Dyno results - my 930 Sucks! - Page 2

Kevin Stewart · 08-15-2005, 11:15 PM

your right those numbers do suck, I hope you find the problem, Kevin

David · David's Garage

I've seen the bushings on the throttle linkage on top of the engine worn or missing. This limits throttle travel so it won't open all the way.

hobieboy · 08-16-2005, 05:58 AM

Steve,
Just re-read your original post and you said that you abort the dyno run because it was running very lean. If it was a wideband O2 sensor, then I would definitely be checking my fuel mixture & pressure first.

But missing 100hp is a lot more than just fuel IMHO. As everyone said, go back to the basics - leak down, compression, cam timing, etc.

Keep us posted...

vlocci · 08-16-2005, 06:27 AM

Looking at that curve, it really looks like your making no boost, even though your gauge says otherwise. I’de be inclined to find another pressure signal source just for the hell of it, even if you just tapped into the brake booster signal under the hood.

2nd thought is some exhaust restriction or some type. You can eliminate the muffler easily with some cheap elbows to simply exhaust under the bumper for little cost. If your on a dyno, I’de even consider some simple flex pipe of some sort for a quick test. A long long time ago I had a Ford that would not make power due to a plugged up muffler thanks to a mouse that went to twn with some steel wool and dog food. This is easy and cheap and certainly worth trying. If your not running thermal reactors it is probably a safe assumption the headers are OK.

Finally, the jagged curve of the dyno makes me thing you might have an ignition related problem. A MSD 6AL and coil are not too expensive and you may be able to simply borrow one from your dyno guy for a few pulls.

While you in there a compression and leakdown are in order (especially if your already pulling plugs) but if your emissions and 02 curves are decent your probably not running without a cylinder or two.

thabaer · thabaer's Garage

You'd all better check the report numbers again, 440Nm at 4000 rpm is about 184kW ==> ~247hp. Since dynos measure torque and hp is just calculated based on RPM, I'd trust the torque numbers first.

rotorhead · 08-16-2005, 01:10 PM

thaber, that is a terrific point. Although I am too stupid to know what it means.

9dreizig · 08-16-2005, 01:28 PM

I concur with Thabaer!! However if you look at the graph,, 400 Nm takes place at around 145 Km/hr.. with my 930 that's right around 3000 rpm.. What gear was this test run, really need it to do the math correctly or the engine rpm.?? Sorry I've never run a dyno test before ?? but the formula is (Torque x rpm)/9550= KW
HP = Kwx 0.746

9dreizig · 08-16-2005, 02:27 PM

OOPs small brain fart!! just re-read your original thread,, Need to know the rpm ( or wheel size) and apply the formula, 4000 rpm of the motor will not be 4000 rpm of the wheels unless it's close to 4th gear which I think get's close to 1:1..
T

rotorhead · 08-16-2005, 02:29 PM

It was a 3rd gear run

David · David's Garage

Boost should start coming in at about 3500 rpm which is about 110kph in 3rd gear with the 4 speed 930 box. Peak torque hp should be about 5500 rpm or 175 kph which the engine didn't even pull to!?

thabaer · thabaer's Garage

There are lots of valid points already made, except nobody mentioned that funny-looking flat spot from 99-105KPH! I agree that the curve shape doesn't look like the typical older turbo, but we also aren't seeing the segment below 86km/h.

The graph seems to peak at 118kW in spite of the 113kW number in the box, and I based my HP calculation on that point being about 136KPH and the max torque plateau ending there but still about 440Nm.

Do you have any more data from the dyno run on hand ? If not, can you take some RPM vs. KPH points in the same gear to get us a rev/speed ratio ?

rotorhead · 09-05-2005, 03:21 AM

OK Guys the engine is out on the stand and boy I am glad I did.... Things I have found amiss

-----> Vacuum advance line broken at the thermatic valve

-----> 4 of 12 rocker arm shafts have travelled (in the 400mi since rebuild!)

-----> Oil line to turbocharger has a leak.
-----> A foreign object had lodged ( and cleared) the air pump pully wheel leaving scarring on the toothed wheel.

On the good side the leakdown was good with 4%-6% across the cyliders. Cam timing was still on the money (Although I think I will replace the timing chains as a precaution)

BoxsterGT · 09-05-2005, 03:41 AM

Don't put the motor back in the car without addressing the lean mixture. Driving for another 400 miles will burn a piston for sure. And that will really put you down on power.

rotorhead · 09-05-2005, 03:44 AM

I'm going to rebuild the CIS before I put it back in. I will also get some pressure guages onto it once its running

beepbeep · 09-05-2005, 04:58 AM

Air pump is not needed. You can remove it and plug the holes unless your local smog laws prevent you to do so.. You don't need aditional enrichment devices for running 0.8 bar of boost either, OEM CIS is good enough. It will supply plenty of fuel, it's main problem is airflow restriction that it's flapper represents.

rotorhead · 09-05-2005, 05:02 AM

Thanks Goran, the airpump was removed when I put the engine back in last time but I left the pulley wheel on as it drives the turbo oil pump. I agree that CIS is good enough for a mostly stock motor, but I don't understand what you mean by " it's main problem is airflow restriction that it's flapper represents."

Steve

Fl Ted · 09-05-2005, 05:35 AM

How about putting the engine on a dyno and working out the problems before you stick it back in the car??

beepbeep · 05:47 AM

Quote:

Originally posted by rotorhead
but I don't understand what you mean by " it's main problem is airflow restriction that it's flapper represents."

Steve

What i was trying to say is that OEM CIS hit's the floor around 400hp when you start screwing up the boost. There is a big "barn-door" flapper in CIS assembly that measures flow of air. It restricts the airflow somewhat so CIS isn't so performance-friendly once you start tuning your engine.

It's nothing you need to care about if you plan to keep your engine stock though. CIS works good enough up to ~1 bar of boost and 350hp.

Maltese Falcon · 09-05-2005, 07:56 AM

Steve, good to hear you are making progress...it is best to investigate and change out the old "ozoned" vac lines , AND if you haven't yet: those intake gaskets@ the injector blocks too

Some of the hose barb nipples @ the vac. servos break off with time also.
CIS limited to 350bhp ? Check this out from the archives , the 930/71 style single turbo 934 used the CIS for 530bhp/ 430 ft. lbs.Tq. WITH the air sensor plate. This is @ 1.35 bar boost.
I use a derivitive of this on my "Other" Porsche.
photo courtesy Werkphoto Porsche AG
Marty

beepbeep · 08:54 AM

As far as I remember, they had to use special CIS assy's on 934's to get enough flow. Only reason for CIS on 934 was homologation rules. CIS sucked then and still does.