myscarab30

I dont know if this has ever been posted... but I was wondering What are the Pros and Cons of Headers and Performance Manifolds..... Stock 330's and gonna do a mild top end this winter ...thanks guys

KAAMA

There's probably about 20-35hp difference between an aftermarket hi-perf exhaust manifold and true full length tubular headers.

Depending on what you plan to do with your "mild top end" project you probably are NOT going to see much of an increase at WOT with either hi-perf manifolds or full length tubular headers on a Merc 330hp engine.

Swapping out aftermarket exhaust manifolds like a GIL, Stainless Marine or something comparable compared to the stock Merc cast iron crude breathing exhaust system your 330's now have will at least be a BIG improvement in the appearance of your engine compartment, save a TON of weight, and you'll have more of a rumble tone...especially if you go with a DRY system. You may also experience a bit of "KICK" in the midrange.

However, if you do some pocket/bowl porting on the stock heads you now have on your 330hp engines, add something like an Edlebrock "Air-Gap" intake manifold you MAY experience a small increase in RPM and top end speed, but I am quite sure you will feel a noticable difference in your midrange cruising speed and acceleration. The key is, is that the more you do to your engines the more performance an aftermarket exhaust system is going to work for your engines. Hope this has helped.

dean51267

man, I would be careful, this exact project cost me $40K and I now have a new set of motors to deal with......... for some it works great, for some a disaster...

I have everything to do a pair of motors on top end with, will take a 300 hp motor to 450 and is very driveable, if interested let me know, all parts are top name and new. But I would recommend just replacing with a new crate motor...

vandeano

Ain't that the TRUTH!

myscarab30

I plan to put new big oval port heads, cams,intakes, and carbs,and exhaust ....which are better manifolds or headers Thanks guys

myscarab30

Dean ..What do you have ...and how much? Thanks

KAAMA

As I have stated in my FIRST post..... "There's probably about 20-35hp difference between an aftermarket hi-perf exhaust manifold and true full length tubular headers."

If you do a SEARCH here on OSO on Merc 330hp upgrades you will find lots of helpful/useful info. If you install an aftermarket hydraulic roller cam with new heads, intakes and carbs along with a better breathing exhaust, then you will probably see anything from 425-500hp depending on what you do/use. If you are keeping the bottom end in it's "stock" form with the stock cast pistons (those are what usually come in a Merc 330hp engine last I knew) and stock 3/8" rod bolts, then you won't want to spin it much more than 5000rpm or so.

My cousin had a pair of Merc 330hp engines that he put hydraulic flat tappet cams in, bowl ported heads with larger valves, dual plane intake manifolds, and GIL dry exhaust. The engines made 461hp @ 5100rpm and 510ft lbs of torque on Tom Earhart's dyno. He went from a 3-bladed 21" prop to a 25" and so far, with the new power his 1988 32' Baja has picked up 10mph in the cruising speed/midrange alone just by switching props and pushes his boat to something like 70-71mph @5100 all trimmed out.

BY U BOY

I SECOND THAT
I DID NEW HEADS MANIFOLDS CAM INTAKE CARB RETRO FIT TO A ROLLER MOTOR IN MAY. 20 MINS OF RUN TIME AND NOW I HAVE NEW PISTONS RODS AND CRANK AS WELL AS REPLACING DAMAGED HEADS AND LIFTERS. I AM STILL NOT ON THE WATER.

dean51267

I have one great running motror, one is trashed on the lower end. The motors are 454's, big pistons, rods, crank, 4 bolt blocks, roller cam (Gen 5 retro roller setup from Comp Cams). Cams are the "Extreme Marine" rollers (do a search on sumittracing for specs). Dart 308 heads.

I am using intake, carb, exhaust on new motors.

These new motrs will likely be for sale in a few months, I have a set of 502 mpi's waiting on engine builder. If they go as planned I will run them in the boat long term, the botors being sold in a few months will have warranty and have intake/carbs, dyno sheets, all that stuff. All are blanced and blue printed motors.

kvogt

I would sell the 330s and replace with a crate motor, it's a more cost effective option. On a 330 the block, heads, crank and rods all need to be upgraded.

I have a buddy that is going to bigger power next year and is selling a pair of low hour merc 400 hp 454s. Gill exhaust is also available.

Kris