triple SUs

[pro240c]

hi all.

i was just wondering why there was never a triple SU manifold cast for the L series...?

i mean, you would think with the great results an L fourpot gets out of twin SUs, surely 2 more cylinders would equal one more SU...?

it just bugs the hell outta me that holden get one for their tractor engines (161ci right thru to 202ci) and yet the almighty L series gets stuck with 2 just because that was the only manufacturer's option.

i'm sorry, i just don't see the logic in it.

alternatively, anyone out there making or know of a kit that uses triple SUs...?

[Alfadog]

Yeah, they exist. But I think (and this is just what I've gathered, dont believe me!) the gains aren't very much unless your engine is decently modified.. someone else will answer that one I'm sure.

But that's not why I posted. :classic: Can you post some pics of your 240C please? Some of us enjoy all Datsuns, big and small!

[kyteler]

If you use the "Search" function on this site and on Google and type in "Triple SU L series" you'll come across a document that doesn't think it's a particularly good idea due to the Firing Order and thereby Air/Fuel per Cylinder ratio.

However, if I walk into my garage, there's one on the workbench that I'm in the prcoess of getting sorted, it may not be particularly beneficial going from a 240Z's nicely tuned Twin SU's to some Triple SU's, but going from a 240K's single 2BBL to some Triple's is always going to be a little bit better.

And even if it's not, it didn't cost me too much and it's worth a try right? ... right??

[Alfadog]

It'll sound better, that's for sure!

(use more fuel too, but shhh!)

[pro240c]

hey guys thanks for the replies.

i'm still getting used to this forum type so it's a bit of a mission getting info at the moment - but time will help i spose.

i don't have any pics of my 240C - YET. it's copping a 1UZFE (sacrelige they say! burn him!) and i'm halfway thru my rack and pinion conversion to make it fit. they're all 35mm pics, so i'll have to scan them and post them up for you all.

i cetainly don't see how triple webers can be great and triple SUs can't. so yeah, i think it is better :classic:

plus the induction roar would be great!

[beandip]

I remember reading the post on the tripple SUs . As I recall the crux of the issue is the dual SUs will flow all the air that is needed and or required for all but the highly modified Strokers. And why the tripple SUs dont work is about the volicity of the fuel air mix traveling through the manifold and head to the cylinder. Because of the fireing order of this engine this flow is disrupted and the "charging" of the cylinder is off cycle and the "charging " effect of the flow is disrupted. Off hand I cannot remember the name of the member who posted the explaination .

[Alan Pugh]

The difference between triple webbers and triple SU's is astronomical, and the two setups should never be compared to one another.

Because of the firing order of an inline 6 cylinder engine, 153624, you can divide the engine into 2 halves, odd and even.

The easiest way to explain it (and follow along at home) is to draw it on a piece of paper and work it out. If you draw 2 rectangles and number the cylinders 1 to 6 with corresponding intake manifolds (one with twin manifold and one with triple manifold) you will end up with the twin setup with each carb feeding 123 and 456, the triple setup feeding 12 and 34 and 56.

Now on each drawing go through the firing order and put a cross at the carb that is conected to the firing cylinder and a dash at the other.

You should end up with a pattern like this on each carb for the twin setup.

+ - + - + - + - + -

Pulse miss pulse miss pulse and so on, each carb has the same velocity and pulse rate going through it.

For the triple setup you will end up with uneven pulse miss rates and each carb won't atomise the fuel the same.

12 + - - - + - +

34 - - + - - + -

56 - + - + - - -

A lot of people will say that is what a balance tube is for but this will only equalise vacuum not pulse or velocity.

Alan P.

[Z Kid]

All this, and yet there were cars (inline 6's) which came out with triple SU's stock, and they work a treat? I still dont follow, I am sure there is a reason, I just dont know of it yet.

[Mateo05]

I think the only way to get the benefits of a triple SU setup would be changing the firing order of the engine via a custom cam.

[pro240c]

i think alan's hit the nail on the head there... and i think the reason it works on other engines is due to the different firing orders.

i understand exactly now. thanks for volunteering that info.

I think the only way to get the benefits of a triple SU setup would be changing the firing order of the engine via a custom cam

but one thing i don't understand is how a cam can change the firing order of an engine...?!?!?! the firing order is pre-determined by the way the crankshaft swings , not by how long/ when the valves open and close.

you would not only need to custom make a crankshaft, but get a dizzy to suit and a whole new camshaft to change the valve timing.

then make it run harmoniously.

[kyteler]

Originally posted by pro240c

i think alan's hit the nail on the head there... and i think the reason it works on other engines is due to the different firing orders.

i understand exactly now. thanks for volunteering that info.

The Holden 6 (grey/red/blue & black) also run a 1-5-3-6-2-4 firing order dude.

[pro240c]

well, then maybe twin 2in SUs would work better on a 202?