Technical Question re Forced Induction

[chuntington101]

Boosted LS1 said:

My 427 lsx has squirters, it doesn't have pistons rods and heads though bit of a bugger that!

i didn't think LS engines had squirters Mike?? have you fitted aftermarket ones or something??

what are you running the LSX block in?? is it the Iron one form GM??

Chris.

[knighty]

stevieturbo said:

knighty said:

high compression is not the main reason detonation occurs.......world rally cars run in excess of 12:1 and are very heavily turbo charged, unlimited boost I think, just a 34mm restrictor........detonation is actually related to piston temperature, particularly localised piston temperatures whereby sharp edges get too hot and act like a small spark plug which pre-ignites the charge and causes detonation........this is why all good race pistons feature a high amount of CNC milling in order to remove all sharp edges from critical areas, like the piston intruder/dome and the piscon cut-outs where the valves clear.

also any decent pressure charged engine should feature a decent piston cooling jet, F1 teams have found that if they reduce piston temperature by only 10 degrees, the engine life extends greatly, hence each piston now has 10.....yes 10 per piston! .......piston cooling jets firing a horrendous amount of oil at each piston underside

I was also recently told the piston cooling jets in the JCB land speed car fire 20 litres per minute at each piston.......now thats a lot!

so next time you are chosing an engine for turbo/supercharging, make sure it has piston cooling jets, otherwise expect grief, like detonation, scuffed bores etc

WRC cars make heavy use of water injection. The restrictor also plays a part in running such high CR, as the engine struggles to ever see normal atmospheric pressure anyway.

As for the oil jets...while nice to have, Ive never run them on my car, and never had any problems. And oil jets will certainly not stop detonation, or scuffed bores.

since when has WRC been running water injection?.......I think you have your wires crossed here, yes they run water injection, but its indirect, (not direct) its squirted on the OUTSIDE of the intercooler in order to cool the air inside.....not down the intake.

piston cooling jets DO prevent scuffed bores, I have stripped numerous road car engines with scuffed bores, the failure mode being swarf blocking the piston cooling jet, its a common failure.

regarding your restrictor theory....on an F3 engibne, yes correct.......on an WRC engine, no.

as for your second paragraph.......oil jets are an absolute necessity for any highly pressure charged race or road engine, I have just spent 5 years working for a major motor manufacturer in the field of base engine design and have also helped design numerous professional race engines - including WRC engines......... when a big piston supplier like MAHLE begs you to use piston cooling jets in order to control piston temperature and detonation, you tend to believe them.

[Boosted LS1]

chuntington101 said:

Boosted LS1 said:

My 427 lsx has squirters, it doesn't have pistons rods and heads though bit of a bugger that!

i didn't think LS engines had squirters Mike?? have you fitted aftermarket ones or something??

what are you running the LSX block in???

Chris.

LS9 squirters Chris. The blocks not running in anything faster then a cardboard box at the moment.

[Boosted LS1]

Knighty said

"piston cooling jets DO prevent scuffed bores, I have stripped numerous road car engines with scuffed bores, the failure mode being swarf blocking the piston cooling jet, its a common failure".

How come they have swarf in the oil ways and why is this a common failure? Which type of engine suffers from this? Seems very careless of the manufacturer. Do the shells suffer as well?

[knighty]

this failure is very common on turbo diesel engines, as they are the majoritty of engines fitted with forced induction and therefore Piston Cooling Jets (PCJ's) there is more swarf floating about in new engines than there should be.......yes, your quite correct, quite careless of manufacturers, cylinder block wash stations are not as effective as they should be......I'm told the Japanese manufacturers have this area sussed, the europeans and US dont.......engine failure due to dirty build is unfortunatley more common than the manufacturers would have you know.

the failure is not very common on NA engines as piston temp is not such an issue for your average road car engine........but a highly strung NA race/fast road engine it is an issue

the new generation of gasoline engines due to debut in around 2010 will be downsized in capacity by around 1/3rd to 1/2 in cc, but will be heavily pressure charged and will feature piston cooling jets as standard, as a guide half the oil flow gos through the piston cooling jets, its very significant.

yes, the shells suffer, but a bearing shell is designed in order to be soft enough and absorb a certain level of crud.......dosent look nice, but will run quite ok once bedded right in.

Edited by knighty on Tuesday 5th August 11:36

Edited by knighty on Tuesday 5th August 11:37

[chuntington101]

knighty said:

this failure is very common on turbo diesel engines, as they are the majoritty of engines fitted with forced induction and therefore Piston Cooling Jets (PCJ's) there is more swarf floating about in new engines than there should be.......yes, your quite correct, quite careless of manufacturers, cylinder block wash stations are not as effective as they should be......I'm told the Japanese manufacturers have this area sussed, the europeans and US dont.......engine failure due to dirty build is unfortunatley more common than the manufacturers would have you know.

the failure is not very common on NA engines as piston temp is not such an issue for your average road car engine........but a highly strung NA race/fast road engine it is an issue

the new generation of gasoline engines due to debut in around 2010 will be downsized in capacity by around 1/3rd to 1/2 in cc, but will be heavily pressure charged and will feature piston cooling jets as standard, as a guide half the oil flow gos through the piston cooling jets, its very significant.

yes, the shells suffer, but a bearing shell is designed in order to be soft enough and absorb a certain level of crud.......dosent look nice, but will run quite ok once bedded right in.

Edited by knighty on Tuesday 5th August 11:36

Edited by knighty on Tuesday 5th August 11:37

Knighty, can you jsut run bigger oil pumps?? would that not compensate for the 50% reduce in oil volume (thanks to the squirters)?/

Chris.

[chuntington101]

Boosted LS1 said:

chuntington101 said:

Boosted LS1 said:

My 427 lsx has squirters, it doesn't have pistons rods and heads though bit of a bugger that!

i didn't think LS engines had squirters Mike?? have you fitted aftermarket ones or something??

what are you running the LSX block in???

Chris.

LS9 squirters Chris. The blocks not running in anything faster then a cardboard box at the moment.

ooowwww right! lol

soare these going on LS1/2/3/6/7or9 blocks?? or GM LSX (iron) or world products Warhawk blocks??? hehe

also why aren't more people running these squierters in the LSx world??

Chris.

[Boosted LS1]

^ I've got them in an alloy block. Machining's required to fit them. As for other people maybe they can't get hold of them, didn't know about them or don't think they need them. Who knows. I got my squirts a year ago

[knighty]

chuntington101 said:

knighty said:

this failure is very common on turbo diesel engines, as they are the majoritty of engines fitted with forced induction and therefore Piston Cooling Jets (PCJ's) there is more swarf floating about in new engines than there should be.......yes, your quite correct, quite careless of manufacturers, cylinder block wash stations are not as effective as they should be......I'm told the Japanese manufacturers have this area sussed, the europeans and US dont.......engine failure due to dirty build is unfortunatley more common than the manufacturers would have you know.

the failure is not very common on NA engines as piston temp is not such an issue for your average road car engine........but a highly strung NA race/fast road engine it is an issue

the new generation of gasoline engines due to debut in around 2010 will be downsized in capacity by around 1/3rd to 1/2 in cc, but will be heavily pressure charged and will feature piston cooling jets as standard, as a guide half the oil flow gos through the piston cooling jets, its very significant.

yes, the shells suffer, but a bearing shell is designed in order to be soft enough and absorb a certain level of crud.......dosent look nice, but will run quite ok once bedded right in.

Edited by knighty on Tuesday 5th August 11:36

Edited by knighty on Tuesday 5th August 11:37

Knighty, can you jsut run bigger oil pumps?? would that not compensate for the 50% reduce in oil volume (thanks to the squirters)?/

Chris.

correct, you just run a bigger flow oil pump when running PCJ's.......not just a washer/shim under the pressure relief valve in order to get more system pressure......you need double the flow, not just a pressure increase.

the best piston cooling jets feature an integral check-valve in each jet that will not open until 2 Bar, that way Idle pressure is not affected and the PCJ's are only flowing once the engine is pushing in the medium to hard range......I have seen other manufacturers do this with a seperate main gallery just for the PCJ's and it features its own check-valve at the entry that will open at 2 Bar.

if you are retro fitting to an existing engine you can drill whats called a "saddle jet" into the main bearing which squirts the piston and bore.......this is considered a cheap way of doing it, and not ideal, but it works, trick is to always aim it at the exhaust side of the piston.

[renrut]

That dynamic compression calculator is one of the most useful links I've seen posted on here!

From that I know my diesel runs a dynamic compression ratio of 32:1 while my petrol runs 9:1. Obviously not taking into account valve overlaps.

[stevieturbo]

chuntington101 said:

Boosted LS1 said:

also why aren't more people running these squierters in the LSx world??

Chris.

Because they work fine without them ???

Nice to have, but not essential.

[Boosted LS1]

^ Could be. I just got them because I was lucky at the time and thought they may help. Oh, the iron truck engines are using them as well. Guess that's because they have a hard life. Pump wise I have a choice of ls7/9 pumps but presume the ls9 pump will flow more volume. I'll get to find out one day, lol

[Mr2Mike]

knighty said:

detonation is actually related to piston temperature, particularly localised piston temperatures whereby sharp edges get too hot and act like a small spark plug which pre-ignites the charge and causes detonation.

No, that is pre-ignition which is not the same thing at all. It can however be a cause of detonation.

[BB-Q]

For those who wish to run piston squirters but don't want to spend a fortune they can be obtained from BMws. It's something we discovered on the Volvo forums when retro fitting earlier blocks, as the Volvo ones are no longer available. They have pressure valves in so are not just open tubes. I'll get the part numbers ASAP.

[Yuxi]

And from Ford. My 2001 1.8 petrol Mondeo has them, all 1.8 and 2.0 "new I4" Mazda designed engines have them. And they have non return valves in them.

[Mr Whippy]

clarenceboddiger said:

Ok I understand engines a bit, but something I keep seeing has me confused.
Why do Forced Induction engines use lower compresion pistons than their normally aspirated counterparts, why not just use less boost? I am obviously missing something as if that were the case people would do it.
So what am I not taking into account then.

The compression ratio is the same, it's the *effective* compression ratio (as that calculator linked to says) that is the issue.

You are compressing twice as much gas at 1bar boost (2bar absolute) into the same space as at normal atmos pressure. That is *effectively* running the engine without boost at double the compression ratio as before!


Brumm. Interestingly diesels seem to have loads of flexibility here, and I'm not sure why. My car runs piston underside jets and 90bhp/1bar boost normally, but can run 1.4bar and 160bhp quite happily with the same compression ratio (but loads more intercooling )

Dave

[renrut]

Mr Whippy said:

clarenceboddiger said:

Ok I understand engines a bit, but something I keep seeing has me confused.
Why do Forced Induction engines use lower compresion pistons than their normally aspirated counterparts, why not just use less boost? I am obviously missing something as if that were the case people would do it.
So what am I not taking into account then.

The compression ratio is the same, it's the *effective* compression ratio (as that calculator linked to says) that is the issue.

You are compressing twice as much gas at 1bar boost (2bar absolute) into the same space as at normal atmos pressure. That is *effectively* running the engine without boost at double the compression ratio as before!


Brumm. Interestingly diesels seem to have loads of flexibility here, and I'm not sure why. My car runs piston underside jets and 90bhp/1bar boost normally, but can run 1.4bar and 160bhp quite happily with the same compression ratio (but loads more intercooling )

Dave

I'm guessing because diesels use direct injection and rely on compression to cause the fuel to ignite. So there is no fuel in there until its ready for it. So there would only be a small fraction of time for pre-ignition to occur. I'd imagine petrol direct injection engines are similarly robust.

[chuntington101]

renrut said:

Mr Whippy said:

clarenceboddiger said:

Ok I understand engines a bit, but something I keep seeing has me confused.
Why do Forced Induction engines use lower compresion pistons than their normally aspirated counterparts, why not just use less boost? I am obviously missing something as if that were the case people would do it.
So what am I not taking into account then.

The compression ratio is the same, it's the *effective* compression ratio (as that calculator linked to says) that is the issue.

You are compressing twice as much gas at 1bar boost (2bar absolute) into the same space as at normal atmos pressure. That is *effectively* running the engine without boost at double the compression ratio as before!


Brumm. Interestingly diesels seem to have loads of flexibility here, and I'm not sure why. My car runs piston underside jets and 90bhp/1bar boost normally, but can run 1.4bar and 160bhp quite happily with the same compression ratio (but loads more intercooling )

Dave

I'm guessing because diesels use direct injection and rely on compression to cause the fuel to ignite. So there is no fuel in there until its ready for it. So there would only be a small fraction of time for pre-ignition to occur. I'd imagine petrol direct injection engines are similarly robust.

not totaly true althoguh i think the fact that your not injecting the fuel till you need it helps!

diesel also burns much slower than pertrol and thus is harder to pre-ignite. you can still get diesels to dept. though. but you need LOTS of boost and LOTS of fuel!

direct injection petrol engines will inject on the compresion stroke, so they fuel is already in the cylinder when it sparks...

Chris.

[Mr Whippy]

chuntington101 said:

renrut said:

Mr Whippy said:

clarenceboddiger said:

Ok I understand engines a bit, but something I keep seeing has me confused.
Why do Forced Induction engines use lower compresion pistons than their normally aspirated counterparts, why not just use less boost? I am obviously missing something as if that were the case people would do it.
So what am I not taking into account then.

The compression ratio is the same, it's the *effective* compression ratio (as that calculator linked to says) that is the issue.

You are compressing twice as much gas at 1bar boost (2bar absolute) into the same space as at normal atmos pressure. That is *effectively* running the engine without boost at double the compression ratio as before!


Brumm. Interestingly diesels seem to have loads of flexibility here, and I'm not sure why. My car runs piston underside jets and 90bhp/1bar boost normally, but can run 1.4bar and 160bhp quite happily with the same compression ratio (but loads more intercooling )

Dave

I'm guessing because diesels use direct injection and rely on compression to cause the fuel to ignite. So there is no fuel in there until its ready for it. So there would only be a small fraction of time for pre-ignition to occur. I'd imagine petrol direct injection engines are similarly robust.

not totaly true althoguh i think the fact that your not injecting the fuel till you need it helps!

diesel also burns much slower than pertrol and thus is harder to pre-ignite. you can still get diesels to dept. though. but you need LOTS of boost and LOTS of fuel!

direct injection petrol engines will inject on the compresion stroke, so they fuel is already in the cylinder when it sparks...

Chris.

Ah that makes sense then... I must admit that modern diesels get their fuel in bloody quick with the rail pressures they use, so yep, I guess the fuel just isn't in there long enough to do anything significant, and even if it does it can't be THAT long before it's meant to combust anyway, and being slow even if it does start a bit early it's not the end of the world... (though not ideal of course)

Will direct injection petrol's run higher CR's on FI installations then? And higher injection pressures maybe (not like diesel, but higher than the few bar they run now?)

Dave

[chuntington101]

dave yes they do run higher comp ratios. they do this by getting much better fuel air mixture in the cylinder, a constant 14-1 throughout the whole of the combustion chamber. VW do this with very strange looking pitson that induce a swril to help get everything mixed up correctly before the spark.

if you Wikipedia direct injjection it tells you all about it.

Chris.