WOW, that is a gigantic air box! Could you give a little info on how you determined trumpet length (design equations?) and why you are after the largest possible plenum? Where will you fit an air filter?!
Awesome project. I have been having fun following it.
Yeah, it is pretty sizeable... Removing alternator and power steering pump gave room to expand downwards
This is Alfa Romeo 155 Supertouring engine + airbox:
That is pretty large too.
I did not start to calculate resonant frequencies for this design. Most things pointed to direction that larger is better because it acts as reservoir after air filter from where intake trumpets suck air to engine with almost zero restriction. If the airbox would be very small, all the air going to cylinder should be immediately replaced air sucked through filter and there is perhaps tiny bit of restriction there. Large airbox should smooth out those pulses.
With smaller one you could perhaps tune it to certain frequency to help cylinder filling at some rev range. I might do that after I got the thing running to see if it should be made bit larger or smaller.
Trumpets are simply sized after S50B30 (200 mm trumpet / limiter 7300 rpm) and S50B32 ( trumpet 150 mm / limiter 7600 rpm) trumpets. This "stock" engine is going to be limited to around 7300-7500 so trumpet lenght is simply halfway between those ie. 175 mm. M42 has slightly larger individual cylinder displacement but that should not affect tuning effect that much.
I also calculated harmonic resonant frequencies (ie revs) on spreadsheet for all of those engines and OEM trumpet lenghts and theory seemed hold well.
Air filter is K&N with 100 mm inside diameter and we made flange between it and 100 mm flexible hose. Similar flange will be fitter to front or bottom of the airbox so I can move filter around to find best location. One idea is to make filter enclosure below radiator to take in air from lower large opening on front bumper.
