Detonation in a 3.2SS

[GBStu]

Gents,

I have my engine back together (new #3 piston and all new rings, I have about 200 mls on the engine)

I've adjusted the warm pressure to get the desired AFR, the graph below shows a couple of WOT runs I took tonight. What do you think about the graph below...specifically the AFR from 3000 rpm to 4500 rpm.



Thanks, Stu

[Steve@Rennsport]

Were those runs done at WOT?

If so, looks too lean to me from 3K to 6K.

[GBStu]

They were WOT runs in 2nd gear.

Any idea why the AFR drops at 5600-6500 so much?? I have CIS injection.

I'll drop the WUR control pressure a couple of psi and re-run tomorrow.

Thx, stu

[Steve@Rennsport]

Originally Posted by GBStu

They were WOT runs in 2nd gear.

Any idea why the AFR drops at 5600-6500 so much?? I have CIS injection.

I'll drop the WUR control pressure a couple of psi and re-run tomorrow.

Thx, stu

This is pretty typical of CIS and illustrates one of the difficulties with modifying these things.

Although long unavailable, an ROW Carrera 3.0 FD & WUR would really help. You may be able to find these components with some dilgent and persistent searchs both in Europe as well as here. At the very least, an ROW early SC FD & WUR will also help.

[GBStu]

Is the fundamental issue the control pressure regulator (WUR) will not flow sufficient fuel, thus, at the higher RPM's (>5700rpm) the outlet pressure drops and the mixture richens?
Stu

[tom1394racing]

Have you tried to richen the fuel distributor itself by adjusting the mixture screw?

[Porsche84]

I had very similar issues 5 or 6 years ago. The bad news is that I ruined two motors before I found the problem. The problem was that I inadvertently closed off the gas tank vent when removing some smog stuff (track car not street in case the Feds are reading). My engine shattered the top ring on brand new euro Mahle pistos and new cylinders. You need to verify that you have a good tank vent. Check to see if the tank has collapsed, that is the first clue.

Good luck

[Steve@Rennsport]

Originally Posted by GBStu

Is the fundamental issue the control pressure regulator (WUR) will not flow sufficient fuel, thus, at the higher RPM's (>5700rpm) the outlet pressure drops and the mixture richens?
Stu

The fundamental problems are that in most cases, the FD doesn't flow a sufficient volume of fuel for modified engines and the control pressure doesn't go low enough to get the most from the FD.

In some cases, we shim the system pressure (at the FD) to the top limit and use an electronically-controlled WUR to get a better handle on control pressures from cold to hot.

The stock WUR's are somewhat frustrating since its difficult to get proper AFR's without overfueling near and at idle. Its akin to squeezing balloons.

[GBStu]

Adjusted the warm pressure to 33psi, see WOT plots below. From what I've read, this seems about as good as I can expect.

What's interesting, the WUR warm pressure spec for a stock 79 is 39-43psi (no vacuum).



Thanks for your help, stu
PS, will be with ARPCA at Mid Ohio this weekend

[Steve@Rennsport]

Although a tad rich for making max power, that red plot ensures your engine will live provided your ignition timing isn't too aggressive for the fuel you use.

A digital WUR would allow you to fine tune that AFR curve to get best performance without compromising reliability.

[KNIGHTRACE]

set timing right, and check deck on al 6 cyls and it will answer itself.