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Old 21st August 2006, 14:34   #31
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But anyway as regards the real world Carb Zen Vs MPFI Zen. My observation is that the MPFI zen adjusts itself to load acceleration and the engine rpm much better than the Carb Zen. Many people could not even extract the full performance potential of the carb Zen, as the driving style of many a Zen owners I know would never get to utilise the power circuit of the Carb!

However if you tune a carb Zen for out right performance, or out right FE then I guess it would keep itself not far behind its MPFI Avatar or performance or FE stakes respectively. But then you could forget FE from a car tuned for Performance and vice versa. So my choice would always be the MPFI car.
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Old 21st August 2006, 15:10   #32
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Quote:
Originally Posted by 1100D
The Carb vs MPFI debate can take another angle when we bring Variable Valve Timing and lift into picture. As far as my knowledge goes a carb cannot adjust the air fuel mixture for the high lift (longer valve open) scenario...
Er... Just to point out, Valve Lift and Lift Duration are two different things. For low RPM, high lift and low duration (less poppet travel/lift, longer open), and for high RPM, low lift and high duration- for gases to flow more freely.

The VTEC doesn't reduce the egine displacement. It fiddles with the combustion volume. The stroke length remains same. EFFECTIVE displacement is same. Only the amount of air sucked in is different. For example, if the Vtec kicks in, at say, 4000 RPM, the engine will suck in 100cc of air (volume) per cylinder uptil 4000 RPM, by opening the intake valve AFTER BDC. When the VTEC kicks in, the engine will suck in more air, for example, say 120cc, by opening the intakes AT BDC, thereby keeping the valve open for more time, and hence taking full advantage of the vacuum and intake charge swirl/velocity.
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Old 21st August 2006, 15:38   #33
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Quote:
Originally Posted by veyron1
The VTEC doesn't reduce the egine displacement. It fiddles with the combustion volume. The stroke length remains same. EFFECTIVE displacement is same. Only the amount of air sucked in is different. For example, if the Vtec kicks in, at say, 4000 RPM, the engine will suck in 100cc of air (volume) per cylinder uptil 4000 RPM, by opening the intake valve AFTER BDC. When the VTEC kicks in, the engine will suck in more air, for example, say 120cc, by opening the intakes AT BDC, thereby keeping the valve open for more time, and hence taking full advantage of the vacuum and intake charge swirl/velocity.


Right VTEC does not reduce actual engine displacement. But in the Civic i-VTEC keeping the inlet valve open till after the piston reaches BDC the compression losses are reduced. What this also means is that some of the air is expelled out when the piston is in the compression stroke (MOVING UP) and the inlet valves are still open. So effectively the engine gets less air. Now engine displacement is measured by BoreXstroke which actually is a measure of how much air the engine sucks in, now if some of that air is expelled out thru the inlet valves, wouldn't it be like saying that EFFECTIVE Displacement is lower?
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Old 21st August 2006, 16:15   #34
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@1100D; Yes, the volume is calculated by measuring the BorexStroke. But what we forget is that the dimensions are taken from TDC and BDC, not the air volume entering the cylinder.

The Engine CC is calculated by Pi*(1/2 Bore, in cm)*(1/2 Bore, in cm) * Stroke(in cm). The air volume inside differs, according to various factors. Compression ratios are calculated from the cylinder volumes, but actual compression is measured in kgf/ psi per cylinder, which can vary with each engine, even if the engines sport similar bore/stroke dimensions....

Also, if incoming charge opposes the intake swirl directions, its not a good thing. You need to push in as much air as possible. Theoretically. In practice, it's good for high-revving engines to keep maximum valve overlap.

Therefore, the EFFECTIVE displacement (theory, cylinder volume) in terms of cylinder volume, remains same. ACTUAL volume, in terms of intake charge, is variable....
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Old 21st August 2006, 16:32   #35
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Quote:
Originally Posted by veyron1
Therefore, the EFFECTIVE displacement (theory, cylinder volume) in terms of cylinder volume, remains same. ACTUAL volume, in terms of intake charge, is variable....
ha ha ha, we are saying the same thing but using different terms. I agree completely with you and I was saying nothing different.

When I was saying EFFECTIVE displacement I was talking in terms of the actual intake charge. The theoritical cylinder volume I was saying ACTUAL displacement.

I will check the text books though!!
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Old 21st August 2006, 19:51   #36
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Quote:
For low RPM, high lift and low duration (less poppet travel/lift, longer open), and for high RPM, low lift and high duration- for gases to flow more freely.
Actually it's the opposite. At low rpm , you want less air to enter the cylinders for better FE, so the valves don't open completely. At high rpm, valve lift is maximised to let in as much air as the engine can take in.

Anyway, getting back to the topic, MPFIs' seem to have a clear advantage over carbs.

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Old 21st August 2006, 20:15   #37
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Quote:
Originally Posted by Shan2nu
Actually it's the opposite. At low rpm , you want less air to enter the cylinders for better FE, so the valves don't open completely. At high rpm, valve lift is maximised to let in as much air as the engine can take in.
Actually, the lift has equal importance as duration. High lift+short duration= lesser gases entering chamber. Low lift+longer duration = good gas flow, plus higher RPM capability due to lesser mechanical loss. High lift+long duration = maximum gas flow. The thing is, at high RPM, duration is of more importance than lift, for example, in interference engines.

Quote:
Originally Posted by veyron1
For low RPM, high lift and low duration (less poppet travel/lift, longer open), and for high RPM, low lift and high duration- for gases to flow more freely.
Sorry, that was a typo. That should actually have read:

For low RPM, high lift and short duration and for high RPM, low lift and long duration(less poppet travel/lift, longer open), - for gases to flow more freely.

In interference engines, high lift and longer duration.

And yes, MPFI's DO have a clear advantage over their carb'd counterparts.

There's another reason I suspect as to why Maruti is promoting carb'd LPG. Isn't the carb'd zen 8V..?
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Old 21st August 2006, 20:27   #38
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Quote:
Actually, the lift has equal importance as duration. High lift+short duration= lesser gases entering chamber. Low lift+longer duration = good gas flow, plus higher RPM capability due to lesser mechanical loss. High lift+long duration = maximum gas flow. The thing is, at high RPM, duration is of more importance than lift, for example, in interference engines.
Maybe, but thats not how Vtec works. Honda uses "low-lift/short duration" at low rpm and "high-lift/long duration" at high rpm.

Shan2nu

Last edited by Shan2nu : 21st August 2006 at 20:30.
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Old 22nd August 2006, 05:10   #39
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After doing a bit of research regarding LPG in vehicles, I would like to reproduce some info(Correct me if I'm wrong).

Quote:
A Carb Zen is definitely better than the MPFI Zen (for LPG)...not only because it can be tuned accordingly BUT because it has a Compression ratio of 8.8:1 where as MPFI Zen has Compression ratio of 9.4:1. LPG fitted cars need lesser air to run the engine the MPFI needs more air to run the engine. So if LPG is fitted in an MPFI engine we can not restrict Air (because when MPFI Zen is on petrol it will run into problems) but we will have to pour in more gas to achieve lower Compression ratio.
There will not be any engine damage even if we use higher octane on vehicles having lower CR. So even if a MPFI Zen has Compression ratio of 9.4:1 it won't create any problem with regard to the fuel. And based on layman's thoughts alone, the CR of 9.4:1 of MPFI Zen is better than the CR of 8.8:1 of the Carb Zen since LPG is having high octane content.

Quote:
The other reason is that LPG has a lower percentage of Octane so using it in a higher Compression engine would not result in best performance.
Since vehicles having high compression ratio(CR) needs higher octane fuels there is not going to be any problem with LPG since it's having a octane rating of about 97.

And since there is already a difference in the architecture of LPG kits of Carb & MPFI, the technological bottlenecks will surely be taken care by the LPG kit itself(I assume so..).

And components like solenoid valve which cuts the flow of LPG when the car is running on gasoline and when the engine is shut off;

The regulator/vaporizer which performs the functions that a carburetor handles in a gasoline engine;

The mixer which is mounted in the intake manifold. The mixer alos takes information from the car's sensors or ECU, and then it controls the amount of gas that flows into the cylinders;

The above given components are all the same in the case of LPG kits of Carb & MPFI.

And the cars with an electronic injection system will probably need two additional items; an electronic emulator & a Lambda Control. When the car is operating on LPG, the fuel injectors will not be sending any information to the other sensors in the car -- this will light up the "check engine" light and give incorrect diagnostic readings. The emulator fakes the proper signals so the ECU can operate properly.

And also MPFI engines running on LPG will not face any difficulties with High Altitude Driving.


So, Is MPFI better than Carb for fitting a LPG kit ?
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Old 23rd August 2006, 04:46   #40
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And after driving both the Carb & MPFI Zens, I have found that the MPFI Zens are having a lot better engine smoothness than the Carb Zen.

I REPEAT, it's the Engine Smoothness that I'm talking about and nothing else like power difference/pickup.
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Old 7th September 2007, 13:56   #41
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Default MPFI/Carb Cars with LPG as fuel

Quote:
Originally Posted by rohitbagai View Post
A Carb Zen is definitely better than the MPFI Zen (for LPG)...not only because it can be tuned accordingly BUT because it has a Compression ratio of 8.8:1 where as MPFI Zen has Compression ratio of 9.4:1. LPG fitted cars need lesser air to run the engine the MPFI needs more air to run the engine. So if LPG is fitted in an MPFI engine we can not restrict Air (because when MPFI Zen is on petrol it will run into problems) but we will have to pour in more gas to achieve lower Compression ratio. LPG is delivered as a vapor to the engine. The other reason is that LPG has a lower percentage of Octane so using it in a higher Compression engine would not result in best performance.
Ok..there is one more logic here...to get best performance from an LPG run engine we have to tweak the timing of ignition which can not be done on an MPFI engine.
The above quote from a fellow friend is absolutely wrong. I am not sure with a moderated groups how people can post wrong stuff.

LPG octane value is more, in other words, it needs more air to do justice for the same. Higher compression ration achevies the same. Now having said that, higher octane petrol also needs higher compression ratio, to give the optimum power.

As far as tuning is concerned, is the knowledge and tools needed. MPFI cars can be tuned properly, as long as you know how to and the tools are there. Carb its a old tech and many street mech knows.

And mind you maruti does a much better job that the stupid koreans, totyotas and Hondas.
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Old 9th October 2007, 16:09   #42
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As far as using LPG is concerned main concern among buyers is initial cost of LPG kit.With carburetor vehicles its around 19 to 20 k & with MPFI its around 2 to 3k more.

LPG is having octane rating of 110. (octane rating of LPG - Google Search) so higher compression ratio infact help utilise LPG in a better way.

The difference between a carb version & MPFI is well known.We have more power with precise fuel inputs at varying rpm levels.There are LPG kits in market which works in same manner like that of MPFI unit having seperate ECU and seperate injectors which gives exact amount of LPG depending upon requirement which translates into excellent performance we can not think of.It virtually eliminates difference in driving due to charecteristic of LPG but...................it costs much more.....may be 50 to 60 k......

So Maruti is correct saying carb version advisable for LPG where we can at least advance ignition up to certain limit.Its advisable till its cost effective to end users.
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Old 9th October 2007, 19:23   #43
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Quote:
Originally Posted by srirams77 View Post

As far as tuning is concerned, is the knowledge and tools needed. MPFI cars can be tuned properly, as long as you know how to and the tools are there. Carb its a old tech and many street mech knows.
Yeah street mechs do know how to adjust the air-fuel mixture, but I doubt if many would be able to tune a carb to its maximum potential ( For power or FE) without affecting the driveability.

Quote:
Originally Posted by srirams77 View Post

And mind you maruti does a much better job that the stupid koreans, totyotas and Hondas.
I am not sure what you mean by that, but I would advice you to check your stuff before posting. Our community consists of all enthusiatics here and posts like this will not get you very far.
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Old 9th October 2007, 19:36   #44
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With revv-limiter and similar goodies, the MPFI engine DEFINITELY has longer life.
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Old 9th October 2007, 21:12   #45
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I think with perfect (and electronic) control over all engine parameters, mpfi has got to have a longer life!
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