Also, as has been stated earlier in this thread, you cant read too much into the chassis dyno numbers. They are really only useful in tuning, or measuring change from a baseline. The real proof will be at the track.
I saw a dyno test on one of the Sunday afternoon car shows and a modern Dodge truck and its powertrain had 18% losses to the rear wheels on the chassis dyno....so it wouldnt surprise me if a 38 year old design had even more losses at ~ 20% ........maybe one of the chassis dyno operators on here can nail that figure down .......I have also seen in british car magazines people sitting on the rear deck lids of ricers running on the chassis dyno I GUESS trying to get a touch more traction for additional numbers on the results .... o No: J
Some interesting reading on loss through the drivetrain, lifted from another forum. <TABLE class=tborder id=post705178 cellSpacing=0 cellPadding=6 width="100%" align=center border=0><TBODY><TR vAlign=top><TD class=alt1 id=td_post_705178>The whole concept of a fixed percentage drivetrain loss in evaluating chassis dyno tests is one of the most absurd things i've ever heard of in my experience as a powertrain engineer, and is the motivation behind this post. First, a primer: energy (or in the case relevant to this discussion -- power) cannot be created or destroyed. Simple enough? Where then, does that power that is transmitted from the crank, to the wheels, and ultimately to the road, go? Most of it goes to friction and therefore heat. Second, an illustration: For argument's sake, take a stock 90HP TDI, and we'll arbitrarily say that it has a 15% driveline loss. That means that the engine would be developing about 104HP (90/1.15) at the crank. The loss through the drivetrain was 14HP (104-90). Now, you do a bunch of engine mods without touching the drivetrain, and you now measure, say, 135HP at the wheels. Adding the customary 15% to refer back to the crank, you get 155HP, but the loss through the drivetrain is now 20HP, a difference of 6HP, WHEN NOTHING HAS BEEN TOUCHED THERE! Do you now see the absurdity of this concept? Firstly, may I submit that 2WD vehicles with manual transmissions have very good mechanical efficiencies, as evidenced by the fact that 2 quarts of non-pressurized, non-circulating oil is sufficient to keep the entire transmission cool and lubricated. In fact, to attach a number to it, manual transmissions are usually over 90% efficient, and many over 95%. That implies a loss through the transmission of between 5.3-11%. Even the best automatic transmissions with lock-up TCs achieve between 80-85% efficiencies. Secondly, may I submit that contrary to popular (mis)conception, flywheel weights, rim weights/diameters and tire type (should) have very little contribution to the HP numbers on a rolling road dyno. Heavy flywheels and rims act as inertial dampers but do not destroy or create energy, nor transform it to heat, as would have to happen to if it is to result in a greater or lesser HP value on the dyno. Tires will shed energy in the form of heat by the simple contact with the ground and also though the flexing of the treads and sidewalls, but this amount is negligable in the scheme of things that it is generally ignored unless you are an engineer for an OEM, race car team or tire manufacturer. More on inertia in a moment. Thirdly, I hope the above underscores that an accurate measurement of drivetrain loss cannot be overgeneralized. For one, it is not constant across the entire measurement range within a given run. In fact, friction increases roughly linearly with speed. In automotive engineering speak, this is quantified by a parameter called the FMEP (friction mean effective pressure), and although it's is not called that, it is manifested in many engine graphs you may read without even realising it. Frictional losses are different at 2000RPM to 4000 RPM, etc., etc. You cannot, therefore, equate the drivetrain loss of a car whose engine is turning at 8000RPM at the maximum rated power to one turning at 4000RPM, because on the basis of the RPM alone, frictional losses at 8000RPM are roughly double that at 4000RPM. That said, yes, it's true: gear selection when performing a rolling road dyno DOES have an impact on HP, but it is not usually borne in dyno results, because the difference is small and within the inevitable variation from test-to-test and also measurement error. Further, engine/driveline design considerations mean that there is a wide variance in frictional losses between different cars; the comparison of mechanical efficiencies between manual- and automatic transmissions have already been discussed above. Cars with AWD, automatic trannies, and large-displacement/many-cylinder engines will tend to have higher frictional losses than small-displacement, 2WD, manuals. Finally, The importance of "motored" or coast-down tests in a dyno evaluation is important and needs to be stresssed, because that is what accounts for your true frictional losses and balances the inertial "ledger sheet" of the different driveline components, including the wheels and tires. The energy that is absorbed in the form of inertia in the flywheel/wheels/tires, etc. is accounted for ("given back," to oversimplify) in this coast-down, and when doing a street (i.e. butt) dyno, also accounts for the very important aerodynamic drag. <!-- / message --></TD></TR><TR><TD class=alt2> </TD><TD class=alt1 align=right><!-- controls --></TD></TR></TBODY></TABLE>
Dan, Now N days $1000-$1500 per tenth is about normal for the 500-700hp running engines. Even more for the higher up HPs guys. Cost big :dollar: :dollar: to go fast :3gears: Hell I have close to $15-$20k just in my motor and it made 630hp on an engine dyno. Don't get to frustraded, just remember this is a hobby and its suppost to be fun and relaxing:laugh: :laugh: :laugh: Just as long as U have an understanding wife and alot of DRINKS :TU:
Hey Dan, My '87 Trans Am with Buick 455 put down 375 HP 428 TQ to the rear wheels. Gessler Heads and exhaust maifolds, Pop Mech. cam, B4B intake and TQ 850 Carb plus the usual other stuff. Nothing too fancy but a good runner. 11.50's@117 best. I did have 3.23's and 700r4 3200 lock up converter with it locked up so that helped the numbers some. 3550 lbs w/o me. I wouldn't worry about the numbers much because you'll have to rev it higher to get peak HP with that setup. With your converter you're probably losing more than I did. Where I do think you're off on is your weight estimate on the Skylark. I had a '75 Skylark Hatchback(which is heavier than the trunk type) and it weighed 3750 lbs without me with 350 Buick. Now your's might be a little lighter but there is no way it is under 3300 lbs unless you completely stripped it and then it would still be tough. The (I think) 74 and earlier models(with the steering box behind the engine cradle) may have been closer to that range but the 3rd gen that you have is way more. If you weighed it on a scale I'd try somewhere else because it is off. Just some info. Mike
I forgot to ask. Why wouldn't you rev it past 5300? You put in a cam good to 6000 rpm and with your setup you'll need to rev it higher to make optimum power. Mine peaked around 5400 rpm.
The Turbo 400 saps a higher % than a TH350 does. In my Riv with the CV joints I estimate about 22% loss.
Whammo, my target E.T is 11.5. We did alot of carb tuning. i think i got my carb tuned in prety tight. the tech mentioned that my converter dosent appear to start locking up until about 4000 rpm. even though i have a 3200 stall speed converter that was supposed to be set up specifically for my build. nolift; the dyno tech said that he didnt like to rev big blocks over 5,500 rpm. (his speciality is LS6 sbc) so he isnt used to the sound of a BB screaming at high rpm. IMHO i dont blame him, that big block makes alot of noise at that RPM, my palms were getting sweaty with nerves. although i was still gaining HP at those speeds, i probably would have gained a few more ponies.
Lets get that car out to the race track Dan. If I really get moving I might have mine ready to go within the month.
Doesn't this assume that the added power of the engine had no effect on the slippage/loss through the driveline? I'm not arguing with his overall premiss, I just think the example is flawed.
I believe the point of the example is that the loss through the drivetrain is more complex than assuming a certain percentage. A hypoid gear diff won't have more drag simply because the engine is producing more power.
