83 Crossfire TA

iTrader: (2)

Conventional wisdom among racers is if you want your engine to last longer you run heavier weight oil to give you better film strength and protect the parts from the beating you're going to place on them.

I've noticed this spring that none of my local autoparts stores stock anything over -30 (you can still get 0w, 5w, 10w-30, but nothing heavier, well I did see one container of 5w-40synthetic), at least in the normal automotive oils. The various valvoline race oils that you saw all the time are gone.

So what about conventional wisdom? Are we to believe that modern oils are that much better that you don't need heavier oils to protect under extreme conditions?

Let me give you a specific example, a stock '80's bottom end with a top end making ~500hp and wanting to turn 7000rpm (I know, the stock rods/rod bolts won't be happy turning that fast), what do you run if you want to protect it?

• 5w-30, that is what it was designed for it will be fine, especially with better modern and/or premium oils
• a diesel something_w-40 oil (I used to do this, but recently I've wondered if this is a bad ideal, diesels don't have PCV systems and create different contaminants and have significantly different loads/run lower rpms so they have very different additive packages)
• Order some "race" oil in a something w-40 or -50 weight
• Something else?

Orr89RocZ

iTrader: (20)

In general, yes. Modern oils are really good, well some of them. Modern engines are tight clearanced and dont need a heavy weight oil. The lighter stuff has plenty of viscosity and film strength

So it all depends on your bearing clearances and such. Ultra high hp pushing the limits of parts tend to run more open clearances and use thicker heavier oils to suit. Some endurance type engines do the same. But a lot of engines run fine with your 30 weights. Then again some class limited or rule spec racers need all the hp they can get and run extremely light oil. 20 weight or less. It looks like water

So it kinda depends on the application. And not all oils are equal to a point. Different levels of detergents and protective packages. Almost need to get the experience of your engine builder or machine shop to get an idea what works for the combination. Or call a good oil manufacturer and get a recommendation.

83 Crossfire TA

iTrader: (2)

Right, I could have answered it to that extent, but I did ask about a specific application where I don't entirely know the answer, again: 80's stock bottom end (small block, high mile, over 100K miles) with a top end that makes 500hp or more. It was originally "designed" for 5w-30, but that was before 100some thousand miles of wear and holding close to 1/3 the HP.

Orr89RocZ

iTrader: (20)

The way i look at it is this...if you run 5-30, whats the oil pressure? Is it satisfactory? Is it low when hot?

Might want to step up to a 40 then if it needs more pressure because engine is worn

Fresh rebuild to stock clearances then use a 30

My 305 idled at less than 15 psi according to stock gauge. I didnt like it and went 10w-40 like i ran in my race street car lol. Idle pressure went up and seemed alot better with rpm

The higher mileage formulas sometimes have more zinc components so offer abit more protection. Look at the spec sheets and viscosity values

PAformula

iTrader: (1)

The T/A I just bought has 4 yr old Amsoil in it, but I have no idea what weight. Before I start driving it, i plan to change it to conventional. The car has 124k on the stock 305. After replacing the sending unit, it holds good oil pressure. What weight conventional would you guys run?

dmccain

iTrader: (2)

10w30

83 Crossfire TA

iTrader: (2)

What exactly is satisfactory? I mean the conventional answer goes something like 10psi/1000rpm. I've never owned a "stock" bottom end that is that low at idle, typically not as high at idle as a lot of people talk about and that pressure builds that fast.

Seriously, give me a range, like hot, over XX at idle and XX at >6000rpm or at least x/rpm.

This is a little embarrassing, but I've never actually installed a gauge on my own engine that I've trusted, I've always just used the stock gauge, and if it reads something not absolutely crazy and it moves in the right direction (up when you rev it) then it's good and oil pressure is OK, at least enough to live.

In this case, when I put the top end back on with the stock 30y/o sender it read super low (somewhere in the teens when warm) and barely moved. I grabbed the sender from my parts car it read kinda a little high but OK, and when the new one came in it read similar but not as high. The new one died after about a week and I stuck the parts car one back in and didn't worry about it.

This one on the Atari (digital) dash, which I question the accuracy of to start with (it does different things with different weather and different system voltage) reads just short of 60psi at cold start. I know it drops down a bit when it gets warm (this car never reads over 178* in the data logs), but I believe it changes about 20psi or less from idle shift rpm, and typically like every stock(ish) short block that I've owned, I think it gains some PSI as you rev it to about 3000psi and stops, I've always assumed it was just the bypass opening.


OK, that engine is a good example, I'm assuming you're talking about the 305 that you put a turbo on. I don't remember the details but I'm guessing a fairly stock, worn, bottom end and 400hp or more. So on that did (or do you, in retrospect) feel that stock pressures with stock weight oil is sufficient or do you feel it needs more protection, pressure or oil weight wise (since at some point the bypass just opens and you don't get more pressure but you have a heavier weight oil in there at the same pressure)? What if you pushed it to 600hp?

83 Crossfire TA

iTrader: (2)

You know, thinking about this some of this is inspired by stuff like the Engine Masters series on Youtube (sponsored by Amsoil) where half the episodes they take a relatively stock engine and do something stupid to it (tons of boost, spray...) and then they supposedly consult Amsoil before abusing it and typically they say they recommended some super heavy weight, $$$, race oil for it just to make sure they don't have a lubrication based failure. And honestly, considering how far they've pushed most of these stockish engines they have had very few significant failures doing it, at least fewer then you'd expect.

I'm sure a big part of that is years of experience blowing **** up and knowing how to prevent it/knowing the signs of it coming, but is some of it the thicker oil film? They never seem to worry about loosing power after dumping honey thick synthetic into the filler.

83 Crossfire TA

iTrader: (2)

Guys, if you vote I'd love a "why" and if you voted "something else" a post to what that is would be nice. TY

QwkTrip

iTrader: (22)

I have noticed the most important thing about oil is putting it in the engine.

Orr89RocZ

iTrader: (20)

Hard to say exactly but the good condition stock motor cars i have seen are 25-30 hot idle. Generally 50-60 wot. 10 psi per 1000 is good estimate
New rebuilds i have seen 30-40 hot idle depending weight and clearances. But this is not to say 40 psi at idle is gonna be better than 25...only way to tell is examine bearings and oil analysis after each change for awhile to track wear. Remeasure clearances etc


Yes it was a 130k mile 305 but car seemed in great shape. However stock gauge says oil was very low when hot with conventional 10w-30. I went to a 40 weight and it went up. I did same thing to my other turbo car because oil was getting to hot i think and causing low pressure. I added a cooler later on that really helped keep pressure up. Did not run a cooler on the 305. But the 40 weight gave me 10 more psi from what it looked like. Protection wise i dont know if one was better than the other. Both same brand just diff weight so my guess is it wouldnt matter as much as long as temp was controlled. I didnt control temp so i left 40 weight in it. Seemed to be ok with that.
The 305 was maybe 330-340 hp.