13 replies to this topic

[Shane.spears.91]

That have the same base as a hiff44 and come of cars with big lumps.
If I stuck one on my 1275, would it increase proformence or not?

[surfblue63]

Depends which carb you have now. The HS6 will flow more than an HS4 but not as much as an HIF44. I seam to remember that David Vizard carried out flow tests on different carbs and even though the HS6 and HIF44 are the same size, the HIF allowed better flow.

[Shane.spears.91]

So you recommend a hiff?

[surfblue63]

The HIF is the better carb.

[Shane.spears.91]

Finding one cheep is the question. Then buy a service kit. Looking at more then a pair of shoes lol

[surfblue63]

But a cheap HS6 is likely to be even more worn out.

[Cooperman]

I once put twin HS6's on a 1330 cc rally Cooper 'S'. Once set up it was fine at high revs, like over 4000, but not too good at lower revs. Where it did score was in the Dolomite Mountains where it allowed the mixture to be the best it could as the air thinned ane we weakened it off a few flats. However, twin H4's do seem better overall. A single HS6 is not far short of a HIF44 in overall terms, especially if it's on a good alloy inlet manifold. On a road car you'll not notice the difference. On a race track you might be a second a lap quicker with the HIF44.

[bmcecosse]

The two carbs are the same diameter and will flow the same amount of air - especially if 'Vizardised' and any silly 'idle valve' removed from the butterfly . However the HIF does control the fuel level rather better than the HS carb - that's what the design is all about!

[Gr4h4m]

The two carbs are the same diameter and will flow the same amount of air - especially if 'Vizardised' and any silly 'idle valve' removed from the butterfly . However the HIF does control the fuel level rather better than the HS carb - that's what the design is all about!

I have never like the bimetallic strip or the choke seals, ESP if you don't use the car all year.

[surfblue63]

The two carbs are the same diameter and will flow the same amount of air -

Read page 75 Fig 7.1 2nd edition Vizard

hs6 flows 210 cfm
HIF6 flows 240 cfm

[Cooperman]

To some extent those figures are a bit acedemic. To achieve the max flow you need a head and cam combination which requires the carb to work a maximum capability. Not many engines actually have that and a road engine is most definately unlikely to. If the engine is only capable of receiving, say, 180 cfm, either an HS6 or an HIF44 will perform as well as each other.

[surfblue63]

But if something produces more flow than another in a standard test then it must have less resistance, thus it will be less restrictive and will allow and engine to breath more easily.

[freshairmini]

But if something produces more flow than another in a standard test then it must have less resistance, thus it will be less restrictive and will allow and engine to breath more easily.

untill it gets to the lower flowing head that negates that extra flow. Which goes back to what cooperman said

To some extent those figures are a bit acedemic. To achieve the max flow you need a head and cam combination which requires the carb to work a maximum capability. Not many engines actually have that and a road engine is most definately unlikely to. If the engine is only capable of receiving, say, 180 cfm, either an HS6 or an HIF44 will perform as well as each other.

[Cooperman]

Think of it this way. If you were trying to pump water into a container and there was a restriction with an area of 2 sq. ins. just before the pump, then if the end of the pipe in the water was 2.5 sq.in. you wouldn't pump any more water. Think of the 2 sq.in. restriction as the head limitation and even if you put a 3 sq, in. pipe end, you could not pump any more water. The carb just needs to be able to slow a little bit more mixture than the head/valves/cam will allow at max revs. and only a head flowmeter can measure this.