Alusil honing services in So Cal.
03-18-2013, 01:08 AM
#31
Racer
Join Date: May 2008
Location: Encinitas, ca PCA National DE instructor PCA San Diego chief driving instructor
Posts: 341
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To be clear, the problem with aluminum bores in a BIG horsepower engine isn't surface hardness, as that can be taken care of with various surface treatments (alusil, nicasil, hard chrome plating, etc) that work quite well.
The problem with aluminum as a bore material is one of mechanical strength - or lack of it - to withstand the forces generated by very high combustion pressures and temperatures (these go hand in hand) that are found in a nitrous engine, or a boosted engine at 45+ psi. In short, they warp all out of shape from combustion pressures and piston side loads caused by the same high gas pressures. The very high temperature of the combustion gasses also heats the aluminum faster than the water jacket can cool it, and as a result the aluminum gets hot enough to soften. Steel - or even cast iron - is a much better material for this use.
The land speed engine I was talking about in my example makes 380 rwhp from a pair of 530cc cylinders.
To put this in perspective, a 2.5 liter 951 would make 896 rwhp if it ran as hard.
I have yet to hear of a 951 engine making this kind of specific output, but to be fair most are used as road racers (or dyno queens
) and don't need to make anywhere near as much power as is needed to go 200+ in a standing mile. I "guess" that a 951 body would take 1000 rwhp to break into the 200 mph club. I don't know of anyone trying, so it's only a guess.
What does all this have to with a road raced 951 at 20 psi? Plenty. The same failure will occur, it just takes longer.
The problem with aluminum as a bore material is one of mechanical strength - or lack of it - to withstand the forces generated by very high combustion pressures and temperatures (these go hand in hand) that are found in a nitrous engine, or a boosted engine at 45+ psi. In short, they warp all out of shape from combustion pressures and piston side loads caused by the same high gas pressures. The very high temperature of the combustion gasses also heats the aluminum faster than the water jacket can cool it, and as a result the aluminum gets hot enough to soften. Steel - or even cast iron - is a much better material for this use.
The land speed engine I was talking about in my example makes 380 rwhp from a pair of 530cc cylinders.
To put this in perspective, a 2.5 liter 951 would make 896 rwhp if it ran as hard.
I have yet to hear of a 951 engine making this kind of specific output, but to be fair most are used as road racers (or dyno queens
) and don't need to make anywhere near as much power as is needed to go 200+ in a standing mile. I "guess" that a 951 body would take 1000 rwhp to break into the 200 mph club. I don't know of anyone trying, so it's only a guess.What does all this have to with a road raced 951 at 20 psi? Plenty. The same failure will occur, it just takes longer.
03-18-2013, 07:55 AM
#32
Drifting
Well Dave everything will wear out at some point and 20 psi with proper heat management on a road car could have around half the service life of a standard boost 944T hopefully ?. Trackdays aren't in my plans so that's why I'm considering Alusil for my 3k miles a year 3.0 project.
03-18-2013, 12:38 PM
#34
Burning Brakes
Tony G, my personal project car , building for shows , and Shelby car club road events. Some mild streeT action on twisty roads as well
+1 on that a racecar is a racecar. Any form of street involvement on a racecar no longer makes it a racecar and the build should follow that rule accordingly. Due to heat, improper tuning capabilities, and an open deck design, sustained high Rpms do a number on our blocks, among other factors . From the sound of his purpose of the car, he should be fine building an alusil motor with stock pistons, maybe invest in vflex with a map sensor to help with tuning and help out the oiling system however you can, extra oil coolers or accusump, Teflon crank scraper / windage tray , etc.. If u do live in the San Diego area, I do as well and can help with any assembly if needed.
+1 on that a racecar is a racecar. Any form of street involvement on a racecar no longer makes it a racecar and the build should follow that rule accordingly. Due to heat, improper tuning capabilities, and an open deck design, sustained high Rpms do a number on our blocks, among other factors . From the sound of his purpose of the car, he should be fine building an alusil motor with stock pistons, maybe invest in vflex with a map sensor to help with tuning and help out the oiling system however you can, extra oil coolers or accusump, Teflon crank scraper / windage tray , etc.. If u do live in the San Diego area, I do as well and can help with any assembly if needed.
Last edited by kev951; 03-18-2013 at 05:04 PM.
03-18-2013, 08:49 PM
#35
Drifting
03-18-2013, 09:44 PM
#36
Rennlist Junkie Forever
03-19-2013, 07:48 AM
#37
Drifting
. I'm not motivated to get stuck in to a rebuild at the moment as my original 80k motor is running just fine. My 2.7 engine and S2 crank can sit on a stand as a garage ornament for a while.
