Hello,

I have been wondering about timing adjustments and performance gains from the earlier 16 valve cars.

I currently have a cat-bypass, flowmaster exhaust, and k&n filter. I'm thinking of doing the timing because....

I understand that the newer 32 valve cars can gain power by using chips and a cat-bypass on a stock motor and exhaust. 10-20HP I believe. I have read that sometimes removal of cats can result in lower HP's.

Suggestions?

Andrew
'84 928S

 

Oh...the chips on the newer ignition advance the timing I believe and it is said that to get a good gain you by-pass cats.

And loosing HP's by by-passing cats, which I also read somewhere, is said to happen if you don't do anything else but by-pass the cats. I think they were trying to say that you have to accomodate it with something else.

Andrew
<img src="graemlins/icon107.gif" border="0" alt="[icon107]" />

hey...where's all the reply?

 

The chips change the timing and the fuel maps. Removing the cats will allow for better flowing exhaust, and can lean the air/fuel mixture out some. I'd be pretty surprised if removing cats would change the fuel mixture enough to lower the power by more than the power increase from the reduced exhaust restriction though. Ideally you'd want to adjust the fuel mixture after removing the cats to get the full potential benefit of the lowered exhaust restriction. You might get some more power by adjusting the timing too, but that shouldn't really be as directly related to removing the cats as the fuel mixture could be.

 

can you get a chip set for 16v cars? is it user programmable and what kind of hp increase do you expect, at which part of the rev range?
also, does anyone know what is meant by a 'piggy back computer' with respect to the above?

 

I'm not sure if anyone makes a chip set for the 16v cars. Autothority makes what seems to be the most common 32v chips, so that would probably who I'd check with if I were looking for 16v chips. Chips are not user programable. You're stuck with whatever the chip manufacturer programmed in there. Those may or may not be the optimal tuning settings for your particular car, with any other modifications it may have. The chips can provide a power increase, but it isn't going to be much on a normally aspirated car. They make more of a difference on a turbocharged car because they generally increase the boost level. Some people have done dyno tests of the chips on 32v cars, and I think they were getting no more than about 6-7 more hp with them.

While chips are a "one size fits all" approach, a piggy back computer is programable to your specific car and the modifications it has. It can also be reprogramed at any time if other modifications are made to the car in the future. Chips replace the programing in the stock engine management system. The piggy back computers keep the stock programing, but modify the signals that the engine speed and airflow sensors are sending to the engine management computers. By modifying those signals, the ignition timing and fuel mixture can be changed. Tis can be done independently of each other, and at different points in the RPM range.

Two brands of piggy back computers that have been used on the 928 are those made by Dastek and by Perfect Power. Their web sites are at:
<a href="http://www.dastek.co.za/" target="_blank">http://www.dastek.co.za/</a>
<a href="http://www.perfectpower.com/default.asp" target="_blank">http://www.perfectpower.com/default.asp</a>

 

Thanks for all the reply.

I talked to a local dedicated 928 tuner "Dr. Otto" and he said that advance timing by 3 degrees will give good top end and 4-6 degrees for midrange. Tuning in between would be good.

He also recommended a rising fuel rate regulator accomodated with a air/fuel mix guage for tuning. And of course his famous X-cat bypass.

Standalone systems are also good, but how much do those bad boys cost?

Andrew
'84 928S

 

How can you get more fuel from stock equipment? Without adjustable fuel pressure regulators?

 

How can I tell what manufacturer made my performnace chips, and what style they are??

What are the ball park cost for the piggy back's?

John D.
'85 928 auto, Black

 

There should probably be a label with the manufacturer's name right on the chips. If there's nothing there, I'd guess the only way that you might be able to find out would be to be able to read the programming on the chips somehow.

I think that the cost of the piggy back units may have come down some. The guy to get in touch with would be Louis Ott. He's a distributor of both the Dastek and Perfect Power piggy back units, and he knows 928s. His E-mail is LouisOtt@cs.com.