Headers Vs. HP Manifolds
 

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

Re: Headers Vs. HP Manifolds
 

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.

Re: Headers Vs. HP Manifolds
 

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...

Re: Headers Vs. HP Manifolds
 

Ain't that the TRUTH!

Re: Headers Vs. HP Manifolds
 

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

Re: Headers Vs. HP Manifolds
 

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

Re: Headers Vs. HP Manifolds
 

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.

Re: Headers Vs. HP Manifolds
 

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.

Re: Headers Vs. HP Manifolds
 

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.

Re: Headers Vs. HP Manifolds
 

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

Re: Headers Vs. HP Manifolds
 

Has anyone heard of these manifolds. I spoke with the manufacturer and was told they are aluminum, have individual runners, coated on the inside and will bolt right up to the factory risers. I have a 7.4 MPI looking for a little more low to mid range power. What do ya think?
http://cgi.ebay.com/ebaymotors/ws/eB...3ARTQ%3AUS%3A1

Re: Headers Vs. HP Manifolds
 

Those are Dennis Moore's mainifolds. He will tell you himself they do not offer much of a performance improvement over stock, just weight savings and a better manifold/riser joint.

Re: Headers Vs. HP Manifolds
 

Here's the website.

http://www.glmmarine.com/manifolds/

Re: Headers Vs. HP Manifolds
 

The cutaway shows individual runners, but you would know better than I. Dennis told me they would improve power slightly but not drastically. I think the weight savings might be worth it. I added three extra Optima batteries and I am just trying to make up for the extra weight. Worth the money?

Re: Headers Vs. HP Manifolds
 

Yep, my bad I read that after I posted. The price is right that's for sure! I think you can get a set with risers for under $600.

Re: Headers Vs. HP Manifolds
 

I think I'll give them a shot. I am not going to have the boat out agian until labor Day weekend but I will follow up with some feedback. Thanks for the info.

Re: Headers Vs. HP Manifolds
 

Don't forget about us if you ever are in the market for a nice set of CMI Headers!!

Kirk
Ateco Engine and Dyno Shop
www.atecoengines.com

Re: Headers Vs. HP Manifolds
 

You may want to consider doing a search here in the tech section on Dennis Moore's manifolds. Someone on here bought some and the quality was lacking, missing harware, as well as poor customer service.

Re: Headers Vs. HP Manifolds
 

I appreciate the feedback. I think I am going to hold off and spend the extra money on a set of proven performance manifolds. I am not looking for a big gain but just a little better performance out of the hole. I have a 26' Envision open bow and it is very sluggish when full of people and coolers. I am not sure how much a set of manifolds will help the 7.4 mpi. All I have done to this point is a K&N filter. Who makes the best bang for the buck when it comes to manifolds.

Re: Headers Vs. HP Manifolds
 

If the only mods you're doing to the engine is a performance exhaust manifold system, then you most likely will not experience any top end gains/speed. The only thing you may see is a "kick" in the midrange which sounds like what you're looking for anyway.

I have always known the Stainless Marine exhaust system to be pretty reasonable, but there are several aftermarket systems available---even more than what I have listed. Maybe some of the other guys can chime in who have had experience with other manifolds.

Stainless Marine
GIL
Eddie Marine
IMCO

Re: Headers Vs. HP Manifolds
 

Very possible a prop change may help.

Also, if you do not have trim tabs, adding them will help out tremendously with 'out of the hole' accelration.

Re: Headers Vs. HP Manifolds
 

I just put (2)pair of Stainless Marine manifolds on my 502 MPI's. Nice quality product with a relatively clean install. Definitely notice a feel in the mid-range, but haven't bothered to see if any gain up top.

Not the cheapest on the market, but I thought it was the best value for what you were buying. Trick Marine had excellent pricing on them earlier this year.

Re: Headers Vs. HP Manifolds
 

I re-did my 1989 330hp 454 last winter. Here is the details - link my summary

End result is I went from being able to only pull 4,100rpm with a full tank and 5 passengers to pulling 4,800rpm. I still have yet to do my prop testing to see how much I can bigger I can go.

Let me now if you want any more detailed information about my build. I did the whole thing for under $1,000 - not bad for +700rpm!