2 circuit dominator conversion

[bmftech]

I want to convert my 8896 to a 2 circuit, can i use any 4150 metering block? could you use 2 metering blocks off a 650 holley?

Is this a bracket / drag car or more of a street deal?

Troy Patterson TMPCarbs.net TMP Carbs

It is street strip car, 600hp 502 chev.

[Troy Patterson]

I see, run a bigger carb. A 1250 would do nicely.

That engine has lots of appetite. The metering blocks from the 750 would be better suited than the 650's.

Troy Patterson TMPCarb.net TMP Carbs

[JDR Performance]

That 1050 will work fine if it's done right. Late last year we were on the dyno with a pump gas 632 c.i. motor and a 1050 I had reworked. The first pull was with the engine builders 1250 dyno carb. This was no junker; nice graph, a/f and bsfc. Since the guy buying the motor owned the 1050, we made a couple of pulls on it and some minor changes. The final pull was 830 something hp and I don't remember the torque numbers but they were way up there. Believe it or not, we ended up roughly 20 hp better than the first base line pull with the 1250. It took some work and the right parts when the carb was built but it worked for him. I wouldn't have suggested a 1050 on a 632, but we made it work and since it's going in a 10.5 tire street car it'll be a lot more fun to drive than the 3 circuit 1250 would have been.

[JoePorting]

What's the difference between the 2 and 3 circuit Dominators? Somebody a year or two ago told me that the 3 circuits were bad, but I can' remember why. Will a 2 circuit work as good as any Holley 4150 HP?

[jmarkaudio]

Everyone has their preference. The 3 circuit Dominator has a tube in each barrel above the throttle blades, it works like the transition circuit to add fuel as the throttle blade is opened. There are a couple of ideas on the original reason for it, one was for use on an IR manifold Ford. Reversion pulses required the 3rd circuit to help transition to the mains. It also can help on 4 cylinder comp engines that suffer similar pulsing even with a common plenum. Someone at Holley go a bright idea if two circuits are good, 3 must be better. The problem is that it makes most race engines STUPID fat in the midrange when used with the factory calibration. Driving one on the street is even worse. The other issue that can arise with the factory setup is when used on an engine that draws a lot of air, requiring more fuel to match. The factory cast 3 circuit metering blocks have idle tubes in the mainwells which create a restriction, as an example a larger engine with a blower on it would max the ability to pull enough fuel through the mainwells even if you take the jets out. Opening the mainwells is not an easy task for the average person. Converting a Dominator to a 2 circuit is easy enough to do with a couple taps and a few drill bits and some patience. The results are a much more manageable carb than the original without a large expense to the pocket, depending on what you want to use for metering blocks you can make the change for under $100. For those that already own an ill Dominator it saves them a large expense to have it fixed if they are willing to attempt it. And yes, I run one as well, a 2 circuit 1250 on an 843 hp small block. None of the "Shift Recovery" issues some will throw at you, nice flat fuel curve.

Can a 3 circuit Dominator be tuned to work? I'm sure it can, the real question is it any better than a 2 circuit Dominator? QUALITY companies start with a bare un-machined Holley main body. They relocate the position of the 3rd circuit tube in the mainwell. In some cases, they drill out the original transition slot and replace it with a slotted plug as it has been inconsistent on length and location from the factory. They replace the metering blocks with billet or substantially modified factory metering blocks, and sometimes use billet boosters. And last calibrate it correctly. And you wonder why they want more money than a new out of the box Dominator. Well, quality work is not cheap. Some offer Dominators for about the same as a new factory carb, beware as you probably are going to get EXACTLY what you pay for and maybe not even that.

[JDR Performance]

The three circuit stuff works well on some things. For example, if you're leaving on a transbrake and won't have a pump shot they're nice. For street driven applications they CAN be made to work but in my opinion have no advantage over a two circuit carb and will cause more tuning headaches. For someone that wants to go from three circuit to two, I would not recommend just slapping metering blocks from a random 4150 on it. Some of them will have emulsion tubes in the mainwells, the IFR in most cases won't be matched to the air bleeds, and more. If you already have one to be reworked they can be done the right way with new metering blocks, boosters, machined venturis, and screw in adjustable air bleeds for less than the cost of a new one and will work quite a bit better. In the end, it's not "cheap" but you'll have something calibrated correctly and fully adjustable. You can spend your time racing instead of trying to fight an uphill battle trying to make a Frankenstein collection of parts work.

[JoePorting]

Are the two circuits the power valve circuit and the transition slot circuit?

[JDR Performance]

Idle circuit and main circuit.

[Eric68]

Are the two circuits the power valve circuit and the transition slot circuit?

The 2 circuit has the Idle/transition circuit and main circuit. The power valve is part of the main circuit.

The 3 circuit carb adds an intermediate circuit which adds fuel in the midrange. Once in a while this is helpful, usually it's a PITA.

[bmftech]

I was fine tuning my 2 circuit dominator today on my 502, all i can say is it runs like the car is fuel injected! My carb started life as a 750 dominator 2 circuit. So i changed to 1050 boosters and followed a tune from a board member, i ended up with this. 84 pry jets with 6.5 power valve, 94's in the rear with power valve blocked, 25 mab, 70 iab, 40 idle jet, 59 t slot jet, angle channel 160, pvcr 79, .28 kill bleed. it runs so much smoother then my old 8896 3 circuit that it sounds like the car has a smaller cam in it. the car can sit for 5-10 minutes and you can reach in and hit the key and it fires up like it is fuel injected. I have been running dominators for 15 years and never knew they could run so clean! The only thing that does not match on my carb from what i have read is that i have about 50ths transfer slot showing, however the air screws work great and i can kill the engine just by closing the front 2 air screws so the engine is getting most of its fuel in the idle circuit not the transfer slot despite the 50ths showing on the slot. Every engine is different and mine works good with this setup. My air screws ended up at 1.25-1.5 turn out on all four corners. I cant weight to see what it picks up over my bone stock 8896 1050 i have been running for 15 years.

[jmarkaudio]

Every engine is different and mine works good with this setup.

That is very, very true. Tuning the idle and transition circuits can be the toughest things to get to work correctly, as no two engines are exactly the same. Everyone complains about a Dominators behavior, but they don't take the time to set it up for the engine it's on. A smaller carb can have a generic tune and be close, the larger carb has to be tuned to get the most out of it. But when it's right... sounds like you are real close, keep an eye on the plugs and jet it for the best MPH at the track.

[MaxHP]

I have to agree with the 2 circuit dominator working better in my marine application. I had a very well known carb builder set-up my carb for the 496 bbc marine application. when I got it back it was so rich at part throttle it would barly run. After trying to open up the itermediate airbleeds from 64 to 72 it made very little difference. In fact I could run without the itermediate air bleeds and still run way to rich through the middle. I got frustrated and plugged the intermediate tubes with a piece of #6 lead shot and the engine has been running great ever since with some minor tuning. Hard to believe there is an application that needs that much fuel at part throttle.

[Troy Patterson]

I want to convert my 8896 to a 2 circuit, can i use any 4150 metering block? could you use 2 metering blocks off a 650 holley?

Is this a bracket / drag car or more of a street deal?

Troy Patterson TMPCarbs.net TMP Carbs

It is street strip car, 600hp 502 chev.

Your 502 cid motor with a 1050 is kinda under carb'd with only 2.09 cfm per cubic inch.

A 350 SBC with a 750 is getting 2.14 cfm per cubic inch.

A 600 HP 502 definitely shouldn't need an intermediate circuit with that carb. I should add that a stock 350 SBC came equipped with a 750 CFM Quadra-Jet from the factory.

Troy Patterson TMPCarbs.net TMP Carbs

[Troy Patterson]

I have to agree with the 2 circuit dominator working better in my marine application. I had a very well known carb builder set-up my carb for the 496 bbc marine application. when I got it back it was so rich at part throttle it would barly run. After trying to open up the itermediate airbleeds from 64 to 72 it made very little difference. In fact I could run without the itermediate air bleeds and still run way to rich through the middle. I got frustrated and plugged the intermediate tubes with a piece of #6 lead shot and the engine has been running great ever since with some minor tuning. Hard to believe there is an application that needs that much fuel at part throttle.

Most applications a person would run a 3 circuit Dominator on don't need it. A good set of boosters and a god tune / calibration will do very nicely for most applications by far.

Troy Patterson TMPCarbs.net TMP Carbs