Thread: Big Cam Really Low Vacuum?

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Originally Posted by skids72

Thanks, Erik... Yeah 800 is pretty low but it runs like a top there (albeit quite lumpy ). I certainly can crank the idle up a few hundred... otherwise, 5" can be considered "normal" with this cam? I'll measure again at a higher idle...

Thanks again,

Chris

Man 800RPM.....I would have this motor idle set to 1,100+.....just to aid in oiling. I am sure it sounds great loping away at 800rpm....but I am sure watching your oil pressure at idle after 15 minutes of running, is begging for a higher idle.....just my 2 cents.

I use to have a 454 with a giant bump stick. And at start up I had 60psi of oil pressure. After cruising around for 15-20 minutes the oil was hot and thin, and my lumpy idle gave me 40psi.....that was a little low, so the idle came back up to about 1000.

Originally Posted by 4speedTerror

but I am sure watching your oil pressure at idle after 15 minutes of running, is begging for a higher idle.....

Not to take this too far OT, but could you explain that one to me? I don't doubt it, since I've witnessed it in my own car, but why does lumpy cam drop oil pressure at idle? Is it simply because of the drop in vacuum? I do know this: on my own car taking it to a guy who knows what he's doing with the exhaust (just had a temp exhaust on it) smoothed things out quite a bit. Don't know my cam specs, friggin builder won't tell me like it's some secret.

Originally Posted by marlinspike

Not to take this too far OT, but could you explain that one to me? I don't doubt it, since I've witnessed it in my own car, but why does lumpy cam drop oil pressure at idle? Is it simply because of the drop in vacuum? I do know this: on my own car taking it to a guy who knows what he's doing with the exhaust (just had a temp exhaust on it) smoothed things out quite a bit. Don't know my cam specs, friggin builder won't tell me like it's some secret.

ok something you said REALLY BOTHERS ME!!!! Your engine guy should ALWAYS give you a cam card with all the specs of your cam. What if you need new pushrods? How are you going to know what you need. And that goes for EVERYTHING in your valve train. So first of all I would slap him around and DEMAND the cam specs. Even if he grinds his own custom cams (which i HIGHLY HIGHLY doubt)

Ok and the idle question is simple.....If your idle is already low at first start up (cold start up in the mornings), then the longer you drive the car, the hotter the motor gets...which makes your oil thinner and thinner. So if you have had an idle of 700rmp in the morning and your oil pressure was 50psi, by time your motor is nice and hot, your oil is much thinner than in the morning. So now of course a thinner liquid will move faster. So your oil pressure falls. And for me a low oil pressure, and an aggressive cam makes me nervouse. I have oil restrictors and all that, but anything that is "splash" lubricated, I am going to make sure it is getting "splashed" very well...lol

Originally Posted by 4speedTerror

ok something you said REALLY BOTHERS ME!!!! Your engine guy should ALWAYS give you a cam card with all the specs of your cam. What if you need new pushrods? How are you going to know what you need. And that goes for EVERYTHING in your valve train. So first of all I would slap him around and DEMAND the cam specs. Even if he grinds his own custom cams (which i HIGHLY HIGHLY doubt)

Ok and the idle question is simple.....If your idle is already low at first start up (cold start up in the mornings), then the longer you drive the car, the hotter the motor gets...which makes your oil thinner and thinner. So if you have had an idle of 700rmp in the morning and your oil pressure was 50psi, by time your motor is nice and hot, your oil is much thinner than in the morning. So now of course a thinner liquid will move faster. So your oil pressure falls. And for me a low oil pressure, and an aggressive cam makes me nervouse. I have oil restrictors and all that, but anything that is "splash" lubricated, I am going to make sure it is getting "splashed" very well...lol

Well, it's an overhead cam, so no pushrods. And this engine doesn't rely on splash lubrication (it's a hot rodded Mercedes...yes, I know, I'm nuts).

The cams were custom ground...I suppose when I need a replacement cam I can just stick it in a cam doctor, no? He did kinda tick me off with that...as well as some other things he did.

Originally Posted by marlinspike

Well, it's an overhead cam, so no pushrods. And this engine doesn't rely on splash lubrication (it's a hot rodded Mercedes...yes, I know, I'm nuts).

The cams were custom ground...I suppose when I need a replacement cam I can just stick it in a cam doctor, no?

I guess I could of asked what you were running...lol...

I just figured conventional v8....lol