are carbs particlaurly fussy about turbos?

can any carb be turbo'd. i've got zzr 1100 carbs to go on my 2.0 vauxhall ecotec, and at some point i'd like a turbo, but can carbs be broken my turbos?

No short answer here but I am happy to answer any specific questions which you have.

I have a pinto running with twin 45 dellorto's and a turbo. It needs some planning but can be done very well. However, and even with my successful set up, I firmly believe that fuel injection has got to be the best way in the long run.

hmm I think with some carbs that vent the float chamber to the outside the fuel can be forced out when the throttle slams shut. Even ram feeding air to the intake can do the same

I would have thought that mapping becomes quite simple with efi but a carb (especially multiple) setup could be very tricky.

ZZR 1100 carbs can be converted for turbo use without a lot of work,kawasaki have already done some of it because the carbs were designed to run with ram air,which is similar in set up,carbs do have their limitations on the zzr 1100 they start to get a bit ragged around 260+ bhp, fuel injection is far better giving smoother linier power and more power can be produced,i have taken a zzr1100 with internal mods,dta ecu,and jenvey throttle bodies to push over 400 bhp and has remained very reliable having covered well over 3,000 miles and over 40 dyno pulls.

Doesn't it depend whether you're talking suck-through or blow-through???

Suck-through carbs on a forced induction engine don't really "see" anything abnormal. Clearly blow-through carbs are a different kettle of fish especially if you don't fit a blow-off / bypass valve for when you suddenly back-off.... Then what the carb "sees" is very different!!

sorry, yeah i'm talking blow through.
hmmm, sounds like a bit too much work (really i just want a dump valve the extra power would just be a bonus)

can't afford anything other than carbs at the moment, but maybe once the cars done and SVA'd i'll start to look towards throttle bodies and turbos

thanks guys!

every carb need a air flow to generate an unther pressure to mix petrol with the air...

sow pressurising the carb and then suddenly when a intake valve opens there is a bit of airflow...

but the biggest problem is that you cant enforce anything on a carbed setup.

with injection you can setup everything there by i think you cant turbo carbs..

and if you can you will be limited by a low pressure.

also bear in mind that many injection systems also inject while there is no airflow/stream... (megasquirt does for example)

so i think that the quantity of fuel needed for the air that passes cant be delivered in suchs a small time by an carb..

my 2$

Tks

ZZR1100 carbs have a feed to the float chambers which equalises the air pressure from the ram air system on the standard bike.

With a bit of fiddling, this could read pressure from the inlet tract, just the same, balancing pressure inside the float chambers to boost pressure.

I know of at least one single seater drive who didn't fully appreciate this and it caused no end of problems. Once this pressure feed was re-established, the engine ran correctly again.

Going to traditional car carbs, the Dellortos fitted to the Esprit turbo have a similar pressurisation system for the float chambers.

If you don't do this, no fuel makes it into the engine as soon as any boost at all is present.

Turboing and blow-through carbs is a doddle to do logistically!

It does have issues surrounding accurate fuelling though which has already been mentioned and in terms of driveability the car's performance can suffer as a result. Thats not to say it cant be done with a bit of ingenuity and an understanding of how carbs work mind you.

Mine, very crudely set-up (still) produces smooth and tractable power with vacuum showing on the boost gauge and, once the turbo has spooled, with boost showing on the gauge. The transition between the two is poorly fuelled though and is a little hesitant, like a very mild flat spot I suppose.

As has been mentioned, you can use bike carbs with blow through if you can pressurise the float bowls and there is a reasonable seal around things like throttle spindles and needle diaphragms. I would think that there would be a maximum level of boost that you could run before more sealing had to be done, perhaps 0.7 - 1.0bar?

Its easy enough to do - after Id finished mine I was surprised how simple the set-up looked.

Geoff

would it be possiblt to build an airbox/plenum which completely encloses the carbs? would that stop any problems with air bing forced out of the carbs and stop the need ofr any extra selaing?

if the carbs are inside the airbox, the pressure inside the carbs will be the same as outside and the carbs won't be trying to blow air out. the only extra sealing you'd need to worry about would be the throttle cable, and depending on how its done, the fuel hose

Guys

This is not too complicated and most of what you need to consider has been discussed already.

I run a pinto turbo at anything up to 15psi (11psi usually) through twin 45 dellorto's. You can get a 'turbo' kit for these carbs to seal them for turbo use. (see pic in my archive)

They key thing to buy is somthing called a rising rate fuel pressure valve. I run a high pressure return fuel system as you would with injection. The valve has a vacume pipe from the plenum and as boost increases the diaphram moves and allows more fuel to the carbs. You do overfuel a bit as you back off and you get a bit of popping and banging through unburnt fuel in exhaust etc but most importantly you don't lean out. This is a basic piece of kit but one which makes turboing with carbs pretty easy.

I have a few mods I will do with mine soon one of which is to fit a lambada/O2 sensor to check that as I play with bigger boost I don't lean out. I have checked on a rolling road with all sensors attached and I have a surprisingly consistent fueling across all my rev range. I checked this at 8psi and at 14psi.

All in all, its not difficult to turbo using carbs.

http://www.locostbuilders.co.uk/photos.php?action=showphoto&photo=3Picture%20007.jpg

[img]/upload/3Picture 007.jpg[/img]
[Edited on 26/1/08 by carpmart]

[Edited on 26/1/08 by carpmart]