In a message dated 11/21/00 6:35:10 AM Pacific Standard Time,
jsimmons@intrepid.net writes:
<< They all promise
to offer the extra zip but I get the feeling that when you get something you
have to give up something in return, >>
True.
The following applies to a normaly asperated engine, turbo engines are
different. Also this applies to engines in general and is not Triumph
specific.
The torque output of a stock engine ( any) is usually a slightly rising and
falling curve. For this example, the engine produces 60 ftlb @ 1000 RPM 100
ftlb @ 4000 RPM and 60 ftlb @ 6000 RPM (redline).
For the first step of upgrade we add a headder,free flow muffler,
larger/different carb and a more aggressive spark curve. Now the power is 70
ftlb @ 1000 115 ftlb @ 4000 and 75 @ 6000 RPM ( + 10, + 15, + 15)
Next we add a mild ported head, milled head for more compression, stiffer
valve springs, step 2 cam. The engine now makes 50 ftlb @ 1000 RPM 130
ftlb @ 4000 and 110 ftlb @ 6000 ( - 10, + 30, + 50 )
Now we add a all out race ported head, larger valves, high compression
pistons ,multiple carbs, larger headder pipes. Now the engine makes: 0 ftlb
at 1000 ( won't even idle without a load) 130 ftlb @ 4000 175 @ 6000 ( -
60, + 30, + 115)
It's pretty easy to raise the power across the RPM band in the first example.
For the second, you see how the torque curve is starting to turn into a peak
and move towards the right.
For the third, the engine puts puts out a very high power output, but over a
very narrow RPM range. The area under the curve stays the same, but we fold
it to a sharp point and move it to the right.
This where the old " you can't beat cubic inches " comes into play. You can
only got so much out of a given engine size. Inorder to attain the high
output in the last example, everything from air intake to exhaust is tuned
for a specific RPM.
With a turbo, you are in essence adding cubic inches.
For a street engine, a slightly larger carb, cam two steps larger than stock,
mild ported head and smallish headder should produce good results.
Harold
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