The first dyno graph is whack. Something isn't right. I know the scales are different for hp and torque, but even a quick glance and you can see that the torque is around 225 at about 5200 RPM's. By simple math you can know that the hp should be about 225 at that RPM as well, but it's only showing 200 or a little less.
Nothing is whack. The pulls were made on a Dynojet 224LxC dynometer, one of the most accurate Dynojets made, and one that can't have the numbers fudged. A stock 5.4 3V isn't going to put out 225HP with 20 inch wheels and tires on a 4x4 -- too much drivetrain and rotational mass loss.
I just wanted to drop by to discuss this a bit - now I have to say right up front that I have NOT looked at the last graphs that Ken posted up, the ones you are talking about, so I can't speak to that directly - I have all the original plots which is where he got his plots, as I am the one who tuned that vehicle, dyno'd it, did all the installation & configuration work, etc. along with my staff, etc., etc., so that is the data I will speak to.
One thing that you will tend to see is that on supercharged vehicles especially, in a number of cases TQ & HP are *not* going to cross at 5252 rpm as some people expect them to - now that may come as a shock to those who aren't very experienced with tuning & dynoing many, many vehicles themselves, who are only thinking about what some books tell you about the traditional mathematical formula for determining HP that preach that HP & TQ are always supposed to cross at 5252 rpm - well, that simply isn't true. HP is merely a different way of expressing torque - it's expressing torque over time - time in this case being represented by rpms.
So having TQ & HP NOT cross at 5252 rpm is perfectly normal in some cases with forced induction engines, especially with positive displacement Roots-type blowers that are continuing to make good power up top, so the HP continues to climb and thus sometimes HP & TQ simply does not cross at 5252 rpm. Some do, some don't of course, not ALL blown motors will do this, but if it's huffing some boost and the blower is healthy, it is somewhat normal to see the HP continue to climb, so that HP & TQ do not match at 5252 rpm in a number of cases. I've seen this a number of times over the years on engines that were configured & running just as they should be, and were well tuned. It happens.
Just as an aside, another condition under which you will see HP & TQ not cross at 5252 rpm is, particularly with regard to these 3-valve mod motors, when the wrong octane level of fuel is used for the tune that is in the vehicle - for example, I had a fellow out in California who used 91 octane on his 87 octane tune - well, it made GREAT power, but only up until 4200 rpm, where the power peaked and from there on, the HP never got any higher. So of course HP & TQ didn't cross at 5252 rpm, and in that type of case, it would be regarded as a "warning" that something was amiss, either in the tune or in the fuel being used - and in that case, it was the fuel being used. What he had done by using the wrong octane of fuel caused the motor to peak it's power early. Why? Well, in other words, his power peaked at 4200 rpm because from about that point on, since the engine was tuned for only 87 octane, the engine did not have enough spark timing (advance) in it to allow enough enough physical time (and in terms of # of degrees of crankshaft rotation) to burn enough fuel at rotational speeds in excess of 4200 rpm, thus the HP never got any higher as rpms increased, as there wasn't enough spark advance - he ran the wrong fuel for the tune he was using. Now in *that* case, HP & TQ not crossing at 5252 rpm was in fact a warning sign that something was amiss - and he had simply used the wrong fuel.
There are a number of legitimate scenarios in which a vehicle will not have HP & TQ cross at 5252 rpm - as a very experienced tuner (I've tuned literally thousands of 5.4 3V F-150's alone, have specialized in F-150 tuning for over 15 years, have tuned EFI vehicles for 20 years and did carbureted tuning for 10 years before that) in my career I have run across many configurations & scenarios in which HP & TQ do not cross at 5252 rpm. Now some of them are "legitimate", like a blower motor making big power up top, and then sometimes it is indeed a "warning sign", letting you know that you need to investigate further - spark curves, knock sensors, fuel quality, etc.
We recently had another scenario in which a gentleman filled up with what the gas pump said was 93 octane fuel, but when we put him on the dyno, it was obvious it was only 87 octane - now this was in a 5.4 3V, and they are set up from the factory to have a whopping 12 degrees of retard capability in the knock sensor system, so the truck did not detonate, but the knock sensor system used every bit of it's 12 degrees of retard capability to prevent it from detonating, and it didn't make the power it should, HP & TQ didn't cross at 5252, etc. That's just one example of when HP & TQ did not cross at 552 rpm that was not "legitimate" - and by that, I mean that something was wrong and needed correction. And the vehicle owner was stunned when he saw the data compared to other trucks running on 93. Now in his case, to get him a band-aid "fix" right away, we "dosed" his tank with a fuel additive that actually works to bring octane up very quickly, made a couple more pulls and then there was no retard from the knock sensors any more, where there had been 12 degrees being pulled out before - and then Hp & TQ crossed at about 5200 rpm as it should have for that configuration.
The main point I really wanted to make is that we do see a number of forced induction engines (and some other situations) where they legitimately do not cross HP & TQ at 5252 rpm - it can and does happen for legitimate reasons, in addition to all the obvious non-legitimate reasons.
Now as I said, I have not looked at that graph Ken posted, so what I have just said may have NOTHING to do with what you saw, but I thought I'd just drop by and talk about this a bit in general.
Before I say anything, I would like to clarify that I think you are one of the best tuners in the business. And you are without question the nicest, most personable tuner anywhere. As a matter of fact, you did the 4 position chip on my old Lightning for me. I loved it. Made great power, got good mileage, and is still going strong. The guy I sold it to still loves it.
All that being said, if you have ever seen any graphs where hp and torque did not cross at 5252, then something was wrong with the calculations or with the scales of the hp and or torque. Why? Well, it has to do with how the term horsepower came to be and the mathematical formulas behind all this stuff. This is the equation.
Horsepower = Torque * RPM / 5252
So how is this formula arrived at, and where did 'horsepower' come from?
Well it's all down to the Scottish engineer James Watt (1736 to 1819), he established that a horse could pull a 550lb weight up from a coal mine at a rate of one foot every second, for an eight hour shift. This converts to 33,000 foot pounds per minute. He published these observations, stating this figure to be the equivalent of one horsepower.
We need to convert from the rotary motion of an engine to a linear motion, like the horse example. Remember we can only measure the torque of the engine, this is expressed in pound feet. A pound foot of torque is the twisting force necessary to support a one pound weight on a weightless horizontal bar, one foot from the center of rotation. Lets rotate the one pound weight one revolution, the distance travel is 6.2832, that's Pi multiplied by the diameter, 2 feet. We have now done 6.2832 foot pound of work.
One horsepower equals 33,000 foot pounds per minute, so if we divide 6.2832 in to 33,000 we can conclude that we at 5252 rpm we are producing one horsepower, we are moving our one pound weight 33,000 feet every minute. Therefore if we multiply the torque by rpm and then divide by 5252 we can calculate the horsepower.
And therefore there is no possible way that the torque and hp can NOT be equal at 5252 RPM's. Again, sometimes they won't cross each other on a given graph due to the scaling of hp being different than the torque. It's all in the math.
Here are the same pulls (except the custom tuning pulls) graphed in an earlier article. I think for the 2nd article the software didn't scale it correctly. I'm going to try re-exporting the images and will see if that corrects it.
FTE Founder. Enjoying life, hitting the throttle and hearing my Ford squeal 'em....
This forum is owned and operated by Internet Brands, Inc., a Delaware corporation. It is not authorized or endorsed by the Ford Motor Company and is not affiliated with the Ford Motor Company or its related companies in any way. FordŽ is a registered trademark of the Ford Motor Company.