blown 944

Ok so I had a little time tonight (no kid no GF) and went out in the garage to see what I could play with.

Decided to to take anaother look at a BMW TB that I picked up a while back. IT is a 65mm unit off of a 90's 6 cyl IIRC.


I pulled my stock tb and matched it up to the mounting flange and it looked like I could just drill new mounting holes and use teh stock intake mainfold. So that is what I did. Fortunately it had enough meat around the outside of the housing to do this and I went and got some longer bolts just to mount it and before I knew it I had it mounted. I did have to do quite a bit of grinding off the under side of it b/c I have a pretty bigg turbo on here. There was some other misc grindign involved and plugging of a vaccuum port. There was also quite a bit of mesing around with the linkage to get it to work. I'll take some pics of that tomorrow as I am tethering now with my phone.

So here are the pics Of the old tb and BMW unit off the car and the BMW unit mounted


the plate sittign on the old tb yes it is about the same size as teh entrance of the old tb


mounted




Now for the results, gonna make this short since I need to hit the sack.

I had been driving around with the boost at 25 psi and my MAF was putting out about 4.39v depending on the rpms. Well it went straight to 30 psi!!! and my AFRs were way lean due to the Fuel pump I think, I've been carefull to keep the boost down some due to this right now). My MAF voltage went up to 4.57 on the first run.

Then I lowered the boost to be right around where I had been runnign it and the voltage was 4.45 vs 4.39.

Here are some screen shots of the logs.

BTW this is just another benefit of E85, short lean bursts don't kill your engine!!

Second run (umm yeah I won't put teh first due to the afrs being crazy lean )


then reduced boost





compared to:




if you take a look you'll see across the board if is flowing more air even at the same pressure and even less rpms.

Over the weekend I will pull the intake and match port it it has about an 1/8" on one half of the opening as and obstruction. I am also changing out this Fuel pump.

I did all of this in about 2 hrs total and probably about 20 bucks. I still need to get a micro switch to get the idle maps back but for now it is just a little rich on idle and on decel.

boerge

Sid,
Your contributon to the 951 world is highly appreciated, you have done a lot of interesting stuff the last years.

We should raise a fund for 951 experiments and pay for your work and findings.
Great work!

Regards
Boerge

333pg333

Be interesting to see on and off throttle response, and with even larger TB's. Some say to retain OEM TBs to keep a more driveable car rather than a light switch reaction. Wonder at what size you reach this trade off?

Thanks Sid.

nick_968

Is it not more important to retain the progressive linkage/ spring setup so that the size effect is masked? There are 928's running much larger TB's without issues? Or a dual plate TB?

reno808

Very interesting..... gave me some few ideas

Chris White

A couple of notes –

The longer shaft will not fit if you have the master cylinder heat shield in place (and that heat shield is a good idea!)

The stock TB crank was reused – and it is not a ‘round’ profile.

928 throttle bodies have a complex non liner linkage.

TPS is different, fine for standalones or other mods –but the stock ECU won’t like it much!

blown 944

Thanks to all for kind words.

To address a few things. No this is not a mod that can be done to a stock setup unless I were to extend the "d" shaft to accept the TPS.

As far as drive ability ... I just drove it into work and it felt no different than the stock piece in low load. It did seem to build boost a little earlier (could be my head).

Chris, I fully understand what you are getting at. I do have a few things off that the normal car doesn't. I have a blanket for the thousing and if I go to track it you can be assured I'll have some sort of heat shield for the brake parts.

I'm not sure of your meaning regarding the 928 tb linkage and why it is a problem that I have the stock crank? Again it feels fine.

I can get away with not using my tps due to the enrichment being based off pressure and MAF signal. Like I said the only problems right now are idle and decel. I do not have a closed loop setup on here due to using a lean burn for particular rpms and loads.


I would be interested in your response regarding the 928 tb as that will be one of the next things on my agenda at some point.

evil 944t

Sid,

The only real problem with a larger TB is, off idle. A tiny opening with a big butterly, moves a lot of air quickly, which requires a quick a/f adjustment. With a standalone, its easy but, with stock Motronic, not so much..

Also, no need to go larger than you just did. Watch the return spring too. Sometimes, the N/A springs are light and tend to stay open a little and then they will start to "drift open" with boost/rev's. We've tested 70mm+ TB's with no real gains. All they do is become hard to tune.

m73m95

The NA TB is larger than the turbo.

Has anyone ever compared the 2? Are the mounting holes the same?

blown 944

Dave, long time!!

To be honest the way it is tuned it works great. I think the MAF does a great job of compensating. It really does drive perfect. Thanks for the info regarding the size. I have an extra spring that certainly closes it.

Mark iirc the turbo tb is bigger than the Na. It has been awhile though.