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#21 ·
Kidnova, I am at a similar point and have been researching this topic. Check out boatheaders.com It is lightning marines site and give dyno results of everything from stellings to center rise manifolds. Very helpful. Another good source would be Dennis Moores high performance bbc book. Has a great section on exhaust and what to look for.

For the moment, I am leaning towards an all cast manifold system that is actually a true header... keith eicherts. I found what I think is a great deal on them at $2k/set. These seem to be the best of all worlds with the cast structure and individual runner (32" long) exhaust system. These are factory installs on the 600XP Volvos, at least last I checked.

Dave
 
Discussion starter · #23 ·
Blue Thunder said:
Kidnova, I am at a similar point and have been researching this topic. Check out boatheaders.com It is lightning marines site and give dyno results of everything from stellings to center rise manifolds. Very helpful. Another good source would be Dennis Moores high performance bbc book. Has a great section on exhaust and what to look for.

For the moment, I am leaning towards an all cast manifold system that is actually a true header... keith eicherts. I found what I think is a great deal on them at $2k/set. These seem to be the best of all worlds with the cast structure and individual runner (32" long) exhaust system. These are factory installs on the 600XP Volvos, at least last I checked.

Dave
Click to expand...

Blue Thunder, I have Dennis Moore's book and have read it cover to cover. Great stuff for the novice perfomance boater {that would be me !!}.

I too looked into the Eichert cast manifold/headers after reading about them in Moore's book. And they do seem to be a good and logical choice, as do the lightnings and some of the others. But what I'm trying to do is keep my Imco Sound Advantage system {similar to silent choice}. Got to be able to keep it quiet at times where we use our boat...in the marina plus the sheriff & DEC guys frequent our lake. I know I can get a switchable muffler system. But add that to the cost of headers and your over the $3K mark. That's allot of $ for the hp gain. That's why I've been researching and asking questions about after market manafolds.

Noth'ns simple is it. Thanks - Bill
 
Discussion starter · #25 ·
Jetmech, Hard to compare your engine to mine. Your set up has to put out quite a bit more hp than my 502/502.

Did you have stock Merc exhaust on it before the Imco's? If so, and if after putting on the Imcos you only saw 1 -2 mph gain, I probably would not see that much of an increase. Agree??
 
Discussion starter · #27 ·
Jetmech, I'm not too familiar with blowers. But Pro Charger and others claim about a 50% gain with their blowers. That's with an intercooler right? Seems like that would put you real close to 500 hp. I thought you had a pair of bbs in your 26 Nova.
 
#28 ·
Kidnova said:
HMMmmm....sounds like I could be out about 2K for maybe 2mph gain. 2K somewhere else into the engine {head work, cam, intake, etc. ?} would likely be a better investment, right??
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The problem there is for other gains to work, the engine needs to be able to flow more air which factory exhaust wont allow,,, with the exception of a blower. Exhaust needs to be the first step in increasing performance, but alone wont net you any huge gains.
 
#30 ·
I may be one step further along than you kidnova. Last winter I did heads, cam/lifters, unshrouded valves, carb work, intakes, imco risers on stock manifolds and msd ignition. This into what were basically 330hp engines. I gained somewhere between 6 and 8 mph. Didn't have gps last year, but that is my best guess based on other boats I run with and the speed I am getting now gps.

If I were you I would do these things first, bigger bang for the buck. Then next year maybe exhaust. The only drawback is how far you can go with cam selection before reversion becomes a problem. Do you have roller lifter cam now?

Dave
 
Discussion starter · #31 ·
Blue Thunder said:
I may be one step further along than you kidnova. Last winter I did heads, cam/lifters, unshrouded valves, carb work, intakes, imco risers on stock manifolds and msd ignition. This into what were basically 330hp engines. I gained somewhere between 6 and 8 mph. Didn't have gps last year, but that is my best guess based on other boats I run with and the speed I am getting now gps.

If I were you I would do these things first, bigger bang for the buck. Then next year maybe exhaust. The only drawback is how far you can go with cam selection before reversion becomes a problem. Do you have roller lifter cam now?

Dave
Click to expand...

Blue Thunder, had the 7.4 330hp engine pulled this spring and dropped in a 502. 9.5 to 1 compression, roller cam, dual plane with 850 Holley, makes just over 500 hp at the crank. Runs very well and is dependable so I plan to leave the engine as is for now. But think it's time for a good exhaust, in case of future engine upgrades

The boat is a Nova 23 that now does about 70 on gps. I'd like to see 75. Don't think the hull is designed for much more. If I decide to upgrade the engine in the future I will look for a bigger hull.
 
#33 ·
If your factory exhaust is in good shape and not rusting out[such as mine] you might get better hP increase on something else, exhaust gives the best increase in the mid range, you might not even get a speed increase of 1 are 2 mph, I am going to change my factory manifolds this winter but it is because of a leak-rust issue, if I pick up one are two mph that will be great also, you might be disappointed
 
Discussion starter · #34 ·
h2x, I hear you. And agree. Most of the guys here on the forum are giving me the same info about maybe getting another 1 - 2 mph. I plan on getting into the internals of the engine eventually to increase the hp. And it seems that at some time it'll need more breathing room.
 
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Kidnova
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