TOPIC:

I don't know if the lower-end getting oil first is the right way to look at it. The pump feeds the main horizontal gallery, from there it goes up and down. Pressure up top is determined by the restriction from cam bearing oil clearance. Pressure down below is determined by the oil orifice holes in the bearing outer races. Volume to both is determined by the size and configuration of the oil passages.

I want to accurately compensate for the HD studs reduction of oil flow up top, bring it back to OEM, without over compensating. If you increase too much up top, you decrease down below at the same time. That could mean insufficient oil at the crank/trans bearings, and/or too much oil up top that can't drain down from the head to the pan efficiently.

Here's a really bad sketch showing OEM, OEM w/ oversized studs, and enlarged head hole ID w/ oversized studs. The head hole is enlarged 1mm to equal the OEM oil passage area past the HD stud in the head. The only difference is we lose the step-down from larger passage in the block than the head.

A guy on the physics forum said the HD studs in the OEM head hole reduces oil flow nearly 50%, and enlarging the head hole 1mm compensates for the 1.4mm larger HD studs (equal passage area to OEM). He also said losing the step-down from larger hole in the block to smaller hole in the head will also have an effect on flow. I'm waiting to hear exactly what that difference is.

What does APE suggest?
Steve

Don't touch it because they haven't seen any problems after all these years.

Here's what mechanical engineers are saying:

"Head Cross Sectional Area for Oil Flow:

[(hole radius)^2-(stud radius)^2] x Pi

OEM:
(5.4)^2-(4)^2 = 29.16-16 = 13.2xPi = 41.3sq.mm. (100% of design)

OEM w/HD stud:
(5.4)^2-(4.7)^2 = 29.16-22.09 = 7.07xPi = 22.2sq.mm. (54% of design)

Modified w/ HD stud:
(5.9)^2-(4.7)^2 = 34.81-22.09 = 12.72xPi = 39.96sq.mm. (98% of design)

Assuming there is enough structural material in the head, I would go with the 11.8mm enlarged head hole."

Sounds good but I wouldn't drill all the way through.
Steve

Some Z-bikes here in Germany using external oil lines to the cylinder head.

Michael

Using HD studs you only need to open out the blocks 2 rear outer stud holes to 12mm.
This is because the stud holes in SOME barrel castings taper in from each end giving a restricted flow halfway up the stud.
It doesn't matter about over compensating on the size of the oil feeds as it is the hole in the cam bearing shells that govern the flow.

zed1015 wrote: Using HD studs you only need to open out the blocks 2 rear outer stud holes to 12mm.
This is because the stud holes in SOME barrel castings taper in from each end giving a restricted flow halfway up the stud.
It doesn't matter about over compensating on the size of the oil feeds as it is the hole in the cam bearing shells that govern the flow.

Drilling out the block will have little or no effect. The stud holes in the head are 1mm smaller diameter. That's where 46% of flow is lost by the oversized studs.

VTEC wrote:

zed1015 wrote: Using HD studs you only need to open out the blocks 2 rear outer stud holes to 12mm.
This is because the stud holes in SOME barrel castings taper in from each end giving a restricted flow halfway up the stud.
It doesn't matter about over compensating on the size of the oil feeds as it is the hole in the cam bearing shells that govern the flow.

Drilling out the block will have little or no effect. The stud holes in the head are 1mm smaller diameter. That's where 46% of flow is lost by the oversized studs.

Yes! I know that. I have been doing this for over 30 years.
What I am saying is that you only need to open out the 2 rear outer block stud holes not all 4.
It's only the 2 rear outers that act as oil galleries and doing the front 2 is pointless.
You also don't need to go all the way through on the head just the first 10mm or so up from the gasket face until you meet the tangential drilling for the inlet cam and the cross drilling for the exhaust side.

K. yes, that makes sense. Thought you meant drill the block only.

Have you ever used the cylinder head o-ring springs? I think they were only used on P bikes.

What do you mean by 'O' ring springs ?