350 exhaust options...

[wca_tim]

I'm upgrading a 4.3 alpha 1 to a 350 or 383 and am considering the exhaust options. I'm currently conbsidering either Hardin (ca. $400) or GLM (ca. $300) aluminum manifolds and using my (almost new) stock risers and manifolds. I plan to tap beind the risers for pressure transducer and measure backpressure I'm once get up and running just to see how bad / good the factory set up is. There seems to be a significant difference of opinion on how restrictive it is. Don't want to pony up the $2,500+ for headers without a very clear performance advantage... May go with the aluminum or stainlsee steel risers or elbows for the above, but will probably just get the manifolds to begin with and go from there. I would prefer not to gain any weight overall on the conversion and the manifolds and risers seem the best place to save on weight.

Has anyone got specific experience with either of the manifolds above or a similar product they would recommend?

Thanks in advance for any thoughts or information...

 

[Mkos1980]

Re: 350 exhaust options...

I did some dyno testing of a 1990 350 Mag 270 HP with a mild cam, rockers and 2 differant set of exhaust on another site. $1000 Revolutions vs the $500 Dollar Al GLM's Both made the same HP and the Revolutions made like 2 extra foot lbs of torque. Both were about 10HP more then the stock manifolds.

 

[yamamarinetech40]

Re: 350 exhaust options...

You won't be able to tell any difference in performance...that is from the exhaust...what boat is this...from 4.3 to 383 should be a huge boost...

 

[wca_tim]

Re: 350 exhaust options...

it's an 18 foot checkmate...

 

[180shabah]

Re: 350 exhaust options...

If you choose aluminum manifolds, then you want to use aluminum risers and elbows too. You don't want different rates of expansion at the manifold/riser joint.

 

[Mkos1980]

Re: 350 exhaust options...

If you choose aluminum manifolds, then you want to use aluminum risers and elbows too. You don't want different rates of expansion at the manifold/riser joint.

What happens with aluminum intake manifolds and cast iron heads as found on cars or LT1 motors are cast block, aluminum heads. How about aluminum exhaust manifolds against cast iron heads on a boat. Leaking fumes into a bilge or even a living area is not good.

I understand what you mean but I dont think it would be that much of a differance.

 

[wca_tim]

Re: 350 exhaust options...

Thanks and good point. I'm thinking at this point either glm aluminum set. can get for 500 complete right now, or stainless marine set-up - more money, but maybe pick up used since I probably have a month or so before will really need the exhaust. I bought a merc 350 complete last weekend. and got around to tearing it down today. An hour or so and the block will be ready for the machine shop. If the crank checks out, I may pony up for Dart heads and go with 355 for the time being. Will see...

 

[Mkos1980]

Re: 350 exhaust options...

Yup picked up a few sets for my dad. $504 shipped to my door. Cant beat the price.

 

[wca_tim]

Re: 350 exhaust options...

I think 180shabas point about the manifold / riser joint is that one leak there and my pretty new engine would be back at the machine shop... or sittin on the carport with the 4.3 back in the boat cause there's not enough cash in the budget to put it back together once I fill it with water and bend / break stuff...

That's exactly the issue that has me thinking hard about a dry-joint stainless steel set-up like the stainless marine, or a decent of used headers (If I can find a good used set-up that isn't more than a half inch or so taller than the factory manifolds... I do spend a lot of time in brackish, rinse with saltaway, etc... but would be more comfortable in the long run with stainless... I'm sure the aluminum would be fine, but I'm a little paranoid about that kind of thing sometimes. would be a real pitty to spend the cash to do everything else right and then blow it with an exhaust manifold failure...

 

[Mkos1980]

Re: 350 exhaust options...

If you are going that route, the Revolutions are dryjoint, Imco Thumbers are along with an offbrand name Offshore Marine sold by CPI Marine I think.

 

[180shabah]

Re: 350 exhaust options...

I think 180shabas point about the manifold / riser joint is that one leak there and my pretty new engine would be back at the machine shop... or sittin on the carport with the 4.3 back in the boat cause there's not enough cash in the budget to put it back together once I fill it with water and bend / break stuff...

Exactly what I was thinkin'. This is a very common failure point, even with all iron, and anything you do to increase risk here would be a step in the wrong direction.