RumRunner

Testing, is only as good as the people doing the testing, and interpreting the information. I never compare dyno sheets when I'm doing A B testing that have more than 1 degree difference in oil temp at the start of the pull, and I normally try to avoid that. The more accurate or (anal) you can be with your testing the better the numbers are going to be. Now here's the tricky part you've got to have someone who can interpret the data for your application. More peak power outside of the range you're running in, but sacrificing your acceleration rate you might not be happy. Just like Chris's customer the engine may have made more power, but may not have been set up for what the racer actually needed.

The main thing is a dyno is only as good as the people using it. I hear on a daily basis how much more power this one makes vs. that one. The bottom line is that the engine needs to fit your requirements. If Your boat runs x MPH, and you want it to run Y MPH within these guidelines (type of fuel, reliability, etc) than the only thing that matters is your boats performance when the engine is done. It's not as masculine, but if I can run 100MPH with 500 HP vs. 80 MPH with 950 HP who cares!

tomcat

Good discussion. Regarding correction factors...recording temp, barometric pressure (and humidity) allows you to correct your readings to "standard conditions". This evens the playing field, otherwise the dyno shops at sea level in cooler climates would always appear to have stronger engines.

However. find out what "standard conditions" are being used. If they are correcting to 60F and 29.92"Hg the corrected HP numbers are going to be a higher than if they are correcting to SAE standard conditons (77F and 29.6"Hg).

Steve suggests one way that the air temp sensor location can be changed to "help" the HP reading, by putting it some place where the air is hotter than that entering the engine. The opposite can easily happen. Case in point; we were dyno testing a centrifugally supercharged engine in a dyno room at 75F, so HP was corrected using this figure. We also happened to be measuring the air temp entering the supercharger (you need this to calculate efficiency) and found it to be ~95F because the inlet was close to the dry dyno headers. We didn't really care because we were doing back to back testing of other components, but if this test was for a customer, would you correct the HP upwards? (Damn right you would!)

GPM

I'm not an engine builder, the dyno and flow bench are tools to establish a base line. For me, the true test is in the boat, but it's nice to have some kind of reference point. HP = speed.

Wobble

Possibly, but it's all about drive ability isn't it? He made the peak horsepower, but the power delivery (torque curve) wasn't suited to the track.

I know that our racing is small time by comparison. But we have gained time by installing a restrictor plate and in one case pulling a spark plug wire on a short slick track.

Point being that you built a motor suited to the application.

articfriends

iTrader: (1)

I'm always slightly suspect of dyno pulls where the dyno operator has also built the motor for BIG dollars for a customer! Tyler Crockett always says_"you can't race a dyno,numbers are for accountants".I don't trust the numbers our local dyno's generate at ALL. The proof is in how fast a boat actually goes. This time when I built my 540 I had it dynoed and it made 944hp and over 950 ftlbs of tq and my single engine baja 272 runs almost 95 mph. Last time I dynoed it the motor made 630 hp/700 ft lbs tq and ran 76-78 mph before turning up the boost and timing further. After installing it in the boat with the 630hp/700 ft lb tq combo one day while out on the water I ran acrossed a identical boat with a carbed 540 that a local marina had built the motor for. I know the marina owner who built it and he had already told me how this normally aspirated motor made 70 hp more than my sc motor made and how my motor must be junk. Well after racing the guy's 700 hp carbed 540 boat and pulling about 5 more mph on him with 500 more lbs in my identical boat he was PIZZED . I don't know if they manipulated the dyno to give him a fancy piece of paper or what BUT he was pulling 200 less rpm's with a 26 pitch prop vs my 28 pitch,shot the credibility of that shop and the place that dyno's there motors all to crap . The guy who owned that boat was happy with his "big"numbers until that,the proof really lays in what pitch prop something can turn and how fast it actually goes. I think they dynoed his motor with step tube auto dyno headers and bumped up the correction factor when it didn't deliver for the 15,000$ he spent,Smitty

cstraub

Wobble,
True, I always say it is 80% driver and car and 20% engine. This ole boy was a 10 + year veteran of the track and a 2 or 3 time past champion. . .you know yourself with that kind of experience you should be able to take advantage of that kind of increase if it was there...

cstraub

Smitty,
The "power knob" is under the consol, turn it clockwise to be a hero, turn it counterclockwise to make the last guy look like a zero. I have gotten dyno sheets with 1.15 correction factor.

At the end of the day it is how it runs in the application.

cobra marty

ArticFriends, Your example is great to show the N/A vs. boosted TQ curve. Again I say forget about HP and look at the TQ curve and Peak. You probably had 50-70 more lb-ft of TQ than his N/A motor. Superchargers and TORQUe rocks.

articfriends

iTrader: (1)

I agree except its probably more like 98 % driver/car set-up and 2% motor on our local short tracks. 5 years ago a local company gave me 50,000$ to build (2) smallblock race motors and (2) back-up motors (just thrown together with leftover parts) for 2 FACTORY STOCK (bombers) circle track cars,I did it for free as a sponsor (it was fun spending SOMEONE elses money on cool parts though). They spent more time hitting the wall and spinning out than anything but they swore they didn't have enough motor!!!! The cars actually were faster with the spare motors I built out of junk because they had 70 hp less and they could control there cars better! It was fun BUT I had to babysit these guys because they would do stupid crap like dumping 3 gallons of nitromethane in 10 gallons of gas without rejetting or changing timing if you weren't at the track every time they raced to keep them from getting stupid,it got old quick,Smitty

cmcnitt

Classic example: I dyno'd a friend's race truck on my chassis dyno. The truck series allows either a 305 homebuilt, or the gm 350 sealed motor. He buys a factory sealed race motor from gm. Gm says set the timing to 32 and max rpm is 5500. I dyno it and sure enough, the power drops after about 5200rpm. I told him to gear the truck to hit 5500 max rpm. So, he resets the timing to 34 and spins it to 6500. two races later the motor is junk. Of course, he says the sealed motors are junk. Some people will never learn.