Mikuni carbs vs. injected ITBs

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Mikuni carbs vs. injected ITBs

Post by german4inline »

I´m currently rebuilding my 76 Renault Alpine A 110 sportscar what I intended to equip with a ITB induction with an Emerald ECU. Now I found a nice Website of an american Volvo tuner John Parker who experienced outstanding engine behaviour along with added power and low torque figures with Mikuni flat slide carbs which were used mainly on Harley bikes. He found big improvements over Weber DCOEs even though the Mikunis were smaller than the Webers. My question is if somebody did a comparison from a ITB injected system ( no matter whatever brand) and the Mikunis. As I´ve heard, basically there´s a significantly better atomisation of the fuel directly at the nozzle with the carbs. He tells about a better throttle response and less consumption as well. Would be nice to get some more experiences about. Here over in Germany it´s completly unknown, I don´t know somebody who uses this carbs on a car. Maybe I will be the first to try it.....
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Re: Mikuni carbs vs. injected ITBs

Post by Chris_Hamilton »

High quality metal, body and paint work
http://www.spiuserforum.com/index.php?t ... inia.9030/
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Re: Mikuni carbs vs. injected ITBs

Post by german4inline »

Thanks Chris :)
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Re: Mikuni carbs vs. injected ITBs

Post by PackardV8 »

Agree with most of what the website says, but the horsepower increase claims are just ridiculous. Yes, the flat slide Mikuni are the best single-barrel carburetors available and will equal ITBs in most performance applications. However, anyone who claims the Mikuni will instantly give a 20-40% horsepower increase over similar size SUs makes me seriously skeptical.

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Re: Mikuni carbs vs. injected ITBs

Post by Truckedup »

I use Mikuni flatslides on my racing and street bikes....Like all flatslides,they have fantastic throttle response...Tuning them is easy if you have a clue to what jets, needles etc to use as a starting point...
I agree with Jack on the silly HP gains..it would only be possible if the other carbs were poorly jetted..
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Re: Mikuni carbs vs. injected ITBs

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Re: Mikuni carbs vs. injected ITBs

Post by englertracing »

Keihin FCR carburetors are much nicer than the mikunis, but the largest you can get is 41mm
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Re: Mikuni carbs vs. injected ITBs

Post by Protech Racing »

I have raced with Parker and he is a nice honest guy. The HP claims that I see are the 20% for the stock , little SU on the MGB. Increasing the area by 30% and using a much cleaner intake track could well make the 15HP increase. Also the stock SU may have been old with worn jets /needles etc.

55 WHP to 70WHP

Most of the time ,the EFI does spray the fuel near the valve. While the carb sprays it further upstream. Might be more power .

The old injected cars sprayed the fuel into the top of the venturi tubes or the Kinsler style , part way down, but still, well above the valve.
If I could run Microsquirt /EFI on my vintage Toyota instead of the twin Webers, I would . Modern programmable , density compensating. I do expect the Webers to make competitive power tho.
IMHO you are further ahead using something that parts are not 6 days away for .
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Re: Mikuni carbs vs. injected ITBs

Post by Truckedup »

A single 42MM Mikuni HSR can support 100 RWHP @ 7000 rpm on a Harley...
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Re: Mikuni carbs vs. injected ITBs

Post by BLSTIC »

Would detailing the ITBs (knife edge, one sided narrowed throttle shaft e.t.c) close the airflow gap to flat-slide carbs?

As an aside, how much power are you making? Modern injectors get some pretty fine droplets coming out and I think you'd struggle to best them with a carby. I don't think things like the tapered 12-hole UC are available in "big" though.
Last edited by BLSTIC on Thu Nov 14, 2019 2:14 pm, edited 1 time in total.
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Re: Mikuni carbs vs. injected ITBs

Post by hoffman900 »

BLSTIC wrote: Thu Nov 14, 2019 2:09 pm Would detailing the ITBs (knife edge, one sided narrowed throttle shaft e.t.c) close the airflow gap to flat-slide carbs?
Why bother? You’re not worried about maintaining velocity through a Venturi for fuel atomization and to maintain carb signal. You can put the throttle body and injectors anywhere that will not only maximize power, but also throttle response, and transient response. In addition to tuning possibilities.

ITB’s when executed well, will be way better than any carburetor. That said, the Minuni’s are very good.
-Bob
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Re: Mikuni carbs vs. injected ITBs

Post by PackardV8 »

In 2012 we dyno tested a stock MGB with SU carbs. We then removed the SUs, and installed a pair of 42 mm HSR Mikunis. With no other changes to the MGB, we were surprised to get a 20% increase in power,
Protech Racing wrote: Thu Nov 14, 2019 11:34 am I have raced with Parker and he is a nice honest guy. The HP claims that I see are the 20% for the stock , little SU on the MGB. Increasing the area by 30% and using a much cleaner intake track could well make the 15HP increase. Also the stock SU may have been old with worn jets /needles etc. 55 WHP to 70WHP
If the carbs being replaced were clapped-out junk, then the claim is deceptive on that score. I wasted some of the best years of my young life trying to make those buzzing little anvils go faster. No one will ever convince me replacing two properly tuned SUs with two Mikuni on the same intake on a stock MGB will give a 20% horsepower increase.
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Re: Mikuni carbs vs. injected ITBs

Post by Truckedup »

PackardV8 wrote: Thu Nov 14, 2019 2:49 pm I wasted some of the best years of my young life trying to make those buzzing little anvils go faster.
:D :D :D I hear you on that British stuff...
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Re: Mikuni carbs vs. injected ITBs

Post by PackardV8 »

Truckedup wrote: Thu Nov 14, 2019 4:18 pm
PackardV8 wrote: Thu Nov 14, 2019 2:49 pm I wasted some of the best years of my young life trying to make those buzzing little anvils go faster.
:D :D :D I hear you on that British stuff...
Only slightly OT, my first venture into carb tuning came after installing megaphones on a '67 Triumoh TR6 650 and it went slower. When I went back to the dealer who sold me the megs, he smiled and held up the richer Amal carb needle. "I was expecting you'd be back for this." Taught me never to do that to customers, no matter how young and stupid.
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Re: Mikuni carbs vs. injected ITBs

Post by german4inline »

If you have a look into Weber DCOE compared to Mikunis flat slide, there´s a huge difference in open CSA, due to the venturi, throttle shaft and pre-atomizers what Webers are suffering from. In my book from Dave Vizard "port and flow test cyl.heads" David tells from an old story (but anyway supposed to be true) from his experiences with his Sunbeam Avenger of the mid ´70s. He claims that Dellorto carbs are significantly better in fuel atomization than Webers and he got considerably more power. I´m not an enemy of DCOEs and went a long time with them, but better is the enemy of good.
I trust the stories of John Parker and the claims of his customers, why not?
To be honest, if you go to ITBs with injection, normally you will provide a set of injectors and put them into the ITB body or the cyl. head , make your mapping and will see what happens. Nobody can claim that there are no possibilities of optimization like position of the injektors, spray angle of the inj. itself, angle of the injector body within the barrels, position of the inj. relativly to the throttle, throttle diameter, type of inj. due to nozzle styling, numbers of spray jets, a lot of boundary conditions which have to be defined whats a big expense if there are no experiences with this engine. All these things will influence throttle response, output, so that nobody can claim that just using ITBs with ECU makes everything work perfectly. Especially atomization will be influenced by these conditions, whilst it will work on an well designed carburettor naturally. The big pressure drop what acts on the jets of a carb can never be achieved on a injector. The biggest advantage of ITBs is to my opinion the eliminating of the venturi and the pre atomizers what the flat slide carb features as well, along with a missing throttle shaft, better cfm figures, and all things what we like to have together with better atomization.
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