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dual webers?

Bill Blue

Platinum Level Sponsor
Okay, think I understand, but still wonder about the value of four butterflys over one butterfly located in a log plenum. How do your individual runner terminate? Individual filters, no filters, common log with filter? Sounds like a pure race setup.

Also, as to TBI, couldn't a person use two "high pressure" MPI injectors, firing either onto the butterfly or into the manifold, rather than the traditional low pressure units? Wouldn't that improve the droplet size? I'd think two injectors from a 350 cu. in. V8 would be about the perfect size.

Jarrid, don't agree with you about the TBI. I had a car setup with it and it was better than any carb car I've had.

Bill
 

RootesRacer

Donation Time
Okay, think I understand, but still wonder about the value of four butterflys over one butterfly located in a log plenum. How do your individual runner terminate? Individual filters, no filters, common log with filter? Sounds like a pure race setup.
Bill

The 4 butterflys (individual throttle per runner) idea is based on using acoustics to give tuned RAM to each cyl independently for the acoustic effects of the other cyls. Running a common plenum hurts throttle response because of the extra volume that has to get filled or consumed from the plenum as the throttles have changed.

Individual throttle per cyl allows much snappier engine acceleration for this reason.

Dual DCOE webers is ALSO individual throttle per cyl, just not injected but the same physics applies.
Individual throttle per cyl is not so exotic, most of the go fast jap cars come from the factory with it today.

Also, as to TBI, couldn't a person use two "high pressure" MPI injectors, firing either onto the butterfly or into the manifold, rather than the traditional low pressure units? Wouldn't that improve the droplet size? I'd think two injectors from a 350 cu. in. V8 would be about the perfect size.
Bill

This has been done, but injecting onto throttle plates when the plates are closed (at idle) causes puddling, and poor atomization even if the injector atomization itself is otherwise good.

My earliest work was using the large 4bbl throttle bodies that holley makes, and adding an EFI controller that actually worked.

One of the biggest probs we faced on emissions applications was the high HCs that were needed to make the engine idle. The atomization was so poor at idle a large percentage of fuel just wouldn't light off, and we had to richen the mixture to compensate for the unburned fuel getting out the exhaust.
What we learned was that if you drilled a small hole in each throttle plate on the side where the puddling occurs, the high velocity of air going through it would pull the fuel through and help to break it up. This helped, but would NEVER yield the idle quality or leanness you could achieve with multipoint, or at least under throttle injection (UTI).

The bottom line is that you really don't want to inject on a cold flat piece of metal when there is no air velocity.

Jarrid, don't agree with you about the TBI. I had a car setup with it and it was better than any carb car I've had.
Bill

I'm sure it ran fine.
Probably even had altitude compensation, which would make it better than most carbs. It wont do anywhere near as good of job of idle fuel control compared to todays port style injectors properly positioned.

I mean, whats going to yield better atomization, 2 giant 80s technology injectors squirting its throttle plates, or 8 of todays smaller injectors squirting its valves?




As for taking 2 1bbl TBIs and mounting them on a stock intake and going that route.
Been there, done that.
Swore I would never do it again.
Car was a triumph GT6, came it with SUs, left with TWM SU replacement air doors. Used off the shelf TBI injectors where each injector was sized for 120BHP. 240BHP of injectors peeing fuel (actually ricocheting off the throttle plates) fouling the air cleaners with gas, wouldn't idle worth a *CENSORED**CENSORED**CENSORED**CENSORED*.

Car smelled gassy all the time, both from the overly rich idle mixture, and the K&N air cleaners saturated from gas.
Customer wouldn't pay the bill, made us take the system off.

TWM took the TBI air doors off the market. Too much injector for the 100HP applications it was designed for. Their replacement throttle bodies are under throttle (UTI) and use 2 port style injectors each.
 

Lester

Donation Time
At some point, the post started speaking some type of math language. I think I am grasping the ideas, but still very close to giberish to a green horn.
Injection is a bit intimidating, but if there are instructions and it improves HP, I'm game for just about anything. I'd like to hear more about these one barrel hollys...
Lester
 

V6 JOSE

Donation Time
Hi Lester,

Multiplying the number of carburetors, only multiplies the problems you will encoulter. Keeping them in sync would be a job. Electronic fuel injection is so much better than any carburetor, and can give better power and economy than a carburetor. It will also cure cold running problems too. Of course, it must be a properly designed system, because some of the early fuel injections were mechanical, and didn't really work that well.

One good carb will work better on a street engine, than will multiple carbs, for the above mentioned reasons. Most race cars today, run just one four barrel carburetor, rather than a multiple carburetor set up.

Elctronic fuel injection isn't that complicated, really. It is new technology, but shouldn't scare anyone who likes mechanical things.

Jose:)
 

Jay Laifman

Donation Time
My apologies.

Jose:mad:

Thank you for the response. I appreciate it. I will repeat that I have often times posted here about how nice the job is that Jose has done. For the person that wants to go that route, there really is no substitute. Personally, as I said, last time I chose not to. Next time, maybe I'll go back to completely stock and simply enjoy it for what it was as opposed to what it could have been, or I may very well seek out the smoothness and balance of the V6.
 

Bill Blue

Platinum Level Sponsor
Jarrid, I have no doubt of the superiority of the port injection system to the TBI. It's just that I was so taken aback about your comment that a carb would be a better solution than TBI. Regardless of stipulations.

I must admit I don't see the rational of using butterlys near the port in order to take advantage of accoustic RAM. Its almost like your saying that without the butterflys the effect is gone. Seems like the butterflys would, if anything, interferre with the effect that I suppose would start at the valve head. It appears the individual runners go to a plenum, but it has no throttle plate or air door. I do see the problems that the throttled plenum might cause, but I have read that the evil effects are caused by undersized plenums. I suppose there is more room under the hood for multiple butterflys that a gigundo plenum.

240 hp worth of injectors on a 100 hp engine. I don't know much about EFI, but I don't think that all the problems of the setup were caused by injecting on a throttle plate. I will agree that probably agravated the problem. Instead of drilling a hole in the throttle plate for the fuel to drain, how about shooting the fuel through a hole at idle?

Bill
 

RootesRacer

Donation Time
Jarrid, I have no doubt of the superiority of the port injection system to the TBI. It's just that I was so taken aback about your comment that a carb would be a better solution than TBI. Regardless of stipulations.
Bill

Well I stand on my original statement, I'd sooner carb an engine than TBI one and thats because a carb has its BEST mixtures at idle. TBI has its worst.
Otherwise they are about the same (except one you tune with a computer, the other you re-jet).


I must admit I don't see the rational of using butterlys near the port in order to take advantage of accoustic RAM. Its almost like your saying that without the butterflys the effect is gone. Seems like the butterflys would, if anything, interferre with the effect that I suppose would start at the valve head. It appears the individual runners go to a plenum, but it has no throttle plate or air door. I do see the problems that the throttled plenum might cause, but I have read that the evil effects are caused by undersized plenums. I suppose there is more room under the hood for multiple butterflys that a gigundo plenum.
Bill

Butterflys must be sufficiently sized so that the THROTTLE SHAFT diameter does not cause a significant restriction. On carbs, that restriction actually becomes part of the venturi restriction, but on EFI is an obstruction.
In any case the butterfly doesn't effect the resonance to speak of, it does reduce the flow at a giver pressure drop, but since you don't have a venturi, it will flow better than the equivalent carb anyhow. The individual runner makes the resonance simple, predictable, and cylinder resonance is independent.

If going to a larger plenum "fixes" induction crosstalk, then you are essentially trading throttle response from the larger volume, for some level of induction resonance crosstalk isolation.


240 hp worth of injectors on a 100 hp engine. I don't know much about EFI, but I don't think that all the problems of the setup were caused by injecting on a throttle plate. I will agree that probably agravated the problem. Instead of drilling a hole in the throttle plate for the fuel to drain, how about shooting the fuel through a hole at idle?
Bill

2 Major issues here, one was the injecting on the throttle plate, which caused the lack of atomization due at idle, plus the fuel bouncing off the plates fouled the air cleaners. The atomization problem is the reason that TBI injection from the factories was short lived and is not used today.
The other issue is that when you have double the fuel capacity (lbs/hr injectors) than you engine can use, the duty cycle will never exceed 50%, which hurts idle controllability. Simply put, 240HP worth of injectors will run half the pulse width time as that which is running 120HP worth of injectors.
The result is a double the error in fuel output (scatter) from one injection pulse to the next.
 

Bill Blue

Platinum Level Sponsor
Jarrid, I guess we all have our life experiences. My EFI car never, in 165,000 miles, loaded up, coughed, or failed to respond when the loud pedal was depressed. Can't say that about any carb I had. The closest was a Carter 410, which no one seems to even remember, let alone say anything nice about. The absolute worst is a toss-up between a computerized Holly-Weber and the beloved Holly 390.

Maybe its just me.

Bill
 
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