[ho428]

I've seen grooves cut into the main bearing saddle of other brands, but I don't recall seeing it on a Pontiac block.
Granted I don't get to see that many bare blocks, but is it a mod that's done to our blocks?
I'd assume you'd still put a couple extra holes in the bearing.

[Tom Vaught]

Tony B does it to the fast Pontiac Blocks he builds. A groove that allows additional oil a bit farther down on the bearing diameter as well as the normal location.

Tom V.

[Tiger Paw]

This mod allows for pressurized oil for a full 120 degrees of crank rotation to the rod bearings. You can drill several smaller holes or 2 larger similar to original center hole at the end of groove in the main housing. Typically done on race only engines, but has found its way into some production engines.

[Half-Inch Stud]

BAD idea, BAD practice, goes against the principals of bearing float pressures, bearing clearances, and fights bearing crush (a precious non-commodity)

Stop it.

Can somebody slap the Block groove cutter for me?



Just groove the bearing shell frontside, or if you are soooo "thaaat" then do it to the bearing backshell.

[Half-Inch Stud]

Slap, slap slap.

[Tiger Paw]

I've seen it used in hundreds of NASCAR engines. Not an exaggeration.

[taff2]

What depth and width of groove are we talking about?

[Half-Inch Stud]

Open to understand; what is done exactly.

PMD grooved the Main Lowers in the 59- early 60's.

We all know about fully grooved (groove too big!?), and 3/4 groove (seems just right).

I have to ask what is better about block saddle grooves and two bearing shell holes, vs a properly grooved bearing? Ultimatley; why not implement the whole thing into the bearing shell?

[Tom Vaught]

Originally Posted by Half-Inch Stud

BAD idea, BAD practice, goes against the principals of bearing float pressures, bearing clearances, and fights bearing crush (a precious non-commodity)

Stop it.

Can somebody slap the Block groove cutter for me?



Just groove the bearing shell frontside, or if you are soooo "thaaat" then do it to the bearing backshell.

I used to think that too, HIS, until we built a Bearing Test Stand (about 10 years ago) and did a lot of bearing feed location testing at work. The concept does work and does have a lot of benefits. We are only talking about adding 15-20 degrees of groove at the 3:00 position of the complete 360 degree circle. We are NOT talking grooved lower bearings.

Send me a pm and I will explain how it works (for you).

Tom V.

[RAIV-Z]

A few pics of the main saddle mod done by BES on a IA-II iron block and an oil pressure distribution diagram posted originally by Tom in my TT-RA-V build thread.

[Tiger Paw]

The groove was CNC machined roughly 5mm in width and depth centered behind the upper bearing shell. The groove is roughly 120 degrees of the 180 available. I'm sure the housing was machined to the min spec for bore diameter thereby having the max allowable crush on the bearing. We typically would very very lightly file the end of the saddle so prevent the parting line from scraping the back side of the bearing. I'm talking just enough to remove the sharp edge, very very very very lightly!
Holes are drilled into the slot on bearing face to match the width of the machined grooves matching the end of the machined slot.

These were the best of the best race prepped engines and not needed on street strip apps.

[Half-Inch Stud]

Tiger-Paw, RAIV-Z, Tom Vaught,

Thanks for the Clarity, and extent. I'd be getting it now. Yet let's be clear about the cut; appears to be ahead of the Feedhole, not after the feedhole. Right?

As a stubborn hack, cannot the desired mod be best implemented, with lower risk in the Upper shell?, for long-Endurance Street-Strip-road-racing builds?

My Spare 455 block & forged Crank are awaiting Assy, and well maybe something gets applied.


Ans surely these things require craftsmanship, and careful edge breaking, and very careful dress.

[Tom Vaught]

The feed groove in the block is confusing HIS but the crank rotates clockwise and the mod is adding more oil on that downward side of the bearing shell.

You need a given clearance for the oil to get out and remove heat from the system.
The added oil allows some cooling oil to escape but still provided more oil to the bearing for
hydrodynamic support of the crank without it touching the bearing under high load.
Merry Christmas HIS.

Tom V.

[Half-Inch Stud]

Okay.

Went to garage and had to verify the Bearing tab (Post 10 - 2nd photo) does correspond to 3:00, or oil pressure feed near 3:00. The mod represents a 2nd feed, timed AFTER the factory feed at high noon.

Seems much more harmless, and potentially helpful then my earlier reading comprehension allowed.

Geez, I'd practice that on the UPPER bearing shells before cutting the block(s) for applications where grime might actually accumulate on the engine exterior.
But then a real Racer would cut the block "once" and renew with unmodified bearings more easily, more reliably.


How's about the babbit Cam bearings? .....already have a few hole in the stock cam bearings.

[Tiger Paw]

We grooved both directions from the oil hole. Undoubtedly Tony builds quality engines as well. The extra volume of oil flows away heat as Tom says. So needed volume is why we used block grooves vs bearing grooves.
I would groove can bearing shell however and oil upstream of oil hole on those.

[Tom Vaught]

Originally Posted by Half-Inch Stud

Okay.

Went to garage and had to verify the Bearing tab (Post 10 - 2nd photo) does correspond to 3:00, or oil pressure feed near 3:00. The mod represents a 2nd feed, timed AFTER the factory feed at high noon.

Seems much more harmless, and potentially helpful then my earlier reading comprehension allowed.

Geez, I'd practice that on the UPPER bearing shells before cutting the block(s) for applications where grime might actually accumulate on the engine exterior.
But then a real Racer would cut the block "once" and renew with unmodified bearings more easily, more reliably.


How's about the babbit Cam bearings? .....already have a few hole in the stock cam bearings.

Some machine a small groove on the back side of the cam bearing that feeds the other holes with more pressurized oil to help support the cam in that area vs resorting to needle bearing cam bearings.

Tom V.

[Tom Vaught]

Originally Posted by Tom Vaught

I used to think that too, HIS, until we built a Bearing Test Stand (about 10 years ago) and did a lot of bearing feed location testing at work.
Tom V.

One of my very high level bosses gave me the name "The Rig King" as I designed and had built a lot of test rigs (which gave us real world data to compare with the 'Electron Boys' analytical tools). Close to 20 rigs over 39 years. My biggest rig was the installation of a dedicated Ford Turbocharger Test Stand in Dearborn Michigan.

I like real data vs opinions. A different boss once said, "One piece of data is worth 1000 opinions".

Tom V.

[Skip Fix]

This mod is also shown in one of the GM published Chevy high performance engine books.

[taff2]

Well, I've learnt something today! Thanks.

[taff2]

Skip,do you have the names of those GM Chevy hi po books?