Why the 1/4 is useless for comparing engine power

[czy18e]

How do you tune for 400 rwhp++ on the street?

Were you cant get booked :elaugh:

[Sydneykid]

SK,

i've had really good results over the years using a drag calculators, always racing back to back after a dyno result, and mph's and et's were fairly spot on, providing the weight figures were correct.

Unfortunately I have had crap results, that R34 GTT is just an example of the sort of discrepancies I have experienced. Maybe because I do lots of things to make a car faster, not just the engine. If you just work on the engine all the time and you gradually increase the power, you MIGHT get consistent results.

But that's not what I do, I train the driver, I tune the suspension, I move the power around (not necessarily change the max power), I change the gearboxes, I take some weight out, I change the 4wd settings etc etc. I can make a car ~1 second faster over the 1/4 with the same power. The drag power calculators simply can not handle that, they keep coming back with the more power answer.

So I simply can't trust them. :cooldance

[Ceffo]

Sorry for the newbie question here but where can i obtain the drag calculator to estimate HP?

Cheers

[rev210]

The 1/4 mile is a measurement for accelleration.

The dyno a tuning tool that measures horsepower.

I wouldn't call the drag strip a better power calculator than a dyno, you have to do more measurements and calcualtions to provide accurate data.

hello silly thread

[2rismo]

Here's the deal, mate.

You said that the 1/4 is "useless" for calculating horsepower and I say you're wrong. That's what we're talking about here isn't it???????

Don't give me half-assed scenarios to disprove what i'm saying - the people that use the drag racing calculations to go backwards to hp know ALL of the variables that i've asked you for and more!

You're being deliberately cheeky to make a point and it's beneath me to continue.

Adrian

[riggaP]

This agument is so pointless on so many levels.

IMHO bottom line is power figures dont mean shit. What we are ultimately trying to do when modifing a car is to increase its overall performance for the application its been built for. Who cares if it has xxxkW? As long as it becomes faster with every mod.

[Lithium]

Power levels mean a lot, its the actual amount of time you spend putting out the highest % of that power which makes you fast though.

Having huge power and not being able to use more than 60% of it for 50% of your time on the strip is an absolute waste of time, but then having bugger all power and being able to put down 90% of it 100% of the time is not necessarily going to be that great either.

[Sydneykid]

The 1/4 mile is a measurement for accelleration.  

The dyno a tuning tool that measures horsepower.

I wouldn't call the drag strip a better power calculator than a dyno, you have to do more measurements and calcualtions to provide accurate data.  

hello silly thread

Hi rev, I started this thread (unusual huh?) because I was getting tired of people saying "dynos are crap" and "the only way to tell how much power your car has is the 1/4". Now we all know that the dyno is only as good as its calibration and its operator. But the 1/4 has many, many more complications that make its results inaccurate and inconsistent.

So this thread is here to flush out the thoughts of people, challenge their thinking and kill off a few myths. And you know how much I like bumping of myths. Best of all it gives a central repository to all those who want to know about such things, a quick link saves a lot of typing.

So hop on for the ride or jump off, it matters not

[WazR32GTSt]

i'm sure that if you include ALL the variables that the 1/4 mile and dyno have respectively then thy probably will both give you the similar power figures by calculations

and each has their own variables, like:

drag:

driver, gearbox, drivetrain, weather, distance above sea level, surface, weight, weight distribuition, power curve, torque, tyres, etc. etc.

dyno (wheel):

gearbox, drivetrain, weather, tyre pressure, calibration of machine, dyno operator etc.

dyno (engine):

weather conditions, calibration of machine, many more?

the point that i see is that for measuring ENGINE POWER then what could be better than an engine dyno? it CLEARLY has the least amount of variables compared to that of the drag strip and that makes any results the easiest to accurately obtain and thus the most convincing in my eyes.

and before anyone says, yes all the above variables i wrote aren't the only variables i just couldn't think of any more as i'm suppost to be writing a thesis and that's on my mind...

cheers,

Warren.

[WazR32GTSt]

but in saying that, i think saying the 1/4 mile is USELESS for measuring engine power is a bold statment...

i believe that with a simple calculation the 1/4 will have a greater inaccuracy than an engine dyno due to a larger numbr of variables, and to calculate it properly by taking ALL things into consideration would be more difficult than what your average joe could do.

[RNS11Z]

A rule of thumb i have come across is, an r33/4 gtst with approx 300rwkw (give or take more or less) using standard 5 speed and diff should do approx 120mph down the 1/4 mile. A few people on here can back this up.

I think the mph can be indicator though diff/ gearbox ratios, tyre size can alter mph. So can weight. Its just too variable. Then ago so are dynos.

My 2c

[WazR32GTSt]

A rule of thumb i have come across is, an r33/4 gtst with approx 300rwkw (give or take more or less) using standard 5 speed and diff should do approx 120mph down the 1/4 mile. A few people on here can back this up.  

I think the mph can be indicator though diff/ gearbox ratios, tyre size can alter mph. So can weight. Its just too variable. Then ago so are dynos.

My 2c

R33 GTS25t, 300rwkw, standard 5 speed and diff --> guy weighs 150 kgs and changes gears like a granny

R33 GTS25t, 300rwkw, standard 5 speed and diff --> lady weighs 50 kgs and changes gears like mark skaife

both cars do 120mph?

and that's only ONE variable.

the variables on the strip are much larger than for that of an engine dyno...

[BNR32]

Never seen so much controversy over a topic because i think there is a confusion of about 3 or 4 different topics...

Why not ask the obvious question like, who invented the dyno and why?

Chassis Dyno's are used to fault find, fix problems under load and many other tasks that are illegal or impractical for a mechanic to do on the road. Chassis Dyno's are simply another tool in the roll cab that tuners use to get the 'nicest' and most 'streetable' tune out of a car. A dyno printout is just one of many functions, the real money is in the drivability of the car (economy & smooth driving).

What race team out there gives a shit about reutrn to idle, low rpm acceleration or fuel economy that a dyno is designed to facilitate?

Using a chassis Dyno to mesure power (as this topic is based on) is just one the intended purposes. A Chassis Dyno is a shortcut and 'poor mans' version of an engine dyno if outright horsepower is your 'bag baby'. That said they all have their own strengthts and weaknesses:

-Chassis Dyno (quick, cheap, sort of accurate, can identify other unrelated engine problems such as clutch g/box diff tyre problems)

-Engine Dyno (long process, expensive, extremely accurate, can identify engine component failure via heat imaging, etc etc)

In terms of comparing which is more accurate for outright horsepower 'Chassis Dyno or MPH', neither are meant for that purpose.

Just as an example:

How many race teams (V8 Supercars, Formula 1, etc) have chassis dyno's? I wouldnt be able to quote a number because i dont know the answer, but i sure as hell know they all rely on engine rooms (engine dyno's) to tune, run in and test component strength and failure...

When you look at examples of race classes where they are restricted to outright horsepower (le mans at one stage, i think??), how did they measure 'outright power', you guessed it an engine dyno.

Race Engines are whacked in the car and a final tune is set during testing on the track. Hell, most formula 1 cars have a different ECU tune for each track relevent to height above sea level, temp, corner entry and exit speeds etc.

So in conclusion to this huge thesis of a reponse, outright power can only accurately be measure on an engine dyno. In terms of the next best thing, id have to say Chassis Dyno combined with track times for someone who likes track work and MPH for those who drag race.

Or simply as sydneykid stated 'horses for courses'..

TG

[Duncan]

hey thats a bit rough for poor old chasis dynos....I've never yet seen an engine getting around without a car strapped around it.....why does it matter how much power your engine puts out, surely its the power that makes it to the ground that matters :confused:

[dangerous_daveo]

hey thats a bit rough for poor old chasis dynos....I've never yet seen an engine getting around without a car strapped around it.....why does it matter how much power your engine puts out, surely its the power that makes it to the ground that matters :confused:

I would have thought HOW it puts it to the ground.

But yeah, I just realised this is a silly argument, skylines etc arent drag cars

[japsky33]

This topic has gotten way off what me and SydneyKid started with so I'm just going to leave it now..

It had nothing to do with skylines being a drag car or racing teams etc etc.

BR,

JH

I would have thought HOW it puts it to the ground.

But yeah, I just realised this is a silly argument, skylines etc arent drag cars

[Sydneykid]

What race team out there gives a shit about reutrn to idle, low rpm acceleration or fuel economy that a dyno is designed to facilitate?

How many race teams (V8 Supercars, Formula 1, etc) have chassis dyno's? I wouldnt be able to quote a number because i dont know the answer, but i sure as hell know they all rely on engine rooms (engine dyno's) to tune, run in and test component strength and failure...

When you look at examples of race classes where they are restricted to outright horsepower (le mans at one stage, i think??), how did they measure 'outright power', you guessed it an engine dyno.

That was a top notch post TG. As yoyu can see above, I have picked out a couple of things I would like to comment on;

Fuel economy is important in Endurance Racing, we worked very hard to save one stop at Bathurst, it was a race winner for another team.

Quite few race teams have both engine and chassis dynos, we actually have 3. One engine, 1 roller and 1 hub.

Porsche racing is class based on power at the wheels. They have a portable dyno and they regularly and randomly stick cars on the dyno to check their power.

Race teams use the engine dyno a lot more because it is very expensive to rebuild race gearboxes, diffs etc. They are all lifed and wearing them out on the chassis dyno (at $10K plus per rebuild) is not very smart.

I should point out that we get just as consistent results from the chassis dyno as we do from the engine dyno. They are both run by the same engineer, he calibrates them exactly the same each time, goes through the same set up procedure each time and they live in airconditioned rooms. If an engine has 15 bhp more on the engine dyno, it will have 15 bhp more on the chassis dyno.

When we have raced away from home and need to check a problem (ie; Philip Island last year) we have borrowed another (local) workshop's dyno (same brand). Our engineer goes through his calibration and setup procedure and produces the same result, give or take a bit of weather effect (non airconditioned dyno room).

My suggestion (as always) is to build up a relationship with your dyno tuner, that way it is in his best interests to give you repeatable results.

[BNR32]

Duncan,

yeah a bit rough on dyno's, i believe in them, i just dont swear on them. I trust a chassis dyno for tuning as a safety point (ignition timing, boost and fuel) so that i can flog around a circuit and not worry about big lean outs, boost spike or irregular timing. Even then i err the paranoid side of things..I totally agree, its what hits the ground that matters.

Sydneykid,

-Fuel economy, i totally agree, but you know what my point was.

-Porsche racing is not F1 or V8 S/Cars, but i agree and take your point onboard.

-Sounds like you have a good dyno, Silverwater Automotive claim about 15% change in calibration every 3 months.

P.s what teams are you involved with? You may know my uncle (Pee Wee Siddle, Goold Motorsport) he has alot to do with Porsche Cup and runs the volkswagon racing team with Stokell and Timmy Leigh, not to mention unearthing Nelson Piquet into formula 1 back in the days, blah blah blah...

Tom Goold

[2rismo]

Quite few race teams have both engine and chassis dynos, we actually have 3. One engine, 1 roller and 1 hub.

Who is "we" ?

Adrian

[DoughBoy]

We is me, mah mohm and mah dahdda. Seriously, SK's been around the pits for ages with local race teams, talk to anyone who has been in competitive club racing for any period of time and they'll know him, or know of him. I was talking to an engine building friend who specialises in drag motors, even he knew SK well enough to say hi if he walks past.

I'm not building SK up to be some god-like figure (too sarcastic for that) but he has enough race experience over a very broad area to put alot of "import tuners" to shame.