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New carbed 383 stroker losing oil pressure at operating temp

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Old 08-12-2018, 06:05 PM   #1  
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New carbed 383 stroker losing oil pressure at operating temp

Starting up initially the engine runs great and the oil pressure is between 50-65psi. It has a high volume oil pump. Drove it for a few miles and all was good. After about 15 minutes of driving around it starts slightly bogging at a stop sign like it has too much or not enough fuel, then the oil pressure drops from around 50psi to 20psi. RPMs bring up oil pressure but at an idle it's only at about 20psi.

The engine only has 50 miles on it and was assembled by a renowned engine builder, and all internal components are brand new and high peformance. It is carbureted and has an adjustable fuel pressure regulator that reads about 7lbs at initial startup. I havent changed the oil since its first startup. I also have 2 gauges for oil pressure and they both were feeding me the same information. Any ideas on what would cause oil pressure to drop after getting up to operating temperature, as well as the bogging down at a stop sign after reaching operating temperature?
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Old 08-12-2018, 06:09 PM   #2  
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Re: New carbed 383 stroker losing oil pressure at operating temp

call your engine builder and see what he says dont keep driving it till you talk to your engine guy
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Old 08-12-2018, 10:00 PM   #3  
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Re: New carbed 383 stroker losing oil pressure at operating temp

Based on researching several SBC forums, for a 383 stroker 20-55psi oil pressure is normal. 20 at idle and operating temperature, 55 at 5500 rpms or cruising is fine. I'll still call my engine builder tomorrow and post his input on this so we have it documented for the future.
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Old 08-13-2018, 06:12 AM   #4  
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Re: New carbed 383 stroker losing oil pressure at operating temp

Yeah call the builder and see what he ran for main clearance and rod clearance. What weight oil does he recommend? Do you run an oil cooler?

if it has alot of clearance it may want a heavier oil weight. 20 is low imo but wont hurt. I like to see 30 at idle. As long as it rises with rpm and is close to 10 psi per each 1000 rpm, it is fine


the sputtering bogging sounds like tune. Get a wideband air fuel monitor and check the plugs. Might want to change oil soon. Carb likely needs jetted. If too rich you may be diluting oil with fuel and causing low pressure. Check plugs, smell dipstick for fuel and call builder
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Old 08-13-2018, 07:49 AM   #5  
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Re: New carbed 383 stroker losing oil pressure at operating temp

How are the cam bearings clocked? What are the bearing clearances?

A brand-new motor built to stock-ish clearances (.002" more or less) with the cam bearings installed correctly (oil holes at 4:00 or so viewed from the front) should have no problem producing over 30 psi at hot idle with a HV pump, even with 5W-20 in it. While 20 psi is "adequate", it's lower than it should be at this stage of the game, and does not bode well for the future of this motor. I'd strongly suggest taking it back to the builder BEFORE it wipes itself out spectacularly somehow and you get blamed for some sort of improper installation or something.

The driveability complaint sounds like the carb and the ignition timing curve need tuning.

IMO 7 psi is too much pressure. Carbs don't work off of fuel pressure, they work off of VOLUME. All they need, is the fuel bowl kept full. If .001 psi is enough to do that, then .001 psi is all you need. There is no benefit to running more pressure than necessary. It is often used as a crutch to hide a delivery problem from someone not familiar with optimizing a carb setup. Something is major wrong with your fuel system DELIVERY RATE - which is a totally different matter from PRESSURE - if the carb won't stay full at 5 psi.
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Old 08-13-2018, 08:59 PM   #6  
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Re: New carbed 383 stroker losing oil pressure at operating temp

Quote:
Originally Posted by sofakingdom View Post
How are the cam bearings clocked?
Since you mentioned this Sofa, here is what I had saved in my notes:

The best placement is #1) 10 & 2 o’clock, and 2 to 3 o’clock for the rest.
GM factory placement is #1) 1 & 5 o’clock, 2,3 & 4) 5 o’clock, 5) 12 o’clock

By placing the bearing's oil hole at roughly the 2:00 position (anywhere between 2:00 and 3:00 is fine), oil is fed into the clearance between the cam journal and cam bearing as the cam rotates clockwise, creating an oil wedge that travels down and supports the cam much better during cam rotation. This forces a superior oil wedge under the cam, to provide oil support at the bottom (6:00) position.

On engine blocks that do not feature an oiling groove on the bearing bores, it is vital that each cam bearing is installed in the correct clock-position, so that the bearing's oil hole accurately aligns with the cam bore oiling hole. If the cam bore features a groove, the bearing should be installed with its oiling hole placed at the 2:00 position (when viewed from the front of the block that features clockwise rotation).
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