What a difference 20mm makes
givemethebighammer - 6/6/06 at 10:13 PM
I have honda blackbird carbs fitted to my 2.0L zetec. As some of you may be aware when fitted to the blackbird these have two very short (30mm two
outer cylinders) and two longer (50mm two inner cylinders) trumpets fitted. This is supposedly to bring different cylinders to peak power at different
time to widen the power band of the motorbike (otherwise it would be all top end I guess).
Anyway the different size trumpets did not suit my zetec engine so I managed to get two more of the 50mm trumpets. The car ran much better with four
50mm ones fitted. However it was still a little flat lower down the rev range. One of my neighbours is a retired sheet metal worker he said he could
make me some longer trumpets to the same pattern as the honda originals.
Result 70mm trumpets made from a single sheet of brass, the craftmanship is staggering, you can hardly see where he has brazed them. Driving the car
was mind blowing as well, lots more torque and low down responsiveness with very little loss of top end.
I just wish I had the skills my neighbour has, nearly seventy years old and still a magician with metal. People like him are few and far between these
days.
see picture
[Edited on 6/6/06 by givemethebighammer]
Rescued attachment trumpets.JPG
garyo - 7/6/06 at 07:30 AM
Any idea what the distance between the end of the trumpet and the back of the inlet valve is now?
Gary
NS Dev - 7/6/06 at 07:45 AM
Oh they are beautiful!!!
I trust you crossed his hands with lots of beer or something!!!
I remember a discussion on here a while back where inlet length was being discussed and the effects on the power and torque curve were said to be
"difficult to notice" by some, which I fervently denied, as experience has shown me exactly what you have found!!!
On most road driveable 4 cyl car engined cars, you want the inlet lengths as long as you can get practically get them.
flak monkey - 7/6/06 at 07:47 AM
IIRC the longer the inlet port the wider the power band, but lower peak power. And the shorter the port the narrower the power band, but you get
higher peak power.
So longer ports would be more suitable for road use...
David
[Edited on 7/6/06 by flak monkey]
NS Dev - 7/6/06 at 08:29 AM
quote:
Originally posted by flak monkey
IIRC the longer the inlet port the wider the power band, but lower peak power. And the shorter the port the narrower the power band, but you get
higher peak power.
So longer ports would be more suitable for road use...
David
[Edited on 7/6/06 by flak monkey]
Yep, but if correctly designed, the longer inlets will lose nothing at peak either. The only real loss is wall drag of the air on the inlets, and this
can be substantially countered by using a constant tapered inlet (see SBD's taper inlet kits)
Even these have proved to be of limited benefit though over a simple long parallel intake.
That's all you need in the real world.
tom_loughlin - 7/6/06 at 09:03 AM
They look awesome, I wasnt going to bother with any for a while, but if you say the difference between thhe three sets of trumpets you tried is
amazing, then i imagine having no trumpets at all would be a mistake!
More $$$ needed then to get myself a set
Tom
givemethebighammer - 7/6/06 at 02:43 PM
quote:
Originally posted by NS Dev
Oh they are beautiful!!!
I trust you crossed his hands with lots of beer or something!!!
I remember a discussion on here a while back where inlet length was being discussed and the effects on the power and torque curve were said to be
"difficult to notice" by some, which I fervently denied, as experience has shown me exactly what you have found!!!
On most road driveable 4 cyl car engined cars, you want the inlet lengths as long as you can get practically get them.
Yup, I will be passing him some beer money. If I had had these made commercially it would have cost me £££££. There's something to be said for
finding people who do this sort of thing for the love of it.
There was no real science to the length we decided on. I just measured inside the sausage air filter and worked out the longest length trumpets I
could fit, still leaving about 20mm or so between the end of the trumpets and the air filter.
I am still amazed at the quality of the work. This bloke's hobby is restoring vintage motorbikes. Some of the parts he has made to replace
original items long gone from the shops are breathtaking. The blokes an artist as well as an engineer.
The photo of my trumpets just doesn't do them justice.
