Modifying HS SU Carbs for Boost
Turbo Mini Forums

Hi all,

I know there are probably loads of threads on here about modifying HIF44's for boost, (none popped up during a search though, probably a memory blank on keywords!) but I'm wondering about the older design HS carbs.

To my knowledge the only major difference is that they have the external fuel bowl (obviously makes a big difference to the bottom half of the carb body), can they be modified for operating in low boost?

The shafts could be sealed, fuel return blocked, and fuel pressure upped, but what else needs doing that is different to a HIF series carb?

Cheers,
TC

www.topcatcustom.co.uk

I guess if you used the tee piece trick connected to the overflow pipe to pressurise the float chamber it could work?

But why?

http://www.turbominis.co.uk/forums/index.p...tid=469104&fr=0

It's not mini based, I have a huge 1930's engine which I am going to supercharge (with an enormous nearly as old blower), and want to blow through 4 SU carbs. I just prefer the look of the HS series SU's as the side float bowls look more "period" IMO. Boost will only be a few psi, more for looks than performance! (And no I don't want to hide an injection system etc etc)

p.s. I did wonder about a boost reference into the top (overflow) of the fuel bowl, but I assume it would need a non return valve to stop it drawing fuel up when running in vacuum, i.e. most of the time?!

Edited by topcat on 6th Aug, 2012.

www.topcatcustom.co.uk

I'm sure someone with a lot more knowledge than me will be of more use, but I don't see why it wouldn't work, so long as you seal it all like you said, then the only difference (that I can remember) is pressurising the float bowl, which sticking a take-off from the Plenum to the overflow pipe 'should' sort out?

http://www.turbominis.co.uk/forums/index.p...tid=469104&fr=0

Search for pilot tube. Sure there is something about them on here.

If something is worth doing, it's worth doing half of.

*pitot tube, just found the couple of threads, seems like a very simple solution so will probably build some into my manifold(s) for the carbs when it comes to it!

www.topcatcustom.co.uk

Is it a v8 your modding for boost?

me and my mate found this hard.

taking the float pressure from before the intercooler may give enough pressure difference to work instead on a pilot tube/proper plenum

other than that make sure it is sealed

Yes i moved to the darkside

Instagram @jdm_brett

Not quite, a straight 8! Engine is 4ft long, and 4 SU's will go on it a treat. I reckon I'll only be running 5psi as it's not going to be performance based and I cant risk breaking the engine as spare parts don't really exist!

Not having an intercooler, just about 6ft of 3.5" diameter pipework, pitot tube should work ok I think, and there will be a few more pipes to make it look even more interesting!

www.topcatcustom.co.uk