will not pull past 4000 rpm?

SimplyOrange

SimplyOrange

New member
took the boat out I been working on and it will not pull past 4000 rpm, the old stock 454 peanut port heads with a performer intake would pull to 4300 rpm with the same pump setup.now it has a 468 dome pistons at 9.5:1, with a comp jet boat cam and large oval port heads and rpm intake. when I am cruising at about 2500 and put my foot in it the boat instantly hits 4000rpm and stays there while the boat picks up speed and loads the pump until it locks in at 55mph. so its locked in at 4000 rpm no matter how much load is on the impeller.i had intentions of running it up to 5300rpm.

anybody have a first place to start looking?
 
D

Disturbed

Active member
Simple stuff first.  Like, is your throttle opening the secondaries fully?  Fuel filter?  Rev limiter? Etc.  $.02
 
SimplyOrange

SimplyOrange

New member
9.5:1 compression.

cam is a comp 11-215-5

Intake Duration at 050 inch Lift  260
Exhaust Duration at 050 inch Lift  260
Duration at 050 inch Lift  260 int./260 exh.
Advertised Intake Duration  312
Advertised Exhaust Duration  312
Advertised Duration  312 int./312 exh.
Intake Valve Lift with Factory Rocker Arm Ratio  0.600 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio  0.600 in.
Valve Lift with Factory Rocker Arm Ratio  0.600 int./0.600 exh.
Lobe Separation (degrees)  110

fuel filter is brand new and the distributer hasn't changed since the first motor.
 
G

Gold Member

New member
I put a cam that size in my cuz jet boat motor without raising the compression and it did the same thing. He didn't want to put a smaller impeller In it to utilize the cam so I put a 228-236 @.050 duration and  .560 lift cam in it and it came alive!


Since then we installed SCJ heads, 11:1 compression and put that big cam back in it  and it don't have an issue.
 
SimplyOrange

SimplyOrange

New member
Motor Head said:
I put a cam that size in my cuz jet boat motor without raising the compression and it did the same thing. He didn't want to put a smaller impeller In it to utilize the cam so I put a 228-236 @.050 duration and  .560 lift cam in it and it came alive!


Since then we installed SCJ heads, 11:1 compression and put that big cam back in it  and it don't have an issue.
Click to expand...

were there any changes to carb or timing dont during your cam swaps? my machine shop guy said that i have enough compression to run this cam. he said i need to be checking fuel pressure,secondaries and timing. i gave him my cam specs when i was getting motor parts and he told me what dome i needed and so on.

im going to check and make sure the carb is opening all the way along with the secondaries, the balancer has not spun any, then im installing a fuel pressure regulator on the manual fuel pump, with a pertronix adjustable rev limiter set to 6,000rpm. ill come back with my findings.
 
G

Gold Member

New member
I would definatly start with those things. I was just telling you what I have experienced. I wasn't saying that's your issue. Let us know what you find.  :smile16:
 
SimplyOrange

SimplyOrange

New member
Motor Head said:
I would definatly start with those things. I was just telling you what I have experienced. I wasn't saying that's your issue. Let us know what you find.  :smile16:
Click to expand...

well you scared the crap out of me  :smile20:, because i REALLY dont want to be changing the cam.
 
duanehydro

duanehydro

Active member
Looking at the cam specs, the cam doesn't hit it's power range until 4000.....I'm guessing too much cam also. Might work in a light gullwing or tunnel, though.
 
duanehydro

duanehydro

Active member
lol, don't panic....was a three keyway timing set used? was the cam degreed in? It is possible the cam is retarded.....unless degreed in, you won't know for absolute sure. But I have seen these sets installed where someone thought they had it on the circle, and it was the oval mark...also, if using a 3 way set, before replacing the cam, I'd try advancing it 4* before I replaced it. (if set straight up)  .02
 
G

Gold Member

New member
I agree with Duane. You can advance a cam and make the engine think it's smaller so to speak.  Just be careful because if the cam has a lot of advance ground in it already you may get the intake valve too close to the piston.
 
SimplyOrange

SimplyOrange

New member
it is set straight up. not a 3 way timing set. and I have a good bit of P-V clearance so I can try adjusting it. ill look into a timing set so I can degree the cam.
 
S

shimp

New member
That engine setup sounds similar to mine except I've got the regular comp cams marine cam in mine, and supposedly my dome pistons make 10:1 compression.  Dual plane Pro-Comp intake with Edelbrock 850 carb, Dominator pump 19' medium layup boat, not sure of the impeller but when it's running good (I have fuel supply problems never bothered to fix) will pull 4900 rpm and 65-70mph.

I'd have to agree with everyone else that if all the other things like timing, fuel supply, throttle linkage, all check out then your cam is too big for your compression.  I built a SBC years ago and thought I wanted a big cam, was a fail.  Would have made way more power with smaller cam.  Had flat top pistons, didn't really know I needed 11-13:1 compression to run big cam, found out the hard way.

I think this is the cam in my motor:  http://www.jegs.com/i/Comp-Cams/249/CL11-232-3/10002/-1?parentProductId=747427

Operating Range: 1000-5000 RPM
Duration Advertised: 262° Intake / 268° Exhaust
Duration @ .050'' Lift: 218° Intake / 224° Exhaust
Valve Lift w/1.7 Rockers: .505'' Intake / .515'' Exhaust
Lobe Separation Angle: 112°

I have no regrets with this setup.  Gets excellent economy, beast holeshot (for a low HP boat) and snappy TR.  If I find the cam papers I'll verify the part number, but I think that's it.
 
E

EMBRACETHEHATE

New member
Duanehydro said:
lol, don't panic....was a three keyway timing set used? was the cam degreed in? It is possible the cam is retarded.....unless degreed in, you won't know for absolute sure. But I have seen these sets installed where someone thought they had it on the circle, and it was the oval mark...also, if using a 3 way set, before replacing the cam, I'd try advancing it 4* before I replaced it. (if set straight up)  .02
Click to expand...
yep, did that before in a stroker vw motor. What a dog it was! Took me forever to figure it out.

Sent from my DROID RAZR using Tapatalk 2

 
R

RandyJET

New member
:smile16: Had the same problem it was my dizzy did everything tried jetting tried carb adjustment nothing helped checked timing it was spot on tried advance retard same thing then I pulled the dizzy replaced with lockout Msd and everything golden.
 
SimplyOrange

SimplyOrange

New member
I checked the cable for WOT,put a regulator and gauge(but it only put out 8psi wide open) replaced the distributer, played with timing and its still doing it, it has a edelbrock 700 on it right now, I just picked up a holley 750 to put on it this week when the weather gets right.if it doesn't straighten up then all I can assume is that the impeller is too big.
 
SimplyOrange

SimplyOrange

New member
i put the 750 holley on it with no change at all, i think the a impeller is too big, with the stock peanut port 454 it would turn 4200rpm, but im thinking that motor made maximum torque and hp at around 4200 unlike this motor that should want 5500.
 
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