Modify SU Manifold for 4 barrel.

Dixie6789 · Post by **Dixie6789** » Tue Apr 15, 2014 9:32 pm

I am going to try and modify my SU manifold to fit a 4 x barrel.

Has anyone got a drawing of the dimensions for the flange on a 4 x barrel carb. I want to get a alloy one made so I can weld in place.

thanks Mark

kiwicar · Post by **kiwicar** » Wed Apr 16, 2014 6:09 am

Hi
The easiest thing to do is buy a spacer for the carb, minimum one inch thick really two, and draw it up. You will need one anyway as if you just stick the carb straight on the top of the su manifold with the pent roof thingy chopped off you will get very poor mixture distribution.
best regards
Mike

Dixie6789 · Post by **Dixie6789** » Wed Apr 16, 2014 11:09 am

Thanks Mike.

Next question, apart from E-Bay, where can I buy such an item?

ta M

DEVONMAN · Post by **DEVONMAN** » Wed Apr 16, 2014 3:22 pm

Dixie6789 wrote:Thanks Mike.

Next question, apart from E-Bay, where can I buy such an item?

ta M

Real Steel do spacers but not cheap.
However the shape may not suit the welding perimeter for a chopped su manifold. You could just buy a gasket to get the dimensions.

DaviesDJ · Post by **DaviesDJ** » Wed Apr 16, 2014 6:10 pm

Not wanting to be a pooper, but the fans/advantages would seem minimal to me- the stansard manifold is not a great design - and a well set up pair of us carbs can flow almost as much as a small 4 barrel - and the manifold will not flow sufficiently to allow to carb to function to its full potential - the signal to the carb may be good - but the sharp turn at the upper portion would cause a lot of drop out IM hO - I would save up a bit and look for a used Eddie performer. A plate and the machining to do this properly would get you 2/3 the way to a good manifold!

kiwicar · Post by **kiwicar** » Wed Apr 16, 2014 7:49 pm

Hi Dave
indeed I agree with everything you say about the SU's, if you look back over the years you will find I have said very similar stuff myself. However no one ever wants a pair of SU's because a 4 barrel looks cool.
Using an adapter plate and a spacer at least isn't that much worse than the SUs it replaces and saves a couple of hundred quid over buying an aftermarket manifold and although it will use more petrol and be a pig to set up it is a 4 barrel. If you add a good manifold then a 4 barrel and a good manifold will probably give you 5 or 7 bhp at peak over the stock SUs and manifold (well until you flow the SUs and set them up properly).
Personally in the incredibly unlikely event I was using carbs on a rover I would buy a high flowing 4 barrel manifold and build an adapter to take a pair of SUs (probably 2 inch ones) and do the basic flow mods or radiusing the piston and set them up properly. But that is not as cool as a 4 barrel.
best regards
Mike

kiwicar · Post by **kiwicar** » Wed Apr 16, 2014 8:03 pm

Hi Again
thinking about it to use carbs on a rover I would probably get an old injection manifold, make up a spacer to make the plenum a bit taller, replace the throttle body on one side and opposite it make a hole and adapt the thing to take a pair of 2" SU carbs one either side of the plenum, it would probably nice to stagger them so they were 1/3 from each end of the plenum. . . . or maybe fit them to come in at 45 degrees to the top of the plenum . . .gosh I am thinking about rovers and carbs. . . what an interesting sensation two new experiences at once

best regards
Mike

ChrisJC · Post by **ChrisJC** » Wed Apr 16, 2014 8:27 pm

I'm running twin 2" SU's, and they run to 250BHP with no flow restriction. I know this because I have a vacuum gauge, and it sits at 0 on wide-open throttle right up to the upshift point at 5500rpm.

Chris.

DaviesDJ · Post by **DaviesDJ** » Wed Apr 16, 2014 8:59 pm

Ahh but then again the throttle response in lifting carbs like su's aret as good IMHO - if you are making adaptor plates then perhaps 2 twin choke webers like on the ford cross flow etc- but I think in general the fuel injection manifold and the SU manifold are poor and "dog leggy" in comparison to the edelbrock performer- it really is a top manifold - and tested - I have now added over 3 inches of spacer to increase the plenum sis on my setup - even on the Landy it's just fitting under the bonnet and the throttle response is great.

Getting back to the topic - I really don't like saying this as this forum (I think) is about giving it a go - and trying ideas - beating the established money boys in our sheds - but I think this idea is a bit of a dead end. Look out for a used performer

Dixie6789 · Post by **Dixie6789** » Mon Apr 21, 2014 1:40 pm

It's not about the money. I actually have a 360 performer on my current motor with a 500 CFM Eddie, so can use that on my 4.6.

I just wanted to have a play, men in their sheds etc. I have never been one for just shelling out on stuff, I much prefer seeing what I can make using the stuff I have.

I didn't want to use SU's, purely because of the looks, they don't look right under the bonnet of a Cobra. But I saw a hot rod the other day with Chrome ones, and it looked stunning.

Mark

Muscle-Manta · Post by **Muscle-Manta** » Mon Apr 21, 2014 11:18 pm

I've got a 2" spacer for sale. Top flange drilled and tapped for the carb studs bottom flange drilled. Both flanges drilled for spread or square pattern. £25 including postage.

Dixie6789 · Post by **Dixie6789** » Tue Apr 22, 2014 7:06 am

Yes please, I will have it.

Do you have PAYPAL?.

Thanks Mark

Muscle-Manta · Post by **Muscle-Manta** » Tue Apr 22, 2014 8:00 am

PM sent.

Dixie6789 · Post by **Dixie6789** » Thu May 08, 2014 7:41 pm

Well I have cut the pent roof thingy off the SU manifold. I suppose the next thing is to cut out all the bits and polish it and weld the spacer on.

The spacer is open, doesn't have a dividing plate, is that a problem, should I weld one in?

Has anyone who has done this before got any advice?

thanks Mark

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kiwicar · Post by **kiwicar** » Sat May 10, 2014 6:02 am

Hi
I would fill in the cap down the middle between the runners and at either end, you don't want fuel collecting in that void under the runners! If you want to keep it simple then radius the runners where they enter the plenum formed by the new spacer the throttle response will not he particularly subtle but it will be simple. If you want to put a divider to separate the two halves of the carb, this will make the throttle response more progressive but you will need to blend everything into the divider and radius the ends that don't have a divider or side of the spacer next to them.
Best regards
Mike