Oil temperature in a small block chevy
Discussion
OK folks, trying to get a definitive figure here for ideal operating range of oil (not water!) temp for a decent tune SBC; there seems to be loads of conflicting figures out there, so I guess this will return a range too 
Motor is a 383 stroker making 500BHP on dart heads, roller cam etc., so a pretty reasonable tune that generates some proper heat. I've just added a second oil cooler and I think at last I might have the ability to actually control the oil temp now by blanking/revealing the cooler(s) depending on use (road or track thrash)
Oil is being measured in the sump (it's a big Canton baffled/trapdoor sump).
There seems no dispute on the minimum oil temp - less than 82c/180f is too cold. I'm working on a reasonable 'giving it large' temperature aim of 93c/200f to 115c/240f...although I'm reading some folks are saying running at 132c/270f is fine (and normal). That just seems real hot to me, especially as I gather Chevy themselves say 137c/280f is the maximum (although that is probably on a 'standard' motor).
So, what would you be aiming to have the oil temp in the sump max out at during a serious track day (or race) session? Main reason is a) I can now probably bring the oil temp up/down by covering the coolers, and b) I'm running a data logger that just alerts on exception rather than giving a continual gauge style readout. So I want to set a reasonable overheat trip on the logger that's still within a safe range (a few more laps) but won't get tripped too early.
Motor is a 383 stroker making 500BHP on dart heads, roller cam etc., so a pretty reasonable tune that generates some proper heat. I've just added a second oil cooler and I think at last I might have the ability to actually control the oil temp now by blanking/revealing the cooler(s) depending on use (road or track thrash)
Oil is being measured in the sump (it's a big Canton baffled/trapdoor sump).
There seems no dispute on the minimum oil temp - less than 82c/180f is too cold. I'm working on a reasonable 'giving it large' temperature aim of 93c/200f to 115c/240f...although I'm reading some folks are saying running at 132c/270f is fine (and normal). That just seems real hot to me, especially as I gather Chevy themselves say 137c/280f is the maximum (although that is probably on a 'standard' motor).
So, what would you be aiming to have the oil temp in the sump max out at during a serious track day (or race) session? Main reason is a) I can now probably bring the oil temp up/down by covering the coolers, and b) I'm running a data logger that just alerts on exception rather than giving a continual gauge style readout. So I want to set a reasonable overheat trip on the logger that's still within a safe range (a few more laps) but won't get tripped too early.
David Vizard in one of his books claims that his dyno testing demonstrates that significant power gains can be had running at 210-220°F (99-104°C) compared to 180-190°F (82-88°C).
He goes on to say 250°F (121°C) is the very limit for mineral but full synthetic are OK to 300°F (149°C).
Elsewhere he indicates best results with mineral oil is to get the coolant at 170°F (76°C) and oil at 220°F (104°C) but does point out that this is very difficult to achieve.
Steve
He goes on to say 250°F (121°C) is the very limit for mineral but full synthetic are OK to 300°F (149°C).
Elsewhere he indicates best results with mineral oil is to get the coolant at 170°F (76°C) and oil at 220°F (104°C) but does point out that this is very difficult to achieve.
Steve
Mine sits at 90'c and can rise to 110 if i'm flooring it. Temperature measured just before it feeds the turbos, taken from blanking plug near the water pump (from camshaft gallery )
I have a 26 row cooler in the front and no thermostat in the sandwich plate - before the I had that cooler, it hit 130'c every time i went out.
I run silkolene pro-r, which is a proper synthetic oil (according to opieoilman!) and has no issues at all with high temps - he said 130'c is fine.
I have a 26 row cooler in the front and no thermostat in the sandwich plate - before the I had that cooler, it hit 130'c every time i went out.
I run silkolene pro-r, which is a proper synthetic oil (according to opieoilman!) and has no issues at all with high temps - he said 130'c is fine.
You've asked a question which has no single definitive answer. The optimum oil temperature for power is that which generates the lowest friction levels and lowest pumping losses inside the engine. The optimum for engine wear and oil life would be different.
Minimum internal friction is achieved when the oil has dropped in viscosity to just above the point at which the oil film starts to breaks down. It should be apparent that this point will be reached at different temperatures with different oils. Synthetic oils will have a markedly higher film strength than conventional oils but also a lower starting viscosity. Similarly if you stick to one type of oil, synthetic or conventional, but change the grade then the optimum temperature will change too.
The first thing to do is make use of the best modern low viscosity fully synthetic oils. At the same operating temperature these will show a power gain over thicker conventional oils. On a 500 bhp Chevy you'd expect to see 10 bhp going to a modern 0-30 synthetic from a conventional 20-50 oil at the same 100c. What is unclear though is how much of that gain is from lower friction levels in the bearings and rings and how much from lower pumping losses because the oil pressure will drop with thinner oil. I'd like to see tests with the same oil but different pump pressures.
If you ran the 20-50 hotter you'd claw back some of that loss but also run a greater risk of oil breakdown. In my experience 130c is the point at which conventional oils thin enough to cause engine damage or failure. Ideally you wouldn't want to exceed 115c. Synthetics can run hotter but you probably wouldn't want to do that deliberately without long term dyno tests to verify reliability.
So the other factor to look at is the pump pressure which you can alter by shimming the relief valve. IME engines can survive at much lower pressures than people realise if the oil film strength is still ok. Thinner synthetic oils achieve both effects at the same time. However the pump pressure you require is also a function of the bearing clearances. The long held conventional view is you give race engines a thou or so more clearance than the factory figure but I've always disagreed. I build my engines very tight and run a lower pump pressure rather than the reverse. I think more people are moving to that view these days.
So I have always had my cranks ground to top limit on the size range rather than bottom limit or even lower as the books might tell you. I then use the best quality low viscosity synthetic oils and a lower pump pressure than otherwise might be required. Bearings run at a tight clearance will build up the required hydrodynamic wedge of supporting oil film at a lower pressure and flow volume than those with looser clearances.
My best guess is that power gains are more to do with pumping losses than friction levels. This means that if you get the bearings clearances right and the pump pressure to match with thin oil you really don't have to worry about running higher oil temperature. You can achieve everything you need to at about 100c with no risk of oil breakdown.
My only anecdotal evidence of my techniques is from many years ago at a Ford Fiesta XR2 race in a very hot summer at Oulton Park circuit. The regs prevented the use of oil coolers for reasons which escape me so the engines run very hot and the Ford CVH doesn't generate high oil pressures either. Oil temp was hitting 130c that day and pressures were dropping from 50 plus to under 40 psi.
I was watching at the end of the main straight and just as the drivers lifted off for the corner at peak rpm the cylinder pressure drops as the throttle shuts and the big end bearing has to cope with the full inertia force of the piston and rod with no cushioning effect from the cylinder pressure to mitigate it. I think 9 engines went pop that day in the same place. It was just a constant stream of engines coming out of the preceding corner and going whap, whap, whap, whap, bang. I had 8 engines running, all of them built tight and none of them suffered any ill effects.
Dave Baker
Puma Race Engines
Minimum internal friction is achieved when the oil has dropped in viscosity to just above the point at which the oil film starts to breaks down. It should be apparent that this point will be reached at different temperatures with different oils. Synthetic oils will have a markedly higher film strength than conventional oils but also a lower starting viscosity. Similarly if you stick to one type of oil, synthetic or conventional, but change the grade then the optimum temperature will change too.
The first thing to do is make use of the best modern low viscosity fully synthetic oils. At the same operating temperature these will show a power gain over thicker conventional oils. On a 500 bhp Chevy you'd expect to see 10 bhp going to a modern 0-30 synthetic from a conventional 20-50 oil at the same 100c. What is unclear though is how much of that gain is from lower friction levels in the bearings and rings and how much from lower pumping losses because the oil pressure will drop with thinner oil. I'd like to see tests with the same oil but different pump pressures.
If you ran the 20-50 hotter you'd claw back some of that loss but also run a greater risk of oil breakdown. In my experience 130c is the point at which conventional oils thin enough to cause engine damage or failure. Ideally you wouldn't want to exceed 115c. Synthetics can run hotter but you probably wouldn't want to do that deliberately without long term dyno tests to verify reliability.
So the other factor to look at is the pump pressure which you can alter by shimming the relief valve. IME engines can survive at much lower pressures than people realise if the oil film strength is still ok. Thinner synthetic oils achieve both effects at the same time. However the pump pressure you require is also a function of the bearing clearances. The long held conventional view is you give race engines a thou or so more clearance than the factory figure but I've always disagreed. I build my engines very tight and run a lower pump pressure rather than the reverse. I think more people are moving to that view these days.
So I have always had my cranks ground to top limit on the size range rather than bottom limit or even lower as the books might tell you. I then use the best quality low viscosity synthetic oils and a lower pump pressure than otherwise might be required. Bearings run at a tight clearance will build up the required hydrodynamic wedge of supporting oil film at a lower pressure and flow volume than those with looser clearances.
My best guess is that power gains are more to do with pumping losses than friction levels. This means that if you get the bearings clearances right and the pump pressure to match with thin oil you really don't have to worry about running higher oil temperature. You can achieve everything you need to at about 100c with no risk of oil breakdown.
My only anecdotal evidence of my techniques is from many years ago at a Ford Fiesta XR2 race in a very hot summer at Oulton Park circuit. The regs prevented the use of oil coolers for reasons which escape me so the engines run very hot and the Ford CVH doesn't generate high oil pressures either. Oil temp was hitting 130c that day and pressures were dropping from 50 plus to under 40 psi.
I was watching at the end of the main straight and just as the drivers lifted off for the corner at peak rpm the cylinder pressure drops as the throttle shuts and the big end bearing has to cope with the full inertia force of the piston and rod with no cushioning effect from the cylinder pressure to mitigate it. I think 9 engines went pop that day in the same place. It was just a constant stream of engines coming out of the preceding corner and going whap, whap, whap, whap, bang. I had 8 engines running, all of them built tight and none of them suffered any ill effects.
Dave Baker
Puma Race Engines
Something I should add to my view about building engines with tight bearing clearances. The "conventional" wisdom about adding a thou or so bearing clearance for a race engine dates back to books written in the 60s and 70s about building things like Mini and Ford Pinto engines. It would also apply to the OP's Chevy. Back then an average road engine produced only 50 bhp per litre or so and revved to maybe 5500 or 6000 rpm. A rally or race engine might produce from 75 to 100 bhp per litre and rev to 7500. However we now have bog standard 4v per cylinder road engines producing as much or more power than a highly tuned 2v engine of yesteryear. Honda Civic type R or BMW M3 for example.
In effect these engines 'are' race engines because the crank doesn't know that the loads it's being asked to cope with are due to 4 valves per cylinder and mild road cams rather than 2 valves per cylinder, ported heads and race cams. It's still 100 bhp per litre and 7500 plus rpm. The difference is these stock 'race' engines are expected to last for over 100,000 miles and the old tuned Minis would need a rebuild after each season.
Do the OE manufacturers give their highly tuned modern engines that thou extra bearing clearance the old timers were taught to use in race engines? Do they buggery! The crank bearing clearances are no different to any other standard engine. A tolerance range from as little as under 1 thou to about 2 thou is common.
Certainly a country mile from the 3 thou or more clearances that the old tuning books promulgated along with slapping in high output oil pumps or packing the pressure relief valve spring up with washers - all totally unnecessary IMO.
When I started building engines 30 or so years ago I thought long and hard about all this and came to the conclusion that just because one was modifying an engine to produce more power didn't seem to adequately explain to me why I should make all the bits inside it a sloppy fit, do even more things to compensate for that like thick oil and shimmed oil pumps and then of course have it all wear out faster than otherwise. So I didn't and the development in the power output of modern road engines seems to have confirmed my thoughts.
For those of you who don't have the 2 inch thick bearing catalogues from Glacier and the like that we rely on when building an engine you can get most of it online these days. Visit the King Bearing web site for example.
http://www.king-bearings.com/cat/html/engines.htm
You can look up the dimensions for all the crank and bearing components and work out the tolerance range of the clearances from the min and max journal sizes and housing sizes. You'll be surprised just how tight a modern 4v engine (or any other engine) can run its clearances if all the tolerances stack up the appropriate way. Like I say it can be well under 1 thou but they'll scream away all day long at peak rpm like that and the owner will never give it a second thought.
The OP's engine is producing about 80 bhp per litre. Nothing special by today's standards and far exceeded by many stock 4v engines. Those stock engines will be happiest on thin synthetic oils, tight bearing clearances, stock oil pumps producing no more than maybe 50 to 60 psi and 100c oil temperature.
If you want to look at really high specific output engines you need to go to the motorbike world. 200 bhp per litre and 14,000 rpm is not unknown there from normally aspirated 4v engines. Do they use massive bearing clearances and thick oil to compensate? You can draw your own conclusions.
In effect these engines 'are' race engines because the crank doesn't know that the loads it's being asked to cope with are due to 4 valves per cylinder and mild road cams rather than 2 valves per cylinder, ported heads and race cams. It's still 100 bhp per litre and 7500 plus rpm. The difference is these stock 'race' engines are expected to last for over 100,000 miles and the old tuned Minis would need a rebuild after each season.
Do the OE manufacturers give their highly tuned modern engines that thou extra bearing clearance the old timers were taught to use in race engines? Do they buggery! The crank bearing clearances are no different to any other standard engine. A tolerance range from as little as under 1 thou to about 2 thou is common.
Certainly a country mile from the 3 thou or more clearances that the old tuning books promulgated along with slapping in high output oil pumps or packing the pressure relief valve spring up with washers - all totally unnecessary IMO.
When I started building engines 30 or so years ago I thought long and hard about all this and came to the conclusion that just because one was modifying an engine to produce more power didn't seem to adequately explain to me why I should make all the bits inside it a sloppy fit, do even more things to compensate for that like thick oil and shimmed oil pumps and then of course have it all wear out faster than otherwise. So I didn't and the development in the power output of modern road engines seems to have confirmed my thoughts.
For those of you who don't have the 2 inch thick bearing catalogues from Glacier and the like that we rely on when building an engine you can get most of it online these days. Visit the King Bearing web site for example.
http://www.king-bearings.com/cat/html/engines.htm
You can look up the dimensions for all the crank and bearing components and work out the tolerance range of the clearances from the min and max journal sizes and housing sizes. You'll be surprised just how tight a modern 4v engine (or any other engine) can run its clearances if all the tolerances stack up the appropriate way. Like I say it can be well under 1 thou but they'll scream away all day long at peak rpm like that and the owner will never give it a second thought.
The OP's engine is producing about 80 bhp per litre. Nothing special by today's standards and far exceeded by many stock 4v engines. Those stock engines will be happiest on thin synthetic oils, tight bearing clearances, stock oil pumps producing no more than maybe 50 to 60 psi and 100c oil temperature.
If you want to look at really high specific output engines you need to go to the motorbike world. 200 bhp per litre and 14,000 rpm is not unknown there from normally aspirated 4v engines. Do they use massive bearing clearances and thick oil to compensate? You can draw your own conclusions.
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