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Discussion Starter #1
Hello,

On my 67 I recently replaced my oil pump with a high volume one. My old pump started to wear out I guess. My pressure never went above 25 psi. So I replaced it with a high volume oil pump. Here is some background...my old oil pump when it worked correctly gave me an oil pressure or 55 psi when cold and as the engine heated up it would drop to about 45 psi. Now with my high volume pump when it is cold it goes to 75 psi and when it gets hot it drops to about 40 psi. Is this right? Is there that much flucuation with a high volume pump? I have always used Valvoline 10W40. Now I was forced to use Castrol 10W40 because the store didn't carry Valvoline anymore. That is the only change other then then pump. Is it the oil? Possibly? Any info would greatly be appreciated.

Stang6767
Bryan
 

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Stick with your 10W-40....your pressure is within the boundaries of normal with a HV pump....sometimes they get the pressure relief set a little higher than others...
The difference in pressures may indeed be related to the oil brand change....I wouldn't be concerned at this point...40psi hot is plenty for a stocker...

I've never complained about high pressure, especially in my racing engines....I remember some of the Cleveland guys jacking theirs up to 100psi to save the mains and rods when spinning to 8K back in the days before external lines and restrictors...

The only thing at risk IMO is the oil pump drive....I'd have a 4130 unit in there if it was my engine...too late for that now though...

Pat
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I've heard a few opinions on the use of heavy duty oil pump driveshafts.

Theory1-pro HDshaft
Normal gearhead logic would be to identify it as a weak link and improve it's durability, since you don't want to twist your OPshaft every other day. Heck, you can get a HDshaft for $20.

Theory2-pro stock shaft
Then again, twisting a stock $5 OPshaft may prevent debris from reaching rod/main/cam bearings, cylinder walls, cam lobes, etc. possibly causing thousands of dollars of damage.

I'd imagine the filter would catch any debris before it reaches vital components.

Which theory has more merit?

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I like the stock $5 drive shaft. I've had an oil pump freeze on me before. The engine's not going to stop simply because the oil pump does so something has to break. I'd rather have the $5 pump drive shaft twist into a pretzel and break than either my cam or my distributor.

When a pump freezes one of those 3 things has to break with it ... I opt for the easy to replace $5 part.

If you always do what you've always done,
You'll always get what you've always got

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Since I work with hydraulics every day and know that it can take 3-5 hp to drive that oil pump at high rpm, it scares me to have it going through that little hex shaft, akin to a long allen wrench and about as strong...

I like theory #1 but only to safely drive the oil pump...no heroic measures here...*G*

Having an oil pump shaft snap at the top of first gear when things are happening real fast in a race car can make for a very interesting ride.....one I don't want to find out about....

Pat
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John,
The HD shafts would break in that scenario too; they just offer a bit more safety cushion when pushing heavy oil at high volumes and pressures under performance conditions...

It's still the same hex at the ends, just made out of 4130 or 4140 instead of 1030 or 1045.....a little more tensile strength and a bit less susceptible to work-hardening...

Most stockers will never see the conditions that obligate the use of a HD driveshaft...but in the hands (and foot) of a adrenaline-filled Pony rider?? *G* Hope for the best but plan for the worst, I always say...

Pat
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That makes more sense. As long as the pump shaft will break before either a distributor shaft, dist. gear or cam shaft and/or gear, I'll change my opinion and side with higher intellegence /forums/images/icons/blush.gif.

If you always do what you've always done,
You'll always get what you've always got

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Discussion Starter #8
A rule of thumb, yo uneed 10 PSI for every 1000 RPM...even Clevelands. So unless your typical RPM range exceeds 4500-7500 rpm, your overkilling. Most of that extra pressure is just being bled off through the bypass anyway. I sopped using HV pumps even in the stock cars. A good regular pump would give me 65psi at 6000 rpm and didn't foam the oil or heat it up. With heavier (40wt) oil and a hv pump, just let the poor oi warm up before you romp on it. They are right, that little stock shaft will break -or_ the distributor gear pin will shear. I ALWAYS drill that out and put a larger roll pin in.

Keep the shiny side up and the greasy side down.
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The HD shafts do snap when there is a reason. I found that out twice last summer.

What they do offer is resistance to twisting. A stock shaft will look like licorice all twisted even if it didn't break yet.

Gene J

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Discussion Starter #10
One other advantage of a heavy-duty oil pump drive shaft is that they have a bit more mass and seem less likely to get lifted up when the distributor is yanked. The stock shaft is about as thick as a pencil and doesn't weigh much more.
 
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