air bleeds do have a little to do with fuel "quantity" but there primary purpose is to time the main system.

too small of an air bleed= nozzle drip and it coming in to early
too big of an air bleed = delaying of main too much so a lean spot shows up between the intermediate circuit and the main

and of course they contribute to emulsion

when you say "bars" do you mean the truck type boosters, thats what they look like anyway?

what did the car run before you did these modifications to the carb(s)?

have you done an test with the boosters being the only variable changed (except for jetting to compensate)?

How much jet did you have to add? I would guess 5-10 square

I agree with the mods you have done except for the booster, but if it works for you great.

I do quite a bit of carb work but for blowthrough turbo/supercharged stuff so thats why I am obsessed with the booster signal.

 

I had a steady AFR at the track last year. It took 10-15 jet sizes to get there.

On the street the AFR does vary, but I have not spent any time tuning this years setup. Last year's street setup and tuning resulted in a steady AFR. I changed the air filters and the fuel pressure this year.

I'll look into air bleeds as an additional tuning tool.

The carbs are 3310s, so that's the booster style. You think doglegs will replenish some signal, I agree. They would also provide additional restriction.

These carbs sit atop a 6-71.

What modifications have you made booster wise. Any data?

 

for a strong signal I would go with annualar boosters, and that is what I plan to do for my blow through set up

for air bleeds just drill out the old ones and tap the holes for 8-32 threads

then buy some brass set screws and a numbered drill set and you can make any size airbleed you want.

I have just modified the contours of my down leg boosters on the inside that the casting process couldnt. on my engine @ WOT is was worth about .1-.2 AFR richer at the same jetting

 

I like the annular boosters also.

Another way to increase signal strength is to machine a step (or steps) diameter just below the fuel outlet on the underside of the booster. I have not done this but will if signal bocomes a problem.

I like the brass set screw idea. I use brass screws for jets in my nitrous kit.

Any pictures of the booster mod? No other data than AFR?

 

Umm, if this is on a roots blower and you have two of these why are you doing modifications to kill signal? You say increase flow, but why? The carburetors are going to flow more than their nominal 750 cfm sitting on top of a roots. I think if you measure vacuum at the baseplate of the carburetors you will find more than 1.5" of mercury if you're really driving the blower hard. If you find more than 1.5" then you can assume you are pulling more air through the carburetor (1.5" mercury being the depression holley used for 4 barrels). How much overall boost are you running?

I once just touched up the casting flash on the inside of a 0-4781's boosters before I sent the carburetor off to C&S. They sent them back in a baggie with a note that said something like "don't touch!" and replaced them (without charging me). They have Rochester's old wet flow bench and are informed in this area. Boosters are an area that really shouldn't be dicked with unless you have a way to quanitify your change. If removing the center bar required an increase in 10-15 jet sizes because of that change alone then your carbs signal is screwed.

I am not trying to be a jerk and I like to experiment with carburetors too, but I don't understand the reasoning behind looking for 60 cfm and destroying the signal and less importantly on your roots, distribution in the process.

 

I dont have any other data than AFR because the car has not been to the track with the blower, I was simply looking for a way to increase signal strength at the booster for being blowthrough.

I do not have a picture of my boosters (mainly because i suck with computers) but I took a inline grinder and lightly worked my way around where the inner and outer parts meet (both top and bottom) and blended it(down leg boosters).

the step method does the same time but I dont have the tools to do the machiniing.

if you have jetted to compensate your only down fall will be some lean flat spots while transitioning to WOT

 

LOL, never mind.

 

markinkc69z. "Roots type superchargers are sensitive to inlet restrictions. Less restriction is more power. And, max power is the name of the game. As long as it's still tunable why do i need super signal strength? Atomization would be the only other concern. Otherwise, I'll take 60 free CFM any day of the week.

As a testament to the tuneability and atomization, I drove 26 miles to the drag strip, laid down a half a dozen low 10 second passes, and drove 26 miles home, on pump gas (fuel atomization problems should show up here as detonation). It makes for a long day in the 85 degree heat, but no problems. This setup runs five pounds boost (10% underdriven).

I have provided you with some before and after data, but certainly solid overall performance data (It's hard to change just one thing at a time and then go and evaluate, time constraints). I do agree booster modification is not for everyone.

All you have provided here is tell us how you fouled up your boosters. You should condem yourself. I've provided some information here on at least what I've done and my results. You're sounding a lot like the guy who complained to me about my propane injection system, check the signature, it worked out well.

lamerandomname...Wow that's insightful, my guess is you are scouring the net trying to define extension tube function. I still don't see what extension tubes have to do with booster signals. Help me out here.

 

master of a-bodies,

hey have you been changing your own boosters? Did you buy or make a tool. Looks like they are pretty hard to come by.

 

What size engine is your supercharger on?

 

454

 

no I have not been changing mine own boosters, I can not find the tool to do it either. It was I huge bitch to get on the under side of them while still in the main body.

If I did have the tool I most likely would have went to a annualar booster from CSU, I might end up sending my carb out eventually for boosters if I start running alot more boost but I will do all the air bleed and emulsion tuning my self, but for right now it is doing pretty well,

 

If you google enough, you'll find one. Eventually I found the tool, but thought it was cost prohibitive. There is also a safety issue. Appearantly not that many carb shops change boosters either. As I remember it was a "C" clamp looking tool.

I may, like I said, machine a step on the underside of the booster for better signal/atomization at some point, but not just yet.

The other side of the coin, at least with my carbs, is cost. Thus far it's all been free. Changing the boosters is going to cost money. I have 750s with vacuum secondaries. I believe the 850 carb uses a larger venturi diameter, which I would like to have, and I would also get away from the vacuum secondaries. Anyway, I think I'd just step up to a better carb rather than change boosters.

Let me throw one more thought out there for ya:

The less restriction, assuming you can tune it and have acceptable driveability, what ever your definition of driveability, the more power potential?

I'm riding a big block w/blower, low speed power is not an issue, detonation is not an issue, throttle response is unbelievable. Why change?

 

Hey here's the tool.

www.aedperformance.com/Tools.htm

 

Not knowing how high you rev this engine I'll take the higher rpm route. I'll say 7000, though I'd bet its closer to 6000. At 7000 rpm if your engine actually had 100% VE and then you added 9 psi of boost you wouldn't be exceeding the cfm rating of 2 stock 750 carburetors. This doesn't take into account the loss of air density from the heated supercharged air.

I don't know anything about the propane injection conversation you had. These threads remain here permanently and I would hate for somebody to look at this as a how-to and think that removing the bar in the booster was a good idea. That is all.

I'm glad you feel its working appropriately for you. By the way poor atomization would not lead to detonation. Detonation is caused by heat of compression combined with inlet air temp. Poorly atomized fuel will not provide as much heat (power) during combustion as finely atomized fuel does as less of it will burn and more will run out of the exhaust wasted.