Exhaust....
 

How restrictive is the stock underwater exhaust? How limited am I with cam profiles? Only a V6, so dont want to put thru-hull on it if it isnt necessary (sound).

Thanks,
Tommy

V-6???!!
Are you on the right website?

This isnt slowlakeboats.com?? ;)

Dont have the money for a 350mag swap, plus, the boat isnt worth putting 4k into a new motor for it. Wette Vette has a 305 for sale, onlt 5 hp more and another 150lb heavier. Not worth it at this point to do that.

You could put in thru hulls , but it probably wouldn't make any difference:( except noise. And believe me V6's stick out like a sore thumb:D

Planing on changing CR and cam profile...

To answer your question, Very restrictive.
I wouldn't go with more than 3* of overlap in a through the prop exhaust. To be totally safe stay with a 0 or a negative overlap.
DAVE

you can make alot of power with a v-6 they have alot of cams also
Port and pocket the heads,,go up on compression ,and add a good cam and it will run well :D

Hey Hyper,
I am going to give you the same advice I give my friends. If it ain't broke don't try to fix it at the begining of the summer.;) Boat hop up projects are great fall and winter projects. I have seen too many boating seasons ruined because of good intentions gone bad. Not to mention speed gains way below the expectations doing just what you are talking about. Just giving you something to think about. Good luck and if you change your mind on the 305 let me know.:)

If you want to reduce the back pressure
through the drive, ( if there even is any)
remove the exhaust bellow, and install the
replacement exhaust tube ( p/n 78458a1
$ 47.39 BAM marine)
I doub't it will make any performance
difference on a 4.3, but it may make a little
more noise :D :D :D

p/s, I second what Wette Vette said.


jt

This is a good point :D :D :D

Ill wait till winter....I will be busy come November, hopefully rebuiling a miata and the boat motor :)

The thru prop Alpha exhaust supports 300 horsepower. If somebody was running a 330hp 454 thru an Alpha (and some are), I'd tell them to go to thru hulls for some free horses.

If somebody is running a 205 horse 6-banger, I'll tell them that they'll see no appreciable performance benefit from thru hulls besides the "louder is faster" phenomenon (automotive equivalent: 4 inch fart pipe on an otherwise stock Civic).

Headwork, cam, intake and carb can deliver another 30 to 40 horses pretty easily. Even with that in the bag, you're not crippling yourself with the thru prop exhaust.

If you're looking for the LAST mph, then do it. If you're looking for the FIRST mph, it aint the answer.

I try not to get into this kind of discussion,but I just couldn't help it.We see on SBC 2-3mph gain with thru-hulls only.And the drive runs cooler.

Okay, so how do we interpret that data into useful stuff for a 4.3 V6?

If a 300 horse 5.7 picks up 3 mph (I'm rounding up), then does that mean that a 200 horse 4.3 picks up 2, and a 120 horse 2.2 picks up 1?

OR does that mean that the 300 horse 5.7 picks up 3,
The 220 horse 5.0 picks up 1, the 200 horse 4.3 picks up a tenth of a mile an hour, and the 120/2.2 picks up nothing?

Does anybody have valid data on a 4.3 for Tommy?
He doesn't want to listen to the (non reversible) thru hull job if it's not going to speed him up.

He will gain nothing by going to thru hull exhaust on the 4.3 V6 in stock form. ;)