Carb recomendations

[Rubths]

I looking for advise as to what the best carb size will be for my setup, 454 full ported and polished Merlin heads, hypertecnic pistons high lift cam, 8:5:1 450+hp. I currently have a holly with vacumm secondaries and I have a dead spot where the secondaries come on. Im not opposed to buying a good used carb if someone has one that will work for me.

[powerplay230]

How much work have you tried doing to carb yet? Quite a few things you can do with it, would try the economical things first to see if it helps at all. You want to make sure not enough fuel is the problem before you spend $4-900 bucks. Just my .01 cent.

[GofastRacer]

Rubths:
I looking for advise as to what the best carb size will be for my setup, 454 full ported and polished Merlin heads, hypertecnic pistons high lift cam, 8:5:1 450+hp. I currently have a holly with vacumm secondaries and I have a dead spot where the secondaries come on. Im not opposed to buying a good used carb if someone has one that will work for me. What size carb do you have?, a flat spot when the secondaries open is because they are opening too quick. First thing to do is take the cover off and check to see if the check ball is there, if it's missing, it will cause the secondaries to slam open, if it's there, you need to get a spring kit, start with a stock one and go from there!. No need to get another one if you have an adequate size carb, just have to do some tuning!. OK Ty (Mr Carbureter), you can take over from here, I'm going to play with my injectors!... wink :D
[ March 19, 2003, 06:19 PM: Message edited by: GofastRacer ]

[rivercrazy]

I'd ditch the vac secondary carb and get a double pumper with mechanical secondaries. On a jet boat you'll get more instant rpm increase, therefore more accel and maybe a MPH or two. A 850cfm would be pretty good

[Froggystyle]

An 850 is good, but a 750 will do just fine as well.
A lot of times I have found people to over-carb jetboats. Jet's love torque, and in the rev range a lot of people run in, a tunnel ram doesn't even work yet, and there is no way in gods green earth they need 1500 CFM of carb.
For a stock application, it has been my experience that the smaller carb will increase your lower end torque considerably by increasing the intake velocity or something. The voodoo is beyond me, but I have had great luck with smaller carbs on jet applications.
Just my opinion. My boat has an 850! (509 Merlin, 6000 RPM's though)

[Hotcrusader76]

Rubths:
I looking for advise as to what the best carb size will be for my setup, 454 full ported and polished Merlin heads, hypertecnic pistons high lift cam, 8:5:1 450+hp. I currently have a holly with vacumm secondaries and I have a dead spot where the secondaries come on. Im not opposed to buying a good used carb if someone has one that will work for me. The vacuum secondary is great for all around use in cruising. The motor only uses what it needs for cfm because the secondaries are utilizing vacuum from the primary bores. This also allows you to run a larger than normal cfm carburetor without any side-effects. As far as the flat spot it sounds like a problem in the opening rate of your secondaries. This can be remedied with some simple spring swapping.
What's the list number on your VS carb? 3310 or what not? If you're on a budget that carburetor is really all you need for fuel metering. A tricked out 3310, converted over to 4150 and all is good up to around 500HP. After that it becomes real restrictive for it's use on a BB.
If you went with a used Double pumper, buyer beware on those found on Ebay, then remember 90% of them have trashed out baseplates due to the amount of strain placed on the throttle shafts. Alot of people who used double pumpers, incorrectly mind you, placed alot of tension via a return spring which causes abnormal wear on the primary shaft. They feel this is necessary to overkill the amount of springs placed on the return. Oh well. Maybe that's why they are selling them in favor of a new one.Hmmmmm idea
I gained this experience from searching for double pumper cores on my remanfactured product line. Basicaly all remanfuctured carbs get new bases after I received them. Ebay mind you is an excellent source for buying a used Holley. I helped a fellow ***boater purchase a rare Holley 850 Center Squirter #4223. He called me up asking what it was and is it good. I told him hell yeah! Buy that "puppy" before I do... :D
Good luck on making a choice.
~Ty

[Wet Dream]

Ty, how much play is too much on the throttle shaft?

[rivercrazy]

IMO in a jet boat, low end torque is not as important as horsepower/torque in the mid to upper rpm ranges. In low rpm mode, jets don't need much low end torque. The impeller spins easy until you get into the mid to higher rpm ranges.
Due to the fact jets love more higher rpm power and a higher cfm carb is why a double pumper is better. Yea you can over carb a motor but this dude's motor is not bone stock and could probably benefit from a 850 over a 750.
Just my .02cents

[Blown 472]

rivercrazy:
IMO in a jet boat, low end torque is not as important as horsepower/torque in the mid to upper rpm ranges. In low rpm mode, jets don't need much low end torque. The impeller spins easy until you get into the mid to higher rpm ranges.
Due to the fact jets love more higher rpm power and a higher cfm carb is why a double pumper is better. Yea you can over carb a motor but this dude's motor is not bone stock and could probably benefit from a 850 over a 750.
Just my .02cents Good point, as the speed goes up so does the load on the motor and the fuel requirement. Low end is nothing in a jet boat.

[Rubths]

Got some numbers off the Holley carb, P80, 10569, 6R 6931-B. Can anyone tell me what I have from these numbers?
Thanks

[Hotcrusader76]

P80, 10569, 6R 6931-BAccording to my references it's a 1975 Truck &Coach 427 California motor application carburetor, either a 4150G or MG version. With the 4150 designation it should have a primary and secondary metering block with a vacuum secondary. This version does include 1850 style bowls and not the normal Dominator style.
If my reference is right, this carb isn't worth the trouble unless your looking for a parts matching carb.
As far as cfm size it doesn't list it. What are the numbers stamped into the butterflys underneath the baseplate when you turn the carburetor upside down?
I hope this helped ya out.
~Ty

[Rubths]

Thanks for the info on my worthless carb :p Does anyone have a 850 or bigger double pumper they are looking to sell??

[SShammy]

There is actually a formula you can use that will tell you whut at size carberator you need. I am trying to remember it but i know that it called for me to have at least a 700-750cfm carb on my 350 horse small block . Ofcourse if your not going to turn the motor over 4000 grand yopu can just leave the 750 on it.You must realize that your motor is set up to flow alot of air with the cam and heads you have but it wont be able to breather at higher rpms if you chopke it back. That is to say that the power will be great until you start asking the the engine to flow more air than your carb can deliver.Let me see if i can find that formula for you.

[SShammy]

Here it is my man. engine size(CID)X MAX RPMS/3456=CFM@100 PERCENT VE(VOLUME EFFECIENCY). NOW BEAR IN MIND THAT YOUR ENGINE PROBABLY ONLY HAS AN 85-90 PERCENT VOLUME EFFICIENCY. SO IF YOUR PULLIING THAT AA IMPELLER 6000 OR TRY ING TOO YOU BETTER CARB UP. I DONT KNOW WHT RPM, RANGE YOU RUNNING BUT JUST TO GET THE BOG BLOCK TO TURN 6000 YOUR PROB GOING TO NEED 900-950 CFM.

[GofastRacer]

Here ya go!.. :)
Formulas for air capacity & volumetric efficiency
theoretical cfm = rpm x displacement / 3456
volumetric efficiency = acutal cfm / theoretical cfm x 100
street carb cfm = rpm x displacement / 3456 x 0.85
racin carb cfm = rpm x displacement / 3456 x 1.1

[Wild Horses]

I run a 502 roller motor with aluminum edelbrock heads, weiand team G intake flowed and ported. At 5700 rpm, 560hp dynoed with a 800cfm holley dp. made 10hp more with a 850cfm dp. More is not always better. :)
Clint

[Rubths]

Ty heres a pic of my boat, look familiar???
http://free.***boat.net/gallery/Hot_Boat_Happenings/Havasu_and_The_River/labor_day_11.JPG

[miller19j]

Rubths:
Ty heres a pic of my boat, look familiar???
http://free.***boat.net/gallery/Hot_Boat_Happenings/Havasu_and_The_River/labor_day_11.JPG Looks like a Miller :)