I did a base line run and would like to get some feedback on the more informed among us (Meaning, I'm too dumb to interpret this data correctly.

I did a dyno run yesterday and peak numbers are respectable.
Power = 248.9 HP
TQ = 228.4 FT-LBS

Car: 1995 993
Miles: 62,xxx
Recently did Plugs, wires, rotors, caps and transmission service.
Used Beru wires, Bosch plugs, rotors and caps.
Transmission service was with Royal Purple 75w-90

The car pulls strong, but I am wondering how to smooth the oscillations shown on the graph from 5k RPM to 6k RPM.
Is this normal? The guy at the speed shop mentioned that mis-gapped plugs may be a contributing factor.

Any ideas?

Thanks in advance!

 

Hi Scott:

I'd concurr that the results look very good,...

I would have also preferred to see an air/fuel graph on there to see what your fuel mixture is. That kind of information is invaluable in this context.

Questions:

1) How many runs did you make?

2) Was this chart the 11th one?

3) What kind of room is the dyno in?

4) What kinds of fans were used?

5) What were the oil temps at these final runs?

Your replies to the above would help confirm what I am seeing on the graphs.

 

I did a Dyno yesterday as well - here is the text of a post I made to our local PCA board. My car is a 97 Carrera S - with ~70k miles.

and here is the graph



Let me also answer Steve's earlier questions:

1) 3 runs made - all have similar numbers with minor differences in the appearance of the traces.
2) This chart is run #3
3) Dyno was in a bay in a shop - shop was ~40' x 60' x 20' high.
4) A large high flow fan (about 42" diameter) was blowing directly across the motor (they new to put it in the back!)
5) Don't know precise temps but I warmed up the car to 9 o'clock on the gauge before the runs.

Ben

 

Steve,
Great questions.
I did the run to base line engine health as I've only had the car a few months.
Next time, I'll get A/F info.

1. Two Runs
2. Chart shows first run. Second run is identical, including jitter, but down about 3-4 HP.
3. Room was about 40w x 50d x 20h Ambient temp was 68F
4. Single high flow 24" fan was used
5. Oil temp was between first hash mark and 9 o'clock position

You make good points about A/F. There is a chance that is could be oscillating between rich/lean. If the plugs are gapped right, then I think the injector spray patterns may be suspect.

Thanks!

Scott

 

Hi Scott:

Let me address both your's and Ben's responses simultaneously, if I might.

First, 911 engines (both N/A & TT) are notoriously difficult to get accurate, consistent results on chassis dynos due to insufficient cooling; both engine and oil. Fact is, almost nobody's dyno installation replicates the airflow through the engine compartment and oil cooler as the car travels between 60 MPH and 150 MPH. I've spent a LOT of time with thermocouples and manometers in the engine compartment of 911's on both chassis dynos and on the road (up to very silly speeds) and the results are quite different.

Oil temps and cylinder head temps play a large role in what you see on the dyno graphs and since oil temperatures always lag behind cylinder head temps, its imperative that the engine operates between 185 deg F and 210 deg F for best performance. When your oil temp guage pointer is at the 9:00 position, you are around 235 deg F and thats just not ideal for maximum power nor does it accurately reflect the RWHP of the car. 911's make best power when the oil temps are in the 190-200 deg F range. Anything over 210 deg F, HP falls off very quickly.

One can see the net affects here by watching the dyno runs with a PST-2 plugged into the car's data port so you can watch knock sensor activity in real time. You can see if the engine is detonating; even just a little bit. This is a very good indication of cylinder head temperatures and you will see those post-5000 RPM squiggles on the graph as the knock sensors are trying to pull a bit of timing back when the engine is at high loads in that range. Sometimes it affects peak HP but most often not, unless its hot outside or the fuel octane is marginal (or both).

New plugs (FR5DTC's) are usually gapped just fine as they are, however old injectors that have not been regularly treated with Techron (or equivalent) can affect the propensity for certain cylinders to knock if the injector spray patterns are not correct. I send them out to be flow tested and cleaned.

FYI,..George's car is VERY lean from 5000 on up and Ben's A/F looks fine. George ought to be checking the functionality of his oxy sensors, and if it was here I'd chip it,..... Best HP is around 13:1.

Hope this helps,

 

Thanks Steve,

Just a few points to further define my situation.

1) I always use 93 Octane Chevron w/Techron and use a 20 oz. Techron bottle every 5k miles or so.
2) The car had it's 60k service within the last 18 months with new plugs installed at that time.
3) I was guessing on the oil temps but neither the car nor the shop was very hot - but I don't have accurate data for you there.
4) All of us used essentially the same warmup time and the same tech ran all the pulls - I think I was the only car to get << HP than expected so I tend to think the shops technique was pretty good.
5) Very interesting point on the timing being retarded - another tech suggested that my cam timing might be a bit off - possibly from stretched chains - and also thought I might benefit from solid lifters.

This is a street/DE car so I'm not too concerned about retaining stock for CR. I checked your website and was noticing your advice on top end enhancements - also very interesting.

Thanks for you input!

Ben

 

Steve,
Thanks for the insight!

Having worked with air cooled power electronic systems (100kw - 1MW), I understand how aircooling can be black magic. Your research is good input on how airflow will affect performance.

I'm not too worried about the jitter, I think this is knock sensor related. To be safe, I plan on running a can of BG44K through the next few tanks of fuel for cleaning..... For reference, I was runnning 93 Octane Conoco.

Thanks again, I may be calling you later this year to talk about the gearing options mentioned on your site.

Scott

 

And Scott - sorry about the thread hijack - I figured you'd be interested in the other 993 data.

If only my VRAM 97 was making the power your '95 is making!

Ben

 

No problem..... Your info is great.
I was at Hooters with George yesterday when you called. He said you'd use the HP numbers as an excuse on your lap times.

We should plan a N.Dallas/Plano get together to talk cars. I'd like to open pandora's box about suspension.

Jonathan (mrsullivan) is making noise about a RUF gathering. I think I'd prefer some beer and B.S.

 

Sounds good to me - are you coming to MSR this weekend for the Drivers Edge DE? George and I will be there - we could do something Sat. Night.

Ben

 

Sounds good...... I'll check with the war department and drop you and George a PM.

 

Figured I'd weigh in on my recent dyno results. I have a 95 C2 with an Andial chip and it has a tendency to put the rev limiter at around 6000 rpm (all run in 4th gear). The first run it went to 6700 but not the following two (could be temp related). Oil temp was about a needle width or two above the second hash (thermostat open) for all runs (had a 4 foot fan over the car and a blower fan on the front radiator). I was running 28% 100 octane with 91 (~93.5 octane) and the room was 20' x 20' by 20' or so. The temp in the room was higher than outside (about 70) by 5-10 degrees. The dyno was a Dynojet.

Peak hp 237-245 around 5900 rpm
Peak Torque 221-222 ft-lb around 5400 rpm.

I was satisfied with the results, but the rev limiter cutting in at 6000 is a bit of downer.

Does the Rennsport chip produce about the same or better results?

 

Ben- Thanks for posting that data. Has anyone noticed that the varioram numbers are virtually identical to the 1995 numbers? i.e. averages are the same:

Varioram:
225 215
248 228
249 228
231 220
239 218
260 240
Avg 242 225


1995:
251 232 (’95)
241 220 (’95)
233 220 (’95)
Avg 242 224

 

Hi Ken:

Yessir IMHO, ours do better than that.

 

Eric:

I'm glad you noticed the lack of substantial peak HP differences between the Varioram and non-Vram engines.

We've dyno'ed a lot of these things and the peak outputs are usually within 3-5 HP. The main differences lie below 5200 RPM where the variable geometry V-Ram intake makes an additional 25-30 lbs-ft from 2500 to 5200. Above 5200-5500, these things are the same.

If one has an RS-spec 3.6 or 3.8 operating between 5000 and 7000 RPM using good close-ratio gears, the V-Ram has little if any benefit on the track, all things being equal. Further, a properly programmed chip can help close that gap.

Fun stuff, yes?