SBC Cam ?
 

Sorry to beat the cam horse again but here it goes. Last winter I rebuilt my SBC (350). I am putting out around 320 hp at the crank. The stock cam was replaced with a mild non roller cam. The heads were alum 64cc Edelbrocks, toped of with an Edelbrock intake and 600cfm carb. This combo ran great all summer but here's the big but. I want more top end palin and simple. Based on your experience what would be a reasonable hp gain expectation from a simple cam change.

THX
Sam

Sam-
What exhausts are you using?

Ask Ratchet on this site, He has 2 SB's pushing a 31 Scarab to 72MPH on gps. That should be good for around 425hp a piece!

Jafo, I am running a stock merc exhaust with 4" thru hull, no mufflers. I have been told many times that an after market system will do little to improve things on a SB.

Sam

SLP;

It isn't that an aftermarket exhaust will improve the flow so much to see a gain in top end speed. BUT, what it will do is allow you to run a more radical cam profile without the fears of encountering a reversion problem. With a stock exhaust, your cam shaft choices are limited due to the length and type of risers.

I was running a stock 260hp 5.7 with a 3500lb boat. I replaced my stock thru-hub exhaust with stainless marine thru-hull exhaust. I picked up 2mph (Per GPS)........

Bad-Habit

What cam do you have now?
 

SLP,
I don't think anyone can tell you what camshaft to step up to without knowing what camshaft you have now. From personal experience I wouldn't go with more than 218/224 intake/exhaust duration @ .050. Don't go with any thing less than 110 or more than 112 degrees of Lobe Separation Angle.
Any larger camshaft and you will have to run the engine above 5,500 rpm to make maximum power.
Your combo with the above cam specs should give you around 340 horsepower @ 5,200 rpm.
Call Comp Cams in Memphis for suggestions.
Sincerely
Dennis Moore
FAMILY AND PERFORMANCE BOATING MAGAZINE

Your right Dennis and thank you. My current cam is the Edelbrock #2103. Specs are 204 intake/214 exhaust @.050 duration. The lobe seperation is 112 degrees.

THX
Sam

This cam may be a little much for your set up, but I'm running the crower 00426 Solid roller in my engines. This was picked based on a recommendation from someone.

250/[email protected]

.380/.398 loble lift = .570/.584 w/ 1.5 rockers or .608/.622 w/ 1.6 rockers (subtract your lash from here to get net valve lift)

on a 112 Lobe center

They idle great, and make PLENTY of torque contrary to what a lot of people may think. Ask scarab 26, he's seen them in 2 boats that I've owned.

SLP - I have to believe that an aftermarket exhaust like stainless marine can only help you. I'm running them, and like them. They are cast individually on the inside till you get to the flange where the riser bolts. They look great, are lighter than you stockers, & I've had no problems & ran them 5 seasons

Just because I, and others have had good luck with crower, I'd recommend them. They seem to be fairly easy on the valve train.

If you'd like the specs on the engines I have, check out this post:

http://www.offshoreonly.com/forum/sh...t&pagenumber=2

If you'd like anymore details, feel free to e-mail me @ [email protected]

When all is said and done........just go out & have a little fun !

I have an identical setup (hull, motor and sterndrive) to SLP except for my motor modifications... my setup is a year newer so i have a roller motor. I went with a comp XM264HR (264/270 - 212/218 - .495/.502 W/ 1.52 rockers, 112 lobe seperation and -2 degrees from straight up of a 106 centerline) roller retaining the stock 217 castings, a performer intake and a 600 vac sec holley and TBolt IV 350 mag ignition module... we were running almost dead even. Later last summer i got a bug up my butt and popped for a pair of Pro Action 220 non CNC cylinder heads and a performer RPM airgap as well as a few other miscellaneous items. I'm somewhere in the 355 - 365 hp range... and i picked up 600 rpm thus far (bouncing the rev limiter).

I want to go the bravo route and at that time more bump stick... XM270HR minimum...

One worrisome thing i noticed on my second go around with the motor was water lying in the center ports of the exhaust manifolds when i popped the risers. I was experiencing some reversion and i realized it, especially coming off of plane in a hurry and down to idle... maybe more of a backflow issue than reversion... i went with a pair of imco stainless risers and all has cleared up... dry as a bone now...

anyone else have any experience with the imco risers on stock manifolds?

SLP - sorry, but I forgot to tell you scroll down to see the post when you click on the link :-)

Same as stock
 

SLP
The camshaft you are running is about the same as the stock marine cam. You should see a big increase if you go with the camshaft that I recomended. Should be fun!:)
Sincerely
Dennis Moore
FAMILY AND PERFORMANCE BOATING MAGAZINE

Re: Same as stock
 

Dennis,

So what are your thoughts on the aftermarket exhaust, such as imco, or stainless marine vs stock ?

Just curious..........thanks

Aftermarket exhaust
 

If you want the most power from a high horsepower small block engine you need something better than the stock exhaust manifolds but there isn't much on the market for the SB.

A small block, with only 350 cubic inches, doesn't create as much exhaust volume as a big block with 454 cubic inches. An engine with 104 more cubic inches creates a lot more exhaust volume that needs to be extracted from the engine. Look at it this way, if a big block needs an 800 cfm carb and the small block only needs a 600 cfm carb (on the inlet side) the same holds true for the exhaust side.

The stock mercruiser manifolds on a 350 do not create as much backpressure as the stock mercruiser manifolds on a 454. There is a much bigger improvement in performance when changing the big blocks exhaust than when changing the small blocks exhaust.
The four inch exhaust (or even 3 inch) from the exhaust manifolds to the transom (or even through the prop) is huge for a small block engine, not so huge for a big block engine (2 1/2 is large for a car exhaust!).
Dennis Moore
FAMILY AND PERFORMANCE BOATING MAGAZINE