Today’s Hot Message Board Topic: Replacing Fuel Injection With SU Carburetors

Photo courtesy Norman Garrett

Ever think about replacing the factory fuel injection with some classic SU carburetors? Well, you have come to the right place.

One of our message board regulars had that same question, and we know a guy who did that very swap: Norman Garrett, one of the main engineers on the original Miata. We pinged Norman, and he explained the swap on the board.

Happy motoring.

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Comments
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Adrian_Thompson
Adrian_Thompson MegaDork
8/2/19 1:08 p.m.

I've often thought a set up like the pic above would be the perfect swap for an MGB.  Especially if you sourced one of the square, ribbed rocker covers from and Escort or Protege, then mill off the words and replace with the classic MG Octagon.  

Knurled.
Knurled. MegaDork
8/2/19 1:15 p.m.

In reply to Adrian_Thompson :

like it!!

Adrian_Thompson
Adrian_Thompson MegaDork
8/2/19 1:51 p.m.

In reply to Knurled. :

It gets better.  My ultimate fantasy, scrub that, let's call it a daydream instead!  Anyway, my 'daydream' was to use the SU dash pot dome to hid an injector and use MS to run it so it looks like carbs, but is in fact FI.  Not sure how MS would like only two injectors running split port intakes thought.  

Stefan
Stefan MegaDork
8/2/19 2:27 p.m.
Adrian_Thompson said:

In reply to Knurled. :

It gets better.  My ultimate fantasy, scrub that, let's call it a daydream instead!  Anyway, my 'daydream' was to use the SU dash pot dome to hid an injector and use MS to run it so it looks like carbs, but is in fact FI.  Not sure how MS would like only two injectors running split port intakes thought.  

Eh, it wouldn't care.  It would be like dual TBI units or a single ITB feeding a 4-cylinder.  Things just don't happen that quickly on a domestic motor where the timing of that would make a noticeable difference on that type of fuel injection. 

Knurled.
Knurled. MegaDork
8/2/19 2:34 p.m.

MS wouldn't be able to do it, not without custom code, and I don't know how well it would work.  You'd either starve the second cylinder in the firing order or overfuel the first, or maybe vice-versa.  

 

I know Subaru didn't bother trying to do port efi with single port engines.  The XT and Turbo EA82s had two intake ports per head.

NOHOME
NOHOME MegaDork
8/2/19 2:38 p.m.
Adrian_Thompson said:

In reply to Knurled. :

It gets better.  My ultimate fantasy, scrub that, let's call it a daydream instead!  Anyway, my 'daydream' was to use the SU dash pot dome to hid an injector and use MS to run it so it looks like carbs, but is in fact FI.  Not sure how MS would like only two injectors running split port intakes thought.  

SU and Zenith Stromberg using our Bespoke Adaptors
Systems for SU H2, H4, H6, H8
Stromberg CD150 and CD175

With our bespoke adaptors you can easily convert your existing SU or Stromberg equipped vehicles to fuel injection.
These adaptors are our own unique design and fit between the inlet manifold and existing carburettor providing a simple and almost " original look " method of mounting the fuel injectors.
Using these adaptors in conjunction with our kits virtually any vehicle currently fitted with these carburettors can be converted to fuel injection.

68TR250
68TR250 Reader
8/2/19 2:43 p.m.

In reply to Adrian_Thompson :

Hiding FI injection inside SU bodies has been done on a '75 TR6.  I believe it was Rick Patton that did it.   I believe he also supplied the setup to Bob Danielson.

http://pattonmachine.com/TBI-Main.htm

http://tr6.danielsonfamily.org/index.htm

 

ShawnG
ShawnG PowerDork
8/2/19 3:29 p.m.

For the full British Car Experience, why not just use bits of the Lucas fuel injection from a TR5? cheeky

 

buzzboy
buzzboy HalfDork
8/2/19 3:38 p.m.

I researched it a lot, adding two SUs with injectors to a 4 cylinder, thinking about doing my B20 that way. Either you need a trick manifold, which do exist for some applications, or use the SUs as throttle bodies and add port injectors.

Foxworx
Foxworx Reader
8/2/19 9:00 p.m.

This seems like fun if you hadn't earlier in life contemplated self harm after having to actually deal with SU carbs on a regular basis.

VegasNick
VegasNick Reader
8/2/19 9:04 p.m.

With that same idea, why not go all out with a 4bbl carb! :)

Tom1200
Tom1200 Dork
8/2/19 11:09 p.m.

I personally would use a pair of Keihin Flat Slides, granted it doesn't look British but being the best carbs ever made they would offer an advantage.

I used Hitachi SU carbs on my race car from 1992 until around 2007 and found them very user friendly. I only ever made minor adjustments to them based on weather conditions in att,to to get the last couple of horsepower. If it had been a street car I seriously doubt I would have bothered. 

ShawnG
ShawnG PowerDork
8/2/19 11:16 p.m.

In my "tuning the BMC A-series engine" book by David Vizard, he tests SU carbs against Weber DCOE and finds the hp difference between the two very negligible. Like "error in the dyno" small.

NOHOME
NOHOME MegaDork
8/3/19 5:36 a.m.

SU carbs are actually very simple and easy to tune. What takes forever to figure out is that they are all worn out a couple of years after leaving the factory and hence can't be tuned because they leak air all over the place.

More recently, setting the float levels has become an issue because the chinesium parts do not work as described in the manual and fuel levels in the jets do not end up where they need to be.

Knurled.
Knurled. MegaDork
8/3/19 6:17 a.m.
ShawnG said:

In my "tuning the BMC A-series engine" book by David Vizard, he tests SU carbs against Weber DCOE and finds the hp difference between the two very negligible. Like "error in the dyno" small.

That just says the bottleneck is elsewhere.

 

On the other hand, I read an interesting article about port design that used the reflection wave from the first IVC event in a port to supercharge the second intake port.  You wouldn't be able to do that with DCOEs, I don't think.  I really wish the article had pictures...

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