Triple SUs

[Bazzateer]

Just curious as to whether this has been done to a L24,26,28? I'm aware of the triple Weber/Mikuni etc but was wondering if this had ever been done? Works nicely on a Jag XK engine................

 

[Rob Gaskin]

Yes it has been done. I'll post a pic later.

 

[AliK]

Lots of people have tried, some have succeeded. One even spliced 3 intake manifolds and made a custom one.

An interesting post here as to why it’s so challenging ...


https://www.classiczcars.com/forums/topic/12406-6-carbs/?do=findComment&comment=117974

Why do I have this info to hand? I want to get rid of my balance tube or restrict it so as to reduce reversion through the carbs. One day!

 

[Bazzateer]

Shouldn't be too challenging. Other than a bespoke manifold the rest should be achievable using and modifying existing parts for the XK set-up. That link ^ goes off at a few tangents (6 carbs?) from what I'm on about.

 

[Bazzateer]

Yes it has been done. I'll post a pic later.

Looking forward to seeing that!

 

[jonbills]

There are lots of threads on here about triple SUs too.
https://www.google.com/search?q=sit...69i57j69i58.4573j0j4&sourceid=chrome&ie=UTF-8

this one is a good starter on the problems.
https://zclub.net/community/index.php?threads/triple-sus.3778/
no idea why the XK works great and the L engine not, they're the same firing order and thus pulse pairings.

 

[Rob Gaskin]

https://zclub.net/community/index.php?threads/triple-su-intake.14723/#post-158803

 

[Bazzateer]

Looks good to me. Lots of opinions on those links as to why they won' work but very little from anyone who's actually done it as far as I can see. All very intriguing though.

 

[AliK]

I think if Project Binky has shown us anything it’s that anything is possible, it’s just a matter of time, skill and effort to return ratio.

For my money if I was going more than two carbs I’d be doing the 6 (Suzuki?) carbs - says the man who is still messing about getting two to work well together!

 

[Bazzateer]

I'm a big fan of SUs and just thought why not? Perhaps a future project for me..............

 

[johnymd]

Although I really like the sound of doing things a bit different, I don't think it will improve things and may even make it worse with the hassle of balancing. Twins work well with the firing order using alternate carbs in succession. Remember that only one cylinder sucks through the carb at a time but using alternate front and back carbs means they can keep up with supply at higher revs. It's not supplying all 3 cylinders at the same time so is sized to feed each cylinder.

 

[AliK]

Well said Johny. [emoji106]

Here’s the text of the link I pasted above which doesn’t seem to work for me - it gives a visual explanation of the point John is making ...


Yes and no. There are more advantages of having 6 carbs. A three carb setup is actually inherently faulty. Sure it works, but not the most effiecient. Actually, a 2 carb setup is supposedly more balanced. Here's why;

3 carb setup;

Carb 1, feeds cyl 1 & 2

Carb 2, feeds cyl 3 & 4

Carb 3, feeds cyl 5 & 6

Firing Order: 1-5-3-6-2-4

So the carbs are working in this order;

Carb 1

Carb 3

Carb 2

Carb 3

Carb 1

Carb 2

or

1,3,2,3,1,2,1,3,2,3,1,2,1,3,2,3,1,2,1,3,2,3,1,2...

Uh oh! Only Carb 2 is working at a steady rate!!!

After Carb 1 feeds fuel to cylinder 1, it has to wait through three firings (6 revolutions!) before feeding fuel again. Then it has to quickly fire again after only one more firing (2 revolutions). Carb 3 is doing the same thing!

So, carbs 1 and 3 may run rich or lean in different stages of the firing order while carb 2 is working steady. The carbs will never be in sync.

2 carb setup;

Carb 1, feeds cyl 1, 2, & 3

Carb 2, feeds cyl 4, 5, & 6

Firing Order: 1-5-3-6-2-4

So the carbs are working in this order;

Carb 1

Carb 2

Carb 1

Carb 2

Carb 1

Carb 2

Bingo! Balanced!

With a 6 carb setup the same is obviously true. Syncing the carbs is not hard. The carbs will also be doing half the work than a 3 carb setup, and 1/3 the work of a two carb setup. This means more precise metering; Especiallyat high RPM's!

Also, smaller carbs can be used since they are doing much less work. Each cylinder only requires about 70cfm's in an L28. A 44mm Mikuni flows ~165cfm's!! Holy cow, talk about overkill. Not efficient! Not to mention they cost an arm and a leg. Even the 26mm will flow almost 100cfm's.

So, I need to find the smallest Mikuni carbs that will be able to flow just enough air/fuel and NOT be smaller than the intake runner, so as not to restrict air flow into the motor.

 

[Rob Gaskin]

Now you need to find the firing order of other 6 cylinder cars with 3 carbs and guess what, its the same! Jag and Healey.

Perhaps 1 carb is the way to go, a nice steady flow ha ha.

 

[johnymd]

1-5-3-6-2-4 or 1-4-2-6-3-5. These are the 2 common firing orders. Neither are ideal for 3 carbs. Both will work but not ideal. They both work well for twin carbs, twin primary collectors and twin turbo but not triple's. I'm not considering twin choke as triple's.

 

[Bazzateer]

Hmmm.........six SUs, now there's a thought!

 

[johnymd]

 

[Bazzateer]

Throttle bodies eh? Too complicated for me.

 

[jonbills]

ITBs are the obvious best answer

 

[AliK]

Jaguar straight 6 firing order is 153624 also.

Looking at the Jag inlet manifold, it looks like an interesting arrangement of 2 balance tubes - I wonder if that’s why the triple SUs work on a Jag!?

 

[Alphabettispaghetti]

Carbs are king. An Injection is what you have near the end of your life.

let’s see some 41mm fcr’s!