Being of a curious sort I've been looking at Rob's dyno charts and ended up calling PowerTech to get the skinny. Here is what I found out...

First off all the numbers are rear wheel numbers. The term flywheel on the torque scale of the chart is the term used by the dyno for the flywheel of the dyno, not the flywheel of the car. No correction was done to convert the numbers to motor flywheel numbers.

There are a couple of things that make Rob's dyno chart look funky. Most obvious is the scale for the torque and the scale for the hp are not the same scale like on most dyno prints. Instead the default overlay the software generates puts the peak at the top of the chart for both torque and hp. This means while being on the same piece of paper they are not aligned like most. The torque numbers are spead out vertically compared to the hp numbers and do not cross at 5252 rpm.

The not so obvious is that the correction for atmospheric conditions that make the hp SAE (all dynos perform this correction so runs made with differing barometric pressures, temperatures, and humidity can be compared) is performed on the hp numbers but not the torque numbers. The torque numbers on these charts are the uncorrected direct output of the dyno. Most dyno charts I've seen do the correction on both numbers. On the day of Robs runs the correction was 1.08. For the torque values on his graph to match those of other dynos then you would need to multiply them by 1.08. So instead of a max torque of 400, the corrected torque value is 432.

You would think the dyno manufacturers would have the same defaults for generating graphs when overlaying torque and hp. Evidentually not.

Hope this clears up some of the confusion. I say congrats to Rob and Lindsey racing for achieving what many considered impossible. Cool car.

 

Great post, maybe Rob can get some rest now from all the A$$hats that hound him everytime he puts something in a thread.

 

A-freaking-men.

And of course it seems the power has gone off at home AGAIN, so I cant post the bench racing cartoon I have on my webserver, which was in my head as I read Robs other thread.

to RKD for actually following up and calling instead of just crapping the thread.

 

this still subverts what's really at question here: the injectors.

 

"this still subverts what's really at question here: the injectors."

Actually, it proves that an injector's rating is not always at it's limit.

I found out my stock injectors, at 18psi, big turbo, exhaust, etc. are only at 79% duty cycle. I am sitting about 285rwp/310rwtq. From what has been said in here they should be maxed out.

So I am sure the same goes for his 55's.

 

I am not a fuel injector engineer or do I know anything at all about the mathematics of injector sizing, duty cycle, fuel pressure, and octane and possible related maximum hp output so I can't knowledgably make any comment on that subject except the few facts I know.

Those facts are: Rob's car has 55# injectors and the dyno run shows 548 rwhp.

In tuning my own 2.5 liter with LR super65 turbo the 55# injectors were too big. The get the car to run at the proper mixture maxing out the lean adjustment on my Mafterburner to achieve a maximum of 4.6 volts to the DME with the 55# injectors required a static fuel pressure of only 25 psi. I tried the stock 36# injectors and it required 70 psi of static fuel pressure to get enough fuel, way too much. With 48# injectors the stock 2.5 bar or 43 psi was still a little too rich. I'm still tweaking on it, but it looks like 35 to 37 psi is going to get me where I need to be with the 48# injectors.

 

that's interesting since:
1) dynapack on their website goes to great pains to explain that their product is not flywheel (ie on the dyno, not the car) based
http://www.dynapack.com/faq/3/

2) dynapacks are advertised as being able to give a printout of flywheel hp (using a scaling factor), that has always been the explanation for flywheel marking on charts that have been generated by a dynapack. and yes, i have been to a dynapack session before.

 

Which injector was it that was known to flow well beyond it's rated capacity? I recall reading in this forum about injectors rated at 55 or 52 lb/hr that flowed closer to 72's in real life. Also naturally FI cars' fuel pressure rises with boost and the lb/hr rating is at a fixed fuel pressure. If he is running a high static fuel pressure and a ton of boost, a 55 can flow as much as a 72 would at 2.5bar.

-Joel.

 

Most fuel injectors that are installed on a rise rate setup flow much more under boost than the specified flow. There run at much higher pressure under boost. 44 psi at the rail +18 psi of boost will give you 62 psi under boost. Check and see what hp output you get when you size your 52 lb injector at 62 psi pressure at the rail. It's probably close to 400 bhp. One could even run more pressure at the rail but could risk the injector freezing up. Fuel is one of the best ways of determaning hp output.

 

Sorry – you missed the concept of changing fuel pressures!

The reason why fuel pressure changes relative to boost pressure is that the tip of the injector is in a pressurized environment. To get the ‘actual’ flow rate of the injector you are interested in the relative pressure differential at the out put end of the injector. If the manifold pressure is at 10 psi and the fuel rail pressure is at 45 psi then the ‘actual’ pressure differential is only 35 psi and that will determine the flow rate.

A good example of this is if you could set your fuel pressure to 20 psi with no changing rate and ran your boost up to 21 psi no fuel would come out. In fact you would pressurize the fuel system with manifold air when the injector open signal was present.

The correct rate of fuel pressure change is a 1 to 1 relationship with manifold pressure.

Chris White

 

The whole point that I made on both of the other threads was for 4 55lb. injectors to flow enough fuel to make 550rwhp there would need to be 165psi on the fuel rail. It's highly unlikely that the pressure is that high and the injectors are actually atomizing fuel.

Now, if there were 8 55lb. injectors it's completely possible at a realistic fuel pressure of 55 psi.

Sorry but I don't see how it can happen, I needed 82lb. injectors at 70% duty cycle to make 460 rwhp running 1.4 bar.

His engine would have to be atleast twice as efficient as a normally asprirated engine and turbocharging kills any chance of that.

 

Posted by Chris: Sorry – you missed the concept of changing fuel pressures!

Many turbo charged and supercharged cars don't use rise rate fpr's and don't suffer from going lean under boost. But even if you were correct. By Rising static pressure your still adding more fuel.

 

The guy running the dyno says he had the correction factor to output motor flywheel torque and HP turned OFF.

 

Chris is correct. Which cars are you talking about? Give some examples please.

 

I dont want to turn this inot a flame war or anything but this car is not capable of 548 at the wheels with 55 lb/hr injectors.I wish it was, afterall it has some of our parts on it! The fact is that it is just not possible with that small of an injector without some crazy fuel pressure.In fact you will need a 1000-1200cc injector to make this type of power without crazy fuel pressure.The BSFC on these cars is about .60 to .65.


The equation for fuel injector sizing @ 3 bar fuel pressure is:

HP x BSFC
______________divided by

# of injectors x duty cycle

548 x .65=356
______________

.80 x 4+3.2

1125 cc injector

960cc will get you there with alot of fuel pressure.A 1000c injector is more appropriate with this type of power. A 1200 cc injector will a good safety net. So there it is.I think that the operator of the dyno must have goofed up somehwere or didnt use the appropriate correction factor.Not a big deal, sh*t happens. The easiest way to solve all the BS is too redyno it on a Dynojet, Dyno Dynamics,Mustang,etc......