I see that so many people are using bike carbs/throttle bodies on various engine sizes easily including 2.0L.

I just find it surprising that the throttle bodies are of a big enough diameter to get good power from said engine when considering they previously fed a cylinder at least half the capacity?!!

I notice the obvious that you now have four openings instead of one on a normal road car, even so the cylinders dont all draw air at the same time so this theory doesnt hold true.... Confused!

please tell me the pro's and cons of this route!

thanks yet again

Think of the flow rate, not engine capacity.

2.0L redline at 7000Rpm
1.0L redline at 14000Rpm

I think the cylinders turn air over so quickly that you can easily assume they draw air simultaneously. Otherwise a plenum MAP sensor wouldn't work. There is obviously some pulsing but it average out i think

No different to using twin webers, most big bike choke sizes are 36~40mm with TB's being bigger, 42~45mm.

Bike engines breath twice as fast as car engines so thats were your argument is canceled out

No need to worry, just look at the Jenvey website at the size they recommend and then look up the size of the bike throttle bodies.

I'm not sure exactly why but they're ample, I'm guessing its partly as the bike revs much higher meaning intake velocities are still high enough with large throttle bodies on a small(er) cc engine...

Most bike carbs from 600cc up are similar in size to Webbers. I think webber 40's have choke sizes around 36mm. My ZX6 carbs are 38mm.

Stu

From the jenvey site showing the equivalent hp/cylinder for the amount of air a particular throttle diameter flow


Up to 30 - 30mm
up to 33 - 32mm
up to 39 - 35mm
up to 46 - 38mm
up to 51 - 40mm
up to 56 - 42mm
Up to 65 - 45mm
up to 74 - 48mm
up to 80 - 50mm
up to 87 - 52mm
up to 93 - 54mm

[Edited on 6/10/09 by liam.mccaffrey]

My take on this is that its the amount of horsepower is directly linked to air/fuel burned.
If the bike engine makes 120 horses then the carbs can flow enough air to make 120 horses regardless of what theyre bolted to
Ray

thanks, those answers have pretty much cleared it up for me, so whats the easiest route for upping the power of my 2.0 pinto i intend to run a mild cam, 4 branch exhaust and some bike carbs or tb's but as i dont know what power i will achieve, and i dont want the inlet velocity to drop too much what diameter inlets should i be looking at? i noticed the tolerances on the previous table were quite close (BHP / venturi size)

is your pinto a std 2 ltr or have you had any head work done on it?

when you say mild cam, what are you thinking as the pinto has many cam options, kent fr32 fr33 fr34, piper 285, there's loads?

what sort of power do you want?

is your pinto head had an unleaded conversion on a carb'd head or is in an injection head?

no head work, and if so it would be whatever is achieveable relatively easily DIY, looking at a fast road cam power band 2300 - 7000, injection head. found some ZX6R carbs looking to use them now. hoping to end up with somewhere around 150-160 BHP? is that totally unrealistic?

our standard injection headed 2.0 pinto made 110bhp@ wheels @ 5800rpm on Bogg Bros Rollers earlier this year. Thats with dellorto 40's and the MK exhaust running the standard transit ignition bits. So roughly 130bhp.

Thats using 35mm chokes, go up a bit and add a decent cam and you'd be getting over 140 I should think.