When I dynoed my car last week my shop inserted the A/F probe into the exhaust pipe that was emitting exhaust fumes while at idle. After the dyno run my shop manager was shocked to see my A/F ratio at 15!! He commented that if that were in fact the case my engine should have melted a while back. Is it able to get an accurate A/F reading with the stock muffler? I noticed that Kevin has an EGC. Is that better for monitoring our engine performance versus an A/F gauge and if so why? I would appreciate it if anyone could shed some light on this confusing topic for me. Thanks

Diederik

 

EGT is better than AF. If you can scan and post your dyno plot showing the horse power and a/f ratio this would help me answer your question, or e-mail it to me at matchou@***.net

 

Hey Kevin I'd appreciate any of your insight on this issue.

 

I agree with MardiGrasMax. The EGT is better unless you can purchase a high end A/F ratio gauge. I currently have the A'pexi EGT and Tomei A/F gauge on my pillar.

Your A/F will fluctuate at idle. As long as you're not running 15:1 on the dyno in the high end of your rpms, you should be fine.

 

Ok Gents correct me if I am wrong but wouldn't it be wise (information wise) to run both an A/F and an EGT ?

 

I could be wrong, but I think it might actually be normal for the engine to run slightly lean at idle and at very low throttle. I know Honda has developed some engines that run something like 16 or even 18:1 at cruise (D16/17 4-bangers in some Civic's). It cuts down on emissions and improves fuel economy and I guess the light throttle load doesn't cause any problems for the engine as far as EGT goes. I'm sure other engines are set this way too, but maybe just not that extreme, depending on the manufacturer, but...

ECU's are programmed to go full-rich when you hammer it to prevent melting your engine from running lean (high EGT). They're programmed that way as a sort of safety feature obviously, because running extremely rich cuts down on performance, but for an engine designed to last over 200,000 miles it's better to run rich than melt pistons

Also, and I'm not sure on this either, but wouldn't probing the A/F at the tailpipe be a bit inaccurate? The purpose of a catalytic converter is to help burn up what didn't get burned in the cylinder so wouldn't this bias a tailpipe reading even leaner?

But yeah, like Kev said, as long you're not running 15:1 on the dyno (at WOT) you should be fine. If you were running 15:1 on a dyno at WOT you would probably be walking home!! :-o

 

If you have the cash, then yes. Ideally, we should run 2 EGT's or 2 A/F gauges (one for each bank)... but that's a bit of bling bling.



Yes, it's normal to drop down to 16:1 (sx7r and CalsonicSE). I have seen mine drop down to that on occasions, but it usually sticks at 14.2:1 (idle or normal crusing) because I bypassed the Hobbs Switch so the SC pump is always on.

 

That's what was so confusing to my shop manager was that it was running 15:1 at WOT. He said that's impossible and that I should be walking home if that were in fact the case. Where is the A/F probe placed in the exhaust path if you are running an A/F gauge? I'll scan my dyno plot with the A/F ratio later this week when I pick it up from my shop. How accurate is it reading the A/F ratio through the exhaust pipe anyways?

 

Hmmmmm..... that doesn't sound right. Are you sure the sniffer wasn't messed up?

The A/F gauge comes with an O2 sensor. You can either weld a bung onto your y pipe or replace one of the OEM O2 sensor with the one provided. The Tomei gauge is VERY accurate. CalsonicSE and I were comparing the A/F on his Tomei vs. the one he got from the dyno.

Here are some pictures of the Tomei http://12.233.210.59/y2kevse/images/...ir_fuel_gauge/

 

So it looks like the A/F ratio is measured with an O2 sensor upstream of the cat is that correct? If so how would such a reading compare to one obtained from a sniffer stuck in the exhaust pipe? What do the Tomei gauges cost and what color do they light up at night? Does Greddy make an A/F gauge?

 

Yes, the O2 sensor is upstream of the cat. From what CalsonicSE and I saw, the reading was pretty much dead on (including the little blip he had that went to 14:1 then dropped back down to 13.X:1).

Tomei costs $430 (I bought this through yo_its_ok), but I'm sure you can get it directly from AEBS. Yes, GReddy makes an A/F gauge similar to Tomei. Jane bought one last week for about $288.57.

The numbers/letters light up white with the Tomei (not really white... they use a clear bulb).

 

Kevin do you have the 60mm or the 52mm gauges? How does Jane like her GReddy A/F gauge? Since I have the 52mm GReddy boost gauge I would like to get another matching GReddy gauge but I don't think they make the A/F gauge in the 52mm size. How does an EGT let you know how the car is running? (I mean does it correspond to A/F ration at all?)

 

All my gauges are 60mm, so I had to enlarge the holes.

She ordered the GReddy last Friday, so it (along with other things) should be coming in today or tomorrow. From what I noticed, GReddy doesn't make a 52mm A/F gauge.

The EGT is just another warning device. With the Tomei, I can tune the car since I can see the A/F fluctuate (haven't been doing a good job of it since there isn't any nice long wide open stretches). You can't do that with an EGT.

If you're running rich, the EGT reading would be somewhere in the high 600C degrees. MardiGrasMax runs about 780 with his SC and NOS setup. I hit from about high 600C to low 700C. If you're lean, you'll see 800C+ on the gauge. I have my warning light set to go off at about 800C, so when I see the red light blink I know it's time to let off. I see 800C if I cruise at high speeds or push the car (hard) going up a hill.

 

I have had a little while to play with my set up. I have peaked at 805c while checking to see if the fields removed the speed limiter on my GXE.

With the full race tune preset selected I got a peak EGT of 780c in a WOT run from 2nd through 4th, and the car was hauling a s s!!!