anyone put motorbike carbs on a car engine?

[pandaah]

hey guys, just thort id ask the question see if anyone has actually done it... i wanna go for a racer rev'vvy sorta engine, which is actually a honda d15b4 engine which is factory twin carb'd..

now i was plannin instead of porting out the head and replacing valves and spending massive money... just getting a set of quad carbies, port matching the runners i have to make, the obvious rejetting and away i go.. only problem ill really have is setting up the idle control system when load is applied on the engine.... so sorta my theory would be port and intake velocity = high ends revs, instead of boring and porting for maximum torque with no high end puff......

its gunna be an experiment anyways just thort id ask here and see if anyone had done it

[petergoudie]

The Honda S600 & S800 had four motor cycle type carbs in its 2-seat sports cars. Many racing cars of the 1950s used a motor cycle carb for each cylinder.

[pandaah]

thats one in the pro's list =)

[thechuckster]

ITBs or get the EFI hardware off a later model engine?

[pandaah]

nah.. its not the point i wanna make a hell revvy engine thats basically a high cc motorbike engine.. otherwise id spend the money and buy a vtec motor

also CBR1000 carbies are only worth like $200 so if the project fails oh well

[AdrianS]

There is an interesting issue with motorbike carbs on a (race) car, and vice versa : motorbikes have almost no sideways G-forces.
Since the bike leans into corners, the carb experiences only a greater vertical load. Some race car applications using bike carbs have had issues with floats sticking and other problems under high cornering loads.
The same is true in reverse : bike carbies are designed for significant vertical loads in high-G cornering, while cars don't have that issue. If my memory is correct, that was one of the problems Ducati had when they went for a car-style Weber carb on the Paso back in the 80's.

Still worth a try if you're keen, and I doubt you'll be seeing the sort of continuous high sideways G forces a circuit racer on slicks can generate.

[pandaah]

yeh thats it, it wont be a race car... i was also looking into the supercharged carby setups on jetskis too might be worth a look but ill see how parts fair up price wise..

[Billzilla]

Yep, on my racing car.
Three main things you have to -
- Run near-zero fuel pressure. I run a conventional small fuel pump and on top of each carby there's a t-piece, then on the last t-piece the return line goes back to the fuel tank but it's longer than the line to the carbies so it makes a touch of backpressure that way, and that's all the pressure I run.
- They have to sit upright, they don't like sitting at an angle or they will run out of fuel around a left or right corner. In the photo below you can see the rubber pipe I used to get them to sit vertically. Note that some bike carbies are built to run at an angle, but again they should still be run at that same angle.
- Mine at Mikuni flat-slides and to work properly with a car engine we had to get power jets added to keep the mixtures right over a wide rev range. It's an easily available kit and not too hard to fit.

[AdrianS]

<off-topic>
Bill - I couldn't help noticing that your adjustable cam gears are not anodised in bright blue/pink. I was under the impression that the lurid colour was required for them to work properly ?
At least the inlet plumbing is a bright enough colour.
</off-topic>
I assume the engine is longitudinal mounted in a clubman or similar ?
Nice point about fuel pressure - I'd forgotten that bike carbs are gravity fed. Also most bike setups have the carbies rubber-mounted like yours - I assume for vibration isolation.

[roadsailing]

OP you know it wont suddenly just make more power by just putting motorbike carbys on right?

[Shifty]

i don't think you understand

putting carbies on does not make your motor rev higher 'like a motorbike engine'

your theory is all wrong

[Shifty]

OP you know it wont suddenly just make more power by just putting motorbike carbys on right?

+1

i agree

not sure if old mate knows what he is doing / talking about

[oldcorollas]

so sorta my theory would be port and intake velocity = high ends revs, instead of boring and porting for maximum torque with no high end puff......

err..
high port velocity = good cylinder filling = good torque, but how big port is depends on your desired rpm.

big porting = torque at high rpm.
small porting = torque at low rpm

but you always want high port velocity at the rpm range you want torque/power

[pandaah]

lol theres always someone that wants to have there say hey.. i know its not gunna rev higher or make power its just something i wanna do...

i want high speed port velocity so i dont waste my money on expensive head porting and bigger valves etc... this is a project not a 100 million dollar developed race car..

thanks for that billzilla that was exactly the information i needed and the pictures were perfect, thats EXACTLY what i wanna do... how does it go? rev? and torque wise?.. compared to if you would of say bolted two big webbers on there?

[pandaah]

oh and btw.. what size motorbike did you pull the mikuni's off?