Fuel injection

Jerry,
Try looking at motorcycle FI pieces. The Lotus Elan guys in England use them all the time on their Twin Cams, coupled with Mega Squirt or some other rather expensive ECM's. I know a guy in Nevada who is installing them on his Lotus Elan Plus2, equipped with a 2L Zetec and a Mega Squirt. Or join lotuselan.net and ask questions there. It is a really good site. Maybe this will help.
 
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.
 
The air/fuel cant tell where it going . 1 cyl, 2 cyl 3 cyl . It should run as well as the carb setup. But any kid can trim the AFR with a laptop.
I would add the injector as far up stream as allowed . It will not be a big deal to convert a pair of carbs to EFI. The rule says " throttle body . "
 
best I could find is "Making for Motorsports" video on putting Throttle Bodies on a MINI.
https://www.youtube.com/watch?v=epfHgEutoQk
 
Have been a long time lurker, always read the tech stuff, as I race vintage minis. The discussion on EFI has me thinking about some research that a friend of mine did 20 years ago regarding the 5 port engine. Here is the link to what he found back then. It may or may not help with ideas. I know things have moved forward with time.
https://www.starchak.ca/efi/siamese.htm
Bruce
 
That is some interesting research for sure. Thanks for sharing.

One thing to not get too wrapped up around when considering this is thinking about injection events as being timed to valve open time.
There is a LOT physically going on with the intake air, and the fuel being introduced, and the harmonics in the columns of air/fuel going down the runners - and it doesn't behave the way we initially imagine.
Remember that a well tuned carb actually runs very well, and there is certainly no "timing" of fuel events with those.
This is not to say that injector timing, or injector location won't make a difference, but it may not behave the way you intuitively expect.

This is a case where getting the big things right is important, and the little things will generally be found on the dyno, or with good data, and analysis from track sessions. One thing is for sure, if you move to a programmable system to control fuel you will create more consistent performance over a wider range of conditions, once you get the tune refined to a certain point.
 
chois said:
This is not to say that injector timing, or injector location won't make a difference, but it may not behave the way you intuitively expect.
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Both you and Mike alluded to this...let's all remember that the allowance for conversion to EFI is to a throttle body injection only (see reg at the bottom). Other than within that throttle body, you will NOT have the opportunity to be dyno-testing injectors locations are anything like that. So that's a moot point.

All you can do is replace your carb(s) with a device that sprays fuel due to fuel pressure differential instead of atmospheric pressure variation...

...you will create more consistent performance over a wider range of conditions, once you get the tune refined to a certain point...Remember that a well tuned carb actually runs very well, and there is certainly no "timing" of fuel events with those.
Click to expand...
Which, coupled to the above, is why I kinda see this as "no big thang".

We drive our race cars within such a limited range of RPMs and throttle positions that unless you find a way to get more airflow (maybe a tad more without the venturis in the way) you simply are not going to find a massive increase in output.

One advantage of EFI is logging and real-time adjustments due to sensor feedback (wideband). But someone that understands carbs and jet/tube tuning can probably do just as good as job with the same airflow as a counterpart will do tuning EFI on a computer; EFI will just get you to damn near the same place easier and sooner. Both are tuning within that same limited small band of working environment.

This option isn't a magic bullet, folks; it's not going to fix all your probs. It's just a way to overcome limited knowledge (and parts) in old technologies that no one apparently wants to play with any more (and by that I'm not just talking about Little British Cars...lol)

GA

"Classifications that have no fuel injection allowance on their spec line may substitute a fuel injected throttle body in place of each of its permitted carb(s). This alternate throttle body must have a Choke with the same diameter of the approved carb(s). A Flat Plate Intake Restrictor matching the specified choke dimension may also be used. The fuel injector(s) must be part of the throttle body."
 
Darryl Saylor said:
Found these 31 mm throttle bodies.
http://www.yuminashi.com/-pcx125-31mm-throttle-body/

I was wondering if you could make a cap to go where the piston is on the su carb where the injector mounts. You would have to plug the hole where the jet comes thru. Take this with a grain of salt because I'm not really sure about any of this
suficap.jpg
Click to expand...

This is a good idea I looked at already. You'll want to get the injector on an angle shooting down the bore and make room for maybe two injectors to make the controls easier.
 
chois said:
That is some interesting research for sure. Thanks for sharing.

One thing to not get too wrapped up around when considering this is thinking about injection events as being timed to valve open time.
There is a LOT physically going on with the intake air, and the fuel being introduced, and the harmonics in the columns of air/fuel going down the runners - and it doesn't behave the way we initially imagine.
Remember that a well tuned carb actually runs very well, and there is certainly no "timing" of fuel events with those.
This is not to say that injector timing, or injector location won't make a difference, but it may not behave the way you intuitively expect.

This is a case where getting the big things right is important, and the little things will generally be found on the dyno, or with good data, and analysis from track sessions. One thing is for sure, if you move to a programmable system to control fuel you will create more consistent performance over a wider range of conditions, once you get the tune refined to a certain point.
Click to expand...

Maybe I misunderstand but absolutely disagree in regard to the rules and a BMC siamesed intake port that has very little divider and overlapping valve events in the same port. The SU carb is pretty smart and will only meter what it needs (not capable of pulling or pushing fuel). In order to just equal that of the carb you will have to pay attention to valve timing events and will require varying injector timing and pulse widths (between paired cylinders/injectors) to achieve a minimal AFR spread from outer cylinders to inner. In this case the "big" thing is injector timing (so you know where to start), and the little things will be injector positions, spray pattern, and eventually fuel trims. Now whether or not you choose to understand the base engine events that make you do this is on you.

As Greg mentioned the one saving grace is our RPM range for limited tuning, but RPM is also an enemy as it increases. Depending on your lucky cylinder head find, camshaft, and gearing the operating range for the 1275 is 5500-7200 which will allow us to focus the mapping more in the "higher" rpms. The tuning issue is more problematic at high RPMs as the injector firing events are extremely close to each other and will require different pulse widths to not over-fuel one cylinder. Even with the carbs there was a lot of effort spent developing split profile pattern camshafts that had different valve timing events for the inner cylinders to delay them from scavenging the paired intake valve and better managing the intake charge and standoff. They work but not always ideal for all conditions.

As the rules are written we are only allowed (2) individual throttle bodies and the injectors must be mounted in them (not the intake, not in the spacer, not in or out of the velocity stacks) which creates the challenges for the BMC injection. There are a few approaches to this project. If we were allowed a single throttle body with some plenum area your statements apply much more as we are closer to a functioning single carb setup.

Maybe we have to ask for a weber 32/36 setup like the 1500 Triumph/Midget to make EFI adaptation a little easier. Maybe we can get an 8 port head approved :ask:
 
Just one note regarding the tunable curve. you gotta get the damn car to start and roll thru the pits to get to grid. current tune on my STU car is VERY nasty at low RPM and the damn thing burps and jumps and spits and bogs at low RPM and throttle position. I'm afraid I'm going to either give myself whiplash or break an axle coming off track with hot sticky tires and then idling to/from tech.
Also starting my car on a hot engine is awful. Car acts like it has no fuel, but I can hear the fuel pump run and then fuel pressure on the AIM. but it'll crank over, fire, and die about 5-10 times before I can get the car started. I'm often the last one out of impound or I have a line of people stuck behind me getting impatient.

....imagine if you spun on track, stalled the engine, and then it took you 2 min to get moving again. I would hate to be the safety hazard/ get myself smooshed / cause of FCY because I couldn't start the engine hot.

so you certainly don't need to worry about getting the maximum power at part throttle and low RPM, but you DO need drivability and hot and cold start to work.

Those are going to be major punchlist items for my tuner whenever I get the new engine in the car.
 
Eric

It’s definitely a non ideal intake tract.
My hypothesis is that between thoughtful injector sizing, and mass air flow data you can deliver fuel closer to the way a carb does than people assume, but can hit the afr goals over a wider range.
Maybe I’m wrong, but I hope we get to see these problems figured out regardless.
 
Matt, Your car needs a tune .
Greg, "The injector must be part of the throttle body."
All of the injectors that I'm aware of, may be removed from any mounting point and are separate from the throttle body , intake manifold, etc. Already the rule is flawed in the description.
FWIW, I spend a lot of time on the dyno, moving cam events, ignition , etc. Each change requires a small AFR tweak on the tuning program. Easy to do with a wide band AFR system. Often I set the tuner program for closed loop during early tune stage. I fine tune later manually .
How many carbed race cars have a wide band? Not many .
If you watch the fuel entry into the engine, it is simply s spray. only at idle will you ever notice a pulse.

Yeah on converting the SU carbs. I already mentioned about plugging the piston holes and jets, Fitting an injector as far upstream as possible .
My vision for these is to replace the piston and cover with a one piece injector holder that angles into the bore , spraying near the top of the bore and at the throttle shaft .
 
I'm converting my street 914's Microsquirt system to these. I'm sure someone clever can make an adapter plate for them for other applications.

https://thedubshop.com/dual-idf-throttle-bodies-outside-injectors-vwss/


Screenshot 2023-12-20 081651.png
 
chois said:
Greg - those look super cool...I'm getting 914 envy over here.
Click to expand...
:cowboy:

For those thinking of taking up such a project, here's an extensive blog on how I converted my 914's D-Jet system to Microsquirt, it'll give you a sense of what's involved in doing aftermarket EFI. It's not for the "TL;DR" crowd...

This conversion, while a lot of work, was a lot easier than trying to convert a carb car to EFI, simply because I didn't have to design and fab the induction. I retained the D-Jet's existing induction - throttle body, plenum, runners, injectors location and lines - and changed all the remaining components to accomodate Microsquirt (TPS, MAP and temperture sensors, injectors, wiring/relays).

If you read through this and get the willies (you really shouldn't, it's not that intense) then consider this work and then add in there having to design and fab up an appropriate induction. I would be surprised if anyone offers an EFI system for existing carb cars that retains the stock intake manifold...All because you don't like carbs.

This is not a warning to stay away; if I had a carb Prod car I'd seriously be researching options. But it's not going to be as simple as plug-n-play. - GA

https://tgadrivel.blogspot.com/2020/03/on-microsquirting-porsche-914-part-1.html
 
Greg, those look like they will be injecting after the butterfly? And is the butterfly the correct diameter for your spec line? Our 1275 LP cars need 2 individual butterfly's 31 mm. A single IDF body like yours could be monted to a single DCOE manifold for the 1275 but I'm not aware of any that are 31 mm butterfly's. What does anyone think about the pre or post relationship to the butterfly ? I'm thinking people with dyno access will be playing with lots of stuff and I hope the keep us informed. Me for now I'm just going to do the 12 to 1 and see what that does for me. Thanks all, Jerry
 
Jerry, those are for my street car. I do not have plans to bring the Limited Prep/historics race 914 into Prod because the PAC has it in FP (I've twice requested moving it and was rejected) and I'm not interested in playing there.

Note that the new reg allows an FPR of the same choke size you have now. So you could order the 36mm version of these TBs and mount it on top of a 31mm FPR.

Greg
 
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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