legacycentral bbs

http://dyno.scoobynet.co.uk/jap/gavin_peake.htm

check it- lost 6 hp across the range with a snorkusuctomy and a "scorpion filter"

What the hell is a Scorpion Filter? That might be the result of lower power output. The "Scorpion" filter is likely a poorly designed filter by a no-name company that has inconsistent flow across it's surface area.

Those dyno runs were two months apart- June and August. There may have been some atmospherical differences, plus the milage put on between the runs may have done something. Just possibilities.

That entire page is bull. Where did they get those numers from? How do you get peak hp and not get peak torque because of an automatic transmission???? They are the same thing mathematically.

And somehow his buddies car was able to get a crank hp and a whp number at this magical place they go to which can get peak hp (but no torque) AND crank hp numbers.

Well, if the dyno can't directly measure engine speed, then an unlocked torque converter would make it impossible to measure torque even though you can measure power, right?

But, yeah, 2 months is a long time between runs. Heck, the aging of spark plugs alone can make a big difference.

They aren't seperate values. Whatever you use measures one value (hp or tq) and mathematically plots the other. The whole thing seems shady.

If you don't have engine rpm the graph will be all messed up. When I had mine dyno'd they couldn't clip the optical pickup thing anywhere, and the inductive pickup didn't work, so they had to get engine rpm through some other method that the dyno had. I don't really know too much. I question whether it's as accurate as the optical pickup, but whatever.

Regarding those graphs that were posted, yeah that seems fishy.

You can't take just a power number and turn it into a torque number. You need to know rotational speed as well. Power is torque times rotational speed.

A transmission can change torque, so if you don't know what the transmission is doing, you can't really infer anything about the torque being produced by the engine. Power is conserved, however, so the power measured at the wheels is the same no matter what the transmission does.

But power at the wheels is a function of wheel speed(known), and wheel torque. If wheel torque can't be measured, then how can wheel power be measured?

You can measure torque at the wheels, but it's not a useful number. You multiply that wheel torque by wheel speed and you get power -- a useful number. Then you divide that power by engine speed and you get engine torque -- another useful number.

Right?

The speed of the drums (or whatever) is a monitored variable.

Know the speed of the drum, know the diameter of the wheels, know the gearing, know the engine RPM enough to estimate a torque number and voila.

To put it another way, the Auto thing is NOT an excuse to not have torque. Hell, the selectmonitor port can tell you engine RPM. It's not a difficult variable to find.

Power is derived from torque, not the other way around. I don't see how you COULDN'T get Torque if you can get horsepower.

Afterall, Roman dynoed his SHO and it's an auto.

Power is derived from wheel torque, but engine torque is then derived from power and RPM.

I agree that you can figure out what's going on with an automatic, and any well-designed dynamometer should be able to... I'm just saying that it's conceivable that a particular dynamometer might lack the ability to measure engine speed, and so must be told what the gear ratio is. Such a dyno wouldn't be able to measure torque with an automatic transmission unless you were able to lock the torque converter and hold it in a particular gear.

Maybe we should focus more on Brat4by4's question of how a dyno is determining crank power...

Most are just extrapolations based on an average parasytic loss. Nothing really scientific.

Tuning by wheel numbers is pretty effective. The only real way to get engine numbers is on an engine dyno and tune it on there, then retune on a chassis dyno.

Wait a minute. HP is calculated by torque x RPM. So how do you get a HP reading without a torque reading?

Because it's wheel torque, not engine torque.

-K- wrote:Wait a minute. HP is calculated by torque x RPM. So how do you get a HP reading without a torque reading?

you can't. I think that's what everyone is trying to say.

here is the exact formula

horsepower = rpm x torque / 5252

Most people that I have seen just use the whp/torque #'s and don't try to extropolate what engine torque is.

an air filter change is likely to make no difference whatsoever. There are numerous studies with K&N, etc. etc. compared to a fresh factory filter in many different cars, showing diddly for power gains. The pressure drop across a fresh factory filter is so low that you might as well assume it is zero.

I think the Scorpion filter fits in the stock airbox. So, how was the air intake configured after snorkus removal ? Sucking in hot engine bay air, or routed to the front to grab fresh air ?

Dynos are helpless to measure small effects like this, that really depend upon the car rolling down the road to get accurate pressures and temperatures at the various intake points.

Yeah. The airfilter does not make much difference until they both get dirty... then the k&n will keep on chugging while the paper just clogs.

And I think we are arguing the wrong points here. They obviously were measuring engine torque because the numbers aren't 5400 lb/ft or whatever ungodly amount a car actually puts to the ground with gearing. So, I think it is safe to assume that the entire web page is nothing but internet fluff that can just be written off as telling us NOTHING. And as for the original statement in the first post... bull. The snorkus is a pressure drop, removing it helps. If you make your car suck hot air when doing it, that is your fault. All you have to do is remove the box and leave the drop tube for the original factory cold air intake and no pressure drop.