I am building a 8-71 blown BBC. I am trying to find out what needs to be done to a set of Holley carbs to make them blower ready.
I have a pair of pro-rebuilt 850 center squirters. I was told to send them to a carb guy(I have a couple of recommendations)for prepping. I was told between $250 and $400 a carb! I am going to use this engine in my lake jet, so all out performance is not my main concern.
Any ideas???
Thanks,
John
Heatseaker,Scroll down to Boost Referencing Carbs in this forum.There is a bunch of opinions regarding this subject.I think the price is too high,but I don't know the condition of your carbs.You may want to contact holley and see if they offer a kit.Good Luck,DEL51
The right way costs money and whatyou were quoted was half of what I was told. So I went the cheap route which works for me. However, I can't compare it to the optimum setup. Holley 4150, list 4779-2, with 50 cc pumps all around (4),primary jets are76, scondaries are 86, power valves blocked off, spring loaded off road needle and seats #6-513, clear bowl sight glasses-floats set high in the hole, primary shooter is 35, secondary shooter is 37, plugs at 032", timing at 28', elevation at 4,400 feet. These are on a 468 with a big bore 6-71. Ran out of time to lean it out more because I started rich and have been working leaner. Had other variables to work with so this is all I (and I am an ametuer)have for now. Start very fat if you are going from scratch. Plan to get an intercooler, this winter after getting more info from a guy on this website. My plug color is a light tan on a medium weight Biesemeyer. Good luck.
When I ran carbs they were two holley 750's.
The power valves were blocked off and they were set up pretty close to snowboats. I can't remember the jet sizes. They were not boost ref. and worked pretty well.
Slowboat,
Has the removal of the power valves caused you a flat spot on acceleration? One of the posts in the boost referencing thread suggests that as a possibility.
The carbs are 4223 850 cfm center squirts with 50 cc primary pumps, #80 primary and secondary jets, and a #25 pump shooter.
I would rather find a solution to the carb set up myself. The 'carb prep' money could be better spent on other neccesities. This set up is for my "family" lake jet. All I want out of it is decent reliability and good power. It's not like I'm trying to trim a couple of tenths of my et.
Thanks for the replies guys!
John
AKA Heatseeker
I have a brand new PFM superchiller still in the box fits 671 or 871 cant use it would like $1150 contact me at jgalowitch@inlandkwaz.com
Heatseeker; ooh! the pain,the proper spelling is Snowboat, might make it to Sunny Cal with a boat some day. Anyway, there was not seat of the pants, lack of acceleration. The power valve was designed to cover the dead spot, so when you take it out, you have to jet up. There is a loss in fuel economy, but I lost that when I bought my first boat. You wouldn't want to do this in a daily driver car. The other thing is that you don't have to dick around to find the right power valve and jet, just the jets.
Guys: Whenever I hear or read anything about power valves causing a dead spot I have to speak up.
It is true that when removing the the power valve you must jet up. It is also true that fuel economy will be affected.
A dead spot in a carb during acceleration most of the time is due to the accelerator pump discharge nozzle not large enough.
Sometimes it is caused by the throttle valve relationship to the transfer slots.
When the throttle is opened suddenly there is an instantaneous increase in air flow. The increase in fuel flow lags slightly. The squirt from the accelerator pump (acceleration system) makes up for this lag. Some engines require more squirt than others.
The true function of the power valve is also called the power enrichment system. It is to make sure there is sufficient fuel at high power settings and allows economical operation at lesser power settings.
Holley chose to have them vacuum operated. On a normally asperated engine under high power settings there is less vacuum and they provide extra fuel flow. Just the opposite under lesser power settings.
Sometimes on supercharged engines there may not be enough carb on top of the blower. What happens is under high power the blower is drawing hard on the carbs and causes a high vacuum (just the opposite of how the power valve should operate). This can shut off fuel flow from the power valves. Not good for obvious reasons.
I choose to not use them on blown engines for several reasons. I just jet the primaries lean enough to be economical and make up for it with the secondary jets. Who cruises around in the secondaries anyway?
ADDED THIS:
HS The setup provided by sNowboat is good. I do not see any need in spending bucks for blower prepped carbs. Just pay attention to the parts he listed. Your first concern should be providing enough fuel flow to the engine and then enough fuel flow to the carbs. Starting with the fuel tank outlet. I have seen guys fail here too many times.
[This message has been edited by Infomaniac (edited December 01, 2001).]
SNOWBOAT,
Sorry for calling you slowboat. Sometimes I turn things around in my head, ever since those experimental acid trips back in the 80's http://free.***boat.net/ubb/confused.gif!
Thanks for the tips. I am going to install the carbs and make a river run(5 minutes from the house)to do a plug reading and I'll go from there. I'll probably have to fatten up the squirters, from the looks of your set-up. I may get by on the jets, with the power valves in place. Too bad it's so damn cold. I'll have to wait until at least March.
The intercooler will have to wait for a while. My wife would casterate me if I popped another $1000 on this blower set-up.
Thanks for all the help!
John
Here is a e-mail address for a man who builds marine high $$ engines. He knows alot about carbs for blowers.He be a good person talk to. Bruce Dudley" <dudley_bruce@hotmail.com>
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