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48 DCO SP or 45 DCOE 152?

April 14 2013 at 11:03 AM
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Mike  (Login Union76)
from IP address 121.219.58.173

 
G'day all.

I am running a STD FJ20E - not looking to modify internals at the moment.

I'm wanting to convert to carbs (not ITB), I am about to buy some Webers.

Anyone recommend or comment on 48's over 45's?

45's possibly suit the FJ20 the best "out of the box" choke/jet wise.

48's choked down to 38mm may offer more torque when compared?

I thank you for your comments and knowledge.

Mike.


 
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Anonymous
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121.222.156.207

Re: 48 DCO SP or 45 DCOE 152?

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April 15 2013, 9:45 PM 

48's you can choke and jet them down but you can't make 45's bigger

 
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Anonymous
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75.68.122.204

Re: 48 DCO SP or 45 DCOE 152?

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April 16 2013, 4:55 AM 

Technically you can by customizing the chokes, but choking down the 48's would be easier... 48's are more expensive and harder to find though.

 
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Mike
(Login Union76)
124.180.204.216

Re: 48 DCO SP or 45 DCOE 152?

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April 16 2013, 10:13 AM 

Comparison: http://www.youtube.com/watch?v=Hx3M5CgDtC8

So, benefits of 48's are or can be an increase in torque/mid range power due to greater air speed.

Slight increase or vast? Pending on application at a guess.

So, I deduce it's worth going the 48's if I want to work the motor at a later stage. These will be more flexible for tuning than the 45's due to them being towards their outer limit already on the STD FJ20.

Interesting ****.

Feel free to disagree.

BTW: The price - from I have worked to have these Carbs to my door in Australia, jetted correctly (by myself):

45s - $1081 USD
48s - $1353 USD

Mike.


 
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Anonymous
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78.110.75.247

Re: 48 DCO SP or 45 DCOE 152?

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April 29 2013, 11:03 AM 

Good idea to use carbs,but waste of money without upgrade to serious cams and decent 4into 2 into 1 extractor manifold.The std cams are a huge restriction and work only with the fuel injection system.
Not to mention the low compression (9.2). Need Euro pistons at 9.6 or some aftermarket,domed one
to bring it to 10.5 to one at least,to reduce the low end drivability.

With the 48 DCPS without cams will need 34 mm chokes max ,a full box of air,fuel jets ,emulsion tubes to experiment
until you find the right combination to work and 50 mm airhorns.
Also you will need to retime your distributor from 24 degrees to 28-30 degrees advance.

Another issue is the gearbox,which is tuned on the FJ20E power/torque delivery curve.
Going with carbs .the low end torque will greatly suffer,and without a lower 2nd gear,or a higher
first the term acceleration will have a new meaning,during gear ghange.

Without the above the std FJ20E engine will not actually gain any power,will loose greatly on drivabilty.

I struggle for one year after buying a NISMO carb set up and spend a lot of time and money on jets
before finally going the correct route

The above are some things to think about,and i hate to see a fellow FJ20 enthusiast go through
the big hassle,like i did in the past.



 
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Anonymous
(Login Union76)
58.170.231.104

Re: 48 DCO SP or 45 DCOE 152?

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April 30 2013, 10:33 PM 

G'day there,

This is the kind of knowledge I was after - Thank You indeed for sharing.

For the 48's the smallest chokes are 36mm and yes I have a box full of Jets/Em.Tubes/etc ready to go. I may sway back to 45's yet!

At this stage I'm not out for maximum performance - smooth "ish" running will suffice to start with.

But what you are saying is relevant - I may have to toy with the idea of modifying a motor on the side sooner than I thought.

I take note of what you are saying Compression and Cam wise.

Gearbox ratio is something I would never have thought of. If it's too bad I may have to investigate changing diff. ratios.

Thanks again for your time and giving me a better idea of what I am about to start,

Mike.

 
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savvas
(no login)
78.110.69.251

Re: 48 DCO SP or 45 DCOE 152?

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May 4 2013, 5:43 AM 

Glad to help.

You may find that 36 mm chokes on 48s are still too large
and these carbs come with 5.5 mm auxiliary venturies for large airflows
which also damp the low speed signal of the main jet emulsion,which is not activated
during the transition period .This will have a huge hole around the 2,500 to 3,500
RPM.

You will have better drivabilty with 34 mm on 45s.and 4.5 auxiliary as a base set up/

While you are at it .something i forgot is that ,you may need a lighter
flywheel to counter the poor low speed pick up,through the gears.

The gearbox gaps from 3.3 first gear to 1.9 of the second and 1.4 of the 3rd gear
are way too big for a std n/a on carbs.

 
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Mike.
(Login Union76)
121.220.74.98

Re: 48 DCO SP or 45 DCOE 152?

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May 30 2016, 11:49 AM 

Well, after a few years, I have finally got some carbs onto my NA FJ.

And, just to say, everything that Savvas has mentioned up there is completely on the money. Credit to you Sir.

At the moment I have out of the box 45 OER's with a SK manifold on a Stock FJ20. Currently it shows all of the symptoms that has been mentioned by Savvas.

I have a few more things to throw at it, cams, better jetting, flywheel etc, but realistically I really need to build an engine to gain some performance.

So, at the end of the day - it was nice to warned to avoid disappointment!

Thanks, Mike.

 
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savvas
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178.132.44.124

Re: 48 DCO SP or 45 DCOE 152?

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June 5 2016, 7:07 PM 

thanks Mike

if you need any add info about the FJ ENGINES LET ME KNOW

 
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