Carrera 3.2 Dyno Results
 

Here's the results - I was pleased.

- US spec 3.2 with 135K
- B&B Exhaust (2 in / 1 out)
- Autothority Mass Air with custom chip
- O2 sensor inactive
- Enlarged Throttle Body
- 7.31 rp with stock geared 915
- 245-45/16 tires
- All runs measured in 4th gear
- 77.1 F / 28.8 in/HG with CF of 1.04
- Fuel: 93 octane Chevron

Dynojust tech suggests 15% drivetrain loss - these numbers are RWHP. Fuel curve very rich - have some tuning to do still.



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I'm not an expert, merely trying to connect the dots. Judging by the chart that was posted by SteveW a few days ago is it correct to say that your car is running on the rich side?

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Ooops, just realized you mentioned that it's running rich.

Yes, as do shorter tires, gear other than 1:1 etc. all of which need to be normalized for legitimate comparisons to other cars.

Bill - as I understand it, the DynaPak automatically compensates for all that (no wheels/tyres, for a start). Does it allow for non-1:1 gearing too?

(edit) - I know that this wasn't run on a Dynapak. I'm wondering about my own readings.

I thought this was already adjusted for since they know your rpms. If they know the torque at their dyno and know how fast their dyno roller (I don't know what it's called, the thing that spins with your wheels on it :D ) is spinning then they should be able to get the torque at your crank (minus driveline losses) for whatever gearing you have in-between by using the ratio between their roller rpm and your engine rpm. From there hp is just an rpm multiplication away.

Cam, the Dynapac is by far the best way to measure hp other than on a big bucks engine bench, it eliminates all of the rear wheel renormalizations but still needs to have the gearing manually entered into the computor so that the dynos internal algorithm can correctly calculate rwhp. Atmospheric variables also need to be accounted for.

Yargk, thats true, but the process is inexact and is most accurate when the widest variety of influencing variables are eliminated. gearing is a big one, wheel, slip is a big one, atmospherics are big ones. etc.

the gearing manually entered into the computor so that the dynos internal algorithm can correctly calculate rwhp

My dude did this (he entered the final drive at 3.875 for an 8:31) and he used 4th. Mind you, my 4th might be 1.0X:1. I can't remember. Newsflash - I checked, and have a 26:26, thus 1:1.

When I had my 930 dyno'd they had set parameters already built in to the software for the car. My gearing is stock, but I am running slightly larger tires (18 inch 996TT rims). These wheels have a slightly larger rolling diameter than the stock 16 inch fuchs. So, would this skew the HP number up or done?

As an aside, if the numbers for mm86911's car are accurate, that is the highest HP 3.2 motor I have heard of barring internal mods.

mm - Sorry if this was answered already, but one kind of chip are you using?

Thanks.

ZCAT3, It would skew the #s down. A dyno only measures torque. The larger tires mean less torque multiplication, ie the dyno sees a smaller torque than it would see with shorter tires.

According to the guys at the shop (and the tuner has been doing this for over 15 years) the HP affects of the 7.31 R/P changes are very minimal. If any affects they would be most noticeable on Torque numbers. I believe someone has a gear chart that we could reference to see variance using 7.31 vs. 8.31.

The only things measured by a dyno are torque and rpm. Everything else id calculated.

Dynojets measure HP and calculate torque... It looks at the change in speed of the big drum over time which is change in energy over time, which is HP.

Gearing won't affect HP results _if_ acceleration rates are the same. So, if your car accelerated the same in 1st and 5th on a Dynojet, the power would be recorded as the same. Obviously this is not the case. The quicker the engine accelerates, the more intertia "saps" power from the rear wheels, so lower gears will provide lower indicated numbers.

On a dyno like a Dynapack where you can set the acceleration rate, the power will be the same regardless of the gear (with a small exception for 4th gear which can be "straight-through" and reduces some gear meshing).

Mr Beau:
I respectfully disagree...any inertial dyno like a DynoJet 248C will measure torque and will calculate hp.... or please enlighten me otherwise... :)
---Wil Ferch

I'm not following the logic of a performance chip and then disconnecting the O2 sensor voiding the computer of a feedback loop...am I missing something?

I thought the only difference between torque and Hp is that one's a measurement based on distance, and the other based on time. Therefore making torque the only thing that's truely measurable and hp being a fuction of torque as it occurs more frequently for a given amount of time.

Mike,

It might be interesting to do another run with the O2 sensor connected. Fuel curves may look better with computer feedback....just a thought.

If you wait a few weeks, maybe I'll join you.

Actually, i'm not sure but i believe the motronic goes into open loop mode during wide open throttle detection so it probably doesn't matter whether it's disconnected or not for the purpose of the dyno run.

A mechanical wheel can only measure torque, which is really just a type of force. The HP is actually the amount of energy (energy = force * distance) being out put per second (Thus HP = Energy/time, or Force*distance/time), and it cannot measure that. It's calculated by measuring the torque and RPM and using the 5252 rule, which I have to say by the way, is presented wrong in the 101 project or engine rebuild book (don't remember which one gave torque figures)

It seems to indicate that 3.2 Carreras have 260 ft/lbs of torque. The Torque is going to be found by HP*5252/RPM.
So, a Carrera delivering 207 HP at 6250 produces 173Ftlbs of Torque.

If you divide the other way, you get the 246ft/lbs number, which is wrong ==>

You can check this by in general as to which way produces the correct number as follows: A Honda S2000 does not produce a lot of torque, so let's use a similar one as an example--a car that produces 240 HP at 9,000 RPMS.

We know that a car like that will not have a lot of torque.
If we use the correct way, we will get 140 fl/lbs of torque (5252*240/9000) = 140 ft lbs.

If we do it the other way(wrong way), we'd end up with a 4 cylinder car with 240 HP at 9,000 rpms producing 411 ft/lbs of torque which is clearly wrong ==> 9000*240/5252 ~411ftlbs ??

Anyway, I'm off on a tangent, but figured I'd mention it since I swore I saw the engine rebuild or the 101 projects book, that 3.2 carrera produced 260 ft lbs of torque.