This might be of some interest, going by some of the comments above.
We have three engines in total, for the 350 racer. One is fairly 'standard', with 70 x 90 bore and stroke, the second has the same bore and stroke, but uses a shorter conrod, based on the dimensions of the very rare 1963 unit Redditch Bullet - I call this our 'Short Rod' engine. The engine we have been running for the last few years is our one off 'Short Stroke' engine - basically a 500 short stroked down to 350, with 84 mm bore.
Of the first two engines, there is little to choose between them, except the Short Rod engine is very slightly lighter, just by having less metal in it thanks to the shorter rod and barrel etc.
The Long Rod engine could reach 8,000 rpm, as could the Short Rod, both peak with 32 - 33 bhp @ rear wheel around 7,200 rpm, with useful power coming on line around 3,500 rpm.
The current 'Short stroke' engine uses a tuned 'Big Head' and will rev to 9,500 rpm, with a 1 1/2" GP carb fitted - this is much bigger than the TT carbs on the other engines - and this engine also produces 32 - 33 bhp, but at the higher speed of 8,500 rpm, with useful power coming in around 5,000 rpm and staying clear of 30 bhp right up to the rev limiter @ 9500 rpm.
So, all have virtually the same power @ rear wheel, the first two being very similar in their power delivery. The short stroke engine is totally nuts and can take anything thrown at it and frequently wins races!
Take your pick 
B.W.
B.W.,
I don't know very much about your short stroke 350, but I ran a few numbers.
If the engine is above 30hp beginning around 5k rpm, it's producing about 30+ ft-lbs torque there. Let's look at 5252 rpm.
30 x 5252/5252 =30 hp.
Okay, so let's look at 6000 rpm, and assume tq is not falling.
30 x 6000/5252 =34.27 hp.
We can follow your report that the engine produces 32-33 hp max, so tq must begin falling somewhere between 5252 -6000 rpm, but not much. However, as rpms increase, hp seems to remain the same, so tq must be falling at approximately the same rate as rpms increase. This produces a very wide powerband, but peak power is somewhat compromised in the result.
At 9000 rpm, the tq has fallen to about 19 ft-lbs.
19 x 9000/5252 = 32.55 hp.
So, I suggest attempting some methods to cause that 30 ft-lbs peak tq to occur at a higher rpm. This would narrow the powerband somewhat, depending on what is done, but it should cause a higher hp figure. We know it can produce 30 ft-lbs, so we won't try to assume it can make more, because 30 ft-lbs is a lot for a 350. We just want to move it up the rpm range, if we can.
Let's see what would happen if it could hold on to that 30 ft-lbs at a higher rpm.
30 x 6000/5252 = 34.27 hp
30 x 6500/5252 = 37.13 hp
30 x 7000/5252 = 39.98 hp
Now, this is all predicated on the plausible premise that you can move that tq peak higher in the rev range. And I think that is a viable premise.
You know the methods.
Shorter pipes, larger pipes, different cams, etc.
On the cam subject, I don't know what cams you have in there, but there is a limit to the late intake closing timing. With the 3500-4500 rpm level(broad flat peak) powerband that the engine is exhibiting, it is an indicator of long inlet timing, or late inlet closing timing.
I would try a bit of cam advance to close the inlet earlier, and open the exhaust earlier. Maybe just a 3-way timing pinion in the advanced keyway, just to get a directional indicator whether it has any benefit.
I am thinking if you could put the peak in that tq curve at a higher rpm, it would give more power, and wouldn't really have any negatives because you have so much rpm in the powerband already that making it a little peakier would be a plus.
Just a thought.
Looking forward to enjoying viewing your team's upcoming season of racing!
Topic: Iron barrel Con-Rod length ? (Read 4208 times)