Modifying a carburetor intake to fuel injection- is it worth it?

I’ve got this idea brewing in my head for a turbo V8 build that would be on an older engine that lacks any kind of fuel-injected intake, and would have to run a throttle-body style injection setup to avoid the problems with carburetors- but I know these can have problems with tuning due to the cylinders not receiving a metered dose of fuel.

But then I started finding threads where people drilled and milled carbureted intakes to accept injectors. I have little experience with metal, but I know aluminum is soft and I have access to (woodworking) drill presses and jig materials. How feasible would it be then, to try and drill mounting provisions for injectors and fuel rails into a manifold, assuming I find rails that are the right length? Do injectors require special positioning in the airpath to work properly? Or are throttle-body based injection systems good enough that it would be a waste to try and build an MPFI setup like this?

Ive done this on an edelbrock victor intake for a small block mopar. 

Angle the injectors at the valve as close to the valve as feasible. Buy the aluminium bungs, and have them tig welded in. You can buy ubdrilled fuel rails and the special bit to make them whatever you need.

What engine are you working on?

I have converted two "primitive" motors to efi with tbi style units. I did so because the siamese port layout did not allow port injection.  Either due to lack of space or charge robbing issues. 

The tbi setup properly tuned was a huge step up in performance, fuel economy and all over drivability over the carburetors it replaced.  Tuning around the inevitable wall wetting and puddling issues was almost a non issue.  My only issue was finding an injector that was able to supply enough fuel at peak power but could still reliably provide the tiny amount needed to make a sub 1 liter motor happy at idle and low load.

As far as modding an existing manifold for individual injectors, that would be optimal if possible.  Just point them as close to the back of the intake valve as you can. I have seen a lot of setups like this

It is easy enough to do and It gives you the option of sequential injection and makes injector sizing so much easier. 

In reply to Dusterbd13-michael :

It'll be some kind of AMC motor, likely either a 304 or 360 due to my own money limitations. 

In reply to Jumper K Balls (Trent) :

Thanks Jumper! Good to know TBI is better than I think- I'm learning from DIYAutoTune and their article on the GM throttle body also has me wondering about it just for cheapness and ease of wiring.

For a boosted motor, would a single plane be better since the airflow won't "matter" due to the compressor?

I couldn't quickly find one, but i sweat there were some chinese single planes with injector bu gs on eBay a while back. 

GIRTHQUAKE said:

In reply to Jumper K Balls (Trent) :

Thanks Jumper! Good to know TBI is better than I think- I'm learning from DIYAutoTune and their article on the GM throttle body also has me wondering about it just for cheapness and ease of wiring.

For a boosted motor, would a single plane be better since the airflow won't "matter" due to the compressor?

Single plane will be fine for two reasons:  First, as you pointed out, the forced induction will cover some sins.  Second, the reason single/dual plane is such a big deal with a carb is because the runners are carrying fuel suspended with the air.  For reasons of maintaining the fuel suspension and the additional mass of the flow means that the manifold style has a bigger impact on the powerband.  If you're doing port EFI and a hair dryer, your big goal is to get the air there.  That is to say, yes, you need a manifold, but the design has a lot less effect without fuel suspended in it.

As I have mentioned, the  TBI units work just fine. What they do not do is provide any kind of a short-cut to the EFI learning curve.  And once you do start to come up on the curve, you learn that a lot of the data tools that you would like to have are not availble on the Fitech or Snipper cause they were designed for people who would not be interested.  But they do work, off to drive mine right now. And berkeley with the settings of course!

This discussion on an AMC board indicates Edelbrock is working on an AMC intake manifold that is EFI ready: http://theamcforum.com/forum/new-efi-intake-manifold_topic91226_page1&SID=38435-5ee2661d2fbfe829839a6989236111.html  Sounds like it is anticipated to be released soon.

NOHOME said:

As I have mentioned, the  TBI units work just fine. What they do not do is provide any kind of a short-cut to the EFI learning curve.  And once you do start to come up on the curve, you learn that a lot of the data tools that you would like to have are not availble on the Fitech or Snipper cause they were designed for people who would not be interested.  But they do work, off to drive mine right now. And berkeley with the settings of course!

So I take it things like an AFM or measuring delta are not possible with those aforementioned EFI systems? I mean, it makes sense but it's kinda funny to me if they had absolutely NO provisions for them at all.

Anyways, the AMC forum boys also informed me that in a few months there's gonna be another TBI setup- I seriously doubt I have the money, but options are options all the same.

In reply to GIRTHQUAKE :

Fitech and Snipper are MAP devices, so AFM does not become part of the vocabulary.

If you are sophisticated enough to even know what 3D fuel maps are, then the TBI systems are gonna bore you .and or frustrate you.

The honest to god truth is that the Fitech and Sniper should work out of the box with very little berkeleying about. If it does not, then your best bet is to start your tuning by investigating the engine parameters and the install. However, the weakest link is the buyer...Most TBI buyers bought the thing because they were not savy enough to do these two things in the first place, and they launch into pushing buttons on the interface. The hillarity starts there with Stupid TBI being uttered.

. 

Pete

Sorry, I always confuse MAP and AFM.

So far it seems like the real question for me is one of price first, tuning second. These EFI systems are running $1,400-1,600 in my studies, but my plot for drilling and making a multi port injection manifold will be half that- heck, for the total parts, a megasquirt ECU and even buying a cheap welder to work with aluminum it still could be less than buying brand new.

Are GM 454 TBI units still available for non-insane money?  One of those, a carb box for boosting duty, and a Megasquirt of some sort seems like the bones I would start thinking about if it were my project.  Never done this, don't know anything beyond what I read around this forum, grain of salt etc.

pres589 (djronnebaum) said:

Are GM 454 TBI units still available for non-insane money?  One of those, a carb box for boosting duty, and a Megasquirt of some sort seems like the bones I would start thinking about if it were my project.  Never done this, don't know anything beyond what I read around this forum, grain of salt etc.

So from what I've found, that kind of setup- along with a HEI dizzy- could work real well as a damn cheap alternative. The real problem would be finding one, junkyard or otherwise. A lot of the handmade fuel injection websites I find are from the late 2000s when you could still find this stuff, but now I think i've seen one 454 in my local yards in years.

Problem with using a GM tbi setup in a boosted app is you will be pretty limited on how much power your fuel injectors can support. Any boosted v8 would hit that max in single digit boost. Not that it wouldn't still be a fast car! 

In reply to Vigo :

Yup! But it's still far better than nothing, and for the cost and advantages of FI it would still be better than a blow-through boost-referenced carb, at least in my opinion.

In reply to Vigo :

Then add cold start injectors Gus Mahon style.  Just kick them at whatever boost pressure it starts to go lean.

It would be kinda nice if someone just made an injector plate to go under a carb. Basically the fuel section at the bottom of the aftermarket TBI systems without the throttle plates, sensors, ecm, etc etc. You could basically just stick it under a carb like a spacer plate, unhook fuel from the carb, and it would more or less turn into tbi without any of the limits of OEM tbi systems and without changing anything about your linkages or filter/intake setup. Basically a nitrous plate with an actual spray pattern.

It’s funny but I’m thinking of going the other way.  TBI in my 86 Nissan to a Weber carb.  It started running really rich and a very good mechanic (in his mind) could not find the problem.  I seriously don’t think he put much effort into looking.  

Vigo said:

It would be kinda nice if someone just made an injector plate to go under a carb. Basically the fuel section at the bottom of the aftermarket TBI systems without the throttle plates, sensors, ecm, etc etc. You could basically just stick it under a carb like a spacer plate, unhook fuel from the carb, and it would more or less turn into tbi without any of the limits of OEM tbi systems and without changing anything about your linkages or filter/intake setup. Basically a nitrous plate with an actual spray pattern.

The trouble with that approach is that your fuel distribution will look like it came out of a random number generator. We've tested a number of throttle body injection systems that used injectors below the throttle bores, and the results were worse than an OEM TBI - which was in turn significantly worse than port injection.

GIRTHQUAKE said:

But then I started finding threads where people drilled and milled carbureted intakes to accept injectors. I have little experience with metal, but I know aluminum is soft and I have access to (woodworking) drill presses and jig materials. How feasible would it be then, to try and drill mounting provisions for injectors and fuel rails into a manifold, assuming I find rails that are the right length? Do injectors require special positioning in the airpath to work properly? Or are throttle-body based injection systems good enough that it would be a waste to try and build an MPFI setup like this?

Fuel rails are an extrusion, and you can get them in any length you please. Or even use extruded square tubing with end caps welded on.

While theoretically injectors should be aimed straight at the back of the intake valve, in practice, just try to get them pointed downstream. I've seen all sorts of non-ideal targeting made to work, both on aftermarket and OEM intakes.

As noted above, I haven't been very impressed with TBI fuel distribution.