Turbo using a Weber, anybody had any success?
Turbo Mini Forums

I turbo'ed my mini using a weber 42 carb and it worked until 4000 rpm then it doesnt get any fuel. I guess this is because the engine sucks fuel from the carb but with boost the air is forced through the carb and therefore doesnt grab any fuel on the way through.

Has anybody made this idea work properly? and if so, could you tell me how to plum the thing up properly.

Thanks!

Sounds like the fuel pressure regulator isn't working/st right or the fuel pump isn't up to the job.

Wil

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

First of all, do you have all the necessary ingredients for the blowthru turbo recipe ? Like boost referenced fuel pressure regulator, return lines etc ?

One overlooked component is the distributor or the advance curve. I have seen one car on rollers that did not pull past 4000 rpm. Closer investigation showed ignition advance at 50+ degrees. Backing it some 20 degrees gave a totally another rev range.

Fuel pressure regulator may be one thing but another major problem may be the design itself. Metro plenum has a brass ring restriction at the carb mouth that creates a kind of pressure differential in the system. Basically this means that the fuel pressure is higher in the plenum than in the carb mouth, thus richening the mixture. Remember that with turbo flowing air at high speed the flow is too fast to suck enough fuel and therefore you end up going over the nose.

You get the same phenomenom if you remove the brass ring from the Metro plenum. Been there, done that ... and put the ring back in ...

You might have a look at my site, www.geocities.com/jharkola. Follow the "new carb" where you should find pics of my setup.

Forgot another thing: naturally if your jetting is way off you get the same problems.

Which carb is it, DCOE or DCNF, chokes, jet sizes ???

Its a DCOE, when I get home I'll take note of all the choke sizes etc.

Got a couple more questions though

1. Above the two air intakes on the carb, there is a little hole which I would assume is a breather, am I supposed to supply boosted air through this aswell? Because I think if I boost this, then fuel will be blown out the carb as required.

2. Does the fuel pressure regulator actually serve a purpose when being used with a weber because the weber has 2 drum floats inside the fuel chamber, and when these lift up the fuel supply stops which makes the pressure regulator redundant, doesn't it?

Thanks.

Edited by MajicMini on 29th Sep, 2004.

The fuel pressure regulator needed is one specific to a turbo application. It increaces the fuel pressure as the boost increases. Basically you need the fuel pressure 3-5psi above boost pressure otherwise no fuel will get out of the float bowls.

I'm sure the fuelling requirements of a carbed turbo engine is described somewhere better than I can describe it. It's basic turbocharging theory.

Wil

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Easiest way is to think of an SU.

In nat asp form, air rushes over the jet, the venturi effect creates a vacuum in the jet tube, and drags fuel up the tube from the float chamber.
As soon as you apply boost pressure to the same carb, the fuel will still try to be drawn up the jet, but will be pushed back down by the boost pressure.

To get round this, you have to pressurise the float chamber (not to be confused with fuel pressure). What this does, is cancel out the pressure in the throat of the carb - eg if you have 5 psi in the throat, and 5 psi in the flat chamber, it will be tha same as 0psi in the throat and 0 psi in the float chamber.

To perfect this however, you actually need a slightly higher pressure in the float chamber than in the throat to mimic that of the 'nat-asp' operation (where you would have a vacuum, or rather a negative air pressure in the throat).

To make this pressure increase over and above the air pressure in the throat, you have to install a restrictor ring at the mouth of the carb, and take the signal line to the float chamber before the restrictor. Hence, if 2psi (for example) is dropped across the restrictor, then the float chamber will always be 2psi higher pressure than the throat of the carb. Too large a restrictor, and fuel will be pushed up the jet however!!!

Fuel pressure is impotant, but so long as there is fuel in the float chamber, and the float chamber is being pressurised, a turbo engine will run, whatever the boost.
All you have to do for continual running is increase the fuel pressure as the boost rises, or rather as the pressure in the float chamber rises. This is why the signal line to the fuel regulator is taken from the plenum side of the resrictor, rather than the throat or manifold pressure.

I don't know fully the Weber, but luckilly for you, Jukka does! Listen to what he says, you won't learn more from anyone else!
I do know the 151 or 152 series webers are sealed for blow-thru appllications, but still need a mod making to the float cover to pressurise the float chamber.

Hope this helps!

Edited by turbodave16v on 29th Sep, 2004.

Thanks guys, it has given me a clearer understanding.

I now know that I dont have enough pressure in the fuel bowl, I'll try boosting the vent hole and see how that goes.

I have weber 45 an I found It needed new gaskets (Top cover, cap etc) to make it air tight, an overhaul kit might be good if its an old one.

Then you need to have the boosted air going through the vent in the side as you mentioned, to pressurise the float chamber,

You will need to make some restrictions at the carb mouth (similar size to the chokes)

And you need a high pressure pump and a turbo regulator as used in the metro turbo

Phil

Mine has been sealed perfectly, It was all rebuilt.

Then you should have no problems, best of luck

Guys have covered most of it but 1) you need to pressurize the float chamber via the vent hole and 2) you need the boost referenced regulator (whatever the carb in blowthru setup, you still need one).

Thanks guys, you've been a great help, I will keep you guys updated with how it comes along :)

Hmmm... sounds like my best bet would be to just pick up a metro turbo carb and go from there.

i am using deloters (almost the same as webers. They pull hard right the way thru the rev range. Only problem is sometimes the engine dies when the throttle is closed and the clutch is in

Caution !!!! Slippery when boosting

staggy ,you may find this is caused by the vrief surge of boost against the closed butterflys in the carb ,pushing a bit more fuel than normal down the idle jets ,this give a flash of rich mixture that can make the engine cut , ,this is only if yuor blowing through the carb ,if yours is the red suck thru one i saw on here ,it could well be cos your condensing effect of the intercooler is causing the fuel to drop out ,and lay on the intercooler walls ,so not getting to the cylinder ,and so giving a brief lean effect .
regards
robert.

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

magic mini, where you take the signal for the boost to the float chamber ,will have a direct effect on your jetting ,.if you take it form a point where the air is turbulent ,you may find it hard to get consistent carburation .if you can find a dynamic take off point ,pointing into the airstream ,eg on the outside of a bend ,you can find sometimes that you wont need to change jetting v much if at all ,this is because as the boost and airflow rise ,you get an artificially high fuel pressure rise , that increases with air velocity ,so compensating for the air density increase. you can also take it off before the intercooler ,and so get another dimension of pressure ratio increase ,since pre ic the boost is a little higher ,and this diff in boost will increasec as rpm goes up and the ic becomes more restricting ,this is omly true if using a tooo small ic ,as seems to be the case on most turbo mins. due to the bloody things having such a cramped engine bay.lol
regards
robert

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

it is an intercooler. it proboalby is not very efficient where it is. Might need to be moved. Surely it would have a cooling effect. The car also runs water/meth injection after the intercooler.

And yes Vegard i am not the best speller in the world but at least u knew what i meant.

Caution !!!! Slippery when boosting

What are the reason for no intercooler. ???

Caution !!!! Slippery when boosting

I've jsut heard on another forum of a chap who saw the intercooler on a 'suck through' turbo instalation explode on a drag-strip...

I'm really not liking the idea of running fuel through an intercooler.. Sorry. :(

well it seems to work. I will test it out on the dyno with the IC remvoed and see what happens and report back. I didn't build the car but it seems to work ok. A cooler fuel/air mix has to be better.

As for exploding hmmmmmmmm maybe thats what the fire extingusiher is for.

Caution !!!! Slippery when boosting

Well the intercooler has been removed today and a new manifold made up. And guess what you guys were right. The car runs heaps smooth, doesn't stall on off throttle and i have even been able to turn the idle way down. I measured the pipe work i had before and it was well over a meter long. The new manifold is only 25cm. The boost has been turned down until the water/meth system is all sorted. Thanks for the help everyone

Caution !!!! Slippery when boosting

Glad to hear it has worked well for you, it is interesting for someone to be able to prove the theory that an intercooler on a suck through system is a no-no.