Heads, cam, 350 wont power pass 4300 rpm

[crazygn]

i belive the manifolds are a stock replacement that exits out the top middle. The riser is a after market mandrel bent pipe 90.

 

[crazygn]

let me ask this, if i cant get over 4300 rpm and 58mph with this setup do you think this cam and intake swap would help rpm and mph

swap to

performer intake and

crane cams 100052 cam

Basic Operating RPM Range1,600-5,400Intake Duration at 050 inch Lift216Exhaust Duration at 050 inch Lift216Duration at 050 inch Lift216 int./216 exh.Advertised Intake Duration272Advertised Exhaust Duration272Advertised Duration272 int./272 exh.Intake Valve Lift with Factory Rocker Arm Ratio0.454 in.Exhaust Valve Lift with Factory Rocker Arm Ratio0.454 in.Valve Lift with Factory Rocker Arm Ratio0.454 int./0.454 exh.

 

[mkhammer]

You speak of advancing the cam, what lobe center is your cam ground on? depending what lobe center you have advancing the cam may give you more low end but you may gain rpm due to your cam is not working in it's power range. If it is ground on a 110 it would help. if it is on a 108 or less it's not really a marine cam to be used with wet exhaust.
If you were to change cams I sell a Hyd flat tappet cam dur. 214/226 @.050, lift 449/462 @ .050 on a 114 install 4 deg $145.00. It' a good marine grind and the install would open your valve at 110deg and close the exh. at 118 deg. that's what you want in a marine engine to prevent water reversion and build low end torque. This cam is meant to be used with good heads tuned exhaust and a 4- barrel carb.
If you have stock compression and stock heads This is about all the cam you can use. It will still pull to 5200 rpm . Most stock 350's run a 19. pitch depending on the boat.
Your exhaust may be killing your engine, and ignition if stock.
I would advance the cam you have first if it is in the range to, then get a good exhaust system.

On timming your engine, start at 32 deg. total advance, record the rpm at WOT. Then move the timming to 34 deg. See what the rpm is at WOT if you gain rpm that's where it should be, then you can try 35 deg. if it gains rpm try 36 deg. but on any change if it does not gain rpm set it back to the prior setting that increased your rpm originally.

 

[crazygn]

Thanks for the info, heres what my cam card says

278h-12

gross lift 498 501
.006 tappet 278 292

valve timing open
@ .006 int; 27 btdc 70 abdc
exh; 77 bbdc 34 atdc

specs are for cam installed @110 intake center line

duration @ .050 in 234 ex 244
lobe lift .3320 .3330

lobe separation 112.0


All engine parts are in the first post. I'll advance it and see what happens, since you seem to be good with boats and cams what do you think i should advance the cam

if this doesnt work i'll save some cash and get back with you about that cam .

thanks again

 

[mkhammer]

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

​

You need 10:1 compression, headers not knowing what cc dish you have in your pistons I don't know what your compression ratio is. I think You have the wrong cam for your setup.
A marine stern drive needs to make low end torque and pull to 5000 to 5500 rpm. Torque is what will spin your prop and not making it so late in the power band, you have a high rpm cam. This cam would work better in a 383 installed 4 deg advance.but the duration is still too much for a marine stern drive small block. A jet boat can get away with this cam because they can spin 6500 rpm and have water injected exhaust. Most jet boats will cavitate some out of the hole and get the rpm up and start hooking up.

We use a smaller spec cams than this in 383 strokers that make close to 500 hp pull from 1500 rpm and up to 5700 rpm before signing off.
You got my cam recommendation that I believe will help your engine , Proper carb, ignition, exhaust system and tuning all play a part in getting your engine to preform.

 

[crazygn]

I see what your saying

i get my taxes back soon so i'll get back with you on that cam .

 

[crazygn]

oh i forgot, the heads are 64cc heads and the pistons are stock 86 pistons

 

[moisturemissile]

I like reading your posts MK, you seem to do your homework!

 

[crazygn]

I might pick a cam up this week, if you think your cam will work alot better then this one i'll buy it this week. How do you take payment, will paypal work .