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Why do bike carbs work on a car?
Slimy38 - 7/9/12 at 05:33 PM

From a complete n00b point of view, why do bike carbs work fine on a car engine? I know I'm oversimplifying it, but if a bike carb is meant to supply a 1 litre bike engine, how can it work on a 2 litre car engine? Why does it not simply 'run out of puff' at half revs?

The reason I ask is that it will answer my second question, in that why use 1 litre bike carbs and not 600cc or 750cc bike carbs?


[Edited on 7/9/12 by Slimy38]

tul214 - 7/9/12 at 05:40 PM

Car engine is double the displacement BUT half the revs.

I and many others have used CBR600 carbs no bother.

JAG - 7/9/12 at 05:47 PM

Yeah, think of it as an airflow device.

A 1 litre bike engine spinning at 12000rpm flows the same amount of air as a 2 litre car engine at 6000rpm.

iank - 7/9/12 at 06:21 PM

Also consider the power, 1 litre bike engine produces a similar power to a 2 litre car engine (both in standard tune).

snapper - 7/9/12 at 07:17 PM

Bike carbs are similar to SU or Strombergs also 1 carb per cylinder and most are 36mm+
Standard Pinto ran 32/36 twin choke.
Pinto on 40's usually ran 33mm chokes 45's ran 36 to 38mm

unijacko67 - 7/9/12 at 07:21 PM

I belive zzr1400 carbs are meant to work (with setting up) on my 8500rpm 2ltr so than now makes sense, this was a question I was gonna ask.

Slimy38 - 7/9/12 at 07:23 PM

quote:
Originally posted by iank
Also consider the power, 1 litre bike engine produces a similar power to a 2 litre car engine (both in standard tune).


That's why I was wondering about 600cc carbs. So I agree with the power match (150bhp is reasonable for both a 1 litre bike and 2 litre car), but an average carb'ed 600 delivers around 100 bhp. Does that mean a 600 carb on a car engine would also result in about 100 bhp?

quote:
Originally posted by JAG
Yeah, think of it as an airflow device.

A 1 litre bike engine spinning at 12000rpm flows the same amount of air as a 2 litre car engine at 6000rpm.


And I guess similar with the airflow. If a 1 litre bike engine spinning at 12k results in a 2 litre car that can get to 6k, would starting with 600cc getting to 12k mean that a 2 litre car can only get to 3600rpm?

motorcycle_mayhem - 7/9/12 at 07:34 PM

Choke sizes are 40mm or so (rather like the DCOE's/DHLA) or Jenvey TB's.

It's why people stop at the bike TB's that I don't understand, there's a beautiful bike engine attached to them too...!

iank - 7/9/12 at 07:44 PM

quote:
Originally posted by Slimy38
quote:
Originally posted by iank
Also consider the power, 1 litre bike engine produces a similar power to a 2 litre car engine (both in standard tune).


That's why I was wondering about 600cc carbs. So I agree with the power match (150bhp is reasonable for both a 1 litre bike and 2 litre car), but an average carb'ed 600 delivers around 100 bhp. Does that mean a 600 carb on a car engine would also result in about 100 bhp?

quote:
Originally posted by JAG
Yeah, think of it as an airflow device.

A 1 litre bike engine spinning at 12000rpm flows the same amount of air as a 2 litre car engine at 6000rpm.


And I guess similar with the airflow. If a 1 litre bike engine spinning at 12k results in a 2 litre car that can get to 6k, would starting with 600cc getting to 12k mean that a 2 litre car can only get to 3600rpm?


Sportsbikes tend to have all their components well overspec'ed in my experience. 600cc carbs will approximate weber 40's, 1000cc carbs weber 45's or 48's

scootz - 7/9/12 at 08:13 PM

quote:
Originally posted by unijacko67
I belive zzr1400 carbs are meant to work (with setting up) on my 8500rpm 2ltr so than now makes sense, this was a question I was gonna ask.




Does the ZZR1400 not have injection?

unijacko67 - 7/9/12 at 08:25 PM

zzr1400, Throttle bodies sorry so yea has fuel rail and injectors, Well thats as I understand.

daniel mason - 7/9/12 at 08:26 PM

it does but i think he was refering to the throttle boddies,not carbs. if the zzr 1400 boddies can be re spaced id say it should be a good idea!

MikeRJ - 7/9/12 at 08:30 PM

quote:
Originally posted by iank
Sportsbikes tend to have all their components well overspec'ed in my experience. 600cc carbs will approximate weber 40's, 1000cc carbs weber 45's or 48's


They are exactly right for the power the manufacturers target from these tiny engines. The Japanese very rarely get this kind of thing wrong.

ali f27 - 7/9/12 at 09:49 PM

Basically an su mixes fuel and air as an engine sucks air in it draws in more fuel mix you could easily put 4 su,s on instead something else the japanese took from uk and improved nothing to do with double rpm

snapper - 8/9/12 at 06:50 AM

It's probably more about port size than original power output
If the engine port can flow enought for a certain bhp and the carb port is the same size then it's only down to the jetting to get the right AFR

tul214 - 8/9/12 at 08:33 AM

quote:
Originally posted by Slimy38
Does that mean a 600 carb on a car engine would also result in about 100 bhp?


My 4a-ge engine (8000rpm) with 45 dellortos was set up at Boggs & Z-Cars and pushed 160bhp.

I swapped to CBR600 carbs and took it back to Boggs.....160bhp again @8000rpm but it drove much better

Slimy38 - 8/9/12 at 08:53 AM

quote:
Originally posted by snapper
It's probably more about port size than original power output
If the engine port can flow enought for a certain bhp and the carb port is the same size then it's only down to the jetting to get the right AFR


Aha, so it is related to the engine it's attached to as much as the carbs itself? That would make more sense.


quote:
Originally posted by tul214
My 4a-ge engine (8000rpm) with 45 dellortos was set up at Boggs & Z-Cars and pushed 160bhp.

I swapped to CBR600 carbs and took it back to Boggs.....160bhp again @8000rpm but it drove much better


That sounds like a good result! Out of interest, why did you go for 600's in the first place rather than the 'traditional' 1000's?

tul214 - 8/9/12 at 10:13 AM

quote:
Originally posted by Slimy38
Out of interest, why did you go for 600's in the first place rather than the 'traditional' 1000's?


Cheaper!

Slimy38 - 8/9/12 at 11:41 AM

quote:
Originally posted by tul214
quote:
Originally posted by Slimy38
Out of interest, why did you go for 600's in the first place rather than the 'traditional' 1000's?


Cheaper!


Just the sort of answer I like!

whitestu - 8/9/12 at 11:52 AM

quote:

quote:Originally posted by tul214

quote:Originally posted by Slimy38
Out of interest, why did you go for 600's in the first place rather than the 'traditional' 1000's?



Cheaper!


An going bigger isn't going to get more power unless the engine is very highly tuned. My ZX6 carbs are 38mm each, which is bigger than the inlet ports of my Zetec.

Smaller carbs [within reason] also tend to give better driveability.

Stu

nickm - 8/9/12 at 07:26 PM

Hi
I had bike carbs on a 2 l zetec and when trying to find somebody to tune them rang Chester Sportscars who do bike carb kits and they reckoned that the rolling road they used got the best results for 2l zetecs from zxr 600 carbs so i think as previously said its not biggest is best.

Nick M