Allright. I listened to the wisdom of everyone on the site over the winter and spent my time ditching the log manifolds from my old 21 Nova with a 302 and going with center rise manifolds out the back with 3" exhaust hose and external flappers.

Luckily, I got everything on eBay and did the job for about $120, because IT DIDN"T GAIN ME SH*T! No more revs, not quicker out of the hole, notta!

BUT... it sounds really bad-ass, so I am not that cracked up about it.

I have a spare set of heads for the motor, and I figure that the only way I am going to get any faster is to get them ported and polished and to match everything else up with them and a cam.

I don't think that I am going to screw with it until winter, (other than props) though, because it is really running well. I just wish I would have gone with my gut and changed out the cam instead of listening to all you guys!!!!!!

My first boat bought new 350mag no thru-hull I ordered thru-hull 600.00 4inch was told 2-3mph gain put 10 hours on it then took it for the exhaust gain nothing. Then was told to go with a cam and lifters did it gain nothing ZERO, just sounded better to more top end. So I ran the hell out of it and blew it up. So I built it balanced and blueprinted .040 over bow-tie block 9 to 1 compression, dart cylinder heads 2.02/1.60 ported and flowed unshrouded roller rockers, comp cam (can't remember the number) eldelbrock performer rpm intake q-jet carb and went from log type exhaust manifolds to headers gain was 5mph gain Tried different props all the so called tricks etc. The best bang for my buck was a hydromotive nose 99.00. This boat is still running and strong burns no oil and has over 500 hours on the motor. Just and get a 502/454 marine crate and save yourself some grief

I just did dart heads,a decent mild cam already had thru hull,intake and holley 650 and got a 4-5 mph gain,I wanted more but this is boating and hp to mph is very hard to get.
I guess I did not do too bad after talking to others and seeing their gains.
What boat you guys have? size weight? top speed?

It takes a bunch of mod $$$ to get any real speed gains, I have a 22 Donzi it came with the Tempest 300 ran 61 flat. I swapped the stock 3" through hulls to 4" dumped the center risers and went to Gil headers, sounded a ton better but only showed 61.3 on GPS. Ok decided to bight the bullet, I built a 383 complete Lunati Pro Mod rotating assy, Dart heads, mild 510 lift Lunati roller cam. Now a few thousand later I am about 4.5 miles an hour faster. Don't expect big gains without going even deeper in your pocket then I did, be happy sounding cool!

Don't get me wrong I am very happy with the overall way my boat runs and now that gas is sky high even more happy its Mouse Motor!

Phil

The cam and\or heads wouldn't have gained you much if they were chocked off thru 3" log manifolds.
Did you use stock center rise cast iron manifolds or did you go aftermarket alum? You sure got it done cheap. I've never seen aftermarket manifolds sell for less than $400 on Ebay, Maybe I just missed them.
Also check how straight your hull is. Take a 4' level and place it different areas of your hull,mainly the back 6'. Make sure it is flat. No hook or rocker.

Are you being serious about the site letting you down ?

Are you serious about expecting more mph from the exhaust change ?

Or are you just playing ?

I ask because I don't know you and reading doesn't give any tone / body language / etc,etc for emotions to pass thru.

Just like an older car with a low hp V8, if engine mods are going to be performed (cam, intake, cyl heads) the exhaust must be done to complement it.

In addition, the old marine log manifolds are a dependability / performance issue anyway.

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You did the right thing on your quest for more performance other than expecting more out of it (mph) right away.

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I hope you got a decent center rise system and not some cheopo or real old system that will rear an ugly head at some time.

Boat type/size/design is very important when planning performance goals.

I added an intake, tuned the stock quadrajet, added a few degrees of timing to a stock 5.7L 260hp 19ft 2800lb boat and gained 3mph. It was then overreving. Went from 19 pitch to 21 pitch prop. Tried different styles and gained another 2mph. Total gain 5mph.

Added 150hp per motor on 38ft offshore , gained 2mph total.

A brick can only go thru the water so fast. Sometimes if you want to go faster, you need to find a better performing brick.

I guess I did well with the 350 with dart heads and cam to get 4 mph,prob is the boat is only seeing 50 so far on gps,it is a big boat,24.5 ft.
I am now having a fuel starvation issue last weekend I was running the bowls empty on the carb (holley) floats are good I am looking into bigger fuel pumps right now,what are you guys running?

[QUOTE=SB]Boat type/size/design is very important when planning performance goals.

I added an intake, tuned the stock quadrajet, added a few degrees of timing to a stock 5.7L 260hp 19ft boat and gained 3mph. It was then overreving. Went from 19 pitch to 21 pitch prop. Tried different styles and gained another 2mph. Total gain 5mph.

QUOTE]
what prop did you end up with? I have ran a 19 and a 21 with my combo,the 19 planes great the 21 does not,top speed is sweet on the 21 but not the 19,I just got a labbed 21 (now a 20p) and found a fuel issue,so I did not get good testing,I plan to get it figured out this weekend.

Could you post a link to where it said exhaust would give you more speed?? Unless it is a high HP application, exhaust does nothing.