Turbo SU HIF6/HIF44 Carburettor - Need Some Info
Turbo Mini Forums

OK I'm trying to modify a non turbo carburettor to work on a blow through setup but in order to do so I need to work out a few things about how an SU works under boost.

I know the HIF44/HIF6 had a factor blow through turbo setup so what I'm really after is some sort of diagram or picture showing what flows where much in the way of the picture on this page:
http://www.zparts.com/zptech/articles/mal_...arb_111601b.htm

The problem Im having is how do I overcome the problems of pressurising the turbo. The only thing I know for sure is I need to seal the dashpot.


Do I put in a high pressure fuel pump with a rising rate regulator or do I plumb the float chamber to the inlet manifold or do I do both?

Where does the vacuum come from to raise the piston if its all under pressure?

I've been searching and calling around everywhere all day and everywhere I called told me it cant be done (Despite the glaring anomaly of the fact it does exist in factory form) or didnt want to listen to me at all. I cant find ANY information on what exactly I need to do to make them work.

Any help would be really really apreciated.

This has been covered in detail on here before, do a search for carb differences.

try this one
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=120963

which seems to say that not much is needed aside from a turbo kit and sealing the dashpot.

The boost pressure is fed into the float chamber through a hole in the plenum/carb flange, It pressurises the fuel (not the fuel pump!) and its important that its there. The fuel regulator is there to prevent the float chamber valve from being overwhelmed by the pressure difference at idle (to run 12psi of boost you would need 16psi fuel pressure at full boost but at idle 16psi would be too much for the little valve) so yes you do need both.

I believe the carb works under boost because of the restrictor plate in the plenum, by giving a slightly higher pressure inside the plenum it fools the carb into seeing a vacuum i.e 12psi is a vacuum compared to 14psi.. in the diagram you linked to Item 5 is "suction chamber air inlet" on a turbo carb that is fed with the slightly higher pressure from inside the plenum. (this is why the dashpot needs to be sealed) it would cause the piston to raise as boost came up. The more the boost the bigger the pressure difference the higher the piston will raise. I think that is also fed via the extra hole in the carb/plenum.

Terry

Edited by Turbo Tel on 11th Dec, 2007.

website:- http://www.terryhunt.co.uk

Thanx for the help, Ive had a look around the site for a few hours before I posted and couldnt find the info I needed but that clears it up for me.

Thanx again.

It's quite interesting how the PPC gang managed to use the standard 2"SU carbs on their Roller for turbo use.

They made no changes to the carb (no changng the seals on the butterfly, no dashpot seal, no nothing). All they appear to have done is pressurise the float bowl to ensure that it has more pressure than is in the carb/manifold.

They did this by taking a pressure feed for the float bowl from near the turbo. This would be 3 or maybe 4 psi higher than the carb sees, as by the time it gets to the carb it's been round numerouse corners and a big fooking intercooler.

Simple really!

The restrictor in the plenum is there simply to feed a higher pressure to the floatbowl than the carb. It's a neater solution than the PPC one but it's the same theory.

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

I guess if you have enough pressure even if some of it leaks out it would still work..

website:- http://www.terryhunt.co.uk

Yeah sealing the Dashpot is too easy of a job to not do it, just some insta-gasket would be enough to seal it up for small amounts of boost. If you were going more just mill a groove into it and chuck in an o-ring.