Tailpipe AFM Sniffer

[Psucamper]

I have four running engines to test. Two 1600 dp and two 2000cc FI. The LM-2 unit looks to be suitable, but the routing of the exhaust gasses into the LM-2 sensor has been the subject of too much speculative engineering and error on many VW sites I have visited. And, many of those sites are devoted to super tuning of "hot"engines. We are VW people with more modest (but not sloppy) requirements
On the mentioned vehicles I do not want, or intend to, weld in a bung for the sensor. The Innovative "tailpipe adapter" is purported to be OK for T-1 peashooter tips. But does it really "fit"? On the buses? How about false air mixing with the real gas stream to be sampled? On the other VW site some say "just stick it in and believe the reading" Really? Is there a problem at idle making the reading falsely low? Does anyone here have real world experience and is willing to share it? Many thanks.

[Bleyseng]

It works but idle is the least of your worries as you want to set the patrolled and WOT AFR correctly first. O2 bung in the best for that and the tailpipe thingie works but I as know now don't go too far as the hot exhaust melts the wiring to toast.

[Psucamper]

Geoff. Thanks for the reply. Yes,I know a bung installation is the best thing to do but on a bug muffler where to put it? I think that's a much deeper problem involving both cylinder banks exhaust gas mixing in the tank body rather than hot gasses squirting out the individual peashooters. You mentioned a "patrolled WOT and AFR...." I know AFR & WOT but "patrolled"? What? I do have a tendency to over think engineering stuff so I'll dig deeper and see what happens.

[asiab3]

My LM-1 tailpipe clamp does not fit in the stock 1600 bay bus tailpipe. It DOES fit into a hacked-off Splitty talkpipe, as Colin and I can attest. Stick it on the damper pipe of the early bus, and make sure to CLAMP IT, ROBBIE. Around 45-50mph, I get odd readings as airflow and maybe backflow instantly cause too much turbulence to read. I imagine a proper rear-facing exhaust pipe would not have the same issue as this sideways damper pipe clamp.

It fits nicely in a '76 FI bus I worked on last year.

Sorry I don't have any experience with the T1 "pea shooters."

Robbie

[Psucamper]

Robbie. Thanks for the reply. Yes, that's exactly what I wanted regarding the Bus application. That leaves the question of the T1 "peashooters. There has to be a hack of some sort that will the allow an adaptation. I'll work it out.

[asiab3]

Robbie. Thanks for the reply. Yes, that's exactly what I wanted regarding the Bus application. That leaves the question of the T1 "peashooters. There has to be a hack of some sort that will the allow an adaptation. I'll work it out.

It might work fine in a dual tip bug setup, but there might also be some weird flow effect with the duel outlets having one blocked. The main issue with the T1 early bus is the tailpipe clamp wanting about 3-4" of straight pipe to insert then clamp onto.

[Amskeptic]

Robbie. Thanks for the reply. Yes, that's exactly what I wanted regarding the Bus application. That leaves the question of the T1 "peashooters. There has to be a hack of some sort that will the allow an adaptation. I'll work it out.

The Type 4 stock exhaust I have been reading from for years. The sniffer is jammed into the curve of the pipe, the clamp barely grabs the pipe at its edge, and I now have a fully internalized sort-of map of the fuel mixture, internalized, because whatever compromises are to be had with this dorky set-up, I no longer care and I no longer compare with others' readings. It is just too variable I think. But anybody can start working immediately with what they have no matter how it gets hooked up. You will need to establish a couple of your own benchmarks. I know my plug color-to-LM-1 fuel ratio. For whatever reason, 13.7 is as lean as I will go at cruise. For whatever reason my readings show 10.9 is the best full throttle ratio at the torque peak 50-55 mph), leaning out to 11.9-12.4 at 70 mph, I came here only by trial and error and CHT readings. I have to do a whole nuther summer with the BobD with a correctly functioning CHT gauge this time, because I finally could not speak for anyone with my individual car's quirks. Go find your own numbers with wherever you get the sniffer to sniff (and you are correct, the bug muffler has no real single take-off point that you can rely on, but you can learn regardless what your engine wants and let the numbers follow the results.
Colin

[Psucamper]

Excellent and informative response. Confirms my guesses with real world experience.Thank you.