heads cam 350 l89 larson senza wont rev over 4300 rpm will this cam swap help

[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 1989 larson senza 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* , . 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



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 Range 1,600-5,400 Intake Duration at 050 inch Lift 216 Exhaust Duration at 050 inch Lift 216 Duration at 050 inch Lift216 int./216 exh Advertised Duration 272 int./272 exh.Intake Valve Lift 454 int./0.454 exh.

 

[NHGuy]

Re: heads cam 350 l89 larson senza wont rev over 4300 rpm will this cam swap help

58 mph is really pretty good. I'd check that the dash tach is right with a shop tach. To go 58 with 4300 rpms you'd need a lot taller prop than that. Does the boat feel good? Does it feel fast?

 

[Bondo]

Re: heads cam 350 l89 larson senza wont rev over 4300 rpm will this cam swap help

Ayuh,... Have ya tried a 19" prop,..??

'n like NHGuy says, Check the Tach....

I do like the shorter cam better though...

 

[crazygn]

Re: heads cam 350 l89 larson senza wont rev over 4300 rpm will this cam swap help

Ayuh,... Have ya tried a 19" prop,..??

'n like NHGuy says, Check the Tach....

I do like the shorter cam better though...

Its a new rpm gauge but who knows, i've never tried any other prop. The boat feels ok but seemed faster with the same rpm gauge and a stock 350 mag engine. Would rev around 4800-5000 when my buddy had it.

 

[Bondo]

Re: heads cam 350 l89 larson senza wont rev over 4300 rpm will this cam swap help

The boat feels ok but seemed faster

Ayuh,... You need Measure conditions, not Seat of the Pants comparisons before you go rippin' the motor apart....

Is that Weiand an open plenum manifold,..??

 

[crazygn]

Re: heads cam 350 l89 larson senza wont rev over 4300 rpm will this cam swap help

it doenst sound like it revs over 4300 but who knows, the manifold i belive is a high open manifold.

do you think maybe just a performer intake and a 19 pitch rop would be worth a try befor the cam swap

 

[TilliamWe]

Re: heads cam 350 l89 larson senza wont rev over 4300 rpm will this cam swap help

Single plane intake manifolds do NOT work well on boats. Just not enough revs to take advantage of the big hole. Plus you NEED low end torque, and that's what a dual plane helps with.

What is your outdrive gear ratio? I ask, because 58mph at 4300rpm sounds too fast for a 1.5 ratio, let alone a 1.65 or 1.81. So I think either your MPH reading is wrong (is it on GPS or the dash speedo?) or your tach is wrong.

 

[crazygn]

Re: heads cam 350 l89 larson senza wont rev over 4300 rpm will this cam swap help

not sure what gear ratio, i can tell you its a 1989 and has a alpha 0ne SE drive if that helps. You guys could be right on the gauge. That reading was with the speedometer and gps. And the tach reads 4300-4400 at most. Wish it was in the water to be able to tell now.

thanks for the replys everyone

 

[crazygn]

Re: heads cam 350 l89 larson senza wont rev over 4300 rpm will this cam swap help

I'll try to look if its not to cold and see whats going on with the tach. Its a summit racing tach hooked to my msd box. Not sure if these tachs are junk or not.

 

[crazygn]

Re: heads cam 350 l89 larson senza wont rev over 4300 rpm will this cam swap help

How does this cam look, this is what is in the boat

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

 

[Bondo]

Re: heads cam 350 l89 larson senza wont rev over 4300 rpm will this cam swap help

I'll try to look if its not to cold and see whats going on with the tach. Its a summit racing tach hooked to my msd box. Not sure if these tachs are junk or not.

Ayuh,... Just so's to cover yer last 3 posts,....

Yes, We've deduced that yer motor is probably not built with the Best choices of hard parts...
But,...
To say it should be torn down, 'n completely swapped about with different parts is atad immature...

It's been stated above, your Numbers just don't add up....
The SEI drive, I'd bet on being a 1.5:1 ratio....
The ONLY Unknown is the values displayed by yer Tach....
I'd suggest runnin' it, side by side, with a known Shop Tach that can be trusted...

And, while yer at it,...
Do a Compression Test, just to see where the motor's condition really is.....

Then, I see a 600 carb mentioned,... Who's carb,..??
Is it Properly Tuned,..?? What do the sparkplugs say about the carb's Tune,..??

Don't be so 'ell bent on rippin' this motor apart just yet........

 

[crazygn]

Re: heads cam 350 l89 larson senza wont rev over 4300 rpm will this cam swap help

the carb is a eld 600, i did play with the jets and the plugs look good so i'd say there not to much off .

 

[Tail_Gunner]

Re: heads cam 350 l89 larson senza wont rev over 4300 rpm will this cam swap help

Heres some ifs...1.5 gear ratio....speed gps verifyed....1.5@ 4200 yeilds 56 @ 0 slip....Actual speed is 58 slip is at -4 nope not working...Tach and speedo

Ok lets go here...... 1.5 @ 4800 nets 64 @ 0 slip.......1.5 @ 4800 @ 58 yeilds 9%....Now were getting close....looks like a speedo so far


Here is a link that i have found one of the best on the web for tinkering around.

http://forum.grumpysperformance.com/viewtopic.php?f=55&t=58

the basic rule is a dual plane intake will almost always be the better choice over a single plane intake if the cam duration is under about 235 degrees@.050 lift



http://forum.grumpysperformance.com/index.php?sid=a603c55a82cbf195fae7f21138e04f0f


You need to verify the speed and tach...That cam is not radical by any means...but that is a opinion...Now if you do a lot of water sports it may be a bit large.....or boat on a small lake cant really even use its potential... That 350 should do what 375hp with a.... 600 cfm carb...hmmmm

http://forum.grumpysperformance.com/viewtopic.php?f=52&t=82


Have fun with that site and dont change a thing until your speed is verifyed...Good luck all of this is just a opinion

 

[crazygn]

Re: heads cam 350 l89 larson senza wont rev over 4300 rpm will this cam swap help

well guys, i put a new comp cams marine cam in and it only revs to 4200 now[ 560 lift dur 218 ] I just dont get it its even slower now with a cam that makes power and tq down low. Runs fine but just slow

I'am going to do a compression test this week. I'am also looking to do a prop change. I have a 3 blade 14.25 x 21 now. what should i try, i was thinking a 4 blade 14.25 x 17 or 18