mx5cartalk.com

So, i've read - read - read and read some more and everybody seems to have the general opinion that 250HP is the line between reliability and a ticking time bomb.

I'm not sure what to make of this because my own 1.8 engine made 303NM at 160WHP, and then there is another 1.6 on youtube making 315NM at 250WHP, and then a friends 1.6 engine just made 460+NM at 250WHP.

Surely, torque is the figure we should be discussing when we talk about max power output on a stock engine - and not HP.

OR am I entirely mistaken?


Cheers.

Dan.

http://www.epi-eng.com/piston_engine_technology/power_and_torque.htm

For example 184 NM at 6,150 = 159 hp (this is my 1.8 ltr natural aspirated)

Torque on a rolling road dyno is absolute BS.

Its 250ft lb at the engine which is the limit which ends up around 250whp on a turbo 5 because of cam profiles and head flow etc.

The issue is that Aussie dynos dont seem to ever calculate torque back from the HP they just display the HP and torque at the wheels, but torque at the wheels is dependent on gear ratios and rolling diameter.

IE a stock na6 makes over 1000ft lb at the wheels in 1st gear, because of the low ratio, like low mountain bike gears going up a hill.

If you take the HP and use the standard hp > torque conversion you can find the peak torque if you work it out at a few points along the dyno graph.


Dann

PS: if you do a dyno run in 1st gear with a turbo car that has a 4.3 diff the dyno will read THOUSANDS of ft lb, but it obviously isnt making that.

Currently making 186rwkw/249hp in my 1.8l not to sure of torque but I'm pretty sure it's around 220+

Seems to be going fine after taking a beating at the track (touch wood )

It also comes down to the way the car is dríven and condition of the engine, tune etc

Sent from my HTC_PN071 using Tapatalk

Well when push comes to shove, I don't think anybody is interested in how much their engine is making alone, as compared to how much torque they have available to be disposed at the wheels. The general concensus is 4th gear pull, no? If it's an general standard, there shouldn't be a massive difference comparing between MX5s. Give or take some because of different diff ratios.

Its more complicated than that, the torque at the wheels comes down to horsepower and gearing, plain and simple.

Its not the same between mx5's because different tyres, diff ratios, gearbox, wheels, how much tread has been used, tyre pressure, all come into play, so you need to take hp and convert it to tq, which is done as standard on US dyno's but on aussie dynos we all get the torque at the wheels reading.

Here is an example, in a 6 speed the 1:1 gear is 5th, so if you used 4th you would put out an extra 20% odd torque, again showing that just putting it in 4th and hoping it all shows realistic numbers is a BS idea.

Ask the dyno operator to have the machine calculate torque from the hp and rpm, not to display torque at the dyno drum.

Dann

That all makes perfect sense.

My car is only running 3.8 psi at the moment, will be taking it back after New Years for its proper tune. I'll ask if they can get the proper torque reading for me.

Thanks Dann.


Dan.