Looking at strokes

This has turned into a composite of several smaller posts.

With regard to Project #001, I’ve been thinking about fuel efficiency. I will have to check this out more thoroughly but it seems to be that the longer the stroke, the better. As best as I can understand it seems that this would mean that the pressure energy developed would have more leverage on the crankshaft. More leverage means less pressure is required for the same torque (force of twist). Less pressure is less air/fuel mixture. Less air/fuel mixture means less fuel. And less fuel means better mileage.

As a result I am seriously beginning to consider using a 4.000” stroke. For those of you reading this that are not familiar with SB Chevs this is a LONG stroke. In fact I believe that you can’t use a bigger stroke in a stock block or else the crank and rods hit the cam.

Here is a displacement table. Numbers are CID (Stock displacements in bold)

Block stock bore (over bore)	3.480” stroke Stock 350 crank	3.750” stroke Stock 400 crank	4.000” stroke ** Stroker!!
350 4.000” (4.030)	349.8 (355.1)	376.9 (382.6*)	402.1 (408.1)
400 4.125” (4.155)	372 (377.4)	400.9 (406.7)	427.6 (433.8)

* This is usually referred to as a 383 stroker motor.

** Anything in this column is a stroker motor!

4.000” stroke is long and it would require some block modification to fit. It also gives a rod length to stroke ratio that is lower than the 3.480” and 3.750” strokes and I don’t like that but I think it is still serviceable. Hell, lots of people are running these strokers so I KNOW that it is serviceable. The question is how does this lower ratio effect efficiency and service life?

Let’s also look at percentage of increase for the strokes

Crank Stroke	3.480”	3.750”	4.000”
Percentage increase over stock 350 crank	0%	7.76%	14.94%

Now that is interesting. When I look at the percentages it looks very different from just looking at absolute number increases. On the one hand a 3.750” crank is over a ¼” longer than the 3.480” crank. This seems like a large increase. On the other hand it is only 7.76% larger. Hardly insignificant but it doesn’t sound as impressive as ¼”. I find the 4.000” crank to be a different story. It is over ½” longer and almost 15% longer. Both these numbers are significant.

Of course this is all just number crunching without experience. For Project #001 the two issues are the influences of these strokes on durability and fuel efficiency. Adequate torque can be accomplished with a stock dimensioned 350. This means that I am looking for a way to increase efficiency.

I have found an excellent forum

http://speedtalk.com/

I have about 500-600 papers to grade but when I am done I will be devoting myself to this forum and see what I find out about the reliability of the 4.000" stroke.

Builder

More to come (maybe)