3 inch su's

[73sprint]

How do these compare against 45 's performance wise. There is a pair on the bay for sale, a bit steep with the price though. I imagine they would be easier to tune than Weber or dellorto carbs ? Obviously a cam and exhaust change from standard would be needed to benefit from these carbs.

[tony g]

3" would be the nuts! Just jesting, I know you mean 2"

Tony

[trackerjack]

I have had the lot!
standard okay but lacked a bit as red line came up 28 mpg mixed driving.
2" Su. these are fine and the car revved more freely and 28 mpg mixed driving.
45 Dellorto these did the lot and sounded great depending on what filter used and 28 mpg mixed driving.
Bike carbs just as good as any of the above and you guessed, 28 mpg mixed driving.

The cam used from 2" Su's onward was a Piper 270.

Driven gently all the above will do better than 30 mpg but I never was interested in economy get a damn oil burner if thats your bag

The one big snag with Dellorto and Weber is finding someone who REALLY CAN tune them and that can cost more than the carbs.

[Dolly-Nut]

Once I've got hold of another Weber/Dellorto manifold for my DHLAs I'll have a full HS8 setup available with a port-matched manifold and linkage etc

My experience with carbs is quite different however I do drive them hard.

I find HS6s lacking in mid-range. My track car still uses them and is surprisingly quick past 5,000rpm and beyond. On a long run absolutely thrashing it and seeing the redline at least once every few miles returned 34mpg for me with an intermittent O/D and an almost entirely stripped out car. These were setup with a colortune on BBT needles.

The HS8s are currently fitted to my Toledo. They drive well and give a good smooth increased power delivery but don't give the nice throbby sound that I like! On a long run with a 4:1 diff and intermittent overdrive I got around 30mpg with UE needles.

My shiny Sprint has DCOE45s fitted and my friend's has DHLA45s, on the same run to RetroRides last year we both got around 25mpg driving exactly the same. The individual bodies sound great but the increased fuel consumption is noticeable. They have a noticeable power gain throughout the rev range from 2000rpm. Both are jetted a little on the rich side but drive well although hold back around 6000rpm (too rich).

All engines are standard internally.
In my opinion a Sprint driven hard or modified benefits from any carb upgrade, even on a standard cam. I'm sure HS6s with a bit of work could deliver more than standard power because my track car was unbelievable last year almost doing 1:27s at Combe with a passenger and standard engine.

[73sprint]

Thanks for your replies. Oops of course I meant 2 inch

[Mad Mart]

My experience with carbs is quite different however I do drive them hard.

You obviously haven't seen Jon drive Dan!

[Dolly-Nut]

I'm getting over excited about track days already!!

[paulsprint]

The2"su is the equivalent of 48 dcoe's Fine for high revving but not so good around town as low down power is poor due to slow airflow. You will need the right cam to take advantage of the extra airflow available. Mine was still pulling past 7000rpm.

[Mad Mart]

The2"su is the equivalent of 48 dcoe's Fine for high revving but not so good around town as low down power is poor due to slow airflow. You will need the right cam to take advantage of the extra airflow available. Mine was still pulling past 7000rpm.

2" SUs are pretty similar to 45s Paul, not 48s.

[xvivalve]

2 x 25.4 = 50.8

It's the twin choke that makes the difference though...isn't it?

[Dolly-Nut]

Yes. It's not the venturi size (40/45) that makes any difference whatsoever, it's the choke size.