht

Have you already purchased the heads. If so have you tried them on your stock HP500's. The HP500 cam is very close to the same size as the 761 cam.
I think you're right to be cautious with cams and AFR heads. They flow so much air that they make the cam seem larger

RLW

If I am not mistaken, the AFR 305 CNC'd Chamber heads have a 121cc chamber volume. The "As Cast" 305's have a 119cc chamber volume. The 114cc chamber volume is available as an option.
I think that would have a direct impact on your compression ratio along with piston selection.
I would contact our own Bob Madara (aka. Rmbuilder) for cam advice and selection.

KAAMA

iTrader: (1)

Yeah, to what he said. rmbuilder/Bob can help you get squared away on your head and cam combination.

cstraub69@comcast

All of the above are really to big. . .they will just give you a narrow power band.

Chris

BadDog

What about the 731?
http://www.cranecams.com/?show=brows...tType=camshaft

articfriends

iTrader: (1)

Jeff,did you ever find out exact specs of cam your running? if it is close to the 761, going bigger,especially with your new heads that flow 15 -20 % better might just shift powerband up higher than your looking. You mentioned dynoing 1 of your motors before freshening them and modifying them,what if you did a head swap on dyno at that point w/stock cam?I'm wracking my brain also trying to decide which way to go with my motor this winter also,good luck,Smitty

cobra marty

It seems that there is so much problems with searching for a cam for the new higher flowing heads like the AFR, etc.
All the cams listed 731, 741, 761, 771, 16hr00004, 16hr00070 are all for older less flowing heads and are slanted for more exhaust duration to make up for the poor flowing exhaust ports of the older heads.
Maybe what we need is a new cam better spec'ed for the better flowing AFR heads and not something designed for something else. Something with 4-5 degree I/E split instead of the 10 degree I/E split of these older cams. Because the heads flow so much better maybe we need smaller cams then we are used to. The 761 is close with the 230/236 .598"/.610" or maybe a 226/230 would be better? Oh yea I'm thinking more for a 540 than 502.
Any thoughts or Ideas?

articfriends

iTrader: (1)

I know what your saying marty,i'm also going from merlin vr's on my 540
(approx 300cfm at.600in,200cfm at.600ex)to afr cnc 315's (380cfm at .600/280cfm at .600ex)and as long as my cam has no damage when i tear down the short block i'm probably going to run it-228/236 at .050,.593in/.612ex lift,110 in c/l,118ex c/l. There might be something out there more ideal but i hate to experiment at 250$ a pop,plus the extra work AND this cam idled at 675rpms 10in vac in gear/12 in vac free running.I didn't have any reversion issuse's with my lightning headers and i'm concerned there might be with heads that flow 25% better so i'm staying conservative,Smitty

WAGS382

First of all, thanks for all the input from everybody.
PatriYacht and smitty, The thought of running the heads on the dyno with the stock cams has deffinately crossed my mind. I asked Dave at AFR about this and he seems to think the 502 needs a bigger cam to compliment the heads. AFR claims they ran a 454 HO crate motor with the 305cc heads with the cnc chambers, victor jr and the 761 cam and got the following results.

rpm hp tq
3500 357 536
4000 423 555
4500 492 573
5000 551 578
5500 590 563
6000 605 529
peak
6100 606
4800 581

I figure with the 502 those numbers might be larger and come in sooner, do you guys agree? The 761 is more duration than the hp 500 cam with only 6* I/E split the hp 500 cam has 8* I/E split. I agree with Cobra Marty that the I/E split should be less with these better flowing heads especially with headers, but will the Gill exhaust offset this and require a little more exhaust duration?

HP 500 cam
in 576
ex 598
in 222* at .050
ex 230* at .050
lobe sep 110*