Well, it's not the fuel pump.

OK, maybe not the fuel pump. I also have an underdrive pulley. I'm just thinking that my numbers aren't really any better than Matt's considering the additional mods.

I assume Mike has the Weather station module or whatever for his dyno, or that could be it as well. It was damn near freezing when we ran my car.

I am just trying to understand the numbers if possible. Maybe we will never know, but thought it might be worth discussion. :P

I think a street race is in order.

Dyno numbers are good for comparing before and after mods on the same car when all other factors are constant. Comparing between cars, because of many different factors, is asinine and pointless.

IBI'llstreeraceyoutodeath.

That's how I solve all my issues :lol:


Dean, like Scott said I do have the same Fuel pump, so it's not that, nor can we blame it on the color. Also, I am catless with Gruppe-s headers.

It was very cool when we ran my car....like 55 degrees, and I also had my 18"x 8" Rotas with meaty Falkens on. :cool: That could be a big part of it.

That was my point, not that the fuel pump doesn't make a difference. I actually thing the fuel pump is a great idea, as it makes the car safer if nothing else. Cheap insurance against running lean.

And I agree with Aaron, we can't really compare, but that doesn't stop us from doing so. ;)

And I was just wondering if any of my other mods might be contributers to my numbers? I've always heard that rotating mass affects real world HP and torque numbers. (flywheel, clutch, underdrive, wheels/tires)

Colder plugs are supposed reduce detonation(?) and thus allow more power to be made???

Mike said something about the fuel pump increased pressure allowed for lower injector duty cycles...

I was just throwing those things around as possible discussion points as to whether they or the weather might impact dyno numbers.

All our cars Rock.

I devoured many Audis, Porsches, a Lotus and a race car or two at Thunderhill, and am still hungry. I want my DMSes back from Oh-Canada... :)

Exactly. "Stage 2" and up can benefit from one step colder, especially before tuning, as I understand it.

Dean...

Your tire: 235/40/17 = 24.4" diameter or 225/45/17 = 25.0" diameter

Matt's tire: 245/40/18 = 25.7" diameter

Matt's car probably makes more hp and torque than yours based on the tire gearing difference alone, nevermind the loss from turning 28lb 18" wheels.

Yes, Dean, rotating mass and tire gearing both make a difference in at-the-wheels power. The pulley is practical negligible, the flywheel makes a difference, the wheels really help, and the tire size gets you another 5% or so torque to the ground compared to Matt.

Oh, and "colder" plugs really are physically colder under hard conditions. They absorb less heat from the combustion cycle, which makes them less hot when that cylinder is on the intake or compression stroke, and they cause less pre-ignition. The downside is they foul more when you aren't getting high EGTs. Tuners pretty much universally think that's a good tradeoff, as long as you aren't fouling them so bad you get misfires when you do go WOT again.

225/45-17s actually. Stockers with street tires were on. So no gearing advantage to speak of.

nos.

You still had shorter, lighter wheels/tires than Matt, just not as much as 235/40s would be.

If the effective gearing changes that are due to the tire diameter changes the horsepower that a dyno reads, then the dyno is not very good at reading horsepower. Actually dynos do not measure horsepower anyway - hp is just a calculated number based on torque and rpm. The dyno reads torque and rpm and then calculates hp from those two inputs. There should be a place to enter the tire diameter in the dyno's computer so that the difference in effective gearing does not change the hp, because changes in gearing just do not change horsepower (except in more extreme cases where the frictional losses change).

Also as far as rotating mass is concerned, if the car accelerates slow enough while it's on the dyno, the mass becomes a negligible factor. The faster the car accelerates on the dyno the more the mass will make a difference in the WHP. If a load-based dyno holds the car at a certain RPM and reads torque then the mass makes no difference.

Because of these and other factors, such as run-to-run variability in dynos and automobiles in general, it is silly to speculate about small differences in two diffent cars' HP as measured on a dyno. The dyno is a tool for tuning and should be used with extreme caution during bench racing.

I doubt Mike said this, because it's not true. The pressure regulator on the fuel rail determines pressure at the injectors, not the fuel pump. The only way a fuel pump becomes a factor is when it runs out of flow capacity, then the rail pressure will drop, and then bad things start to happen.

Speaking of Fuel rails. When depending on mods should they be installed on a wrx?

I've never seen a tuner that calculates and enters tire diameter on a dyno per run. I'm willing to bet Matt and Dean were dyno'd with the same settings.

Furthermore, dyno's are easily +/-5hp from run to run, let alone from car to car on different days. i.e. It's ridiculous for Dean to be trying to figure out why he made more hp than Matt. My post regarding the tire sizes was an attempt to demonstrate that Dean's speculating on things that probably make no repeatably observable difference, while he's ignoring things that are known to have more of an effect on numbers.

In reality, I would say anything +/-20hp on a dyno is pretty much similar enough to write off as "the same". On the track the faster car between Matt and Dean will be based on the driver, not the dyno'd hp. Trying to figure out vf39 vs. vf43 based on the data in this thread is a waste of time. According to the data and the margin of error involved, the turbos are equivalent. Same goes with all the rest of the differences between Dean and Matt's cars.

When/if you hit 450awhp, then you might need fuel rails. The factory design is pretty damn good on our cars. Don't buy the stuff you might hear/read about certain cylinders going lean due to the fuel rails. There are plenty of people maxing out 800+cc fuel injectors on the stock rails.

I think you and I are agreeing here, but I came at it in a different way.

With statistical analysis you could detect small changes or differences, but the sampling size would be large - maybe like dyno'ing both cars 10 or 20 times.

The best practical measure of "real-world" horsepower at the wheels is to run the car on the dragstrip several times and watch the trap speed (not the ET). Trap speed is a good indicator of HP because the gearing, tires, and a relatively competent driver have little to do with it, but power does. Here again though, it takes a sample size of maybe 10-20 runs to see small changes.

So what I am hearing is that I need more stickers to have more HP than Matt. :rolleyes:

Exactly^ NOW POST THAT FOOTAGE OF THUNDERHILL!!!!!!!!!!!!

Just out of curiosity.... Did Mike measure the RPM at the engine or did he just use wheel speed? If wheel speed is used to determine engine RPM was it modified for each car or just left at some generic multiplier/ratio?

You can't leave it measured off of the roller speed for different cars, that would not work and would give some funny readings.

All cars are setup on the dyno, rolled, restrapped, rolled again than set at 3k in the gear being used to dyno in.

We do not use any weather correction, tried it once found the results to variable to uninstalled the contraption and threw it away. Our Mustang is configured off of one setting so cold weather will come into play as will hot weather (like real world, cars with cooler air make more power).

I hope this helps somewhat, personally I think the headers, uppipe and turbo are the differences.

Mike

So who has the biggest hp car on here...???? I bet i have yo beat as of this last monday....