Ok, I am building an EFI system for my 12A. I am using a megasquirt ECU and I am going to run four injectors. Question of the day is do I go with throttle body injection or place my injectors after the throttle body.

This is a budget set up so I am using the stock intake manifold, with slight modifications and I have turned the carb into a throttlebody. My original plan was to cast an aluminum spacer plate to go inbetween the carb and the intake manifold that I could plumb the injectors into. But I have been presented with the idea of doing a throttle body intake with the injectors right above the throttle body. The car is going to street driven and autocrossed. I want the EFI for 2 reasons 1: to see if I can do it, and 2: to avoid the fuel problems associated with hard cornering. Any suggestions as to which way to go?

Here is a pic of the throttlebody.

 

thats disgusting!!!!! you need to fix that, where does the tps go? get a twm throttle body, at least it will run! wht about the venturies???yuk! if you are on a budget , keep it carburated!!!! do it right or else dont do it at all!!! EFI that it...... go carb turbo if your on a budget.... as long as your on boost in the corners..... no problem!

 

you should get better a twm induction trottle body and a racing beat weber manifold , heres the link for the trottle body is www.twmindution.com and for the manifold www.mazdatrix.com or www. racingbeat.com because you gonna spend more money trying to do it the way you are doing it right now.

 

You probably wish you never asked!

If you don't like what they say above just do it your own way. At least you'll learn from your mistakes.

 

For a low-budget experiment, get a throttle body injection unit from the local auto wreckers, and adapt it to the stock manifold. That'd be much easier than trying to fit injectors, rails, tps, etc to a dirty old Nikki. With a suitable TBI unit you'll have tps, IAC for fast idle, and integral injectors.

Buying bolt-on parts is the easy way. Adapting parts and building your own EFI system may or may not be successful in the end, but you'll learn more than you can possibly imagine; certainly more than simply spending your way out of a problem. Go for it!

 

I agree with renns - go for the used/aftermarket throttle-body. I don't know what kind of custom fabrication sources you have at your low-budget level, but you're going to need a lot of close-tolerance custom components to fabricate, test, tune, and run your own.
Personally I can't even picture using a Nikki body, it's comparable to using an abacus for an ECU.

 

Yeah you are gonna have to the turn it sideways, do u grasp the firm reality of the way TB's work?

I honor your willingnes to invent, but lets save you some time here, look a tried and true inventions and then copy off them

 

There are a multitude of TBI (note the I) systems that sit vertically. GM and others took that route as a quick method of converting existing carb engines to FI. There's likely dozens of candidates in any auto wrecker on this continent. Adapting one of those would certainly be easier than fabricating all the necessary stuff as was described at the start of this thread. I'm sure a TBI could be made to work well, but wouldn't be nearly as impressive in the sig.

 

You could always use a 12A Turbo Throttlebody.




I happen to have bought this one off ebay for 27 bucks.

It uses a Nikki Throttlebody, so it "bolts-on" to the stock carb mount.

I plan to have my tuner make copies of the top, so he can make 12A Blow-through kits using the stock Nikki carbs.

There's still no place for the fuel injectors though. As the 2 injectors on the 12AT are on the center plate just like the GSL-SE's.

 

You're a complete moron. The guy wants to do something original and all you do is insult his ideas and try to sell him expensive parts? Ever heard of constructive criticism?

Adam,
I think it's a great idea! I plan to do a project with the megasquirt too, but that's a little ways away for me. I think it would be simplier to put your injectors in the manifold, plus you'll get to use injectors that are widely available. A TPS braket shouldn't be hard to fab up at all, and a fuel rail isn't that expensive to have made if you want to use one. If you did it this way, you'll have a system you can easily upgrade by boring out the venturies and upgrading injectors.

If you want a TBI system then I'd get one of the GM or Dodge units out of the junkyard because they already come with the right kind of injectors and all the electrical hookups you need.

I'd like to see more angles of that nikki and and explanation of what, exactly, you did to it.

 

Well my friend is handeling the conversion of the carb to a throttelbody for me. It was his idea to use one and it was on old worn out carb that he had just lying around. I have a couple more pics that he sent me, I have not actualy looked at it myself.

I think I have decided to ditch the TBI idea and have started building the sandcasting blank for a spacer plate. I will plumb the injectors in as shown in the picture once I get the paice casted. I know this ideas is kinda out there but it is not costing me to much and I just want t see if I can do it.

I was thinking of using 500cc injectors for the secondaries and 300cc for the primaries.

 

another

 

interesting idea there, i have a buddy trying to convince me to go FI, so keep us informed on how you do it and of course how better/worse it is.

 

MAP/engine flow profile will be different whether it's running on 2 or 4 barrels. If the throttle bodies action remained seperate, whether the 2nd set of barrels are vacuum operated (perhaps not good) or mechanically operated (I see more reason this wouldn't be good) or RPM activated (solves lots of tuning issues) where would you source your MAP signal?

I've brought up a bunch of my questions and babbling about this over in the 2nd gen section, "Aftermarket EFI on NA motor" might take a peek and see what you think.

I'd like to keep whatever bottom end the stock 4 barrel type system picks up by running off just 2 runners/ports at low rpm, keeping velocity up...But HOW?

Making all 4 barrels open together from 0-100% throttle would solve many issues, but give up whatever bottom end advantage the stock system might provide. I think the throttle would be very touchy as well.

 

put one injector in each of the ports, in the manifold of course, is better because the way you have it planned it not gonna distibuit the gas on each port. the way im telling you is gonna gave the gas were it need it. for example of were to put them, like the hondas, one in each cilinder. im gonna try to find a pic of what im talking about.

 

1 in each port can be good. Yes, it can solve issues. Not the easiest when we're going for cheap and using existing parts/minimum fabrication.

Most likely my initial setup on my 12A (stock carb manifold like this thread originator's setup) will place 2 injectors in the carb manifold runners. I guess the RX-7 manifold would mean if they're on the outside, that'd be the secondaries, perhaps not what I want to do. The earlier 12A's I believe had the manifold the other way around, true? (2 holes closest to engine on carb flange fed the side iron ports..I could have these 2 situations wrong 100%, but I'm certain I recall mention that the early manifolds were backwards from SA22C/FB manfiolds)

Actually, many max HP EFI engine setups however try to inject fuel as close to the throttle body as possible, for complete vaporization? of the fuel. (Discussed some time ago on either DIY_EFI or Megasquirt mailing lists) Personally I like port/near port as the "dry" manifold is easier to tune for, no falling out of suspension/etc. Manuf's went for port for many reasons like emmissions, low rpm drivability, blah blah blah. Not that I think there'd be enough performance advantage to be worth trying to do it the other way, nearest the throttle body.

R

 

id go with what some one mentioned already and use a SE center plate. The you only need to worry about the secondary injector locations.

 

Secondaries? We don't need no secondaries!

Stock SE injectors ran to 80% duty cycle ought to be enough for most every street NA 12A.

I'd LOVE to have a 13B SE center plate in my motor!Many of us doing the low $ efi swap don't want to tear our motors down to do it.

 

Um, the GSL-SE only runs 2 injectors.. but there is no good way for you to only run 2 with the setup you have..


Either way, i would get a different manifold and TB.. The stock one has TONS of room for improvement. and you could easly pick up a webber manifold (cheap) and then either buy a TWM TB, or pick up an old used webber..


-Zach

 

BTW a map single is easy to get.. just put a port on the intake manifold to one of the runners..



Edit: one more option would be to buy a 12A-13B adapter plate and modify a later engine intake to work with the 12A..


-Zach

 

ONE intake runner wouldn't be the best signal source for a MAP reading. IRTB cars are often setup with vac nipples on each runner, all ganged together for the signal. I'll have my signal feed come from a plenum, question is which one

Did someone say SE's had anything other than 2 injectors somewhere in this thread?

No good way to run 2 injectors...Why not? Just like the SE setup, giving fuel to just 2 of the ports. When I said 2 injectors (SE injectors) I was talking in the context of running a 13B center plate. Then fuel would be delivered exactly like a SE.

I think I can get a modified carb manifold to do well enough. Street ported 12A's with worked Nikkis have made some big power, and I can get a bit more aggressive with things not worrying about fuel falling out of suspension/etc.

"Cheap" and "webber manifold" haven't materialized together for me yet. TWM=big $.

R

 

Well, running a GSL-SE center plate requires a rebuild, which isn't cheap.. and when i said cheap it was not about the TWM, it was about picking up an old webber and converting it.. The TWM is ~300 Retail, so it is not terribly expensive either..


And as for the map single, What is the problem with using 1 runner to get it? ALL turbo RX-7s are done this way..
If you really have a problem with it do 2 or 4 ports on different runers and run a accumulator and get your single from that..



-Zach