Your welcome!

Its all fun!

 

Just wanted to share the results of my dyno testing.

I tested three different chips (stock, authority, GIAC) and 2 air intake systems (powrhaus & stock) and a couple of other minor things.

Rather than posting all of the results and various combos (over 20 different runs), I'll simply say that two things:

1. the best HP produced was this combination:
- GIAC chip
- Stock Air Intake
- RSR Mufflers
- RS pulley

2. There was a 19hp difference between the worst config and this one.

Here is the chart:


Cheers,
Boris

 

The shop tech said he Ran it in 4th gear.

 

Whether or not dynos of the same model should dyno with the same numbers, the power curves should look similar. I took Mike's dyno and another one from a similar car (one from the other thread) and overlaid them with some interesting results. There is a small difference overall between the two curves, which could be because of environmental differences, fuel, etc - but the real thing to look at is the top end. If you look at Mike's hp/tq curve, it's kinda flat past 5K, where the other shows a nice gradual curve. Might be misfire, or the engine might be sensing high rpm knock and be pulling back the timing (due to engine temps, lack of airflow from a fan, or a crappy batch of fuel perhaps), or might be unusual restriction in intake or exhaust - once found that a squirrel made a nice home in the airbox of my 91 MR2 turbo Just some ideas. Here's the dyno:

 

Nice job, Flatair. You called it right off the bat. The 'composite' dyno chart you made (photoshopped?) really shows where Carrera Mike's car has a flattened power delivery at high RPM. It is very impressive how the two graphs lay over each other. They are quite close together.

If 18" wheels were the cause of the difference, wouldn't they simply run parallel, one under the other? Larger wheels do make a difference, as they generally take more energy to accelerate (and that's what we're
measuring on the dyno). I just don't think that is what caused your differences.
This is good stuff. Thanks for sharing, guys.

 

Flatair and Derrick,

Thanks for the pointers and graphs. The other thing I remembered too is I told the Tech Driver driver not to red line the car, so I don't know if he lifted the acell pedal as he pass 6100rpm. The shop was openning too that day, so it was their first day doing it. My car was the first one too to have a dual distributor that day, so they have to figur out their connection. I'll try again next week with a shop who's known to do porsches and will do it in three pulls.

 

Graphs, numbers, etc aside, I'm not meaning to alarm you btw Mike It definitely could be the 'driver' letting off, or the flat top end might just be something environmental - i.e. if there isn't a fan blowing cool air over the engine, the heat in the engine bay could spike causing hot air to be drawn into the engine as well as slightly raising the overall likelyhood for triggering the knock sensor. Here is a GREAT article in Car & Driver about this very thing:

http://www.caranddriver.com/article....rticle_id=8020

Similar model dynos *should* give fairly similar numbers between similar cars under very tightly controlled environmental conditions, but these environmental conditions are what can vary the output numbers by a huge margin (as illustrated in the article linked above). Steve Dinan found a variance of *77* rwhp on a Dinan S2 tuned BMW M5 simply by adding a big fan in front of the car. It would be interesting to try the same thing with the 993...hmmmm!

Brad

 

Brad, That article is very enlightening. Engine being cooled down by a big fan while they run it makes a huge difference!

Let me ask you guys who got at least 240HPs, did your dyno shops have a fan blowing into the 'oil cooler radiator, and maybe directly onto the engine when you did your pulls? 'cause mine, all they did is have the engine hood up

 

Mike - they had a big fan blowing onto the front of the car, but the back was just sitting there with the hood up. The back was, however, only a couple feet from the big overhead door.

 

Squirrel cage fan was blowing into the oil cooler on my runs and one onto the engine bay. Cooler air going into the intake could account for some of that 15hp difference, but not all.

A fan on the oil cooler will keep the car cooler for during several pulls, but if your oil temp is in the normal position at the start of one run, I don't think a fan isn't going to make any difference for that one run.

Chip

 

mine did not have any fans...

 

Boris, I'm sorry. I was actually typing my response to your chart/graph at work early this afternoon when I got pulled out to the flight line for some issues.

How long did it take you to do all these switching and testing? Must cost a fortune. Did you actually test the stock twin pulley vs the RS single pulley? How much difference? I'm taking mine back this tuesday for a 3 pull session.

 

Bob and Chip, I talked to the dyno shop thats going to do my car next Tuesday. I expressed to them my concern on cooling/ventilation effect on temp sensors that retards the timing and richens(is that a word) the fuel/air mix. We'll see..

 

mike,

it took me 2 hrs. but i didn't take the rs pulley off or try it without the mufflers. i tried 3 different air intakes & 3 different chips.

btw, mine is a '95 993 so it does not have varioram.

cheers,
boris

 

If I might add a few thoughts,....


1) Knock sensor activity can be observed in real time with a scan tool (OBD-II) to see if that is a factor. If in doubt, run 50% or more unleaded race gas.

2) 993's seem to vary and IMHO, this is partly due to variances in cam timing from the Factory.

For the folks who do not clearly understand the implications of this, you should know that slightly retarded cam timing results in a bit more high RPM power and slightly advanced cam timing gives more low-end power. In short, adjusting cam timing shifts the power and RPM up or down a bit.

When I see low output numbers, I will perform a leakdown test and then watch the knock sensors with a scan tool during initial dyno runs before the engine get really hot,...