j28s

Why is it when we see posts (i.e. Dyno at 178HP, but stock rating is 235HP), we see such a huge drop? That is almost a 25% drop (note: that is a HUGE difference). Why? On average, there should only be a 12 to 15% drop in rear-wheel drive vehicles, and a 17 to 18% drop in front wheel drive cars. Anyone know???? Is it just in the truck market everyone says there trucks have more power???

chuck3

You loose a lot of power thru the drivetrain, especially in the auto's. I beleive the #s are from the crankshaft.

Push Rod

You've got two reasons why trucks don't dyno up to the manufacturer's specifications:

1) The manufacturers all rate their engines at the flywheel. Dyno runs are all brake horsepower. As such, you'll see some waste between the flywheel and the tires. Standards are usually in the 20% area, autos in the 30% area.

2) The manufacturers rate on an average. Some trucks will roll off the line with less power, some with more. I've seen a 20% difference over the years.

Another thing to keep in mind is that dyno runs can be destroyed by an incompetent operator or improper setup. In other words, you could make a stock truck run 300 HP or a heavily modified truck run 200 HP if you don't know how to operate the dyno or you're trying to skew the numbers for some reason.

A dyno which is improperly calibrated (or operated) is very easy to spot. There is a formula, which is simplified but holds fairly true:

HP = Torque X RPM/5252. In other words, if you see a dyno run like 220 HP/800 lbft of torque at 2000 RPM, you'll know something is up. The numbers just don't jive.

Rod

dieselgeek

I have experience with Mustang, Superflow, and Dynojet.<br><br>If your numbers are off a Dynojet, subtract 10% or more to get what you'd see on a Superflow or Mustang dyno.<br><br>Haven't dyno'd my truck, but have been building drag race cars all summer long - made 15 dyno trips this year alone to three different shops - and our experience is that you're WAY better off tuning on an eddy-current dyno, or one that can simulate the actual mass of your vehicle. On one car, we noted 300 degree LOWER CHTs on the dynojet, so if it were tuned properly on that dyno it would be lean on the street. NOT GOOD when you're squeezing 2HP per cubic inch under boost... on a gasser that is...<br><br>Also - all of our cars lose a LOT more than 17-18%, and the difference is more relative to the trans type. On our 94 camaro, we were running 770 RWHP through the stock six-speed trans. We swapped to a TH400 and lost 150HP at the wheels - nothing else changed!!!<br><br><br><br>

j28s

I guess I may be missing something...who knows. I have my race car (SCCA &amp; NASA road racing, no drag racing) dyno'd about 10 times per year (always adjusting something). And looking at the stock rating (agree, HP @ the flywheel) there was a 17% drop, which of course is the amount lost in the drive line (note: this was on a front wheel drive car and on a DynoJet). Then talking with other folks that race rear wheel drive cars, they were only losing 14%. Additionally I've always hear the DynoJet was one of the more accurate dyno machines...but who knows...may just be an opinion.

Are other makers (i.e. Ford's Powerstroke, and Chevy's Duramax) doing the same thing (that is the 20% drop from flywheel HP)? Also, could the higher % drop be a result of being a 4x4 (more drive line parts)???