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Discussion Starter #1
(from thread http://www.ferrariforum.net/forum/viewtopic.php?t=2202

The bore:stroke ratio is likely to affect the torque curve shape, but Mr Newton says that the T curve must cross the HP curve at 5252 rpm (imperial units), and we can't argue with him 'cause he's dead. :green:

In my opinion, different bore:stroke ratios should have almost the same engine characteristics (torque, power) if everything else stays the same, but usually it doesn't. For a given cyl capacity, a bigger bore allows bigger valves and/or less valve shielding by the cyl wall, plus wider valve angle. If the same heads are used, any advantage seems to be limited to a lower piston speed (less friction, but a heavier piston and longer rods) and less rotational inertia of the crank.
 

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You are so right, can't argue with dead people. It's at times like this that I wish I had gotten some formal technical training in this field. At the time I thought there wasn't much of a future in it!

Anyway, back to topic.
I would love to run the following test to see the difference in HP and Torque curves of two very similar engines that run very differently. (This of course acknowledging the HP/Torque croossover at 5250 RPM).

Take a Chevy small block 302 cu.in. engine (Z28) which basically has the stroke of a 283 and a bore of a 327 and place it next to a 307 which has the stroke of a 327 and bore of a 283.

I found by 'seat of the pants' testing that although the 307 seemed to have a fair amount of torque it was an absolute dog next to the performance of the 302. What a screamer. The next best thing to the 302 that I found was the 327. A very fun engine!

DJ
 

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Discussion Starter #3
So what are the specs for the 302 vs 307? What differences are there in valves / lift / cam timing / compression / head design? Is there anything that can give a hint at why they perform so differently?

I would expect the 307 would have a lower rev-limit due to mechanical stress limits, and therefore to have been designed "around this characteristic", ie better to build it for better bottom-end performance if it can't rev as high anyway.
 

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Better flowing heads and cam profile for the 302 from the factory. I have seen some 307's with head and cam upgrades etc... and they just didn't rev as easily as the 302.
Nonscientific observation of course but nobody in my crowd would go near a 307, especially for drag racing..

It would be fun to prep both engine identically, heads, cams and compression ratios, just to see the difference in curves.

DJ
 

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i have one "fun" term for you guys.


TURBO

Ed-
 
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