Twin SU's

Post by **alanworland** » Sun Aug 24, 2008 9:12 pm

I am building for my sidevalve an inlet manifold to use 2 rebuilt HS1 carbs. Each carb has its own connection to the block to supply two cylinders and I am about to join the two together to make it 'one manifold assembly'
However all the manifolds I have seen (including the one my carbs came from - Austin Healey) have the two inlet ducts joined together?
Any ideas why this is?

Post by **mike.perry** » Sun Aug 24, 2008 11:18 pm

Its a balance pipe but don't ask me anything technical. I have a twin carb inlet manifold and enough H1 carbs to make up a pair. All I need is the linkage. Also a decent 4 branch exhaust manifold would be useful as twin carbs with the standard manifold would be a waste of time. What needles do you intend using?

Post by **alanworland** » Sun Aug 24, 2008 11:46 pm

Balance pipe! thats what it is, but Webers don't seem to use them - strange. I think I will just join the two short manifolds together with the possibility of balancing later. I am going to use the standard exhaust manifold for now (its a new stainless system!) and see how it goes and perhaps look at the exhaust at a later date. Is a 4 branch manifold sold for the sidevalve? or is this something I will have to make/have made?
I was going to use GG needles to start with as it is these that are used in the Healey Sprite setup whee they allow the engine to develop about 35BHP
I have the linkage but will need to replace a couple of bits.
Not sure weather I should try and use the original silencer or go for something different, ram pipes?

Post by **RobThomas** » Mon Aug 25, 2008 11:49 am

Like this? Not much power improvement due to the extra carb, but, it helps power by removing the hot-spot heating of the inlet charge and straightens the otherwise tortuous path that the air has to flow through to get to the cyliders. This is why it is a good method of improving performance. The balance pipe helps smooth out the pulses of inlet air since the firing order means that one carb sees 2 pulses and then 2 pauses without the balance pipe (IIRC).

Exhaust manifold? I got some backplates laser cut and bought a 4-cyl motorbike manifold from a scrapyard but wasn't happy with the result. there was some talk of manifolds from Aus but nothing so far.

Post by **RobThomas** » Mon Aug 25, 2008 11:50 am

Helps to add the picture!<br>

<br>

Post by **alanworland** » Mon Aug 25, 2008 2:01 pm

I see you have a balance pipe option on you manifold(s) Did you run with a pipe or were they blanked off? and was it it better/worse with/without?
I would assume that the carbs would prefer and be more efficient with a continuous flow through them.

Post by **mike.perry** » Mon Aug 25, 2008 2:37 pm

If there is a demand for it I will chase up that Australian exhaust system. It's likely to be expensive with the shipping costs.
I will find out what needle setup is used in the Alta twin carb head.

Post by **alanworland** » Mon Aug 25, 2008 5:57 pm

I take it that the Alta head used twin H1's?
The exhaust you are refering to, does it replace the front section back to the silencer?

Post by **mike.perry** » Mon Aug 25, 2008 6:35 pm

I know of an Alta head with twin H1s and a 4 branch exhaust

Post by **alanworland** » Mon Aug 25, 2008 9:08 pm

For sale?

Post by **mike.perry** » Mon Aug 25, 2008 10:48 pm

No chance

Post by **Keith** » Tue Aug 26, 2008 9:22 am

I know of two also....they aren't for sale either!...

The Derrington 4 branch can replace the front section to the silencer, although they did make a complete system.

I have a 4 branch made for my Alta Shorrock set up, I just need to collect it from my friend who made it, I'll post a picture when I finally do collect it...it may help.

I have a picture of my Derrington manifold somewhere and one of a Derrington on a car with twin carbs, I'll look it out...

Post by **alanworland** » Tue Aug 26, 2008 11:41 pm

Is the Derrington exhaust section still available for the original sidevalve?

Post by **Keith** » Wed Aug 27, 2008 8:35 am

unfortunately not. regards Keith

Post by **RobThomas** » Wed Aug 27, 2008 3:16 pm

C'mon, Keith. Give us the name of your mysterious welder / fabricator so we can have a crack at getting some more manifolds made (or are you going to be selling some?) Bet it'll be better quality than mine.

Caaaaaaash waiting!

Post by **bmcecosse** » Thu Aug 28, 2008 12:11 am

I'm guessing these carbs are ex Mk1 Sprite - in which case they need to be mounted horizontally. Can you get that inlet manifold in past the original ex manifold ? Balance pipes like that will be ok if joined up with stout tubing - but they really won't do much, if anything! I would (and did) just run with straight pipes and no balance.

Post by **RobThomas** » Thu Aug 28, 2008 7:15 am

IIRC, H1 carbs off te Mk1 Sprite have 20 degree float chambers. 30 degrees for Minis and zero for MMs. Certainly the Mk2 Sprite used 20 degree float chambers. If you have a pair of MM chambers then you acn change them over?

Possible that I've got it wrong.

Post by **Keith** » Thu Aug 28, 2008 5:16 pm

Rob, I wish I could get him to make some more, it took me ages to convince him to make a set for my Alta Shorrock combination.

The set he made is no good for the standard or Alta engined cars as the pipes are bent around to miss the Shorrock compressor....plus they dont have the twin SU manifold fabricated.

I will post the pictures of my standard Derrington manifold and provide dimensions if anyone is thinking of getting some made.

regards Keith

Post by **alanworland** » Thu Aug 28, 2008 9:48 pm

I am still progessing with the twin carb mod, even though other projects keep coming along -new shed, greenhouse dismantle etc!Some pics of where I am at:-

http://i248.photobucket.com/albums/gg17 ... ifolds.jpg

http://i248.photobucket.com/albums/gg17 ... fitted.jpg

http://i248.photobucket.com/albums/gg17 ... fitted.jpg

I am at present trying to combine he carb inlets so that they can draw air through the orignal silencer

Post by **mike.perry** » Thu Sep 04, 2008 12:31 am

Looks good but I would fit a couple of heat insulator spacers between the carbs and manifold otherwise you are going to get fuel vaporisation problems which I think we have already discussed.