SU carb conversion

[BigJ]

Reading through some adverts for the SU HS6 carb conversion for the 2.25 petrol engine it seems that some use a separate inlet manifold and K&N filter arrangement, presumably for improved airflow.

One version however, retains the existing manifold arrangement and allows for the original oil bath filter to be retained.

I’m wondering then whether the oil bath arrangement is so restrictive as to make a noticeable difference to performance compared to the K&N? Has anyone tried either setup and can comment?

[Tanuki]

I ran a SIII with a home-made adapter, onto the existing manifold. A length of 2-inch exhaust pipe bent nearly-90-degrees MIGged to a pair of flanges milled from 1/4-inch plate [use carb gaskets as templates!].

2-inch SU from a dead 4.2-litre Jag XJ6.

Not liking K&N type filters (they don't filter too well and suck hot air from the engine bay which isn't a good thing), I used a large oval paper-element and metal 'frying-pan' type casing, which I arranged to be quickly removable from the carb to improve access when needed. I think the can/element was from one of the old 1970s Vauxhall Victors/Ventoras. A length of convoluted plastic heater-duct tubing from the end of the 'snout' down to in front of the radiator gave a cool-air feed to the carb so helped reduce potential fuel-vapourisation problems.

The result was a lot more responsive than the orginal downdraught Solex monstrosity. If I was running a 2.25/2.5 these days I'd use the later Defender manifold and twin-barrel Weber carb.