single downdraught carb mainfold for 18rg????

[Screamn_Sleeka]

It will be FINE with a single "normal" carby. But use a 32/36 weber or something decent instead of the rubbish 18R-C one. Im not suggesting a 32/36 as a performance carby, as its not, its jsut a plain carby that is easy to use and has no vacuum operation's.

Just make the manifold out of pipes.
There is nothing special about the 18R-G that needs the solex's, you'll get much better economy with a normal carby. And 18R-G's are only good for putting along so there is no point in wasting the fuel.

[MWP]

MWP, its called lumpy cams. These engine work best with virtually zero runners (ITBs), so anything hampering the flow will net a bad result... and your engine can run into serious problems in the high RPM range.

So all those big V8s running lumpy cams and down draught carbs must suck!

... sorry, but this doesnt make any sense to me at all.
In fact, by my thinking, lumpy camed engines should run better with down draught carbs as they will see a more consistent air flow and therefore meter fuel better at low revs.

But you are right of course about running an 18RC carb on a 18RG... it will choke higher up the rev range.
Not just that either... the 18RC carbs are just crap, they dont meter fuel well at all.

Mike, get along to your nearest u-pull-it and grab the carb + manifold off a XE/XF falcon (the ones with the Weber 34ADM carb).
The carb itself its very good and ive also heard of someone bolting the manifold with two runners cut off onto an 18RG.
Itll cost you $40 max.
Dodgy, yes, but itll work a lot better than the 18RC carb.

[o_man_ra23]

Screamer... ever felt the velocity that air gets sucked through the 40mm Solexs at 3000ish rpm from an 18RG?? I tell you its a lot more than most 2Ltr motors would suck. A 32/36 would be a huge restriction, and thats not good for bearings, rings or mixtures... as the carbies rely on air velocity to suck in/vapourise the fuel. Basically you would end up with a really rich mixture, that burns lean because the fuel sorta comes in in droplets instead of vapour.

Cheers, Owen

[o_man_ra23]

MWP... V8s have a fairly direct path from the carby to the intake, the fact the heads are on an angle ensure this. Performance V8s will often use straight intakes which are at the same angle as the heads, with ITBs... they also have space issues to worry about, and I havent come across too many which make decent HP/Ltr numbers without being a quad cam injected motor.

18RGs dont do much at low RPM, so as it might be smoother there to have a more consistent airflow, the engine is designed to run at high RPM, where the extra airflow impedence is a problem.

Cheers, Owen

[MWP]

Screamer... ever felt the velocity that air gets sucked through the 40mm Solexs at 3000ish rpm from an 18RG?? I tell you its a lot more than most 2Ltr motors would suck.

Every 4stroke 4cyl 2000cc engine running at 3000RPM will draw the same amount of air.
Its physics.
Yes, VE comes into play, but it doesnt make that big a difference.

[o_man_ra23]

I beg to differ, the amount of time the valve is open, and the size of the valve allows the 18RG to suck more air in, where others would have the valve close before they could get their fill. They also have cam overlap, which allows the escaping exhaust gasses to suck some fresh air in. Look up your dynamic cam theory again.

Cheers, Owen

[Screamn_Sleeka]

Yes, ive owned a 18R-G and i even put 45mm webers on, its nothing special.
And 18R-C and 18R-G's have the same cranks and bearings, a 18R-G wont be stressed by intake restriction.

2.0ltr pinto's make over 140hp with side drafts.

All "v8 supercars" run ITB's.

Fiat 2ltr twin cams (very similar, but made 10yrs before 18R-G's), have single carby conversion kits in euro cause fuel it too expensive, they run fine.

And stock 18R-Gs cams do not utilise the advantages of twin cams, and they can be matched by single cam engines.

[MWP]

I beg to differ, the amount of time the valve is open, and the size of the valve allows the 18RG to suck more air in, where others would have the valve close before they could get their fill. They also have cam overlap, which allows the escaping exhaust gasses to suck some fresh air in. Look up your dynamic cam theory again.

As i said, difference in VE... which between similar sized engines doesnt change a huge amount.

[o_man_ra23]

but it does change a huge amount when you consider the difference in size of the valves, and the amount that is allowed to fill the tubes. The head and cam design play a big part in this, and it puts a lot of extra strain on the throats.

Two engines, with equal displacement, and identical heads... yeah the volume of air sucked in wont vary much with exhaust design, manifold design etc... but with the different heads, this can vary by amazing amounts.

Cheers, Owen