Curious Dyno Results

[David K.]

Today I dyno'd my ep at Jotech Motorsports in Dallas. Vital stats are as follows: 5:06 to 5:26 pm, temps were cool, low 60s, hood open, Dynojet dyno. My car currently has stock airbox w/ Hondata modifications and a drop in K&N filter, stock header, ebay test-pipe, MBRP 2.25" mandrel bent mid-pipe, 02blksi ground wires, and fresh Mobil 1 0w20. Rims are 16" with 205/40/16 Kuhmos, approx. same weight as stock, not sure of brand(!). All runs used 87 octane.

Runs 1 through 3 were performed in 4th gear and the numbers are as follows: 135.1hp, 134.8hp, 137.4hp. Run #3 was the best, with 137.4hp/120.4tq. My A/F ratio is somehat rich and I do show a cel from the test pipe. Jotech's Snap On scan tool cannot read the code, refering to it as a dealer specific code, but it can reset it. Resetting the code did not show any power gains or A/F changes. These numbers are not spectacular but considering the 87 octane and lack of intake/header I consider them acceptable.

Here is where it gets weird. I decided to make a 4th run, only this time in 3rd gear. On this run my power dropped significantly, down to 111.7hp/90.7tq. The A/F ratio was significantly richer throughout the entire run. I made another 3rd gear pull with similar results. At this point the oil is checked and I have plenty and it looks good. So the tech checks all the dyno connections and they look fine as well. So now we do another 3rd gear pull and again, the same low hp/tq numbers as before.

We tried another 4th gear pull and power jumped back up to 135hp. At this point I have made about 8 runs for the price of 3 so we call it a day.

Does anybody have any idea what is going on here? On the road my car feels fine, pulls well through all the gears, and fairs well against the competition. I was expecting more power, especially with the test pipe on, and now plan on changing all fluids, plugs, and getting my cel read at the honda dealer. Any help, ideas, etc. are appreciated.

[STP03BlueSI]

IF I AM CORRECT...(but if i am wrong please say so)

I think 3rd gear is whats called a long gear. So in terms it is a tad bit longer or wider than the others being in the center. THAT IS ONLY my guess.

Mods or ne one if i am wrong please dont bash me. just takin a guess.

Thanks
Chris

[fsugatorbait]

From what I've heard 3rd gear is suppost to be the best, but im far from an expert. Ive also got the test pipe and have noticed a fairly dramatic loss is my mpg since i put on the pipe, which could be accounted for if im running rich. Im interested to hear what the honda dealer has to say when you talk to them about the code.

[02SilverSiHB]

yeah, I did my dyno runs in 4th gear also, but I've seen others do 3rd gear and get bigger numbers. Not bad for not having a cai and header

[David K.]

Anyone else have ideas? My first post was a tad long-winded, so let me sum it up: Why would my car show a huge power loss on a Dynojet when I make a 3rd gear run? In 4th gear I made 137.4hp, while in 3rd it only made 111.7hp. What the hell?

[ATRIOT]

Bump in search of a rational explanation. Im curious too.

[Hondata]

The reason is that the knock sensor is pulling varying amounts of timing between runs. The scan tool should show you the ignition advance.

When ignition is retarded, AF becomes richer.

[David K.]

Originally posted by Hondata
The reason is that the knock sensor is pulling varying amounts of timing between runs. The scan tool should show you the ignition advance.

When ignition is retarded, AF becomes richer.

That makes sense, but what I don't get is why it would pull timing in 3rd gear more than 4th. Wouldn't the torque-multiplication of 3rd gear actually place less load on the motor than performing the same run in 4th gear? I understand most vehicles are run in 4th gear due to its 1 to 1 ratio, but in our cars 4th is slightly overdriven, and I would think this would place more of a load on the engine than if it was in 3rd gear, which is slightly underdriven. The dyno doesn't recognize 3rd or 4th gear, it's only measuring acceleration of the drum, correct?

Remember, after my 3rd gear run which only showed 111.7hp, I immediately did another run in 4th gear and power jumped back up to 135hp. WTF?

[andy]

I'm not anywhere near as smart as the Hondata guy(s), but I always
thought 4th gear was optimal because it was nearly 1:1 (as someone
else mentioned). Heard this for multiple cars. So wouldn't third just
have the wrong ratio, hence the poor results?

Also, I missed this post at first, but interesting about having the
test pipe and CEL and not seeing any A/F changes (at first). Keep
us posted, por favor.

[David K.]

Originally posted by andy
I'm not anywhere near as smart as the Hondata guy(s), but I always
thought 4th gear was optimal because it was nearly 1:1 (as someone
else mentioned). Heard this for multiple cars. So wouldn't third just
have the wrong ratio, hence the poor results?

Also, I missed this post at first, but interesting about having the
test pipe and CEL and not seeing any A/F changes (at first). Keep
us posted, por favor.

Correct, a 1 to 1 ratio is optimal, but we don't have one so 3rd or 4th can be used since both straddle the 1 to 1 ratio. The dyno doesn't know what gear you are in, it just measures your car's ability to accelerate the drum. The difference btwn. our 3rd and 4th gear is not huge, but I figured if anything 3rd would show a slight power INCREASE due to the lower ratio, even if the increase was false. What is puzzling me is the approx. 26hp LOSS on all my 3rd gear pulls.

As for the cel, I'm going to have it scanned at Auto Zone to see what code it is, as Jotech's scan tool could only identify it as a "dealer specific code." I called Lute Riley Honda, and they want me to make an appointment and pay $88.00 to have it scanned, so fuck that. If I cannot identify the code I'll probably just replace both O2 sensors and put a simulator on. In any event I'll dyno again after all this to see if improvements were made.

[idrive]

im no expert... but could it have anything to do with the way youve been driving your car daily? and the maps that your ecu has been building off those? did you try resetting the ecu and running on new maps? because our ecu's are adaptive if im correct? and if youve been running 87 since forever... that could have an effect on the ecu retarding your timing...

i pulled a 141hp/122tq in 3rd on 91 octane... i didnt try 4th..

[David K.]

Originally posted by idrive
im no expert... but could it have anything to do with the way youve been driving your car daily? and the maps that your ecu has been building off those? did you try resetting the ecu and running on new maps? because our ecu's are adaptive if im correct? and if youve been running 87 since forever... that could have an effect on the ecu retarding your timing...

i pulled a 141hp/122tq in 3rd on 91 octane... i didnt try 4th..

I don't think that's it, but possible. I drive the snot out of my ep daily, going to redline several times. Never abusing, just good hard running. And I would think the maps wouldn't change so much btwn. gears, either. I'm still researching possibilities. Nice numbers on your car, BTW, I wish I had 93 octane in my car the day I dyno'd; it was kinda a last minute decision to do it.

[!@#$%]

how much did jotech charge for the runs? I'm thinking about getting mine done.

[David K.]

Originally posted by !@#$%
how much did jotech charge for the runs? I'm thinking about getting mine done.

It's $75.00 for three runs and an additional $50 to run a scan tool and monitor A/F ratio. I can't complain about price considering I made 8 runs for only $125, even though my car is acting up.

[myeverlovinsir]

All of my runs have been in 3rd, dynojet and dynopack. I have never seen such results. Not sure about the knock, but I would expect that you would have more load on the engine when you run in 4th vs 3rd. The mechanical advantage in 4th is less than 3rd, so your results are quite perplexing.