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1988 TBI question

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1988 TBI question

opus-#002 opus-#002
New User | Posts: 2 | Joined: 12/05
Posted: 12/03/05
01:41 PM

I have a 1988 K-2500 with a tired 305 TBI motor,(200k miles)and was toying with the idea of putting a mild 350 long block in it.I need to use the original TBI system because of emission laws here in NH,and the auto 3 speed tranny is controlled by the TPS sensor.(I know at least the kick-down is).But after looking through a bunch of posts here,it dosen't look like that would be a good idea if I used the original computer.If I get a TBI out of a truck with a 350 in it and install a custom chip in it,would that work?  In all honesty,I'd rather just scrap the whole TBI set up and go with a carb,but I really don't want to loose my kick-down funtion. Any ideas?



oldbogie oldbogie
Guru | Posts: 1195 | Joined: 08/03
Posted: 12/05/05
11:36 AM

This is not that far from doable. Your existing TBI will feed a 350 with a change to 350 injectors and a chip. Actually, if your not doing this for performance where you intend to run a lot of top end RPM you can get by with the existing injectors and just a chip.

There's a several ways you can go at this.

1) an entire 350 TBI injection, with wiring and computer from a wrecking yard.

2)  a 350 computer from a wrecking yard, these should interchange with the 305 the difference being the part number of the chip rolls from the 305 to 350 with a different program this also changes the computer part number.

3) 350 injectors installed in your TBI to get the larger flow capacity the 350 requires. This gets into duty cycle. That's the time the injector is switched on compared to switched off. A 305 injector would have to be switched on longer than a 350 injector so a custom chip would be required to make this happen. The chip is a replacement for the one presently in your computer. The down side is that the 305 injectors are switched on for a longer period which causes them to run hotter, that can shorten their life span. The use of a 350 get around that problem. But there are people feeding 350s using a 305 TBI and injectors and I don't hear of any reduced life span for the injectors.

4) a custom chip for your existing computer, this can be for the 305 injectors on the 350 engine or a conversion to 350 injectors; some of these people can help.


If memory serves, NH along with most, if not all, New England states adapted California standards back in the early/mid 1990s. California law allows engine replacements as long as some guide lines are followed. Here's a JTR link on the subject:

What you propose is quite legal as long as you follow the receipe. Just refer to this as "an engine replacement" not "an engine swap" and you'll be fine.

Now I haven't checked to see if NH requires a trip through a techncial "referee" as does California. If not or even if so, I'll suggest that a 305 and 350 look the same from the outside. I wouldn't borrow problems by  telling the state you took out the 305 and put in a 350 if you don't have to. With the smog gear hooked up and functional, these engines should look the same on a sniffer test. They don't test for absolute amount of exhaust product in cubic feet or pounds, they check for ratios of bad stuff (unburnt hydros, CO, NOx) to benign stuff like CO2 and H2O. So this engine replacement should work for you without any problems.




opus-#002 opus-#002
New User | Posts: 2 | Joined: 12/05
Posted: 12/07/05
05:55 PM

I'm definitely not planning on building a high rev motor.It will probably never see over 5000 rpm. I don't go much over 65 on the highway,and don't use it on the highway much anyway. Summit has a "computer friendly" bump stick for the 350 that's good for "stump pulling torque" as they put it. Sounds good to me.

 I'm not too concerned with the emissions test. I'm certified to do them at work,and don't have to plug it into the tester because it's not an OBD2 vehicle,which start around 1995 or so. Also,even if you fail the emissions side of the OBD2 test,you still pass because the state hasen't agreed on what date to start.Along with the fact that 2005 vehicles no longer use serial communcation at the port,and the new inspection computers can't communicate with the cars,they have no idea what to do.   Smile  As long as I leave the emission stuff hooked up, I'm good to go.

Thanx for the tips!