Carb Identification Help

[ylopez]

Being beaten by Toyotas all the time.

yep... i can imagine that... maybe i have to work more in the rear bull bar
now, i´ve been looking and it results to be an Hitachi 306 carb what i got there..
http://datsun1200.com/modules/mediawiki ... ifications
i´m gonna get the rebuild kit for this carb and then i´m gonna make a decision

[Johnny Roadkill]

Hi ylopez,

I think you'll have 2 problems with a carb that small fitted to the P motor. Firstly, lack of top end power - the carb just won't flow enough air to get the P motor interested at higher rpm. Secondly, because the P motor is over 3 times as big as the A12 the carb's idle circuit will never get used - even at a nice slow idle it's likely the carb will already be operating on its primary circuit. This would explain the angry hissing noises, and it may also mean you won't pick up any of the fuel economy benefits you might expect from a smaller carb.

But these are just my thoughts - if you persist with it please let us know how it goes !

cheers,
D

[ylopez]

That is right, the previous owner is who make that conversión, i'm pretty sure it's the wrong way, it sounds like when you are sucking an empty glass whith ice in it
I'm looking for a japan truco carb because it's more easy for me to get one

[ylopez]

Truck not truco

[bosque]

As you may know, if you see a chevy or gm with a 6 cyl engine it may have a GM Rochester Carb and these work pretty good and easy to rebuild yourself.
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There seems to be a problem with loading a pic, sorry.

[ylopez]

so, for the P engine, how many CFM´s are we talking about?

[Esteban]

so, for the P engine, how many CFM´s are we talking about?

Check this post with some notes by Johnny Roadkill about the CFM for the P engine. Very interesting reading, and according to him, between 250-350 CFM.

http://www.60patrol.com/forum/viewtopic ... &hilit=cfm

[moore_rb]

A very simplified CFM equation (that does not take air density or temperature into account) :

((RPM x Cubic inch Engine Displacement) / 3456) * VE (volumetric efficiency*) = CFM (air flow) that the engine will pull at that particular RPM

So, for the Patrol: 4.0 liter = 244 cubic inches, and so the formula becomes:

(4000 max RPM x 244 cubic inches) / 3456 = 282 MAXIMUM CFM that the Patrol engine could pull when it is running at 4000 RPM

* Now, more about that VE adjustment - the result above demonstrates what the Patrol engine could achieve if the VE = 100%. But, no internal combustion engine can generate 100% VE - high RPM Formula One race cars can actaully EXCEED 100%, but since the Nissan P engine is a low compression, low RPM "undersquare" engine (meaning the stroke is much larger than the bore), my guess is that itprobably generates about 75% VE at best.

so, we take the max theoretical CFM calculated above (282) x .75 VE = 212 CFM as a real world example of what the Patrol engine can pull when it is screaming at its 4000 RPM redline


So, a carb that flows at least 212CFM is mandatory- anything smaller would hurt performance.

Going with a carb that is bigger than 200CFM would not hurt, but it also won't help - if you put a 700CFM carb on an engine that can only pull 250 CFM, then the carb is only a 250CFM carb by default

[moore_rb]

Being beaten by Toyotas all the time...

[miksum56]

A very simplified CFM equation (that does not take air density or temperature into account) :

((RPM x Cubic inch Engine Displacement) / 3456) * VE (volumetric efficiency*) = CFM (air flow) that the engine will pull at that particular RPM

So, for the Patrol: 4.0 liter = 244 cubic inches, and so the formula becomes:

(4000 max RPM x 244 cubic inches) / 3456 = 282 MAXIMUM CFM that the Patrol engine could pull when it is running at 4000 RPM

* Now, more about that VE adjustment - the result above demonstrates what the Patrol engine could achieve if the VE = 100%. But, no internal combustion engine can generate 100% VE - high RPM Formula One race cars can actually EXCEED 100%, but since the Nissan P engine is a low compression, low RPM "undersquare" engine (meaning the stroke is much larger than the bore), my guess is that itprobably generates about 75% VE at best.

so, we take the max theoretical CFM calculated above (282) x .75 VE = 212 CFM as a real world example of what the Patrol engine can pull when it is screaming at its 4000 RPM redline


So, a carb that flows at least 212CFM is mandatory- anything smaller would hurt performance.

Going with a carb that is bigger than 200CFM would not hurt, but it also won't help - if you put a 700CFM carb on an engine that can only pull 250 CFM, then the carb is only a 250CFM carb by default

Wow, all the brain matter on this site amazes me!