jfkaminsky

Hi all-

I can't find the original thread where we hashed this all out, but I wanted to post some progress <snip> Blah, Blah, Blah. I finally found a place to do this on the recommendation of another Rennlister - Turbo Technology in Tacoma, Wash.

Jeff Curtis

Jon, a friend of mine had his car dynod last week at a facility that had a portable chassis dyno. His car ('93 RSA) was the most difficult to tie down at the rear.

The operator used wheel straps over the banana (trailing) arms...that seemed to work well.

He pulled 245hp at the rear wheels which I assume is with some error being that our cars are supposed to put out 247 at the flywheel, out of the factory!

They were using a figure that took the rwhp measurement and dividing by .8 for flywheel HP which I enthusiastically disagreed with being that we (911s) shouldn't have a 20% loss out of the drivetrain!!

This figure gave my friend 306HP at the flywheel...I THINK NOT!

My friend and I just have drilled out airboxes and a lightweight flywheel/clutch setup, that's all the mods we have...and the LWF/clutch shouldn't add HP, it should add torque.

I figure at least you could use a chassis dyno to judge whether a modification has actually increased your HP, significantly or slightly...but in no way is it accurate in my book. I say this because I would guess drivetrain loss in a 911 transaxle setup would be quite a bit less than 20%, let's use rwhp and divide by .95 ...this would yield 257HP at the flywheel, a much more acceptable number!

Now, after installing my exhaust mods and custom chip next week...I would imagine converting a number that would wind me up in the 290-300HP range, at the flywheel. ...we'll see!

FlyYellow

Jeff,

Just to pass along some information - dyno runs on stock 964's tend to be in the 205-210 HP at rear wheels, which correlates to a 15-17% loss from flywheel.

Now, I'm with you I don't believe that he dyno'ed at 245hp with a stock setup and just a drilled out airbox. From what I've heard to get 250hp at rear wheels you must do the following and be lucky in your setup:

- chip (custom built for exhaust mods)
- ram air intake with k&n cone air intake
- primary muffler bypass
- cat bypass
- the luck is that you started off with one of the better motors from the factory.

So that's my humble opinion. Now I've made all those mods to my car and I have a g-tech. I don't believe it is the most accurate way to measure rwhp, but I get a whopping 211 rwhp. I'm dying to actually dyno the car - i need to find a shop in the SF bay area that can dyno a 964....

hope that info helps..

boris

jonfkaminsky

Thanks Jeff. That helps. I will call them again, and see if I can't talk to them into doing it. I was also wondering about attaching the tow hook to the rear bumper as suggested by another person in the other 911 group.

yeah I'm with you on the number. I could care less about whatever value I get back, I just want to know the delta's after making the mods.

I'll believe the factory figure of 247HP at the flywheel, take a look at whatever they return at the rear wheels, and then whatever rear wheel values are returned after the mods.

Kevin

Jon

Are you taking your car to Turbo Technology? Just curious. Good luck

jonfkaminsky

Hi Kevin-

No. Not initially anyway. I was scheduled at ProMax (just around the corner from Turbo Tech) on 56th and STac Way). I have Turbo Tech's number but they haven't answered all weekend or today. I also put a call into Bill's Dynatune (who wouldn't do it) and Blood Enterprises in Auburn who said after Nov 8, they could probably do it.

Do you have some pos/neg info on Turbo Tech?

Kevin

Jon;

Is that Pat Austins place (Pro Max) good old detroit iron. At least give Turbo Technology a call, or check them out. Keep us informed. I'm up north, its tough battling I-5 all the time.

neil williams

Don't know if this helps, but in NZ they often run the strap through the cabin, with the doors open!!

cheers

Neil

jfkaminsky

Okay first results are in. Man I wish we had the original thread where all the particulars were discussed.

Anyway, today we ran stock and then ran with the drilled airbox modification. Guess what? No significant difference except noise.

The system is not letting me upload pics at the moment so I will add those when it is possible to do so. The data are summarized as follows:

1991 964 Carrera 2 (July 1990 build date)
Ambient temp: 48 deg F
Barometric pressure: 30.27 in. steady
Humidity: 81%

Run 1: Stock configuration
Max HP: 229.5, Max torque: 217.1 ft-lbs

Run 2: Drilled airbox
Max HP: 227.6, Max torque: 216.5 ft-lbs

Run 3: Drilled airbox
Max HP: 228.9, Max torque: 214.0 ft-lbs

Runs were performed out of fourth gear, flooring the throttle at 2500 RPM, running to about 6300 RPM. Fourth gear transmission ratio: 1.086, (1.0 optimal).

Calculated at the wheels, the 229 HP value corresponds to approximately 8 percent loss through the drivetrain. It's in ballpark anyway, compared to other figures I've seen. I'll try to remember to ask the guy if they add-in some figure to try to back-out loss, or what his thoughts might be on the high value. Or maybe I just have a more kick-*** car than the rest of you!

Dyno was the chassis inertial type. Don't be surprised by the higher numbers. As I have maintained from the beginning, I am not looking to claim any number as accurate, I am just interested in the delta. As long as I use the same dynometer, It should be okay.

Next planned runs will include the "Cup" primary by-pass pipe, and then the DME firmware change.

Drew_K

Jon, VERY interesting because the other dyno results I've seen have rear wheel HP at about 209 HP, which translates to about a 15% loss. My basic (*very* basic) understanding of drivetrain loss is that it's typically more than 10%. I wonder where the discrepancy is coming from.

Regardless, I bet the dyno result is accurate at least to itself, meaning that your tests indicate that the drilled airbox makes no difference. Thanks for sharing the results.

Drew
92 C2

FlyYellow

Yes I've seen numbers like 205-210 for stock rear wheel hp. i'm really surprised by the higher number.

jfkaminsky

Here are the plots for today's runs. I will show stock and one of the drilled airbox runs and then a plot with all three.
Porsche specifications are as follows:
SAE max power: 247 HP @6100 RPM
SAE max Torque: 228 ft-lbs @4800 RPM

The data are summarized as follows:

1991 964 Carrera 2 (July 1990 build date)
Ambient temp: 48 deg F
Barometric pressure: 30.27 in. steady
Humidity: 81%

Run 1: Stock configuration
SAE max power: 229.5 HP @6100 RPM
SAE max torque: 217.1 ft-lbs @ 4700 RPM


Run 2: Drilled airbox
SAE max power: 227.6 HP @5750 RPM
SAE max torque: 216.5 ft-lbs @4800 RPM


Run 3: Drilled airbox (plotted with the preceding two runs)
SAE max power: 228.9 HP @6200 RPM
SAE max torque: 214.0 ft-lbs @4800 RPM


Note that I performed another run with the drilled airbox "just to make sure." Again, I am not implying that the max power and torque figures are accurate, and I don't want to start a debate on that. I am interested in changes from the stock figure from the various enhancements I will be testing.

Adrian

Dear Jon,
Thanks for this data. Kinda proves that certain bum dynos are not so inaccurate after all.
I am keen to see the results of the rest of your modifications. I would love to see somebody carry out similar tests before and after with these K&N filter installations.
Anyway great job Jon,
Ciao
Adrian
911C4

PS: Your transmission loss is the least I have seen. Typically it is around 15%. This may well be the methods used by the testers. However ti si the figure comparison that counts.

jfkaminsky

Hi. Thanks for the support Adrian.

So I was thinking about the data and came up with a possible solution to my seemingly small drivetrain loss factor. Torque as measured on a chassis dyno is relative to the gear ratio used. A ratio of 1.0 is optimum for obtaining direct accurate measurements (assuming the dyno is perfect). The closest I could get is 1.086 using fourth gear (manual G50/03). The transmission ratio would serve to multiply the torque measurements upward when greater than 1.0, as the dyno doesn't know the difference.

Therefore, using the 1.086 value in some equations, we can recalculate the "true" torque and then use that figure to derive a new value of max power.

Porsche spec SAE power: 247 HP
From data collected on dyno run #1
Power = torque * RPM/5252
Torque @6100 RPM = 197.2 ft-lbs
Power = 197.2 * 6100/5252 = 229 HP (see plot #1)
197.2/1.086 = 181.6 ft-lbs
Recalc Power = 181.6 ft-lbs * 6100/5252 = 211 HP

Drivetrain loss = [1 - (211/247)] * 100 = 15%

So there is the "magic value" of 15% loss everyone seems to throw around for drivetrain loss.

Cheers,
Jon

Adrian

Dear Jon,
Your figures now match very closely what I have received from many others in their dyno reports. Good luck with your other mods. Your efforts with your permission should go into my book. Is that okay with you,
Ciao
Adrian
911C4