Engine 88 got oil question

Comp Cam

Jan 11, 2019
What's up, so it's time to change the oil in my GT. It's HCI bigger throttle body rockers and Pushrods with gt40 heads. For some odd reason he used 20w 50 racing oil in it for a recent oil change (before I bought it). Unless he's trying to hide unwanted noise (witch I fear). Should I go ahead and use 10w 30 or stick with w20 50 instead?
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John Dirks Jr

there is enough sticking out to grab on to
5 Year Member
Jun 28, 2013
Some engines are built with slightly more bearing clearance for racing purposes. I dont have a technical explanation for why. The 306 in my 93 vert was built that way by a previous owner. If I run 10-30 in that motor, hot idle pressure drops too low for my liking. So I run 20-50 Mobil1 full synthetic and its perfect. My 92 was built with factory spec bearing tolerance and I run 10-30 in it.

Wayne Waldrep

Before I post a pic, do you have one of yours?
15 Year Member
Apr 14, 2003
Cuba, AL
My original engine went 248k miles. All it ever had in it was Castrol 20w-50 conventional. Like has been said above, either is fine.


i'm familiar with penetration
Mod Dude
Feb 18, 2001
Can you put a good oil pressure gauge on the car and see what you have for pressure now, and then see what you have if you change to 10W-30? That will likely give you the answer you need once you see how the different oil affects pressure (either cold or hot)


SN Certified Technician
Aug 27, 2012
In the garage
as long as you dont live in a cold climate, you can run it fine. Just to throw you a curve ball, I've been running Rotella 15w40 in my N/A fox body cars for decades and 20w50 castrol in my supercharged ones.

John Dirks Jr

there is enough sticking out to grab on to
5 Year Member
Jun 28, 2013
Correction. Above I said I run 20-50 Mobil1. They dont make it. It's 15-50. Doh!
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