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250 I-6 Injection

Hossbaby50

Hossbaby50

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I am currently debating 2 different ways of injecting a 250 I-6 motor that I want to run in my rock buggy build. I want to hear your opinions on what you think.

My options are Holley Pro-jection, or TBI from a 88-92 Chevy Astro van 4.3L with megasquirt injection.

I like the holley because it is a complete kit ready to run with all new components for just under $1000. I like the megasquirt w/ GM TBI because it is totally programmable but the components will be used and the system will probably need to be rebuilt which will probably cost in the $1000 range or more and balance out with the Holley setup in price.

What are your opinions.

Harley
 
Why not just get the whole system out of an Astro Van or S-10?

A throttle body, computer, and wiring harness can be had for $100.00 or less. Throttle bodies are cheap to rebuild as long as the throttle shaft is still tight, in fact most of them can be cleaned and run as is. Computers are quite reliable (especially the 7747 ecm) and the harnesses are fairly easy to clean up and make work on an inline motor.

I've injected several jeeps with the 258 doing what I just described and the stock 4.3 chip works perfectly, the hardest part is making an adapter to bolt the throttle body on the stock 2bbl intake.

I'm pretty sure it wouldn't be any different on a Chevy 250 other than most used a 1bbl intake and would be difficult and inefficient to adapt to that. The other advantage with using a stock tbi computer is having computer controlled timing is quite a bit easier than the other options.

Bottom line is a GM tbi setup can be done for under $350.00, that price includes new sensors and an inline fuel pump. If you wanted Painless makes a harness for around $250.00 that will save some time. I will bet the stock 4.3 chip will work just fine, but worst case you have someone burn a chip and that would be around $150.00. So worst case you'd be $750.00 but you'll be able to go anywhere and buy parts for cheap if something fails.
 
You can get a Clifford 4 barrel intake for the 250s and 292s, just use a 4 barrel to TBI adapter on top of that, and you're ready to rock and roll :)
 
Another vote for TBI. TBI is good in one respect, which is also one of its flows, its stupid. It has no idea, nor does it care a whole lot, what that throttle body is sitting on top of. It just needs to see Vaccuum, TPS, and O2 sensor readings, and you are good to go. If anything I would expect it to run better on a I6 because it would have a chance to get more cylinder sampling with a single exhaust pipe(if you don't have a dual exhaust header).
 
Is the MAP sensor with the TBI need to be plumbed into the manifold or just need vacuum somewhere? I had thought about straight TBI but I wasn't sure if the 250 was close enough to the 4.3L to have the computer work with the 250 I-6. I know the CID is close but not exact.

Bolting the TB up shouldn't be the problem because I planned on using a Clifford or Offy 4brl intake anyway.

So to run TBI how do I plumb the MAP sensor? How do I make the computer control the timing? I plan on using an HEI dist. on the 250 but I am not sure that the HEI on the 250's is compatable with timing control from the computer.

How bumpy of a cam will TBI take? I am thinking about running a 252 or 260 cam in the motor.

Harley
 
Another thought.........................

I read on 67-72 Trucks that GM MADE tbi 250s, for the export market (Mexico). Wonder how hard it would be to find one?????
 
Good point. You could probably just make one with the guts from either an early FI 4.3 or 2.8L.
 
With regards to your questions about the MAP sensor, timing, and camshaft:

MAP sensor just needs an intake vaccum source. Draw off the baseplate of the throttle body, or drill a hole into the intake and thread a nipple in.

Timing, this would probally be the biggest challenge. First thing I'd do is see if the distributors are different between the inlines and the V6s, if so, next thing I'd do is see if you can stuff the guts from a V6 big cap HEI from an early TBI rig into a regular inline HEI from a mid 80s rig. If that can't be done, you'll probally have to look into an aftermarket ignition system then accepts EFI control, like an MSD or something.

As far as a camshaft goes, the key for EFI is a nice smooth running engine. You want as little valve overlap as possible, becuase the fresh oxygen that can make it straight into the exhaust causes the O2 sensors to read wayyy off and totally mess your ECM up. Your goal is usually to have a fairly short duration, and a fairly wide LSA

I also imagine that your knock sensor wouldn't work properly in the inline engine, so you'd want to keep an ear open for pinging.

Otherwise, the 250 (4.1L) and 262 (4.3L) are very similar in displacement, and both make strong vaccum signals, which means they will have very similar fuelling requirements. If you had a camshaft that was good for EFI, I imagine you'd be able to get away with a stock 4.3L V6 chip to run a 4.1L.
 
From what I learned while gathering parts for my 292 TBI motor the factory system will work even though the cubes are slightly different.
As for the dist. I remember being told that towards the end of the 250/292 production run they came with the spark advanced dist. in California only.
250's made in Mexico and farther south did come with TBI but I was never able to locate a intake for one.
All that I have been told is that a cam with those spec's will not run correctly but I have heard of several motors running grinds with a 110 L/C and getting away with it . I know I did not answer any of your questions but I hope this info might help shed some light on the subject for you .

Tom
 
Trust me everyone's advice and comments are paying off alot. Between the info I am getting here and on a Inline 6 cylinder board I am figuring alot of cool stuff out.

Right now (I may be wrong) I am thinking I can use a stock GM TBI setup off a 4.3L & a Califonia Emission distributor from a '84 250CID motor and be setup on all the parts I may need. I am trying to comfirm this but if that is all that is needed (beside the fuel pump, wiring, etc) then I am set. I am going to have to start piecing together a TBI system if I am correct (am I usually wrong though :doah:).

Harley
 
Sounds like you've about got it figured.

As far as the camshaft goes, I really can't tell you, since I have no idea how an inline engine behaves with different cams...

Maybe hit up the guys on the I6 board, and ask what would produce a smooth idle, with high vaccum signals, and very little valve overlap.
 
You don't need any special HEI distributor any old one will work. Just lock out the advance with a couple of welds and leave the vacuum line off of the vacuum advance.

The pickup will wire directly to a TBI ignition module (observe polarity) and everything else is plug and play. Can't get any simpler than that.

The camshaft is a little big for a stock chip. I'd recommend you stay under 205 duration (@ .050") and keep the lobe center in the 112 -114 degree range. Small motors are a lot more sensitive to camshaft selection. A largish cam or narrow lobe centers can hurt idle vacuum to the point where it'll take a lot of messing around with the chip to get it to idle decent.

Now get down to the salvage yard and get you a TBI setup and get it done!!
 
I don't even have the motor to put the TBI on yet, I just know I am going to run a 250 so I am researching it now so I dont have to later. I am currently looking for an older non-integral head 250 with a solid bottom end so I can start gathering the parts for the motor and get it built. The sooner I get the majority of the parts the sooner I can start building the buggy. :D

So from what your saying this would probably be a better cam choice to get the TBI to idle ok.

http://www.compcams.com/Technical/Search/CamDetails.asp?PartNumber=61-232-4

Harley
 
That cam should work just fine. Crane makes a couple of cams that are a dual pattern (more exhaust lift and duration) that work better if you keep the stock exhaust manifold.


Good luck on your search for a usable motor. You may end up having to buy a whole car to get a decent runner.
 
I vote for TBI also. Keep in mind that Holley injectors are slightly better than warm crap and are typically not simple to ID and get correct replacement parts on the first try.
Been there trying to help customers out--eventually got them, but it wasn't quick or cheap.
I still have some miscellaneous I6 parts left (not sure what or how much), but stuff that might come in handy. If you're interested, let me know when you find a motor and what you get with it.
Might check over on the 67-72chevytrucks board. See I6 stuff once in awhile.
 
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