I have a stack of timeslips - lots from my old 5.0 Mustang and a few from this Grand National clone here. My best ETs and my best MPH are never on the same timeslip!
Drivetrain Loss Help
- Thread starter LS1GN
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Of course not but both came from the same gear. Maybe when aerodynamics or something else came into play it could be slightly different meaning you could get a better et from one gear and better mph from another but not likely by much. And as a starting point the mathmatical optimum gear should get you very close and then test & tune might provide a slight advantage one way or another on et or mph but its still the best starting place. Hope that helps. 🙂
A cars best ET is not necessarily its fastest MPH. It is hard to understand the complexities of it, but it is true. It has to do with gearing, tire size, and where the engine's hp/torque are optimal.
If you go on dragtimes.com you'll see thousands of runs (I'm in there with my 5.0) there is not a linear relationship between ET and MPH
If you go on dragtimes.com you'll see thousands of runs (I'm in there with my 5.0) there is not a linear relationship between ET and MPH
The question that no one seems to be able to answer is this:
When a calculator spits out a horsepower necessary for a particular trap speed, is this representing the average horsepower over the run or a one-shot peak horsepower?
The reason I need to know is if it is average horsepower, I have transmission and rear gearing issues. If it is in fact peak hp then I have engine trouble.
When a calculator spits out a horsepower necessary for a particular trap speed, is this representing the average horsepower over the run or a one-shot peak horsepower?
The reason I need to know is if it is average horsepower, I have transmission and rear gearing issues. If it is in fact peak hp then I have engine trouble.
Drivetrain loss is more than you may think, I have a 84Z28 that I dropped a pro-built 383 stroker that dynoed 486hp at the crank, I took it to a chassis dyno for some carb tuning and was shocked at outcome, 352hp rwhp, that was going thru a stage2 700r4 with a 2400 stall and 3.42 rear gears in a 7.5 10bolt and 245-50-16 tires.... that was on a in-ground dynojet machine, that equates to @ 30% loss
LS1GN Sorry I don't know.
MCSSracer Always read all things being right (they often are not) drivetrain loss should be between 18 & 22% for a 200-4R, a little more for the 700-R4, th350, and a little more for a th400.
MCSSracer Always read all things being right (they often are not) drivetrain loss should be between 18 & 22% for a 200-4R, a little more for the 700-R4, th350, and a little more for a th400.
Horsepower is a wonderfully misconceived term. Many people take it to mean a force. Horsepower is not a force, its WORK over TIME. It is also a direct derivative of torque, where Torque is a FORCE. Torque is what a dyno measures using water brake, and strain gauges, and horsepower is a theoretical calculation that is 100% accurate, derived from the torque.
This is why the online calculators are approximate.
The WORK in a 1/4 mile is moving your car from the start line through the traps. TIME is time. Its a straight calculation, and "average or peak" doesnt really apply.
When a calculator spits out a horsepower number, its talking about PEAK numbers needed to run that ET. From my explanation above, it would make sense that they derive the peak power, from an average needed power, although im not sure! I suspect this to be the case, because they are usually way off for BOP engines, which make alot of torque, and not as much HP, since their redline is less than 5252 rpm.
They usually talk about wheel horsepower, although some of them will list crank numbers (hopefully they specify). For you to have 350 AVERAGE Horsepower, from a 2000 to 6500 RPM range, your peak would need to be much much much higher. We're talking 500+hp engine. This is why a engines with more torque, and the same HP (usually big blocks), can outrun a high winding engine on the track, because the former has a higher Torque, and usually higher Average HP for the same RPM range.
See attached. This chart is courtesy of G. Bohannon (I hope I spelled that right) from a Buick Forum. I refer to this chart ALOT. Its self explanitory. But with a 107mph, you should be running a 12.40 ET with a 1.74 60ft time.
(EDIT: I cant attach PDF files, but I can e-mail it to you if you want)...
Sorry for the mud. But your question is a loaded one, because there are all sorts of derivations happening to SHOW people what they WANT to see, versus a straight calculation.
This is why the online calculators are approximate.
The WORK in a 1/4 mile is moving your car from the start line through the traps. TIME is time. Its a straight calculation, and "average or peak" doesnt really apply.
When a calculator spits out a horsepower number, its talking about PEAK numbers needed to run that ET. From my explanation above, it would make sense that they derive the peak power, from an average needed power, although im not sure! I suspect this to be the case, because they are usually way off for BOP engines, which make alot of torque, and not as much HP, since their redline is less than 5252 rpm.
They usually talk about wheel horsepower, although some of them will list crank numbers (hopefully they specify). For you to have 350 AVERAGE Horsepower, from a 2000 to 6500 RPM range, your peak would need to be much much much higher. We're talking 500+hp engine. This is why a engines with more torque, and the same HP (usually big blocks), can outrun a high winding engine on the track, because the former has a higher Torque, and usually higher Average HP for the same RPM range.
See attached. This chart is courtesy of G. Bohannon (I hope I spelled that right) from a Buick Forum. I refer to this chart ALOT. Its self explanitory. But with a 107mph, you should be running a 12.40 ET with a 1.74 60ft time.
(EDIT: I cant attach PDF files, but I can e-mail it to you if you want)...
Sorry for the mud. But your question is a loaded one, because there are all sorts of derivations happening to SHOW people what they WANT to see, versus a straight calculation.
I read the first page and almost replied with the same thing above. It is useless to go after HP numbers ESPECIALLY when talking drag racing. I'm not sure what gear you have or what trans you have or even how much your car weighs but with an auto car the HP numbers are just about as useless as if the radio is on or off while making your pass
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