The fallacy of mods, part Duex.

[Okiespaniel]

Last week there was a spirited discussion on mods and the amount of power and torque they generate.

People glean a lot of information off the internet and U-tube. While both are good places to get a feel for what might work, both are riddled with misinformation and exaggeration.

While chassis dyno runs are give you an idea of the power your vehicle generates, they are not real world tests of the vehicle itself. There's a very important distinction between tying a vehicle down to a set of rollers versus driving one in a set distance and measuring horsepower and torque from information gained during that.
So much so that automotive engineers devised a formula to measure actual power versus dyno information.

I usually judge my truck performance based on 1/4 mile drag strip runs, taking an average of two to four passes. The BS stops when the Chrondecks start. FYI Chrondecks used to make all the timing equipment back in the day

About 3 years ago, I ran my truck. The two quickest passes that day were elapsed times or ETs in the 17.9 second range with a trap speed of 75.xx miles per hour.
The truck was relatively stock, mods being a cat back exhaust, a hemifever tune, a polished (not bored) throttle body, and a 14x3 air cleaner. with a 5 inch lift with 305 tires and 3:55 gears. The transmission has a shift kit, deep pan, and cooler. oh, and the light bar.

Using factory info and a scale, I determined curb weight of the truck was around 5500 lbs with driver and full tank of gas.

Edit: Of important note here is to add weight for larger tires and rims. Unsprung weight has a real effect on performance, as does pushing big front tires through traction juice! I ran 55 lbs in my fronts and 45 in my rears.

Using the formulas provided by this site, I determined the truck was making about 188 rwhp or 222 hp at the crankshaft. That's multiplying 188 x 1.18 (18 percent drivetrain loss)= 221.84 Truck had around 153k miles
Site: https://www.ajdesigner.com/phphorse...speed_method_increase_horsepower.php#ajscroll

Fast forward 3 years...and 7k miles.

In the last year, I added 4:10 gears with a Tru Trac differential, shorty Gibson headers, and a 53 mm throttle body. Those changes cost me about 4200.00.

I got two decent passes running 17.4xx at 77.xx mph. Using the same formulas provided above my rwhp is now 202. Crank is 238.
I gained 16 hp which increased my trap speed 2 mph. I contribute this to the headers/TB

Remembering gears are torque multipliers, that would explain the half second drop in et.

Some other notes. Watching the videos. which I can't post here, and comparing the 60ft, 300ft and 1/8 mile times and mph (1/8 mile) the truck is quicker but power is falling off at the 600 ft mark and gone by 1000 foot. The truck shifts into 3rd around 1000 ft, and while the et and mph are better it's only two mph and .5 seconds.

I titled this post The Fallacy of Mods because in the real world, adding modifications doesn't cumulatively add power. There's a sliding graph gently trending downwards as they are bolted on. There's even a point where you start to lose power without tuning.
I tell you this because Gibson used to claim 30 hp with their shorties. Throttle bodies have claimed big numbers. I have to say that Rolf hasn't done that but throttle respsonse is awesome!

Speaking of that, my tune likely needs updated. Yet, there were no real issues, other that I may have hit the rev limiter on one pass. The truck ran straight down the track and shifted fine, although I may adjust the throttle pressure cable to shift a bit quicker.

Some of you will note the lower than advertised crank hp. I believe Dodge claimed 245 net. It's the "net" where things get gray and murky. That number is determined on a series of engine dyno runs without accessories. Between the power steering and alternator you probably lose about 15 hp. At 161 K there's probably some compression loss. However the truck doesn't use oil.
Playing with formulas a bit I got one to tell me I was making 247 crank horsepower. It claimed my 4x4 was getting a 22.5% hp loss. No doubt there's a bit more loss at the drive train with a transfer case.

I welcome mature comments on this post and hope I will get a discussion on real world figures vs claims.

 

[Fast69Mopar]

I have always felt the biggest problem was how different bolt-on modifications were advertised by the manufacturers especially when they claim there are large power gains. Their claims me be true to a certain extent. Their product may make more horsepower and torque on the engine dyno or a chassis dyno but it may not make the same amount of power once it is bolted on to a different motor in a customers vehicle. Depending on where the buyer lives in the country or the world can have a huge effect on how much power a certain product makes. The ambient temp, barometric pressure, DA, humidity, etc. all effect power gains. There are too many variables to consider that come into play once that modification hits the street on a used, high mileage engine or even a fresh rebuild. Real world results can and will differ.

 

[Okiespaniel]

One common test back in the day involved the K&N FIPK and their new at the time stainless single Catback exhaust running 3 inch pipe.

The system(s) were installed on a (then new) 2001 off road ram. A chassis dyno test showed a 17 ft lb torque and 13 hp gain. The testers remarked the the truck felt a "bit better" on the street. Indeed you might notice the torque increase but 13hp? No, you wouldn't. The 13hp came in at 3000 rpm and hp dropped off quick after that, just like a stock truck.

 

[El Huapo]

I definitely like Okiespaniel's post about the gain from modifications and the COST(!). So here's a story for us folks with older trucks who want more get-up-and-go but maybe don't have a lot to spend---no offense Okiespaniel, I'm just tight with a buck:
In 2016 with about 150K miles on my truck, I found that my compression was uneven and low when doing a minor tuneup. So I felt I needed a valve job at least. I pulled the heads and found no undue wear in the cylinders, still showing some cross-hatching, couldn't catch a fingernail on the ridge (my old Dad's rule). So I stuck with just the valve job. We did find some tiny cracks between the valve seats on a couple of cylinders but my machinist assured me that they weren't in a water jacket area and were very unlikely to cause me any problems. We reground old intake valves and seats, new exhaust valves and their seats plus new seals, etc.
The seat-of-the-pants feel from my refreshed engine was great, cannot guess a horsepower figure but without a doubt it was a nice gain in performance. Going downhill the compression pull-back was the most noticeable, kinda like I was down a gear. Here in California, I won't be trying to do any major mods for horsepower gains due to smog regs, but with parts and labor at a local machine shop the valve job cost was ~$300 by me doing the R&R of the heads---I also did the grunt work in the machine shop to keep costs down. I actually felt personally embarrassed when I realized how much my old truck needed the attention and I hadn't got on it sooner. Just food for thought, hope it helps someone. Happy trails
PS: It's now at 170K and running fine.