Power lost from engine to wheels

[GraemeWi]

Folks, the 'fixed' or 'rule of thumb' power loss is a fallacy.

Lets say Car A has a 100 hp engine, and measures 70hp at the rear wheels. Thats a 30% loss through the drivetrain.

The same Car A, except I replace the engine with a 350 Chev rated at 300hp. Without changing anything in the transmission or drivetrain, is it fair to say there still will be a 30% loss? All of a sudden the transmission and drivetrain is soaking up 60 more hp for no reason? Nope.

Without putting an engine on an engine dyno, any power at the crank figures are pure guesswork. Look at the top fuel cars in the States - for years they have been working out their engine power using mass x acceleration, reconing that their engines produced 6,000hp...not so long ago they worked out how to measure the torque they output with a special torque sensor in the drivetrain and now say their engines are putting out 9,000hp! Thats a 3,000 hp difference. The guys who did the initial calculations are like the top engine builders, so they are in no way backwards or stupid.

Car manufacturers also measure their engines power outputs in different ways (eg with no accessories like alternators or power steering pump) so what they may quote in their sales brochures has as much substance and use as a used tissue.

Be careful with the car weights as well, I used to own a G-Tech and once measured my car on two different certified weighbridges on the same day. Weight 1 with a full tank and me was 1535kg, weight 2 was 100kg less. Both of these weigh bridges were commercial and recently tested and certified. I figure the 1535kg weight to be the correct one.

G

[EVOIV]

9000hp cars!! Is that even possible? Unless we're talking about jets here and not cars? I thought Japan would be one of the best for high hp cars, and I thought the max would be around 1500hp. No where near 9000hp!?

[GraemeWi]

These are Top fuel cars - they look like a long rail with the engine at the back. Can't compare them to any form of road car! Does the quarter in about 4.6 seconds at about 300 mph.

Picture big alloy v8's of about 8.9 litres pulling 8500 rpm, a supercharger pushing in 1,640 cubic meters of air a minute, burning 4 litres of nitromethane a second (the fuel is 3 times more efficient than petrol)

G

[EVOIV]

Sheesh! That's some serious stuff!!! I'm guessing you'd soil your pants too when behind the wheel of one? Just a question, why a supercharger? What are the benefits of that over a turbo? I know that superchargers have less (or no) lag cos they don't use exhaust gases to spool them up. But why is it that nowadays the turbo seems more popular than the supercharger? Anyone?

[GraemeWi]

Superchargers are driven off the crankshaft and rob a fair about of power - their main advantage over a turbo is that they produce boost at all revs. On the flip side, they can be noisy, they use belts which need checking and careful maintenance. And cost lots!

I think turbochargers are more popular for economic reasons - they cost less, and produce some very nice results as our Skylines can attest.

Oh and those top fuel engines - they last one run on the drag strip. Often when you watch them on TV you can see a cylinder or two die halfway down the strip...sometimes they expire in spectacular fireballs. The crews rebuild the engines between runs, it's amazing to watch them work - look out for the NHRA drags on ESPN etc.

G

[EnricoPalazzo]

GraemWi: No they do not rebuild the engines every run. They ususally just take off the sump and make sure all the gallieries are cleared and some other general maintanice. But they definately dont rebuild them all the time.

Also that puff of smoke that u usually see is most of the time just wheelspin. Some times it is an engine letting go, but almost all of the time, the top fuelers loose traction down the strip and make puffs of smoke.

[EnricoPalazzo]

Also back on topic, 4wds have huge loss. Look at WRX's. Come ou with 162kws, and their lucky to get over 100kws atws. Usually between 90-100.

[skylineakt]

Nar DanS15 we didn't do any run tesing for 0-100 or 1/4 mile times. The road we were testing were getting a bit busy, so we left it hehe . I'll try again with next time with a different weight measurement. This time we will take in consideration of our weight and the fuel weight. Maybe I'll have to test it near an empty tank as I wouldn't have a clue how much fuel will weight at full tank etc.

Predator: Yeah that will be intresting to know what's going on at the dyno day. Do you know when is it or where is it??

SORRY GUYS maybe I should of mention this earlier but don't know it this matters or not to my rw output but my car is an AUTO...

[hippy]

take another 20kw off for auto ... thats at the wheels .. i think ..

[skylineakt]

You SERIOUS?!?! another 20kw off for auto?? Man didn't know auto will take that much off!! Can anyone else confirm this?? Not saying your word is not true hippy, but that's really alot.. DAMN. I hope you are only kidding.

[ex_zero]

yeah, the torque converter robs more output to the wheels, i'm not sure of the real figures, it's also different for different torque converters(?).

[GraemeWi]

Originally posted by EnricoPalazzo

GraemWi: No they do not rebuild the engines every run. They ususally just take off the sump and make sure all the gallieries are cleared and some other general maintanice. But they definately dont rebuild them all the time.

Also that puff of smoke that u usually see is most of the time just wheelspin. Some times it is an engine letting go, but almost all of the time, the top fuelers loose traction down the strip and make puffs of smoke.

I've watched drag racing for quite a few years, there is quite a big difference between loosing traction and a cylinder carking it.

G

[JimX]

Originally posted by GraemeWi

Superchargers are driven off the crankshaft and rob a fair about of power - their main advantage over a turbo is that they produce boost at all revs. On the flip side, they can be noisy, they use belts which need checking and careful maintenance. And cost lots!

Supercharger units themselves don't actually cost that much more than turbos. You can get a Yella Terra roots style blower for around $2000. Even the Vortech centrifugal blowers aren't much more than that for a smallish one. But then you need the manifold mods, the belts, bigger injectors, computer reprogram, water injection, etc, which is why you usually see Commodore (etc) supercharger kits for around $5000-6000 (or more).

The advantage of turbos on our cars is we already have everything there - when upgrading/replacing the turbo (unless the replacement is a huge monster) then we just have to buy the turbo unit itself. We also get a small refund if we manage to sell our old turbos

The main reason why superchargers tend to cost at least a little more than a cheap Garrett turbo is because they're mostly made in America. But compare a Vortech or Powerdyne blower with a HKS or Trust turbo and you might find the superchargers are quite a bit cheaper.

EVOIV - I think the main reason that turbos are more popular than superchargers with performance enthusiasts aside from the cost savings on cars that already have turbos is because you can play with the boost.

If there was an NA car that you wanted to put forced induction on, a turbo would be the way to go for big power gains, although it would generally cost more to do properly than a supercharger.

A supercharger is generally a budget option because they have relatively low boost and drain power from your engine to run (cost more in fuel, less power from same pressure as a turbo). It's more of a "set and forget" mod.

[blind_elk]

Originally posted by Ronin 09

This should be true, as i understand. GTRs are basically RWD until they detect rear slip (on a dyno there shouldn't be any),...

There is slip at the rear, relative to the front wheels (the fronts are stationary). That's why you have to disable the front drive of a GT-R on a RWD dyno.

[Ronin 09]

Aha, i see... but why would there be little difference between awkW and rwkW for a GTR?

[EVOIV]

Thanks for the info. on the supercharger vs turbocharger. I didn't really know how the supercharger worked..but thanks for the enlightenment, which makes sense why turbos are more common for power upgrades. But I still am a little confused as to why a GTR with 2 wheels spinning on a dyno gives the same reading as the same car with 4 wheels spinning on a 4WD dyno. The physics of it just doesn't make sense? Weird...oh well. Just shows that GTR is king!!!

[JimX]

Power is rate of work. If you have 4 wheels spinning on the dyno, you have half the power going to each end as you would if you just had the rears on. Of course you have to throw in a little 4wd drivetrain loss as well if you're running all 4 wheels, but it should work out to be roughly the same.

[EVOIV]

Which doesn't make sense. Because a GTR with 2 wheels spinning on a 2WD dyno makes the same power with 4 wheels spinning. So, when it's AWD the GTR miraculously makes double the power? Because it's the same power each time. Anyone explain?

[blind_elk]

Maybe it was a mis-print.

[JimX]

EVOIV, I don't think you read what I wrote properly. You have half the power at the wheels using 4WD, but you have twice as many drive wheels. What does a half times 2 equal?