I was recently reading in an old Jowett Sport magazine a reprinted letter to the Hofman Motor Co in USA from Jowett Cars where they mentioned that carburettors should be fitted with tuned length stack pipes. These could be purchased from Jowett Cars. Does anyone know the length of these pipes or any other details.
Neil Hood
Tuned stack pipes for carburettors
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Neil Hood
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I raced for a couple of seasons with inlet pipes made from tin cans but shaped into a sort of hyperbolic shape to smooth intake. This was after a visit to the rolling road which showed the AC air cleaner reduced power by 5bhp.
These were replaced with Piper air cleaners that allegedly reduced power by very little.
I have had serious problems with petrol starvation caused by standing waves on the Javelin when using Delorto carbs and the standard air cleaner. Replaced with paper pancake filters, so that there is no interference. Had the same problem when preparing for the Sahara when I used a big air cleaner (ex Renault 16TS) shared by both carbs. Hence the Piper air cleaners (with vacuum cleaner bags for the sandstorms).
These were replaced with Piper air cleaners that allegedly reduced power by very little.
I have had serious problems with petrol starvation caused by standing waves on the Javelin when using Delorto carbs and the standard air cleaner. Replaced with paper pancake filters, so that there is no interference. Had the same problem when preparing for the Sahara when I used a big air cleaner (ex Renault 16TS) shared by both carbs. Hence the Piper air cleaners (with vacuum cleaner bags for the sandstorms).
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Srenner
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Tuned stack pipes
Okay, I have a set my Dad ran in 1952. I seem to recall that I also have the factory blueprint on this, but don't hold me to it, just in case my memory is a s bad as I fear.
I am in the big thrash to get a couple of cars ready for the Monterey Historic, so I can look for them after Aug. 21.
I am in the big thrash to get a couple of cars ready for the Monterey Historic, so I can look for them after Aug. 21.
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ian Howell
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From 1967 to '87 Black de Luxe Javelin MKC 1 (later 6469TU). (Sold as non-runner with tons of spares, 1987)
From about 1980 to '87 ex WD Jowett stationary engine. (Sold on)
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Taken in a part-repaired state to the 2010 Centenary Rally, returned to a roadworthy state by 2013. - Given Name: Ian
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Just a small (helpful?) contribution.
In the 1970's I worked for a firm that had taken over the premises of the then defunct Nerus Engineering - quite a well known performance tuning specialist in the 1960' and a bit later.
Among their products were cast aluminium induction pipes, mostly for minis and Escorts, but I suspect the design principal is valid: -
The rim of the 'trumpet' had a very thick lip to it, really a circular section rim about 1/2" in diameter. Their ex-tuning manager told me that the outside shape was as important as the inside shape (of the trumpet) as waves built up at resonant frequencies around sharp lips.
Does this tie in with any other contributor's thinking?
In the 1970's I worked for a firm that had taken over the premises of the then defunct Nerus Engineering - quite a well known performance tuning specialist in the 1960' and a bit later.
Among their products were cast aluminium induction pipes, mostly for minis and Escorts, but I suspect the design principal is valid: -
The rim of the 'trumpet' had a very thick lip to it, really a circular section rim about 1/2" in diameter. Their ex-tuning manager told me that the outside shape was as important as the inside shape (of the trumpet) as waves built up at resonant frequencies around sharp lips.
Does this tie in with any other contributor's thinking?
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Yes I get resonant frequencies when kissing girls with sharp lips!
But seriously, smoothness is all important, especially at a boundary such as at the end of the pipe. The ideal shape is hyperbolic, I think, and of infinite length, unless you want to tune the throat to a particular frequency to get high pressure at the inlet valve when on the cam. As I said elsewhere, if you get it wrong power is seriously degraded and the carb will become totally confused.
But seriously, smoothness is all important, especially at a boundary such as at the end of the pipe. The ideal shape is hyperbolic, I think, and of infinite length, unless you want to tune the throat to a particular frequency to get high pressure at the inlet valve when on the cam. As I said elsewhere, if you get it wrong power is seriously degraded and the carb will become totally confused.