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Q: I am going to be swaping out my stock '85 XR4 EEC for a 87/88 TC EEC. Would putting in an upgraded computer chip into the TC EEC be overkill?
A:
Yes, and a waste of time. There's lots of differences amongst the EECs for turbo motors.
We'll focus on drag racing here, with drivability a secondary consideration, and rate the
available processors (EECs).
#1 85.5 SVO PE
UNPLUG THE KNOCK SENSOR! Runs hard, sometimes wants to detonate at 3500 rpm. Constructed
of unoptanium. I've only ever SEEN 1.
#2 86 SVO or any reman PE processor,
UNPLUG THE KNOCK SENSOR! Runs just as hard, yet smoother. Detonation free to beyond the
limits of the stock turbo.
#3 87-88 Turbo Coupe 5 speed.
The same year automatic processor may actually be just as fast, but no evidence yet. If
you have an 87 and up A4LD automatic, you have no choice. Use the 87-88 TC automatic
processor. Both of these require major rewiring to go into any other turbo car. It's not
difficult, you just move pins in the EEC's 60 pin connector. You MUST add an Air
Charge Temperature (ATC) sensor, by drilling and tapping the intake manifold. This
processor has much nicer drivability than the others, because of 2X processor speed, 2X
ROM size, and evolutionary development improvements.
Note: Internet gossip reports that a Superchip doesn't make any of the above processors any faster. They do raise the rev limit, though. But it doesn't make economic sense to spend $300 on a PE and then $300 more on a Superchip.
Now, the other side of the coin. Let's say you have a 1985 Merkur XR4ti and you want to install the larger VAF meter. If you have an intercooler installed, you can get a Superchip that plugs into the XRs EEC, but has the air, spark, and fuel tables for the SVO's intercooled engine. This works good, and saves you money over buying a PE, and you get the 7Krpm rev limit in the deal. I use these often on XRs. Supposedly, they are the SVO PE table with the rev limit changed and some other slight changes.
Note: DO NOT expect mucho more HP from a "chip".
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************** SO, if you have a Merkur XR4ti, any year... ***********
***** or any other car with the small VAF and 35 lb injectors *******
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You can do one of the following:
1) SVO PE EEC and big VAF, does not require rewiring
or
2) 87-88 Turbo Coupe EEC and the big VAF, requires rewiring
or
3) My custom Superchip with the big VAF, does not require rewiring
If you're not gonna change the VAF, then don't bother changing the EEC.
The SVO PE has the most aggressive, least elegant programming. I
sometimes have these for sale, used.
The TC EEC has the best drivability, and is available cheaply. Probably $50-150, used or
remanf.
The "Hybrid" Superchip is basically the PE programming but with a bit more fuel
and spark, and a rev limit raised to 7000 rpm.