Su hs6 or hif6 su which is better?

[lwalton]

I have the option of using hif6 twin su as opposed to hs6 is this worth doing or stick with hs6 carbs? It is to go on a 1980 sprint

[cliftyhanger]

HIF??

If so they are a better carb (my opinion, others will disagree) as they have PTFE bearings for the spindles which is a great improvement. Plus a concentric fuel bowl which is handy if the car gets thrown about.

However, go on the carb condition may be the safest bet?

[lwalton]

Either way they will be reconditioned I just did not know if there was a performance difference?

[cliftyhanger]

I doubt it. The normal HS6 will be more visually appealing to those who like originality.

[VanIsleSprint]

I am running totally rebuilt HIF6s on my car.
The HIF6 will flow 240 cfm as opposed to 210 cfm
for the HS6. Make sure you use dampers with part
number CUD 2907 (flat top) for adequate bonnet
clearance.

[lwalton]

Thanks for that advice on the dampers they do look a little tight with regards to clearance. Is there any other modifications that have to be carried out to fit these on a sprint?

[VanIsleSprint]

I was able to use the existing connecting linkage for both
the choke and throttle. You will have to modify the air cleaner
to match the intake side of the HIF6 carb if the standard one
is being used.

[lwalton]

What about the vacuum and fuel delivery? Sounds relatively straight forward conversion, did you notice a performance difference?

[MIG Wielder]

Not sure about the HIF-6 version; but I have a pair of HIF-4's on the MGB. I assume the HIF-6 is merely a larger version for increased cc cars. The essential difference is that the HIF -x versions have the float chamber integral with the base of the jet assembly. So when you go round corners, less variation in fuel height in the float chamber.
The problems occur when working on them.
* If you have a leaking float chamber valve it will flood from the usual place but you have to remove the carbs; from the manifold and completely dismantle it to replace the needle and seat valve. You will need a gasket kit as well.
* The mixture adjustment is not via an 11/16 (?) short spanner above the jet, you need a short wide blade screwdriver to fit in the side orifice of the carb; Even the Haines manual states you need to gently tap the side of the float chamber to allow the jet to settle between adjustments. It has a thermostatic element to it to compensate for temperature changes and it sticks badly if not lubricated.
On the MGB you need to remove the air filters to adjust it.
So ... is it better ? Maybe . More complex to fix. . Just different when it comes to adjustment.
HTH,
Tony.
.

[Jon Tilson]

While the HIF is a superior design in terms of flow I would say its advantage is negated the first time you get
a blocked float valve.

You do get a better control of the jet fuel level on an HIF too, so you can get them tuned more accurately/evenly than an HS6
which has a variation between float chamber fuel level front to back.

If you use HIF's an inline fuel filter is essential.

Jonners

[wiggybum]

If I recall correctly, the HIF (integral float) carbs use a bimetallic strip under the jet. This does a much better job of tweeking the mixture for temperature than the HS waxstat design. Add an vacuum lean out port for part throttle, involuted throttle cable arm for more delicate accelerator action off idle, auto choke on the side and a fuel cut off solenoid for overrun (Maestros had them) and you have the "Ultimate Option Pack SU"! Still needs a good rolling road session to get the maximum benefit.

[VanIsleSprint]

A few pics of he HIF6 installation on my Sprint.
As they flow more air and I'm running a Newman
Phase 1 cam, I have BAW needles, slightly richer at
the top end than the BBTs.