Dave,
Since you've recently turned to the dark side (right at the release of episode 3, I might add) this should be right up your alley.

Greg,
If you're trying to pull someones chain, it worked.

Very impressive in the pic. If the carbs came from DW, they are likely 45DCOE carbs. They look big & very impressive. Unlike the variable venturi SU, the Weber has a fixed choke (venturi).

What isn't commonly discussed, is that inside that huge Weber carb is actually a pair of much smaller chokes (venturi tubes). To run three of these on a Big Healey would require the smallest recommended choke of 28MM. This gives a total venturi area of about 5.7 sq. inches. The available range of chokes for the 45DCOE is 28MM to 40MM. So you have big impressive looking carbs with little holes through them.

To compare, a pair of SU HD8 carbs also have a venturi area of about 5.7 sq. inches. The SU has the variable venturi advantage which the Weber does not have. If you go full throttle at lower rpm with the Webers, the engine will just bog down. The SU will only open as wide as needed, no matter how far you push the throttle. The Weber has four different jet systems that must be optimized. With six barrels requiring a change, experimenting to find the right combination can get expensive & frustrating in a hurry.

Either setup will give good power up to 7000 rpm. The Weber may have a slight advantage over the SU above 6000 rpm due to it having a straighter shot into the ports than the SU's with manifold.

Much fun.
D

Hi Dave,
Pulling peoples chain? Yes and no. They don’t exist on my car, yet. Look again, those are 6 Mikuni HSR42 motorcycle carbs. No butterflies, Flat slides, variable venturies like the SU, but with accelerator pumps. The manifolds are Weber IRs with an adaptor plate to mount 2 Mikunis per manifold. The guy who is doing the conversion for me put 2 carbs on a relatively stock MGB. Between the squealing tires in 2nd and a great full throttle sound, it was a fun ride. I had to slouch in my seat however because I kept hitting the back of my head on the convertible top bar from whiplash. There is a member of this forum who has been doing similar conversions for Triumphs. www.prirace.com/induction.htm

Hi Greg,
Now I see. Getting blind in my old age plus not paying enough attention.

I have worked with Mikuni's on motorcycles for a long time. They can't be beat. Even the Amal copy of the Mikuni was a large improvement.

My first Healey had a Chevy small block with a huge four barrel Holley. I'm keeping the present one as stock as possible.

Neat idea for those who wish to be a bit "different". Definitely a good, probably better, alternative to the Weber.

It will be interesting to hear how it works out for you. Keep us informed.
D

Edited:
After looking at the HSR42 carefully, I come to the conclusion that it is not just like the SU. Unlike some of the other diaphragm operated slides on Mikuni's, this model has strictly mechanical operated slides. They are not constant velocity. Their recomendation for size seems to be one HSR42 per about 1200 cc's of engine displacement. Three of these on a big Healey would be likely to cause the same overcarburetion problems as the Weber's. What am I missing?
D

Hello all,

I remember in the sixties, a very well respected British car journalist, L.J.K. Setwright, writing about his project of fitting six Amal motorcyle carburettors to his (six cylinder) Bristol based on their airflow characteristics as there was no throttle disc and the only obstruction was the needle at full throttle. Amal even got around that obstruction with their remote needle GP carburettor (hugely expensive compared to their other units) which had the needle outside of the choke so full throttle was totally unobstructed. Whether the cost justified the expense is probably arguable as more airflow could be achieved by going to a larger choke size.

Alec

Carburation for our cars is an interesting subject. The problem , as related above, is that the eventual benefit is directly related to how much air you can flow into the head, get it mixed with fuel, and then ignite. Therefore the carburetors are only part of the equation. Cams, valves, etc. play a big role. Just changeing carbs will spice-up the engine bay but most likely not really help the performance much.

My racing Jags have all run with 3 45mmDCO3's but the customer versions were origianlly sent out of the factory with twin SU's. It all came down to what you did with the air once you got it in there. My Healy has twin 45mmDCO3's when the factory sent the custonmere cars out with twin SU's as well.

My 1956 Jag was origianlly built with sliding throttle fuel injection. However, in the period, the factory eventually found out that this was not a real gain over the performance of the tripple 45mmDCO3's. It looks great on the car though!

I also have a 1930 Riley Brooklands that was built with a very special engine utilizing 4 Amal carbutetors instead of the twin SU set-up. My experience and investigation with the Amal's is that they are like an on-off switch. Either great at full open throttle or not great at all. The SU set-up is much more flexable in power delivery. Therefore if you are racing on a very long legged track the Amal's can be great. However if you are using the car for normal street use, or on a medium speed road course which forces you to utilize the throttle with varying degress of application, the SU's will work better.

The best ticket is to get a system that you can be happy with for your own specific application and then have it set-up on a rolling dyno. That way you can jet the carbs, select the best fuel grade and set-up the system to optimize your selection. That way you will get the best performance possible. Most likely spending money dynoing-in your engine with an expert will give better gains in performance than changing parts on the engine.

GregJ

Hi Randy,
OK, it may work fine for you. If I remember correctly, your engine is much modified & could well be able to use larger venturis. I may have wrongly assumed that Greg's engine was not so highly modified. In any event, the carbs need to be matched to the engines air flow requirements & how you are going to drive the car. On the average street car, for driveability, I would prefer to err on the smaller side.
D

Hi Greg,
The supercharged 107 inch chopper is likely capable of using more air than a 180 cu in Healey.

The Healey could "swallow" a maximum of about 400 cubic feet per minute of air at 6500 rpm.

There are exceptions to every rule of thumb. It all depends on what you & the engine can agree on as acceptable behavior.

Let us know how it works out.
D

Well, after a very long time I’ve finally gotten the new carburetors. As you can see, I downsized from 6 to a tri-carb. setup. I had done a mock-up of the 6 and it would have been quite the yoga move to adjust the idle screws. The rear carb just clears the steering column by maybe a quarter inch. I’ll have to see if the carbs go straight up when the engine revs, or if they go out and up. That could be a disaster. Next on the list is figuring out the linkage, plumbing, heat shields and a few other odds and ends before I can test fire this thing and see how it runs. I do have one question regarding the steering column. Can it be adjusted outward any at the front to give more clearance?

Thanks,
Greg

Thanks Dave,
Just exploring the options. That would be a last resort. I’d sooner put the stock carbs back on than ruin my ride. (though some may think I have already)

Actually the U jointed column is not a bad solution. It keeps the original correct steering geometry & has the added benefit of preventing the steering column from being driven back into your chest in case of a solid front end collision. I have considered it as a safety feature but have not gotten the motivation to undertake the project. If I were racing the car, it's definitely a modification that I would consider. The thought of being speared by the column in a front end impact is scary. It's the one flaw in the Healey design that I really don't like. I don't know that this problem has actually happened very often, but the possibility is there. Many newer cars have this safety feature & their steering boxes are not nearly as close to the front of the car as is the Healey's.

BTW, I think you will be much happier with the three carbs instead of the six. Six big holes is ok on fuel injection since the system does not depend on venturi velocity to draw fuel into the air stream. Obviously not the case with carbs.
D

guys,very interesting and educational repartee on this subject!but if i may?most everything ive read on the "ticarb"set up seems to announce negativity,ive worked on,tuned rebuilt,transfured the three carbs onto a two carb car,etc.and found it does add power and smoothness to the engine operation,i just had a discussion on this subject with a sharp and knowledgable young healey mechanic and hes one of a few that agrees the improvement is very noticable,and not just a physiological effect,as some have said.[because we hadnt dynoed the cars], in most cases the improvement was profound!now i agree the webbers do look way cool as well as the bike carbs,but does what added performance these systems 'may'supply realy justify the expence?im much more satisfied with straighter line performance across the r.p.m range then a quarky system that limits the range of usable function,and one that is or may be approuching "track"specs.i love having power under the bonnet too!but i dont want to have to lift it at every stop light to make adjustments,i guess im just gettin to old and lazzy for all the experimentation!imho i think theres much to be said for the three carb set up,people shouldnt listen to the neg.blog on these guys.and just learn how to tune them!ya i know ya can never have enough power.

Hi Greg, You may get a bit of additional clearance by shifting the under dash bracket but that will put a compressive load on the grommets that go thru to the engine compartment.You might entertain the thought of shimming the area between the frame mounting and the motor mounts a bit.---Fwiw---Keoke

Hi Anthony,
When I first thought about putting six carbs on the Healey I thought it was a pretty unique idea. As I researched it, I found out that this modification has been done for years. PRIrace has been converting TR6 motors for example. One of the main reasons I went with Mikuni, is reliability and ease of tuning. Turns out, the guy who wrote the tuning manual is the same person who did my conversion. That was lucky, huh? As far as expense, the three Mikunis AND tri-carb manifolds as well as labor and fabrication, cost about the same as only two HD8’s from Moss and half the price of a Weber conversion.

gregw,now that makes alot more sence!1-yes you are lucky,2-cant beat that price,3-gimmy his name.

Well, I was able to fabricate a fuel rail this week and did a test fit today. (I was a little disappointed I couldn’t buy the part off the shelf ). I haven’t made the brackets to hold it yet. I want to incorporate the throttle cable into the design of the rear mount.

I’ve given some thought to the steering column issue. I’m going to mill the adaptor plates down a ¼”. That will move the carbs in but down also. To avoid bottoming out on the pedal box, I’ll need to cut a section of the box out and weld in a recessed piece. Keoke, I’m not sure if shimming the motor mounts will give me enough clearance, but I’ll check that out before starting to cut stuff out.

grgw,nice looking set up!what are ya thinkin about as far as the air filters are concerned? anthony7777.