Anyone explain this? - Civinfo
 
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post #1 of 8 (permalink) Old 6th March 2013, 00:34 Thread Starter
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Anyone explain this?

OK bit confused here.

I understood Honda was dropping VTEC in favour of turbo because of emissions but then someone a while back said emissions are tested at idle. So why does VTEC make emissions so high?

Also on the same subject, why can't Honda produce a VTEC that does 11-12,000 rpm as surely that would be unbeatable on the road.

Now I fully understand race engines are rebuilt after every race and road cars need longevity, but many road going motorbikes reach such dizzy heights without losing longevity or needing rebuilds so why can't such a car be built?

Finally, is there any technical reason why Honda couldn't use 3 sets of cam followers instead of 2 to perhaps overcome some limitations to produce a kind of tri-vtec setup? So eg cam would lift at 4,000rpm then again at say 9,000rpm.
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post #2 of 8 (permalink) Old 6th March 2013, 07:21
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Too technical for me
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post #3 of 8 (permalink) Old 6th March 2013, 09:50
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Re: Anyone explain this?

Key difference between car and bike engines is the size of the moving parts and the strain/forces they are under. The numbers involved dont increase in a linear fashion with the size of the engine.
Also its down to the use of the vehicle. Majority of sports bikes are 2nd vehicles so essentially a toy where as the car is for everyday use, so the expected longevity is different. I had a biker friend at college and we often discussed this subject (college was often dull)

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post #4 of 8 (permalink) Old 6th March 2013, 10:09
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I'm not sure VTec is going, the point of VTec is to allow the engine to rev higher by effectively having a high lift cam but this is bad for low rpm so the VTec solves this issue. It is not a contributor to emissions as the test is done over a complete cycle which means it covers urban, extra-urban etc. It covers a range of speeds, keeping the VTec crossover high (which it is) keeps it out of the cycle. The issue is because the engine is NA, so to produce the power needed it can't rely on the turbo to help. It is not a question of either or, they can coexist. The issue is you can get the power without the emissions when using a turbo over using NA. Basically a turbo engine is having a small engine with a bigger engine equivalent output but with less emissions.

Last edited by delta0; 6th March 2013 at 10:18.
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post #5 of 8 (permalink) Old 6th March 2013, 21:28
 
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Quote:
Originally Posted by Alsone View Post
OK bit confused here.

I understood Honda was dropping VTEC in favour of turbo because of emissions but then someone a while back said emissions are tested at idle. So why does VTEC make emissions so high?

Also on the same subject, why can't Honda produce a VTEC that does 11-12,000 rpm as surely that would be unbeatable on the road.

Now I fully understand race engines are rebuilt after every race and road cars need longevity, but many road going motorbikes reach such dizzy heights without losing longevity or needing rebuilds so why can't such a car be built?

Finally, is there any technical reason why Honda couldn't use 3 sets of cam followers instead of 2 to perhaps overcome some limitations to produce a kind of tri-vtec setup? So eg cam would lift at 4,000rpm then again at say 9,000rpm.
Are VTEC emissions that high?

The 1.8 i-VTEC has CO2 output of 137g per mile for 140bhp, whereas the Ford Focus 1.6T has exactly the same CO2 output for only a few more bhps. Not bad for an engine that is effectively 8 years old in its design...

An engine revving as high as you suggest will probably end up with pretty bad mpg, and would have to be built to a pretty high spec to last 100K miles. By its nature, it would probably end up with low torque as well.

The tri-stage setup you suggest has already been done:

Honda - VTEC - 3-Stage VTEC
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post #6 of 8 (permalink) Old 7th March 2013, 23:30 Thread Starter
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Quote:
Originally Posted by bodgerx View Post
Are VTEC emissions that high?
I understood that is what had been given as the reason for going turbo over NA.

Quote:
Originally Posted by bodgerx View Post
The 1.8 i-VTEC has CO2 output of 137g per mile for 140bhp, whereas the Ford Focus 1.6T has exactly the same CO2 output for only a few more bhps. Not bad for an engine that is effectively 8 years old in its design...
I don't disagree maybe it scales badly with power.

Quote:
Originally Posted by bodgerx View Post
An engine revving as high as you suggest will probably end up with pretty bad mpg, and would have to be built to a pretty high spec to last 100K miles. By its nature, it would probably end up with low torque as well.
I guess that would be true at 11or 12,000rpm but then again how many people would spend much time at those rpms. Most people would be happy if mpg was great at town revs, ok at medium and poor only at the very top.

Quote:
Originally Posted by bodgerx View Post
The tri-stage setup you suggest has already been done:

Honda - VTEC - 3-Stage VTEC
I didn't know that.
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post #7 of 8 (permalink) Old 8th March 2013, 00:01
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Euro IV V VI etc is a test manufacturers have to pass and dont relate to MOTs as such.

VTEC will probably be replaced by AVTEC.
VTEC is not the issue as such....AVTEC will have more volumetric efficiency across all the rpm range..instead of just two points..

Main emmisions concern is NOX, CO, Hydrocarbons and Particles/Smoke.
More power per litre normally increases NOX..as does most tuning attempts and especially raised compression.
2015 cars need to meet EURO 6.

Understanding Engine Exhaust Emissions
Quote:
NOx = Oxides of Nitrogen (This is only seen by a 5-gas analyser) Only seen with dynamometer or engine under load. NOx emissions rise and fall in a reverse pattern to HC emissions. As the mixture becomes leaner more of the HC's are burnt, but at high temperatures and pressures (under load) in the combustion chamber there will be excess O2 molecules which combine with the nitrogen to create NOx. NOx increases in proportion to the ignition timing advance, irrespective of variations in A/F ratio. This gas is related to the exhaust gas detoxification systems ( in conjunction with Co and HC) , exhaust gas recirculation systems. Those systems bring some of the inert (processed) exhaust gas back in to the engine to be burned again. This time around this gas has no O2 extra molecules and prevents high combustion temperatures and further increase in NOx formation. NOx is Very Dangerous Lethal Gas and air pollutant!
See the problem with tuning ...and MBT.

Surplus oxygen = NOX.
Surplus fuel = HC

Only way to square the circle is to get 100% chemical reaction...and a stoichimetric ratio at all loads one assumes.
If you can lower combustion temps in the process...hence EGR....




Last edited by Relic; 8th March 2013 at 00:11.
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post #8 of 8 (permalink) Old 8th March 2013, 02:05
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