Where did the horses go??

toyman · Jun 11, 2009

I finally got onto a dyno and I'm trying to figure out why my tune isn't delivering the numbers I would have guessed. 274 rwhp @ 5000 rpm and 356 ft-lbs of torque. AFR avg 11.7 (11.0 - 12.3). Max boost 8.04 psi. Results are from a Mustang Dyno. Seems pathetic given the mods in my sig. I was expecting something closer to 350-375 wrhp and 400 ft-lbs of torque.

I'm at a loss as to where to find the missing horses and torque or am I just too conservative with the timing at 28*.

HGFireHazard · Jun 11, 2009

I would have expected a little bit more, but I'm not sure how much more.

I hear figures from 5%-16% difference between a mustang dyno and a dynojet, it really depends on the dyno operator and how they run it.

For a comparison, I tuned with what I have in the sig minus the driveline components at 10psi (with a powerpipe) at 313hp 374tq on the stock longblock.

You have heads, cam, and a different style blower over me, and I have long tubes and 2 more psi. It's tough to compare these two blowers as they make the power at entirely different RPM's. I'm not sure of the flow numbers on those heads or know very much about that cam. Maybe someone with more experience with the KB can give some insight, but I still certainly would have expected a little bit more.

HISSIN50 · Jun 11, 2009

Auto trans.

Dino Dino Bambino · Jun 11, 2009

Auto tranny vehicles don't dyno well on load-type dynos such as the Mustang due to torque converter slippage. You'll get better results on a Dynojet.

Stanger007 · Jun 11, 2009

Welcome to the ego deflating combo of a MustangDyne and an Auto.

On a tuning note:

- I lock the transmissions in their 1:1 gear and pull from there. If you can datalog converter slip or at the very least engine RPM vs wheel RPM (the MustangDyne can do this when an RPM pickup is used) you can see how well the converter is doing.

- 11.7:1 sounds good on a 14.64-ish stoich wideband.

- 28* timing sounds fairly stout for 8psi on 93 pump.

For your combo I would be looking for around 400rwhp (265 * (14.7+8)/14.7). The correction on our dyno to local DynoJets is around 15% on N/A cars and a bit higher on blower and turbo cars.

Depending on where your 11.0:1 was at, that will typically drop you some power vs an 11.7:1 ratio.

I didn't see if you had any ignition mods, but as you approach 8-10psi or so it becomes important on the factory ignition system to have a strong spark.

Post the graphs with PSI and AFR -- we'll go over them.

Wes

P.S. Take it to the track and post up what it runs. That will tell all.

donkey_punch · Jun 11, 2009

just wondering if you have anything else besides an off road H pipe? are you still runing stock headers and cat back?

Pokageek · Jun 11, 2009

I wouldn't worry about it. I have seen SEVERAL cars first hand on one guy's dyno go mid 300's rwhp on mustang dyno and no change in mods hit mid 400's on dyno-jet. The are ALL different. Maybe this one in particular is conservative but I am convinced that comparing dyno numbers from different shops is as subjective as anything can be. Not to mention shops that inflate numbers just to gain more business.:Track:

toyman · Jun 11, 2009

Stanger007 said:
Welcome to the ego deflating combo of a MustangDyne and an Auto.

On a tuning note:

- I lock the transmissions in their 1:1 gear and pull from there. If you can datalog converter slip or at the very least engine RPM vs wheel RPM (the MustangDyne can do this when an RPM pickup is used) you can see how well the converter is doing.

The rpm from the dyno closely matched the rpm on the tach which usually matches the rpm as read by the EMS. However, converter slip may have been present. The AODE and converter were custom built a week earlier but 2 days before the dyno run I had an issue wherein the rpms when in 3rd and at WOT just increased without a matching increase in speed. It was suggested that something was stuck in a solenoid that may have caused this slippage. The link is to Click Click Racing

How can 3rd gear slip? - Click Click Racing Forums

-11.7:1 sounds good on a 14.64-ish stoich wideband.

- 28* timing sounds fairly stout for 8psi on 93 pump.

By stout you mean safe?

For your combo I would be looking for around 400rwhp (265 * (14.7+8)/14.7). The correction on our dyno to local DynoJets is around 15% on N/A cars and a bit higher on blower and turbo cars.

Depending on where your 11.0:1 was at, that will typically drop you some power vs an 11.7:1 ratio.

AFR was falling through the pull. Starting at about 12 and dropping to 11 @ 5000rpm

I didn't see if you had any ignition mods, but as you approach 8-10psi or so it becomes important on the factory ignition system to have a strong spark.

MSD coil, wires and 6AL box. However, I did pull the #5 plug to check its condition and discovered that the gap wasn't .032" but rather .042 ". Although there were no obvious signs of spark blow out I suppose the wider gap may have played some role in the numbers.

Post the graphs with PSI and AFR -- we'll go over them.

I don't have a scanner but I will try taking a picture and posting it later.

P.S. Take it to the track and post up what it runs. That will tell all.

I'll probably do that later this summer as it's a 2 hour drive from home.

Where did the horses go??

toyman

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