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383 build using Log exhaust.

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BearlyFunctioning

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I'm doing a Merc 383 build for a 1982 24' express cruiser

I have two items possibly limiting my build.
1. Still going to use log style manifolds and through hub exhaust.
2. Rear deck (engine is under the floor) that is only 4" above top of carb (without flame arrestor) with the stock intake manifold.

This is going to be a ground up build, budget is some-what a concern, hence the log manifolds stay.

My engine builder (who is going to dyno break-in and tune the engine) is telling me there is not much more to gain past vortec heads or even aiming for excellent quench by going to aftermarket alum heads with a larger chamber. How true are his statements ?
 
How true are his statements ?
Click to expand...

Ayuh,..... Pretty much Absolute,......

Vortec heads, a quench of .040, 'n inverted dome, or D-dish pistons to keep the compression ratio just at, or just below 10:1,.....
 
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BearlyFunctioning said:
I'm doing a Merc 383 build for a 1982 24' express cruiser

I have two items possibly limiting my build.

1. Still going to use log style manifolds and through hub exhaust.
IMO, the log style exhaust manifolds with the rear elbows are going to restrict this engine.

2. Rear deck (engine is under the floor) that is only 4" above top of carb (without flame arrestor) with the stock intake manifold.
what is you concern here...... not being able to use a center-rise manifold and elbow?

This is going to be a ground up build, budget is some-what a concern, hence the log manifolds stay.

My engine builder (who is going to dyno break-in and tune the engine) is telling me there is not much more to gain past vortec heads
You will gain if you use a LCQ (low compression quench) style piston with the Vortec cylinder heads, and if you aim for a .043" quench dimension.

or even aiming for excellent quench by going to aftermarket alum heads with a larger chamber.
I am not sure why he would suggest larger chambers..... unless he is also suggesting F/T pistons.
Even with F/Ts and 76cc chambers, the .270" additional stroke will give you an excessive S C/R.

Aluminum cylinder heads will generally help keep cylinder temperatures down. But, the chamber volume must compliment the piston profile and/or visa-versa.

How true are his statements ?
Click to expand...
 
My builders point to me was that with not being able to install a taller intake manifold (rear deck clearance issue) combined with keeping the log style manifolds (budget consideration) there would not be much to gain upgrading the heads past the vortec.
 
If you were building a Hot Rod engine, yes..... a tall, long runner, intake manifold might be great.
However, with a Marine build, a Dual Plane intake manifold will work just fine.

I would save my money and spend it on a pair of center-rise exhaust manifolds and elbows.

The other issue may be the older A drive!
You may want to verify this..... but the A drive is apparently good up to 300 HP only.



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Unless the log manifolds are on a boat that spent its entire life in fresh water or are on the "inside loop" of a "fresh water" ( with heat exchanger)system they have fairly short life and their reuse is false economy.
 
Ditto for aluminum heads--you MUST use closed cooling with them (and anti freeze) or they will corrode rapidly. Ditto for aluminum intake manifolds.

Assuming this is a cruising application, not a hot boat, a 383 makes sense. Stock Vortec heads also make sense (and excellent mid range torque--the ticket for economical cruising). Any manifold design will work with such an application, though center dumps supposedly make more hp (but not necessarily more torque). Older Chryslers converted to center dumps were no different in power compared to their owners (from the Marionette website)

Jeff
 
Jeff is correct.
With the use of the aluminum cylinder heads and/or an aluminum intake manifold, you must fit the engine with a Closed Cooling system.

As for the center-rise manifolds/elbows, I do believe that these would be a better choice over that of the log style with rear elbows.
Your additional .270" stroke is going to provide the added torque!


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