i want bike carbs!

[jayjay]

hey guys, i had a bit of spare time so i drew this in paint. lol!



so... what do you reckon of the design. i dont know much about carbs but i do like their noise.

i found this which was produced by gti engineering.



the main reason for my design is to minimise the hot air above the exhaust. it also means i dont have to cut into the rain tray and breathe my leaky exhaust. :j

gimme some feedback. i'm sure there are heaps of you guys in much much more know re: carbies. is the idea too convoluted? my biggest quarm was clearance issue above the rocker cover but after seeing that gti engineering design i'm a bit more optimistic.

cheers guys

[jayjay]

alternatively, manifold tubes could run all the way to carbs, except, bike carbs are usually equally spaced and the 8v counterflow which i have, has the inlet ports of cylinders 2 and 3 really close to each other and 1 and 4 heaps further spaced apart

like this


this means that the runners will be slightly different length. does that make much difference?

[Mischa]

get rid of the plenum, you want the best airflow possible.

modify the carbs to suit the spacing of the intake and keep the equal length runners.

imo

[jayjay]

lol. thanks mischa.

hmmm... i'm also worried about whether the runners are too long.

apparently short = high rpm power, long = low down torque.

i'd obviously want something in between, but that's also where my plenum idea comes into it. ultimately, in a perfect world, the plenum would have zero negative pressure on the intake side and it would essentially be the same as single point fuel injection like in the SEAT 1.8s and golf mk3s.

[Valver.]

You're making this way too hard

Just get a crossflow 8v head and forget about the dilemma altogether I cannot understand why people fit ITBs or carbs right above the exhaust manifold when you can buy an ABA head for literally 50USD and maintain a sane intake temp

[Jarred]

I've got or had, a set of bike carbs lying around. PM if you're seriously interested.

[velly_16v_cab]

if you want to fit bike carbs.....here is how you do it

http://www.clubgti.com/forum/showthread.php?t=180712

[jayjay]

You're making this way too hard

Just get a crossflow 8v head and forget about the dilemma altogether I cannot understand why people fit ITBs or carbs right above the exhaust manifold when you can buy an ABA head for literally 50USD and maintain a sane intake temp

haha. i can imagine how much easier an aba is. but my head has had a whole bunch of work that a new aba (that i cant afford) wont have. the intake temperature wouldn't be that different to stock though, would it? the manifold would be in exactly the same place.

can you guys tell me the feasibility of this? i can discourage myself enough.

i wouldn't want to build it, have my engine backfire, and have a nice big box full of vapourised petrol under pressure...

[jayjay]

velly, that's a lot easier with a crossflow/valver.

i think it'd be stupid to just have throttles facing the fire walls. nor do i want to point them up and make a fully sick bonnet scoop.

edit: i dont think i'd have any hesitations/issues if i had a crossflow motor.

[Jarred]

just depends on room.

bike carbs are pretty versatile, interms of running them lying down or facing up etc.
heat sheild over the exhaust., custom manifold with approx 45 deg up turn, and custom cold air piping is what I'd do.

With a short enough manifold, there'd be plenty of room and they wouldn't be up against the fire wall unless you get really long ram tubes!

[Valver.]

haha. i can imagine how much easier an aba is. but my head has had a whole bunch of work that a new aba (that i cant afford) wont have. the intake temperature wouldn't be that different to stock though, would it? the manifold would be in exactly the same place.

can you guys tell me the feasibility of this? i can discourage myself enough.

i wouldn't want to build it, have my engine backfire, and have a nice big box full of vapourised petrol under pressure...

All this is in one of the VW performance handbooks, but not only did the ABA head flow better than a ported AGG one, the same car also made another 11hp at the wheels due to the better ram air effect at the front of the engine and the lack of heat resonating from the firewall.

Counterflow engines are a complete PITA to work on, which is just another good reason to change.

You'd have to have sunken a lot of money into your current head (as in a proper big valve conversion) to warrant keeping it

... Or just put on a 16v head, which will yield 13.5:1 compression - it'll be nice and torquey then... you'd wanna be pretty sure about your timing marks, though

[Preen59]

You probably should pay me for those pistons before you think about buying anything else, Jayjay!

[twin eng, twin turbs]

You need to have the intake runners shorter than your design without a plenum. If the runners are to long the fuel will form into larger droplets and will not burn in the combustion chamber as well as posible, which means less power. Jarred sumed up the design for a good setup i reckon if your keeping the original head and not going crossflow.

I made up a an adaptor years ago to mount a 45mm DCOE webber off the front of a MK1 GTI intake manifold. It was terrible down low due to the plenum and only went hard above 5000rpm. Experimenting with designs is good fun but when you look at all the carbs on bikes the manifolds are quite short without plenums for good reason.

[Golf Loon]

Jay you should at least run the engine in and drive it befor adding carbs etc.

If you want to change later, you could always sell your engine and bung an aba in.

Or get another car.

[Valver.]