More Thoughts Re Budget

Wow. I thought I had a good idea of what I would be spending.

Not a clue.

I repeat, “I did not have a clue”

I was planning on forking out about $1,000. Well. . .I am about two thirds of the way through pricing out the parts list and I think I’m already over $2,000. The truth is that most of this is just idle circling around until I can get my hands on the necessary information for determining what the engine needs to give me the performance I want. Carburetors, crankshafts, connecting rods, pistons, oil pumps. . .they are all fun but the source of the engines power, or lack thereof, is the cylinder heads, more on that later.

Builder

Connecting Rod to Stroke Ratios

I spent some time, in the last post, discussing rod-to-stroke ratios but never actually looked at them. So here is a quickie.

First, rod-to-stroke ratios are determined by dividing the rod length by the stroke length.

For example, the stock 350 connecting rod is 5.7” from center to center. Rod lengths are determined by measuring the distance between the center of the big end hole and the small end hole. The stroke for a stock 350 is 3.480”.

We then compute the ratio as follows:

5.7”
-------- = 1.64
3.480”

1.64 is the rod-to-stroke ratio.

I have yet to see a reason for not putting the longest rods you can in an engine. The longest length you “can” fit depends on the purpose of the engine. If you stretch the rod lengths too far then you get troubles with the piston. As you increase rod length you have to decrease compression height (compression height [or distance] is the distance from the center of the wrist pin to the top pf the piston*). As you decrease compression height you begin crowding the rings and that can lead to reliability issues. There are various tricks to reducing compression height, like using a smaller diameter wrist pin, but these tricks are both expensive and relatively short lived. So for me the longest rods I “can” fit are with pistons with compression heights that permit reliability and a long service life. For the purposes of this evaluation I’m choosing (somewhat arbitrarily) 1.2” for the minimum compression height. Further research will determine what my true minimum is.

Back to rod-stroke ratios. All of the previous to say that I am presently trying to put the longest rods possible in the motor and want to see how these ratios look compared to each other.

Stroke	3.480”	3.750”	4.000”
Max Rod Length	6.08”	5.95”	5.82”
Rod-Stoke Ratio	1.747	1.587	1.455

It is ironic that as the stroke increases, and you need a longer rod to maintain rod-stroke ratio, the maximum rod length decreases.

Well, I don’t know what to do with these numbers but I know I don’t like the ratio for the 4.000” stroke.

More study is needed

Builder

* This isn’t strictly true with domed pistons but if you cut the dome off so the piston was flat, then you would have the compression height.

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)

It looks like I am back. . .for now

Well, it looks like I have access to blogger.com again. I don't know how long it will last but it is here for now.

I have been writing in the mean time and will start posting from what I have written. It is kind of strange, or rather it feels kind of strange writing to nobody but it does feel good to write down what I have been thinking.

So enjoy the following.

Builder

Interuption

I have not been able to load this page from where I live so I will soon be posting a lot at once.

Builder