Pliant

Comp Cam
1.Behive springs...allows for 1.6 lift with no head work
2.Compcam 266 cam or the 270...lsa is 112 should not casue reversion
3. eldobrock intake...Only game int town for a 4.3
4. 600 cfm carb..You will have to rejet..

About 1800 if self installed...You should net about 280-300 hp...You will more than probably have to change your drive gears to 1.5 or 1.66 depending on drive type.

After market exhuast wont help

prostock85

Not sure if any could help you in the marine world but look up parts for a 91 syclone or 92/93 typhoon. I had a 93 ty with stock turbo, chipped and was probably around 300+ hp and 400 tq.

http://en.wikipedia.org/wiki/GMC_Typhoon

speedboatr

i installed the elderbrock intake and carb. the boat will only go to 4,000 rpm. it still has 1/4 tthrottle left but the rpm, speed, engine does not change in the last 1/4 of the throttle?? this is with the carb set up from elderbrock. when i try to re-jet it i get a miss around 2000 rpm?? any thoughts?

davidwillson

Brodix makes a real nice aluminum cylinder head in a big and smaller port version. it has a non vortec intake flange, so you can use a Edelbrock intake.

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fkboatman

whats your total timeing, i will look tommorow in my merc book and see what rods,springs, jets that merc usus in there carb. if that motor is brand new you need to let it break in and loosenn up some before running it wot.

speedboatr

Stock distributor, set it at 10 BTDC (thinking stock) I spoke to Edelbrock today and sounds like I need to try a richer metering rod or move to a 92 jet instead of the 89 that is in it. Think I will try the rod 1st and if that takes care of the missing around 2000 rpms i will take it to the lake and see where the RPMS end up at WOT. I have 6 or 7 hr on the motor. Only saw 4,000 for a min or two. I have varied the rpms for the first 5 hrs not taking it over 3500. Let me know what you find out

Thanks for info!
Speed

fkboatman

take it for a good run and shut her down pull a plug from each side of motor and look and see if they are reall light in color, grey or white is lean. light brown is perfect. have somone run the boat and close choke butterfly and see if motor cleans uo, if it does its lean.

fkboatman

merc shop manual sais as follows, 89 primary jet. yellow springs. 89 secondary jet or a optional 95 secondary jet. merc number for rod is 16-6857. now edlebrock 4.3 calibration is as follows. 89 primary. .068x.057 rod. pink spring. and 89 secondary jet. Merc sais there carb is a 600 cfm. I remember a couple years ago i had to up secondary jet to the 95 because of a lean condition on top end. let me know if you need anything else. Frank

speedboatr

Thanks fkboatman,
I currently have 89 primary and 89 secondary with a .69 x .47 rod and pink spring. My thought was to try a .63 x 47 rod 1st and see if that cleans up the miss around the 2,000 rpm range. If so, try it at the lake and see what happens with WOT. If not try a 92 primary.
I know just enough to get in trouble with Carbs…… so thank you for any info!!
I will be out of town and cannot try the changes until week after next . I will let you know how it goes.
Thanks again,
Speed

fkboatman

if you read the edlebrock book on carb. it clearly explains how to richen up or lean down carb in the idle power and wot section. how did you set your timming on the motor, we know you use a light. but is there a bypass on your dist. to set base timming?