OUTLAW EAGLE MANUFACTURING

[Aluminum Squirt]

I've currently got a poorly set up Holley 750 DP that has mechanical secondaries, no choke etc. Its obviously time for a rebuild and some set up work that will come when I finally get a new ZZ4. A friend has a Holley 4160 model #HLY-0-1850s for sale at a good price. It's been used very little and is totally stock. My questions are: Is 600CFM enough for a ZZ4? Are vac secondaries a bad idea on a race boat? its does not have adjustable floats, is this an issue?

Remember I'm a carb idiot, so be easy on me. Any opinions, especially from seasoned FX racers and ZZ4 users would be appreciated, Thanx-Aluminum Squirt

[AR]

I have a BG 750 Speed Demon on my ZZ4 and I don't think it could work any better. I bought it used and it's the first BG I've owned and I'm a believer. It sits on top of a 2" spacer on the stock manifold.
I did end up riching up the jets one size in the front and two sizes in the secondaries. I can't tell you what I ended up with because it's written on the float bowls and my boat is in storage. According to the "C" class rules that's a legal carb to run. I'd try an 850 if I had one, but I don't. But that wouldn't fit the rules.

Squirt,
I'm anxious to hear how your boat runs. Mine won't run over 79 mph. It's to slow to tow out there to race, but its a blast back here.


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[WILSON]

Well, it depends on how fast you want the engine to turn:

Basically, you multiply the displacement times the RPM's you want to turn, and you get how much air you will move in the engine.

The complete formula is:

CFM = CID x RPM x VE ÷ 3464

VE is the Volumetric efficiency of the intake manifold. (In terms of strict engineering, should be the efficiency of the whole system, but anyway)

Since the ZZ4 doesn't come with a fancy intake, you can suppose it is 1 or close to one.

350 (C.I.) X 5250 (RPM) / 3464 = 530 CFM

So, the 600 CFM should be enough.

I have no idea on why the mechanical secondaries are better, but all my friends who know advise me not to use Vacuum secondaries.

[AR]

[Aluminum Squirt]

OK, well based on Wilson's calculation, the 600 CFM is enough but vac secondaries are no good and based on AR's seat of the pants explanation, I'll pass on this one. Thanx for the input.

AR, 79 MPH is fine on an FX boat. My little sprint hull will probably never see 79. Some of the light weight step tech's and the river wild boats I think are getting mid 80's. I say 79 is plenty, that puts you in the range where if you keep it running and drive a good line, I think you could compete-Aluminum Squirt

[WILSON]

I use a 750 CFM with mechanical secondaries.

I chose that because that's the maximum allowed by the AWJA rule. And if this is the maximum allowed, should be the best, right? (Bottom line: the guys at AWJA know better than me!)

Rule: For maximum performance, select a carburetor that is rated higher than the engine CFM requirement. Use 110% to 130% higher on single-plane manifolds.

Example: If the engine needs 590 CFM, select a carburetor rated in the range of 650 to 770 CFM for a single-plane manifold. A 750 would be right. An 850 probably would cause driveability problems at lower RPM. A 1050 probably would cause actual loss of HP below 4500 RPM. For dual-plane manifolds use 120% to 150 % higher.

For further discussion, see

http://www.fortunecity.com/silverstone/chrysler/45/formulas.htm

[AR]

Wilson, I agree with you completely.

That is why I recommended to use a 750 cfm to begin with. I just happen to have grown fond of a BG carb.
But, I do think at 4500 rpm and above a 850 would show more HP and speed in a Jetboat with a ZZ4, don't you ?
A vacuum operated carb is very streetable and forgiving, especially if you over size because the secondaries will only open as much as the engine requires. I think the 3310 vac. sec. was the most popular and used carb Holley ever made. It came on 302's and up to 454's with 450 HP on 1970 Chevy's
My $ .02's


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[AR]

Aluminum Squirt,
You have the right Carb.
Just find someone to rebuild it for you. It's one of the easiest carbs there is to rebuild if the shafts are tight and the screws aren't all stripped out. If you want a chock just put an electric one on it, it's no big deal.
I don't run a choke either, just pump the gas a couple times and it fires right up, of course I only go Boating when its WARM !


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[Aluminum Squirt]

Thanx for the info AR. I don't think the carb is garbage or anything, just thought that if the model # in question was a good carb, I may be able to pick it up for a good deal. I'll save my money for a new ZZ4. I figured the one I have was OK, and I'm starting to figure out jetting, power valves, etc. I'll just have somebody reputable look it over and make sure its mechanically sound and then I'll get it all set up when I eventually get a ZZ4. No choke needed down here in Cali, that DP squirts enough fuel to get it richened up for starting-Aluminum Squirt