LA3 vs LB3 (yes I have searched already)

[smoke3006]

Like I said I did search on the subject (both here and on TurboFord) and found information on these computers. However some of the information is contradictory...

So from what I've gathered so far:
The LA3 is meant for a 5-spd.
The LB3 is meant for an auto.
The LB3 can be used with a 5-spd.
The LB3 is more aggressive in it's timing settings due to assumed lower boost levels.
The LB3 is set to use lower boost, but a MBC makes that a moot point.

Now for some fuzzy points:
The LA3 can be used with a tuner, but the LB3 cannot? But then some people say that the LB3 does work with a tuner...
A few posts list evidence that pwer was lost after installing a LB3, but this seemed to only be one or two people siting their experience...
The LB3 when used with a MBC can create leaner conditions then a LA3...

I have an auto '86 XR4TI that I'm going to be putting a T5 into. From what I've read I need to change my computer out as well and most people suggest the LA3 (along with a big VAM).
Someone offered to sell me a LB3, but I don't want to spend $50 on a computer that's going to work against me.

What are peoples thoughts on this?

[MerkXRTurbo]

You don't HAVE to swap it out... but is definately preferable.

Also, I have no idea how the two compare.

[John Brennan]

And don't forget the PE!

[smoke3006]

And don't forget the PE!

Of course....



What's the PE??

[DPDISXR4Ti]

So from what I've gathered so far:
The LA3 is meant for a 5-spd. Correct
The LB3 is meant for an auto. Correct
The LB3 can be used with a 5-spd. Correct
The LB3 is more aggressive in it's timing settings due to assumed lower boost levels. Wrong (see below)
The LB3 is set to use lower boost, but a MBC makes that a moot point.
Too many different ways to answer this one
The LA3 can be used with a tuner, but the LB3 cannot? Wrong

First off, there is no REQUIREMENT to swap PCM's when swapping a C3 for T5. The various Turbo Coupe PCM's are calibrated for the Big VAM and having an IC present, so you probably want to have that covered before thinking about doing the PCM swap.

The timing for the LA3 is marginally more agressive than a LB3, and the fueling is a bit richer. They are very close however. I'm not sure about boost, but as you indicate, that becomes a total non-issue if you go with a MBC of any sort.

PE is the '85.5 / '86 Mustang SVO PCM, and had the most agressive timing tables. It's also a drop in replacement in the XR (no re-pinning required). It's also the most expensive, routinely going for $150 or more. If you're thinking about going with a Tuner, don't bother with any of this. Your PK calibration can be changed so that it effectively looks like a PE.

[smoke3006]

Firstly, thanks to everyone whose responded so far.

First off, there is no REQUIREMENT to swap PCM's when swapping a C3 for T5.

Oh I misunderstood this. I was under the assumption that the stock auto computer won't work correctly once the T5 was installed.

My main concern is of course to avoid lean conditions as I increase boost. That being said I didn't plan on really going beyond 20psi, more like running 15-17psi normally.

So far my engine mod plans were:
MBC
BOV or BPV
FMIC (not sure of what type yet)
Ranger roller cam
Big VAM

This is in addition to maintence/repair considerations (I'm replacing all gaskets for example).

So if the LB3 is ok for this appilcation I might as well buy one rather then fighting for a LA3.

As far as a Tuner is concerned I wasn't planning on using one, but I figured I would look at a computer that had the capibilites for one just in case.

[smoke3006]

Oops I forgot to ask if the installation of a LB3 is the same as a LA3?
I did purchase an ACT already...

[DPDISXR4Ti]

So if the LB3 is ok for this appilcation I might as well buy one rather then fighting for a LA3.

Have you checked to see what are LA3's going for? They shouldn't be that rare or expensive. Over the years, I know I've sold a few for $50, maybe less. It's not a big issue one way or the other - I've run the LA3, LB3, and 8UA, and you really can't tell a difference between them. They are readily interchangeable (answering your question above).

[thesameguy]

I may be screwed up here, but -

Isn't it true that the auto XR has less aggressive initial timing and less boost than the manual cars?

Any idea why they reversed the timing decision on the TurboCoupe?

And, what the heck is an LA2?

[vcallaway]

I think the LA2 is from the 86 Tbird.

I'm getting ready to swap my EEC out. The plan is to use it with the tweecer ( www.tweecer.com ).

I've picked up several LB3's for $25 - $35. In my opinion they are a bargain. From the maps I've seen I cannot tell the difference between the LA3 and the LB3. I originally went looking for the LB3 as part of an A4LD swap for one of my cars.

Since I'm going to be changing the tables the choice of computer came down to processor speed and the larger tables of the L series. The base mapping was not as critical to me.

Like was stated, the PE is the most agressive in it's mappings of the big vam computers. It is also going to cost more money. I have a couple on my shelf and would not sell them for less than $200 each. Mostly because they are hard to come by.

If you are not going to change out the VAM the PF3 is the best computer to use. It is the most agressive in its mappings. It is also just plug and go. You can usually pick one up for $20 or so. I have a few of them if you want one.

[Whatchamacalit]

even though this is slightly off topic and is in other thread I just wanna make sure I got this right. The MegaSquirt setup completely replaces the chip, whatever it maybe, currently in your car?

[DPDISXR4Ti]

I may be screwed up here, but -

Yep, you are.

Isn't it true that the auto XR has less aggressive initial timing and less boost than the manual cars?

Yes, this part is correct, although the difference in timing maps is minimal. The performance difference is primarily a result of 10 lbs vs. 15, when using the stock BCS setup.

Any idea why they reversed the timing decision on the TurboCoupe?

They did not. Who said they did? But again, the difference in timing maps between the auto and 5-speed PCM's is negligible, and thus NOT a significant factor in any performance differences.

And, what the heck is an LA2?

LA2 was found on the earliest 5-speed '87 Turbo Coupes. I actually just stumbled across the first one of these I've ever found, just this week when I stopped at the junkyard on the way home. I left it behind.