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Starting up a dry sump engine car.


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#1 mariner

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Posted 30 May 2014 - 18:31

Historically, starting racing cars with dry sump (DS) lubrication was lengthy business. From towing it round the paddock through grinding it over on slave battery to spinning the oil pump sprocket with an air wrench it was a sort of a  ritual.

 

However lots of road cars have dry sump systems now - as have bikes for years. There you just get in, turn the key and go.

I know you are supposed to still let the oil warm up etc. but there is no chance for the system to be primed or pre-lubed. In fact modern high power ignition systems will  fire it up in just a few crank rotations and go straight to high idle

 

I can see that the 911 series which has always had dry sump benefits from the very low cylinder position but cars like the Z06 Corvette and the BMW M5 are " twist and go".with Vee engines.

 

Was the old ritual never really necessary or is it the new multi grade oils which allow no priming with a dry sump.

 

I do notice that road car DS systems usually locate the dry sump tank very close to the oil pump , e.g the Corvette and 911. Maybe with short lines no priming is required?

 

 



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#2 BRG

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Posted 30 May 2014 - 19:02

We ran a dry-sumped Miilington Diamond in the rally car.  Just started it up as normal, although waited a second or so for the oil pressure to come up before revving it at all.  This was indeed on Mobil 1 oil, so maybe you've got something there



#3 Siddley

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Posted 30 May 2014 - 19:41

Could production cars use an accumulator system to ensure start up pressure ?



#4 Lee Nicolle

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Posted 30 May 2014 - 23:29

My only dramas with dry sumped race Chev was when the car had sat for several weeks [or months] was just priming up the system again. Which was actually simple enough. Slip the belt off and turn the pump by hand for a minute or so.You can feel the pressure come and then put the belt back on.[After checking for nicks from stones]

Every other time is simple as a seperate ign switch, crank the engine for a couple of sec watching the guage, when it starts to move turn on the ignition. With a one way valve from the tank to the pump most of that is not nesecary anyway. Though I have never seen a race system with one. 

So many people however mount the tank in stupid positions causing all the grief mentioned. Tank must be fairly close to the engine and above the oil pump. So simple but so many big time teams seem to stuff it up!

I have looked at Nascar style cars, V8 Supercars etc with the tank down low in the back of the car. What are they thinking? The weight of all those lines alone defeats the weight of a 10 litres  of oil.And any more is a waste.  And the drag of those lines does reduce oil pressure meaning you have to crank up the oil pressure to blazes to compensate making the pump work harder dragging more power.

I managed to talk a fellow competitor who was having minor oil issues to move his tank forward about 6 foot. 20lb more oil pressure was the result so then he had to turn down the pressure. And no more replacing the bearing shells every 2nd or 3rd meeting! And some of these cars have 12-15 feet of hoses. Go figure!


Edited by Lee Nicolle, 30 May 2014 - 23:32.


#5 mariner

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Posted 31 May 2014 - 08:21

I hadn't thought of anything as simple as a one-way valve.

 

Thinking about that here is conflict in a dry sump system as you want all the oil in the tank and none in the crankcase when running. However oil , being a liquid, will find it's own level if left long enough and it will drain from the tank into the crankcase unless the bottom of the tank is down level with the bottom of the sump.

 

So systems whch have the tank bottom higher, either for installation reasons or  to ensure the pump always sucks in oil when running, would have priming problems as the oil has to be scavenged , sent through the oil lines and cooler etc before the pressure pump gets it.


Edited by mariner, 31 May 2014 - 08:31.


#6 gruntguru

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Posted 31 May 2014 - 08:31

If the tank is located so the level of the pressure pump is somewhere between the bottom of the tank and the normal oil level, a lengthy period of no running will only see the oil drain down to the pressure pump level i.e. there will still be some oil in the tank.



#7 bigleagueslider

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Posted 01 June 2014 - 00:12

In terms of the small delay in the oil pressure pump producing operating pressure levels in the oil circuit, there should be no real difference between the two. Both systems, if properly designed,  provide a ready feed of oil to the pressure pump inlet port at start-up.



#8 Lee Nicolle

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Posted 01 June 2014 - 23:15

I hadn't thought of anything as simple as a one-way valve.

 

Thinking about that here is conflict in a dry sump system as you want all the oil in the tank and none in the crankcase when running. However oil , being a liquid, will find it's own level if left long enough and it will drain from the tank into the crankcase unless the bottom of the tank is down level with the bottom of the sump.

 

So systems whch have the tank bottom higher, either for installation reasons or  to ensure the pump always sucks in oil when running, would have priming problems as the oil has to be scavenged , sent through the oil lines and cooler etc before the pressure pump gets it.

Honestly I have never seen the tank lose much level. I guess the gears themselves stop oil drainback to the engine pan. The scavenge sections are quite efficient, on my pan the pickups were fully at the bottom of the engine pan. Turn the engine off and take the hoses off and you may get 50ml of oil out of the pan. 

Though again many 'experts' go out of their way to cock up something simple and probably have a lot more oil flailing around on the crank. But it looks pretty or they can get the engine and inch lower in the car. Which on a Sprintcar is superflous as the practicality of the chassis prohibits a very low engine anyway. 



#9 Canuck

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Posted 02 June 2014 - 00:47

Harley's solution on the Evo and Shovelhead at least, was a check ball and spring on the main oil passage. It wasn't uncommon to have some bit of debris get under the ball and have the oil fill the crankcase over the winter.

Due to Harley's crankcase breather routing, the customer complaint was often "my carburetor is leaking oil!" as the breather system pumped it all over the garage floor.

#10 desmo

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Posted 02 June 2014 - 03:01

There really is no customer friendly way to route a puke tube.



#11 MatsNorway

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Posted 02 June 2014 - 06:20

Harleys and i guess then other motorcycles got roller bearings and such in the crank-rod joint. So im not sure if they are good to compare with Since no car that i know of have that. Why not btw? a small car engine should just fine work with that. Improving efficiency?...



#12 Lee Nicolle

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Posted 02 June 2014 - 08:48

Roller bearings on conrods [or mains] do not have a very high service life. It seems that is acceptable on a motorcycle but not on a passenger car. The only advantage is they can get away with less oil. Really does any 'normal' race engine use needle roller on the crank? Even needle roller rockers dont last all that long, even in comparison to a normal tin rocker. Surprising to some but true.



#13 Patrick Morgan

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Posted 02 June 2014 - 12:56

One other consideration - if the engine has roots type scavenge pumps and one pump per chamber you run the risk of snapping the quill shafts that connect the pumps. Roots pumps are very good as sucking oil and air but offer a lot of resistance with just oil alone. If you see us start an Indycar at Goodwood you will notice us "bumping" the engine twice before spinning it to evacuate some of the oil before cranking.

 

I have seen several engines with reed valves in the scavenge system to prevent or reduce bleed back over time. 

 

The twin turbo F1 cars (with low mounted turbos) have and additional problem with oil - when stopped the turbo scavenge lines, being low and a large diameter, tend to fill and in turn flood the compressor and turbine. For this reason we take the oil out of the 98T every night so it doesn't smoke the next morning. 



#14 Magoo

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Posted 02 June 2014 - 13:38

A forum search will find a number of productive discussions on dry sump systems around here over the years. 



#15 Lee Nicolle

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Posted 03 June 2014 - 09:34

One other consideration - if the engine has roots type scavenge pumps and one pump per chamber you run the risk of snapping the quill shafts that connect the pumps. Roots pumps are very good as sucking oil and air but offer a lot of resistance with just oil alone. If you see us start an Indycar at Goodwood you will notice us "bumping" the engine twice before spinning it to evacuate some of the oil before cranking.

 

I have seen several engines with reed valves in the scavenge system to prevent or reduce bleed back over time. 

 

The twin turbo F1 cars (with low mounted turbos) have and additional problem with oil - when stopped the turbo scavenge lines, being low and a large diameter, tend to fill and in turn flood the compressor and turbine. For this reason we take the oil out of the 98T every night so it doesn't smoke the next morning. 

Your perspective on engines is entirely different to mine. Thoroughbred all out racing engines. Mine is all production based.Though it seems the problems are not disimilar.

Though I have never seen a shaft break in a pump. Seen them jammed with valvetrain trash, and a conrod nut! Probably good that got sucked up!

With my description of priming the pump by hand it is interesting to watch the pump go backwards, sometimes 2 or 3 revolutions just with resistance of the oil. That with gear pumps.



#16 bigleagueslider

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Posted 04 June 2014 - 03:09

One reason for spinning a dry-sump oil pump on a race engine prior to starting is to make sure any oil that has drained from the tank into the sump is returned to the tank. The tank outlet to the pressure pump is usually located at the bottom of the tank, and the tank is usually located well above the pressure pump and sump level. Unless the pressure pump plumbing provides some form of siphon break, it might be possible that left for a long period of time, the oil in the tank could slowly drain/siphon down into the sump.



#17 Canuck

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Posted 04 June 2014 - 14:22

Dejavu



#18 Bloggsworth

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Posted 04 June 2014 - 21:25

The only time I worried about oil pressure was on a rebuilt engine, I just took the plugs out, spun up the oil pressure, the put the plugs back in. Normally on my FF Merlyn I just started it up as normal.



#19 bigleagueslider

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Posted 07 June 2014 - 03:42

The journal bearings used for crank mains/rods can operate safely for short periods of time on just the tiny amount of lube oil present in the bearing gap. The flow of lube oil to these journal bearings from the pressure pump is needed mostly for cooling purposes. The journal bearings will not overheat in the 3 or 4 seconds of running it takes after starting to get oil pressure in the lube circuit.



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#20 Lee Nicolle

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Posted 07 June 2014 - 06:33

The journal bearings used for crank mains/rods can operate safely for short periods of time on just the tiny amount of lube oil present in the bearing gap. The flow of lube oil to these journal bearings from the pressure pump is needed mostly for cooling purposes. The journal bearings will not overheat in the 3 or 4 seconds of running it takes after starting to get oil pressure in the lube circuit.

That depends on how much compression you are banging on those bearings. Believe me, start a race engine with no oil pressure and that bearing shells will scuff and sometimes lose their crush. All in 2-3 sec. You NEVER light the fire until you have oil pressure. And remember a race engine does not usually run smooth or idle immediatly upon start up.

A std street gunker engine may [and usually do] live for these couple of sec. With maybe 9-1 compression and operates at under 3500 rpm. Try 12+-1 and 7000 rpm and the rods will be spinning bearings or hanging out the side of the block.


Edited by Lee Nicolle, 07 June 2014 - 06:37.


#21 mariner

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Posted 07 June 2014 - 11:45

On my own , rather basic "toy car" there is a start up problem because it is a BBC pushrod engine and its not recommended to run it below 2,000 rpm on start up to be sure enough oil is flung around to lube the followers. Having a dry sump execerbates the probelm.

 

 

So I give it  few short cranks with ign off till I see the oil pressure rise. Then I start it and hold 2,000 rpm for  a while.

 

I think the " rev it upon start" advice was aimed at flat tappet cams with high ramp angles and mine has a roller cam. However I've never been rave enough to ignore the advice


Edited by mariner, 07 June 2014 - 11:50.


#22 Canuck

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Posted 07 June 2014 - 19:44

I would think that a cam optimised for an engine running to 7000 rpm would have an overlap such that even a 12:1 compression ratio would not present an "unbearable" load at starting. Apart from that, what lunatic starts and runs his (or her) full-scale engine to 7000 rpm in the first two or three seconds of running?

#23 Lee Nicolle

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Posted 08 June 2014 - 08:58

Noone sensible runs and engine to 7k on start up but starting those engines which generally have a lot of advance also is madness with no oil pressure. And yes there is huge amounts of load with a 12+ -1 engine whatever the overlap. 

I have seen the results on numerous occasions on engines I have done or just observed coming apart. Take the caps off and the shells just fall out. After one meeting. Do it as I say and they will run a full cycle and still be ok. The longest I went was aprox 2500km of short races over a couple of years. Bearings were 98% and were useable again. Unfortunatly the crank was cracked so I have another  set of good used shells! That on a 12.1-1 350 Chev making 580hp.



#24 bigleagueslider

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Posted 11 June 2014 - 04:40

That depends on how much compression you are banging on those bearings. Believe me, start a race engine with no oil pressure and that bearing shells will scuff and sometimes lose their crush. All in 2-3 sec. You NEVER light the fire until you have oil pressure. And remember a race engine does not usually run smooth or idle immediatly upon start up.

A std street gunker engine may [and usually do] live for these couple of sec. With maybe 9-1 compression and operates at under 3500 rpm. Try 12+-1 and 7000 rpm and the rods will be spinning bearings or hanging out the side of the block.

Most auto/truck diesel engines experience much higher forces from intake compression on the rod and main bearings during start-up than any F1 engine does, since they tend to use higher geometric CR's and have a better trapping efficiency due to much less valve overlap. Not to mention the diesel engines usually tend to get cranked for much longer periods during start-up than a race engine does.

 

The thickness of a hydrodynamic oil film in an engine journal bearing that supports the forces produced by pressure applied to the piston is less than 50 microinch, and the contact area of that oil film is just a few mm^2. So the volume of oil required to produce this hydrodynamic oil film is quite small. The volume of oil left trapped in the gap between the bearing and journal surfaces at shut down is sufficient to maintain a hydrodynamic oil film at the bearing contact for a couple seconds of crank rotation. Going longer than that will create excessive heating of this small mass of oil, and this will result in a large drop in the oil's viscosity and thinning of the oil film thickness to the point where it transitions to boundary contact conditons and possibly scuffing. One thing that helps is that the bearing and journal surfaces are usually relatively cool when started, which reduces the intial rate of heat input to the oil film.

 

Consider the lube conditions that exist in the roller crank bearings of a typical 2-stroke engine. These roller bearings actually operate with hydrodynamic contact between the rollers and race surfaces, similar in principle to that of journal type crank bearings. While the film pressures and associated surface bearing stress levels are higher in the roller bearing, why is it possible for these roller bearings to operate with so little oil feed in comparison to journal bearings? The answer is that the 2-stroke roller bearings do not rely on oil flow for cooling like the journal bearings do, instead they are cooled mostly by the air passing thru the crankcase.



#25 gruntguru

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Posted 11 June 2014 - 06:43

Consider the lube conditions that exist in the roller crank bearings of a typical 2-stroke engine. These roller bearings actually operate with hydrodynamic contact between the rollers and race surfaces, similar in principle to that of journal type crank bearings. While the film pressures and associated surface bearing stress levels are higher in the roller bearing, why is it possible for these roller bearings to operate with so little oil feed in comparison to journal bearings? The answer is that the 2-stroke roller bearings do not rely on oil flow for cooling like the journal bearings do, instead they are cooled mostly by the air passing thru the crankcase.

A hydrodynamic bearing tends to squeeze the oil film out when loaded. Elasto-hydrodynamic lubrication (as in rolling element bearings) similarly squeezes the oil film out of the high pressure zone, but the oil remains attached to the sides of the roller or ball bearing and is therefore still in a region where it can remain useful. The volume of oil required to maintain the elasto-hydrodynamic film is also much less because both the film thickness and the load-bearing area are much smaller than journal bearings.

 

EDIT. I believe the minimum lube flow requirements are more closely related to these factors than to air vs oil cooling.


Edited by gruntguru, 13 June 2014 - 05:50.


#26 bigleagueslider

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Posted 13 June 2014 - 03:01

A hydrodynamic bearing tends to squeeze the oil film out when loaded. Elasto-hydrodynamic lubrication (as in rolling element bearings) similarly squeezes the oil film out of the high pressure zone, but the oil remains attached to the sides of the roller or ball bearing and is therefore still in a region where it can remain useful. The volume of oil required to maintain the elasto-hydrodynamic film is also much less because both the film thickness and the load-bearing area are much smaller than journal bearings.

The main difference between hydrodynamic and elastohydrodynamic fluid film contact conditions is their lamda ratio, or film thickness to surface asperity height ratio. Engine journal bearings typically are designed for much lower fluid film pressures than rolling element bearings, since the surface fatigue strength of the engine journal bearing shells is much lower than that of hardened steel rollers and races. With either type of bearing, it is usually not practical to design the bearing to operate at EHL conditions. While operating at EHL conditions would give best efficiency, the margins between hydrodynamic, EHL and boundary conditions is incredibly small. And once the contact degrades to boundary conditions, things go bad real fast.



#27 gruntguru

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Posted 13 June 2014 - 05:50

Agree with most of that but my point was something else. See the edit to Post #25.



#28 bigleagueslider

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Posted 15 June 2014 - 00:44

With either hydrodynamic or EHL fluid film contacts one of the primary concerns is the flash temp rise within the lubricant at the contact area. The heat transfer situation there is quite complex, since you have a relatively large amount of heat generated from viscous shear that must be transferred into the lubricant film and into the surfaces of the bearing and journal. If the journal and bearing surfaces do not efficiently conduct heat away from the fluid film contact area, then more heat load will be forced into the lubricant film. And this will reduce the viscosity of the lubricant within the fluid film, which in turn will reduce the thickness of the fluid film, creating a self-perpetuating type of condition that often results in a scuffing or scoring type of failure. If the flash temps in the fluid film get to levels above about 375degF, it can create thermal fatigue problems with rolling element bearing materials or engine journal beaing materials.



#29 Lee Nicolle

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Posted 18 June 2014 - 00:48

Somewhere in Smokey Yunicks Power Secrets book is reference to hammering the bearing in the centre, a result of a lack of oil. And believe me it happens quick! Sometimes the bearing even looks sort of ok, but loses its crush.

Road car engines also do this, most shells fall on the ground once the cap is cracked. But they are not subjected to sustained high rpm and often high oil temps too. I doubt too the start up loads on a low performance diesel is the same as a 12+-1 race engine. Though are substansial. Diesels also tend to have larger bearings which is stronger in a low rpm engine but a real drama in a high rpm engine.

And in my experience smaller passenger diesels last less than their petrol brothers. And cost a lot more to maintain too.



#30 indigoid

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Posted 18 June 2014 - 11:31

Funny you should have mentioned the one-way valves Lee, I was watching a Leno's Garage today about his Porsche 356 twincam... and he'd had a one-way valve fitted to stop it burning heaps of oil at startup after sitting for a while.

 

Hashtag #EnormousGarageProblems ;-)



#31 Canuck

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Posted 20 June 2014 - 22:35

I would think that even a low performance diesel has a higher compression ratio than 12:1.  Add to that, that this low-performing diesel's peak rpm is likely somewhat less than 3000 rpm so it's cam timing and overlap is going to be optimized for low speed performance.  If we're assuming the same cylinder displacement, I can't understand how the bearing load at start-up would be lower in the diesel than in the 12:1 performance engine.

 



#32 bigleagueslider

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Posted 21 June 2014 - 04:54

Most current auto/truck turbodiesels use CRs around 17:1. But when comparing the loads created on the conrod/main bearings from this compression pressure force, you should also consider that diesel engines also have much lower bore/stroke ratios than something like a highly over-square F1 engine. Even though the compression pressure of the diesel is higher, for a given displaced volume per cylinder, the compression pressure force acting on the F1 engine piston will not likely be much different due to the larger piston area the compression pressure is acting on.



#33 Lee Nicolle

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Posted 21 June 2014 - 09:06

I would think that even a low performance diesel has a higher compression ratio than 12:1.  Add to that, that this low-performing diesel's peak rpm is likely somewhat less than 3000 rpm so it's cam timing and overlap is going to be optimized for low speed performance.  If we're assuming the same cylinder displacement, I can't understand how the bearing load at start-up would be lower in the diesel than in the 12:1 performance engine.

The way the engine produces the power is the load. Start a race engine and it is harsh and sharp. Petrol is far more volatile so a bigger bang than diesel. Say 600hp compared with maybe 200 if you are lucky.

Most diesels are between 14 and about 21-1 so high loads are undoubtedly there. But a lot smoother at idle and just above. Though diesels are very susceptible to dirty oils and filters and are very reliant on good oil pressure for any decent service life.. They generally pump higher volumes of oil too.And carry higher volumes too often.  Far easy to control on a low rpm engine.

Really it is plain commonsense.



#34 Canuck

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Posted 21 June 2014 - 14:12

600 hp at idle?

This thread, and your statement, was about oil pressure and bearing loads durIng start-up. I don't don't doubt that peak bearing loads during useful operation are higher in the performance engine, but - still - find that difficult to accept during the start phase. This is why I asked if you're loading the engine and revving it immediately upon start.

A performance engine with overlap optimised to develop peak power around (your example) 7000 rpm is going to have (comparably) little cylinder load at idle as the overlap is pumping a good deal of the intake charge out the tail pipe without ever having compresed it. 12:1 compression of very little still equals very little.

Conversely, the diesel is already idling at the start of it's power band, already "coming on cam" and is running ~17:1 give or take. Granted, as pointed out by BLS, the area the combustion force is acting on is smaller, the total force applied is still higher. That's common sense. The discussion about dirty oil or volumes is incidental and has nothing to do with the load.

Additionally, while gasoline may be more volatile, diesel has more energy per unit volume, on the order of 13.5% more.

#35 Lee Nicolle

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Posted 22 June 2014 - 03:08

600 hp at idle?

This thread, and your statement, was about oil pressure and bearing loads durIng start-up. I don't don't doubt that peak bearing loads during useful operation are higher in the performance engine, but - still - find that difficult to accept during the start phase. This is why I asked if you're loading the engine and revving it immediately upon start.

A performance engine with overlap optimised to develop peak power around (your example) 7000 rpm is going to have (comparably) little cylinder load at idle as the overlap is pumping a good deal of the intake charge out the tail pipe without ever having compresed it. 12:1 compression of very little still equals very little.

Conversely, the diesel is already idling at the start of it's power band, already "coming on cam" and is running ~17:1 give or take. Granted, as pointed out by BLS, the area the combustion force is acting on is smaller, the total force applied is still higher. That's common sense. The discussion about dirty oil or volumes is incidental and has nothing to do with the load.

Additionally, while gasoline may be more volatile, diesel has more energy per unit volume, on the order of 13.5% more.

Obviously not,, but a whole lot more at 2000rpm than the diesel  has at max power, and whole lot less smooth.



#36 bigleagueslider

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Posted 23 June 2014 - 02:50

During start-up, the loads on conrod/main bearings are only those created by intake compression pressure and inertia forces created by the reciprocating/rotating masses. This is true for both gas and diesel engines. Once the engine fires, the power required to maintain an unloaded idle speed is proportional to the friction and inertia losses of the engine itself.



#37 John Brundage

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Posted 23 June 2014 - 16:41

 

Though diesels are very susceptible to dirty oils and filters and are very reliant on good oil pressure for any decent service life..

 

 An old two stroke Detroit Diesel would have a hot idle oil pressure at about 5psi, and a 3psi low pressure switch.