IDA Tuning - Venturi versus Air Corrector Relationship....?

[Shane Noone]

Hi Guys,

What are you thoughts......?

Everyone that doesn't have access to dyno / tuning equipment probably reads that there are some basic general rules about jetting relationships that will get you in the ballpark but every engine is different and has it's own set of particular jetting requirements and dependant on how you want to use your engine....

So with that in mind, we hear, select your Venturi size, general rule = 1 or 2 sizes below your inlet valve size, ie 42mm inlet valve, commonly no larger than 40mm venturi. Next based on Venturi choice select the main jet. General rule somewhere between  multiply by 4 to 4.3 times the venturi size, ie 40mm venturi = 160 to 172 mains fuel jet.

Now to my question, the air corrector ! - it seems some people suggest this should be 200 or larger in fact I was told for a 44mm choke I should be looking at a size 220 with maybe a 190 or 195 main jet......
Others would say jet around a 180 air corrector.

Last dyno session I had I tried the 190 and 195 mains / 220 air combo versus 170 and 175 mains and 180 air combo and we saw very little difference in power and AFR. As my friend who operated the dyno said, the engine will dictate what it needs and we jet accordingly and he wasn't really suprised that the " bigger " jets combo didn't make any real difference.

It was an interesting experience that was also puzzling based on what I had heard in the VW Air Cooled drag racing scene.

So, back to my question. Assuming no tuning equipment available. Ballpark air corrector jet recommendations. How do these get calculated / guesstimated in the same way mains jets do in relationship to the venturi choice....

Thanks,
Shane.

[Andy Sykes]

Did they fit ?

[Shane Noone]

Hi Andy - installed today - will PM you - Thanks Shane.

[dannyboy]

dunno mate just get efi and come into the modern age 

[fish]

With the numbers above you are in the ball park already, but remember those formulas are based on good fuel usually containing Lead.

Today's fuel dictates slightly fatter jetting IMO, better to start rich and work your way down.

More efficient engines respond better to jetting and/or timing changes, if one is altered the other needs to be tweaked.

There is also no mention of your emulsion tubes as these will also dictate your jetting.