Why the 1/4 is useless for comparing engine power

[Sydneykid]

This topic was quite interesting on another thread. But it was off topic, so I thought I might start one over here. The story so far.......

What you can do is get each others REAL drag MPH from the track and match those up.

Br,

JH

Sorry japsky33, but I find that method less than reliable.  An example, I was at WSID last month doing some suspension tuning for a guy (no not a Skyline).  He did 7 runs during the day, 3 in the morning when it was cool and no wind.   One run was aborted, due to a half track oil down (not ours) and 3 runs in the afternoon when it was hot and there was a strong head wind.  The three runs in the afternoon where all slower both ET and TS, even though the 60' times where quicker.

Did the car suddenly loose a whole lot of horsepower?  Well it lost a handfull  because of the increased ambient temperature, but the real reason was because of the oil down and the strong head wind.  That was on the same track on the same day with the same driver, what if went to a different track on a different day with a different driver?

Not a chance, I'll stick to the engine dyno for my power numbers thanks, at least I don't have to worry about the weather (it's in a climate controlled room) and track conditions stuffing up my readings, not to mention driver skill.  :burnout:

Sorry SydneyKid I disagree.

As i race my cars at the track frequently and recieve the same MPH or with in 5mph everytime regardless of day/weather/track conditions.

if you get a good clean pass through all the gears your mph is a great example of the power that you are making. I have watched my cars through the modifications and had great success with this method I also get Dyno prints. Ive tried tyre sizes/pressure/suspension and different tunes and gear ratios all similar effects to the MPH.

My car made 277rwkw on the dyno yesterday is this an accurate figure of power ? Other days with different tyre sizes pressure and rubber ive made over 300rwkw. The amount of power lost through the wheels spinning made it inaccurate 4 people in the boot and strapped down tight didnt help it.

Some people like there dynos id rather MPH shows alot about the overall power of the car. IT also seperates the dyno read out bullshit artists and the true performance of your car and its modifications theres no better way in my book.

for instance,

SR20 180sx 14.1 @ 96mph

RB26 180sx 14.0 @ 126mph - Offuisly copious amounts of wheel spinning are causing his Time to be slow but look at the mph he has since bettered that time to a 12.2 @ 128mph showing simliar mph but better Time.

So an oil down effected his MPH what about an uncalibrated Dyno effecting his power output ? this could go on for ever, im talking clean dyno run V's clean drag run.  

BR,

JH

The bottom line for me is, I can have a "clean" dyno run anytime I like and you can never have a "clean" drag run because you always have factors outside of the engine working on the result.

An example, one that I have used many times.  When I worked in the car industry we did some testing changing only the diff ratio, driver, engine, gearbox, tyres etc were all exactly the same.  We did over 50 runs down the 1/4 using 9 diff ratios from 3.5 to 1 to 4.9 to 1.  I am not even going to attempt to tell you the differences in ET and TS, even if I could remember them all.  But 2 stuck in my mind;

1. The 3.9 diff gave the best TS but not the best ET, the 4.9 gave the best ET

2. The 4.9 gave the best acceleration and ET but the engine ran out of rpm before it got to the end of the 1/4, so the TS was crap.  It was 10 mph lower than the highest.

So the car was 10 mph slower with EXACTLY the same engine power.  So how can TS tell you how much power your car has?

I will leave you with this, why does every drag racer want to run at Death Valley USA?  Because it is 285 feet below sea level and the engine makes more power there than at any drag strip. :burnout:

I dont use it to say I have ex amount of power, i use it to show the power I have and have gained from different mods becuase when it comes down to it there to be driven on the road/track not on the dyno all its life.

As for the 10mph difference well you said it yourself the car ran out of rev's ?  

If it hadnt run out of revs probably would have run the similar MPH.

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I have seen different dyno readings from just tyre pressure.

-

If the dyno wasnt in shoot out mode and you had the dyno 285fbsl you also would see more HP. Even in shootout mode The power would be different just from being a different dyno!  

As I said this could go on for ever thanks for your input

Br,

JH

[czy18e]

I agree jap sky (pissing in pocket)

P.s go team.

[Roy]

The more power you are making the harder it is to use as a real indicator. Sure the mph is a reasonable indicator of an individual cars power, but i tend to think there is still a lot of grey in comparing hp of cars by looking at mph.

Plus i like my gearbox, clutch and diff too much to regularly look at drag racing. hell i cringe when they do power runs in 4th gear on the dyno.

[RB26VL]

The more power you are making the harder it is to use as a real indicator. Sure the mph is a reasonable indicator of an individual cars power, but i tend to think there is still a lot of grey in comparing hp of cars by looking at mph.

Plus i like my gearbox, clutch and diff too much to regularly look at drag racing. hell i cringe when they do power runs in 4th gear on the dyno.

well said Roy that is exactly how i feel, i got a RB26 in a VL and recently ran at drags and in the 2 meetings i came home with something broken.

started with the diff spinning upwards on the axle housings and causing the rear uni joint to snap.

next time snapped the front uni joint, fully bent the diff lower arms like an L shape and also snapped the uni joint holder on the gearbox yoke which is unfixable and i spent like 6 months looking for the yoke and it cost $200, so now i gotta get a new one, or change to auto for less impact on the driveline.

twin plate clutch and 10" slicks dont help the breakages.

so now im deciding to put engine in a gts-t and stay well away from the drags to save my box, and uni joints, and the like.

oh btw i ran a best of 12.04 @ 118mph

sorry for the ramble hahaha

Brad

[DCIEVE]

Try some nitto's and a slightly kinder launch technique and you should be able to avoid those kind of sudden loading breakages...btw saw the car at the plex, looks mint.

With s/o mode i'd be inclined to say the dyno is the more accurate measure of power, whereas the track would show which car is actually faster (and quicker)-

[dangerous_daveo]

So how does MPH tell you your power??? Is there some tricky forumla???

[Sydneykid]

With s/o mode i'd be inclined to say the dyno is the more accurate measure of power, whereas the track would show which car is actually faster (and quicker)-

Side by side maybe, but then driver skill is always a factor. Plus lane choice becomes important on many days, I have seen a car drop 0.3 sec with only the lane change. :uhh:

[AssM@N]

i'd say, no one's right, no one's wrong

dyno: higher power reading doesn't mean faster car down the strip, just shows peak power

drag: depends on car setup(as in 200kw vs 200kw) + driver + condition

ie: one's turbo may spool quicker

in reality, i think dyno is better use, i mean not everyone take's their cars to the drag and has a test, i dare to say more people have dynoed than dragging their cars

having said, the dyno has its limitations as brought up by jaspky: which dyno, dyno mode, wheel spinning

commonn factor would be the weather as its affects both just as much

at the end of the day, some prefer dynos, some hate the dyno queens and go for the drag

who cares?

AssM@N

[ylwgtr2]

Someone died at the local drags here last time......he got bored to death....the poor guy didnt even stand a chance

[Duncan]

Someone died at the local drags here last time......he got bored to death....the poor guy didnt even stand a chance

trying......really....hard.....not......to......laugh.......

[DoughBoy]

I don't understand the whole dyno fascination, the engine is only part of the whole equation. With drag MPH you can more accurately show how quick/fast the whole car is, not just beat your chest over some dyno graph where the rollers were spiked.

What's the point of having a 600rwkw motor if you can only use 200 of it? Either limited by component failure, traction, driver talent... etc? Now that's pointless...

[2rismo]

trying......really....hard.....not......to......la ugh.......

Back in your box, Handley!

I'm sorry dyno-lovers but more than 100 years of drag racing mathematics disagree with you. Moroso Calculator anyone?

Adrian

[Sydneykid]

Back in your box, Handley!

I'm sorry dyno-lovers but more than 100 years of drag racing mathematics disagree with you.  Moroso Calculator anyone?

Adrian

Hi Adrian, the reason the drag guys use the calculator is because the engines don't last long enough to run them up on the dyno...

7,000 rpm for 6 seconds = 700 revolutions of the crankshaft

Time for a rebuild, new pistons, rings, rods, reseat the valves etc

7,000 rpm for 6 seconds = 700 revolutions of the crankshaft

Time for another rebuild, new pistons, rings , rods, reseat the valves etc

Doesn't give you much time to run it on the dyno, so to GUESS how much power it has you have to dig out the trusty calculator and punch in some numbers. :headbang:

[KamikazeR33]

if u wanna know what real power an engine is making, put it on an engine dyno, not a car dyno

if u wanna go fast put it in something light with a good setup

simple

[Sydneykid]

if u wanna know what real power an engine is making, put it on an engine dyno, not a car dyno

if u wanna go fast put it in something light with a good setup

simple

The engine dyno is great, build an engine, run it in on the dyno, tune it, make sure it is making the power it should then stick it in the car and go racing. In a climate controlled roo,m the results are repeatable with very small variations (eg; less than 2 bhp in 625 bhp). Works for us.

But (there is always a BUT) sometimes they don't go as fast as they should and you simply don't have time to pull it out and run it up on the engine dyno to find the problem. Sometimes it's an installation problem, it makes good power out of the car, but loses 50 bhp when you put it in the car. Then the chassis dyno really comes into its own, you can check the installation, search for problems, make changes (eg; exhaust pipes) and check results quickly.

As usual it's horses for courses :cooldance

[discopotato03]

I think the engine dyno train of thought is a valid one . Being able to repeat the same conditions over and over would have to be invaluable . I reckon on the strip there are too many variables beyond the drivers control .

[DoughBoy]

Hi Adrian, the reason the drag guys use the calculator is because the engines don't last long enough to run them up on the dyno...

7,000 rpm for 6 seconds = 700 revolutions of the crankshaft

Time for a rebuild, new pistons, rings, rods, reseat the valves etc

7,000 rpm for 6 seconds = 700 revolutions of the crankshaft

Time for another rebuild, new pistons, rings , rods, reseat the valves etc

Doesn't give you much time to run it on the dyno, so to GUESS how much power it has you have to dig out the trusty calculator and punch in some numbers. :headbang:

You can't get an engine or chassis dyno that reads high enough for full bodied drags cars in the 6's - that's over 2500hp! Even the Outlaw 10.5 cars in the 7's are running over 2500hp, most of them have twin T76's or a single 103mm inducer sized turbo at that level.... At most they would use a dyno for is for bedding in a new motor and light throttle work.

[DoughBoy]

Hi Adrian, the reason the drag guys use the calculator is because the engines don't last long enough to run them up on the dyno...

7,000 rpm for 6 seconds = 700 revolutions of the crankshaft

Time for a rebuild, new pistons, rings, rods, reseat the valves etc

7,000 rpm for 6 seconds = 700 revolutions of the crankshaft

Time for another rebuild, new pistons, rings , rods, reseat the valves etc

Doesn't give you much time to run it on the dyno, so to GUESS how much power it has you have to dig out the trusty calculator and punch in some numbers. :headbang:

You can't get an engine or chassis dyno that reads high enough for full bodied drags cars in the 6's - that's over 2500hp! Even the Outlaw 10.5 cars in the 7's are running over 2500hp, most of them have twin T76's or a single 103mm inducer sized turbo at that level...and some of the more budget conscious (not front runners) can go for a season before a rebuild. Still think they are 6 second grenades? At most they would use a dyno for is for bedding in a new motor and light throttle work.

[2rismo]

Absolute hogs-piss. Take one Moroso calculator, apply it to ANY car at WSID and your results will probably surprise the hell out of you, Sydneykid.

It isn't just used for 6sec theorhettical pie in the sky dragsters that run sub 6's.

Some of the fastest Super Sedan teams in this country and the states use it almost exclusively to estimate the horsepower their engines makes. Dyno's are just an estimate as well. Lets not forget that.

At the end of the day, usable, real world hp is what interests most people (leaving out the obvious dyno queens) and MPH is a fantastic and vastly underated measure of power.

Adrian

[dangerous_daveo]

After reading most of that again...

I have worked it out.

1/4 for compairing car, both speed, acceleration, highway car or strip car etc. ie to see how the car goes, or compair it to someone elses car as in a race.

Dyno for compairing actual engine power, with a handy break down so you can see what it did throughout the rev range. Ie to find problems, run in the engine, see how much power you make without having to have a degree in physics.

So in other words... STOP FIGHTING DAMN IT!!!