Roushcharged 2006 GT

[p1tst0p]

FYI

 

[p1tst0p]

Ok,
I think better results from the DynoDynamics,

404.6hp @ Flywheel
384 ft-lb Torque
pretty much constant 11.5 A/F

Only figure thats weird again, is bhp @ wheels, this read 302.5bhp.. which would equate to roughly 25% loss...

This proves dyno differences i guess.. im comming to the US on Saturday so im going to buy the Smaller Supercharger pulley, fit that and get a custom tune when i return home!

 

[LV51FER]

Hi Will,

Don't get too bogged down in numbers. Dynos vary a lot and I've seen results that are just as weird the other way. Factors like engine cooling and intake temperature make a huge difference on a blower so I'd stop chasing bench racing numbers and just get out on the drag strip. Your times will tell you what power it has.

I've never put mine on a dyno and don't intend to either. It's just a lot of money for a number that's often calculated. At the drag strip, there's no bluffing, just a time slip. It's the only one that counts.

There again, since the drag strip is too far away from me to bother and my car seems a lot faster than all the other traffic on the road, I don't do that either although I did with my old Z28. Now that ran a 13.8 at 105 just rolling off the line and clearly the blown Mustang is a whole lot faster so you have to decide whether you're going to be forever risking breaking it for the sake of a figure or just enjoy driving it.

 

[kooldawg6]

The flywheel and torque are very nice #s. Like LV51FER says don't sweat the #s, if it feels fast then it probably is
If you do make it to the track, don't concentrate too much on your ET as tire spin and other factors can greatly affect it. Look more at your trap speed as it will be a far more consistant #. Have fun and be safe

 

[300bhp/ton]

Ok,
I think better results from the DynoDynamics,

404.6hp @ Flywheel
384 ft-lb Torque
pretty much constant 11.5 A/F

Only figure thats weird again, is bhp @ wheels, this read 302.5bhp.. which would equate to roughly 25% loss...

This proves dyno differences i guess.. im comming to the US on Saturday so im going to buy the Smaller Supercharger pulley, fit that and get a custom tune when i return home!

Hi there mate,

I'm also in the UK. Judging by the pic you posted it looks like the front of Atlantic Sports Cars in Luton?

As for the dyno issue there are IMO several possibilities that exist:

1. Incorrect (or expected) dyno readings
2. Something wrong with the Stang
3. A combo of the above.

1. Addressing the first point.

Chassis dyno numbers are in many ways a false and inaccurate way to measure engine HP. This is not due to the dyno's themselves but the preconceptions and lack of info that is associated with them.

First off, there are many different types (makes) of dyno. These all work slightly different and will derive HP differently.

In the US Dynojet dyno's are the most popular, but by contrast are also one of the most inaccurate and optimistic dyno's out there. Hence nearly EVERY US muscle car is always though of as being "under-rated" from the factory when people use the 15% rule to work out engine bhp.

This is down to how a Dynojet works. First off it’s worth noting that car engines are not rated in HP (although, they are often incorrectly advertised as such). ALL car engines are rated in BHP.

"B" stands for brake. And this is how HP is derived on a 'Brake device', more commonly known as a dyno. Ships and railway trains are also rated in HP but it is derived or calulated differently, often iHP or dHP is used. These are totally different to BHP.

A good analagy is a US$ and Aus$. Both are dollars but represent totally different currencies.

Back to the dyno. A Dynojet generally uses a static brake device (a big weight on the rollers) to load the engine. This results in rather high BHP figures being produced compared to what the engine is really making. So be wary of comparing such numbers with other dyno derived figures.

Another common dyno in the US is the Mustang Dyno. This uses a varying load brake device to load the engine, usually electronic but could be hydraulic. This means that the faster the motor spins and the more torque it makes the more load it can apply to the engine. This is much better for tuning and will often return a truer BHP figure but it will be LOWER than that of a Dynojet.

I am not familiar with the dyno you used first but this is something to consider. Dynodyamics dynos tend to show lower figures than Dynojets also.

There is another aspect and that is Standards and Correction factors. Standards are things like SAE Net and DIN. These layout standards such as intake air temp, altitude correction, ambient temp, accessories attached to the system.

Correction factors use calculations to correct to a standard normally. If the dyno gives figures in STD this means that is what it produced there and then. So a cold day will produce more HP (higher density charge) and a hot day less HP in STD corrected form.

If it was corrected to SAE or DIN then this is the HP it would make at 'x' temp and 'y' humidity and 'z' altitude. This figure should be reproducible anywhere in the country on the same dyno no matter the conditions.

On a 400rwhp Trans Am test proved that a variance between STD and SAE could be as much as 25rwhp.

There are other aspects such as graph smoothing as well. All up all the variables could conceivable produce up to a 40rwhp+- variance between dyno’s on a car such as yours.

Also remember that how the dyno was setup could have a bearing on the numbers too. A supercharged Stang needs good cooling and airflow to be provided by the dyno room. One or two smallish fans near the car are no good at all.

Also supercharged Stangs will suffer heat soak from the engine into the air intake manifold and blower. If you’d just done a decent motorway journey or left it ticking over for a bit the air intake charge will be hotter and less dense. Meaning lower bhp.

One last thing to add about dyno’s. Is that NONE of them can accurately convert wheel derived bhp (rwhp) to flywheel derived bhp (engine HP as some claim).

Yes there is the 15% rule, but this is only a guesstimate and often wrong. There’s also the 12% + 10bhp rule, but this too is not accurate. This is down to many reasons.

Some dyno’s will try and measure the drag of the transmission and then use that as a basis to derive flywheel bhp. But this is also flawed. Mostly to Newton’s Laws pf physics which state that every action has an equal and opposite reaction.

So drive line HP loss is more than that required to rotate the drive train, the more HP you make the more you loose.

But that aside, remember if your rwhp number is wrong to begin with, you will never get an accurate estimated flywheel bhp number.


2.

The second point – something up with the Stang.

This is possible. There could me a major issue with it, but in all honesty I’d doubt this. I can see a few potential areas where there could be issues however.

First of check for any boost leaks. This is not that likely with an engine mounted twin screw/roots type blower but can happen. You’ll really need a boost gage to check and see what its boosting too.

Second the tune might be off a bit if it’s a out of the box tune. US 91 octane is somewhat similar octane rating to UK 95 RON petrol. So make sure the tune you have is not for US 93 octane as this will be no good unless you are running a good super unleaded (99 RON).

If the tune is out the Stang ECU might be pulling the timing to prevent pinking. This will hinder HP and performance.

To further this, adding an exhaust shouldn’t loose you any power. Not directly anyhow.

Essentially a good exhaust will reduce exhaust back pressure, which is a good thing. Although a catback will have limited affect. Reducing back pressure means that the pressure in the engine is less and this will reduce the psi being seen from the blower.

Now this actually means MORE HP not less. This is because the blower is still flowing the same cfm (amount or volume of air). But at a lower pressure (psi). Remember psi is a measure of resistance not of volume of air. Think of a bike tyre, you can have 40psi of pressure but the volume of air would be a lot less than a Land Rover tyre also at 40psi.

Reducing exhaust back pressure means you can run the same HP with less psi, or more HP with the same psi as before.


Sorry for so long, but I hope this has helped a bit

 

[LV51FER]

Well you could have provided a bit more detail to be honest......

I think one of the above posters could also be right. 415bhp less Gordon Brown's 10% import duty (41bhp making 374bhp) plus 17.5% tax deduction on power output (65bhp) makes a grand total of 309bhp. So I blame Gordon Brown.