Author: Tom Kerrigan
Date: 11:52:20 08/28/03
Go up one level in this thread
On August 28, 2003 at 00:31:23, Robert Hyatt wrote: >>Well, as the saying goes, you can either have high displacement or high RPMs but >>not both... unless you're Ferrari. How many I4s redline at 8000-9000 these days, >>and how many V8s under $100,000 redline in that range? > >Not many stock motors that appear in _any_ vehicle redline up there. IE, >for comparison, my son's SHO taurus redlines at about 7K. The current 4.6 >ford V8 redlines in the same area. As did the SVO I4 with turbo. > >A bit more exotic is the Honda S2000 at near 9K, but it has no torque, >after driving one. Honda and Toyota both make engines like that. S2000, RSX, Celica, probably some others. If the S2000 puts down as much torque at 9000 as some other car at 7000, does it matter if it lugs at 1000? >>>We are talking pure motor issues here. Horsepower is important. But so is >>>torque, which is a different way of measuring horsepower. 8 cylinders will >>>produce more torque, even at the same displacement. A V10 is better still. >> >>That may generally be the case, but torque technically depends on the shape of >>the cylinders. I'm sure it's easy to make a V6 that has more torque than a V8 >>with the same displacement. > >No idea what you are talking about when you say "shape of the cylinders." The >_only_ shape being used is a perfect circle of varying radius, with a taller >or shorter swept area controlled by the stroke of the crank. Isn't it obvious that I was talking about bore/stroke? >However, it is definitely impossible to make more torque with fewer cylinders, >if all else is the same. Just compare the difference between a power pulse >every 1/4 revolution vs every 1/3 revolution. That's why v12's exist. More >torque. Smoother since power pulses are closer together in terms of 1/6 of >a revolution between power pulses vs 1/4 or 1/3... I don't have the time to go looking for any specific datapoints, but if your stroke is much longer you're going to get more torque per cylinder, right? So why do you think it's impossible for a V6 with a really long stroke to make more torque than a V8 with a really short stroke? Surely there's some crossover point. >>>The problem with the turbo is lag. The V8 supplies torque _right now_. The >>>I4 is going to die at low RPM, and waits until the turbo spools up to get >>>moving. A good example is the old SVO mustang with an I4. Yes, it runs like >> >>Which is fine, because if you're drag racing you can spool up the turbo before >>launching, so turbo lag is not an issue unless your car is so poorly tuned that >>you experience lag after you upshift at redline. Turbo lag is only significant >>for rolling starts and actual race courses. > >The turbo won't spool up. It depends on exhaust volume. A free-wheeling >engine won't produce the exhaust gas volume that an engine under load >produces, you simply don't pump as much air through the engine, nor as much >gas, which translates into less exhaust volume. No exhaust (not "less exhaust") means the turbo doesn't spool. I know from experience that you get at least some boost from an Eclipse when you launch at 5000 RPM. And plus, what car takes any significant amount of time to get to ~10 MPH, where a typical turbo will be hitting max boost in 1st gear? (Which is the only time you should even possibly be seeing turbo lag in a drag race.) >>That's great, but the gearing could have been different, the turbo could have >>been tuned poorly for the 1/4, and the friend might not have been launching >>right. Actually, unless he had a race clutch, I doubt he was launching right. > >This was a regular drag racer, using a comp clutch and pressure plate, using >drag radial tires. He knew what he was doing. I drove the car myself and we >were within .1 of each other... Fine, there are still other variables. It's easy to find circumstantial evidence to prove my point: check out the Evo 8. 2L turbo I4 making 271 HP and it's pretty much exactly as fast as a Corvette with a 5.7L V8 making more (345?) HP. -Tom
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