Why use chev journals

[70's Looker]

Pros and cons I'm just seeing if I go with 5.5 rods are they needed I kinda get the feeling they are smaller for tossing a stroked crank around the in the case but just never really knew why they used em...

Also while I have you taking a stock crank what's it take to put 912 Porsche rods onto it?

[Geoff]

Hey Kevin, before we can answer we need to know the size of crank you will be using (82mm or larger?) or are you talking stock 69-78mm crank? if so use stock length rods

[Jerome]

There are some fantastically useful threads on thesamba.com concerning this topic... as usual the "Search" button is your best friend.... but the short answer is the clearance issue and a small difference in speed at which the con-rod rotates over the crank surface ( a longer rod also has a similar effect) meaning slightly less friction. After my searching and reading i sought out a set of 5.6 chevy rods and an 84mm crank. From what I've read, if you are OCD enough you will notice the difference between a 5.6 and 5.7 rod on the same cc ( 2L +) engine. the 5.6 will pull a bit harder in the mid upper and the 5.7 a little more grunt down low. If I remember correctly the longer rod accelerates and decelerates the piston at a more even rate due to its length and has shorter dwell times. A short rod accelerates the piston faster and has a longer dwell time at TDC & BDC.

[70's Looker]

I am fighting between 69 And 74mm crank for the cal engine I saw online a 74mm crank with chev journals and didn't get it cause I thought it was something with case trimming I have chev 5.7 rods in the 2332 And when it makes it's way out here I want to go to a 5.5 rod I just don't care to trim out the engine bay blah blah I do not search the samba I find to much shit before I get my answer

[Jerome]

I find to much shit before I get my answer

Thesamba has a really good thread explaining it. Does a much better job than I did, not too hard to find. Another thing with the longer rod is that it has a more linear intake velocity. Doesn't seem like much at first glance, but it is a good consideration in your overall setup. I want a torque monster and so small(ish) valves will do me good there. And in combination with the long rod/stroke combo I'm hoping to have a well setup motor. I've had a motor with mismatched parts before,( cam, crank, intake, exhaust all not thought out) and it didn't perform very well at all. For myself, a little trimming here and there to accommodate a nice street engine is small work.

[Darren]

 Here's a quote from Reher-Morrisons site from David Reher and his thoughts on the subject-

" We also wanted to point out some of the common myths and misconceptions about high-performance motors. For example, I've seen dozens of magazine articles on supposedly "magic" connecting rod ratios. If you believe these stories, you would think that the ratio of the connecting rod length to the crankshaft stroke is vitally important to performance. Well, in my view, the most important thing about a connecting rod is whether or not the bolts are torqued!

If I had to make a list of the ten most important specifications in a racing engine, connecting rod length would rank about fiftieth. Back in the days when Buddy Morrison and I built dozens of small-block Modified motors, we earnestly believed that an engine needed a 1.9:1 rod/stroke ratio. Today every Pro Stock team uses blocks with super-short deck heights, and we couldn't care less about the rod ratio. A short deck height improves the alignment between the intake manifold runners and the cylinder head intake ports, and helps to stabilize the valvetrain. These are much more important considerations than the rod-to-stroke ratio. There's no magic - a rod's function is to connect the piston to the crankshaft. Period."
This is located in the tech article "by the book" if anyone else wants to read the whole thing.