02GF74
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 posted on 16/8/06 at 03:09 PM |
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trumpets - length?
wot is it that determines what length trumpets one fits to one's dellorto 40's?
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MikeRJ
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| posted on 16/8/06 at 03:37 PM |
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Idealy ones rolling road session results!
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02GF74
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| posted on 16/8/06 at 04:12 PM |
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DIY Si
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| posted on 16/8/06 at 04:28 PM |
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About 50-75mm seems to work well. Depends upon state of tune, intended use etc.
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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Surrey Dave
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| posted on 16/8/06 at 04:58 PM |
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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]
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Findlay234
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| posted on 16/8/06 at 05:10 PM |
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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
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Confused but excited.
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| posted on 16/8/06 at 05:10 PM |
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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.]
Tell them about the bent treacle edges!
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Findlay234
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| posted on 16/8/06 at 05:26 PM |
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S.I. units
meters (m)
seconds (s)
[Edited on 16/8/06 by Findlay234]
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Findlay234
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| posted on 16/8/06 at 05:36 PM |
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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.
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Confused but excited.
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| posted on 16/8/06 at 06:45 PM |
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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.
Tell them about the bent treacle edges!
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Findlay234
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| posted on 16/8/06 at 06:59 PM |
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yep area is in sq.meters, volume in cubic meters
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DavidM
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| posted on 16/8/06 at 07:06 PM |
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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
Proportion is Everything
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DavidM
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| posted on 16/8/06 at 07:12 PM |
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This is the link. It was DIYSi:
http://www.locostbuilders.co.uk/viewthread.php?tid=46508
David
Proportion is Everything
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Confused but excited.
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| posted on 16/8/06 at 07:47 PM |
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Findlay 234,
Thanks for the info mate.
DavidM,
Thanks.
That's the bugger. I couldn't find it.
Cheers guys.
Tell them about the bent treacle edges!
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MikeRJ
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| posted on 16/8/06 at 09:33 PM |
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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?
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Findlay234
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| posted on 16/8/06 at 10:07 PM |
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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......
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Findlay234
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| posted on 16/8/06 at 10:28 PM |
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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
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Jon Ison
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| posted on 16/8/06 at 10:38 PM |
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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
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procomp
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| posted on 17/8/06 at 07:12 AM |
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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
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Findlay234
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| posted on 17/8/06 at 08:53 AM |
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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.
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02GF74
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| posted on 17/8/06 at 09:00 AM |
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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.
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NS Dev
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| posted on 17/8/06 at 12:02 PM |
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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.
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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Findlay234
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| posted on 17/8/06 at 12:22 PM |
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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.
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NS Dev
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| posted on 18/8/06 at 07:22 AM |
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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......
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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