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 A Result, achieved the hard way!

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Trevor Amos

Number of posts : 876
Registration date : 2010-08-13

PostSubject: A Result, achieved the hard way!   Fri Aug 08, 2014 9:18 pm

I came across this brief report a couple weeks ago on another 2t race site, a few modest lines, but of great significance. I have copied it here, just as it was originally posted on the web site forum, warts and all!

"rode the bike today and it pulls 1000 times better below the pipe than the last cylinder. probly because the ports arent sky high i suppose. mostly the transfers probly. before it seemed to have 1000 rpm wide powerband. below that and it couldnt recover without down shifting 1 or 2 gears. now it pulls back to the pipe alot better without down shifting ( in most situations). i left some meat on the bone so i can make more cylinder adjustments if needed. any body got ideas how to get more power without the midrange dropping out, like the last cylinder ? at some point the ports get so high you gain nothing but over rev which is useless with no torque."

The engine in question here is another example of garden shed race tuning on a roadster 125, so us Bantam men will immediately be able to identify with it. The most important difference is its 5 speed gear box compared to our meagre 3, so if a 5 speeder can`t cope our 3 has no chance!

The lessons we can take from this example adds credence to the advice that has been available on the Bantam Forum for some time. By taking note of the conclusions offered by this tuner you may just avoid including a totally unsuitable porting layout in your next barrel!

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john bass


Number of posts : 1742
Age : 89
Localisation : Bensberg, Germany
Registration date : 2006-12-06

PostSubject: All Quiet Again...   Wed Sep 24, 2014 5:44 am

All quiet on the western front again, Trevor!

I awaited replies and there were none.

No matter. I was taken by a bit in the last sentence, "... you gain nothing but over rev which is useless with no torque."

I thought this raises the old query of understanding what is/was meant by the difference of Torque** and Power*** since with NO TORQUE there´d be NO POWER....
Some might say, here, that I am being unnecessarily emphatic on trivia (pedantic) but in my career of diesel engine development I was contantly irritated by confusion of these two factors in engine performance ....
Some might say `No Pull´ with lots of revs under No-Load.
With low torque high revs are impossible under LOAD. Only with low-load or no load can a low-torque engine rev high.
To repeat: thsi mearely means that an engine will rev to high RPM ONLY AT NO-LOAD condition.
Tractive Effort (TE) has to be greater than Tractive Resistance (TR) for the engine revs to increase anyway,
and the engine will only rev up to the speed where the TE = TR.

The ideal torque curve is high at the lower end of the rev band and lower at the top end of the working speed range which is impossible with naturally aspirated (NA) engines. This shows up clearly with this year´s Formula One car racing. The high performance of F1 cars this year are using turbocharged engines which have a `Flatter´ torque curve than the NA engine can achieve.

With diesel the turbocharged torque curve can give a "Torque-Back-Up" which means when an increased load is applied -- such as driving onto a hill -- the Torque (& TE) increase as the speed reduces.
With a transport company in Burundi, Africa, the 400horsepower Volvo trucks were slower up hill than Mack trucks with only 250horspower. The reason was the Mack engine had 29% torque back-up against Volov´s 16% which meant when operating in hilly terrain the Mack returned a better fuel consumption for same load & weight.

** Torque is instantaneous work, or EFFORT, whereas ***Power is the RATE of doing work (or using effort).

That is all by the way.... because the point you were making, Trevor (I apologize for this unnecessary blurb here ...) -- was the waste of a barrel by over-ethusiastic port hacking, particularly the exhaust.


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Number of posts : 280
Age : 65
Localisation : Cambridge
Registration date : 2006-12-04

PostSubject: Torque back up   Wed Sep 24, 2014 6:11 am

John's mention of the above reminded me of when I was involved with Naturally aspirated Diesel engines in Dumper trucks. The torque curve was designed to keep the driver out of trouble when ascending slopes which got steeper. Paddy would have a full load in the bucket, and his foot to the floor. As the slope increased, the truck and engine speed reduced, until torque back up came in and equilibrium occurred. This was achieved by fueling alone, with no real smoke limits to be concerned about. (Those were the days).

One day we had a truck returned without its cylinder barrel (or head). The torque back up was clearly too much for the faulty casting.

Happy days

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john bass


Number of posts : 1742
Age : 89
Localisation : Bensberg, Germany
Registration date : 2006-12-06

PostSubject: Hey Peter...!   Thu Sep 25, 2014 4:54 am

Hey Peter!
So there you are -- I´ve been adrift with my PC lately in that e-Mails became impossible and I saw in my Bantam In-Box a message fromk you which in spite of me trying to open the damn box, remain locked so I could not reply to your personal message.

Hope you are survining retirement.
It must seem hard after Dunton.
There´s a widow we see often at our Coffee Bar whose late husband worked at Ford Merckenik and she was highly amused when I told her I had worked in "Resting Ops" at Ford Dunton.

Haven´t heard from Andy for ages -- I think because of my e-Mail difficulties which have been got over but I guess just for the moment because Microsoft have told me (many times) that my XP system is no longer supported by them. I am hanging on for a bit because stories of Windows 8 suggest there are difficulties with it.

Back to the silly technical bit I scribed -- I had some fun at Simms with injection pumps on Ford engines in that the Ford Applications Engineers often got the `Industrial´spec mixed up with `Highways´ spec and the tight governing caused lots of bother and I´d get called to sort it....

Would be fun to chat over those times, with a beer, as well as Bantam Racing -- before its too late.

Take care,


John-Boy -- almost ex.....
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