boost referencing carbs

[dyam]

Can anyone get me up to speed on boost referencing holley carbs on a blower moter?!
I have a 1998 21' eliminator daytona with a 502, superchiller, b&m 250 and dual holleys with no power valves. It runs a max of 6lbs of boost.
It's jetted very fat.
I want to add the power valves so I can idle through marinas and not load up or have black smoke all over!
HELP!
Do I need to boost reference the carbs with this amount of boost?
Can I do this myself or should it be done at a shop?
Next question-where should the ride plate be installed in relationship to the bottom? I know it's not supposed to be level with the bottom but at what degree should it angle upward?
Last question-does anyone have any experience with the dual impellers on the jets?
I am running a setback Legend with an A impeller(I think)-85mph @ 5500rpm.
I would like to get that awsome holeshot everyone says a jet should have and I would also like to get just a little more speed at 4000rpm. Currently I'm running about 40mph @4000rpm.
Any help would be appreciated!!!

[Unchained]

I know everyone says that you need to boost reference the power valves but that is only needed if the vaccuum draw at WOT is enough to close the power valve. Example, 1 in. vaccuum at WOT, no problem, 6 in. vaccuum at WOT, boost referencing required. The power valve will be open when the vaccuum drops below the power valve rating. I use 4.5 power valves and they are in the primarys and secondarys. In my blown 540 Arias engine I don't have boost referencing and my vaccuum at the carb base at WOT is 1 lb. I am running 14lbs. boost. When you put in the power valves you will have to jet way leaner because they account for about 6 to 8 jet sizes. Check the vaccuum right at the base of the carbs at WOT. Your carbs need at least primary power valves or the engine would have a major flat spot.
The ride plate wants to be about 2 degrees up from the keel line. This can vary from boat to boat.
I put in a cavitation reducer impeller and it helped slightly, Now when I floor it from a dead stop the RPM will overrev by about 800 rpm and then the pump loads and away you go. Before the engine would overrev wildly and could not be floored from a dead stop. If you want to go real fast shim the ride plate down until the pump intake pressure gets up to 30 or 40 lbs. You will be amazed at how much the hull will lift at high speed. You should be running faster than 40 at 4000 rpm.
The 21' daytona is a great boat. I am going to buy one soon. Post a pic of your boat. My 19' Cheyenne is a fun drag boat but too small to carry back seat passengers, They get scared riding next to the monster.

[dyam]

Thanks for the info.
I'm going out next Sunday so I'll get some vacuum readings then.
When you installed the cavitation reducing impeller did you increase the size of the main impeller? Who installed it?
I don't understand how shimming the ride plate down will increase the pump intake pressure but I am going to shim it down.
I think I'm at about 5 degrees now.
It tends to porpose slightly at part throttle, 35-45mph. Will shimming the ride plate help with this problem? I'm hoping it does. It's not a big problem but it's kind of irritating.
I've got a droop snoot, with a 4 degree(down) wedge added and a place diverter.
Everyone has told me the diverter should take care of the porposing and it does under hard acceleration but not at part throttle.
I have a handheld GPS unit and it's supposed to be pretty accurate. 40mph @ 4000rpm really sucks.
I'll post a pic when i figure out how.
THANKS again.

[DEL51]

Hello unchained, I am putting together a 486 chev 871 blower motor and I am curious about carb size. If the carbs are not large enough would this increase the vaccuum reading below the carb.What size carbs do you run and what would you reccomend for an engine of 468 cubic inches. I was also wondering about what suction piece pressure is considered optimum.Thanks for your time.DEL51

[Unchained]

Sorry, I mis,spoke that one part, I meant shim the shoe down to increase pump intake pressure.
No, I didn't increase the main impeller size. I'm running a AA now. The cavitation reducer just brings the water to the main impeller so it does'nt have to draw it in. As Don says, the cavitation reducer is unschrouded so it will flow more water than the main impeller can use. I pulled the shaft and machined the step and the keyway in it for the Cav. reducer myself. It is easy if you have access to some machine tools.
Anyway try to have the ride plate about 2 degrees up from the keel and experiment from there. Maybe that will help with the porpoise problem.
So you have a 2 degree down wedge. I had to put in an up wedge so my diverter wouldn't drag in the water because I have a Place droop and a 5 degree intake.
Del51, I questioned about the carb size that I am using because the guy at Fowler Engine told me two 850s were way too small for my 540 engine. He told me I would pick up 200hp by going up to two 1050 dominators and had run the dyno tests on other engines to prove it. So I took a carb base vaccuum reading and got about 1 in. at WOT so I concluded that the carbs can't be restricting that much. You know how with boats and engines you ask ten different people and get ten different ideas.
For your 468 I would run two 850s better too much than not enough. I know everyone says you need blower carbs. I just bought two off the shelf Holley 850DP and they have run fine. We even water ski with my boat. I did rejet smaller than what came in the carbs because the plugs were reading a little rich.
Pump intake pressure wants to be 30 to 40 lbs. at high speed but any pressure is better than the pump sucking the boat down to the water at high speed.
I am by no means a jet boat guru so don't take my opinions too seriously but I hope I can give some ideas that you guys can use.

[DetroitJim]

Hey Unchained, saw you at Brower Park. I had the blown Sanger flat. You have a wild ride there. Anyway, del51, for what it's worth I am running an oval port 454 with a Mike Kuhl 8-71 at about 7-8 lbs boost. Everyone said I was crazy to use 2 750 Edelbrocks so I did. I stepped up the secondary jets to .113, the biggest made. The needles and seats are the larger .110 diameter. The carbs run about as perfect as you could ask. The pipes are dark gray, no soot whatsoever. Throttle response is crisp, no bogs. Total investment in carbs less than $500, 94 mph on gps.
When I go to a 540 next year, then 850's or 950's would be my choice.
Jim

[ponponracing]

Dyam, powervalves don't really affect idling carbs adjustments. They will affect part trottle mixture conditions, and in certain cases the wot conditions. There are other ways to lean the idle mixture with Holley carbs. Tune them right first, you may drill the butterflies, then you may add v-wires in the metering system, you may also tune the mixture with the idle air bleeds, on top of the carbs.
A good "tuner" may be very helpfull in setting your carbs for blower application. Do it properly or you will need a spare motor......or two.

[dyam]

Hey ponponracing, thanks for the info.
I'm trying to avoid the second and third motor thing!!
My thinking is, if I install the power valves I can then lean out the primary jets and then reduce the amount of fuel used at part throttle.
thanks for the tip on drilling the butterflies. I forgot about that! I'll try that before I put it in the water next Sunday.
The V-wires and the air bleeds I'll have to find some help on.
Again THANKS for the info!

[Unchained]

Detroit Jim, Was your boat the one with the yellow, orange, and purple stripes ? That one was a beauty. Put a picture on the jet performance page boats/names post.

[ponponracing]

Dyam, drilling the butterflies is a matter of obtaining the right butterflies position in relation of the transfer slot. Drilling them when they need to be drilled gives you a cleaner idle.
If you run a heavy boat, don't bother about powervalves, you will be always running low vacuum. If you run a small or very light boat, then you may benefit using powervalves. Look in blowers engines preparation books and you will find how to reroute the vacuum signal to the powervalves. Instead of the powervalves being activated by the vacuum signal directly under the carb., you pick up the signal from underneath the blower itself. If you run powervalves, you have to make sure your carbs are equiped with backfire powervalves protection, since a blower backfire and there go the powervalves....