Tigers
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| posted on 8/2/05 at 04:40 PM |
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Another really stupid question ;)
Hi!
As I'm not a specialist in engines... Just wondering why does quite a lot of people want to change from injection to carburators? To make it
simple or to get more horses out of engine?
And also - I have noticed that some guys put individual throttle body for each cilinder - why is that? To make "intake mainfold" shorter
(therefore get more high RPM power)? Also BMW for M engines does the same.
Sorry for my ignorace 
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Avoneer
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| posted on 8/2/05 at 04:50 PM |
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I think most injection systems are junked due to the complications of the electronics in what should be simple locost cars.
Pat...
No trees were killed in the sending of this message.
However a large number of electrons were terribly inconvenienced.
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NS Dev
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| posted on 8/2/05 at 05:22 PM |
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Carbs are usually used to replace "road car injection systems" for convenience and simplicity.
HOWEVER..........increasingly (almost completely now) production car injection systems also incorporate the ignition system, and are distributorless,
so an aftermarket eletronic ignition system is needed anyway, even when fitting carbs.
I would also strongly dispute the "simple and cheap" claim for carbs.
A pair of good webers will usually come not too far short of the cost of a set of throttle bodies, and you will normally need an ECU to operate the
ignition system with the carbs, and an ECU with fuelling and ignition is little more to buy.
I.e. throttle body injection and mapped ignition is not really more expensive than new webers and ignition system.
Mapping an ECU (as long as the control software is easy to use) is also in my opinion easier to do than setting up carbs accurately. It's easy
to change numbers on a laptop, and you know EXACTLY how much you have changed injector opening times/ ignition advance, when you read it on a screen,
that's much harder when fiddling with bits of drilled brass and advance springs!
As for the individual runners and butterflys, (usually referred to as throttle bodies) these enable accurate tuning of the inlet pulses in the inlet
system, so enabling improvement of breathing and thus power at certain rpm. Unfortuantely nothing in life is free and there is usually a loss of power
at other rpm compared to a cross-pulsed system, as used by many OE manufacturers on production injection systems.
E.g. my Vauxhall 16v XE engine makes the same torque now on 48mm throttle bodies as it did on the std inlet manifold, and it makes that torque higher
up the rev range too so in fact it is actualy breathing "worse" at lower rpm (the std inlet manifold provides for cross-pulsing between
cylinders 1 and 4, and 2 and 3) but the throttle bodies flow better and allow "independent pulsing" (i.e. resonance on each runner) and so
make better torque higher up the rev range and thus more horsepower, this being a function of torque and revs!
Baiscally, std vauxhall XE engine on std injection system complete is approx 150hp, std vauxhall engine on std inlet manifold but no airflow meter =
175hp, std engine but with throttle bodies = 200hp. Peak torque with each system is between 150ftlb and 165ftlb, but at different revs.
[Edited on 8/2/05 by NS Dev]
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Tigers
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| posted on 9/2/05 at 03:22 PM |
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OK, I got it now! Never thought about the pulsations in inlet mainfold although it's actually very similar as at exaust side
Thanks!
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