$600 question!

[bakerjet]

thinking of buying a new carb,running a tunnell with a single four top and a holly 750cfm vacum sec. 454 with @ 400hp and a 100hp nos, should i get a 850 or stay with the 750? :idea:

[77charger]

better off getting a good dual plane manifold.despite what others say a 750 will do fine.On my old jet i ran bbf with a 750 carb and a 100 shot NOS.motor was a 429 mainly stock internals just a cam swap

[cyclone]

forget about running that single carb tunnel ram deal. fuel distribution is pitiful. either go with dual carbs or a single deal. I'd skip the vaccuum secondary carb too. Your jet boat will accelerate much quicker than that diaphram will operate even with the lightest spring in it.

[HotRod Sprint]

An Edlebrock Performer RPM and a 750 DP will most likely get you FASTER down the lake on LESS gas. IMO.
Rod

[jstwkd]

I ran a single carbed tunnel ram with a biggs 950HP 500HP.....Lost three pistons all outer cylinders.Go duals!
Cyclone is right fuel distribution sucks....and it will run better with a mechanical.......

[bakerjet]

that sucks i have performer rpm on the shelf :cry: will the 850 be to big and will a single plane manifold be better than a dual?

[77charger]

that sucks i have performer rpm on the shelf :cry: will the 850 be to big and will a single plane manifold be better than a dual?
the 850 will not be too big it will work.If you had a 750 that will work too but i was saying dont ditch a 750 thinking you need an 850.A dual plane will work better to 5500 rpm a single will work better from there up.Performer rpm and that 850 will be fine.

[QuickJet]

First off, in general, jet boats have way too much vacum to run a vacum secondary carb. Secondly, dual plane intakes require bigger carbs to run corectly. Dual planes split the carb in half. Run the bigger carb and make sure its maunual secondaries.

[Oldsquirt]

First off, in general, jet boats have way too much vacum to run a vacum secondary carb.....
Quickjet, the "vacuum" that operates the secondaries on a Holley VS carb is not manifold vacuum. It is venturi vacuum. The port is in the primary side venturi. Venturi vacuum builds as airflow increases. Any "manifold" vacuum that you may have in a jet boat engine plays no part in the opening of the secondary diaphragm.
I ran a 3310-2(750 VS) for nearly 18 years on an Olds in my old Tahiti. Never had a single performance problem with that carb. Did some back-to-back testing against a double pumper and the only difference I think I noticed was a slightly quicker holeshot with the DP.

[77charger]

I ran a 3310-2 for nearly 18 years on an Olds in my old Tahiti. Never had a single performance problem with that carb. Did some back-to-back testing against a double pumper and the only difference I think I noticed was a slightly quicker holeshot with the DP.
same thing here ran a 3310 on my jet did sub a 800dp for a weekend no real difference.If a 3310 is set up properly you will not notice any difference in a jet hit the gas you go to max rpm now.
I did dump the rear metering plate and got a metering block so i can use jets in the secondaries and fine tune it.It did help out.also did the spring change.In a v drive or i/o i would think different about a dp vs a cacum secondary

[Oldsquirt]

I did the rear metering block conversion and quick change kit for the secondary diaphragm as well, but not until the carb was about 10 years old. Ultimately I think I ended up only one size bigger on the secondary jets than what the metering plate was, but it did give me something to fool with when I was bored.:)
I also agree that the prop boats would not take to the VS as well as a jet.
Bakerjet, what setup do you currently run and why are you considering a change?

[bakerjet]

thinking of buying a new carb,running a tunnell with a single four top and a holly 750cfm vacum sec. 454 with @ 400hp and a 100hp nos, should i get a 850 or stay with the 750? :idea:
my corners are a little lean with the tunnell and single four, was thinkin bigger carb but now i think i will keep the 750 and go with the performer rpm that i hung on the shelf when i went with the tunnell ram hoping for more top end which didn't happen.

[77charger]

my corners are a little lean with the tunnell and single four, was thinkin bigger carb but now i think i will keep the 750 and go with the performer rpm that i hung on the shelf when i went with the tunnell ram hoping for more top end which didn't happen.
do that and put the money you would have spent on a carb into pump work you'll get more bang for the buck.IMO

[Jordy]

If it's the tunnel ram I'm thinking of, it ran great when the engine in my boat was mild, like 8:1 compression, with an 850 on it. It was only when I bumped it up around 10:1 that I started noticing leanout issues. :D

[bakerjet]

If it's the tunnel ram I'm thinking of, it ran great when the engine in my boat was mild, like 8:1 compression, with an 850 on it. It was only when I bumped it up around 10:1 that I started noticing leanout issues. :D
same ram jordy,but the nos up's the compression and causes a lean problem,right or wrong?

[Jordy]

same ram jordy,but the nos up's the compression and causes a lean problem,right or wrong?
I'm not sure about changing the compression, but I do know that it will cause a lean condition because it's adding more oxygen into the combustion process and burning the fuel more completely.

[SmokinLowriderSS]

If the NOS is ported it shouldn't cause a problem due to the fuel that is dumped with it. If it is carb-plated and you have any chance of leanout issues from the tunel-ram, it WILL likely make them worse.
I'm runing 8.5:1 454, all iron, 400HP (once I get my headers she will, the logs are killing her) Performer RPM Air Gap manifold, carb-plate 150HP N2O boost (27 years now, since '79), orriginal 700CFM 4150 Holley (mech sec). Runs smooth and hard. pulling an "A" berk at 4700 (5000 on N2O) No mixture problems and she's proven her ability to carry the nitrous as long as the bottle (or my foot) hold out. I'd up-carb her but (according to desktop dyno) there's not nearly as much gain there as there is from headers OR an eventual porting job. Only a quicker ET to the bottom of my 22Gal tank. :supp:

[bakerjet]

yea i'm yankin the ram loosing some bling-bling but the boat ran better on the performer manifold.