In the most recent issue of Classic Motorsports there was an article about
improving the engine performance of a 75 TR6. As you might suspect, the mods
were head modification (grind to 9.2;1 ratio, porting), Goodparts GP2 cam,
Pertronix ignition, rebuilt distributor, and improved carbs. In this case they
used two Weber 45MCHH sidedraft carbs, which they say are essentially a single
throat version of the classic 45DCOE. They come in a kit that included
adapters, linkage, etc. They acknowledged that well tuned ZS carbs can perform
very well, they wanted to try out a new product - which they no doubt got for
free. While that was interesting, what got my attention was the fact they used
a rolling dyno to measure stock horsepower at the wheels and then measured the
effect of subsequent modifications. Using the dyno to tune it added another 6
HP & 5 lb/ft and reduced 0-60 from 9 seconds to 8.4 seconds.
They stressed that doing only one of the modifications would probably not do
much good by itself. Rather, to get the benefit the motor needs to be
considered a complete system from the time air enters the carbs to the exhaust
tips. Reading between the lines it's obvious that taking the trouble to locate
a dyno shop and tuning your existing car might uncork more power without any
modifications.
The stock horsepower was measured at 74 HP with peak torque at 95 lb/ft. 0-60
time was 13.4 seconds. Pretty anemic. By the time they finished the car
measured 100 HP and 115 lb/ft with 8.4 seconds 0-60. The use of the dyno to
precisely tune the ignition and air fuel mixture was very insightful. The final
settings were 12.5:1 mixture and ignition timing of 37 degrees BTDC at 4000 RPM
(vacuum retard disconnected).
The article was pretty instructive to a bone head like me. While I'm not a
big fan of the magazine (too many ads and fluff photos, not enough content),
this article was quite useful for anyone considering improving his own motor.
Hope this helps someone.
Jim
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