Sameer

Friends,
I was just thinking about the 934. It ran at 1.3 bar or maybe even more using a huge turbo, I think the K31 or maybe bigger and produced about 480-520bhp. Now all this on CIS....hmmmm. How did they manage to do this and keep the engine alive with the limitations of the CIS only upto 480bhp max. Can anyone answer this cause I for one am still wondering how..

AZ930

It was my understanding that the 934 had 2 CIS systems working together....

Sameer

2 CIS systems working together? I seriously doubt that or it's a first to me.

Steve Weiner-Rennsport Systems

934's had a custom airflow meter and FD made specifically for those cars.

Having raced one, they had TERRIBLE drivability and boost lag which only improved after IMSA/TransAM permitted us to update the motor to a 935 MFI system.

Man,...they were really bad,....

Sameer

Steve,
Would you know which custom airflow meter they used?and what did they do to the fuel distributors to be able to cope with that kinda power? There are 934 owners around the world and I'm sure they are running around with this setup safely?
I do have this CIS venturi metering plate I bought off Performance products long time back, how is this venturi plate different? any ideas?

Steve Weiner-Rennsport Systems

Oh yes, its a long-out-of-production 934 setup. Porsche race parts made specifically for that one model,....

The FD was also made for this engine and did NOT run lean at peak RPM & boost. It simply had horrible drivability.

Sameer

Steve,
Thanks for your prompt replies.

So cant these FD be built for our cars? Also any idea on the metering venturi plate I got on my car which was from Performance Products? Isit similar to the 934 venturi metering plate?

Steve Weiner-Rennsport Systems

The 934 stuff is totally different in every way,.................

The street-based CIS stuff has nothing in common with it.

If you look through some books on Porsche race cars such as John Starkey's Turbo book or Excellence Was Expected by Ludvigsne, you'll find a picture of the CIS 934 engine and it will be instantly apparent how different that entire system is.

SoFast

What I think Sameer is trying to get at is the ability to break the HP barrier on his current CIS system without breaking the bank for the EFI conversion.

Steve Weiner-Rennsport Systems

Yessir, I understand that quite well,....

All I can tell you is that the 934 CIS system supports HP up to 500 but none of those components resemble any street Turbo parts and they are long NLA.

There are a lot of different opinions about how much power a production Turbo CIS system can safely support and all I can offer is that I'll not exceed 450-460 HP on our engine dyno, even with a LOT of modifications. The A/F simply goes far too lean to be remotely safe beyond 1.0 bar.

Sameer

Steve,
thanks.

blackboy

Let's say someone is planning on having an engine rebuilt and make it more powerful. If you are going to keep it under 500hp is it better to forego EFI and stick with the CIS, or is there still an advantage to going with EFI?
Also, does cost now become the deciding factor?

goldminer

Here's a dumb question. What's the big deal about running lean? Presumeably it causes engine damage. The reason I ask is that I recently lost a fuel pump which caused the engine to misbehave under boost. Could I have done some damage?

jhunt@huntinter

If I can chime in. 450hp on our chasis (with no electronic aids) is quite a bit to handle by any driver. Even the pro's back in the 934-935 days were intimidated. You go much above the 450hp and you need to start looking at what the factory did to make parts stronger. Machined Titanium gets expensive.

The 934 CIS parts looked the same as ours, but were different inside and they were repositioned in the engine bay... nearly directly over the turbo (no air cleaner needed when you rebuild your engine after each race). The air to water intercooler was a pretty cool setup and allowed for the early whale tails (vs the later tea trays). That is why the front bumber had those big holes next to the center oil cooler.

Steve will correct me if I am wrong here but to "make weight" the 934's even kept the radios and electric windows.

Sameer

blackboy,
You will find a difference between 450bhp CIS and 450bhp EFI. With EFI you can tune much more accurately and run more efficently plus a lot more room for improovement. They are just 2 different ball games.

goldminer,
hard to say we dont know what your AF ratio was while you were running lean when you had lost the fuel pump.