Question for you guys,

What are the pro's & con's of full radius intake trumpets?, there must be engineers out there who can answer, I'll even listen to half baked theories.

As always I await your replys.

Dan.

Half baked theories? That's my specialisation!!! He's a half remembered theory, that was probably half baked at the time :

The vacuum in the carb/trumpet/manifold causes a pressure difference between it and the outside world, which causes air molecules to be drawn through the carb via the trumpets, unfortunately, the air is not drawn in a straight line directly into the trumpet, it comes in at different angles. So, what we have is air starting at all sorts of different angles, and finishing going in straight lines. The result? Turbulence. If the trumpets were simple straight bog roll tubes, the air drawn into the centre of the carb barrel would have travelled a relatively gentle angle, great. The air at the edges however would have started at somewhere approaching 90 degrees to where it finishes, not so good. What radiused, and to a even greater extent full radius trumpets attempt to do is guide the air through a gentler turn, the result, less turbulence, more air, more power, great!!

I've got all this written down in a book, so I'll copy that here when I've got it to hand, and all will become clearer, hopefully.

To what degree full radius trumpets improve airflow when compared to less radiused trumpets, I have no idea, anyone got any experience of this? They do however come in cool anodised colours, which, although only you will probably ever see them, does make a difference !!

Kingr

Sound good, does that mean the longer the intake length the more settled the air will be when it reaches the carb, the only problem with this is that I can see it looking silly if the trumpets are say 125mm long with only little sock air filters on the end

Cheers kingr, anyone else have a view?

Dan.

The fastest one handed typing in the south

[Edited on 5/2/03 by scutter]

I believe also that short trumpets are preferd for higher rpms and longer ones increase torque. All this of course depends on wether you can fit them in your filters!

Audi have engineered a variable inlet tract which varies the length of the 'trumpets' with the rpm, it has a helictical cylinder within a spirial outer aluminium casting to acheive this. More torque at lower rpm and more power at 4500+

Still drives like a grandads barge, so perhaps it does not really affect the driving pleasure!

lengthening and shortening the inlet tract (from valve seat to intake) moves the tourque around the rev range in some places trhe torque increases some it will reduce it

radiused edges venturi shapes trumpet lengths pulse plates etc etc all depend on the engine and the only real way to find out is to book a rollin road or dyno and test

that is my take on readin a lot of different books but i think dave walkers engine mangement goes into it in a bit of detail


but cant check rent it to a fella aint seen it sense

i think the btm line on this one is any radius on the entry will only at worst not make things worse, and usually make things better without getting into the too technical bits...

wot sorta garbage have i put there ??? i know wot i mean.........

'What sort of ........'



Relatively subjective but not necessarily wrong.

Enjoy.

[Edited on 5/2/03 by jollygreengiant]

I thought it was BMW that made the variable inlet tract? Doesn't look all that clever anyway - as far as I can see, it's just a long trumpet, that opens a butterfly part way down when the engine reaches a certain RPM. Genius, how do they think of these things. Just sounds like another thing that doesn't do much except break. Maybe I'm just over cinical.

Kingr

Well there is a science behind it. its to do with pulsed induction. its only really useful for naturaly aspirated engines. when the inlet valve is open air moves through the inlet tract at high speed. when the valve closes the fast moving air hits the valve and causes a high pressure build up. this area of preasure is reflected off the valve back down the manifold to the plenum or the ends of the trumpets. the pulse is then reflected back down into the engine. if you can time the intake to open as this high pressure pulse hits the valve then you get a small amount of forced induction. the rate at which the valve opens is governed by RPM and the time that the pulse hits it is governed by the speed of sound(340m/s). looking at this then, it means that to get a well tuned intake it needs to be meters long. not practical in a locost. so instead of making a long intake runner you can tune the engine to take the 3rd or 4th pulse.(as the pulse will travel back and forth between valve and plenum)

tuning the length of the runner means that it will only work well at an optimum revs. heres a graph from a magazine at the bottom of the page.

cheers
fin


ps oh and while i was writing this i found a site thatll probably give it to you in better detail and better hinglish.

Rescued attachment inlet.gif

This, I Guess, is pretty much the same sort of thing as tuned exhaust lengths which I presume help to scavange the cylinder better.

Much in the same way as people have experimented with variable length inlet tracts I think there were motorcycles at one time with a variable length tail pipes conected via the thyrottle linkage.

Not relavent I know but interesting.

Phil

I've got a pic of the old M5 engine, dunno how standard the trumpets were though.

Thought you'd be interested...


Rescued attachment BMW M5 engine.jpg

If you like your physics and know your maths then have a look at this students site on the subject. his page on intake theory is very involving..................

http://www.eng.fsu.edu/~shih/eml4421/students' web pages/manifold tuning/index.htm

have fun
fin

[Edited on 6/2/03 by Findlay234]

I'm thinking those guys probably don't get out much!! Interesting though it is, I can't quite be bothered to trawl through 101 theoretical equations so that I can add 1HP at a specific RPM and take it from another. Good luck to anyone that does though.

Kingr

yeah v. true a lot of effort for a couple more geegee's but think what you could do in the locost race series with tuned intake, tuned exhaust, blueprinted engine, mildly ported head(dont know if this ones allowed) and some carbs..... your car would be a winner........ as long as the drivers any good..........