Jason Judd

I need a little bit of education...

Just had a recent dyno pull on my car using a Mustang unit, and I got some numbers that concerned me.

My A/F ratios were, at times, in the upper 13 range, and even topped into 14.1 once or twice. Isn't that too high? Please keep in mind my car is a 968 turbo and not a N/A version.

My RWHP and TQ numbers were lower than compared to the Dynapack my car was originally tuned with, too.

RWHP now shows at around 305; where The Dynapack showed around 325.
RWTQ now shows at around 350; where the Dynapack showed around 380.

So, my question is, firstly, do the A/F numbers look a little scary...too lean?

And, secondly, does the Mustang dyno traditionally run conservative, because it reads differently...that is, the power loss due to a roller type of situation rather than a unit that bolts directly on to your hub.

Thanks,

Jason

Eyal 951

dynapack tends to read a tad high since the rim and tire isnt being turned and its bolted to the hub. The mustang always reads pretty low. You would probably se #'s like 315RWHP and 370 RWTQ on a dynojet.

eospeed

Yes way to lean you should be no more than 12.2 at wot shoot for 11.8

Jeremy Himsel

That's scary high and I'd be very concerned. I guess from 2000 miles away I would question the accuracy of the A/F readings because at high 13's and 14's under boost I'm shocked that you 1. don't hear detonation, and 2. you haven't popped a head gasket. Without knowing information about your boost levels, induction and fuel system it's pretty hard for us to guestimate HP.

toddk911

Yea, maybe try a different shop and compare.

You don't have a wideband with a 968 Turbo project?

Jason Judd

You don't have a wideband with a 968 Turbo project?
__________________

Man, I don't even know what you just said!

Sorry,

Jason

TRWright

14.1 Yah-- a little scary would certainly make for the understatement of the day. Tell us a little bit about your engine management and fuel system. .

special tool

I agree - probably not accurate. You are in big trouble on the dyno with zero air through the intercooler at those AFR's.......

Jason Judd

OK,

I'll check with those that did it and see what I can dig up.

Thanks,

Jason

Tom M'Guinn

Just as reference, I blew my head gasket on a 20 minute test drive when my car accidently went to 14:1 or so under (lots of) boost. I'd fix that before getting on the boost again. There are long painful debates here and elsewhere about the relative accuracy of the Mustang and other dynos.

Geoffrey

I would not rely on the results of a Mustang Dyno in comparison to another dyno since they are all user calibrated so they have a wide range of numbers it will produce. Were these tests performed at the same boost pressure? What about the gearbox, was it fully warmed up? What about engine temp and dyno cell temp, what were they? Further, the length of time of the run will largely dictate what your torque curve looks like and how much torque it will produce. A quick run will not load the turbo properly and for your engine I would run an 15 second test from 1500 to 6500 for your engine. I use Dynapack and Dyno Dynamics dynos on a regular basis and have found both of them to be consistend from dyno to dyno and when compared against a DTS engine dyno that I also use. I find that Mustang and Dynojet dynos to read higher than either a Dynapack or Dyno Dynamics dyno on a regular basis, but for different reasons.

Most of the internally stock 944 3l turbo engines I've done produce between 300 and 325rwhp on a dynapack depending on boost (1bar to 1.2bar), turbo and exhaust configuration.

Jason Judd

Thanks for all the input.

The guys that did the dyno run were basically doing a fun run. They had my car in for an alignment and decided to throw it on the dyno for kicks since they had the car. They didn't put a lot of time into it, because it was basically a free-bee.

They were doing the alignment as a barter for some parts I sold them, and did the dyno run as a bit of a bonus. When they picked up the A/F numbers, they thought to mention it to me.

Lot more than just throwing it on the dyno, I guess.

The dynapack numbers Geoffrey mentioned almost mirror what my car registered originally at my mechanic who also uses a dynapack. So, I guess the Mustang was pretty close, considering the difference in measuring methodology.

I wonder about those A/F numbers...probably something worth looking into, though.

Jason

Geoffrey

"They didn't put a lot of time into it"

Anything worth doing is worth doing correctly, it would have prevented you from having a heartattack due to AFR numbers that would appear dangerous.

RajDatta

Jason, not accusing them of doing this but could it be possible that they were trying to set you up to get work from you. Its easy to scew numbers and by getting you all alarmed, he could benefit from you telling him to fix it, when there is no fix required.
I am not a conspiracy theory believer but in this case it seems highly suspect.
Raj

PorscheDoc

You can easily ask them to print out a graph showing the AFR's which will rule out any think such as this.

We have a mustang dyno in house, and it is more conservative than the other dynos out there. The saying we typically go by, is "If you want to tune a car properly, buy a mustang dyno....if you want to make money....buy a dynojet." Being that the mustang dyno has a lot of capabilities to tune under a simulated load, etc that a dynojet or dynapak does not have. And a dynojet, while not only being a lot cheaper, will give higher horsepower readings, which is what everyone is after...meaning the owner will typically choose to run his car on a dynojet over a mustang if he knows they read higher.....then he can impress his buddies with his numbers.