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carb sizing and ram tubes with filters


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#1 Mickl

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Posted 24 September 2012 - 05:20 PM

Hello
I am a learner on this topic so I am seeking some help to get me going with my carbys....I have a `77 2+2 with two round top SU type carbs equipped with circular paper air filters about 150 mm diameter. I have been told that removing the filter housings and replacing them with ram tubes equipped with foam air filters should result in a noticeable improvement in performance.
My questions are:
is the above info correct?
If so, how do I size the existing carbs so that I can buy the correct size ram tubes? And where best to buy them?
Is this conversion simple to do for a mug like me, and is it worth doing?
Thanks in advance
Mickl

#2 Gareth. J.

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Posted 24 September 2012 - 08:07 PM

What about the factory airbox? It has 50mm ram tubes built into it, fit a K&N or uni filter(they make them to fit the stock airbox). Then run some ducting to one of the holes in the radiator support panel, cold air intake too.....

#3 luvemfast

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Posted 24 September 2012 - 08:12 PM

Pretty much what Gareth said.
But, you need to account for other mods to your engine. If that's stock. I wouldn't get carried away.

#4 Roberto

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Posted 24 September 2012 - 08:19 PM

The only difference you will notice taking the air box off is more induction noise. No power difference.

#5 d3c0y

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Posted 24 September 2012 - 08:49 PM

Those round paper filters are crap especially if they are old. Just put a stock 240Z airbox on it and if you dont have 240Z hitachis you should put them back on too. Definitely a noticable difference over stock 260Z carbs.

#6 260Coupe

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Posted 26 September 2012 - 08:27 AM

The only difference you will notice taking the air box off is more induction noise. No power difference.


Standard 240z airbox made around 10% more mid range power and torque over ram tubes alone...........Lou Mondello and I tested this on the engine and chassis dyno a few years ago on both a race L24 and a stock L26...........results were conclusive........So yes put the air box back on

The factory did not spend millions of yen developing airboxes for people to remove them thinking they would make more power !............more noise yes.....more power definitely not.

Al.

#7 Mickl

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Posted 27 September 2012 - 06:12 PM

Thanks for the responses gents. Seems a no brainer now and I will go and search the shed for the old blue air filter box and put it back on. I presume it will fit on the round top su carbs.
Cheers
Mickl

#8 oldmates260z

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Posted 23 September 2015 - 09:34 PM

Just wondering if this advise is still valid or if anyone has done anymore testing? I know there has been work on tubes fitted to the Solex's on the Sports with good success but from this it appears that the Hitachi SU's on the Zeds that the tubes make little difference?

 

Before I read this I fitted a couple of short tubes on mine on the weekend and it felt like it went better. Must be mind over matter ???


Edited by oldmates260z, 24 September 2015 - 06:34 AM.


#9 dat2kman

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Posted 23 September 2015 - 11:37 PM

Stck Z arbx base plate with its pressed metal sort of ram tubes are good.
Better are tapered lnger machined tubes with at least a hapf roll out at the mouth, ie like a half a donut.
Testing by the guys that have to se them has clearly shown they make a difference.
Do not then slde a foam sock over t, as that stuffs up the airflow.
Fit a tallsh K&N type filter.
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#10 oldmates260z

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Posted 24 September 2015 - 08:54 AM

Stck Z arbx base plate with its pressed metal sort of ram tubes are good.
Better are tapered lnger machined tubes with at least a hapf roll out at the mouth, ie like a half a donut.
Testing by the guys that have to se them has clearly shown they make a difference.
Do not then slde a foam sock over t, as that stuffs up the airflow.
Fit a tallsh K&N type filter.

 

Thanks Jason

Do you need a special plenum box to fit the K&N? Do you who makes the machined tubes?



#11 d3c0y

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Posted 24 September 2015 - 09:05 AM

For the work done to your motor, I honestly wouldn't bother with the extra expense. If you want more HP fit triples or injection.



#12 dat2kman

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Posted 24 September 2015 - 01:37 PM

Thanks Jason
Do you need a special plenum box to fit the K&N? Do you who makes the machined tubes?

The K&N filter assembly includes the base mount plate, the filter, and a top cover plate.
You'll need two f these, one for each Hitachi/SU
The base plate may need a bit of filing r drilling to fit the Hitachi, but they do supply them for British SU's
Get them as tall as possible, ( measure clearance, the filter assy will either be round, or oval.
Fit say a 50 mm long trumpet so that the filter base plate s held on by the bolts holding the trumpet.

Only drama, you are sucking hot air, whereas the stock airbox, with ts smaller standard metal trumpets, can have a larger diam metal snout welded on, and a bit f 3" flex to suck in air from front f radiator.
Maybe fit a pid filter out there, and no need to worry about a genuine oval paper filter.

Lots f options!
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#13 oldmates260z

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Posted 24 September 2015 - 07:58 PM

For the work done to your motor, I honestly wouldn't bother with the extra expense. If you want more HP fit triples or injection.

 

Thanks for advice you are no doubt correct. Previous owner fitted triples and said it did not go any harder and just used more fuel....I assume he just had the wrong set or setup...keep tossing up the idea for triples but I have enough trouble with the twins on my Sports.



#14 Andrew_L26

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Posted 25 September 2015 - 12:05 PM

http://community.rat...a-ratsun-price/

Not sure how I feel about this but I guess it would work?



#15 d3c0y

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Posted 25 September 2015 - 02:08 PM

Those filters are less efficient than a factory airbox.

 

 

Thanks for advice you are no doubt correct. Previous owner fitted triples and said it did not go any harder and just used more fuel....I assume he just had the wrong set or setup...keep tossing up the idea for triples but I have enough trouble with the twins on my Sports.

Drop your Sports down to CnJ too. They will sort it out too, triples don't have to be that bad to live with. 

 

If the zed didn't pick up any HP with triples then there is something wrong. One of the San Maru Garage cars is making 180RWHP with a 74 degree cam and the same engine setup yours is with 44OERs.

https://www.youtube....h?v=kv4lRveuaMU






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