Leathl_WS6

Ok I'm using educated guesses here because I did not have a chance to put the motor on a dyno before installation.

Bam's calc says a 7500 lb boat should go 82 with 1000 hp my boat is 7000. I added the extra for me and fuel.

The slip calc is right on. It says 7000lb 25 pitch 5000 rpm = 70mph. Thats exactly what I have seen.

Motors:

502 CI
Air Gap Intakes
Holley 850 DP Carbs
GM 188 Casting Rec port heads. Pocket Ported.
Comp Cams Extreme Marine Cam 234 244 on a 112 LSA matching springs.
Stock CR, heads were milled maybe .003 for cleanup.
Forged Weisco Pistons
25 Pitch Mirage Props

Motors run good, rpm shoots to 5k then its like I hit a wall at 5k.

Carbs have 6.5 Powervalves front and back. 82 Primaries and I have tried from 82 to 86 secondaries with no change at all in rpm or speed.

Timing at 11 Base I am running the V8-24 modules so total should be 35. Total has not been verified. I will do that this wekend.

Exhaust is crap I am running the Mercruiser log style manifold with gil dry risers.

I would think this combo even with the ****ty exhaust would be good for 500 each. They were 435 to start with.

Why can't I spin a 25 pitch prop past 5000?

Thanks Rob

WETTE VETTE

What Sutphen said!!! Exactly.

WETTE VETTE

I have run motors with too large of cam and not enough compression and the only way they would make any decent power was with the timing jacked way up. I am talking about a 500 RPM gain by raising the timing from 36 to like 43. I am not recommending you try this. You have to make cylinder pressure to hold up a large cam and adequate compression is the best way to do that. Jacking the timing is the destructive way!!

Leathl_WS6

Sorry guys typo on the cam its 234 244

This is it here:
http://www.compcams.com/Technical/Se...umber=11-240-4

When I called comp I told them it would be between 9 and 9.25 CR. thats the cam they suggested. I was going to run one bigger but they said I would need 9.5 or better to run the next one up.

After reading your post about CR I checked stock CR and it was 8.75 I though tit was 9.25. so the Wiseco pistons did up CR to 9.2. thats not really that low is it?

Stock these motor went 72 with your props bill. I woul love to try them again and see if it will still do that. I have a set of 4 blade 22's I'm going to try this weekend just to see what they will do.

Leathl_WS6

Cams were put in straight up. They were not degreed in. Ignition is a TB IV so there is no rev limiter. I do have MSD limiters installed but they are set at 8k right now. Valve train was set up by a reputiable local machine shop. There is 3/4 turn of preload on the lifters. I am still running stock rockers. I'm sure the exhaust is costing me at least 50 hp but I would expect the motors with good exhaust to be over 550. I can't see any way they wouldn't make at least 475 like they are.

Leathl_WS6

Any chance that I could be at max flow for these manifolds. I guess my thought is that maybe they can not support more than 5000 rpm.

That would explain why I can get to 5k in seconds but can't make it over. Anyone somewhat local have a set of 27's I can try?

DanB

I seriously doubt your making any were near 550hp. I had a similar combo that made 485 with dyno headers. Your stock exhuast is hurting you too.
Not knowing your boat or setup, sounds like a set of good headers and maybe labbing props may help but if all you have is 70mph now, you may see 74-76 @ 5200 if everything is perfect.

HPJunkie

Borrow some Mirage plus 23's and retest and compare. Give that cam and those heads some breathing room up top. It very well could be any of the other problems as well.
As far as power my brother Boatn70 just built the same motor you had described (Slightly smaller roller cam and dart intake) and dynoed it with headers :



rpm tq hp

3500 523 348.6
3600 520.1 356.5
3700 519.2 365.7
3800 520.8 376.8
3900 525.5 390.3
4000 528.8 402.8
4100 531.5 414.9
4200 535.2 428
4300 539 441.3
4400 543.3 455.1
4500 547 468.7
4600 550.2 481.9
4700 552.9 494.8
4800 554 506.3
4900 553.2 516.1
5000 549.6 523.2
5100 546.6 530.8
5200 544.2 538.8
5300 539.6 544.5
5400 534.6 549.7
5500 528 552.9
5600 519.9 554.4
5700 511.9 555.5
5800 505.3 558
5900 495.7 556.9
6000 485.5 554.7

A/F ratio between 12.57 and 13.33


we eventually got 562 HP out of it. Greg

Leathl_WS6

Dan

The odd thing is it honestly makes it 5k and 70 mph in seconds. 3500 is about 50 if I nail the throttles at 3500 within 10 seconds I'm at 5k and 70. I can not tweak another mph or rpm out of it. It's like I hit a wall.

I doubt I'm making 550 right now too. But I even if they are only making 450 each every caculator I have tried says the boat should go 78+. It ran 72 with the stock 502's with the exact same exhaust.

The lake is going finally calm down today. I have a set of 22 bravo 1's I'm going to toss on and see what I get.

DanB

I retract my first statement. My 485hp came with a different cam. You should be getting closer to 500 +/-hp
Have you checked the basics? Verify total timing, be sure the throttle/carb cables are opening all the way. Floats set right? Can you disconnect the rev lim temp? Are these the same props you saw 72 with?
What kind of boat is it?