67mustang302

Since the issue of dyno numbers and dynos in general always seems to come up, it seems to warrant a thread of it's own. That and it was somewhat off topic in another thread, so I'd figure I'd post here.

Basically like I've said before, dynos lie...a LOT. They're a great tuning aide, but for guys like us that should be IT. A tuning aide ONLY. And a questionable one at times. Dynos are REALLY good for setting a baseline on an engine/car, but sometimes in the real world the car wants something different than what it can handle on the dyno.

http://www.prosystemsracing.com/amerigo.html

That's an article from Pro Systems, they build high end race carbs for a wide array for race and street cars. Including NHRA and other high end carbureted race engines. The important part dealing with dynos and tuning is the last several paragraphs. But I suppose the rest of the article is relevant in other ways.

Stone629

I agree. Dynos are tuning tools ONLY. The numbers they kick out are entertaining and exciting, but thats it. I put my Balt on the dyno back in mid 2010 sometime, at about 90 degrees, lots of humidity, etc. It put down 240 at the wheels according to the numbers the tuner was showing me. I went back in November I believe, with a shorty header, intake, and some cat-back work, in 50 degree weather.... and it showed 250 whp. THEN, the tuner said, "watch this", and uncorrected it for the cooler temps and said, "this is what you're actually making in this cooler weather", and showed me 268 at the wheels. Basically, they can make it read wtf ever they want. The important thing to look at while dynoing isn't the HP/TQ numbers, but what the car is doing throughout the RPM range. A good tuner knows how to spot detonation before it happens, knock, where in the RPM range to make A/F tweeks, etc, etc. Hell, I'll put my SS on the dyno tomorrow and tell the tuner to show me 300 whp and I guarantee you he'll whip me up a 300 whp Cobalt dyno sheet in no time, lol.

MrRogers

I agee with both of you. The numbers are pointless. It's how and where the power is being made. Also using the chart can help you determine better shift points.

bluebeastsrt

People LOVE their dyno numbers. It's so easy to strap your car on a dyno and let it do it's thing. It's not so easy to cut a 1.6 sixty with FWD or a 1.4 sixty with RWD. Not so easy to cut a good lap around a road course without hitting the gravel runoff area.

67mustang302

Dynos also may not show you transient issues that crop up. Carb'd cars are notorious for transients....car makes great power at WOT, but issues off idle, throttling down, throttling up, gets sudden lean/rich conditions that cost a bunch of throttle response. Many also don't show BSFC, or brake specific fuel consumption(some of you have seen me mention this before). Fuel consumed in lbs per hp per hour. When tuning a car you have to ask if it's worth gaining 2% power, but consuming 10% more fuel to do it.

You guys do make some really good points though. A dyno graph may be inaccurate as far as the numbers, but the overall curve tells you WHERE your power is, letting you know the best place to shift to make the car go faster. And being able to drive it is a matter for another thread entirely =P But I guess it's a lot easier to race dynos.

Though dynos can cost performance, especially for road course cars that cycle up and down through the throttle and rpm. Just because you can get the highest number with 4* more timing and a bunch of extra fuel, doesn't mean that extra fuel won't load the cylinders as you throttle out and lose rpm, only to get a transient rich the next time you throttle back in coming off a turn.

jmdgto

agree. i have seen high number cars run like crap and low number cars run like a raped ape.

Mishri

yep, exactly what the guy who owns the dyno I had mine on said, these are for tuning, the numbers don't mean anything. His is known to read about 10-15% lower than other dynos.. I got 285whp on it most people with my mods are somewhere around 300whp

Riptide

Traps the best indication of power you can get.

Tuners frequently talk about how much "power it made" on the dyno. They certainly seem to believe in their "accuracy".

67mustang302

That actually brings up another interesting point. Once the car is dyno'd you have a baseline, but you almost always get a bit more(or sometimes a lot more) power by tuning on track. Once it's baselined, play around with the tune a bit at the track and see what gives you the best mph. Tuning for mph at the strip 9/10 times will yield more power than tuning on a dyno....not a whole lot typically on EFI cars, but it can have a HUGE impact on carb'd cars.

As far as their accuracy, in what regard? The numbers themselves are truly accurate? They do have accuracy in that if you gain power, use more fuel or less fuel etc, the dyno can show it. But even then only to an extent.

I keep mentioning carb'd cars a lot because they make excellent examples of dynos lying. Carbs deliver fuel based on airflow, which is dictated by the way the engine loads.....and engines load differently on a dyno nearly every time. It's not uncommon at all for a carb'd car to get a dyno tune and pick up a lot of power on the dyno(and by a lot I've seen street cars pick up as much as 40-50rwhp on a dyno on an already well running car), only to run like total crap and lose a lot of mph, foul plugs in some cases, lean out and surge in others....and in some cases run so poorly as to not even be drivable.

EFI cars are a lot less sensitive since they don't deliver fuel based on airflow dictated by load, but by engine operating parameters. Rpm is rpm, throttle position is throttle position, manifold pressure is manifold pressure, mass air flow is mass air flow. And once the car is baselined, the ECM tries to always operate at that dyno baseline, adjusting as necessary. But again, the power a car makes on a dyno may not always equal real world performance. Sometimes the car is faster down track with a little more or less fuel, a little more or less timing etc.

One thing too worth mentioning is inertia dynos. Basically they have some large mass that is accelerated, and based on how quickly the mass was accelerated from whatever speed to whatever speed, it determines approximate horsepower. They then mathematically calculate backwards to determine torque. While not the most accurate way of determining power/torque on a car, they have proven to be extremely good for tuning purposes. Since the car/engine is simply trying to accelerate against a load as quickly as it can, it most realistically mimics real world operation of the engine. They've proven through use that while their power numbers aren't accurate(and sometimes way off), inertia dyno tuning results in the best real world performance of cars that are tuned on a dyno.

mustangmancp

See i like this thread. People always get caught up in dyno numbers..mine made 300 on a dyno recently when it should be about 320-330..now that could be the low compression or what..but i hate them they're just good to see where you're making the power.

I do drive tunes most of the time to check AFR and everything. I tihnk that is a WAY better way to do things...