With decades of racing engine building experiance it seems like there are more questions than answers still.
Not talking about any particular engine. But rules in general that are valid.
FOR EXAMPLE. Exhaust should flow 80% of intake.
Lighter is better up to the point of failure.
the object is to drive it onto the trailer not winch it. ( that's the cheapskate in me )
If you drove it up into the trailer and it doesn't blow itself into worthless bits, you overbuilt it.
- Colin Chapman
Just as a point of clarification, was ACBC talking about driving it onto the trailer AFTER the race, or when he and the lads had finished adding the lightness out of it BEFORE the race?
aircooled said:If you drove it up into the trailer and it doesn't blow itself into worthless bits, you overbuilt it.
- Colin Chapman
That approach just doesn't work for GRM people. Racing is about fun. Not endless expense. Perhaps in professional racing it may have a place. But even Formula 1 & NASCAR have penalties in place for engine durability reasons.
The old adage about race engines: You can have cheap, durable, or fast. Pick 2 because you can't have all 3.
Purple Frog (Forum Supporter) said:The old adage about race engines: You can have cheap, durable, or fast. Pick 2 because you can't have all 3.
Choose cheap twice!
Once you get down to the physics involved there are a bunch.
Stoich is 14.7, your engine is actually an air pump, and your aluminum pistons will melt at 1.2k degrees F regardless of how much you spent on them.
Most of the really good tuners or builders I read sound like physics majors.
Purple Frog (Forum Supporter) said:The old adage about race engines: You can have cheap, durable, or fast. Pick 2 because you can't have all 3.
80whp out of a 3L
Happy with being shifted at redline for hours on end
~25 seconds behind the race leader's hot lap
I know which two my team has chosen.
Purple Frog (Forum Supporter) said:The old adage about race engines: You can have cheap, durable, or fast. Pick 2 because you can't have all 3.
That's why I choose JaguarV12's. They scare everybody except they work like any 4-6-8 cylinder car. For that reason they are cheap, cheap, CHEAP.
You'd be amazed at how many perfect V12's are sitting around not running because the purists want only original equipment parts. So they go to the Jaguar dealer to pay $300+ and wait 4 months for a Lucas ignition module. If they picked it up and turn the plastic cover over it's a regular GM part you can buy anywhere for $10-$15. Etc.
CrustyRedXpress (Forum Supporter) said:Once you get down to the physics involved there are a bunch.
Stoich is 14.7, your engine is actually an air pump, and your aluminum pistons will melt at 1.2k degrees F regardless of how much you spent on them.
Most of the really good tuners or builders I read sound like physics majors.
On Gas stoich is 14.7 E85 it's, 9.85-10.7
frenchyd said:With decades of racing engine building experiance it seems like there are more questions than answers still.
Not talking about any particular engine. But rules in general that are valid.
FOR EXAMPLE. Exhaust should flow 80% of intake.
Lighter is better up to the point of failure.
the object is to drive it onto the trailer not winch it. ( that's the cheapskate in me )
Exhaust flow makes assumptions based on your flowbench's pressure ratio capabilities.
The best exhaust ports are supersonic, and will flow VERY badly on a traditional flowbench.
frenchyd said:That's why I choose JaguarV12's. They scare everybody except they work like any 4-6-8 cylinder car.
I don't think the fact that its 12 cylinders that scares anybody off. I agree with alot of your points about what scares a lot of people away from them, but the cyl. count ain't one of 'em
In reply to Pete. (l33t FS) :
That's interesting Pete, if we can't flow bench test it, how are we to know?
What sort of RPM are we talking about?
I'm focusing on pistons speeds under 3000fpm since most production or low cost pistons are cast not forged where the higher pistons speeds are required.
In reply to frenchyd :
Cast vs forged is kind of a crapshoot, based on oldthink. Old forgings were strong not because of the forging itself but because of the materials used that made forgings possible in the first place, which also required so much clearance that they passed a lot of oil. Modern castings are far, far better, and a lot of them have steel inserts for the ring lands for strength. And most modern engines have piston cooling, so you don't have to worry so much about temperatures.
Pete. (l33t FS) said:Cast vs forged is kind of a crapshoot, based on oldthink. Old forgings were strong not because of the forging itself but because of the materials used that made forgings possible in the first place, which also required so much clearance that they passed a lot of oil. Modern castings are far, far better, and a lot of them have steel inserts for the ring lands for strength. And most modern engines have piston cooling, so you don't have to worry so much about temperatures.
I hadn't thought of that, but its a very good point!
03Panther said:frenchyd said:That's why I choose JaguarV12's. They scare everybody except they work like any 4-6-8 cylinder car.
I don't think the fact that its 12 cylinders that scares anybody off. I agree with alot of your points about what scares a lot of people away from them, but the cyl. count ain't one of 'em
I use cylinder counts only as an identifier. BMW, Mercedes Benz, Ferrari, Aston Martin, Lamborgini, Jaguar, etc etc all are terrifying to most car guys who haven't built a lot of engines.
They are all 4 stroke engines. You have to have Spark, fuel, and timing to make them run. Same as any car.
Once OBD2 took the mechanic out of the equation and parts replacers could figure those out, suddenly even the Jaguar V12 started getting a good reputation.
Look at the price of a 1995-96 V12 Convertible. 4 years ago they were selling at $1500 Today they are pushing $15,000+ for nice ones and in England £30,000.
Same basic car. I don't know BMW, Mercedes, etc. but aren't their V12's a very soft market compared to the same year V8's. I'm guessing there are cheaper than dealership parts available for them that are just as good.
CrustyRedXpress (Forum Supporter) said:Once you get down to the physics involved there are a bunch.
Stoich is 14.7, your engine is actually an air pump, and your aluminum pistons will melt at 1.2k degrees F regardless of how much you spent on them.
A thousand times no!
You can move all the air in the world through an engine and not make an ounce of horsepower.
Engine technology, at the onset, leaned on firearms technology. The metallurgy, the machining. And THAT is what is important for an engine: not moving air, but capturing combustion, using its force to its maximum, and reloading the most quickly and efficiently for the next cycle. Engines are not air pumps, engines are machine guns.
frenchyd said:That's why I choose JaguarV12's. They scare everybody except they work like any 4-6-8 cylinder car.
I use cylinder counts only as an identifier. BMW, Mercedes Benz, Ferrari, Aston Martin, Lamborgini, Jaguar, etc etc all are terrifying to most car guys who haven't built a lot of engines.
They are all 4 stroke engines. You have to have Spark, fuel, and timing to make them run. Same as any car.
Once OBD2 took the mechanic out of the equation and parts replacers could figure those out, suddenly even the Jaguar V12 started getting a good reputation.
Look at the price of a 1995-96 V12 Convertible. 4 years ago they were selling at $1500 Today they are pushing $15,000+ for nice ones and in England £30,000.
Same basic car. I don't know BMW, Mercedes, etc. but aren't their V12's a very soft market compared to the same year V8's. I'm guessing there are cheaper than dealership parts available for them that are just as good.
That's why I only quoted the one sentence. ( it implies something else ) Was not disagreeing, only clarifying. I agree strongly with the point you are making with the "misunderstood" = "Scared of"
I know a guy was lead mechanic at a bike shop... others mechanics there would take their boat to the dealer! Claimed they didn't know how to work on a boat engine??? Rusty would ask 'em "you do knot that engine needs the same things to run as a bike engine, right"
Pete. (l33t FS) said:In reply to frenchyd :
Cast vs forged is kind of a crapshoot, based on oldthink. Old forgings were strong not because of the forging itself but because of the materials used that made forgings possible in the first place, which also required so much clearance that they passed a lot of oil. Modern castings are far, far better, and a lot of them have steel inserts for the ring lands for strength. And most modern engines have piston cooling, so you don't have to worry so much about temperatures.
We agree on that. Newer technology have made massive improvements and are required to comply with modern emissions. But 3500 FPM piston speeds is still forging area while castings are limited to around 3000fpm.
Remember a piston goes from 0 feet. per minute at the top and bottom of each stroke and production cars try to keep speeds under 2500 ft per minute at peak.
Post WW2 Jaguar with its long 4.17 stroke was pushing the very edge of technology at 5500rpm
When they went to the 2.75 stoke in the V12 they allowed the potential of 8300 RPM before the production pistons exceeded safe speed.
I'm sorry I keep referring to Jaguars. They are numbers I'm familiar with. If I knew Miata's as well I'd use those numbers.
03Panther said:frenchyd said:That's why I choose JaguarV12's. They scare everybody except they work like any 4-6-8 cylinder car.
I use cylinder counts only as an identifier. BMW, Mercedes Benz, Ferrari, Aston Martin, Lamborgini, Jaguar, etc etc all are terrifying to most car guys who haven't built a lot of engines.
They are all 4 stroke engines. You have to have Spark, fuel, and timing to make them run. Same as any car.
Once OBD2 took the mechanic out of the equation and parts replacers could figure those out, suddenly even the Jaguar V12 started getting a good reputation.
Look at the price of a 1995-96 V12 Convertible. 4 years ago they were selling at $1500 Today they are pushing $15,000+ for nice ones and in England £30,000.
Same basic car. I don't know BMW, Mercedes, etc. but aren't their V12's a very soft market compared to the same year V8's. I'm guessing there are cheaper than dealership parts available for them that are just as good.That's why I only quoted the one sentence. ( it implies something else ) Was not disagreeing, only clarifying. I agree strongly with the point you are making with the "misunderstood" = "Scared of"
I know a guy was lead mechanic at a bike shop... others mechanics there would take their boat to the dealer! Claimed they didn't know how to work on a boat engine??? Rusty would ask 'em "you do knot that engine needs the same things to run as a bike engine, right"
That's valid. And noted. "Scared of" pejorative , while misunderstood is more civilized.
Thank you for the correction.
In reply to Pete. (l33t FS) :
I thing the "air pump" quote was first started as a way of explaining "if you cant get more air in, and more exhaust out - you cant make more power." True in its self, but def. does not tell the hole story!
I like your machine gun analogy... like an Internal Combustion Engine, a cartridge does not have an explosion going off inside. It has a REALLY fast burn, that "pushes" the bullet away from it. The engine just has a piston in the "barrel" that gets brought back into place to be pushed again.
I have built a bunch of engines over the years and the number one thing that I see people screw up is not being realistic about the real needs they have for the motor that they are building. Truck/tractor motors are not sexy but most peoples needs are much closer to the truck side of things and yet they seem to think a high reving race car type motor is what they need.
Lean is mean.
"An engine doesn't know what name is on the valve covers."
Mo cylinders mo money.
to each their own.
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