Throttle body injection IDF's

[garion]

Someone on the Facebook forum was asking about switching from carb to FI, and I posted wondering about the possibility of throttle body injection as a step up from the carb, but not full FI.

In my wanderings, I came across this, a TBI dual IDF kit!
http://www.extrudabody.com/servlet/the- ... ITB/Detail

From what I can tell, that doesn't come with injectors, or a computer, but imagine the sound of dual carbs, with the convenience of FI? Expensive, but could be fun eh?

[vandor]

I put TWM IDF-clone throttle bodies on Jeff's Coupe 5-6 years ago. Whatever we did, they did not make power over 6000 rpm. Tried different manifolds, different headers, different cams, the result was always the same.
After a few years of pulling our hairs out we simply bolted on a set of 44IDFs and the car made power over 6000 rpm. Heck, the rev limiter was set to 8000 rpm and sometime he'd hit it by mistake.
Why bother with individual throttle body FI when there is a proven formula that works?

[sptcoupe]

I might add that the "experiment" included over 180 dyno runs, and the results were amazingly consistent - no power beyond 6000 rpms (although it rev'd beyond that - just no power), and the max RWHP figure was always amazingly close to 138 RWHP, no matter what we did in the way of changes. In fact, you couldn't tell from looking at the dyno sheets which engine produced them. I might also add that the only way we could get it to 138 RWHP (maybe 142 on one or two runs?) with the FI system(s) was to run it rich, which caused premature ring failure in two engines. And the engine we put the carbs on after finally giving up on the FI suffered premature ring failure as well, as it had been run rich while trying to make the FI work (meaning getting all the HP we should given the extent of the mods we did) prior to switching it to the carbs.

After four engines and trying everything we could think of in the way of cam profiles, exhaust headers, intake manifolds, fuel maps and on and on to get more than 138 RWHP, we slapped a set of 44 IDFs on exactly the same engine with the same cams, headers, big valves, HC pistons, etc, etc. I did one dyno pull just to do a sanity check on the jetting and got 152 RWHP. It revs to 8000 readily, and makes HP to 7200 + rpm. And it runs as smooth as your daddy's Buick in everyday driving, and is a real hoot on the track. I'll eventually get it to the dyno and do some pulls to play with the cam and ignition timing, and report it. For now, I'm just having fun driving it and smoking ABARTHS and Minis.

Car manufacturers spend millions in perfecting the tunes for FI motors, with purpose-built/designed intake manifolds, headers, etc. For some reason that we never broke the code on, we found that the 2.0L TCs we built with IDF TBs would hit some sort of wall at 6000 rpms (and we tried some custom intakes along the way - expensive!). I suspect it is the intake design, but we simply could never make the cylinders fill fully above 6000 rpms with the IDF TBs. I just think it is pretty hard for a do-it-your-selfer to really get FI tuned to the point that you are getting your money's worth out of all the other mods, like pistons, cams, etc.

But, 130 +/- RWHP (about all we could get without running them rich) isn't too bad and really wakes up our TCs, and you can get them to be very tractable and run just fine. So I am not saying that one is better than the other - I'm just relating our experience where we mounted a full-on effort over several years and motors to try to make FI really work (again, meaning getting the HP we should, given all the mods that were made). It just depends on what you want. If you don't have big power gains as your objective, then I would suggest not going to the expense and trouble of the TBs, and do something along the lines of what Brad Artigue and Mark Allison and Csaba Vandor might recommend. Use the stock FI, with a mild cam, raise the CR, add a decent header/maybe an intake, and lighten things up (flywheel, pulleys, etc), rather than go to IDF clone TBs, a different ignition, and the process of tuning and the expense of dyno time. You'll have a very responsive, tractable and torquey engine with somewhere around 125 RWHP, or more.

The coupe motor has these performance mods:

2.0L with 85mm cylinders
GC 3A cams
GC tapered valve guides
85mm forged pistons/10.1:1 CR
Curillo forged rods
Big valves
Allison header with 3" exhaust all the way back
Computronix ignition (Allison)
44 IDFs on ported Alquati style manifold
Properly ported/CC'd 2.0L head
Lightened crank, flywheel, pulleys
adjustable cam pulleys (Miller's Mule)
Cold air box system
Tightly regulated fuel pressure system with consistent 2.7 psi pressure

[bradartigue]

It is not a simple task to do ITBs. I see ITB kits here and there (one claims to be only one in the world, laughable), but you'll note the design is just a retro-fit of a carb intake manifold. Take a look at them and then go and look at the various fuel injection manifolds FIAT built for TC engines over the years...very different. When FIAT did use ITBs it was on 1800cc rally cars, and the configuration required a different head (16v in some cases) and the injectors, just like the Bosch L-Jetronic configuration, sprayed horizontally (more or less) into the head. Certainly you can get ITBs to work, but the journey might not be worth the effort, gains will likely be minimal on an 8v head vs. carburetion, and less than a (relatively simple) Bosch retrofit.

Path of least resistance: big Weber (34ADF, 36ADL, 38DGAS/ADL) on 1800cc manifold
Path of moderate resistance: IDFs or DCNFs
Path of higher resistance: retro-fit L-Jetronic on a TC that didn't have it before
Path of never driving your car, but talking about it a lot: ITBs, Megasquirt, etc.

Categories this under "better places to spend $2000" - buy a carburetor, a manifold, camshafts, pistons, adjustable camshaft wheels, and a lightened flywheel. You'll save enough money for beer, have a reliable car, and blow the socks off of the guy who installed ITBs, spent $2000 (at least) and keeps pulling over to reprogram some stupid map in a computer hooked to a car with an electrical system that barely ignites the cigarette lighter.