Gunny Highway

iTrader: (1)

My father's spare car is a 90' Cop Caprice w/ a 350 TBI. Will the TBI unit work on my 305? If so, what modifications would be necessary for it to work?

kevm14

They are the same TBIs!

All that would be useful from the Caprice's TBI are the 65lb/hr injectors.

Gunny Highway

iTrader: (1)

So it's a direct bolt up? The computer won't have any issues?

kevm14

The only problems I can imagine having is a compatibility problem between TPS harnesses. But that's a simple enough problem...should be a direct bolt up, though another 3rd genner might be a better resource than I on this topic...

Gunny Highway

iTrader: (1)

What's the rating of my stock injectors?

kevm14

I think they are 40lb/hr. Some members will disagree.

So I'll settle it this way.

Here are some various color codings that GM used on TBI V8 injectors. Take off your air filter, remove the plugs for the injectors and see what color code you have:

Application: Colour Ident: LB/HR Rating: Part #:

*L03/305 green/white 40# 1712400,5235279

*350-truck orange/black 55# 17112493

*350-L05/9C1 yellow/brown 65# 17112560,17084327,17112412
(1989-91)

*350-L05/9C1 yellow/brown 68# 17100372,17100373
('92-'93)

*454-truck purple 90# 17111784
(1987-'89)

*454-truck NA NA 17112249
(1990)

*454-truck blue/black 80# 17112560
(1991-on)

I don't think there are any other GM V8 TBI injector sizes, also...

Gunny Highway

iTrader: (1)

So basically I would just be getting more fuel, right? What kind of hp/torque difference can I expect from this, or am I just going to take a serious hit in gas milage?

kevm14

You're gonna need some custom programming and change the injector constants at the least. It would run too rich with the bigger injectors and I don't think the ECM has enough "room" to compensate by O2 alone...especially 40 -> 65.

Gunny Highway

iTrader: (1)

Damn it! I knew this was starting to sound too easy.

kevm14

Raise the fuel pressure!

alohamike

so, at what point, modification wise, do the stock 40# injectors become unable to provide enough fuel? If I just swap in a mild cam and pick up say 30-50hp, do i need to move up? I guess I'm looking for a recommendation at what hp/torque level should each of those injectors be used?. Flow wise, a 305 can only flow about 400cfm at 85% efficiency so the stock TB should be plenty for almost any application. So, it would seem that as your requirements to feed the increased power go up, one should just have to find an injector that can provide enough gas.

kevm14

Let me put it this way...is there a pressure that will force enough fuel volume through the injector opening during each pulse to help you make the max HP your engine is capable of putting out? Absolutely there is.

Now it gets complicated...there are two issues: programming/drivability and the injectors themselves.

Depending on who you talk to, the peak & hold TBI injectors work great at 20-30psi levels (and possibly beyond). Others say once you get to the low 20s, you should upgrade (or don't even try to compensate for small injectors with higher FP - just upgrade outright). I'm not sure where the truth lies.

But I can definately tell you that the car won't run right if you simply buy a static FP regulator and crank it up to make the 40 pounders put out the fuel at WOT and high rpm...the low rpm/low load/idle will suffer immensely. You need some sort of vacuum compensated regulator. Now your sweep needs to be the 10-15 range at idle and high vacuum to 20+ at WOT...some say it's hard to compensate for that in programming.

This is probably why the favorite thing is to upgrade the injectors. Especially since, theoretically at least, when making significantly more power than stock (i.e. enough to be considering an injector upgrade) you should PROBABLY be custom programming anyway...

That's my $0.02.

PS. according to my calculations, raising the FP from 11psi to 25psi in a stock L03 should allow enough fuel flow for ~255hp @ stock-like duty cycles (not 100%).

Gunny Highway

iTrader: (1)

Well, as you can see by my sig, I'm not exactly making tons of power just yet. The whole point of this, was the fact that I would like to send off my TBI unit to get the ultimate mods done and was hoping that the TBI unit off of the 350 would suffice until I mine got back.

That being said; if there is going to be computer issues, then I'm not even going to try it. I'll just see if I can get the other car running.

kevm14

Oh......
You know you can just pull your injectors out and put yours in the Caprice's throttle body!!!

alohamike

So, if I were to tap my o2 sensor with a voltmeter and then adjust the fuel pressure to be .950mv at PE/WOT, I should be OK? If the injector can't pass enough fuel to get the .950, then I probably need a bigger injector? That seems to be the conservative way to dial in the right injector/pressure setting with just basic tools...maybe?

AdmiralNahohkta

Just put it on and see what happens. It only takes like five minutes to swap throttle bodies.