exhaust question

[Hallett19]

I have a 460 in my 19 footer with mild mods, but I have one question, does exhaust make that big of a difference on these things? I have a set of Holman Moody exhaust, but I don't know if they are considered headers and if they are holding me back, they are big manifold things and have water running through them, are those considered logs ? if so, what are the disadvantages, and I have a coment for those who say carb sizes for certain engine sizes should stay low, I was told my someone on this site a 650 is more than enough for my 460, however in this months ***boat mag, there is an article stating that a 454 bbc ran strong with a 850 dp, but ran faster and harder with dual 750's and that it is very hard to overcarb a jet, I am going to throw on a 850 dp and see what happens !! wish me luck

[Hustler]

Hallet19, keep in mind that you can add a 850 to your motor make what ever changes you want, But you also have to remember that your putting more air into the motor with restrictive exhaust, making a motor breath better also includes geting that air out. with a set of good headers you can add up to 50 HP. is you motor covered? if not you can get set of water injected thru transom headers for about $700 I think.
Hustler

[77charger]

as far as the carb goes whats your max rpm.a 750 will work for most apps.if under 5500 if you plan on revving higher or a b cubic" motor youll want the 850.I have tried an 850 on mine with no change.and the motor is well set up.

[Hallett19]

I have through transom exhaust and the motor is covered, so I want to know what setup I can pick up the most HP with. Also, I want to rev the piss out of this thing, make it fly, so should I maybe think about going bigger ? its a 460 decked block, stock heads, isky cam and I dont know the specs, weiand stealth, total seal rings, and I want to put an 850 dp, does anyone recomend another setup ?

[Cas42]

as hustler said, the more air you let in, the more air you're going to have to get rid of. I've seen quite a few motors run real well with a properly set up 650 as well as 750's and 850's. I've also seen a few people go with a bigger carb and the only thing they accomplished was a larger gas bill.
Others can give you suggestions but it boils down to what is going to work best for your motor. One thing I wouldn't expect is to get a new carb off the shelf and think it's set up right for your motor. Shelf carbs are set up to run on numerous vehicles, mostly cars, not just for one application. Especially a jet boat.

[LVjetboy]

I couldn't find that reference to the 850 dp versus dual 750's in this month's HB. But I do remember Harold Bruce saying something about jets like 850's in an earlier issue. Were the dual 750's vacuum secondary? Could make a difference. I'm still not sold on the big carbs with low (less than 5500) rpm's, jet or no jet, but I'm open to testing. Good luck with your new carb and let us know how it goes.
jer

[Hallett19]

In the Sept. issue witht the DCB 34 on the cover, there is arcticle on stern drive tech where Tyler Crockett tells someone running a 260ci. to go with a 750 holley, and in "Jet Tech" Harold Bruce takes a question asking, "......I have a berkely jet and a chevy 454. Do you recomend a larger carb than a 750 ?", and I am guessing the motor is mostly stock considering he gave no other specs on the boat, and the response in a nutshell was, "The 750 is good, but you increaser performance with a larger carb.", he goes on to say jet boats are VERY hard to overcarb, unlike prob boats, jets love CFM, with no lo-end performance loss. But you guys are right and I trust you, there is no way to find out what works..... untill you try it.I run at just about 4500, depending on the day and load of the boat, and I want at least 5000, I just boat a gps so next time I take it out, despite the ticking lifters, I will put up some speed numbers!! I have my fingers crossed

[Cas42]

ticking lifters? there's probably a pretty good loss of power right there. Can they be adjusted or are they in need of replacement?
If the lifters are making noise, more than likely they are not allowing the valves to open all the way. If that's the case, you could very well be losing 30% or more of the fuel mixture and I doubt very much changing the carb will do you much good.

[Hallett19]

Oh, I know, well, whats even better is when they have been ticking for most of the day, they don't even open the valves and above 3000 or so, it dies completly, I just need to find the time to fix it. That will be done before any carb is put on there

[squirt]

first cas is right fix your ticking problem then if you want more hp out of your setup then you should look into a set of headers. If you want to keep your engine covered look into water jacketed headers(very spendy). I think a cheaper way for you to increase your cfm is to put a scoop in your engine cover and use a free flowing air filter. These mods (headers & cooler unrestricted air) will give you a good boost in hp, then after that maybe a bigger carb. I've not done this myself but maybe you could try a run with the engine cover off or open with a better flowing filter and give it a shot. Sure beats spending cash on a carb if you don't need to

[squirt]

and yes exhaust makes a big difference!

[squirt]

and yes exhaust makes a big difference!