Need Cam Recommendation

[Ric 232]

I currently have a 1998 Baja 232 Islander w/ a 454 Mag MPI (serial #0L035450). The boat runs 66 - 68 at 5000-5050 rpms with a stock 23P Mirage Plus. The motor has 150 trouble-free hours. Compression is stock (8.6:1). I have recently made the following mods:
1. Gil Magnum Choice exhaust
2. Vortech flame arrestor
3. ECU reprogrammed by Arizona Speed & Marine
4. Adj. fuel pressure regulator - set at 48psi per Arizona's instructions.
Unfortunately, I have gained NO noticeable increase in top speed. So, being persistant in throwing good money after bad, I'm considering a cam upgrade. I would like to stay with the stock valvetrain. I also have to be careful with my cam profile so as not to have water reversion with the exhaust.
I was considering GM cam #24502611 (211/230 dur & 511/540 lift), but a VERY well-respected (nationally) marine engine expert (whom I should probably never second-guess) has told me that I might not gain much performance and should go with GM #12366543 instead(the 502/502 cam) w/ 224/234 dur & 527/544 lift. I'm concerned about having water reversion with this cam and the possibility that I will lose a great deal of low-end power.
All suggestions and comments are invited and welcomed.
Thanks,
Ric Adkins
Orlando, FL

[Dennis Moore]

Dear Rick,
Thanks for the kind words.
When I was writing my book I had a hard time coming up with the exact camshaft timing specs for the stock Chevy marine camshafts. I actually pulled some cams out of some marine engines and sent them to Comp Cams. They measured them and sent them back with a camshaft spec sheet. I would suggest that you do the same and then ask them for some recomendations on a more powerful camshaft for your engine. They are really nice people, they perform services like this everyday and the turnaround was very short. The price was quite reasonable too.
As far as roller camshafts are concerned they will also regrind your stock camshaft (this is a real deal because it will save you the cost of a new core). The only problem I had was that they couldn't make the lobe sep angles as tight as I would have liked (the camshaft had 115.5 and the tightest they could make it was 113 after regrinding the cam). The cams worked great and I think the total cost was around $100.00 - $125.00!
I just slid the cam back into the engine and sent the engine/boat on its way!
I hope this helps someone! wink
Sincerely
Dennis Moore

[Dave F]

Going with a larger cam without increasing your compression ratio can end up decreasing performance.
Where that point may be, is where you'll need to do your homework. You'll need to inspect cam cards and see where valves will open and close and inspect the recommendations of the cam company for compression ratio.
Nothing is more important than matching your parts.
The 502/502 cam has around 9* of overlap. If I remember correctly it's set on a 107 intake centerline.
In contrast the HP 500 cam has a little less duration (222/230) but is set on a 105 intake centerline. It has 6* of overlap. The lift is a tad higher at .576/.598 So springs may be an issue as stock springs tend to bind after about .550
Now, not to disagree with Dennis, because I don't. I am, however, offering you an additional choice.
I am also raising the question, would you actually get more performance with the larger cam without increasing static compression ratio?
In my opinion, I'm not sure you would. The 502/502 and the HP500 engines are both around 9.5:1.
Maybe I'm right, maybe not.
Maybe Dennis could comment?
DAVE

[Ric 232]

Dennis,
I'm glad you realize that I certainly don't mean any disrespect. I'm simply being ultra-conservative. If 9 out of the 10 most respected marine engine experts in the country told me that a certain cam was okay, and you were the sole dissenting person, I'd go with your recommendation.
I'll tell you specifically where my concerns come from on the 502/502 cam.
1. I've seen in Powerboat Mag at least twice that Bob Teague has said that the 502/502 engine is not good for marine use. He specifically says that with the 502/502 cam, "water reversion is likely." And my guess is that he's talking about reversion with an exhaust system with longer risers than mine (i.e. WITHOUT diverters).
2. Similarly, I learned from reading Bob Teague's response to a reader letter that the early HP500 (carb) motors were ingesting water with the Gil manifolds (again, even w/o diverters). He mentioned that Mercury later changed the risers to a higher/longer riser to prevent this and then, of course, switched to CMI's on the HP500 EFI. From a water reversion standpoint, it doesn't appear that the HP500 cam (222/230 dur & .576"/.598" lift, 110deg LSA)is as radical as the 502/502 cam.
Anyway, thanks for the advice on Comp Cams. I will contact them. Do you think they know much about the water reversion aspect of the cams?
Thanks,
Ric

[Dave F]

Oh! Another issue you might need to consider heavily is the MPI might have a problem at idle with a lopey cam.
DAVE

[Dave F]

It is true that there were reversion issues with that cam and gil exhaust.
I'm thinking with the MPI to stay some where in the neighborhood of a 218/226 114 depending on which springs you want to use depends on the lift you can use.
Just some more ideas
DAVE

[Ric 232]

Dave,
The 502/502 compression is 9.6:1, BUT the HP500 is only 8.75:1, comparable to my engine.

[Ric 232]

Just to clarify, I'm trying to stay with the stock valvetrain, so I don't want to go any higher than .544" lift.
Ric

[565edge]

Ric 232:
Just to clarify, I'm trying to stay with the stock valvetrain, so I don't want to go any higher than .544" lift.
RicGet a hold of bullet cams,john partridge knows his shit,I can get ther number for you,also remember bigger cam means more idle rpm,which in turn bangs the outdrive when shifting,i am a jet guy but i talked to partride about my buddies 502 and his cam was similiar to the one teage sales for the upgrade to the 502/502 cam,my buddy has a 25 daytona with a bravo.

[BBC502]

Last year I went the 502/502 route. I had the heads slightly massaged, roller rockers, and reground the cam from 527I to 563I and 544E to 585E (cost $125 at Crower). The 502 dyno'd at 600ft/lbs of tq at 4,200 rpm and 540 hp at 5,400 rpm. I am running lightning water injected headers and I added a valve to shut the water down prior to idle due to reversion. Reversion was not much but I didn't want any. The valve springs are capable of .625 of lift according to GM performance. I don't think I'd go more than .600 at the most. It's a strong motor but I think a different induction system would help. dual plane vs. single plane and a professionally done carb. My quarters worth