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2 inch SU info

Started by LC-GTR-1969 , Feb 09 2016 03:38 PM

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#101 _2ELCS_

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Posted 01 March 2016 - 06:43 PM

And what are you doing after morning tea OJ ?...


#102 _oldjohnno_

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Posted 01 March 2016 - 06:52 PM

And what are you doing after morning tea OJ ?...

 

a couple of Bex and a good lie-down I'd say Wayne...


#103 _Agent 34_

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Posted 01 March 2016 - 07:38 PM

Jesus Christ Dave I had to have 7 Red Bulls, 4 lines of coke, 9 pingas and an apple turnover (with cream) just to read that lot...

 

john - watch the cream it's bad for your heart.


#104 N/A-PWR

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Posted 02 March 2016 - 12:15 AM

OK,

 

This is what I have compiled so far, as information comes in,

 

I will update:-

 

Attached File  CARBURETTOR FLOW COMPARISONS.jpg   62.51K   11 downloads



If you open image in a new tab, she is bigger to read.


#105 N/A-PWR

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Posted 02 March 2016 - 01:36 AM

Correction of the 350 Holley, as tested with only 1.5Hg,

 

and should be 128cfm @ 1.5Hg as Oldjohnno stated the Holleys are rated at 3Hg:-

 

Attached File  CARBURETTOR FLOW COMPARISONS 2.jpg   57.12K   2 downloads


#106 LC-GTR-1969

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Posted 02 March 2016 - 05:47 AM

OK,

 

This is what I have compiled so far, as information comes in,

 

I will update:-

 

attachicon.gifCARBURETTOR FLOW COMPARISONS.jpg



If you open image in a new tab, she is bigger to read.

This is fantastic...

 

great work. I am really interested to see the results of the 45 dcoe. 


#107 N/A-PWR

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Posted 02 March 2016 - 02:10 PM

Cheers,

 

This is fantastic...

 

great work. I am really interested to see the results of the 45 dcoe. 

 

Added the 40dcoe as advertised elsewhere just to start,

 

and spread the other bits and pieces so they are more clear:-

 

Attached File  CARBURETTOR FLOW COMPARISONS 3.jpg   81.46K   4 downloads


#108 N/A-PWR

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Posted 02 March 2016 - 04:03 PM

Hello All,

 

Fined tuned so inputs from other field testers are recognized in future additions:-

 

Attached File  CARBURETTOR FLOW COMPARISONS 4.jpg   110.55K   4 downloads

 

all recommendations accepted. 


#109 SA EH

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Posted 04 March 2016 - 07:11 PM

Hey all you fellas with 2" su carbs....

Have a look at the underside of the main piston(where the needle goes in) & tell me if you have the two air transfer holes in each piston or not.

I hav a set of hd8's here & 2 have no holes, the other has them.
I guess the question is, which one is better? The one with the transfer holes seems to travel up & down quicker, the other two not so quick.
Not sure if the pistons with the holes are an update version or what, or if they are from the hs8's and the hd8's had no holes....

Anyone?

#110 N/A-PWR

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Posted 04 March 2016 - 07:44 PM

Here you go Jonesy,

 

Warrenm's post:-

 

post-70-0-93153500-1295742215.jpg

http://www.gmh-toran...em/#entry566261

 

Jag vs Rover SU's.



Hey all you fellas with 2" su carbs....

Have a look at the underside of the main piston(where the needle goes in) & tell me if you have the two air transfer holes in each piston or not.


#111 SA EH

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Posted 04 March 2016 - 08:26 PM

Perfect Dave, thanks a heap.

Exactly what I was after.

Pro's & con's of either?

#112 _oldjohnno_

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Posted 04 March 2016 - 08:57 PM

Either is fine so long as the passageway remains open at full lift, which will be the case anyway so long as you don't mix and match slides and bodies.

 

Resist the temptation to frOck with these - the volume of air flowing through the holes is tiny (maybe 200ml in total from closed to open) so hogging them out just makes the slide flutter. And big openings in the bottom of the slide will only create turbulence which will hurt flow.

 

CV carbs are also very common on bikes and it amazes me how many people think they know more than the carb designers and simply can't resist opening up every passageway they find. But of course it just makes them worse...


Edited by oldjohnno, 04 March 2016 - 09:05 PM.

#113 SA EH

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Posted 04 March 2016 - 09:23 PM

Hmmm, not frOck with them...

Now how the hell am I going to do that?!?
Might have to actually take someone's advice at some point in time.

#114 N/A-PWR

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Posted 04 March 2016 - 09:30 PM

we need flow test information at least Jonesy,

 

that way the tests will show the differences between the others here.  :spoton:



Oldjohnno has put the flow bench to work for us.


#115 _Bomber Watson_

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Posted 04 March 2016 - 09:59 PM

CV carbs are also very common on bikes and it amazes me how many people think they know more than the carb designers and simply can't resist opening up every passageway they find. But of course it just makes them worse...

 

 

This is super true. 

 

Back when I had a Harley, I knew another lad with the same make and model, and another bloke who swore by this factory 40mm cv carb mod, all you had to do was drill out the air tranfer hole in the piston. 

Fair enough, other mate with a stock harley goes out and drill the hole out to what old mate specified, proceeded to throw her back together and frOck me swinging the gains he got!!!! Or so he said. 

 

He ranted and raved about it and asked why the fudging elma fud I hadnt done it yet, the gains were so great!!!!

To be honest I rode his bike after the mod and thought it felt snappyer than mine....

So we decided to test it, I lined up beside him one arvy in a rather quiet location and we let loose for a few impromptu drag sessions, best to 100kph or there abouts. Due to not having a starting girl we decided roll ons at 40kph were most effective, untill he lsot to me four times, then we agreed that standing starts would show the true benefits of the mods, where I again beat him multiple times. 

 

Turns out, yeah his throttle responce was slightly better, but thats all. Evreything else was down.......

 

Shoudl add I was 10kg heavier than old mate back then and the bikes were almost identical so yeah.....

 

Cheers. 


#116 warrenm

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Posted 04 March 2016 - 11:00 PM

If you have a close look at the piston on the right above, you'll notice a white plug that I fitted. There was a small hole in the piston that would allow the piston to rise until the hole was exposed then the piston wouldn't rise any further. I eventually plugged them so that they operated like the piston on the left. I've seen a few learner legal 600cc bikes setup the same way. My mates 600 Kawasaki would free rev to the red line while stationary, but nowhere near the red line whilst riding, it worked like a govenor.


#117 _oldjohnno_

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Posted 05 March 2016 - 06:14 AM

This is super true. 

 

Back when I had a Harley, I knew another lad with the same make and model, and another bloke who swore by this factory 40mm cv carb mod, all you had to do was drill out the air tranfer hole in the piston. 

Fair enough, other mate with a stock harley goes out and drill the hole out to what old mate specified, proceeded to throw her back together and frOck me swinging the gains he got!!!! Or so he said. 

 

He ranted and raved about it and asked why the fudging elma fud I hadnt done it yet, the gains were so great!!!!

To be honest I rode his bike after the mod and thought it felt snappyer than mine....

So we decided to test it, I lined up beside him one arvy in a rather quiet location and we let loose for a few impromptu drag sessions, best to 100kph or there abouts. Due to not having a starting girl we decided roll ons at 40kph were most effective, untill he lsot to me four times, then we agreed that standing starts would show the true benefits of the mods, where I again beat him multiple times. 

 

Turns out, yeah his throttle responce was slightly better, but thats all. Evreything else was down.......

 

Shoudl add I was 10kg heavier than old mate back then and the bikes were almost identical so yeah.....

 

Cheers. 

 

The "performance" world is full of this stuff. It's not just bikes either, how many people have pulled the check ball from a Holley vac secondary or wound back the spring tension on an air flap and then claimed it went faster? Are the carb engineers (those idiots that spend years and millions developing a product) so stupid that some tool in a Unit tshirt with a Ryobi can improve on their work in 30 seconds with a 1/4" bit? Why the hell would they think that opening the throttle faster is a good thing anyway? It nearly always slows acceleration. To be fair though introducing a slight hesitation or bog can actually make the car feel quicker. Slide type carbs like Mikunis and Keihins need some amount of common sense to be used, particularly in a car where the power-to-weight is usually much much lower than that of a bike. You can't just mash the pedal to the floor in any old gear and engine speed and expect the engine to like it. Your brain is the ECU; it needs to be used to modulate the throttle opening to the engine speed and load. And if you can't manage that then you're better off with CVs.

 

Mark Twain could have been speaking specifically to the performance guys when he said this; countless millions of hours are wasted doing stuff for little (or negative) return that would've been better spent elsewhere.

144cab7acd25aa18bb38ec6309e0e317.jpg


#118 SA EH

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Posted 05 March 2016 - 09:47 AM

So the main thing you're really telling me here is not to touch the piston transfer holes, and somewhat resist the temptation to mess with the carbs altogether.
Funny enough the only thing I didn't do on my 1 3/4" set was modify the transfer holes, it was suggested in one of the su carb books I have here is to take the breather hole in the top of the dash pot out from 1mm to 3.2mm/ 1/8", which seems like it would have the same effect. This was said to "help solve any slight hesitation under maximum acceleration".

#119 _oldjohnno_

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Posted 05 March 2016 - 04:34 PM

it was suggested in one of the su carb books I have here is to take the breather hole in the top of the dash pot out from 1mm to 3.2mm/ 1/8", which seems like it would have the same effect. This was said to "help solve any slight hesitation under maximum acceleration".

 

Horseshit. "Any slight hesitation" is almost certain to be made worse by quicker opening, unless of course it was way too rich to start with. And in that case I guess you could, I dunno, tune it?  Don't change anything unless you have substantiated proof that it doesn't actually make things worse.


Edited by oldjohnno, 05 March 2016 - 04:34 PM.

#120 SA EH

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Posted 05 March 2016 - 07:20 PM

This of course is all based on non real world situations where someone says I have a flat spot under acceleration but is actually an ignition problem....

#121 warrenm

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Posted 05 March 2016 - 10:28 PM

What he is saying is good.  :spoton:


#122 rodomo

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Posted 06 March 2016 - 08:46 PM

Piston lift speed is a science of it's own with side draft carburettortoriethingamabobs.


#123 SA EH

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Posted 07 March 2016 - 11:21 PM

Lets talk needles for a second....

 

I've gone over some of Warrens posts in another 2" su thread to confirm what carbs i have actually sitting here.

Three HD8's, Two appear to have Rover pistons, the other is a Jag.

 

The two rovers have AAB needles which are .090" swing

The jag has a BCC needle which is .100" swing

 

Both rover pistons open to about 7/8 lift.

The jag opens fully.

 

Question is, with jag pistons that fully open, are they supposed to have .100" needles or .125"?

I just checked the needle position at wot and it hasn't come out of the jet at the bottom, so why the need to go to .125"s?

And how would you get the .125" to fit as they are a fixed needle compared to the .100" swing?

 

With everyone suggesting to run UM/UX/UP needles, I guess i need to make it happen but I'm a little confused as it doesn't correspond to Warrens info here: http://www.gmh-toran...m/#entry566261 


#124 N/A-PWR

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Posted 08 March 2016 - 12:08 AM

hey there Jonesy,

 

you make an interesting conversation, so here is another:-

 

http://oldholden.com/node/90207

 

 

Question is, with jag pistons that fully open, are they supposed to have .100" needles or .125"?


#125 warrenm

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Posted 08 March 2016 - 06:06 AM

What you really need is 3 carbs the same, all "Rover" type or "Jag" then convert them to .125" needles. When you say that the pistons only lift 7/8, you"ll have machine some off the bell to allow full travel. The guide that the piston shaft slides in is too long, so needs to be reduced in length, then the shaft on the piston will come above the bell at full lift so it will need to be shortened as well. I hope these carbs weren't on a running engine, were they?

The jet in the "Jag" carb should be .125" & some dragsters use a .100" needle to allow the needle to lift clear of the jet when running alky.


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