Anybody here got Quarter Jr or another drag sim program in their computer?

 

Wish I had Quarter Jr or even Crew Chief Pro just to try them out. I have Dyno/Drag 2000 and only use it to play "what if". It has never spit out the same results as any runs I've made.

 

I simulated an engine on my son's Desktop Dyno program and wondered how it would do. Jeff Smith of Hot Rod magazine usually runs a simulation of engines he builds for the magazine on Quarter Jr. "What if" was all I was looking for. The engine I simulated was similar to the one we are building. It was rather generic, I didn't have my cam card with me so I only picked from the menu what I thought would be like the intake, heads and cam we have.

 

Garbage in/garbage out. All the dyno simulation programs will give you the results based on the data you give them. Since I don't have accurate flow data for my heads, the software can't give an accurate dyno run. Accurate cam data is also required. You can have 2 different cams with the identical lift and duration. If the cam timing (when the valves open and close) is different, the cams will perform much differently.

All the dyno simulation programs will also give the best possible results which you'll probably never achieve unless on a real dyno. They can't guess at changes because of timing, jetting, plug gap, crankcase vacuum, etc. There are so many factors that can affect the engine's power that you can only really see the results while on a real dyno.

Like I said, the simulation programs are good for playing what if. They're not a substitute for a real dyno. Don't be disappointed if real dyno results are far less than what a simulation program says you have.

On the other end of the scale, I use a track dyno. I know the race weight of my car. I run the 1/4 mile at xxx MPH. It's a simple formula to calculate HP by moving a specific amount of weight a specific distance to a specific speed. You could also use ET but it's too dependent on traction to give an accurate result. Track dyno results will always be different because how much power an engine makes will always be affected by weather.

 

Thanks for all that, Stephen. But if the engine data is off, and the predictions for E.T. are off and you know that going in, you still get a ball park idea, right? If it says 665 hp @ 7500 and 557 ft/lbs @ 5000 and you know that's high, but you feed the numbers into Quarter Jr. and it says 9.50/157 mph in a 3200 lb car then would it be wrong to think that 10.0-9.75@ 140 mph would be more likely?

 

Dyno/Drag2000 says I should be running 9.0 even while racing at altitude. Based on my best timeslip, I try to fudge different numbers around in Drag 2000 and if I can get the ET/MPH close to the same, the numbers for the rest of the run don't add up.

I've got an old DOS program called Dragstrip Plus (go a google search) that is probably more accurate than what I've seen DD2000 do.