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Megasquirt question

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Atrus

Atrus

Jedi Warrior
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Hi all,

I have a question regarding a Megasquirt install. I am at a crossroads, and unsure of what would work best:

Option one, I’m considering using a downdraft TBI from a Geo Metro/Tracker or Suzuki Swift/Samurai. Option two, I’d use the throttle valve assembly – no injector (Chevy 2.2L? Later model Geo/Suzuki?). As these use a multiport setup, I’d have to put the injector in the manifold directly behind the throttle valve.

My questions are:

1) Do you see a problem with the downdraft Geo TBI setup being mounted vertically as a sidedraft setup? Would I see gas leaks at low speeds, or should intake volume be sufficient at idle to not have a problem? (I’m not set on the sidedraft setup with this TBI, I could go either way – downdraft or sidedraft).
2) Would there be an issue with using the throttle valve and spraying the injector into the manifold behind the plate?

My thoughts are that the Geo TBI setup is a single unit, and that the unit is engineered to atomize correctly – I’d be just spraying fuel into the manifold with option #2. The throttle valve assembly, however, is a little more modern and sensors are cheaper and more readily available, plus I could choose a standard GM injector to save on cash – I know I could find one cheap. I think the throttle valve assembly is also more aesthetically pleasing (the TBI is ugly in my opinion). I couldn’t really care less if the setup looks original or not, but I do want it to look good.

Is there one method you’d see as better than the other, or are they equal? Any suggestions or anything I
should be aware of?
 
If you go the "throttle valve" set up, I would highly reccomend building a custom plenum style manifold with an injector spraying into each port. I agree that the TBI setup will be fugly, but for fast and cheap, it's the way to go. All of the sensors you need save for the water temp sender will be on the TBI itself. In my set up, I found that using MAP for acceleration enrichments works better than TPS. You can do this with MSnS Extra.

If you are feeling adventurous and would like to help me develop my setup which uses the stock manifold and carbs as throttle bodies, you can send me your carbs and manifold and I will build you injection adapters at my expense.
 
I was hoping you’d chime in Morris – forgive me, but I couldn’t remember your name to ask you directly. You’d think I’d remember Morris, not a difficult one to remember! I’m old at 26 ;-)

Makes sense to me to do the throttle valve setup then over the throttle valve/separate injector.

I’d seriously consider your adapters as well, if you say MAP seems a better route than TPS. Sounds as if your setup would be much easier to run as I wouldn’t have to fab a manifold. Can you fill me in a little more on your setup? I am just really starting to look into the Megasquirt, but I am extremely interested in doing it. For example, how do you handle cold starts? I was looking at a full TBI or throttle plate setup mostly due to the ease of using a TPS and IAC (ease over converting HS2’s to TPS in my mind). So, your system would utilize coolant temp, the barometric pressure/MAP, O2, and two injectors?

Any information you could give (or be willing to divulge at this time) about your setup would be great! I actually have a set of “junk” carbs – the pistons are scored/warped, so I purchased a set of new HS2’s that I am currently running. I’d think I’d be able to use those junkers for your setup as basically I’d need them solely as a throttle plate, correct? Silly question, but why would you need the manifold? Are there modifications to be done to that as well?
 
Whoops, nevermind on my question about the manifold - for the MAP provision I am assuming.

By the way, what sensors are you using (standard GM, or what?)
 
Basically, my setup uses a machined adapter that fits between the carb and the manifold. this is where the injectors sit. Because I have only designed this on paper, I will need the manifold to test fit everything. On my car (a 1500) the GM temp sensor is fitted into a tee in the coolant return line. The air temp sensor is a Holley unit that fits in the air cleaner housing. Cold starts use the stock choke and warm-up enrichments calculated by the MS computer. There is no IAC. The MAP is built into the MS computer. Using the MSnS Extra software, you can program the computer to inject more juice when MAP suddenly falls. This replaces the function that the TPS serves.
 
Bummer news Kevin... I don't think my approach to injecting the A-series will work too well after all. Check out this info form https://www.sidedrafttbi.com :

"The firing order is 1-3-4-2. Basically each injector would need to double up when firing. If you consider the intake as two separate manifolds; Injector A fires to fuel number one cylinder. Injector B fires to fuel number three. So far so good now comes the problem: Next to require fuel is number four and it's injector (B) just fired and injector A in the other manifold section is now firing so number 4 cylinder will not get enough fuel.

That's pretty much the way it works with the ECM we are now using. Even if we were to fire both injectors at the same time, the manifold loads up with fuel and the first cylinder on an intake stroke will grab it. The next cylinder to fire is on the same manifold section and will be shortchanged. While that was happening the same scenario is happening to the other manifold section. The balance tube helps offset this but does not completely solve the problem.

The real solution is to able to fire the injectors in sequential fashion A-B-B-A and to date nobody has addressed that. Perhaps it could be done with a high end ECM or Megasquirt using four injector circuits and diodes to prevent feedback (two circuits firing the same injector?) with a cam sensor to synchronize the works. That's not really my strong point so will for now leave it up to others. There is a lot of interest in solving this problem and some are experimenting now. Sorry to say nobody has told me of a solution yet."

This may not be quite the problem with Megasquirt that it is with the GM ECM, but I suspect it is always going to be a little bit of a problem. This would explain why the dual point Mini injection system was never as well regarded as the single point. That one always stumped me.

Basically, your best bets are going to be: 1) stick with the Geo TBI plan or 2) acquire a single carb manifold such as this https://cgi.ebay.com/ebaymotors/Austin-Mi...1QQcmdZViewItem
in conjuction with my injector adaptor and an HS4 (it'll look alot better than the Suzuki/Geo set up for sure).
 
...Or buy one of those expensive seven port heads with integrated intake manifold.
 
Jollyroger, who used to be a regular on this forum, has a CNC milled reproduction of an 8 port fuel injection head developed by the BMC racing department. I think he can sell it and the cam for roughly $3000-4000. The head was capable of enormous horse power but I cannot remember exact numbers right now.
 
Thanks for the info Morris, that is a bit of a disappointment. And that head sounds like it'd be amazing, no way I could be dumping that much cash however.

I created a new post. I'm definitely not opposed to the HS4 route, however, it seems it'd be more restricve to me. I could be completely off base in my thinking though.

And now I think to myself, why not just go for a modern throttle plate setup, and fab an intake manifold and incorporate a single injector near the plate, as what would be done on an HS4 anyway.

Ah, decisions, decisions....
 
Morris, another thought...

The initial plan was to fab a spacer that would go behind each carb to provide a port to spray fuel into, correct?

This might seem a little out there, and I am unsure of the space issues, but what if a spacer was made to fit between the head and the manifold and run a dry manifold setup? My thought is you don't have all the linkages there and whatnot, so you'd have a little more space. Now, bear with me here, but I am thinking why not go with 4 injectors on this setup. One "in front" of the manifold, one on each "inside" and one on the "rear" of the manifold. I am talking almost horizontal. Each could be slightly angled, and in essence, we could have a cheap multi-port setup on the siamese port. There'd be a fairly funky fuel rail setup with this method, but I think it could be handled decently and look respectable.

Since you've run and understand Megasquirt, could 4 injectors be utilized in this manner, or would 4 injectors require a more complex system of sensors (CPS, etc?). My thought is that it would handle it, given you were running 2 injectors, I'd think it could handle 4.

Thoughts? Opinions?
 
That sounds like a pretty interesting undertaking, but I don't think it would solve the problem. Megasquirt can handle that many injectors, and it would not require any special modifications, but the trick is getting Megasquirt to fire the injectors in such a way that # 1 piston does not steal all of #2's gas (or vice versa). At present, MS does not support sequential injector firing (firing one injector per cylinder just before the valve for said cylinder opens). MS will support this soon, but there would still be the problem of timing this. Most modern ECMs use a cam position sensor to do this. Such a thing would be quite a problem to set up for a push rod engine. I quess it could be possible using an inductive pick up on a spark lead.

MS does support alternate batch firing and it may be possible to program MS to fire in the A-B-B-A pattern needed to evenly disperse fuel to all cylinders, but it would still be a trick to make it sync up to your cylinder firing order. As far as I can tell, MS just "listens" for a spark, counts 4 and calls that an engine cycle.
 
So, in your opinion, back to basics of just having a single throttle plate, and one or two injectors firing into the manifold, letting vacuum sort out which cylinder pulls the fuel?
 
Sounds simple enough to me, I like simple. I'll have to fab up an intake manifold, but that's no biggie.
 
My only hesitation about using the HIF is that I'm drastically cutting down intake flow in my opinion.

Now thinking Chevy 2.2L or a 2.8L TB.
 
Why not use a twin SU manifold with 2 Suzuki Hyabusa throttle bodies? The bike uses 4 of these to get 180HP out of 1200cc, I bet 2 would support anything a non turbo A-series would put out. The Brits use these in pairs all the time on Ford 4-cyl engines and I believe they have a lot of "overhead" in their airflow capacity.
 
There is a thread on this subject over @ the Westfield sports car club BB. See "techie talk" Seems that a single 38mm GSXR-600 TB will flow fuel at 220cc/min @ 3 bar pres. Enough for 2 to support 125HP out of 1700cc. This is with a Megasquirt system.
 
The issue is, as Morris pointed out, when using two injectors, cylinder #4 will be starved for fuel. You'd need either a multiport setup with sequential firing, which megasquirt can't do and would be more complex than I'd care to get into, or you'd need to do a single TB with 1 or 2 injectors. The latter method sounds way more easy to me.
 
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