Jenvey throttle bodies air box.

[marki]

Am I right in thinking I should try and make the box as big as possible ?

Thanks for the replies Mark.

[john.r.davies]

Bernouille says that as velocity increases, pressure decreases, energy is transferred from potential to kinetic. That's what "sucks" fuel in a carburettor.

The air flow to the intakes should be as slow as possible, else the engine will need to work against a pressure lower than ambient to draw air in.

 

So yes, as big as possible!

John

[Peter Cobbold]

Am I right in thinking I should try and make the box as big as possible ?

Thanks for the replies Mark.

Within reason, but a too-big surface area will pick up heat and warm air is less dense. So keep it away from the exhaust manifold and fit a reflector plate between the two.

http://www.brisbanehotairballooning.com.au/wp-content/uploads/air-density-table.png

If the air heats up to 40C from 20C the density drops by 6%, and so will power.

 

Ideally taper it from the front so the rear cylinders are not starved:

http://s137.photobucket.com/user/pokinacha06/media/109040d1297343030-v6-plenum-design-plenum-concept.jpg.html

Google Images 'plenum chamber design' for ideas.

 

And keep the mouths of the trumpets at least a choke-tube diameter away from the wall facing the trumpet. Get dimensions from the cfd images in my post above. You want the wall to be in the Mach0 zone, depicted as darkest blue.

 

Peter

Edited August 31, 2016 by Peter Cobbold

[rogerguzzi]

Hello Mark

Here is a big selection

 

http://www.ebay.co.uk/itm/262114425349?_trksid=p2060353.m1438.l2649&var=560882690405&ssPageName=STRK%3AMEBIDX%3AIT

[marki]

Hi Roger.

I've got the ram pipes, just need to work out the dimensions of the air box.

Hi Peter.

That's a great help I wasn't aware that it would be better to taper it, I'm going to have a go out of Ali and see how it turns out. I can't bring myself to spend £3/400 on an air box.

Thanks again guys Mark.

[Guest ntc]

The airbox is pointless not required

[john.r.davies]

As usual, Neil goes his own way.

John

[Guest ntc]

http://www.revingtontr.com/fuel-brakes/ram-pipes-and-trumpets

[Peter Cobbold]

Those listed are for SUs. There's no point at all in fitting a trumpet to an SU (unless the carb is so badly undersized that the piston/air valve becomes fully lifted). All a trumpet does on an SU is reduce the pressure dropped across the mouth. This results in the piston/air valve rising to assume a new position that restores the 'Constant Depression' in the choke tube. And the mixture will richen as the needle rises too. The CD stays the same, and mass air flow stays the same. With a trumpet the air velocity across the jet slows so atomisation may be worsened. The mouth 'entry loss' is fraction of the 'constant depression' and both can be calculated.

 

Trumpets on Webers and injection are fine, but they work on entirely different fluid mechanics than SU.

 

Hot air is the big problem with underbonet air intakes, for any carb or injection. Air at 40C throws away about 6% of power **, across the rpm and load ranges, compared with ambient 20C. The engineering effort and expense needed to increase volumetric efficiency by 6% is substantial, so why throw away 6% by not fitting a relatively cleap cold air intake?

 

Peter

 

** calculated as 1.127/1.205 = 0.935

http://www.engineeringtoolbox.com/air-properties-d_156.html