427 engine (part 2) - RHS block

[Rich Z]

Well, there was a break in the storms on the radar and the rain in the front I was watching passed right by us with just a light sprinkle, so I decided to run the car out for a bit. Didn't get very far, just made a short loop of about 11 miles, but better than nothing I guess. I wanted to drive longer, but I could see some heavy clouds moving in from the northwest, so I figured I had better head on back. I JUST got the car back into the garage when the rain started. Quite heavy this time. So I guess that freshly graded road is going to get messed up again.

I was monitoring the oil pressure a bit since Shane had commented on it when he had the car, as did Aaron when it was in his shop. It was around 40 psi when I left the garage, which seemed OK to me. But by the time I got back from that short drive, here's what I saw:

• Coolant temp = 208 degrees
• Oil temp = 226 degrees
• Oil pressure = 23 psi

Oil in the car is Brad-Penn SAE 10w30.

I've sent those figures to Bryan at LME to see what he thinks.

But what actually determines oil pressure? I know the oil pump is pushing the oil out of it, but what is the oil being forced against in order to generate a pressure reading? Aaron put those big lines on both of the valve covers going to a sort of catch can with an air filter element on it, so does vapor pressure in the block from ignition byproducts contribute to the oil pressure reading? And I've got that PCV line running to another catch can between the valley cover and the throttle body. And what about the oil being pumped to the turbos? Does that affect the crankcase oil pressure? Are the oil lines running too close to the headers and heating up the oil on it's trip to and from the turbos?

Just trying to figure out what I am actually seeing....

Maybe going to a 40 weight oil might help?

In any event, the car drives really well. The clutch feels just like stock and I have no trouble at all moving from a dead stop or shifting gears. No rattles or odd noises at all. That MGW shifter is pretty stiff, but it might just be my feeble right elbow complaining about it.

[navy2kcoupe]

The major cause of low oil pressure, aside from the pump, is increased bearing clearances.
Rod, main, and camshaft bearings all contribute to the pressure. The tighter the clearance,
the higher the pressure will be. Are you reading the pressure with a mechanical oil pressure
gauge, or are you getting it from the hud or dic? Those 2 are not as accurate as a
mechanical gauge, and should be compared with a mechanical gauge to see if there
are any inconsistencies. The filter might be a contributor as well
Andy

[Rich Z]

Originally Posted by navy2kcoupe

The major cause of low oil pressure, aside from the pump, is increased bearing clearances.
Rod, main, and camshaft bearings all contribute to the pressure. The tighter the clearance,
the higher the pressure will be. Are you reading the pressure with a mechanical oil pressure
gauge, or are you getting it from the hud or dic? Those 2 are not as accurate as a
mechanical gauge, and should be compared with a mechanical gauge to see if there
are any inconsistencies. The filter might be a contributor as well
Andy

I used both the gauge on my dash as well as the DIC display. I'm assuming they are both reading the same signal.

[navy2kcoupe]

Yep! Both come from the oil pressure sender that's either under the cowl, or relocated
somewhere else. Mine does the same thing. Starts out at about 40# then drops after the
engine warms up. I really don't know how accurate those senders are.
Andy

[Rich Z]

Well, I've been looking around on anything I can find concerning oil pressure, and it mostly seems related to the clearances on the bearings. It looks like my main crank bearings having .0025 inches is in the high side for an aluminum block, but most people say being on the loose side is better than being on the tight side. The negative drawback is lower oil pressure readings.

I guess what is important is whether oil is getting where it needs to be. Lower pressure can actually mean higher flow, which isn't a bad thing. Pressure is actually resistance against flow. The oil pump shown on the engine spec sheet is a Melling HP ported pump, pn #10295, which from what I am reading is designed specifically for higher flow in engines with wider bearing clearances. Which seems to be exactly what I have here.

So far the direct feedback I have gotten from some engine builders is that the oil pressure is OK.

Bryan at LME got back to me and suggested going to a heavier weight oil, specifically Joe Gibbs 01607 15W-50. Since he is the guy who built the engine, then he's pretty high on the totem pole as to who I think I should listen to. BUT, I need to check into this. I think this is a RACING oil, so I'm not sure Bryan realizes this engine is in a STREET car. From what I understand there are some differences in the two types of oil that I need to become more versed on before making a decision. I thought racing oils did not have detergents in it to help keep the inside of the engine clean. But it's not like I am going to let the engine go for long stretches without changing the oil.

Ah well, guess I just need to keep filling up my head with car and engine topics.... My cup runneth over....

[navy2kcoupe]

I'm not sure if they make a multi viscosity engine oil WITHOUT detergents.
I always thought that the straight weight oils were the only ones to come in a non-detergent
formula, but I'll probably be proven wrong on this one as well........
Andy

[Rich Z]

Originally Posted by navy2kcoupe

I'm not sure if they make a multi viscosity engine oil WITHOUT detergents.
I always thought that the straight weight oils were the only ones to come in a non-detergent
formula, but I'll probably be proven wrong on this one as well........
Andy

Heck, I don't know..... They all seem to have a healthy dose of snake oil in their advertising copy as well........

[Rich Z]

Took the car out for a drive of 33 miles today. And I set the DIC to display the oil pressure so I could monitor it the entire trip. I also toggled to the oil temperature every now and again as well.

Started up cold (well 85 degrees, since that was the temp inside the garage overnight) the oil pressure was at 49 psi. While driving out of the driveway it was hitting 50 psi. By the time I got up to Tallahassee, oil temp was 208 degrees and oil pressure was running 35 psi at around 1500 rpm. Sitting at idle it was around 26 psi with what looked like 950 rpm. Stayed pretty much stable on the drive back home, but idle oil pressure did drop down to 23 psi while sitting out in front of the garage before pulling it in. I could see the oil pressure keeping track with engine speed pretty easily and uniformly while driving, so that seemed normal to me.

So obviously the oil (Brad-Penn SAE 10W-30) thins out substantially when hot. Also, I have read that aluminum blocks will expand quite a bit when hot, so that makes bearing clearances wider when the engine is hot, which also contributes to lower oil pressure. This certainly seems to be the case here. But the engine builders I talked to said that as long as I have at least 10 psi of oil pressure per 1,000 rpm of engine speed, then there is nothing to worry about. They also said they would much prefer building an engine too loose than too tight. Especially when it can produce substantial amounts of power. As one said "If you make the crank bearings loose, no one knows. If you make them tight, everyone knows." So I'm guessing tight clearances can be a bad thing on those crank and rod bearings.

So anyway, I feel like there is nothing really to worry about with the oil pressure. I'm still going to try that 15W-50 weight oil to see what it does to the oil pressure, but if I hadn't already ordered it, I probably wouldn't bother with it at all.

Oh, btw, I did check with STS to make sure that heavier oil would be OK with the turbos and scavenge pump. I was told there would be no problems whatsoever.

Anyway, the clutch felt good and shifting was without any issues. But I did have a bit of a scare at a stop light when I distinctly smelled gasoline. I started sweating it thinking I wished I had thrown a fire extinguisher into the trunk before I left. But it must have been someone else, because after pulling away from the light, I didn't smell it again. Whew...... I guess I'm going to be pretty paranoid about stuff like this for a while yet.

I will say this about the car.... It doesn't take much pressure on the gas pedal to get it to M-O-V-E........

[shakedown067]

The car is actually accumulating miles! Awesome. Who knew you'd have to take it to a dealership to get it in running order?

After a bad coolant leak on my truck (2 freeze plugs blew), it took a couple of years before I quit freaking out every time I smelled coolant when stopped at a light (which is amazingly often). I'm pretty sure I used to be able to smell someone open a coolant jug at least 5 houses down. If your lawn mower runs just a tad rich, you'll know it for a while, but you will get over it sooner than one might think.

[craig04c5]

I am not surprised it took a dealership to fix it. If they have a good certified tech it can make all the difference. I don't know if the other people that worked on the car were certified and had as much experience. Your dealership tech nailed it with the driveshaft being the issue and did the correct thing advising you use a stock setup.
We have a Master Tech at the local dealership here in Stuart Fl that loves working on Corvettes. I was having GMPP warranty work done a few years back to replace a bad slave and I asked how much to put an LS7 clutch and PP in since there would be no labor charge while they were already in there. The Tech said GM does not yet recommend this setup (this was when people were just starting to put the LS7 clutch in C5's) and said the LS6 upgrade would do fine for my mostly stock LS1 C5. I was thinking the 4:10's might need a better clutch but he said I would be fine. Anyway, the LS6 clutch has been flawless and I could not be happier. We all now know the LS7 will work just fine as long as you keep the LS1 slave. I always ask if he will be working on my car before I take it in. The service writer and I have a good relationship. I always bring him a gift card at Christmas time.
Glad it seems to be working well for you Rich. Was following your thread on the CF.