When is Motronic just not flexible enough?
 

Hi,

At what point is Motronic just not flexible enough?

My car's idle leaves a lot to be desired. It's very poor when cold, poor once warmed up, and almost always dies when falling from high RPMs. Drivability is good, but I'm guessing it's not optimal.

I have a 1991 964 engine, freshly rebuilt and is stock, except:

- balanced
- ARP rod bolts
- Andial valve springs
- Euro RS cams
- Autothority MAF
- 6.85 lbs flywheel (connected to 915 transmission)
- no power steering pump
- single belt fan/alternator assembly
- 1 3/4" 914/6 headers w/ dual in/out muffler
- stock DME with Autothority chip & Huntley Racing Air/fuel Ratio Calibrator

Do I:

a) Keep wrestling with the idle speed motor and A/F calibrator until the car runs and idles well?

OR

b) Replace the DME with a TEC3? I think everything for a TEC-3 would be $3500, and I'm hoping I could sell the factory brain/harness/chip for $500, MAF for $500, and A/F calibrator for $500 (sound about right?), so the net difference is $2000?

Thoughts?

-Steve
'74 914 3.6

Also, I must admit that I'm somewhat tempted to go for the Tec3, because I've had a turbo project in the back of my mind for a while... (but that's probably a year off still or so...)

-Steve

I'm a big fan of the TEC-3 - it can be used for any engine with the right sensors and adapters. The trouble is, to get maximum benefit from one of these systems, you need individual throttle bodies. The Motronic intake is good, but not ideal. Tboddies are expensive - tack on another $2500 or $3K.

However, you can make the TEC-3 work with the stock intake runners, and upgrade later on if necessary.

Your 964 engine honestly sounds like it would run better without all of the aftermarket stuff. I suspect that the Motronic chip is not well balanced for the equipment that you have installed.

The TEC-3 is not a direct replacement for the DME - it requires changing out the entire system and installing all new sensors (some can be recycled). It would be cool to tool around with the TEC-3 though...

-Wayne

Steve:

Just to add one man's opinion based on a fair amount of experience with what you are asking,....:)

From your descrption, there is no doubt that your engine management setup, perhaps a sensor, and programming are not doing their job. If you do not need to deal with smog compliance, you are free to seek much better alternatives to the hardware & software you currently have.

If it were me, I would install a six-butterfly throttle body system and a proper engine management system like DTA. No single throttle intake will ever have the crisp, snap-your-head-back throttle response of a six-butterfly setup. Further, this permits you to use any cam you wish (to a point).

IMHO, TEC-3 does not compare to DTA and its a classic "you get what you pay for" situation. :)

We've done some of these engines and the results are very nice to drive,....:)

Steve, I'm not very familiar with DTA. What does it offer over the TEC-3. I've talked for hours regarding the TEC-3 with Rick Clewett, and it seem to be very featured packed. The TEC-2 was missing some elements, but they seem to have been added to the TEC-3.

Also, good point about the camshaft. You must pick a mild cam to use with the intake system if you use it with the stock 3.6 intake (too much interference with the airflow from the 'reversion' from the high-lift cam).

One of the best arguments for an engine management system is that it can grow with you and the car. You don't really need to ever purchase anything else ever again. It can also be moved from engine to engine, or car to car. And from what I can tell, resale values on these is very high (you almost never see them come up used on eBay...)

-Wayne

Thanks for the info.

Wayne, I spoke with Rick Clewett, and I do understand that he has some new sensor maps that lets you use many of the stock sensors. The stock DME 60-2 wheel can be used as the trigger, and the stock knock sensor can be used (although only on one side, whereas the Motronic supports both sides). Stock CHT sensor is used, and if using the stock intake manifold, I believe even the stock idle valve can be controlled by the Tec3. Let's see what else is there...

Steve, I too would be interested in your comparison of the DTA and Tec3. What do you get for the extra $ (I'm not even sure how much extra $ it is...)?

-Steve

Just my 0.02 opinion.................

At what point is Motronic just not flexible enough?

After 550hp you could go higer but is a fine line.............

I can tell you that it appears that your problem is on the chip,that much I can said,the factory motronics is VERY GOOD NOT as good as a EFI aftermarket set up, but good enough to support more hp of what you are making.

DTA for one has a launch control feature, I will let you know as I am installing one of them in my car Pro 8 I know for fact that is far superior than electromotive.

Of course thats just my 0.02