Any test results from reducing crank journal size alone?

[BradH]

Anyone have, or know of, testing data that focused on improvements from reduction in rod journal size? I know there has been a trend towards reducing the rod journal size, (e.g. I could swap out the same length rods for one of my builds and reduce the journal size from 2.375" ID to 2.200" ID while keeping the same 3.75" stroke), but what gains have been seen from taking this approach? Thanks. - Brad

[ProPower engines]

I doubt you would see a gain by just changing the journal size alone. It would have to be considered as part of the complete package when doing the build.

Most cranks with small journal sizes are in need of less bobweight because the reduction in throw weight has been designed into the crank by the manufacture. That said most times its easier to get some better rod options as far as length goes with smaller sizing of the journals thus power increases could be had.
But changing to just the smaller size I don't believe it would make more power to warrant that single change

JMO

[Walter R. Malik]

The smaller the journal with the same bearing clearance will produce less oil flow and throw-off for its size.

[pamotorman]

it reduces friction. some builders even reduce the width of the main bearing inserts to reduce the friction.

[bigjoe1]

I have done things like that years ago, and there was VERY LITTLE ( if any ) difference in power. It is not cost effective in most cases. I myself do use 350 mains instead of 400 mains whenever I have the choice-- I try to look a the BANG FOR THE BUCK wherever I can


JOE SHERMAN RACING

[SchmidtMotorWorks]

If you do it, you need to adjust your counterweight layout to one that is more fitting to a more flexible crank.
In short, making the CWs more opposite of the pins and the end CWs need to be symmetrical.

[Abbottracingheads]

I was told years ago on an A Econo Dragster bbc motor that the reduced bearing sizes in the mains and rods was worth 7 hp through the whole power band.

[bigjoe1]

My results were about the same


JOE SHERMAN RACING

[pamotorman]

I was big with NASCAR restrictor plate engines where 1 HP means a lot at daytona

[barnym17]

For an average bracket build or street build it's picking pepper out of fly poop. But in a restrictive rules environment he who picks the most pepper out of the poop wins.

[engineguyBill]

Reducing crank journal sizes and bearing length will not result in much additional horsepower output. However in an engine combination designed for maximum effort racing it is just one of those small details that will possibly result in a winning combination.

[Walter R. Malik]

Along with being lighter weight ... It has a lot more to do with oil control than friction reduction.

[Kevin Johnson]

http://www.fev.com/fileadmin/user_uploa ... dbyCAE.pdf

Table 1.

[pamotorman]

ford used hollow journals in the 427 NASCAR engine back in the day. the hollow was filled with oil so it is not a free lunch as far as weight goes

[BradH]

I was told years ago on an A Econo Dragster bbc motor that the reduced bearing sizes in the mains and rods was worth 7 hp through the whole power band.

I recall Ron Shaver had said the improvements he'd seen only showed up at high(er) RPM, but he didn't say what sort of gains those were.