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Old 03-19-2007, 02:29 PM
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400 Small Block oil problems

I built a 415 stroker with Eagle crank, rods, Ross pistons in the lower end with a Mildon 7qt oil pan and pickup, high volume oil pump. Running Dart Pro1 heads with a Comp Cams solid mechanical cam and lifters and roller tip rockers. My problem is I have 25 to 35psi at idle hot, 50 to 60 psi crusing speed and when I get into the motor oil pressure climbs to 70psi then suddenly drops to 25psi or less at around 4000 to 4500 rpm and a soon as I let off the throttle oil pressure jumps back to 70psi. I have removed the motor replaced oil pump and pickup checked all bearing clearences old bearings look like new, replaced all bearings with new installed a widage tray bigger oil pan new pickup and pump and still have the same results. I do not uderstand why the oil pressure drops. I am running 8qts of oil with the filter and do not believe that all of that oil could go to the heads and puddle. I put 300 miles on the motor before tearing it apart and could not find anything wrong with it. Anyone have any ideas?

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Old 03-19-2007, 02:57 PM
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How confident are you in your gauge & sending unit? Which oil pump are you running?
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Old 03-19-2007, 02:58 PM
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Have you tried another known good oil pressure gauge....??

EDIT....
Big beat me to it :-)
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Old 03-19-2007, 02:58 PM
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Simple things, but maybe some how you missed them so I'll throw out a few:

Oil Filter / Oil Filter brand - were all 3000 miles on the same filter or same brand filter? Maybe some freak problem/s that a different brand could fix.

Oil Filter Bypass - Could something be broke in the filter bypass or the spring is messed up? They are easy to swap out just to rule it out.

Oil Pump pickup installed height - you said you have changed the pump and pickup - did you measure the height of the pickup off of the bottom of the oil pan during installation? A pickup that is too high or too low could cause this problem.

Broken Gauge - possible nothing is wrong in the engine and the gauge could have something crazy going on. Kind of a long shot, but it is very easy to just swap on a different gauge.
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Old 03-19-2007, 03:08 PM
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When i changed the pump and pickup i used a mildon pickup that matched the pan and checked the clearence with clay about 3/4 inch clearence and the new pickup has a guard on the bottom preventing the pickup from touching the oil pan. As far as oil filters go I have tried using a Fram HP and AC filter with the stock setup and a non-bypass setup from Jegs. Nothing seems to change what is going on.
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Old 03-19-2007, 03:10 PM
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As far as gages go I have tried a mechanical and a electronic with a sending unit and both give the same results. I have only checked the oil pressure at the top of the block by the distrubuter. I don't know if it matters where to check it.
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Old 03-19-2007, 03:13 PM
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I am using a Melling HV oil pump
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Old 03-19-2007, 03:52 PM
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Is your crank a cross-drilled crank? If you don't know, if it is a forged 4340 unit, it is cross-drilled. If it is, what kind of main bearings are you using?

tom
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Old 03-19-2007, 04:05 PM
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Quote:
Originally Posted by bac6772
When i changed the pump and pickup i used a mildon pickup that matched the pan and checked the clearence with clay about 3/4 inch clearence and the new pickup has a guard on the bottom preventing the pickup from touching the oil pan. As far as oil filters go I have tried using a Fram HP and AC filter with the stock setup and a non-bypass setup from Jegs. Nothing seems to change what is going on.
3/4 is too much. 3/8 is what you need.

Tom knows what you need.

Didi you gring out all your oil return holes?
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Old 03-19-2007, 04:06 PM
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The crank I believe is crossed drill it is an Eagle forged steel crank and I am using Clevite 77 H series
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Old 03-19-2007, 04:14 PM
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I do not believe that the clearence on the pump is a factor I had a 5 qt pan with stock pickup and had the same problem, changing too a 7 qt pan and diffrent pickup and widage tray had no effect. The motor has great oil pressure at cruising speeds but when you get into it the oil pressure drops and as soon as you back off on the gas it go right back up.

I appreciate all replies and am will to try just about anything at this point.
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Old 03-19-2007, 04:18 PM
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I purchased the crank kit new, all balanaced, came with rods, pistons, crank, rings, bearings, fllexplate, harmonic blancer, The block was purchased as well with splayed main caps installed. When I pulled the motor I replaced all the bearings and rechecked clearences just to make sure and still ended up with the same problem.
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Old 03-19-2007, 04:58 PM
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The only thing that I can think of is that the cross-drilled crank is supplying too much oil to the rods and that is bleeding out past the typical Eagle too-big oil hole chamfers. This probably isn't helped by the typical .030" rod side clearance seen in these assemblies.

tom
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Old 03-20-2007, 12:10 AM
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my guess is the pickup should be 3/8 from the pan.
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Old 03-20-2007, 06:03 AM
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Yep 3/8's is what I have set my last two at.

Are you running anything in the valley area that would slow oil drainback?
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