What are the main pros and cons of destroking? Other than the fact that the power would be dispersed over a much broader band ,I don't see many other benefits. I know you can turn more rpms, but that is necessary to make the same amout of power as in a non-stroked engine. Anybody every destroked a 400 small block??
to destroke or not to destroke
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I found thid article on a destroked 400 interesting. http://www.airflowresearch.com/articles/article03/A3-P1.jpg
Sean James
Sean James
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lighter rotating assembly may also allow you to rev up more quickly. Also, the rod stroke changes as outlined in the article. However, a shorter R/S ratio will pump more air by means of quicker piston accelleration, which should make for a slightly higher volumetric efficiency.
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some people have mentioned having bad experiences dealing with www.speedomotive.com but they have a really neat destroke kit for a 400 block that uses a 3 & 9/16'' stroke crank (3.562'') and a longer rod to yeild a rod stroke ratio almost identical to a 327 and it displaces 386 cubes. That ought to rev pretty well and still have some grunt on the bottom end.
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I read an article awhile back in one of the one-off mags put out by peterson publishing that talked about the best small blocks and went a bit into the rod/stroke ratio debate. They said that a ratio like the old 302 Z28 motor was well suited to constant high-rpm because the roughly 1.9:1 ratio would keep the stress on the rotating assembly down by reducing instant accelleration of the piston and reduce side loading of the rings against the bore.
The article claimed that for an accelleration engine, a 1.8:1 ratio was about optimal. They also said that many high-rpm race endurance motors run 2:1 ratios and higher if I remember right.
As far as it effects quench design and detonation resistance, I imagine there is a point of diminishing return, but I couldn't say where it is. The article sited from the AFR website is good testament to the advantages of a 1.9:1 ratio though. If it could run 11:1 compression on 87 octane, you could probably get away with a point more on 93 pump gas.
The reduced piston accelleration theoretically will decrease volumetric efficiency however, as a faster accelleration should create a more efficient pump. Also, a long rod/short stroke combination will make it more difficult to make power in that the rod will have less leverage over the crankshaft. It is kind of like trying to push open a heavy door from right next to the hinge (short stroke) as opposed to at the outer edge of the door (long stroke). It is easier to push the door open from farther from the fulcrum.
The article claimed that for an accelleration engine, a 1.8:1 ratio was about optimal. They also said that many high-rpm race endurance motors run 2:1 ratios and higher if I remember right.
As far as it effects quench design and detonation resistance, I imagine there is a point of diminishing return, but I couldn't say where it is. The article sited from the AFR website is good testament to the advantages of a 1.9:1 ratio though. If it could run 11:1 compression on 87 octane, you could probably get away with a point more on 93 pump gas.
The reduced piston accelleration theoretically will decrease volumetric efficiency however, as a faster accelleration should create a more efficient pump. Also, a long rod/short stroke combination will make it more difficult to make power in that the rod will have less leverage over the crankshaft. It is kind of like trying to push open a heavy door from right next to the hinge (short stroke) as opposed to at the outer edge of the door (long stroke). It is easier to push the door open from farther from the fulcrum.
Yeah, I read over some of there articles on AFR's site the other day. It sounded pretty promising if I could douplicate their results in some form. As for your other input, thanx it really makes sense (your little analogy with the door). It explains why higher rmps are neccesary to make the larger amounts of power. I don't know if I will find the optimum ratio, but I think I'll stay in the hunt. Thanx again.
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