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.
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.
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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