...and what about camshaft?

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antiekeradio
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Post by antiekeradio » 16 Nov 2005 11:40 pm

ha, always nice to disagree with each other on technical subjects.

of course does injection have an influence on power.....

in practice, a injection car always has more power than a carburetted version. the reasons for this are economical as well as technical.

- a carb needs to be 1 unit, or you need to mount a number of them. Thats expensive, so in street cars like the B172k you are stuck with a single intake body, with divisions and curved channels to each cilinder. not ideal for maximum power...

- even if you would mount a separate carb and throttle valve per cilinder, tune it for ideal mixture settings, i.e. maximum power configuration, you would still have a certain blockage in the intake tract, being the venturi(s). A carburettor needs a venturi to suck up the petrol from the float chamber. To be able to do this, the venturi must put a certain drag on the air flow (much larger than, lets say, a air filter). if you look at a carburettor you will see that the venturi has a much smaller opening than all the rest of the intake tubing.

with an injection system, ideally electronic multipoint injection, there is no need for any obstruction other than the air filter. less restriction, a better cilinder filling (is that the correct term? guess not..), more powerrr.. A 360 has one of the older electronic injection systems; it still uses a air flow sensor wich also puts some obstruction on air flow (metering flap). more modern engines use a MAP or MAF sensor wich don't restrict airflow at all.


in practise, the advantages James pointed out are more important...
electric fuel pump => instant starting,
electronic regulation => much more precise
lambda regulation => "

more precision makes it possible to have optimum power or optimum economy. that depends on how the system is tuned.. :-)

classicswede
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Post by classicswede » 16 Nov 2005 11:44 pm

A venturi does not actualy restrict air flow it changes the air speed.
Perfomance increase on fuel injection engines is usualy acheived by manifod design.

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foggyjames
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Post by foggyjames » 17 Nov 2005 12:12 am

In principle, ITBs (ie: the injection version of sidedraft carbs) will make more power than sidedraft carbs, because they don't have a venturi, nor a jet arrangement to get in the way. We're talking tiny, tiny margins here though. The MAJOR advantage is the accuracy of the tuning you can achieve.

However, a 'normal' "big carb" setup is twin sidedrafts, and a 'normal' "big injection" setup is a single large throttle body. That means the carbs win. That's why I'm making more power than JTBO, on an otherwise identical engine (same cam, etc). ITBs are rare and very expensive, too.

EFI *should* always be more economical than a carb, all other things being equal, but a B200K does much better MPG than a B200E. Why? Ignoring the engine setup (in this case, cam), the throttle plate area is smaller, and on top of that, the throttles are sequential, meaning you have much more accurate control over how much throttle you have on.

As an aside Dai, the throttle body on your new manifold is a twin sequential one like a carb!

cheers

James
VOC 300-series Register Keeper
'89 740 Turbo Intercooler
'88 360 Turbo Intercooler
'85 360 GLT
'81 343 GLS R-Sport
'79 343 DL
'70 164
...and some modern FWD nonsense to get me to work...

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Post by volvorsport » 17 Nov 2005 12:15 am

not being anal , but ultimately the engine will be restricted by the venturi/chokes - power will be lost becuase of the increased restriction .

Thats something fuel injection doesnt have to overcome .

Something to be considered , is that in multi point engines , the manifold could still be a bad design , but would not suffer the same problems as a carb engine , altho most MPI systems do have a good manifold .

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