Stub stacks and SU carb sizes

[Karlos]

I was looking at stub stacks for my carbs on ebay. I asked him if the HS4 stacks fit 1.5" SU's he said yes they do, I then asked him to measure the stub stack and he says it's 1.25". So I question him if that is correct for a 1.5" SU, so he says :

" Im afraid you wrong we have stub stack that measure 1.5" but they are for HS6 carbs NOT HS4 or HIF4

The diameter of a Hs4 and HIF4 carb is 1.25" on air inlet side and 1.5" on engine side.

Regards "

I have not measured my carbs yet and they are HS4's, but is he right?

[marko]

He's wrong. The HS4 and Hif38 are 1 1/2"

[Karlos]

Thanks Marko.

After all what is the point of having 1.25" and then 1.5" on the other side, the amount of air will be restricted to whatever 1.25" can send regardless of how big the other end is.

[tony g]

The smaller diameter on the engine side causes the venturi effect. This speeds up the air as it passes through the smaller diameter. 48mm webers rarely have a 48mm hole down the middle. Is this what you mean?

Tony

[cliftyhanger]

Get some off an mgb.....fitted as std and actually a pretty good design. Many are not too clever.

[marko]

181312823924 on eBay

[cliftyhanger]

cheap, but not a great design, Better is available...

[theclassicera]

On the subject of carbs- I have just bought a Dolomite which has started to be modified for competition and in the spares is a twin su inlet manifold (I presume from a Spitfire?).
Is there enough room for twin SU`s to clear the servo?

[GlenM]

On the subject of carbs- I have just bought a Dolomite which has started to be modified for competition and in the spares is a twin su inlet manifold (I presume from a Spitfire?).
Is there enough room for twin SU`s to clear the servo?

Yes, it will fit on a 1300 Dolomite but, IIRC, you might also need to change the exhaust manifold and downpipe. It does make a fair difference to the 1300 engine though. Are they HS2's or HS'4? Either way they will probably need different needles, although HS2's may have come from a 1300 Spitfire and might not be far off, in terms of fueling.

[Karlos]

181312823924 on eBay

I tried these previously, they did not match up the intake side of the carb, the diameter was smaller on the stack by about 1/4 ".
Same deal with these on ebay: 200864867551.

[cliftyhanger]

http://mmoc.org.uk/mbimage.php?src=1284938973_8115

They are the calver tuning ones, but Ithink they have stopped making them. They actually work......

I have a redundant pair along with some K+N's off my old 1500 engine....somewhere.

But the proper factory MGB ones are similar.

[Jon Tilson]

A dolly 1850 comes with HS4's like a Spit 1500.

An MGB has HS6's or HIF 44's

Stub stacks for an MGB will not fit a a dolly 1850 therefore, unless its up carbed with HS6's from a TR7, which is a good mod.

HS4 engined dolomites are all weak at the top end, which explains why autocar could only get mid 90's when they tested a late 1850 but berg carbed early 1850's would do 105. I reckon there is mileage in experimenting with needles on an 1850 from the minty lamb site.

On another note I now run 1850 ABK's in my spit 1500 with good results.

Jonners

[GlenM]

A dolly 1850 comes with HS4's like a Spit 1500.

An MGB has HS6's or HIF 44's

Stub stacks for an MGB will not fit a a dolly 1850 therefore, unless its up carbed with HS6's from a TR7, which is a good mod.

HS4 engined dolomites are all weak at the top end, which explains why autocar could only get mid 90's when they tested a late 1850 but berg carbed early 1850's would do 105. I reckon there is mileage in experimenting with needles on an 1850 from the minty lamb site.

On another note I now run 1850 ABK's in my spit 1500 with good results.

Jonners

I thought the early ones had HS4's then they switched to HIF4's in the 70s. My parents have a very late chrome bumpered MGB Roadster and I am sure they are HIF4's (with integral float chamber) and 1 1/2". The HIF44's came later and are 44mm (1.73"). There was also an HIF38 (38mm or 1.5"). I don't think they fitted either of these metric ones to the MGB.

[Karlos]

I measured the throat of the HS4 carb, it is 1 3/8" on the air filter end. The stub stacks are only 1 1/4" so I will not be getting any of those, as I think they will cause a restriction instead of improving flow.

[cliftyhanger]

I thought the early ones had HS4's then they switched to HIF4's in the 70s. My parents have a very late chrome bumpered MGB Roadster and I am sure they are HIF4's (with integral float chamber) and 1 1/2". The HIF44's came later and are 44mm (1.73"). There was also an HIF38 (38mm or 1.5"). I don't think they fitted either of these metric ones to the MGB.

Spot on!