bike carbs on 2.0l 8v ?

i am building a track day/sprint/hillclimb mk1 on a budget and have been told that a cheap way to get more power is to got to carbs or more specific motorbike carbs. has anybody had any experience (good or bad) of this conversion?

 

you want to be speaking to these
http://www.boggbros.co.uk/about.html
heres a couple of posts of the mk1 owners site to get you going
http://www.vwgolfmk1.org.uk/modules.php?name=Forums&file=vie wtopic&t=7859

http://www.vwgolfmk1.org.uk/modules.php?name=Forums&file=vie wtopic&t=6911

 

looks good thanks but no real insight into weather there is more power? and if so how much

 

Good choice.... if i can help just ask or pm me, oh and this may help depending how far you've got.


http://jasonmoyleracing.bravehost.com/

 

190 bhp from an 8v 1800 my target is 200bhp per ton i'm reconing on 150bhp from a 2l 8v some head work cam and bike carbs hopefully this is a conservative estimate saw your feature (forget which mag) your car just like mine only heavier
Edited by: racer

 

193 Actually !


200 bhp per ton will be a piece of cake (mine currently at 260 bhp per ton) and depending on the head and cam (and the size of the bike carbs/chokes) 170+ hp should be your starting point.


what does your's weigh ?

 

I say go for it as it is a cheap route to take

I'v also read the article in PPC and realised just how good design bike carbs are!

I just got some for my g'frnds mk1 1.1 of e-bay for 21

They are CBR600 carbs, am really impressed with the quality

Probably gona get bogg bros to make me a manifold and advise if they need rejetting

Doing this for a bit of laugh and also to ditch the crapy standard carb

If it works out ok i might just go same route for my mk1 with 2.0l valver instead of itb-s, purely for simplicity
Edited by: sambo

 

dont know what weight yet but still lots to come off (fiberglass boot and bonnet, lose dash,spare wheel well,lightweight wiring loom!!!! managed to lose 14lbs from each doorand probably either glassfibre or no bumpers)

 

Sounds like yr going to run in a mod-prod type class instead of road going. you should be able to get down to around 700kg's or less.


Fibreglass tailgates arnt really worth the money (about 100 quid) as the difference over a steel one is onlya couple of kilo's after you strip out the lock and wiper, the weight is in the glass. The bonnet will save you 8kg's


The bike carbs could work quite well but make sure you get the induction length right.

 

Unless you're doing very heavy engine tuning and running high rpm's, bike carbs would be a bad idea.

When you consider they are designed for engine's that deliver peak power at about 16000+ rpm, they aren't too well suited to an engine redlining at 6 - 7k even when re-jetted.
On a 16v they might work ok, but an 8v bike carbs would be terrible.

I had quite a bit of experience running twin weber carbs on an 8v mk2 and unless you're doing major head work it's a waste of time. I knew someone who did get close to 200bhp at the flywheel from a 2.0l 8v on twin 45DCOE's and he ended up going down in choke size to 32mm as this provided better power for the 8v, so he didn't even need 45's 40's would have been ok. I used to run twin 40 DCOE's on an 8v and used 32mm chokes aswell, except my engine wasn't in a high state of tune so all that happened was i lost mid range torque and power and gained a fraction top end.

 

I THINK most bike carbs (maybe all ?) use a sliding piston like an SU carb, so the piston(in the carb)will only rise in proportion to how much air the engine needs to draw in, regardless of rpm. I would however imagine fine tuning maybe a bit tricky (getting a needle profile close to correct throughout the rpm range) and at a guess, a stiffer spring (if they use such a thing) to slow down the rise of the piston over the lower rpm that the car engine is going use. Or maybe the requirementsoffset each other to a degree... bigger cc and slower reving car engine instead of smaller cc high rpm bike power ?


DCOE's dont tend to make much more power on 8v'ers in a low state of tune but most i used to see on the rollers were just bolted onto a manifold and hoped for the best (by the owners that is). The manifolds as they come (at least for the 8v) are... cak ! They have puny ports and need a fair bit of work with a die grinder to open them up and shape them towards the head, only then will they have a half decent chance of starting to work.


DCOE's also dont need to lose youmid range power if set up properly, my 1800 8v'er has more power at 4000 rpm than a standard 8v GTi, and thats using 48's with 39mm chokes, a hotrod spec head and a race (318 degree) cam.


Almost 200hp from a 2ltr 8v... yea no problem, on 32mm chokes..

 

Yeah i always thought it was strange to be on such a low choke size but apparently that's what was in there. I never saw them out of the carbs with my own eyes though.

 

As you save the carbs meter fuel via the airflow, more air lifts the diaphram/slider which lifts the needle increasing fuel flow.

A 600 cc bike (rev to 16k) at 12000 rpm would roughly digest as much air as a 1200cc car at 6k rpm.

Idle mixture contol may be a little tricky, new pilot jets should sort that out.

Car carbs are hideously designed when compaired to bike carbs.

 

i thought that too, a 1000cc bike engine at 16ooorpm has to be using the same amount of air as a 2000cc car at 8ooorpm. and then its just a matter of getting the fueling right with jetting. correct me if wrong but is a 40mm choke on a bike the same as a 40mm choke on a weber.


the obvious question is how far can you tune a standard k-jet injection? i know you dont need to, it just increases the fueling with an increase of air flow but surly there is a limit. if this is the case will i be able to get more power with carbs?if so then bike carbs it is

 

Anythings possible really, carbs can be cheaper to be tuned up whereas an injection system might require custom ECU and bigger injectors, but then below 200bhp it probably wouldn't be too complex.

The main thing is, twin carbs/bike carbs sound awesome!!

 

Before fuel injection became the norm bikes aimed at racing often came with
flat slide carbs barely thicker than a fag packet and totally uncompromising.
Some of the homologation specials would have set of CV carbs fitted and a
set of flatslides, air filters and exhaust system in a box that came with it.
Not really convinced that you'd get any much more out of bike carbs than
DCOEs or DHLAs and bike CV carbs are on the whole less tunable as they
don't have a big range of jets, slides and needles. Add that to the fiddle of
fabricating a manifold and sorting out fuel delivery and the controls and well
you could get that far and still never get it to run right. DCOE stuff is off the
shelf, easy to tune and well understood by tuners. It's a no brainer.
Barkstar

 

One of the biggest problems with using bike carbs is the way the throttle quadrants are geared. Bikes due to their low weight can handle very quick initial throttle openings compared with a car. This isn't a massive problem if you don't mind making your own throttle quadrant but is something to bear in mind.

 

i think it is a no brainer for me. if nothing else to be different. i have got to strip tank and fuel lines out anyway and have you seen the price of bike carbsless than 50, how much are DCOEs? and i can sell my working k-jet! maybe these new red glasses i bought have something to do with it but i think pros for me outweigh the cons (watch this space)

 

It`s worth a crack! CBR6 main jet will be in the 160# region, plenty of oversizes to choose from (we have boxes at work). Can`t see it being that difficult to tune, worste part of tuning bikes is removing the things (fairing, tank, airbox out and the rest..).

 

IF... a bike carb has a bore size of 40mm from entry throughout the body of the carb it'll be a touch too big on full throttle unless your producing around the 200hp mark, but as its a rising piston type design you may get away with it. Also bear in mind that to have a manifold made is going to be in the region of 150-200 quid, plus jetting, plus trumpets. DCOE's do (as someone else also pointed out) have a huge range of adjustment and a manifold is available off the shelf for around 90 quid (though it WILL need internal work), second-hand Webers will come with something more of a starting point and usually some trumpets, are more of a known quantity, butthey need to be bought with caution !


Good luck if you do go down the bike carb route, will be interesting to see the results (tuning would have stood still if no-one tried something different).


From experience, K-Jet works well with cams of up to around 70 degree's of overlap, (around 150-155hp)after which, low-end driveabillity and idle deteriorates, 300+ degree cams give strong mid-top end power but SH*%E idle !... until you go for a seperate choke or throttle body per cylinder, then it all changes !


The basic answer is, more power with carb's ?.... OHHH YES !


BUT.... Whatever you go with, DCOE'S or bike carbs, (and i'm not teaching granny...) dont just hope to bolt them on and get an instant 20-30hp, it does'nt work like that.