Max Power bottom end will handle?

jungle

3 AYC Bars
Lifetime Member
Location
QLD
First Name
Simon
Drive
1 PFL & 1 FL Legnum
Ok, try this on for size, this response is from very well known a suspension engineer in the motor racing industry Australia. Yes i know a few of you will go- so what does a suspension engineer know about hp, engines and drvietrain loss?? Well pretty much everything really, as he builds them, sets the up. and then races them. And yes he's had a hand in pretty much every category in Australia.
I've included the date to show you how long people have debating this topic.

22 Dec 2003, 07:50 PM Post #18

Hi guys, as Steve has already posted, we have an engine dyno and a chassis (roller) dyno (2wd and 4wd). I have also tested a hub dyno (2wd and 4wd) a couple of times, they keep trying to sell us one. Based on this experience I favour the fixed loss methodology.

It is pretty simple really, Newton's law says energy can neither be gained or lost, it can be transformed into other types of energy. Now, I know Einstein disproved this with E=MC2, but there ain't no atomic reactions going on in my Skyline.

So let's say I have a gearbox that transforms 20 kw of power (torque X rpm), or kinetic energy if you like, into heat. Why would it suddenly transform 40 kw if I double the power output of the engine? Secondly where the hell is the extra 20 kw of heat going? Noting how much heat a 1 kw radiator puts out, with 40 kw I could fry eggs on the gearbox case in a couple of minutes of running.

The percentage loss methods just doesn't work for me. Especially when you start tripling or quadrupling the power output, the heat would melt the aluminium gearbox case on the dyno.

Some examples;
I know that an R32 RB20DET is rated at 215 bhp by Nissan
When I put one on our usual dyno they make 140 rwhp
That's a loss of 75 hp through the drivetrain, tyres rollers etc

I know that an R33 RB25DET is rated at 250 bhp by Nissan
When I put one on our usual dyno they make 170 rwhp
That's a loss of 80 hp through the drivetrain, tyres, rollers etc

The above is based on the real world results for over 20 Skylines on our usual Dyno Dynamics roller dyno. Dynos are different and different operators get different results. This is our results, but I don't believe that you can simply transfer them to someone else’s dyno. BTW hub dynos show less power loss, due to their lack of tyres, friction and rollers.
 

frozen

1 AYC Bar
Lifetime Member
Location
Queensland
First Name
Josh
Drive
1990 Mitsubishi GTO
Formerly: 1996 Galant VR-4
the extra power goes to more tyre wear, more stress on the gearbox and parts, probably some more heat too, i dont think it would be a fixed amount OR a fixed percentage, but rather similar to what brad said, where it is an initial percentage and perhaps varies the more power you are able to put out. Now thats a complete speculation, seeing as i have no background in ANY of it nor past knowledge, but i think it makes sense.. i done some electrical engineering for a while too, which touches on the other disciplines but hell no where near enough to sort out this age old discussion :p
 

SiliconAngel

1 AYC Bar
Location
Perth, WA
First Name
SA, Trevor
Drive
'99 Legnum VR4 Black MT
There is only one way this argument can be sorted out definitively, and that's to take a stock car, dyno it at the wheels AND at the flywheel. Upgrade the engine, dyno it at the wheels and at the engine again. The difference is drivetrain+tyre loss, and you can determine the percentage loss for both performance figures. Sounds like a lot of work I know, but anything else is pure speculation.

Speaking of speculation, I believe the statement about heat to power is incorrect:
So let's say I have a gearbox that transforms 20 kw of power (torque X rpm), or kinetic energy if you like, into heat. Why would it suddenly transform 40 kw if I double the power output of the engine?
If you have something generating energy and you have a percentage heat loss due to certain factors, with all else remaining the same doubling energy output will result in EXACTLY doubling heat output. Its a law of physics and has been proven innumerable times.

For example, take an incandescent light bulb. If you have a particular globe that puts out X amount of heat for Z amount of light, to achieve 2Z you'll end up with 2X.

In a combustion engine if you have X heat developed (made up of F heat from friction, and E heat from burning fuel and oxygen) for a given power of Z, doubling Z (ie 2Z) will give you 2F plus 2E = 2X. To get twice the power you will produce twice the heat. In a gearbox if you produce F heat from friction due to transference of Y power, doubling Y will double F.

This is why there are billions of dollars spent in automotive R&D to come up with higher wearing, lower friction, faster heat transferring materials, because that way you are changing some of the parameters so you can get greater values of Z for incrementally smaller increases in X.

That's just my 2c from what I know about physics, though - I'm not and don't purport to be any kind of motor vehicle expert and you have infinitely more experience than me when it comes to stuff like this, Simon, and I respect and take in everything you say on the subject. I'm just not seeing how basic laws of thermodynamics could be circumvented in this scenario.
 

jungle

3 AYC Bars
Lifetime Member
Location
QLD
First Name
Simon
Drive
1 PFL & 1 FL Legnum
They aren't being circumvented. It doesn't happen. When you get home from work tomorrow, get under the car and feel the rear diff. Then jump back in it and take the car somewhere and give it a good flogging. Get out and feel the diff again. It's going to be hotter yes, but probably nothing your hand can pick up and it's certainly not going to absorb the heat a crap load more power is supposedly giving off in some of the comments above.

Yes some of the power is absorbed by the tyres, but this is why they should be inflated to 40psi- to reduce the hp loss on the dyno. Practically, on the dyno, you should the hardest friggin compound tyres you can find, this will give the most accurate hp figures...that's if you are concerned about getting a certain number to impress your mates, I just use it as a tuning tool, not a dick measurer :ROFLMAO:

Here's a real world example. Case in point. I used to fly a plane with supercharged engines. Now, once at height, you would set a cruise power. In this case it was 700bhp. The Pratt and Whitney manuals explained that the power loss to turn the reductions gearbox, cam timing , spin the superchrager, generator, hydraulic pumps, fuel pump air pumps etc etc regardless of what cruise power was set, be it 700, 800, 900 was wait for it.... 100bhp! So for those that missed it, here it is again. Regardless off what power was set, the power loss for running all the other bits in the engine was 100bhp. Questions?

Now this engine also produced 1500ft/lbs at 1000rpm (idle) and 5200ft/lbs at take off power- 1450bhp. Your Legnum won't get anywhere near these figures, so i'm happy to hang my hat on the fact that regardless of the output of your car, the loss due to the drivetrain will remain fixed.

I placed my faith in the people from Pratt and Whitney long ago, as they do know what they are talking about, not just throwing up what they think might happen with absolutely nothing to base it on.

This is all i'll say on the matter. Doesn't matter if you don't aggree with it, in the immortal words of Kevin Bacon in A Few Good Men, these are the facts and they are undisputed. :D
 
G

Guest

Unregistered
ok this is starting to go over my head, so do we have a answer to the tread question?
as said before, isnt valmes pulling some rediculus amout of power from stock internals? i know that a large hp figure will majorly reduce the longjevity of the engine but cant we use his hp figure as a base to this question?
 
G

Guest

Unregistered
The percentage loss methods just doesn't work for me. Especially when you start tripling or quadrupling the power output, the heat would melt the aluminium gearbox case on the dyno.

Some examples;
I know that an R32 RB20DET is rated at 215 bhp by Nissan
When I put one on our usual dyno they make 140 rwhp
That's a loss of 75 hp through the drivetrain, tyres rollers etc

I know that an R33 RB25DET is rated at 250 bhp by Nissan
When I put one on our usual dyno they make 170 rwhp
That's a loss of 80 hp through the drive train, tyres, rollers etc

The above is based on the real world results for over 20 Skylines on our usual Dyno Dynamics roller dyno. Dynos are different and different operators get different results. This is our results, but I don't believe that you can simply transfer them to someone else’s dyno. BTW hub dynos show less power loss, due to their lack of tyres, friction and rollers.


This sort of analogy raises another point why when you add mods to a car does the power loss percentage drop??

IMO The amount of energy needed to over come the initial friction has passed 20-50hp ago and therefore every hp gained after this point would be less affected and also with every Kw gained there is a torque gain as well. So inaffect the 2x power added = 2x power gained rule is slightly bent with automobiles. Or so my brain thinks so. lol



Oh and I am not arguing just putting my ideas out there so if I am wrong someone who is more knowledgeable can put me on the right path to enlightenment
 

SiliconAngel

1 AYC Bar
Location
Perth, WA
First Name
SA, Trevor
Drive
'99 Legnum VR4 Black MT
I think I'm being contentious (and possibly confusing) by talking about a slightly different point - I was saying that if you have heat generated by a certain amount of friction as a result of a particular power output, then doubling that power output will double the friction and thus the amount of heat generated.

However, if you take into account just how much heat is generated by friction as a percentage of power output, you're talking quite a small number. So while this number may well double with doubling of power, if you're getting 100kw for every 5°C increase from friction, another 5°C to go to 200kw really isn't that big a deal.

And I think I may have forgotten something important - your first 100kw will be subject to inertial friction and lower temperature lubricants than your next 100kw.

Anyway, I think you're right about the power draw from certain equipment and I think the functional variable for working out drain from the driveline may well be static as the impact of increased friction as a proportion of total forces at play will be minimal, but there's no way that friction won't be increased as power increases unless you maintain the same engine and driveline RPM despite your power increase - it's just that it won't be a significant factor in your calculation.
 

Peter_D

Leaving Skid Marks
Location
QLD
First Name
Pete
Drive
Cab Colt & Evo 6
What it boils down to is "all engines are different". Some will make more power than others. Just look at the difference in figures between Mel's 96 Leggy and my 02 one. Both are essentially the same vehicle with different methods of transferring the tractive effort to the wheels (manual/auto). yet Mel's makes more power than mine and I've spent a few more dollars modding mine trying to match hers in power.
Therefore doesn't it stand to reason that the "BREAK" point of the standard internals will be different for each vehicle.
 
G

Guest

Unregistered
also it will matter if the car has has a hard life before you got it..
the previous owner might not have changed oil for 20,000 k's who knows..
 
Top Bottom