Oil weight in regards to engine clearances.

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steve40th

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I have a Chevy Corvette, with stroked and bored out LT1 engine. The clearances arent loose, or tight per sey. But is there a general rule of thumb for oil viscosity for clearances within bearings etc.
My engine build was many years ago, and I was never given a recommendation other than Mobil 1 10w30 will be fine. Not a confident answer, just an answer.
I just re ringed it, and clearances havent changed but I have been using Shell Rotella synthetic, at Wal Mart. My oil pressure is 45 psi at 180 degree oil temp. I have a high volume regular pressure GM oil pump in there from Mellings. The pressure is a little high, but I bypassed the oil filter bypass to ensure oil filtration (WIX) continuously.
What oil would you recommend? Shell fine? No oil analsys yet.
Or should I go a higher quality oil, aka more expensive with higher base stock.
Thanks, Steve
 
Quote:
but I bypassed the oil filter bypass to ensure oil filtration (WIX) continuously.


I'd recommend undoing this feature.


Please read this thread and try and figure out just where this practice originated.
 
You are probably fine with your oil choice. It is a heavy duty oil. I would, however, switch to an amsoil EaO24 oil filter as it is one of the few Chevy filters with a bypass still built into the filter itself, and is a very free-flowing media. Right now if you start it on a cold morning and the oil cannot pump through the filter media fast enough, it may collapse the media or blow the filter up, since most chevy V8 oil filters do not have a bypass.

If you do switch back to Mobil 1 oil, consider the HM 10W-30 oil as it has more AW additive and higher viscosity than the regular or EP versions, affording your type of (high performance) engine better protection.
 
What is the displacement of the LT-1? I assume 383 since this was and continues to be a popular build.

Assuming it is a 383 which requires a different crankshaft (3.75 in stroke)than the stock 3.48 in stroke.

So we have two variables from there...

1.) a cast steel scat or eagle crank shaft, which would be 'standard'

2.) a stock cast iron 400 ci crank, which would be turned down 10/10

Given the clearances are set depending on journal diameter, the bearing clerances 'should' be about .024-.025 since the journal diameters are 2.48 on the mains and I think 2.10 on the rods but that is all hypothetical since you/we don't actually know.

This is the weights I usally run in regards to the main bearing clearances.
clearances... .020-.025 10w-30 (you could probably run a 5w-30 with no problems)
clearances... .025-.028 10w-40
clearances... .028-.030 20w-50

Now all of those weights can change depening on rpm range, the higher the range, the more weight. (people may argue with that but you have a street engine not a 9,000 rpm screamer). And the other way around works as well


Two comments on your oil pressure... 45 lbs I idle? if so that's a pretty tight clearance... if that is at or near WOT then you have loose clearances.

I have a 327 with .025 clearnaces running Brad Penn 10w-30 with a standard volume oil pump and I have 25lbs at idle and 50 at 5,000rpm. With 20w-50 in the summer I have 40lbs at idle and 65bls at 5,000. I'm sure you know but a good rule of thumb is 10psi per 1,000 rpm.

Again this info is not a rule book but just common information that has worked for me and alot of other people.

Hope it helps
 
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Do you also subscribe to the defeated bypass "faith based" notion?? (yes, I'm being a wise***
grin2.gif
) ..any insight in who brought this down from the mountain cast in stone??
 
would you use clearance list on any motor? I just lloked up my service manual, and it states bearing clearances are between .025mm - .071mm. OM recommends 5w30 or 10w30 for all climates.

with PP I get about 13-17psi at hot idle, and 37psi at 3000 rpms. On redline 10w40 I was getting 28-30psi at idle and 45psi at 3000 rpms. These psi readings are takin at the head, and from what I have read, the head gasket is a pressure reducing gasket to lower pressures in the head. I am not sure on that though
 
I don't know what engine you have? Since you are stating a metric form of measurement I assume you have a different engine that a small block chevy.

But by the way, no, I would only run those clearances with the recommended oil weights in a SBC only. Every engine likes different things so those I posted are not universal. Different SBC like different things just depends how the bottom end is built but those should be solid figures for a warmed over street small block.

No, a head gasket cannot affect oil pressure only bearing clearances can affect this. I think you are refering to compression ratio... a 'thicker' head gasket will reduce cylinder pressure which has no relation to oil pressure.
 
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genynnc- thanks for the info


I have a Chrysler 2.4L DOHC 16v TurboCharged 4Cyl.

Standard Measure is 0.0009–0.0027 in.

Manual also states that idle PSI needs to be 4 psi or better, and 80 psi max at 3k rpms. I guess I will just stick to Xw30 (usually ASL - used to be TSO)
 
Originally Posted By: genynnc
Two comments on your oil pressure... 45 lbs I idle? if so that's a pretty tight clearance... if that is at or near WOT then you have loose clearances.


In the 355 I built I have about 80-90 PSI at idle with 10W-30. I made the mistake of putting a high flow oil pump in, and I'm somewhat worried that I might be prone to oil leaks because of it.
 
Do you subscribe the defeated bypass theory too??

(someone has to twitch here - I'm determined
grin2.gif
)
 
Originally Posted By: Gary Allan
Do you subscribe the defeated bypass theory too??

(someone has to twitch here - I'm determined
grin2.gif
)


Negative. I wasn't even aware of the practice back then.
 
mech is correct... excuse my typo... add another '0' to the front of those number... thousandths is what they are supposed to be...

i.e.- .0025 instead of .025.
 
Originally Posted By: Gary Allan
Do you subscribe the defeated bypass theory too??

(someone has to twitch here - I'm determined
grin2.gif
)


I'll bite.. I bypassed the GN's filter bypass at the filter mount. Reason being the spring was 20 years old and the plastic valve was worn a bit. I was worried about it sealing properly (when not in bypass) so I threaded the hole and put a plug in it. I do make sure my filters have a bypass though. At nearly 90psi cold idle with a 70psi pump relief, there's a good chance it's going into bypass.
 
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