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Maximum Compression Ratio On Olds 455 - What's Your Problem?

Puking Oil
Gerald Lum; Rolling Hills Estates, CA: I'm running a Melling M55HV oil pump in my 427ci small-block. With Castrol 10W-40 GTX oil, it gets about 50 to 55 psi at a steady 2,700 rpm. When I autocross the car, I get some oil barfing out of my valve cover filters. The oil is coming out of the outside valve covers at high rpm on a skidpad at 1 g. It even blew out my dipstick. I never had that problem with my 355ci iron-block engine at much higher engine speeds with the standard Chevy oil pump using the same valve covers. Should I just replace the high-volume oil pump with the standard Chevy one? Would that solve my problem? I think it's because the Melling M55HV may be putting out too high a volume of oil for my 427 at high rpm on a skidpad and flooding the outside valve cover with too much oil. The oil has nowhere to go except into the breathers on the outside valve covers. I know some racers use a high-neck filter or the Moroso setup in which tubes from both valve covers connect to a single filter to solve that problem. I'm wondering if the HV pump could be flooding the valve covers.

Jeff Smith: It is true that the typical small-block Chevy will tend to push quite a bit of oil into the valve covers under extended rpm. By your description, it appears that the addition of a high-volume (HV) pump will tend to move more oil up into the valve covers, which could easily result in a portion of that oil taking residence inside the breather, creating the barfing (a great adjective by the way) that ends up spraying all over your valve covers and headers. The Moroso solution is really nothing more than a length of tubing (I've used radiator hose) to connect the two valve covers with either a single or multiple breathers. This places the breathers higher, which will prevent the oil from escaping. It also helps to include a vapor separator in either the valve cover or inside the breather stands above the valve covers. These separators will prevent oil from reaching the top of the breathers. At first, it appeared that the high-volume pump was likely the culprit. But engine builder Kenny Duttweiler says most NASCAR engines run with large volumes of oil in the valve covers to help cool the valvesprings. He didn't see anything wrong with retaining the high-volume pump and the amount of oil in the covers. As long as you don't have an oil starvation problem in the corners that would cause the oil pressure to drop (because there's more oil in the valve covers than there is in the pan), it appears that creating a decent breather system would be the best solution. You are correct that changing to a standard-volume pump will reduce the amount of oil pumped to the top of the engine.

However, your comment about the dipstick pushed out is cause for concern about excess crankcase pressure (blow-by). Perhaps the engine does not have sufficient venting. This would cause the dipstick to push out from excessive pressure. It's worth mentioning that excessive crankcase pressure is generally linked to poor ring seal. Once pressure leaks past the rings, it ends up in the crankcase and the rest of the engine and tries to push its way out. It would be best to identify if there are specific cylinders with problems or if all eight holes share a common affliction. The first test is to perform a cylinder leakdown test. A leakdown tester pressurizes the cylinder (with both valves closed) and is fitted with a gauge that will indicate a percentage of leakage. A relatively new engine at operating temperature should deliver a leakage of less than 10 percent. Despite all the claims you will read on the Internet, 8 to 10 percent on a new engine is not all that unusual. What is bad is if you see 30 or 40 percent in one or more cylinders. These numbers are based on testing with the engine at normal operating temperatures. If you test the engine cold, the leakage will be significantly higher. It's possible that all eight cylinders are experiencing difficulties.

I'm assuming this is a relatively new engine, so it's possible that the engine builder mistakenly installed a top compression ring upside down, which would instantly create this situation. If all the rings are inverted, that is the root of the blow-by problem. While this is an easy fix (I would suggest a new set of rings rather than reusing the old rings), it obviously means you have to remove the pistons to repair the problem. At the very least, I would suggest a thorough cleaning of the cylinder walls.

Assuming that the leakdown is higher than acceptable, the solution is time consuming but not difficult to repair. Jeff Latimer at Jim Grubbs Motorsports (JGM) gave me some great insight into aluminum block engines. He said JGM routinely hones all aluminum blocks with torque plates on both sides of the engines along with fully torqued main caps to simulate the stresses these engines experience. He also told me that honing an engine in which only one torque plate was used causes the stones to skip and you will see major shadows on the cylinder wall that indicate the cylinder was not round. This occurs because the cylinder walls have moved as a result of block distortion. Latimer said this is extremely common with aluminum LS engines. Many machine shops do not use dual torque plates because it doubles the investment they must make in tooling for each engine. I'd suggest asking the machine shop its exact procedure for torque plate honing. Let them tell you what they do-don't ask if they use two plates. If you do not know how the machine work was accomplished and the leakage numbers are high, then it would benefit you to completely disassemble the engine and have the cylinders honed with this procedure. Latimer also mentioned that JGM uses the same head gaskets that will be used in the engine and the same fasteners (studs or bolts) if possible. This helps to ensure that the engine is stressed as closely as possible to the way it will run in the car. We've heard of shops that will even bolt engine plates and motor mounts to the block.

More Info
Jim Grubbs Motorsports (JGM)
Valencia, CA
661/257-0101

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