I wanted to see how my car does now, since the last I had it on a dyno was 3 years and 35,000 miles ago. I'm now up to 155,000 miles on the original engine and transmission. Nothing special. I made 207 WHP with 219 Torque. The pulls were made in 3rd gear. I have a question about my air/fuel ratio though. This time the sniffer was in my tail pipe. It shows slightly above 14 air/fuel ratio the whole time. Three years ago when I had the car tuned I had an open cutout and a open air box. I now have a test pipe, stock cat-back, and velocity stack. My air/fuel ratio 3 years ago was in the 12.8 range with the sniffer in the open cutout. Does the sniffer being in a different location account for the different air/fuel reading?

New Dyno:
Attachment 27672

Old Dyno done in 2nd Gear:
Attachment 27673
Attachment 27674

So were these sorta just progress/verification dynos? As in you didn’t do any adjustment on the VAFC?

In any case, you mentioned you have no cats, so that’s a little strange. I noticed when I still had my main cat in place, my tailpipe readings were a little leaner than my actual WB readings which were before the cat. After I went cat-less, my WB readings up front and tail pipe readings were the same. I’d say it might be time to add some fuel in there.

Also, I have noticed that my readings overall were lower when in 2nd gear, most specifically, the torque numbers were quite a bit lower, as I see the same with yours. I’d say stick with 3rd gear. 2nd gives you more RPM range, but it starts at such low speed, it really doesn’t get the juices flowing like it should.

Did you get the actual runfiles? Those would be good to look at as far as comparing the AFR at a higher resolution.

Yes. This was a run to see if the car was doing the same numbers a few years later. What's weird is the first tune needed to take anywhere from 2 to 4% fuel out to get to the 12.8 afr range. So, I din't change any settings on the vafc. Now this dyno shows the car is running lean with the only change being a velocity stack instead of GAB and now a test pipe with stock cat back combo instead of cutout. I don't get it. My test pipe has a bung welded in for a O2 sensor. Maybe I should find a friend with a wideband and do some street tuning. For now, should I zero out my vafc settings to be safe? The place I was at recently is mostly a LS1 GM performance shop, so they didn't seem to care enough to give me any useful advice. I was concerned about the lean condition, and they said not to worry about it, because there was no knock detected. I don't have the run files. They wanted extra for that, which is ridiculous, but whatever. I'll email them to see if I can get them.

By the way, I have this test pipe: 1989 1998 240sx s13 s14 JDM High Flow s s Down Catless Performance Test Pipe | eBay

I'm assuming the bung on that is too long to use for the wideband. I would need to have a different one welded on, correct?

It’s insane the times I hear that shops charge for DRF’s. Whatw as the rate/number of runs for what price? I live in a fairly rural area where dnyo’s are pretty few and far between. My main shop is dedicated to Mustangs, very fast ones at that, and they always have good advice and give me props for getting as much hp as I have out of my car NA.

In any case, test pipes add some power, as do intakes, and also, in turn require more fuel. So, IMO, the addition of those 2 items together to your set-up significantly changed airflow and thus fuel needs. I would either find a friend with a WB system, go back to the shop and re-tune, or, get some peace of mind and pick up a relatively cheap WB system. I have the ZT-3 with gauge. I decided I didn’t need all the bells and whistles for my needs and opted for this unit with no logging capability (although it’s easy to add if in the future I decided to). All I di is street tunes and some dyno time every now and then. IIRC out o the box it was 230$. And you already have an O2 bung in there so, it should be fine. Most WB systems have a certain angle they want the O2 sitting at in the exhaust stream. With that said, I would just go with that set-up in your test pipe and if it’s not as the WB manual states it should be, plug it and have another bung welded. They’re relatively cheap (10-20$ IIRC).

A WB system is fairly standard for AFC owners just to keep an eye on things since they can, do and will change, as you’ve seen.

I was charged $70 for 3 pulls. They charge extra for run files and graphs. I'll be buying a wideband as my next purchase. NmexMAX, I appreciate your advice. I have noticed you are always willing to help out a fellow org member who doesn't know as much. Thank you.

I have an appointment Friday to rent some dyno time. I'll report back with hopefully some better numbers and a safer air/fuel ratio.

I rented dyno time this morning to richen up my air/fuel ratio. The red line is where my car currently is. You can see that my car makes less power when it's in the low 12 afr range. It makes about the same power at 13afr as it did in the mid 14 range.
Attachment 27600

The blue line was +1% across the board on the VAFC.
The red line had the following settings: 0 correction all the way up to 4200RPM, +1% correction for 4400 and 4600, -1% correction 5600 to redline.

Forgot to mention. I checked my spark plugs today, and they are ready to be changed. I let theses things slide for too long. Here's a funny question. Will I need to re-tune my car when I get fresh plugs in? I really hope not!

Do you still have all those Mods in your Sig or did I miss something...:D

No, you didn't miss anything. My car is down on power quite a bit from where it should be. I'm not sure why. The only obvious thing I need to do is replace the spark plugs. It burns oil, but that shouldn't affect power that much. It accelerates smoothly, and it doesn't feel like anything is wrong at all. Either way I'm done with modifications. The plan for the car from here on out is to keep it well maintained. At one point my car made 233 wheel horsepower, but now it doesn't. There has to be a reason why. I'm just not sure what that reason is.

No codes at all, and was it the same spot you dynoed before?...:D

I have a code for the evap canister, but that shouldn't matter. The recent dyno runs were at a different spot than the one that made 233. I wouldn't think there would be a 26 horsepower difference. They are both Dyno-Jets. The torque numbers are about the same, but the old numbers were achieved from a 2nd gear pull. The latest ones were 3rd gear pulls.

Our cars are set-up a little differently, but I never saw that much difference in AFR with only 1% change in AFC settings.

I usually go between 8-12% in order to see a noteable change.



Here is a leaning of 6-8%.

Attachment 27495

I might try a different Dyno shop next. This last time I was at Late Model Throttle in Waukesha, WI they had a issue getting the wideband to read correctly. Twice the air/fuel ratio shot up into the 18's during a pull. They said there was too much air, and they re-positioned the sensor. Then I talked to a friend of mine who has a 650 horsepower Chevelle. I didn't know it when I went, but he was at the same shop to do some dyno pulls a few months ago. He said his car dyno'd way lower than at other places. He heard their dyno isn't calibrated correctly if that's possible. I'm done blowing money on the car this year. I'll try a different dyno shop next spring before drag racing season begins.

NmexMax, I got about the same change in air/fuel ratio with 1% to 2% correction as you did with 6% to 8% correction? That doesn't make any sense at all.