Fuel injection

Good find!

Those are cool.


Steve Eckerich said:
Borla Induction makes a 1.5 SU style TB. Would work on some spec lines and might be choked down to 1.25".

https://www.borlainduction.com/2700-series.html
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ERVRCG said:
Nothing great and certainly not in the 1-1/4"...and why would you make a system with the choke point (in the aftermarket)? Either way you'll have to make sure you have a choke in throttle body similar to the Webers. Check out the Moss Motors MGB setup, pieces and parts can be adapted. There are some motorcycle throttle bodies that are close too. I think modifying the carbs would be a good idea too.

Parts are easy, the biggest challenge will be getting the proper fueling for the siamesed port on individual throttle bodies. With our firing order and cam timing events it will be interesting to try and balance the fueling between cylinders. Getting the most out of it will be quite the development and I'm personally excited to give it a go (good or bad).

There's lots of reading out there to discourage anyone from trying this but it's not impossible.

Feel free to reach out.
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Alright I'm reaching out 303 856 8149
 
Is anyone working on this yet? I can help engineer it /tune it .
All I see is a naked carb body with the piston as the throttle slide( no shaft or plate) and an injector spraying into the venturi . That still fits the rule as its written at this point .
 
Remove throttle shafts .
Attach throttle cable to the top of the piston, like a bike carb .
Fit the inlet trumpet with injectors.
You will need an RPM signal, map sensor, maybe TPS, Wide band system, one of the many stand alone ECU.
There may be an optimal spray direction for the fuel. It might be easier with a pair of wideband sensors on the center and end bores.
 
I have not gotten to this yet and the rules require stock intake and throttle body injection...so injectors can't be mounted in the "trumpets" or outside pointing into the bore. Mike's idea is not a bad one for the slides but there are small throttle bodies in the world to use that already have TPS integrated. 4 injectors is the best way to go with an ECU to get you started.
 
Where is the definition of throttle body injection? If they are not in the intake or head, they must be TB injection. Maybe the trumpets would have to be welded to the carb to be one piece. Kinda like the old days with epoxying the wheel spacers to the wheels.
 
Half serious suggestion: Use CIS or something similar where fuel is metered by pressure not pulsewidth and the flow is continuous.

Another half serious thought - would it be legal within the rules to have the throttle body(s?) / injector(s?) external to a plenum that fed the manifold? You'd probably get a lot of fuel dropout at low RPM but it might be OK at high RPM. This is basically how the old TBI street cars worked, the TBI fed a plenum that fed runners.

Speaking from no experience I can easily see how a short injector pulse on a siamesed port could wind up feeding one cylinder far more than another. With a 1:1:1 injector / port / cylinder setup I don't that that timing is very critical. For instance, 1980s Ford V8 port fuel injection fired the injectors in banks of 4 at once.

Having said all that, I wonder if it isn't an awful lot of work for minimal gain?
 
I'm not sure from some of these suggestions that you are aware of the layout of a 1275 Spidget engine, 2 siamese intake ports, 3 exhaust ports, 2 and 3 siamesed. Do you really think removing the butterfly completely and making the SU piston into a slide throttle will be acceptable to the CRB ? And those that talk of motorcycle FI set ups just give me a brand and part number so I can see what you are thinking about. Thanks
 
The injector will simply spray the fuel at a metered amount, exactly like the carb jet. The resulting spray will be distributed along with incoming air flow . There will not be a huge difference from the carb's jet spray . Simply better regulated . Air and fuel make power.
IMHO the minor variance in cylinder to cylinder is not that important. I run the dyno a lot and watch the power change from 12.4 - 12-8 and its not enough to worry about . Using an AFR wideband sensor in each exhaust tube will be usefull to see how much variance there actually is .

Like I said , if the carb works, this will work, and be a little easier to tune. I doubt that any power increase may result . Any power increase will be the result of eliminating the carb throttle plate and or piston. Possibly spraying the fuel from the top of the bore may help a tiny bit .
Also the injectors do not actually pulse at any RPM range that we worry about. If the required PW is too low I can reduce the fuel pressure and increase the PW. AT WOT there is simply a constant spray .
BTW . if I had one of these cars, I would be along this road by now.
 
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