Mustang GT's True Horsepower?

Steveng93 said:

ford advertises it as 300 hp.. im hearing 275 ish.. is that true? and if so.. wtf how is that possible to drop 25 horsepower, or what is ford doing so that they can advertise at 300 hp.. or was it never 300 and they are lieing.. can someone just explain it all to me please?

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Understand that the steel bearings in the differential, the extremely over weighted 2 piece stock drive shaft and stock windage tray that puddles the oil on to the crank causing uneccasary resistance can be replaced with an aluminum drive shaft, ceramic coated bearings and an efficient windage tray to let loose about 15 of those horses. But thats if you feel that route would be a good choice given the cost of aluminum drive shafts and the durability of ceramic coated bearing. Beleive it or not and Ive tested this theory but a larger oil pan with a good draining windage pan can relieve allot of that HP loss with properly draining the oil away from the crank as to not constantly slop it back on to the crank leaving more oil and resistance to drag down the performance. Even though its not behind the flywheel once that energy is dispersed all the way through to the crank shaft it has a cause and affect starting from the pulley all the way back. Weve played with this Idea at the shop and tested it with an actual gain of over 300 on a stock motor with a stock tune. But again thats Aluminum crank pulley to the larger capacity oil pan with a good windage tray, to a aluminum groung flywheel to a aluminum drive shaft to a differential with ceramic coated bearings, all in all about $1600 for the total. Is it worth it, sure if you have money to blow but that $1600 is a good chunk for saving towards a supercharger, hands down the best possible mod dollar per HP you can get.

I've never seen an auto company that rated at the rear wheels. As everyone has said all cars are rated at the flywheel.

For example, here's a blog entry for the Corvette ZR-1. It's rated at 638 hp at the flywheel and the dyno measured 535 rwhp. That's a 16% drive train loss. Pretty much what you'd expect.

Corvette ZR1 dyno'd at 535 rwhp

Not to be confused with net hp vs. gross hp. Prior to '72 most auto manufacturers used gross hp ratings, that is a test engine running on a stand with no losses at all. Totally unrealistic. Today's ratings are net hp, so an engine measured with everything, except drivetrain loss. It's much more accurate.

For example, a 1971 Corvette with a 454 big block was rated at 365 hp. That sounds impressive doesn't it!

The 1972 Corvette basically the same engine, rated with the now common SAE net standard was 270 hp. I'm guessing with a 15% drive train loss it would have dynoed in at 230 rwhp.

GAP said:

Unless of course the manufacturer is misleading the consumer by over rating their motors like the OP was suspicious of. I remember Mazda being sued by Miata owners years back because the motors werent putting out near the claimed power. If I pay for X amount of horsepower, I expect the car to produce it.

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The manufacturer was up front and honest on their claim to horsepower produced. The consumer also has some responsibility to understand what they are buying. The horsepower rating standard adopted 30 years ago was to help insure that the consumer was not being misled. Unfortunately, most of us are not going to pull the engine and dyno it to check it.

These engines likely have a Go/No Go test they are put through. I don't know what Ford does exactly but I would imagine each engine goes through a Hot Test and a minimum hp (and many other parameters) has to be reached to be considered a Pass. This would be an automated test and the results recorded against the engine serial number.

It appears that the OP didn't understand that the rating published is at the crank and not the ground. He further claims that he won't buy a car that doesn't deliver as advertised. Based on those two conditions, he will not buy another car from any manufacturer.:headscratch:

I saw a show on how motors are rated by SAE and it is no joke. The motors are set up on the stand EXACTLY like they will be in the car right down to all the accessories and entire exhaust systems. The SAE has a testing regiment that all motors, all manufacturers must go through before they can make claims, advertise, etc. Representatives oversee all aspects of the testing regiment. The feeling I got from the show I watched was that the SAE people were “The Man” and passing the test, getting good numbers, etc was very, very important. The engineers I the show certainly were suffering from some anxiety during the testing process.

I think in this day and age it’s fair to say that the manufacturers are not going to be able to make any outrageous claims and get away with it.

As for comparing crank hp/tq to rwhp hp/tq that will always be a very, very rough calculation. The variables in using the chassis dyno are potentially huge. I know from thousands of hours of dyno testing that it’s very, very hard to get repeatable runs. The smallest thing can affect the run and there are a lot of “smallest things” that can crop up. Then add to that all the parts from the flywheel to the tires and you have a whole new list of variables. I have seen tire pressure change hp readings 5%+/-. Another big factor is the temp of the fluids in the Trans and rear end. There is a big, big difference between hot and cold.

The claimed numbers from the manufacturers, because of oversight are very close to actual outputs. Some will be more, and some will be less due to tolerance stacking during assembly and inconsistencies of the weight of parts, etc. That’s why simply blueprinting a motor can be worth as much as 10% hp. The process of blueprinting eliminates or greatly reduces these variables.

Everyone should always take rwhp numbers with a grain of salt. There are a number of ways of skewing the results to justify claims. It’s easy. And even if someone is not trying to pull a “fast one” it’s still hard to get repeatable runs even for the best operators. Comparing two different cars on two different dyno’s is simply stupid. Comparing dyno runs with the same car and the same dyno but a couple months apart is just as stupid. For the best, and only nearly “scientific” results dyno runs need to be made back to back and if parts are being changed they need to be changed as fast as possible and all engine and drivetrain operating conditions must be identical. And lastly after a parts change a new map must be made to support the change. This is the most prevalent thing I see skipped in magazine tests and that is a big no, no.