wjk_glynn

Hi folks,

As part of the NorCal dyno test last week (see <a href="http://forums.rennlist.com/cgi-bin/rennforums/ultimatebb.cgi?ubb=get_topic&f=15&t=010700" target="_blank">http://forums.rennlist.com/cgi-bin/rennforums/ultimatebb.cgi?ubb=get_topic&f=15&t=010700</a> ) I got a chance to dyno my stock 110K mile '91 S2 with rather surprising results.

Over 4x runs, average SAE-Corrected RWHP was 187 BHP @ 5,700 RPM with very reproducible results over the runs. Average max-torque at the wheels was 182 ft.lbs. The dyno was a Dynojet 248H. Ambient temperature was 70F (it was ~10 AM in the morning).

Applying the 15% rule, this implies the crank was making 220 BHP. On an S2

The factory number for an S2 is 208 BHP.

So... I think one of the following applies:

(1) I've got a very strong S2, especially after 110K miles.
(2) The dyno was reading ~5% high.
(3) The PO did something I'm not aware of. But what...?

So my initial suspicion was that the dyno was reading high. There was only one other unmodified NA car there that day (all the rest were modified Turbos) to compare against. It was Jeff's 968 and it made 199 RWHP which is right in line with what you'd expect (15% loss yields 234 BHP at the crank). This implies the dyno was accurate (on a sample of one). I also checked up on Dynojets. Their reported tolerances are +/- 1 BHP.

Does anyone else have S2 dyno results?

Karl.

'91 944S2

PS - The folks there (Dyno-Spot & car-owners) were great to meet and uniformly a nice bunch. I got a load of tips and advice (thanks Trevor). Thanks to you all and in particular to Danno for setting it up.

Tom R.

Karl
What were you producing at about 3000 rpm?

My clutch started slipping at about 100hp at about 3000 rpm when I had my stock S2 dynoed a few months back.

Im curious if I was on the same curve as you.

BTW a 5% error from what Porsche posted seems right. Imagine the lawsuit you would want to start if it was 5% the other way! Remember the mustangs of a few years back when that happened.

Danno

Hi Karl <img src="graemlins/xyxwave.gif" border="0" alt="[bigbye]" />

Glad you had a good time. Here's a chart of an S2 vs. S2 with Huntley's MAF installed. The scale can be a little misleading because it doesn't start at zero:



Stock S2 got 180rwhp and the MAF gave it 187rwhp. Looks like you've got a good sample of an S2; production tolerances CAN give you a car where all the pieces are on the good side. When all the planets are in alignment, halleluyah!!!!

Please post your chart!

wjk_glynn

[quote]Originally posted by Tom R.:
<strong>Karl
What were you producing at about 3000 rpm?</strong><hr></blockquote>

Hi Tom,

at 3K RPM I got the following range over 4x runs:

85-90 BHP
155-160 ft.lbs.

Karl.

wjk_glynn

[quote]Originally posted by Danno:
<strong>Please post your chart! </strong><hr></blockquote>

Hi Danno,

thanks for posting your chart. I'll try to post my chart next week as I only just asked the shop this morning to send me an electronic copy. They said it might take them a day or two to get to it.

Karl.

wjk_glynn

BTW, I forgot to mention that I had a $2,600 service done on the car ~2 months ago which obviously included fresh fluids and filters. Maybe the brand new air-filter is helping.

Karl.

Manning

I had always understood that loss through the drivetrain on a RWD vehicle was closer to 20%, some say more like 25%. That would be even more impressive, no?

Andy S2

That sounds pretty good for a stock engine , I had my S2 chippped a few months ago and it was getting 214bhp up from 207 before. This is slightly down for a euro model as they are supposed to have 211bhp as std. but as it has done 125,000miles I was quite pleased to have only lost 4bhp. I was getting about 100bhp and 185lb/ft of torque at 3000rpm , I'll post the charts as soon as I can compress them to below 180Kb so Rennlist will let me upload them. Any body know how?

Andy <img src="graemlins/jumper.gif" border="0" alt="[jumper]" />

wjk_glynn

[quote][QB]I had always understood that loss through the drivetrain on a RWD vehicle was closer to 20%, some say more like 25%...[QB]<hr></blockquote>

It varies by car model but I've talked to people and 14-15% seems to be the number for 944 cars.

This is based on conversations with folks from Frey Racing and Bauer Racing. Those folks dynoed a 944 engine both at the crank and then installed in a car. The saw a 14-15% loss from crank to rear-wheels. However I don't know that type of differential was used and whether this would have any effect. When they tested a Miata in the same manner, they saw an 18% loss.

A car has the minimum drive train losses when everything in the drive-train is warm. Then engine is looser, the lubrication fluids are warmer, etc. Or so I'm told.

My car was fully warmed up before we put it on the dyno.

Karl.

wjk_glynn

[quote]Originally posted by Andy S2:
<strong>...I had my S2 chippped a few months ago and it was getting 214bhp up from 207 before.</strong><hr></blockquote>

Can you remember what the rear-wheel numbers were?

[quote]<strong> This is slightly down for a euro model as they are supposed to have 211bhp as std.</strong><hr></blockquote>

I've heard that the different numbers is actually related to the measurement methods.

In Europe, the DIN number is quoted while the SAE number is usually used in the US.

I don't know the specifics but I hard that the DIN method typically (though not always) yeilds a slightly higher number than the SAE method.

[quote]<strong>I'll post the charts as soon as I can compress them to below 180Kb so Rennlist will let me upload them. Any body know how?</strong><hr></blockquote>

I'd love to see it and also I'd like to know how to post an image (never did it before).

Karl.

Danno

"I had always understood that loss through the drivetrain on a RWD vehicle was closer to 20%, some say more like 25%..."

Any engineer that lets a car out with a 20-25% drivetrain loss should be fired! Check out this thread, <a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=18&t=002392" target="_blank">Rear Wheel HP vs. Flywheel</a> and follow the links within.

Tom Pultz

This is my dyno chart. Sounds like this '91 has a strong engine. Maybe that different DME in the 91s really does do something of value

Manning

Danno wrote:

[quote] Any engineer that lets a car out with a 20-25% drivetrain loss should be fired! <hr></blockquote>

Better bust out the pink slips Danno, because a lot of high power muscle cars from the 60's through the 80's lost as much as 30% from the crank to the ground.

Also, in the post you tried to link to, one of the posters comments on the fact that a Miata they used to compare BHP to RWHP lost 18% through the drive line, which as I stated originally is closer to 20%.

But, I will concede that the loss appears to be on the order or 15% for our cars based on the limited imperical data provided

wjk_glynn

So after much delay, I've finally been able to post the SAE dyno results of my 944S2 as follows:

<img src="http://www.weissach.net/images/DynoCharts/My944S2_Dyno-SAE_20020907.jpg" alt=" - " />

Note that the timestamp is a little off. The runs actually happened around 10:00-10:30AM and the ambient temperature was ~70F.

So the average is:

Run #1: MaxPower = 185.6, MaxTorque = 182.3
Run #2: MaxPower = 186.4, MaxTorque = 182.3
Run #3: MaxPower = 187.5, MaxTorque = 180.5
Run #4: MaxPower = 188.6, MaxTorque = 181.6
-------------------------------------------
________Average_ = 187.0 _Average__ = 181.6

So looking at Danno's and Tom's results above, it seems my S2 in stock form is making as much power as a MAF'ed (Danno) or chiped (Tom) S2.

The planets were in alignment

Karl.

wjk_glynn

[quote]Originally posted by Tom Pultz:
<strong>...Maybe that different DME in the 91s really does do something of value...</strong><hr></blockquote>

Hi Tom,

I never realised there was a difference in the '91 DMEs either. Do you know any details?

Thanks.

Karl.