First post here. I've RTFF and I don't think I've seen this topic discussed before, so here goes:

Is it possible that swapping to headers from Merc manifolds could save fuel? CMI Dyno data suggests it might be!

My application is an Alpha-One drive SBC 22' Wellcraft Elite. Like some of us, my boating is limited by the cost of fuel for this, so I'm interested in any fuel saving opportunities I can get.

While perusing the CMI website, I came across their dyno data for their SBC headers:
http://custommarine.com/headerapps/dyno_data4.php
Note: this is for a 383.

Of interest to me is the increase in HP through the rev range with little associated increase in fuel flow (I would post a chart, but I can't yet post attachments).

But according to the power curves in this 383 application, a 4000rpm cruise with the standard exhaust could be reduced to a 3750rpm cruise with the CMI headers (by propping up, the same power level (260 Hp) could be maintained at a lower engine speed). This enables a 15.8 lb/hr reduction in fuel flow for the same power output.

What this means to me is if I purchase a set of these headers for $2400, at $4.00/gal, I could potentially recoup my money in just over 225 hours of cruising runtime. I'm not sure if this makes the purchase justified, but it's an effect I didn't expect.

So has anyone noticed a reduction in fuel flow when they freed up their exhaust system?

Can of worms here !

It would be cheaper and more fuel effective to leave your 70 gallon cooler at home.

The boat itself (bottom design, water displacement, etc,etc) along with it's weight is by far the most important part of the equation when it comes to fuel mileage.

2nd is propping.

I have a light little boat with mod'd 350 and you would be more than jealous with what little fuel I use when cruising.

At the same time, you'd crap yourself with how bad the ride is thru confused waters.

Hard to have your cake and eat it too.

Do whatever you can for less drag and less weight.

SB,

I agree with you wholeheartedly, but no cooler doesn't have near the cool factor that shiny pipes do!

Anyone notice lower fuel flows when they installed headers?

I'll answer this technically since you did not get it:

No ! Not on your application.

Your boat is somewhat a 'pig' for it's size. That's why it rides good for it's size.

If the engine is in a good state of tune, your boat and driving habits are responsible for it's fuel mileage.

Headers help engine's with a decent amount of cam overlap. Overlap and tuned exhausts work hand in hand.

FYI: I weighed a merc sbc exhaust vs an sbc EMI system. The EMI's where just over 80lbs lighter. Weight = speed and fuel economy.

What about my hull specifically makes it a 'pig' other than its weight? I'm aware this is a comparatively heavy boat, but admittedly am ignorant of hull design. I'm an engine specialist.

A 'pig' is not necessarily bad, so don't take that as an insult. I am speaking in terms of fuel mileage

It's pretty heavy and it rides in the water vs on it.

Again, great for stabil ride....not so great for mileage and top speed.

Can't have your cake and eat it too. Everything about boating is a tradeoff.

I'm not insulted at all, I'm aware my boat is heavy. Thanks for your input.

Now back on topic: Has anyone noticed lower fuel flow when they switched to headers?

On the dyno, not on the boat.
Dyno mariginal on 330hp sbc manifolds vs headers. Customer long time ago ran both. Fuel use was down just a tad. Hp was within 5.

Own mild 502 years ago. Dyno'd manifolds vs Gil vs dry headers and tons of other things. Slightly less fuel on dyno. Real world on the water NADA.

Broken record here. Fuel mileage on the water is more to do with weight being pushed and load thru the water then it is engine effeciency....oh, driver too.

I'm done. My record fell off the turntable. LOL.

Broken record.

You can buy a lot of fuel for the price of a set of headers