I replaced the oil pan and pump on my 74 Vette last weekend. It has a 396 big block motor. The Milodon 7 quart pan was hanging too low for comfort. I put a new GM heavy-duty LS-7 oil pump (part # 3969870) that was the correct match for the new 5 quart Corvette LS-7 pan. Everything went well. After initial start up the oil pressure seemed to jump right to 65 or 70 and then stayed there. I drove it around the block one time and it seemed to stay around that level even at idle. The oil was reading around thirty to forty at idle before changing the pump. I can't drive it much more then that becuse the car is still in progress and not inspected. Is this O.K. or is something wrong here? Any thoughts would be appreciated.

 

Sounds like the pump you got is a high volume pump? Personally, I don't like that kind of pressure @ idle. It puts a much higher load on the cam gear. My 454 runs about 40 PSI cold idle, going down to about 30 PSI hot idle. It maxes at 65-70 PSI at high rpm. This is with a standard volume melling pump.

 

High volume pump is OK, but your pressure relief spring is too stiff. Take out any shims, change the spring, or cut a pinch off until your pressure is back to normal. Excessive pressure is just heating up your oil, sacrificing power, will wear out your pump prematurely, and is opening your filter bypass even more, resulting in less fitration time. As long as you have about 10-12psi per 1000rpm, you're fine. I like about 25 at idle.

 

Sorry to disagree, but if he weakens the spring the pressure will be too low at high rpm.

 

I would also do any testing with a professional gauge

My '73 SB reads about 15 pounds at idle and around 35 at 4,000+ RPM which scared the hell out of me when I first noticed it
I connected a SUN pro gauge at the source and it read around 30# at idle and 60# at higher RPM.

I do have a new gauge and tube but havnt had had a chance to install it yet but I know that when my stock guage reads 35#'s It's really around 60#'s

 

My 72 454 runs about 70psi when cold and then drops down to about 30-40psi when warm.

My engine was rebuilt about 3 years ago and I doubt I have over 1,000 miles on it. I don't remember what oil pump I put in it (a friend rebuilt it for me). i think we used a regular oil pump (not high volume).

 

I don't believe I said anything about compromising proper oil delivery.

Excessive pressure is a problem with several downsides which should be delt with, what ever measures are necessary to do so (even if that means changing the pump to a different unit), as long as adequate pressure and supply are maintained. It may be a PITA, but doing so will result in better performance, less heat to shed, and longer component life.

 

The LS-7 pump/pan assy is one of the best ever built by GM. It just works well. Not sure if your 396 needs it..but it can't hurt anything.

Did you use same weight oil? How long did it really run?

The original LS-7 pump is sort of between a stock and HV I believe as far as gear length I think..but they may have just gone to making it a regular HV unit by now.

I would expect your idle pressure to the 45-50 psi range when it's all warmed up (assuming regular hyd lifters here?) depending on oil viscocity. You might be able to drop oil weight some to help.

I've run lots of oil pump combos over the years. One of the best has been a stock pump with the High pressure spring in it....but clearances need to be pretty tight to keep idle oil pressure up. A HV does a great job keeping it up at low speeds...which I personally like. I have solid roller lifters and like all the oil pressure I can get to keep a lot of oil moving through their orifices to the axles at low speeds.

I've yet to ever wear out a dist gear I don't think. And I've used HV pumps on daily driven street cars for years. I even ran a bronze dist gear on the street for several years and it still looks new.

I would run it long enough to make sur eoil is good and hot and see what it does at idle. It should drop back some..if it never moves..then possibly the relief piston is sticking in the pump. Did anyone weld the pickup on by any chance?


JIM

 

Submerged Moroso pressure balanced HV pump...

 

You could also simply try a lower viscosity oil. If you are running 20w50, then 10W40 or perhaps even 5W30 might give you what you want, reasonable idle pressure with good high rpm pressure. Its easy and worth a try without costing you a bunch of time or money. Sometimes the simple solutions are the best.

Though you could start up a whole debate about this because the average hot rodder/racer doesn't think of it in these terms, the real reason for different viscosities is to alter oil pressure. A lot of people are under the impression that thicker oil gives better protection. The truth is that viscosity has nothing to do with oil film strength. And oil film strength is what protects an engine, not its thickness. Its that film strength that keeps metal from touching metal. And film strength is determined by the oil's base stock and its additives. You can see this when looking at oil load test data. You'll find that there is no difference in the point of galling, when comparing different viscosities. So we're right back to viscosity controlling oil pressure.

Case in point is hardcore racers who use the watery thin 0W? Royal Purple Racing Oil. It can barely hold any pressure, yet after a lot of hard racing, the engine internals look brand new. Thinner oils can be your friend, less hp loss, better cold start-up flow for reduced wear, and the increased flow at all temps also carries away heat from the main and rod bearings better. Something to consider.

 

Well stated. Bear in mind that one fly in the (thin) ointment could possibly be increased consumption, especially with poor seals and worn guides. Thoughts??

So the above begs the obvious question: What oil are you using??

 

Well, I'm not done building the 540 big block for my old hotrod yet. Mock-up is done, but still doing some final prep to things before actually starting final assembly. But I have every intention of using 5W30 Royal Purple XPR Racing Oil (yeah, the high buck stuff), assuming of course that the oil pressure is in fact reasonable with my particular setup. I believe it will be, from comparing notes with buddies who have similar clearances to what I'm setup at.

BTW, Joe Sherman (yeah, THE Joe Sherman)told me that he found an additional 30 hp in a 600 hp SBC, by switching from Valvoline 20W50 dino Racing Oil to 5W30 Royal Purple Racing Oil (all their oil is full synthetic). But from what buddies have told me, while there are definite benefits to using their street oil as well, you won't really see a noticeable performance gain with it. So, I guess you get what you pay for. If you want the additional hp, you've got to pony up the extra bucks for their racing stuff. 540's are not budget builds, so why cheap out now, right?

I can say that I am currently running 5W30 Royal Purple street oil, that I get at Pep Boys, in two of my late model cars. No smoke, no leaks, no consumption, no problem. Yeah, you could say that I've become a believer in Royal Purple oil, after doing extensive in-depth research.

Along the way, on a lighter note, I had read on some Forums that Royal Purple (street) oil gave a smoother idle and faster idle. I thought, yeah sure, whatever you say. But Geez, laugh if you will, like I did at them, but I did in fact observe in my own car a smoother idle, and you guessed it, about 100 rpm faster idle too. Go figure, I never would have believed it if I hadn't seen it myself, with my own eyes, in my own car. Sure there are some other fine oils out there, but for my money, you just can't beat the purple stuff. Try it you'll like it.

Parting comments on viscosity:
The best viscosity to run in any given engine, is the thinnest oil that will provide the desired oil pressure. Any thicker than that is counterproductive to both performance and start-up engine wear. Also keep in mind that for example, 5W30 and 10W30 are the same viscosity at normal operating temperature. But the 5W30 flows better on cold start-up, so it would be a better choice when a 30 weight provides the needed oil pressure.