Oil

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Sorry guys I’m having technical difficulties here. Purchased matching #s Dart Swinger 340 4 years ago. Lots of documentation with car. Except for engine. Hand writ note saying “bored 30 over, hydraulic H cam. Purple bigger, compression ratio 10.5:1” I’ve been running VR1 20w50 based upon recommendation of local speed shop, but recently was told that oil was too heavy. Thanks guys!
Too heavy?? who decides that?
Tell them they can be a minimalist with their own crap. 20 when cold and up to 50 when hot probably in the middle mostly .
Factory, back when we had GOOD OIL , said straight 30 weight oil was what they designed their clearances around.

Straight 30....
I've run 10 30w, 20 50w, 5 30w syn, non Syn, para syn, etc...
After trying all that stuff over the years the only thing that seemed to make a difference was the brand of oil. Regular off the shelf synthetic/conventional oils suck , no matter how heavy....the viscosity does not hold up to heat.
All you are going to mostly get here are opinions.. and like assholes...most stink.
Soooo run what ever weight you think you should. Just remember that unless you use a designer oil ...it will turn to water ,damn near , after long freeway trips and hard wot back to back blasts...so you might consider more viscosity is better than less..
 
It isn't far off
Kinematic viscosity of water at 68 F is a bit over 1 cSt.
vs
10W-30 at the same temperature is around 200 cSt
and a
20W-50 is around 550 cSt.

get the oil up to 210 F and a
10W-30 viscosity will be around 11 cSt
20W-50 viscosity will be around 18 cSt

but push that oil up to 250 F
10W-30 drops to 7 cSt
20w-50 drops to 12 cSt

Had an engine that would run oil temps over 260 F on long highway runs ( not coolant, just oil)
and yes it did get 20w-50

had another engine, a staight 6, that when fully heat soaked would start to loose pressure over 60 mph.
That engine was just worn! A high volume pump and thicker oil only marginally helped. But it kept running..:)

and yes, there is a range of viscosity allowable within each grade. You can get the info from most manufactures or send out for testing if its important enough.

For the original poster it seems to me he just needs to get in the ballpark.
 
When the oil is cold, it is so thick that even at idle a bunch of it goes out the relief valve on the pump instead of through the engine.
When the oil gets up

That statement is wrong. The relief valve does not dump the oil out of the pump. The oil is recycled in the pump. This allows oil to go out through the main cap into the engine and at the same time regulates the oil pressure. The oil pump does not have a hole in it for excess oil pressure to leave the pump.
 
That statement is wrong. The relief valve does not dump the oil out of the pump. The oil is recycled in the pump. This allows oil to go out through the main cap into the engine and at the same time regulates the oil pressure. The oil pump does not have a hole in it for excess oil pressure to leave the pump.
So is it safe to safe if the pressure is too high for a moment the oil pump rat races excess oil and some oil is still being sent through engine?
 
So is it safe to safe if the pressure is too high for a moment the oil pump rat races excess oil and some oil is still being sent through engine?

There is no excess oil. There is excess pressure. The relief valve is pushed open x amount, depending on how hi the pressure is. With the valve open, the oil in the pickup tube slows or stops. Even with the relief valve open the pump is still pumping oil into the engine.
 
There is no excess oil. There is excess pressure. The relief valve is pushed open x amount, depending on how hi the pressure is. With the valve open, the oil in the pickup tube slows or stops. Even with the relief valve open the pump is still pumping oil into the engine.
 
That statement is wrong. The relief valve does not dump the oil out of the pump. The oil is recycled in the pump. This allows oil to go out through the main cap into the engine and at the same time regulates the oil pressure. The oil pump does not have a hole in it for excess oil pressure to leave the pump.
I agree. Your description is more accurate.
There is no excess oil. There is excess pressure. The relief valve is pushed open x amount, depending on how hi the pressure is. With the valve open, the oil in the pickup tube slows or stops. Even with the relief valve open the pump is still pumping oil into the engine.
Well said.
So is it safe to safe if the pressure is too high for a moment the oil pump rat races excess oil and some oil is still being sent through engine?
You can also think of it as something like this.
tenor.gif


Some gets in.
How much makes it to the other end and at what pressure - that can be the kicker.

It's one of the reasons to get the engine warmed up before hammering on it.
 
I had a mild 383 a long time ago in a 4-speed A-body, 3.23 gears... oil pressure was about 10 psi higher at both idle and operating RPM with 20W-50 vs. 10W-40. But it made an 0.3 mpg difference to the fuel consumption (averaging around 12.4 vs. 12.7 mixed city/highway). So the thicker oil was wasting some horsepower...
 
My two cents (likely overpriced):

I read oil viscosity threads until my brain hurt. The common recommendations seemed to land between 10W-30 and 20W-50. So I decided to go with this and call it a day.

Good luck.
 
For what? 85w/90
I accidentally posted that with out finishing post. I clarified earlier in thread. Engine oil for 340 with purple cam( unknown specs as I didn’t build engine) I don’t race it just drive it on the street here in Massachusetts from spring to early fall
 
I accidentally posted that with out finishing post. I clarified earlier in thread. Engine oil for 340 with purple cam( unknown specs as I didn’t build engine) I don’t race it just drive it on the street here in Massachusetts from spring to early fall
Ahhh... Royal Purple 10w40 is my choice for you in Massachusetts. I switched to 10w30 RP in my ramcharger and it quieted it down and runs smoother since I started using it.
 
Man, just run 10w30 in the thing like Chrysler recommended. This ain't rocket science. Simply make sure to run an oil with plenty of ZDDP or run an additive. I run 10w30 Lucas Hot Rod Oil in my 75 F250 and in my 64 Valiant. It already has 2400 PPM of zinc. That's all they need. No need for anything fancy.
That’s what i run in my built 340. And our daily only thing I don’t run it in is our 4x4 just run 10w40 for that but agreed all reccomend
 
Im running 15W-50 mobil one full synthetic. Engine builder recommended it, from what i remember he opened up the oil passages some and im sure he knew what the tolerances were. Having the engine builder tell you what to run is a good basis to go off of. But if you cant talk to the engine builder it makes it a little harder to make a decision, honestly 20w-50 or 15w-50 should be no problem even in about 30 degree weather. I used to run 20w-50 mobile one and had to change to 15w-50 mobil one because they discontinued the 20w-50. I have the 15w-50 in year around and even in the 30’s it does perfectly fine. All depends on engine tolerances
 
Im running 15W-50 mobil one full synthetic. Engine builder recommended it, from what i remember he opened up the oil passages some and im sure he knew what the tolerances were. Having the engine builder tell you what to run is a good basis to go off of. But if you cant talk to the engine builder it makes it a little harder to make a decision, honestly 20w-50 or 15w-50 should be no problem even in about 30 degree weather. I used to run 20w-50 mobile one and had to change to 15w-50 mobil one because they discontinued the 20w-50. I have the 15w-50 in year around and even in the 30’s it does perfectly fine. All depends on engine tolerances
 
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