Front Cam Tower Oil Mod - Problem

[importwarrior]

Thanks Tim and Dad great information .

 

 

[Tim_C.]

Okay, I may need to eat my words. LoL! I just looked at a new marnal I've had in a box for about 8 years, and it has the teardrop shaped oil feed hole indentation on the head gasket surface. It also has the 3/16" hole all the way through on the #1 cap. LoL!

So I guess it matters what year the head is, who makes it, etc... Mitsu improved the heads almost every year. The '88/'89 heads had the teardrop, but I'm not sure about the larger oil feed hole to cap #1. Dad said it was necked down to 3/32" on the 'T' head he looked at. It seems that some aftermarket manufacturers made life easier for themselves and just drilled 3/16 all the way through. To be honest, I don't think it matters so much on our heads. I do know that it is a normal practice to reduce hole size not only to add pressure, but to reduce the amount of oil that goes to the top of an engine. Not necessarily the G54B. This is because there is a time that it takes for oil to drain back, and too much up top can starve the bottom end. SBC's have restrictors in the passages for certain applications, to restrict oil to the top.

To better explain my low pressure post above: This is for the main bearing clearance. I've had low pressure on a build that was on the loose end of tolerance. New pump. Still in tolerance, so shops will get it there and call it good, but it is much better to be middle to tight side of tolerance with the mains. This is something we did with the same engine. A new machinist looked at it and didn't like the tolerance. He said the pressure probably wasn't good, and I verified it was like 15 PSI at idle. I had to take apart for other reasons, so he took it tighter, and the warm idle went to 40. This can be the difference between spinning a rod bearing or not at higher rpm.

[importwarrior]

Thanks for the update.

I have seen the larger hole on my old stock head

can tower but many varients on newer heads.

[Dad]

Take light and look closer down in the holes... just sayin

[importwarrior]

here is something i have read about last night.

since our power curve on most stock cars seem to drop off about 5000 RPM or higher like jumping off a cliff.

 

what i have read is the restricted oil flow to the head and lifter cam and rockers, at higher RPM the oil pressure

is not enough to keep the lifter properly pressurized casing them to start to collapse. with out the proper flow

and pressure this causes the hydraulic lifter to collapse and the valves now do not open fully.

 

YES you have great pressure but where is the pressure being tested. before the restriction on the head cam tower?

 

 

 

i like this explanation in this video

 

please check out from 4:15 to 5:55 in the video that is where his theory is about oil restriction in the head.

 

http://youtu.be/5rdolOvBOP4

[ucw458]

here is something i have read about last night.

since our power curve on most stock cars seem to drop off about 5000 RPM or higher like jumping off a cliff.

 

what i have read is the restricted oil flow to the head and lifter cam and rockers, at higher RPM the oil pressure

is not enough to keep the lifter properly pressurized casing them to start to collapse. with out the proper flow

and pressure this causes the hydraulic lifter to collapse and the valves now do not open fully.

 

YES you have great pressure but where is the pressure being tested. before the restriction on the head cam tower?

 

That's what I said.

 

I enlarged my marnal head per indiana's website. I have not noticed any detrimental affects.

 

Where the oiling improvement helps is in the higher RPMs. It keeps the lifters more stable at 5k + rpm.

[importwarrior]

Oh yes.

I reread it.

Thanks.

[Tim_C.]

I looked at 2 sets of cam caps that I saved. OEM cam caps from various heads that I've long since thrown out. I save the caps just in case I need to line bore and put bearings in them. One set has the larger hole, one has the smaller restriction down in it. so both styles came OEM. One factor is the teardrop shaped oil feed hole on the front head stud where the head gasket also has the teardrop shape. In early heads, only the gasket had the teardrop. In later heads (post '87 and marked 'T'), the shape is machined into the head. I think Dad said his 'T' heads both had the restriction hole. I have a 'T' head in storage that I could look at, but I really don't want to go find it, and pull the rocker assembly to take a look. My thoughts are the heads with the teardrop machined in, also have the larger hole, but Dad found differently on his.

Normally, an engineered hole size is what you want to stay with. These engines have an OEM redline of 6K RPM. The OEM valvesprings new will start to float at 5800 or so. The smaller hole will keep the lifters pumped better, given there is sufficient volume. It will provide more pressure than the larger hole. It is a trade off between hole size and pressure. Again, the main bearing clearance has a lot to do with it too. Tighter on tolerance = more pressure.

So unless there is a volume issue, the smaller hole should provide better pump to the lifters. We don't have different pumps to choose from, so improvements / changes should be performed with some DATA to show the difference. Otherwise, there is some risk involved when changing the design in an apparent 'bigger is better' simple math. That isn't always the case, especially with oil passages feeding the top of an engine, so there is always some risk involved, albeit most likely minimal in this case. Like I said before, it is probably fine either way, but I wouldn't jump to drilling it out, just because the head has the smaller hole. And as was mentioned in a recent post, it is difficult to know for sure what the pressure is in the rocker shafts that feed the lifters. It would be fairly easy to drill the firewall end (so you are reading the opposite end of the feed hole) of a shaft for a gauge fitting, and then run the small line out for a test. Then plug the shaft when you are done. That would be very interesting and helpful info.

[ucw458]

The idea that a smaller hole on the inlet to the head increases pressure to the lifters is wrong. Think of it as a garden hose. You kink the hose and it raises upstream pressure while lowering downstream pressure because you lose flow downstream. The holes responsible for the oil pressure in the head are all the oiling points like lifters and rockers. If those clearances are too wide the head loses pressure. If the feed to the head is too small and can't flow the same volume the head oiling points can then you lose pressure.

 

 

The thought that if too much goes to the head you may lose volume to the mains is a valid question. Most of us remove balance shafts so right there you are blocking off 3 bearing oiling points increasing pressure on the rest of the system. I have my head modified per indiana's website so the oil feed to my head is enlarged. I don't have balance shafts. So you can say my head has more oil flow potential. Running 10w30 in the motor I get normal oil pressure readings from my mechanical gauge on the filter housing. If opening up the head was a bad thing I would have seen those gauge readings drop but I didn't.