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 Post subject: 3 Circuit Dominators
 Post Posted: Fri Dec 23, 2011 10:56 pm 
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Location: Auburndale, Florida
I am by no means sold on the 3 circuit deal especially using stock cast blocks. However, I am not one to slam a door shut on any idea unless I've really looked it over thoroughly before making a decision.

The current carb on my engine is a custom BLP mainbody with a 1.78 venturi and 2.125 throttle bore, and .950 booster skirts with .500 ID booster inserts with 12 holes. It also has the transition slot re-located by BLP. It now has a pair of BLP 3 circuit wide body metering blocks with my calibration in them. These blocks have no idle tubes in the mainwell. The idle circuit is fed just like a 2 circuit block. In fact, these blocks use a #2 taper in the mainwell.

In Reynolds, GA it was 2MPH faster than last year with the 1050 2 circuit. I needed to add time to the timer in order to run 10.90. I don't think the 3 circuits are making it faster, it's the venturi and throttle bore size accounting for the difference I believe.

What it does do is run smoother through the run in a non-throttle stop run. Not sure why that is but, to me it's worth investigating. Both my 2 and 3 circuit carbs have the same emulsion package. One has an intermediate circuit and the main jet sizing reflects that.

Mark and I intend to do some track testing with my car to prove or disprove some ideas I have regarding this carb.

That said, my car and engine setup has gone it's fastest as a two circuit.

And to further muddy the waters, we have a 3circuit E85 Dominator out in the field.

So let's have us a nice little discussion here.


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 Post subject: Re: 3 Circuit Dominators
 Post Posted: Fri Dec 23, 2011 11:32 pm 
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To me the most important modification is the T-slot position. Depending upon which direction its been moved will be the result. Blade proximity and range of effect per degree of opening is altered so figure out for yourselves how that affects the fueling from the t-slot. The total fueling of the barrel has to be consistent and if the booster is supplying more (because there is no idle feed tube restricting it) then the 3rd circuit will be able to carry most of the fueling load that has to be done by the T-slot. The t-slot will be supplying less fuel with the proper operating 3rd circuit. T slot fuel is in the worst place it can be inside a carby. You will get better atomization at WOT from the 3rd circuit than you will from the t-slot. In some situations of high CFM flow the T-slot becomes an air bleed (really leaning off the booster) but Ive only seen evidence of this when using small IAB's and small IFR's. However I dont know by testing what happens in that situation with a normal Holley style 3 circuit block. I would suspect it would be worse, forcing tuners to up the intermediate circuit flow. I recon they would be chasing the wrong thing.
The reason why the t-slot is moved would be to reduce the range of operation of the slot and allow the 3rd circuit to take over. Fueling via the 3rd circuit covers over t-slot issues.


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 Post subject: Re: 3 Circuit Dominators
 Post Posted: Sat Dec 24, 2011 8:15 am 
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Yea I don't know but what was the difference between the 2 carbs as far as size/bore/booster?
Cause some guys would kill for 2 mph!!!
Knowing what you and Mark know that 2 circuit is tuned perfect so it's had to swallow
that that other carb body made it 2 mph faster... #-o

Also my beretta has gone 8.08 to 8.18 all over 169mph???? Now just can't understand why
it has only picked up .85mph between the slowest and fastest mph.. oh and all the 1/8 mile et's
are 5.180 to 5.184 all at 136mph..

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 Post subject: Re: 3 Circuit Dominators
 Post Posted: Sat Dec 24, 2011 12:14 pm 
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Location: Tell City, IN
Could it be Aerodynamically challenged? Hitting that 169MPH brick wall.. :-s

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 Post subject: Re: 3 Circuit Dominators
 Post Posted: Sat Dec 24, 2011 4:15 pm 
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Location: Auburndale, Florida
This particular main body started life as a 1050. I was chasing some ideas I had regarding the throttle bore to venturi ratio. My original idea was to use a 1.72 venturi and a 2.125 throttle. In the talk back and forth about what venturi size I wanted there was a minor misunderstanding. BLP understood that I in fact wished to have a 1.688 venturi (stock 1050) instead of 1.72 I desired. During final assembly the main body (the 1.688 venturi) was flowed and exhibited turbulence after the venturi minor diameter. After a discussion with BLP it was decided that a 1.78 may better fit what I wanted. At this point it only required re-profiling the venturi.

As to the transistion slot: The 2" bore Dominators have the transition well in the same location. The 2.125 bore carbs have the transition well moved to accomidate the throttle plate diameter. When a 1050 main body is bored to 2.125 the transition well is breached and is plugged. A specially designed plug containing a new transition slot in installed. The slot location itself is slightly altered and subsequent boring ie: throttle blade enlargement, does not affect the T-slot location at all. I chose the 2.125 throttle blade size as it is a stock and easily obtained. Larger blades are available but only available at BLP or a place like that.

I chased the tuneup a little. Especially with the 2 circuit. It had a large spike in AFRs at the shift. Going to the 3 circuit eliminated that and made for a smoother running unit.

As shrinker surmised the intermediate circuit in this carb is lean. .035 jet, .045 outlet, and .073 AB. i'll come up with the full tune in a day or so as I can't remember it right off hand.


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 Post subject: Re: 3 Circuit Dominators
 Post Posted: Sat Dec 24, 2011 5:21 pm 
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Spike at the shift??? Went lean??

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 Post subject: Re: 3 Circuit Dominators
 Post Posted: Sat Dec 24, 2011 8:17 pm 
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Blasphemy!!! =;


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 Post subject: Re: 3 Circuit Dominators
 Post Posted: Sat Dec 24, 2011 8:40 pm 
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The larger blade alters the t-slot actions.


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 Post subject: Re: 3 Circuit Dominators
 Post Posted: Sat Dec 24, 2011 9:55 pm 
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Location: Auburndale, Florida
Barry, a large spike as in wow, we don't see that usually.

Working with these wide body metering blocks make all the difference. They're the only reason I even tried the 3 circuit tune up. It's been running good and exhibits all the good characteristics of our 2 circuit tune ups. Starts well, can idle for a long time without fouling plugs, and is good in the water and coming out. It's still on the car because we've been so wrapped up in other projects to try anything else.

What I think it''s not so good at is it seems to be slower to 60 ft than my 1050. I think that's a function of size and not how many circuits it has. We intend to test that theory and then throw 2 circuit blocks back into it and see what happens.


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 Post subject: Re: 3 Circuit Dominators
 Post Posted: Sat Dec 24, 2011 11:08 pm 
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nomad wrote:
What I think it''s not so good at is it seems to be slower to 60 ft than my 1050.


Do this test, take the carby off the engine with it full of fuel and slowly tip the carby so the fuel assumes the angle it would be under acceleration. You will see why its slower to 60'.


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 Post subject: Re: 3 Circuit Dominators
 Post Posted: Sun Dec 25, 2011 2:08 am 
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I know what you all are doing. Your trying to flush tuner out. =; =; =;


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 Post subject: Re: 3 Circuit Dominators
 Post Posted: Mon Dec 26, 2011 9:14 am 
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shrinker wrote:
nomad wrote:
What I think it''s not so good at is it seems to be slower to 60 ft than my 1050.


Do this test, take the carby off the engine with it full of fuel and slowly tip the carby so the fuel assumes the angle it would be under acceleration. You will see why its slower to 60'.


So why would a 3 circuit do what your thinking and not a 2 circuit??? My car just picks up the front a few inches for a few feet..

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 Post subject: Re: 3 Circuit Dominators
 Post Posted: Mon Dec 26, 2011 10:19 am 
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Barry, I think what shrinker is referring to is how the liquid will react in the bowls @ 2 Gs +/- during launch. With a 3 circuit carb and shrinker's experiment, I expect one end (front) to have fuel dribbling out of the 3rd circuit nozzles and the other end would be lean as there's no 3rd circuit jet extensions that I know of. Remember, we run jet extensions on the rear jets but there's no extensions made for that 3rd circuit jet. A fix for that might be to turn the carb sideways, like a 2 carb setup. :-k Seen that done too.

We tune for down track MPH and by that time the fuel level has somewhat settled down in the bowls. So our fuel mix at near static conditions is NOT what we'll have at the hit, hence the slower short times.

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 Post subject: Re: 3 Circuit Dominators
 Post Posted: Mon Dec 26, 2011 1:05 pm 
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So your saying that the G's would force the fuel in that 3rd circuit to run/drip into the manifold?
If so is there a way to do some type of extension or something to eliminate that??

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 Post subject: Re: 3 Circuit Dominators
 Post Posted: Mon Dec 26, 2011 1:15 pm 
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This is just MY opinion on this and I'm sure that shrinker will correct me if I'm wrong, but fuel in the bowl can and does stack up against the metering block in the front. That's why we run vent whistles on the primary side. Likewise, fuel will go AWAY from the metering block in the rear, hence the need for jet extensions. I'd be willing to bet that at some point after the hit that the fuel level in the bowls is at as much as a 45* angle.

Since that 3rd circuit feeds from the bowl I'll bet that the rear ones get uncovered at launch and on out for some distance until the G forces drop off and the bowl level comes somewhere near "normal". There is a way to calculate what the fuel level angle would be for a given G force but I can't remember where I saw it. Maley and I spoke about this several times over the years so that may be where I remember it from.

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