Twin SU update

[haynes]

Just fitted a maniflow inlet manifold to my twin 1 1/2 SUs and gained 8hp at the wheels! The manifold unleased a whole chunk of power above 6000rpm. So well worth the £100 and hassle of fitting it, certainly better than the expense and aggro of fitting a webber.

[Cooperman1]

To me the SU's always seem to give the power in a more 'friendly' way, if you can understand that. The Weber will, I guess, usually give a bit more right at the top end, but at the lower rev ranges the SU's seem smoother in the power delivery.
It's very interesting to have the power improvement with the Maniflow intake quantified. There is a mod you can do to the standard twin SU manifold, but it's a bit involved as you have to block off the balance pipe and do lots of other things as well.

[phil hill]

Wow, that's a big improvement !! 8hp is about 10% of the 'at the wheels' figure from a 'hot' road mini, so for the money that's good.

What type of manifold did you have before ?? I've got an aftermarket rather than genuine item, which flows better than standard, but I've been contemplating changing to the Maniflow.

I've also got a pair of HIF38's (from an Allegro of all things....) which I'm overhauling ready to try. I modified my existing HS4's slightly (butterfly shaft halved, screws countersunk and locktited, butterfly plate edges filed, internal casting 'flash' tidied up etc) so I'll be doing similar to the HIF's just for s#!ts and giggles....... Maybe I'm wasting my time, but tinkering time is "free" if you see what I mean !!

When Mike Barratt and Keith Calver were developing their aftermarket twin point injection setup they used the Maniflow manifold.

>> Edited by phil hill on Friday 4th June 11:31

[haynes]

Phil, I also modified my HS4s as you described. The manifold made little difference up to 87bhp at the wheels, then at 6000rpm it gained a big chunk - pushing it up to 95. As i have a 296 cam 99% of the time it would be used with a webber, but it was cheaper and easier to stick with the twins and i'm very pleased with the result. So i wouldnt like to say what improvement it would have on a 286 cam road engine. My previous manifold was an aftermarket job, purported to be the 'best flowing' by the seller.

The fuelling isn't a 100% as we ran out of time, so ive got to go back to the rollers after a few more mods, like an 8mm fuel line and move the regulator to under the bonnet, it really drinks the juice when you floor it! Anyone any advice on fuelling in corners with HS4s, due to those float cambers?

[Mr2Mike]

haynes said:

Just fitted a maniflow inlet manifold to my twin 1 1/2 SUs and gained 8hp at the wheels! The manifold unleased a whole chunk of power above 6000rpm. So well worth the £100 and hassle of fitting it, certainly better than the expense and aggro of fitting a webber.

Amazing, I knew the standard manifolds were pretty poor, but not that bad!

[LeeBee]

Haynes, what spec engine are you running?.I am interested in getting one of these manifolds for mine

Is it an easy swap? (cables etc)

Cheers

LeeBee
P.S don't suppose you have a picture of it in place do you?

[haynes]

there is a pic of the manifold on the minispares website, although i got mine straight from maniflow as i wanted a servo take off. My engine is practically a race spec engine, 1380, 296cam which gives you loads of power at the top end but nothing below 3000 and with the noise of the straight cut box its certainly not a daily driver. So bascially most people would fit a webber with this spec but i wanted to try my SUs. I doubt if the power gain on a road engine would be nearly so great certainly anything less than a 286 cam, because all my gains were at the top end. As for fitting it, you need to fabricate a throttle cable stop, it took me a good half a day trying to sort it all out, twin SUs are fiddly at the best of times. You'd definately need a rolling road session.