Heads, cam, 350 wont power pass 4300 rpm

[crazygn]

I'll try to make this short. the cam must make power to high maybe. Should i try to advance the cam to drop the power band 500 rpm or so lower in the rpm's

The 350 engine wont power past 4300 rpm with a 14.25 x 21 mich wheel SS prop. Its in a boat that's 21ft i would guess is around 3000 dry. 3300-3400lbs with me and gas. My fuel pressure is 6psi and timing is 9* with a advance of 21* total of 30* , i cant tell if the advance works but it should do so around 2600-3000 rpm. 93 gas also. Here are the parts on the engine.

stock 4 bolt main truck block

Pro Action Redtopline Heads 180cc x 64cc
Comp Cam Beehive Springs Good For 550 Lift
Ferrea Valves 1.94 Intake / 1.50 Exhaust

billet msd dist and box

Weiand Stealth Intake Manifold & 600 carb

Comp Cams 12-244-4 "Xtreme Marine" Hydraulic Flat Tappet Camshaft & Lifter Kit
Fits 265-400 cu.in. small block Chevrolet V8s
Comp Cams "Xtreme Marine" camshaft is the latest series of hydraulic cams to take advantage of the newest development of camshaft design and valve train technology. It has an aggressive lobe design that produces better throttle response than other cams with the same duration and they still deliver strong engine vacuum. "Xtreme Marine" cams can be used for any high performance application where both low to mid-range torque and good throttle response are desired.
RPM Range: 2,000 to 6,200 rpm
Duration @ .050" lift: 234/244 (int/exh)
Valve lift: .498/.500 (int/exh)
Good for jet boat with A or B impeller, good off shore high performance cam, rough idle.
Comp Cams 12-244-4
• Aggressive lobe design
• Excellent throttle response
• Strong vacuum
• Excellent in high performance applications
• Good low to mid-range torque


should i advance the cam and prop down to a 17-19 maybe to get in the higher power level of this engine

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[crazygn]

I've seen a dyno sheet for cams this size and bigger and max TQ for all these are in the 3800-3900 range, 390 to 415 tq . Must be something wrong with this engine, maybe a compression test is due

 

[meantrump2]

600 cfm?

I would be runnin a 750cfm double pumper on an engine like that, rather that of a holley or a eldebrock. I would also degree the cam, the engine could be fighting itself otherwise. as far as advance, is it mechanical or vac. eather way I would adjus them to kick in FULL advance at the same rpm the cam comes in at. Probably 2500 rpm. Thus because of the intake your runnin.
Mallory ign makes an awesome set up that I think would impress you. check em out .

 

[crazygn]

i was just talking to my buddy on here about a 750 carb, maybe this 600 just isnt putting the fuel out . small jets, because my plugs looked pretty white after the runs.

I might be checking the cam and advance it if i can

 

[wca_tim]

I would bet a 750 carb will not do much on the top end and will do worse on the bottom. What carb is it and how is it jetted?

I think you're overpropped

how fast do you expect it to go? That's quite a bit of duration for a 350 in a boat - with that cam you're making peak horsepower (determines speed at wot if you're propped right) where about 5500 rpms? with that combination of components you're making probably 350 horsepower max, maybe less? so low to mid 60s? you're overpropped by a good bit.

what is your compression - static and when you do a compression check with a gauge??

if you're plugs are white, fatten it up before you burn it up... check for vacuum leaks as well...

 

[ezstriper]

put a 750 DP holley on it and a 19 prop....

 

[crazygn]

Its my buddys old boat, he had a heads cam 350, small cam and i'am pretty sure it would rev around 4800-5000 with this prop and his pistons where so busted up its not funny . Looking to do around 60mph or what ever it will do. It just seems this should have more power then it does.

The block is a stock 4 bolt truck block with 64 cc heads, not sure what compression this engine has i bought it how it sits. No compression test yet.
As for the carb its a eld 600, belive its a stock jet carb, the meter rods are 7047's. What the chance i can change the rods and push the carb to its limits to see if it should be bigger. Hate to spend the money for nothing.

And the prop, new to this and just dont get it i guess. If i run the 21 now at 4300 @ say 50mph and change to a 19 at say 4600 its going to do about the same mph right. Or will it push me in the power band of the cam more and hope to pull more rpm's

 

[mateman]

If your plugs are white, I would rejet the 600 before trying the 750. The 600 should be enough carb for that engine if its jetted right.

 

[wca_tim]

Its my buddys old boat, he had a heads cam 350, small cam and i'am pretty sure it would rev around 4800-5000 with this prop and his pistons where so busted up its not funny . Looking to do around 60mph or what ever it will do. It just seems this should have more power then it does.

The block is a stock 4 bolt truck block with 64 cc heads, not sure what compression this engine has i bought it how it sits. No compression test yet.
As for the carb its a eld 600, belive its a stock jet carb, the meter rods are 7047's. What the chance i can change the rods and push the carb to its limits to see if it should be bigger. Hate to spend the money for nothing.

And the prop, new to this and just dont get it i guess. If i run the 21 now at 4300 @ say 50mph and change to a 19 at say 4600 its going to do about the same mph right. Or will it push me in the power band of the cam more and hope to pull more rpm's

use a prop slip calculator online like the one a bam and play around with it. assume about 10% slip to be safe and it should give you some idea of how much a change ion pitch will make a difference.

presumably on your guestimate above, but remember that if you have a big increase of horsepower between 4300 and 5500, you might could turn a 17 or 19 fast enough that the boat will go a good bit faster. Without an idea where your peak horsepower is, you're shooting in the dark...

you need to know which springs and which jets are in the carb too... a 600 would go almost as well with my 383 as the 750 Iput on it - that's when that engine had a similar cam and a good bit better heads on it than your does now. I would try rejetting it first before going with a bigger carb. as an aside, I just relized that i've got the 750 edelbrock that came off when I upgraded the top end and went with a different carb. it was working fine and I'd sell it with a complete set of jets, metering rods and springs... not really worried about selling it, just thought of it as i was answering your post...

let us know what mains and springs are in your edelbrock... lets see if you can get it jetted right first...

 

[crazygn]

thanks man that should help me out alot. I'll check on the springs and jets friday after work and post it up.

thanks again

 

[crazygn]

Well i pulled the edl 1405 carb apart and found a problem. The meter rod on the one side was broke off and sitting in the jet [ not sure how bad this is but cant be good ] .

Here is what it had in it

meter rod 7047
spring - plain color spring
jet - 400

 

[mateman]

That would lean the mix out. Unless anyone has a suggestion on what metering rods and jets might work better with you setup. I would replace the rods and bolt it back together, and try it out. Always look around for a reason the rod broke....binding ect... Looks like youre on the right track.

 

[mkhammer]

I would say you have a little to much cam in it, Install 4 deg advance would help low end and close the exhaust sooner, which is what you want in a marine engine. The cam you have has too much duration in it. What's your compression ratio, What ignition and exhaust are you running?

 

[wca_tim]

I'd agree on too much cam for the aplication... and maybe some other "mis-matched" parts...

I'd try to replace the metering rods you have in there - and check to see what the mains are while you have it apart. what color were the springs?

Just getting the fuel mix right for what you've got will be a good start to getting it running at least ok for the time being.

 

[crazygn]

meter rod 7047
spring - plain color spring
jet - 400 [ i think they are .100 ]


your right the cam and intake are to much for what i need, i bought the engine like this , it will be rebuilt and changed in the winter.

 

[crazygn]

Well guys, i jetted the carb and it runs around 57-58 mph with 3 people, not sure if thats good or not for my boat. Now i dont know what to do, leave this cam and advance it with a 17 or 19 prop and see what it does.

Or i have a small 440 lift cam and performer intake i could try if you think it would run better and get the rpm's up or mph.

 

[Jimway]

I did a quick calculation on carb size and a 350 ci engine running at 5500 with volumetric efficiency at .85 is pulling less than 600 cfm if I did the math right.

 

[crazygn]

i think the 600 is ok but not sure if its worth a cam change.

the one in the boat is 2000 to 6200 rpm

the other i have to swap is 1000 to 5000 rpm

if i wont pick up anything from the swap then i'll keep this one in.

from what ive seen this boat does around 58 mph stock with a stock 350 mag

 

[karzrus]

Now that you got the carb working better, what exhaust system are you running? If it's stock your not going to get far with your other mods.

 

[moisturemissile]

I dont think 30 degrees total advance is enough timing. with that big of a cam your static compression is lower than you think. I`d run 34 degrees total advance and if you have a decent exhaust on it it should make the #s you are expecting. As you are increasing timing keep checking your plugs. If they start showing too much heat start putting bigger jets in it or back the timing back off.