wot is it that determines what length trumpets one fits to one's dellorto 40's?

Idealy ones rolling road session results!

About 50-75mm seems to work well. Depends upon state of tune, intended use etc.

I expect some clever clogs could make an Exel calculator for us all...........p l e a s e .

[Edited on 16/8/06 by Surrey Dave]

[Edited on 18/8/06 by Surrey Dave]

Basically it depends on the engine speed you wish the intake to be tuned to. You cant really change any of the other variables so easily.

The choice of engine speed is down to the intended use. High speed for gaining maximum power for racing applications or tune it to lower rev ranges if you wish it to be civil on public roads.

Depending on the engine and if you have also tuned the exhaust it is possible achieve greater than 100% volumetric effiency.

If any one is interested in further info there are old threads in this forum or i can write some of the theory and application here.

cheers

Formula is very interesting, as I want to design and make my own fuelling system. It would be of greater use if some units for the quantative values had been included. Are we to assume Kg/cm/sec?
The formula is meaningless without them.

EDIT: Sorry that sounds like I'm griping. I'm not, I am genuinely interested.

[Edited on 16/8/06 by Confused but excited.]

S.I. units

meters (m)
seconds (s)

[Edited on 16/8/06 by Findlay234]

ive also got quite a bit of stuff on exhaust tuning as well.

Also a funny thing... part of the dissertation requires a viva-voca examination which is basically a presentation of your work slash grilling about how much you learnt. Chatting to my second reader about the project he pipes up say that hes doing a similar project for industry.

After speaking to a few other lecturers it turns out the 'industry' hes helping with their intake and exhaust design happens to be none other than the merc-mclaren F1 team... i instantly shat myself that i had one of the world experts (well im guessing hes up there with the best if a F1 team asked for his help) marking me on a project he knows everything about. fortunately he didnt rip me a new one and gave me a good mark. Turns out there are educators who dont expect you to know as much as them.

Findlay234;
Thanks for that. Just to clarify, pipe area is in square metres, yes?
Viva-voca, jeez I bet that made you pucker up. What an oportunity to quiz someone of that calibre tho'. Afterwards of course.

yep area is in sq.meters, volume in cubic meters

There was a post on here in the last couple of months giving details of air flow for different shapes of trumpet. Some were much better than others, so you'll need to take account of this too.

David

This is the link. It was DIYSi:

http://www.locostbuilders.co.uk/viewthread.php?tid=46508

David

Findlay 234,
Thanks for the info mate.

DavidM,
Thanks.
That's the bugger. I couldn't find it.

Cheers guys.

What units are 'N' in? RPM or Rads/s?

Please correct me if I am being thick, but with engine speed on the top of the equation, this means longer inlet lengths are required at higher RPM. Is that correct? It seems to go against conventional wisdom that longer inlet tract lengths give better peak torque and shorter give high peak power?

AAAAAHHH F@#K

sorry chaps the man is right, i tried working from the Helmholtz Frequency formula i had in my head which was evidently wrong.

this is the corrected formula......

ive made an excel sheet for people to use. yes with the correct formula in it. lol.

although it would be a good idea to check it please....

oh and the engine speed is in rpm

with fixed lengths on the trumpets you will only get it spot on in a certain rev range, have you seen the way the F1 trumpets move up and down with rev changes

Hi i think you should look at some of dave walker (CCC dave) as he has done a lot of experimenting with this and came to the conclusion as jon has said you need variable so he made a set with small motors on to alter the lenght but never really got it to work.

What we do is for the engine we are running is put it on the dyno or rolling road and play with the lenghts so you get the bump of the curve at max revs rather than the dip in the curve at max revs. it is ussually only a bump or dip of 5bhp of the mean curve but the bump is still 10bhp more than the dip if you see what i mean.It will not make that much difference on std cams . Can be used to iron out big dips that you can find on power curves that you get with some engines with upprated cams such as the cvh.

cheers matt

yeah variable intake lengths are the way forward but if you want simplicity then just using fixed is good enough. Itll still be better than just bodging it and using any old length which is what most people use. Youll find factory intakes and exhausts are designed to give a peak volumetric efficiency around the middle of the range.

OK, I';ll tell ya why I asked.

I have 1300 crossflow with twin del, 40s and K&N type air filter.

RD do 4 different trumpet length,s from memory 12, 20, 30, 40 mm. I have about 80+ m beween filter baseplate and top; obviously a really long trumpet will be too close to the top so no good.

I went for the 30 mm; no real reason other than I think longer is better (ooh err missus ) but 40 mm could have done just as well I guess but getting closer to the top plate.

time for my soapbox moment!!!

For pretty much ANY road driveable 4 cyl engine (which is what a lot of us are using on here) you need the longest inlet tract you can get in without it sticking into the wrong lane on the motorway!

Tongue in cheek but for sensible rpm the tuned length for most 4 cyl engines will be limited by physical constraints of the car that the engine is fitted to.

well you can try and utilise the fourth wave...

the system of tuning uses wave reflection theory to work. When the piston moves down an expansion wave (low pressure) is created and travels up the inlet manifold till it reaches an abrupt change in pipe diameter. At this point there will be a reflected wave along with a wave transmited forward. If this change is from a smaller area to a larger one like a pipe joint or opening to atmosphere or plenum then the reflected wave will be of the opposite form (in this case a compression wave) Tuning the pipe length allows you to time the compression wave to hit the intake valve just before it closes giving a strong charge of air and, if there is suitable overlap in the valves, helping to push out the burnt gasses.

Now the valve closes and the high pressure at the valve is reflected as a compression wave back toward the area change (joint, plenum, trumpet end) Again the reflected wave is of the opposite form, now a compression wave. This bouncing back and forth of pressure waves and signs happens all the time in the intake and eshausts with waves overlapping and moving past each other. If you now tune the intake to a length which utilises the next pressure wave to hit the valves you can greatly reduce the length of the intake. This may mean you dont get as much of the charging effect but it is better than nothing.

an alternative view is to have all the inlets different lengths to spread the torque peak.......

just thought I'd throw that one in!

Same with exhausts, match the extraction on cyls 1-4 and 2-3 but not all 4......