Removed the original theme because, what a surprise, Carryfast has jumped in with his usual attempts, 20 of them so far on this one thread, to bludgeon every one else into conceding that he is the font of all knowledge about life, the universe, and everything.
Well Slartibartfast we know that you are an acknowledged planet designer, and that your favourite domicile is doing slightly better now following your unexpected modification to reverse its direction of rotation, but its orbit is now taking it away from the earth, on a trajectory which will not see it return for the next five millenia.
So forgive us if we just say bye bye and wrap up warm.
Firstly to bust the myth of high engine speeds being needed the turbocharged 14 litre Cummins big cam produced its peak torque at 1,300 rpm the Detroit 8v92 T produced more torque than the Cummins at 1,400 rpm.Peak power rpm also being close enough to make no difference.
While large two stroke marine engines operate at the same if not lower rpm as 4 stroke.
In all cases forced induction seems to have been an essential and strangely missing factor, in making the design principle work efficiently from the start.
Which leaves the question what if and what was stopping Foden and Detroit taking the scavenging aid blower up to forced induction levels, instead of, Detroit at least, finally using turbocharging ?.
Can’t help yourself can you Carryfast, trying to make yourself look clever.
The turbocharger has advantages over the roots type blower, which loses efficiency as speed increases.
If Fodens hadn’t ■■■■■■ all the development funds up the wall in what eventually became a futile exercise trying to build the two stroke engine they might not have gone out of business as soon as they did in 1980 !
They used to run up on the A6 through Kendal and climb Shap then turn around and return to Elworth five days a week with a noisy artic loaded with test weights.
Not sure which size engine they were testing though but IIRC it was a Steer unit !
To be fair Bewick naturally aspirated two stroke, or Cummins, v Gardner ( 8LXB specifically ) no contest or argument which is a decision I only came to gradually by looking objectively at the numbers and the maths.
By the same logic even a turbocharged Cummins isn’t going to beat a turbocharged Detroit.Gardner isn’t even in that race.
Foden were on the right track but were tryingt to do rocket science on a less than Gardner budget and setting their sights at Detroit 6v71 N level accordingly.
That’s no disrespect to Fodens engineering team.
If they’d have created the turbocharged 92 series Detroit before Detroit did it and then a larger capacity, lower speed, inline 6 cylinder development, running with massive multiple turbo or better compound supercharging and turbocharging forced induction boost, the story might have been different.
It was a rhetorical question partly to dispel the other myth, held by many including you, that the blower in either case was a ‘supercharger’, that provided anything more than natural aspiration, to ‘aid’ scavenging.The definition of scavenging meaning that the exitting exhaust gasses draw in the new inlet charge during the exhaust and induction overlap period.That 93,000 hp marine engine also surprisingly uses turbocharging not electrically driven forced induction.
Sorry if I offended you for stating facts.
It’s no myth, call it what you like or for use it for other purposes, its a supercharger as tens of thousands of hotrodders and ultra-high performance engine builders will lay testament. A light globe, used as a resistor is no less a light globe.
“The increase in air chest pressure from about 7 psi at full power on blower scavenged engines to something of the order of 15 psi at full power on turbocharged engines increased considerably the quantity of air leaking into the crankcase and raised the crankcase pressure. This made the oil reluctant to drain back down from the fuel pump cambox to the Roots blower and a lot of testing was necessary to develop a crankcase breather which would relieve the crankcase pressure without oil carry over. The breather was threatening to be the same size as the engine air filter till technology came to the rescue.”
A supercharged engine by definition means forced induction.
You agreed that the Detroit N series means Naturally Aspirated ?.T means turbocharged ?.
The same applies in the case of the Foden except it’s designers forgot or couldn’t afford to eventually get round to turbocharging it.
A two stroke diesel scavenging assistance blower by definition ain’t the same thing as a supercharger.There is no forced induction from the scavenging process including from the blower.
That’s why a turbocharger is used to harness the energy of the exhaust gasses to provide forced induction.In addition to the energy of the exhaust gasses being used to provide scavenging in either case.
Superchargers and turbochargers are both high volume low pressure pumps.
Both have advantages and disadvantages. Two strokes have died out in road vehicles due to ever more strict emission laws. The US military still use a lot of V6 ,V8 and flat 12 two strokes but they are exempt from any emission legislation.
Compound supercharging and turbocharging forced induction and bringing peak power engine speeds down to well below those of 4 stroke levels would have been the next best move.
They’ll obviously need to do some work on that air chest isolation though.
Let’s get this right.Is that saying 7 psi relative to atmosphere ?.
Or 7 psi over boost from the blower ?.
Which certainly would be a supercharged two stroke v the unarguably and stated naturally aspirated Detroit.
I didn’t even know there was a turbocharged Foden two stroke.But not surprised it’s blowing everything out of everywhere at 15 psi boost.
To add by definition it’s exhaust gas scavenged the blower only acts as an aid to that in low or no exhaust gas flow situations by pushing inlet charge air into the cylinder to sustain combustion, as opposed to the exhaust gas flow drawing it in behind it.
A two stroke blower by definition doesn’t scavenge anything.
At full power exhaust gas flow and the resulting scavenging effect is obviously at its peak.
7 psi,( relative to atmosphere ), would equate to normal natural aspiration 20 hg inlet port cylinder vacuum level.
Forced induction is obviously always termed in boost pressure over atmosphere.
Unless Foden’s engineers really did also try to use the blower as a forced induction supercharger ?.Doubtful.
