triple SUs

[Zedrally]

Originally posted by Alan Pugh

snip.....

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 - + - + - - -

Alan P.

Can of worms and many questions....

Wouldn't the same hold true for triple webbers?

Obviously not, so why are they different?

MOM

[1971rb26dett]

Originally posted by 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.

As far as I know all straight 6s fire 153624

[abas]

Originally posted by Zedrally

Can of worms and many questions....

Wouldn't the same hold true for triple webbers?

Obviously not, so why are they different?

MOM

Triple webers setup are more akin to having 1 carb for each cylinder as each weber carb has 2 competely separate intakes/internals, whereas each SU (on a triple setup) would be feeding 2 cylinders from 1 intake.

Presumably firing order and stuff is not relevant for triple weber setups at all in that case.

[Alan Pugh]

I have opened a can of worms haven't I.

All common inline 6 cylinder engines use a firing order of 153624.

This firing order is actually a balancing feature of an inline 6.

Triple webers versus triple SU's, the simple answer is 6 venturi's for the webers and only 3 for the SU's.

In AUS as Z Kid pointed out there were production cars that came out with triples fitted, Torana GTR XUI pops to mind. These cars were great performers and for street use were a fast car of the time, I know because I owned one.

Triple SU's for a fast street car would work fine, and I know of a couple of guys that swear by them on there old Holdens, but having said that the manifolds are readily available and still cheapish by todays standards.

I would not go to all the trouble of finding or manufacturing a special manifold for an L series engine when the gains for money spent are not there.

When you are looking for performance you need everything to work together smoothly and i'm sure everyone would agree that airflow to cylinders is a very important part of any sort of performance.

Alan P.

[kyteler]

How much do you think a setup would/should cost? At what point would you say, "hell no, I'm not paying that!" ?

[Alan Pugh]

For me personally that cost would be whatever I could buy two good/new SU's for that bolt straight up to the twin manifold and I believe at the moment I could pick them up for around $450 AUS.

The extra hassle of the third carb for no real gain other than looks (in my opinion) is not worth it.

Alan P.

[kyteler]

That's alright then.

What I have cost me less than that, so it's all good.

If I could have got a Twin SU setup for the price I got the triple manifold and 4 carbs (2 sets of twins) I probably would have gone that route. As it is I still have to fabricate linkages and fuel lines but it will still come to less than that price mentioned when I'm finished.

I've never dealt with SU's before and these aren't Japanese SU's so I'm pretty much flying blind, but I'll figure it out, it's just a matter of time.

[beandip]

There is far more to engine building than just adding carbs. This ballancing act as Allen said, is another reason the 4 barrel carb is not a reasonable mod. I experimented with a air craft carb on a superchaged large V-8 . We had it on a dyno on a engine stand and were trying water injection with this set up. Idle speed was excess of 2K and the engine diden't perform worth a damn. I went back to multi carbs. This was in the old days and I couldent afford fuel Injection , also it was not for a street engine. You can over carb an engine and it will only perform at near red line . I dont think this is what you are looking for. These little 6s work great on SUs . Just tune them. My 2 cts.

[kyteler]

There is far more to engine building than just adding carbs.

Yes, well aware of that.

This ballancing act as Allen said, is another reason the 4 barrel carb is not a reasonable mod. I experimented with a air craft carb on a superchaged large V-8 . We had it on a dyno on a engine stand and were trying water injection with this set up. Idle speed was excess of 2K and the engine diden't perform worth a damn. I went back to multi carbs. This was in the old days and I couldent afford fuel Injection , also it was not for a street engine. You can over carb an engine and it will only perform at near red line . I dont think this is what you are looking for.

No, of course it isn't.

These little 6s work great on SUs . Just tune them. My 2 cts.

I know they do, I'm also well aware of that, and if I had twin SU's on my L24 I WOULD just tune them. However, I dont. I have a single 2BBL Hitachi DD carburettor. I'm trying this out simply because I got the setup for far far far cheaper than a twin SU setup would have cost me.

As has already been said, there are vehicles that come with Triple SU's standard, I fail to see how those 6's would perform and yet the almighty L-series collapse.

I'm not in a hurry to do it, I'm just trying it out, I still have to finish fabricating all the linkages and fuel lines etc. as I want it to at least run and look OK, even though it may not be better than twins SU's.

[mperdue]

Another triple setup for you guys! (I have no clue if this is real or not! My guess is not....) And anyway, there are probably more than 3 - maybe 6?

Michael

[mperdue]

Oh and one more thing maybe a little more applicable to the discussion. I found this chart while doing my own research for a SU setup on my 210 (still working on that by the way). Anyway, this could be helpful. The 240Z carbs are 1-3/4". According to this triples would work best on 2L-4L - which fits the Z engines nicely.

I got that here: clicky

[Bambikiller240]

Well, 2400 cc's is toward to lower end of the 2000 - 4000 cc and 3 x 1-3/4" line on the graph. This looks to be more for apprpriate for the high HP (highly modified) L24

On the 1500 - 3000 cc line the 2.4L motor is more in the middle of the range using 2 X 1-3/4" This looks to be more appropriate for stock to mildly built L24's

Also see Note #2