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L31 + twin 2inch SU's build questions


ovenfood

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Bluestag, nice car :) I do hope when it comes to it I can find an SU guy but I don't like my chances..

 

In AUSTRALIA???? Are you daft, lad?

 

Isn't the island just lousy with Brit cars?

 

I am next to sure that some old codger of a Brit has retired to your suburb, and is aching to tune your SUs.

 

Just to keep his hand in.

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:) well I hope I find this fellow because each time I think about it I think about cheating and hiding some injectors in the false SU's, actually I keep hopping the next Brit contractor we get is an SU nut :> (I love learning from the old contractors they teach you so many tricks)
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Dyno the car on a rolling road with proper SU indicating needles to tell you station and height, and turn your own needles on a lathe from brass rod.

 

It's the way it's been done since the beginning, and will work better than any store-boughtten needle you stick in there!

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Dyno the car on a rolling road with proper SU indicating needles to tell you station and height, and turn your own needles on a lathe from brass rod.

 

It's the way it's been done since the beginning, and will work better than any store-boughtten needle you stick in there!

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Yes, they are specially marked needles. I used some bluing compound to colour the needles and scribed them every .010" to tell me when and where I needed to change what in which direction.

 

Then I went FI.

Edited by Xnke
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Nope---there is a TOOL that comes in the SU TOOL KIT that has a gauge, as well as a little 'L-Shaped' rod that goes into the dome to indicate PRECISELY the height of the SU Suction Piston when the engine is running under load. From those notations, you can then transcribe to the needle from interpolated height where you need a thinner needle, or a thicker needle and make the adjustments accordingly. Always work from a LEAN situation into RICH. Why? Because you can always make a rod THINNNER, but if you make it too thin (go rich) then you have to start the whole damn thing over!

 

SU%20Tool_1.jpg

SU%20Tool_2.jpg

 

Actually silver solder makes for quick work if you 'oops'... then you can turn a needle from final dimensions afterwards.

 

And yes, 1979, for a MONTH sitting backwards watching needle station positions with detonation stethescope on and yelling orders to the driver as to throttle position change and brake application to this day makes me LAUGH my ARSE off everytime someone posts 'carbs are easier to work with'! :blink:

 

Like Xnke, I JUMPED at the ability to "shift, arrow up....shift arrow down" and simply watch an AFR gauge.

 

As to "adjust the needle up or down" that works if EVERY station is off the same amount. This is usually not the issue. You have needles that work CLOSELY, but generally each car needs some more fuel here, a little less there. A rolling road and AFR meter is about the only way to see it. You will be amazed at how much better your car drives when you go do the needles like that!

 

But for me: "Shift, control arrow up....Shift, control arrow down" FOREVER MORE! I'm NEVER going back!!!

 

Oh, and you can use the rods to check suction dome synch as well like this:

 

SU%20Tool_3.jpg

 

On a Single-SU setup like I was tuning, it was more important to know station height...if there were TWO on there... EGADS!!!

 

 

 

 

 

 

 

 

AH, this IS how you guys are doing your SU's on the car, right? I mean, you don't depend SOLELY on the FSM as the total performance guide to SU performance, right? I mean, these things were around for DECADES before Japan picked up on them... there IS more than one way to performance tune them...but really all the good shops seem to congregate around the original tooling for some reason. Perhaps because it works? B)

Edited by Tony D
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ok I think Tony has sold me on EFI. I think I'll still attempt to hide the injectors in some SU's (don't want to waste those hand polished manifolds...) however I may go another route (ITB or standard EFI) but I think this will consume me to much if I go down the SU path.

 

 

THANKS Tony and every one who posted, if there is any more input feel free to share but I'm pretty set on EFI now :)

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There are kits to put GM TBI injectors in your SU's and it is a simple matter to put a spacer behind the SU's with a pair of forward firing Bosch-Style injector (a pair of 550's would handle what...200HP?) (Or put them underneath, I don't care)...

 

Patton Machine makes some nice stuff for what you got!

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^^ sweet Mr D I'lL check it out but chances are I'll fab it myself at work or get the machine boys to turn it up for me :) I'm definitely going to need to work out what will best combination of positioning and appearance for my application. Someone mentioned hiding 4/6 injectors in the air filter box pointing at the SU's mouth, that may be another option.

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couple of larger ones is easier and less trouble prone. Shoot in at a 5 degree angle to wet a wall down inside the SU someplace to initiate a tau layer, and the rest is golden...

 

Mitsubishi Starion Turbo TBI injectors are 'short pattern' Bosch type, the same style of holder the Ford 5.0 HO TBI used in 84 or so will position them like you need, and give you a decent template to work from Because the mitsus are so short, they fit in the stock air cleaner nicely!

 

Not that I have given this any thought... B)

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