Dominator - 2 or 3 Circuit - Team Camaro Tech
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post #1 of 29 (permalink) Old Oct 28th, 09, 03:23 AM Thread Starter
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Bob
 
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Dominator - 2 or 3 Circuit

I've rebuilt my Shafiroff 540 BBC (725hp, 680tq). Installing a 1050
Dominator. Question is do I use a 2 or 3 circuit carb. Car is weekend
street driven with the occassional expressway racing. I was leaning
towards the 8082 2 circuit but the builder said use 3 circuit. Hearing
the 3 circuit runs rich. Need input on which to use. Thanks!
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post #2 of 29 (permalink) Old Oct 28th, 09, 04:54 AM
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Rich
 
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Re: Dominator - 2 or 3 Circuit

The 3 circuit will offer a little bit better driveablitly.They were designed for tunnel ram applications where at low speeds{such as tooling around the pits} the throttle plates would be open such a small amount that the boosters wouldnt get any signal to move fuel and the idle circuit wouldnt supply enough fuel.If you have a 3 circuit carb on a single 4 barrel application and it runs rich try enlarging the intermidiate air bleeds,this should make it better.Good luck.
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post #3 of 29 (permalink) Old Oct 28th, 09, 08:05 AM
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post #4 of 29 (permalink) Old Oct 28th, 09, 08:30 AM
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Eric
 
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Re: Dominator - 2 or 3 Circuit

DO NOT do a 3 circuit for street car -- you will be horribly disappointed. I have converted SEVERAL 3 circuit Dominators from 3 to 2 circuit with great results. Some of which have the same fancy sticker on them as the carb pictured above

This is the issue -- with a 3 circuit, the emulsion tubes in the main well really restrict flow. It is very difficult to get enough fuel at WOT UNLESS you add a bunch of fuel with the intermediate circuit. When you add a bunch of fuel with the intermediate circuit to make it correct at WOT you wind up stupid rich at cruise. You will have a plug-fouling-pig-rich-black-smoke-belching-PITA with a 3 circuit on the street.

The place for a 3 circuit Dominator is on a strip only car that uses a trans brake! In these cases the 3rd circuit helps richen the mixture when on the brake. Personally, I can still make a 2 circuit carb work very well in those circumstances too.

E85 racer and E85 carb builder
www.horsepowerinnovations.com

68 Camaro, E85 powered 427" small block. 9.96 @ 133 MPH, 1.319 sixty foot on motor. 5.92 eighth @ 116 with a 1.42 sixty breaking beams with back tire on the bottle
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post #5 of 29 (permalink) Old Oct 28th, 09, 05:55 PM
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Rich
 
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Re: Dominator - 2 or 3 Circuit

Quote:
Originally Posted by Eric68 View Post
DO NOT do a 3 circuit for street car -- you will be horribly disappointed. I have converted SEVERAL 3 circuit Dominators from 3 to 2 circuit with great results. Some of which have the same fancy sticker on them as the carb pictured above

This is the issue -- with a 3 circuit, the emulsion tubes in the main well really restrict flow. It is very difficult to get enough fuel at WOT UNLESS you add a bunch of fuel with the intermediate circuit. When you add a bunch of fuel with the intermediate circuit to make it correct at WOT you wind up stupid rich at cruise. You will have a plug-fouling-pig-rich-black-smoke-belching-PITA with a 3 circuit on the street.

The place for a 3 circuit Dominator is on a strip only car that uses a trans brake! In these cases the 3rd circuit helps richen the mixture when on the brake. Personally, I can still make a 2 circuit carb work very well in those circumstances too.
I dont get the connection.The intermidiate circuit has it's own air bleeds,and has nothing to do with the emulsion on the high speed circuits.As for the application,I cant see a 3 circuit having an advantage with a trans brake car since the car should be WOT on the brake{unless using a starting line enhancer} and very little fuel would be pulled from the intermidiate circuit since that would require vacum at the tubes themselves and there isnt much vacum at WOT during low air demand.

The intermidiate circuit actually got it's start on the old 6214's back when they were being run on IR intakes,the cigar style boosters were so unresponsive to weak signal that they needed the 3rd circuit just to move air during part throttle transition.As for getting the curve right,you can lean out the intermidiate by opening up the bleeds,and fatten up the high speed by resticting those bleeds.There really isnt a need for a 3rd circuit on a single 4 barrel race car because most current bracket engines are fairly large displacment and move sufficient air at part throttle to generate some signal,a smaller displacemnt tunnel rammed engine wont move fuel at low speed ad needs the 3rd circuit.I have no problem running an intermidiate circuit on my fairly mild 427 with an 1150{old6214 converted to regualr boosters}.Thats just my $.02
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post #6 of 29 (permalink) Old Oct 28th, 09, 06:25 PM
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Re: Dominator - 2 or 3 Circuit

Quote:
Originally Posted by RichSchmidt View Post
There really isnt a need for a 3rd circuit on a single 4 barrel race car because most current bracket engines are fairly large displacment and move sufficient air at part throttle to generate some signal,a smaller displacemnt tunnel rammed engine wont move fuel at low speed ad needs the 3rd circuit.
If you do not need a 3 circuit carb in a race car you certainly do not need or want the 3rd circuit on a street car! The 3rd circuit does help with a race car (yes, a transbrake ride on the two step) because it provides extra fuel and tuneability when staging (especially when the signal gets goofy on the two step). As I stated earlier though, personally prefer a 2 circuit even at the track.

The third (intermediate) circuit gets its fuel from the float bowl directly so at cruise (on the street) the 3rd circuit never shuts down and only makes the mixture excessively fat. When you make the intermediate bleed larger as you mention is necessary (kind of an admission the 3rd circuit makes it too fat on the street ) you take fuel away at WOT. Then if you compensate by adding more jet OR going smaller with the high speed bleed you are again too fat at cruise most likely have a non-linear fuel curve.

With a traditional Holley 2 circuit carb, the transition circuit gets its fuel from the main well, directly behind the main jet. When the 2 circuit gets up on the mains at cruise the transition is competing for fuel with the main and effectively shuts down allowing a lean cruise. The 3 circuit carb has fuel dumping in from the float bowl to the intermediate circuit, and the transition circuit is getting its fuel from the intermediate so it doesn't shut down either. So even if you remove the intermediate bleed on a 3 circuit carb you still are getting fuel into the carb through the transition circuit. All of this extra fuel flow contributes to a fat mixture at cruise and a lean mixture at WOT when you try to "tune through it."

Quote:
Originally Posted by RichSchmidt View Post
I have no problem running an intermidiate circuit on my fairly mild 427 with an 1150{old6214 converted to regualr boosters}.Thats just my $.02
What mods did you do to the 3 circuit (or what is your tuneup) to make it work on the street? Have you ever tried a 2 circuit?

E85 racer and E85 carb builder
www.horsepowerinnovations.com

68 Camaro, E85 powered 427" small block. 9.96 @ 133 MPH, 1.319 sixty foot on motor. 5.92 eighth @ 116 with a 1.42 sixty breaking beams with back tire on the bottle
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post #7 of 29 (permalink) Old Oct 28th, 09, 06:32 PM
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Eric
 
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Re: Dominator - 2 or 3 Circuit

PS. If you Google "3 circuit to 2 circuit conversion" or similar you will see there is LOTS of discussion on this on the net. This isn't just my opinion -- lots of others hold this opinion too!

Here is one for starters

http://motorsportsvillage.com/forum/...php?f=6&t=3742

E85 racer and E85 carb builder
www.horsepowerinnovations.com

68 Camaro, E85 powered 427" small block. 9.96 @ 133 MPH, 1.319 sixty foot on motor. 5.92 eighth @ 116 with a 1.42 sixty breaking beams with back tire on the bottle
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post #8 of 29 (permalink) Old Oct 28th, 09, 08:48 PM
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Sean
 
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Re: Dominator - 2 or 3 Circuit

Here's an interesting read, from Patrick James of Pro systems regarding 3 vs 2 circuit dominators. http://www.prosystemsracing.com/gurus.html

If you are rarely racing it and performance is not the primary concern I wonder why you are even going to run a Dominator to be honest. A well built 4150 will be great for the type of use you describe.

Sean

1968 rs, with an old school, antiquated "junkyard, never even had the valve covers off" 354" SB2.2 pump gas motor........

"I aint never seen talking win me nothin'" -Marshawn Lynch
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post #9 of 29 (permalink) Old Oct 28th, 09, 09:15 PM
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Ron
 
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Re: Dominator - 2 or 3 Circuit

I have a 3 circuit 1050 by Quick Fuel. It runs fine on the street. the front boosters are stepped to make them work better at low throttle penings.
Looking down the bores, the intermediate circuit shouldn't even be engaged when cruising. The throttle plate would have to be open quite a lot. Mine smokes the tires at very little throttle opening.
That said, I'm no expert. Maybe a fine 2 circuit would make the car faster? I don't have another grand to try one. On the dyno, fuel curve was spot on. And it works decent at the track.

ron

69 Nova
Single turbo alum 5.3 LS
9.45 @ 145.35 so far.....
2000 C5 Corvette Auto 10.99 @ 123.8 NA

I'll be back for you Jack, and I'll let the machine speak!
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post #10 of 29 (permalink) Old Oct 29th, 09, 05:18 AM
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Rich
 
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Re: Dominator - 2 or 3 Circuit

I want to know hwere this "expressway racing" is going on
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post #11 of 29 (permalink) Old Oct 29th, 09, 07:57 AM
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Sean
 
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Re: Dominator - 2 or 3 Circuit

Quote:
Originally Posted by RichSchmidt View Post
I want to know hwere this "expressway racing" is going on
Haha, me too, our local "expressway" track was shut down awhile ago....

Sean

1968 rs, with an old school, antiquated "junkyard, never even had the valve covers off" 354" SB2.2 pump gas motor........

"I aint never seen talking win me nothin'" -Marshawn Lynch
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post #12 of 29 (permalink) Old Oct 29th, 09, 11:42 AM
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Eric
 
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Re: Dominator - 2 or 3 Circuit

deleted -- getting too wound up

E85 racer and E85 carb builder
www.horsepowerinnovations.com

68 Camaro, E85 powered 427" small block. 9.96 @ 133 MPH, 1.319 sixty foot on motor. 5.92 eighth @ 116 with a 1.42 sixty breaking beams with back tire on the bottle

Last edited by Eric68; Oct 29th, 09 at 12:01 PM.
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post #13 of 29 (permalink) Old Oct 29th, 09, 11:56 AM
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Sean
 
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Re: Dominator - 2 or 3 Circuit

Quote:
Originally Posted by Eric68 View Post
Needless to say I differ with Pro Systems on this. I have helped correct too many three circuit carbs that were too rich on the street and went lean up top at the track. Since Pro Systems sells 3 circuit Dominators I can see why they would defend this position.

My opinion, if you need a third circuit to compensate for lean spikes at the gear change your tuneup is off to begin with. Most likely either the carb is too big, the emulsion configuration is off (air bleed too big, too many holes, etc.), or the fuel delivery path (mainwell, cross channel, or booster ID) is too big. Again, I will say that on a race car the third circuit is helpful for tuning on certain cars, but not my preference.

And I will ask one more question, if a 3rd circuit is really necessary for drag race why doesn't ProSystem sell 3 circuit 4150 carbs?

Hmmm???

Sorry if I sound a little "anti" ProSystems, but he has a history of using his bully pulpit to attack the little guys.

I really don't know one way or the other, the only dominators I have worked with are on top of a sheet metal tunnel ram on a race car, so as for street I don't claim to know. I think a street oriented motor with performance secondary should consider a 4150 personally.

As for Pro systems, I can tell you I personally have dealt with Patrick, as have four different close friends with their race cars (10.50 bracket car, super gas and super comp cars, and outlaw pro street cars) as well as others on their dual purpose street/ race cars including myself and and have had absolutely excellent experience with him. The guy knows carbs as well as anyone I have seen in racing and gives customer support like no other business, that's my experience with him and I know others have had similar experience. But I also know he has crossed paths with guys that disagree with him from time to time, which is fine, but I can't dispute either side since all I do with them is related to tuning a race car, I don't build carbs (thats what Patrick does... )

Quote:
And I will ask one more question, if a 3rd circuit is really necessary for drag race why doesn't ProSystem sell 3 circuit 4150 carbs?
Hell if I know, ask Patrick I'm sure he has a reason.....

Sean

1968 rs, with an old school, antiquated "junkyard, never even had the valve covers off" 354" SB2.2 pump gas motor........

"I aint never seen talking win me nothin'" -Marshawn Lynch
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post #14 of 29 (permalink) Old Oct 29th, 09, 11:57 AM
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Sean
 
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Re: Dominator - 2 or 3 Circuit

Quote:
Originally Posted by Eric68 View Post
deleted -- getting to wound up
Heck Eric it's all good, if you are not passionate about stuff why even bother caring I figure.

Sean

1968 rs, with an old school, antiquated "junkyard, never even had the valve covers off" 354" SB2.2 pump gas motor........

"I aint never seen talking win me nothin'" -Marshawn Lynch
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post #15 of 29 (permalink) Old Oct 29th, 09, 03:31 PM
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Rich
 
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Re: Dominator - 2 or 3 Circuit

A third circuit could help big time on a car with a ton of carb on it.My engine makes 640 hp and uses maybe 700 cfm of air to do it.I run an 1150 carb on it.Why?because if I ran a 750,I would have to pull 1.5" of pressure drop thru the boosters to get maximum fuel flow.With the 1150 I can run less then a .6" drop at 7200rpm.wen my engine comes off the gear change{3500# car with a powerglide} and the engine drops to 5500rpm,the engine is using far less fuel and is generating far less pressure drop,and at this point the drop may not be enough to pull fuel especially with a lot of air bleed correction.If I decrease the bleed size I can pull fuel sooner{I know I should be doing this with the emulsion tubes},but the engine will go fat up top.The 3rd circuit provides a ton of room for improvement at any point of the fuel curve.If you have a perfect air fuel ratio during every inch of a dragstrip pass with a 2 circuit carb,you most have a very short powerband and very little change in air demand,or you have a carb that is towards the small side and are loosing power through having more pressure drop then you really needs.
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