O2 sensor location to prevent revision

Steve C · 02-11-06, 08:36 AM

Can anyone tell me the optimum place to install an o2 sensor for a FI engine? I have been told by a large engine mfg that installing the sensor in a GT40 exhaust is a problem as the pipes after the sensor are straight (no backpressure) and as a result of no backpressure a "revision effect" is present wherin ambient air is ingested fooling the o2 sensor to believe there is more o2 than really in the exhaust gases and therefore calling for more fuel and an effective much richer than needed mixture. Make sense?? If so what is done to overcome this condition?? Common baffled muffler that takes imput from both headers?? Baby cats and baby individal mufflers?? If I end up needing cats and FI to meet my emissions needs of 220ppm HC and 1.2% CO I dont want the o2 sensor calling for MORE fuel and worsening the emissions issue....HELP & THANKS Steve

Fernando Gonzalez-Bunster · 02-11-06, 11:47 AM

Steve, if you're going the route of FI, o2 sensor and CATS, aren't you going to need an AFM and a computer brain to which the o2 sensor will report its findings. Generally you'd want the sensor before the CAT so it measures uncatalized exhaust and sends the reading to the ECU and in turn to the AFM which makes the adjustment of the incoming air. The CAT in a sense is the final filtration.

David York · 02-11-06, 02:42 PM

Hi,
YOu should have no problem running a Lambda in the collector of the exhaust. I ran one in my Caterham and the exhaust was very straight.

Assuming you go FI you should be able to map the engine with a "emissions" profile to get pass your needs. It will be down on power but will pass. THen you can upload the power map once you have passed the test. Most of the programable ECU's will allow you to do this.

Steve C · 02-11-06, 04:43 PM

Fernando GB....If i can't feel cmfortable to pass my emissions reqt w/ a 427FE carbed engine w/ cats ( still hoping someone can advise me if I can)...I will use a Roush FI 402W (or they tell me their 427 W is more benign) 8stack system complete w/ management. Dave York ( ah someone from the UK who may have some MOT emissions understanding and how the MOT test relates to my need to meet 220ppm HC and 1.2% CO????????). Thanks for your comment w/ regards placement of the O2 sensor not causing problms on your Caterham's straight pipes.....now I'm confused as it was Roush engineering that told me the first GT40 install they did on a SPF showed "revision" and a false high O2 signal causing a call for more fuel than really needed. Roush suggested installing a baffeled muffler after the sensor to create some back pressure and aleviate the revision effect....also some discussion as to need for cats as well to pass my emissions limits but, WILL ALLTHIS FIT???and no one on this side of the pond seems to know any of this for sure????? HELP Steve

Fernando Gonzalez-Bunster · 02-11-06, 06:28 PM

Steve, doesn't Mass. let you register as a 1965 model year? Thus not requiring emissions test. Would you consider a Maine registration that has a non-resident registration program (thus no emissions for MA). I registered my GT40, that resided in CT, with Maine plates.

Ron Earp · 02-11-06, 08:21 PM

Steve, there are definitely people on this side of the pond that know the answers - just ask more directly. I'm not one of them, but I've an idea...for the O2 sensor and reversion one thing we've done on motorcycles and one race car with a short exhaust was simply to clamp on a couple extra feet of pipe beyond what we normally used. Then, we tuned the motor with good effects and removed the pipe.

Sure, removing the pipe has some effect and in theory would throw off the tuning, but it is small and in practice allowed us to get around the problem of having the O2 sensor within a couple feet of the atmospheric exhaust. And the car ran like a champ. Theory and practice don't always equate.

Steve C · 02-12-06, 12:08 AM

Fernando GB....Mass will not allow registration as 65 model yr...now requires registration to call out "replica of XX yr built in year of completion" and yr of block does not matter one must meet Calif level emissions but, will give "exemption" to the levels I have noted in earlier post........Your idea of Main non resident registration is appealing but, I have a PITA neihbor who would like nothing better than find a reason to have the authorities down my throat.... Ron thanks for you suggestion re adding extra pipe during tuning to compensate for reversion....good idea! Still hoping to get some real world response re my emissions levels...I really need to know that I can meet them B4 I committ to engin build. Steve

Peter D · 02-12-06, 06:03 AM

Steve, I also had to do the "emissions thing" for rego, but here in Oz (NSW) the RTA had a test setup on a dyno that involved following a pre-set drive cycle for about 3 mins. A giant sniffer at the back cought all the xhaust gases (& in my first run, all the unburnt HC that was leaking out faulty filler cap necks). Unfortunately, the RTA's standards are expressed in gm/km as measured over the test, & this does not translate into the % figures that you are looking at.

However, in relation to your questions on CATS & the exhaust system, perhaps the attached pic of my functional (ugly) initial setup will help.

I was advised early on that there was no way a carb engine would pass, CATS or no CATS, so EFI was the only choice - & CATs would be mandatory. The pic shows the CAT & muffler setup that got us through (just) - the O2 sensors are located in the collectors, just in front of the flanges, & point down/out at 45deg.

With the big loop-back exhaust system, we were able to get reliable & realistic readings from the wide-band O2 sensors - she stayed in closed loop all the time.

(It even passed the noise tests - but not without the help of half a dozen s/s pot-scrubbers up each tail-pipe) !

Conventional wisdom here in Oz said that we would never get an 8-stack to pass, but my engineer had other ideas ! He matched specs for the AFR heads, cam & injectors to get what he wanted, then told me that the injectors had to be mounted inboard (like the TWM setup) so that they pointed straight into the ports. It was a challenge, but it all worked in the end - after 5 attempts on the RTA test cell, we finally just scraped through.

BTW, the induction trumpets also had big oil-soaked filter socks on to cut out any HC from spit-backs going into the sniffer.

I started out with a real mind-set against EFI, but I was forced to go that route - I am now so glad I did ! The ease of tuning, the brilliant diagnostics, the reliability - all good stuff !

Sorry I couldn't help with the emissions levels, but maybe the exhaust setup will be useful.

Kind Regards,

Peter D.

Steve C · 02-12-06, 09:54 AM

Peter....Thanks for you imput....Picture youreferenced did not show up...will you please resend as it will be most helpful! Steve

Peter D · 02-13-06, 01:57 AM

Steve, sorry about that !

Peter D · 02-13-06, 02:21 AM

The reason that the CATs are pointing outwards is that the centres of the collectors on the DRB crossover setup were only 90mm apart. I couldn't find CATs big enough to do the emissions job & skinny enough to sit side by side on 90mm centres.

The CATs have been a big PITA - I lost ignition on 2 cyls the other week (crook connector on a coil igniter) & limped a few kms home backfiring, etc. When I opened the rear clip, the LHS CAT was bright red-hot & the muffler was almost the same ! The huge unburnt fuel load going into the CAT really got that catalytic process going !

The net result was that the rear half of the element in the CAT melted & got spat out as little (expensive) lumps, & a whole bunch of the f/glass packing in the muffler also melted into little lumps of glass which rattled around inside !

I have since "cleaned out" both the CATs (I found that a foot-long 1/2" masonry drill was most effective for this "cleaning" exercise !) & had the muffler emptied out & repacked.

All in all, CATs are a pain - even when everything is working correctly, I am willing to bet that they raise the engine bay temp quite significantly. Quite a while ago, Adam posted a huge technical treatise on how expansion chambers could effectively emulate the effect of equal length tuned headers - perhaps the new "clean" CATs will serve this purpose (apart from looking legal) !

Kind Regards,

Peter D.

DavidTC · 02-13-06, 02:02 PM

Peter
Do I take it from this that your catalytic converters were ceramic monolith design ?. Performance cars, (and performance motorcycles) for that matter, always use wire wound systems which are more expensive but stand all of the bumping around.
Just thought I would ask.
Regards
David

Peter D · 02-13-06, 10:35 PM

David, I assume that mine (were) the monolith type - a cylindrical block of ceramic stuff with millions of tiny holes running from front to back - like honeycomb, but with square holes. My "cleaned" CATs should now stand any amount of bumping around !

Kind Regards,

Peter D.

Eric · 02-18-06, 12:14 AM

Those readings will be achievable, but I guarantee you will need cats no matter what. If it is just an idle test, you could probably cheat/squeak it through with a carb but anything under load, forget it, you will want efi.
Just to give you an idea, a little Honda Civic with no cat on it will fail those readings.