V6 Essex with 290º Cam - Hydrocarbon problems
Discussion
Has anyone experienced trouble with non standard camshafts and MOT emission rules recently?
The limit for post 1975 cars/pre early 80's is 1200ppm - I am having trouble getting it below about 1400ppm at 2500 rpm (allowable rather than idle speed if idle HC's are too high - mine are 3000 at idle!). Using a V62 290º Kent Road/Rally cam, I'm guessing the 74º valve overlap is causing this trouble. Short of widening the rocker arm to pushrod gap for the MOT, I reckon a milder cam is needed - V63 looking the best.
Just to add that CO is 2.3%, O2 is about 5-7% on machine & I've tried all sorts to try to get the reading down (luckily I have access to a good emissions testing machine). I'm running triple 40DCNF Weber carbs too.
Of course there may be another reason/reasons for the problem such as incorrect jetting/ignition etc and am currently checking everything again, including cam timing (was altered by my rolling road) but I need to find out first what it's been set to, if this is wrong then that's the first thing to change.
Any advice would be very welcome.
The limit for post 1975 cars/pre early 80's is 1200ppm - I am having trouble getting it below about 1400ppm at 2500 rpm (allowable rather than idle speed if idle HC's are too high - mine are 3000 at idle!). Using a V62 290º Kent Road/Rally cam, I'm guessing the 74º valve overlap is causing this trouble. Short of widening the rocker arm to pushrod gap for the MOT, I reckon a milder cam is needed - V63 looking the best.
Just to add that CO is 2.3%, O2 is about 5-7% on machine & I've tried all sorts to try to get the reading down (luckily I have access to a good emissions testing machine). I'm running triple 40DCNF Weber carbs too.
Of course there may be another reason/reasons for the problem such as incorrect jetting/ignition etc and am currently checking everything again, including cam timing (was altered by my rolling road) but I need to find out first what it's been set to, if this is wrong then that's the first thing to change.
Any advice would be very welcome.
I had problems this year with my M. I'm running a JW270 cam with high efficiency, unleaded heads from JW Developments. The car was also set up by him. My O2 was at 7.5%. After about 1 hour we got this down to 3% - thanks to the guys at The V8 Centre in High Wycombe for taking the time.
Chatting to the MOT guy there, he said that this was all part of the Government's plan to get older cars off the road.
He reckons some cars are never going to be able to meet the new regs. He also said that soon the emmisions will be logged direct at the DVLA (or whatever Quango it's called). BB is watching you!
Chatting to the MOT guy there, he said that this was all part of the Government's plan to get older cars off the road.
He reckons some cars are never going to be able to meet the new regs. He also said that soon the emmisions will be logged direct at the DVLA (or whatever Quango it's called). BB is watching you! 
On teh decatted cerberas the HC value is always sky high .. typically 2000ppm .. you can get them through the mot tho by massively retarding the ignition. I've had HC of 140ppm on a decatted cerbie and they're a very very dirty engine normally. The problem you're gonna have on a carb engine tho is that as you retatrd the timing you'll have to open the throttle more to get the revs up .. you may go outside the idle/progression and into teh main jet area of running so you'll have to pay close attention to how you've got that bit jetted. On ECU cars of course you can dial in whatever mixture you want at any part of the rev range.
I'd very much advise you to go fully mapped if you want to make your classic car drive better, more fuel efficient, cleaner and more powerful
I'd very much advise you to go fully mapped if you want to make your classic car drive better, more fuel efficient, cleaner and more powerful
I used to have this problem on my trick engined Taimar. The two MOT stations I used were very forgiving:-
The first (when it had gone off the end of his scale at tickover) said as long as it comes down as you rev it then thats ok with me.
The second one said it will fail however all you are going to do is tune it to pass and then set it back again, isn't it.
A more friendly MOT station might be the way to go. BTW I had a Kent V63 so maybe that won't help you.
davidy
The first (when it had gone off the end of his scale at tickover) said as long as it comes down as you rev it then thats ok with me.
The second one said it will fail however all you are going to do is tune it to pass and then set it back again, isn't it.
A more friendly MOT station might be the way to go. BTW I had a Kent V63 so maybe that won't help you.
davidy
Thanks all of you!
Will post my findings once I get time to sort it, however it's a little worrying for the future of classic cars. The MOT test includes a set procedure for emissions now and this can't be bypassed unless the probe is plugged into another car, or if the tester is "kind". The engine is still not 100% so I know there are 1 or 2 things that need changing, possibly mid-range jetting is too rich, and also cam timing as already mentioned.
I'd rather sort it out properly as the fumes are a problem on the M Series cars for making your clothes smell. Engine mapping sounds like a good (but expensive) idea, shame I can't adapt a VVT pulley to work on the Essex engine - that would sort it out...
Will post my findings once I get time to sort it, however it's a little worrying for the future of classic cars. The MOT test includes a set procedure for emissions now and this can't be bypassed unless the probe is plugged into another car, or if the tester is "kind". The engine is still not 100% so I know there are 1 or 2 things that need changing, possibly mid-range jetting is too rich, and also cam timing as already mentioned.
I'd rather sort it out properly as the fumes are a problem on the M Series cars for making your clothes smell. Engine mapping sounds like a good (but expensive) idea, shame I can't adapt a VVT pulley to work on the Essex engine - that would sort it out...
Just for info. I had a reply from Piper today says basically alter cam timing temporarily to reduce lift at TDC, then swap it back again afterwards.
I like the carb idea better, and guess also that as air/fuel flow is distributed differently on a triple carb setup, a single carb will not have the same pulsing effect.
I can see some fun hours of testing ahead
I like the carb idea better, and guess also that as air/fuel flow is distributed differently on a triple carb setup, a single carb will not have the same pulsing effect.
I can see some fun hours of testing ahead
Interesting reading here:
http://chevyhiperformance.com/howto/71498/
Basically confirms overlap problems, but also some interesting ways to help idle mixture troubles.
http://chevyhiperformance.com/howto/71498/
Basically confirms overlap problems, but also some interesting ways to help idle mixture troubles.
3000MV6 said:
Just for info. I had a reply from Piper today says basically alter cam timing temporarily to reduce lift at TDC, then swap it back again afterwards.
I like the carb idea better, and guess also that as air/fuel flow is distributed differently on a triple carb setup, a single carb will not have the same pulsing effect.
I can see some fun hours of testing ahead
Alter the cam timing temporarily.
On an Essex.
So that's drain oil, sump off, alternator belt off, crank pulley off, timing cover off, retard cam - assuming you have an adjustable cam gear - refit timing cover with new gasket, refit crank pulley, refit sump with new gasket, refit alternator belt, refill with oil and test: then repeat until correct result is achieved.
Then repeat again after the MOT.
I think I'd rather try running it lean...
Valve stems are new, as are guides 
I'm still thinking maybe leaning off the jets & playing with the timing for the test. However turning down the CO doesn't drop the HC at idle 650rpm so I am thinking the 2500rpm test is the way to go, however I need the mixture leaned off at this point as that is what's causing the trouble - as I managed to get it down to about 1400 at 2500rpm then a leaner mixture at this point would work. Just need to figure out what I need - whether its air corrector, emulsion tube, idle or main jets. More studying in progress
I'm still thinking maybe leaning off the jets & playing with the timing for the test. However turning down the CO doesn't drop the HC at idle 650rpm so I am thinking the 2500rpm test is the way to go, however I need the mixture leaned off at this point as that is what's causing the trouble - as I managed to get it down to about 1400 at 2500rpm then a leaner mixture at this point would work. Just need to figure out what I need - whether its air corrector, emulsion tube, idle or main jets. More studying in progress
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