Small changes..

[Boumsong]

[Funky Diver]

Those carbs are beautiful... nearly as beautiful as the set I have for mine

did you bother with the whole wavetuning black magic on the inlet maifold or just blag it together?

[Boumsong]

I made a plate which blots to the head with 4 40mm long straight tubes welded to it, then plugged some silicone onto them, then onto the carbs. Easy, better than a chopped down 16v mani anyway.

[Funky Diver]

How's she running like that? I'm gonna need to be a bit more creative as I need to use a slightly shaped manifold due to the exhaust. Bogg Brothers said "we WON'T do it..." I said I'll get it done..

How are you handling Vac / etc?

[Boumsong]

It's a bit lumpy at low revs, wakes up around 3000rpm and pulls like a slag in Manc then again at 5000rpm theres a massive step in power and it torque steers and spins the wheels and sods off into the distance.


I've just left the breather and vac pipes kicking around. Theres a good seal onto the manifold and carbs so I've had no issues there either.

[Funky Diver]

did you rejet the carbs or just slap 'em on as is?

And did you uprate your cam shaft or is the lumpiness all down to the carbs... questions I know, but hey ho, I'm beavering away arm chair mechanicing atm. Currently designing the inlet manifold using a gasket as a template

[Boumsong]

Drilled the main jets out to 1.7mm and left it at that.

I used a gasket for my manifold plate as well! Dead easy! The lumpyness is due to how short the inlet manifold is. Supershort inlet has a similar effect to lumpy cams, i'e more air in per revolution due to the shortness of the intake length. And at high revs it smooths out and goes like stink. If you have a longer inlet it'll be smoother lower down the revs, I wanted all out top end power though so thats what I've gone for. 5000rpm in 1st, 2nd, 3rd and 4th it'll spin the wheels. Doesn't really wake up until 3500rpm either. Its awesome.

[walkinginperu]

Dare I ask how much fuel its drinking in that state?

[Boumsong]

In it's current state at this level of tune we're looking at 8 - 12mpg. With a good tune up and a rolling road session to get it sorted it'll be more like 18 - 20mpg ish. At that though, we're looking at an easy 165bhp so I ain't complaining!

[walkinginperu]

Worth it for the BWWWWOOOOOAAAAARRRRRR sound you'll make everywhere you go!

[richieA]

how have you got the dizzycap in? im confused! i got mine on but the king lead was no-were near EVER EVER fitting...!

[Chaps]

[quote="Boumsong"]If you have a longer inlet it'll be smoother lower down [quote]

Increasing the inlet tract length also moves the power band down the RPM scale.
When I was designing my inlet for R1 carbs I was looking to to make the inlet tract about 13" which would give max power at around 5000rpm. Inlet tract is from valve seat to the tip of your intake.

Boomsong - did you chamfer the edges of your inlet to where it joins the silicon tubing? or is there still quite a step? Looks good whatever.

[Funky Diver]

Just on a completely related note to the fast becoming "how to fit bike carbs" thread of the century.. I came across this on my moochings.

Bike Carbs in Cars - Total Vauxhall Guide but still relevant

The other thing I'm thinking also is the trumpets... are they necessary on this conversion, ie I'm guessing they just channel the air a bit more effectively. But will performance suffer greatly if they're not on/ Ponderings...

It does praise Bogg Brothers highly, but if you're doing this conversion on a cross flow head, they won't do it. I DO know however that it can be done as I've seen it on a Mk2 Goof (will try and find the link!!)

[Chaps]

Its a great article that is. i fully rebuilt my carbs using that guide! Bogg Bro's at the time of writing that artice were one of the only companies making manifolds for bike carbs.

And yes, trumpets aid the smoothing of airflow into the carbs. plus most trumpets are tapered which helps get more air in too. Another benifit of trumpets is that you can alter the overall inlet tract length using them, which can significantly change where peak power is and the gains or losses at a given RPMs.

If you want to know more google 'pulse wave tuning' I think its a very interesting subject....

[Funky Diver]

Aye, I did a little light reading on PWT. If you can call it that, lol.

It's all a bit OTT for my little roadcar project, in terms of getting exact pulse wave length, besides, as soon as I drive to Jabasco's house I'm jiggered anyways as the altitude will be all wrong

One element I couldn't quite fathom out was the length of the trumpet and at which point it ceases to be a trumpet and becomes "air", lol.

I'm using a cross flow engine, so my carbs are going to be on the back of my engine. I'm guessing circa 26" of tubing would be optimal as my power band is lower (fast road cam - Newman 268). Now 26" of trumpet would put my air intake somewhere next to my Stereo, which isn't desireable really. THEN I got to thinking of getting 4 26" tubes... and bending them so that htey enter by the side of the engine, with a hollow "space", air box for example with filter in it, or an induction kit with a cone style, possibly sealed, filter arrangement.

Good plan or complete gibberish?