Dominator - 2 or 3 Circuit [Archive] - Team Camaro Tech

: Dominator - 2 or 3 Circuit


Ramrodd 69
Oct 28th, 09, 04:23 AM
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!

RichSchmidt
Oct 28th, 09, 05:54 AM
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.

R/T
Oct 28th, 09, 09:05 AM
Not cheap
http://www.prosystemsracing.com/svseries.html
http://www.prosystemsracing.com/i//sv1black1.jpg

Eric68
Oct 28th, 09, 09:30 AM
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.

RichSchmidt
Oct 28th, 09, 06:55 PM
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

Eric68
Oct 28th, 09, 07:25 PM
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."

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?

Eric68
Oct 28th, 09, 07:32 PM
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/viewtopic.php?f=6&t=3742

68rs406
Oct 28th, 09, 09:48 PM
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.

ron498
Oct 28th, 09, 10:15 PM
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

RichSchmidt
Oct 29th, 09, 06:18 AM
I want to know hwere this "expressway racing" is going on:)

68rs406
Oct 29th, 09, 08:57 AM
I want to know hwere this "expressway racing" is going on:)

Haha, me too, our local "expressway" track was shut down awhile ago....;)

Eric68
Oct 29th, 09, 12:42 PM
deleted -- getting too wound up ;)

68rs406
Oct 29th, 09, 12:56 PM
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...;) )

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.....:D

68rs406
Oct 29th, 09, 12:57 PM
deleted -- getting to wound up ;)

Heck Eric it's all good, if you are not passionate about stuff why even bother caring I figure. :thumbsup:

RichSchmidt
Oct 29th, 09, 04:31 PM
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.

camaro_fever68
Oct 29th, 09, 04:39 PM
Well Said Eric!!!! :thumbsup:



I agree on everything as I have converted quite a few myself....even the ones with the pretty stickers above.

Eric68
Oct 29th, 09, 07:36 PM
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.

I have two 1050's and an 850 I run on my 427. All are two circuit carbs, the two 1050s have annular boosters. One 1050 is a Holley Dominator and one is a Quick Fuel 4150 body. Both have been modified by me for E85 and both run excellent on the street and track. There is no lean spike on the shifts at the track and throttle response is killer with both, I just don't need that 3rd circuit. My 427 SBC makes right about 680 HP at 6400-6600 RPM.

Since I started converting and building carbs (mostly for E85) I have run a number of different carbs on my 427 to test prior to shipping. I have run everything from an aerosol 1250 Dominator to smaller stuff at 750 cfm. I don't tune everything I do for my motor, I run it on my motor for testing (there's a big difference!) Even the 1250 aerosol deal (after I sleeved the .250" ID methanol boosters to work properly with E85) it ran great through the entire RPM band . . . with 2 circuits!

Any carb you can make work with 3 circuits, I bet I can make work with 2 circuits. Even very large carburetors. The key is setting up the boosters and emulsion system properly and making the transition circuit overlap properly with the right amount of fuel.

That said, I agree that there is a place for 3 circuit (or even more than 3 circuit) carbs, I just don't think that the place for them is on the street. It all goes back to the way the fuel supply is designed in the blocks -- a two circuit will allow the intermediate circuit to shut down at cruise. A 3 circuit block will allow the intermediate and transition circuit to stay active at cruise -- this makes the car cruise rich!

Regarding power bands. Most all drag race engines have a similar power band. When a converter is correct for an engine there will be about a 1600-1800 RPM spread between launch and shift points. A 2,000 or even 3,000 RPM spread is not difficult to make flat at WOT. IMO WOT is easy to get right -- its cruise and part throttle that get hard.

PS. One more thing. ProSystems new single venturi carb is only a 2 circuit. Hmmmmmm.

ron498
Oct 30th, 09, 12:10 AM
I pretty much drive on the street to get it to the track. But I do take it for groceries as well. And putts around town.
BTW....the plugs stay clean! Carb has a front PV. and unfortunately, no vacuum advance.
Wanna send me a better 2 circuit to compare?
This almost seems a pointless debate as far as street is concerned.
Tell me which one runs better at the track.

ron

Eric68
Oct 30th, 09, 06:57 AM
If you ran E85 I'd seriously consider sending you a carb to compare. I don't have any 2 circuit pump gas stuff laying around though. I have plenty of 3 circuit metering blocks though -- you want a set of ProSystems 3 circuit blocks?

Would you would be willing to purchase a 2 circuit E85 carb if it ran better on the street and faster at the track? An E85 Dominator would be right about $900.

Maybe its pointless for you but there are plenty of guys that are tired of having to change their plugs every weekend or two.

68rs406
Oct 30th, 09, 08:55 AM
This almost seems a pointless debate as far as street is concerned.
Tell me which one runs better at the track.

ron

X2 :yes: Are we really worried about idle and around town drive abilty with a Dominator.... so who builds the most fuel efficient dominator? ;)

We are likely going to either have Patrick rebuild our carbs for the race car this winter, or we actually just talked about looking at Patricks' new carbs. I think they are a bit unproven as of yet but our buddy that builds nitrous systems has worked with Patrick on these new carbs I guess, it will be interesting to hear what he thinks, I'll let you know what we find out if anyone cares..
Bottom line, there may be some Pro systems haters out there, but I bet the number of happy customers far outweigh them. To each their own, but so far Patrick has proven pretty respectable in the racing world.

ron498
Oct 30th, 09, 11:58 AM
Hi Eric,

Unfortunately, E85 is not readily available here in Oregon. I know it can be had, the turbo guys use it, but as far as I know, no where close to me where I could drive over and fill up. Maybe there is, but I don't know.

At only 9.4:1, would it add perf to my car?
I haven't done the research to know what I'd need to do to my fuel system. I might need more than a Mallory 140. All the rest is -10 braided hose. I suppose if I freshened the engine with new high CR pistons........don't get me going. :D

Alcohol by nature doesn't foul plugs...correct?
The only time mine get black is when I don't fully warm it up, in other words messing with it in the garage etc. A short drive and they clean right up. In fact, I haven't changed them in 3 years.
also, I run extended tip street heat range plugs. Even on the nitrous, and they look perfect after a bottle pass.

Personally, and this is just between me and you....:D, I think guys who foul plugs all the time run the wrong plugs and don't get the idle/slow speed mix right. And you don't need a dominator to have those issues.
Vacuum advance helps a lot, but most race style carbs don't have ported vacuum available. I actually added it to my old 950HP, worked like a charm!

BTW......you and I are about dead nuts the same in performance from totally diff engines. Makes me want to upgrade the old 496...it has 6 years on it now.

Ron

If you ran E85 I'd seriously consider sending you a carb to compare. I don't have any 2 circuit pump gas stuff laying around though. I have plenty of 3 circuit metering blocks though -- you want a set of ProSystems 3 circuit blocks?

Would you would be willing to purchase a 2 circuit E85 carb if it ran better on the street and faster at the track? An E85 Dominator would be right about $900.

Maybe its pointless for you but there are plenty of guys that are tired of having to change their plugs every weekend or two.

Eric68
Oct 30th, 09, 01:53 PM
Ron,

I haven't tried E85 on anything with compression that low other than a 9.2:1 blow-through setup. It was hard to start when the weather started to get cold -- IMO not enough heat from compression to get it firing easily. That and a very cold plug for the blower tune. E85 really likes 12.5-13.5:1 compression from what I have observed.

If you had E85 out there in OR and freshened the motor up I would put the compression at 13:1 and let it eat. It's cheaper than pump gas per gallon, but will cost a hair more to run than 87 or 89 octane gasoline because it gets lower mileage. Here in MI it costs about the same to run as 93 octane. You would make a fair amount more power with more compression on E85.

E85 will still foul plugs if you let it get too rich. The gasoline content will make carbon, but as long as the tune is ball park plugs stay clean. I used to run extended tip plugs (the Autolite 3923, 3924 worked great) but with more compression and N2O on top I think the Autolite racing 3934 is safer. Stays clean on the street too.

As far as running a Dominator on the street I do it all the time. There is really no reason not to -- they behave very well and can be docile to drive when setup correctly. In fact, my Dominator was for a long time more street friendly than my 850 -- until I swapped in new metering blocks with my specs. I think the idea that "Dominators aren't for the street" is an old wives tale and may be related to bad results with guys trying to put around with 3 circuit setups.

Sean, be aware I am not a ProSystems "hater" -- I like their 4150 carbs that I have played with. Been rubbed the wrong way over the years by Mr James but I don't hate them.

68rs406
Oct 30th, 09, 02:45 PM
Sean, be aware I am not a ProSystems "hater" -- I like their 4150 carbs that I have played with. Been rubbed the wrong way over the years by Mr James but I don't hate them.

Understand totally Eric, and I know where you are coming from. I know you would not be the only guy that has 'crossed paths' as far as an opinion with Patrick. He has just been very good with my buddies who recommended him to me originally, and helped me with some questions I had for him with a carb I didn't even buy from him. I know he has a strong opinion on certain things but he is very accessible for tech help. He's a dang good carb builder for sure, but I respect your thoughts on the matter as well, you've had good success with your stuff for sure.

As for the Dominators and any carb for that matter I'm no expert at all, I certainly feel comfortable tuning one (or two..lol) but my experience on a Dominator is on a race car period, can't relate that to a street car.
I agree with you that a Dominator can run on the street as well (look at Ron's, that thing hauls the mail and he drives it to the track..). I was actually talking about with the OP not really concerned about racing whether a Dominator was even a concern, of course if he has a Dominator intake then why not.
It's all good, nice to see different opinions :thumbsup:

JOHN WILSON
Oct 30th, 09, 10:13 PM
I pretty much drive on the street to get it to the track. But I do take it for groceries as well. And putts around town.
BTW....the plugs stay clean! Carb has a front PV. and unfortunately, no vacuum advance.
Wanna send me a better 2 circuit to compare?
This almost seems a pointless debate as far as street is concerned.
Tell me which one runs better at the track.

ron

Sweet Jeebus! This is one issue that has been beat to death and easily as much or more polarized than the old oval vs rectal debates. All I'll say is I KNOW my way around a carb, I've owned/tuned many and I have no problems with making a 3 circuit 4500 as crisp/clean as a 2 circuit on the street WITHOUT running into fuel starvation issues.....yes....even with the idle tube in the main well. I have to admit, I even bought into the fuel starvation issue with the 3-circuit idle tube/main well deal on Q16 and bought a set of BLP 3-circuit blocks with divorced idle well. Guess what, I didn't need them. :noway: I managed to kill 12 avg hp by over jetting a 3 circuit carb on Q16 going from 96/97 to 98/99 jets with a holley block with a .159" tapered well (on a 870+hp sbc). AND, I think that's the key some folks miss, the well is tapered as well is the idle tube. Anyhow, my intention is not to discredit the "2-circuit movement", I'm sure it works fine. All I'm saying is I've never found a need to re-engineer a 3 circuit to a 2 circuit. FWIW, Stephen Kim, the writer that did an article on my car a couple years ago likened my 3-circuit 4500 to "fuel injection" while we drove through neighborhoods and highway feeder roads during the photo shoot. His words, not mine.

Ramrodd 69
Nov 6th, 09, 08:47 PM
Hello everyone, back again. I talked to Patrick at Pro Systems and from what he said I should go with a 3 circuit. Has any used his and how are they. Told he builds to what you have and when you get it, its for the most part right on (maybe a little tweeking). Back to question, better his carb or a Holley (Dominator, each one) Thanks! Bob

68rs406
Nov 7th, 09, 10:02 PM
Patrick is usually spot on with his carbs if you provide him with all the correct info, and in the case he misses your combo he will get it right, his support is really second to none.
A holley dominator from say Summit is just a generic carb, one from Patrick has been dialed in to your combo. Several of my buddise run his Dominators on their race cars, and a few have his 4150 carbs including myself. This winter we are planning to send the dominators to him for race car I'm involved with.
He still uses a Holley carb (except for his new one), but modifies it with his own restrictors etc.
Again the only dominators I have dealt with have been in a race car application so I can't speak for street use, but I wouldn't hesitate to have Patrick do what he thinks is right to build you a carb.

Ramrodd 69
Nov 8th, 09, 09:00 AM
Patrick is usually spot on with his carbs if you provide him with all the correct info, and in the case he misses your combo he will get it right, his support is really second to none.
A holley dominator from say Summit is just a generic carb, one from Patrick has been dialed in to your combo. Several of my buddise run his Dominators on their race cars, and a few have his 4150 carbs including myself. This winter we are planning to send the dominators to him for race car I'm involved with.
He still uses a Holley carb (except for his new one), but modifies it with his own restrictors etc.
Again the only dominators I have dealt with have been in a race car application so I can't speak for street use, but I wouldn't hesitate to have Patrick do what he thinks is right to build you a carb.

Thanks for the reply. Probably going to use his carb. Most people have
said his carbs are for the most part right from info supplied. As you also
said, the Holley is generic and needs worked to get it set. Besides, Pat
knows its for the street (mainly) so he knows what the set-up is being
used for. Thanks to all for your responses! Bob