My car's going on a dyno tomorrow..

Nathan M · Nathan M's Garage

I've been unhappy with the performance and want to make sure everything's OK. What sort of horsepower should I expect at the rear wheels? (1989 US spec 3.2 Carrera with cat bypass)

The guy doing it isn't into Porsches. What should I ask him to check eg air/fuel mixture?? (what should it be?)

Sorry if this is a dumb question but I'm new to this and want to make the most of my time on the rollers.

Nathan

Wil Ferch · 10-25-2002, 07:08 PM

Hey Nathan:
Never a dumb question...especially if it's never been done before.
You should expect rear wheel hp to be anywhere from 180 to 200..I collect a number of dyno runs on 3.2's and would like to get a copy of your run too. If your car is stock, i will predict about 185-190. Let me know.
You will likely see a dip in torque around 3800 rpm ( going from memory here, my notes are filed away as I write this).
If you have the stock DME set up, there isn't much you can ask the dyno operator. Air/fuel mixture will be all over the board, if under O2 sensor control and if you do both part throttle and full throttle. When full throttle, you will likely be rich instead of stociometric ( say, closer to 12.5:1 instead of 14:1 or so). I would, however, ask the operator that the run be made to print out "SAE corrected" hp. This would normalize your run against a theoretical ambient condition of 70 degrees F, 50 % relative humidity, and sea level ( 14.5 -14.7 psia) conditions. Doing so allows fair comparison to other dyno runs around the country, using the same style machine. Will your dyno be a DynoJet 248C ?

---Wil Ferch

dickster · 10-26-2002, 12:29 AM

i got about 220 crank/190 rwhp.

the same dyno usually measures around 230rwhp for row cars so it should be pretty reliable.

wil,

didn't know you were collecting - i'll have to try and get mine scanned for you. its in damn metric which i hate.

nathan,

its reassuring to know the numbers so fingers crossed for you, good luck!

Nathan M · Nathan M's Garage

Wil, just got back - disaster. The place I went had some antique rolling road - basically the rollers and 2 dials indicating HP & speed (and only went up to 200hp) so sorry, no graph.

First run and the dyno broke before we had chance to get a reading. 15 minutes later and it was fixed. During this time my car was left idling, with no apparent problems. Second (and final) run produced 184 at the rear wheels...

After the first run I commented to my friend how nice it was not to see any smoke from the exhaust as the car was being hammered. After the second run the car was left idling and blue smoke was pouring from the exhaust. The operator said it would clear so I took the car for a quick run, but it didn't. Now the car constantly is burning oil at idle. I've driven home (30 miles) and it's still doing it. I'm rather concerned as it NEVER has smoked before. I'm guessing it's valve guide/seal related as I came down a big hill on over-run and when I hit the gas at the bottom had a cloud of smoke behind me.

I've read all about top-end issues but surely it's a gradual thing? What could have caused this to happen so quickly? Could he have done something to cause this?(overheated the engine).

I regularly hit the rev limiter whlist driving and have never had any problems. I guess it's under no more load on a rolling road than in real driving?

The car performs just as it did before, with no noticeable loss in power.

Could a valve stem oil seal have dislodged somehow? If so can this be fixed with the engine in the car?

Any advice appreciated as I'm now wishing I hadn't gone.

Thanks,

Nathan

Nathan M · Nathan M's Garage

Oh, forgot to add, the temperatue gauge never went above the halfway mark, and it's fairly chilly here today (9 degrees C)

dickster · 10-26-2002, 07:57 AM

what a bummer

but it can't just happen like that. it must have just needed a push....

sounds like valves guides by your description, and an engine out job.

i am sure other more experienced guys can help you.....

Doug Zielke · 10-26-2002, 08:13 AM

"The guy doing it isn't into Porsches. "

That should have been your warning sign.

Milu · 08:19 AM

Most likely it's as the Dickster says and it was just waiting to happen. When mine went sick it happened almost overnight with lots of smoke and loss of power, from perfect to crap in about 150 miles!

You mentioned you weren't happy about the performance so the rolling road might have been the straw that broke the camel's back! Alternatively you might just have a lot of oil in your exhaust that needs to be burnt out. Aside from the smoke how is it running, any worse than before the rolling road, any new exhaust resonance?

Probably best to get it checked out by a Porsche specialist, there should be quite a few in Yorkshire.

Nathan M · Nathan M's Garage

performance doesn't seem to have suffered at all since the smoking started. the reason for having the dyno test (just a simple power run - no tuning) was to determine whether the car was putting out enough power, as it doesn't feel much quicker than my golf Vr6. I guess by other peoples comments it is OK at 184 rwhp and it must be me expecting too much.

i've let the engine cool down for the last couple of hours and just started it and it now idles cleanly?!?! Not even any smoke on initial start up. If it was the guides wouldnt it do it all the time? I'm going out for a run now to see how it goes.

Back later.

Nathan

Nathan M · Nathan M's Garage

Started the car this morning and not a sign of any smoke. Just been out again and given the car an hour long thrashing and it's still clear. Even the downhill test is clear. However, I can't get the temperature anywhere near where it was after being on the dyno yesterday. Could it be the oil overheated (or went so thin it was getting past the valve seals?) It's running Mobil 1 fully synthetic (and has for the last 12 months) but I'm not sure of the weight. Could very hot (very thin) synth. oil cause this problem even of the guides/seals are good, or is that just wishful thinking?!

Thanks for any advice.

Milu · 10-27-2002, 03:02 AM

If the car is now running ok I wouldn't worry. Give it an oil and filter change to put your mind at rest. Synthetics on older engine designs can leak a bit. Try using Mobil1 15/50, usually available from Halfords.

Wil Ferch · 10-27-2002, 02:37 PM

Nathan:
Sorry to hear of your difficulties....
I guess it could happen rather sudenly, but I would try another brand of oil, just as a curiosity stop-gap measure. It might prolong the inevetiable and reverse some smoking tendencies for a while. You may want to try Shell Rotela - T, which has stopped smoking for a number of my other high mileage cars ( 15W-40). Don't know if it'a available in your part of the world.
---Wil Ferch

GeorgeM · GeorgeM's Garage

I just had my '89 on the dyno yesterday. I had it done last year with a cat bypass, modified stock muffler and a generic Autothority chip.

I just installed SSIs, a Monty single out and a chip made by Steve W and the reults were basically the same, about 210 at the wheels. That makes for 247 at the crank using 15% for driveline loss.

I expected more from the SSIs.

I'll scan and post both graphs tomorrow.

George

nostatic · nostatic's Garage

Seems like sometimes it does go quick. Richard LeSchander didn't have the smoke, but did have the oil consumption change almost overnight:

Time for a rebuild...

Wil Ferch · 10-27-2002, 06:16 PM

GeorgeM and others:
I've posted before a summary of reports by Bruce Anderson and others that the peak hp for SSI's can be fairly duplicated by the combination of:
-Porsche pre-muffler in lieu of cat
- chip
- single in/dual outlet muffler mod to standard muffler ( or aftermarket dual-out)
This combo is nice in that it doesn't require re-routing an oil line, and you can easily re-insert a cat whenever you like ( or need to). SSI will still produce a fatter torque curve in mid range...but the two are supposedly close. My personal experience with the pre-muffler set-up comfirms this...200 rear wheel hp from a USA spec 3.2 ...within 10 of your Euro....
---Wil Ferch

Wil Ferch · 10-30-2002, 10:41 AM

Nathan:
Funny how other thoughts pop up when you go over this thread again ...carefully...after giving it a rest for a little while.
I'd be curious to know th eweight of oil used previously, and if it was Mobil synthetic. It seems your smoking problem has disappeared...and maybe you needed to run heavier weight oil. I agree that 15W-50 is likely to be ideal for air-cooled 911's. Again, don't forget the Shell Rotella-T if you go to mineral oil instead...and report back.
---Wil Ferch

surflvr911sc · surflvr911sc's Garage

Is it possible that the oil level was a bit high and by heating up higher than you normally would, it expanded enough to blow oil into the intake? It was just the first thought that went through my head when you said that after it cooled down it no longer blew smoke.

Wil Ferch · 10-30-2002, 12:47 PM

Good point ! : .....
Many people fill to the "full" mark, and when the car gets nice and hot, the excess gets pushed into the intake system, where it makes a mess and burns up. Later, there is an "aha"..and the drill starts all over again. Oil level looks low, fill to the "top". Result? Many complain of high oil consumption when in reality it is not. Fill to the "mid" ( or even lower) mark...and all will be fine. Maybe you'll be amazed at the improved "oil consumption" you now have !

---Wil Ferch

Nathan M · Nathan M's Garage

I made a point of checking the oil when I got back from the rolling road and it was around the halfway mark.

I've checked up on the invoice from the last service and it only says "Mobil 1 Synthetic", but I think in the UK this is usually 0W-40. Mobil also offer a synthetic 15-50 but this is referred to as "motorsport" oil.

Is 0W-40 too thin?

Thanks for you help guys,

Nathan

Wil Ferch · 10-30-2002, 04:02 PM

Nathan:
Although my "gut" says the oil might be too thin...I have to remember that Porsche uses 0-40 for new fill...and that they now recommend this weight for older cars too.
Having said that...I still believe the root cause may have been a "near full" condition..especially since you said you found the car at mid mark AFTER the run. Fine...keep it there, and don't fill further up. Only later, try 15W-50. However, I have run 15W-50 for a long time now with good results.
---Wil Ferch