Chassis dyno...
#1098523
10/21/11 12:33 PM
10/21/11 12:33 PM
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Joined: Oct 2003
Posts: 21,345 Marysville, O-H-I-O
70Cuda383
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Marysville, O-H-I-O
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I know that hp at the wheels is typically 20-25% lower than at the crank due to driveline losses... What about torque? Does the drive line also consume 20-25% of the torque?
I'm thinking that it would have to since the torque is a function of the RPM, but then again, 5000 rpm on the dyno chart (engine speed) is not 5000 rpm of tire speed due to gear reduction and tire sizes.
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Re: Chassis dyno...
[Re: Dunnuck Racing]
#1098525
10/21/11 02:26 PM
10/21/11 02:26 PM
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Joined: May 2004
Posts: 3,210 robin hood country
deaks
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master
Joined: May 2004
Posts: 3,210
robin hood country
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My car was chassis dynoed at 460 hp at 6300 but was still climbing, i now run the limiter at 6500. Car is 3200 race ready, i reckon my flywheel hp is somewhere close to 600, which would equate to around 25%. Best tuning tool around. Mick
69 Dart GTS 440 mopar .590 cam, Edelbrock heads, 3200# best et 6.45, 106.78, 10.14, 132.88 mph, 1.47 60ft best 60ft 1.36
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Re: Chassis dyno...
[Re: 70Cuda383]
#1098526
10/21/11 02:27 PM
10/21/11 02:27 PM
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Joined: Jan 2003
Posts: 13,356 Marion, South Carolina [><]
an8sec70cuda
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 13,356
Marion, South Carolina [><]
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I'm assuming you're about to put your car on a chassis dyno...don't put your car on it just to see what kind of power it is making. It has been discussed here many times, but the dyno is just a tool. Don't get discouraged if it only says you're making 300 hp, but don't get excited if it says you're making 700 either. Same car, same day, on 2 different dynos can yield very different results.
CHIP '70 hemicuda, 575" Hemi, 727, Dana 60 '69 road runner, 440-6, 18 spline 4 speed, Dana 60 '71 Demon, 340, low gear 904, 8.75 '73 Chrysler New Yorker, 440, 727, 8.75 '90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt '06 GMC 2500HD LBZ Duramax
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Re: Chassis dyno...
[Re: an8sec70cuda]
#1098527
10/21/11 03:31 PM
10/21/11 03:31 PM
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Joined: Oct 2003
Posts: 21,345 Marysville, O-H-I-O
70Cuda383
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yes I know about dynos and how much they can change from brand to brand, shop to shop, operator to operator, even day to day on the same dyno. shop in town was doing 3 basline pulls for $30, figured with my new 5.9L in the dakota, might as well go see what the torque curve looks like, find out where the best place to shift it ought to be, find out if I'm really running out of head flow above 5,000 rpm and the power is dropping WAY off, etc. but, since it's spitting out some rear wheel power numbers, and it seems the vast majority of folks out there talk about crank hp when talking about a certain combo, since that seems to be the "universal standard" that takes out gear ratios, autos vs sticks, etc. on power output. I know that there's no good way to take a chassis dyno and calculate flywheel power, and vice versa, since every vehicle combo will be different, and that the only way to know either number for sure, is to dyno it! that all being said, I know that Hp is a calculation of Torque vs RPM, and that at 5252 every dyno graph hp/tq curve crosses. but was just curious as to whether or not a chassis dyno uses different formula's to calculate the Hp/Tq, since there's gear reduction/torque multiplication in the rear differential and tire size diameter, and that the torque the chassis dyno is seeing is rear wheel torque, not flywheel torque...and how that correlates to flywheel torque. ok...now that the dyno pulls are done, I made 285hp and 325 torque. does that mean I'm in the 375 hp ballpark at the flywheel, and 400 ft lbs of torque ballpark at the flywheel? or is my motor making 375/325?
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Re: Chassis dyno...
[Re: 70Cuda383]
#1098528
10/21/11 03:58 PM
10/21/11 03:58 PM
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Joined: Nov 2006
Posts: 2,255 IL
furious70
top fuel
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top fuel
Joined: Nov 2006
Posts: 2,255
IL
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You would apply the correction % (whatever you decide to use) to both the TQ and HP numbers. As was said, HP is an equation derived from TQ and RPM, so HP cannot go +20% unless TQ does.
70 Sport Fury 68 Charger 69 Coronet 72 RR
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Re: Chassis dyno...
[Re: sshemi]
#1098533
10/21/11 04:55 PM
10/21/11 04:55 PM
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Joined: Nov 2006
Posts: 2,255 IL
furious70
top fuel
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top fuel
Joined: Nov 2006
Posts: 2,255
IL
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It has to do with the force required to accelerate being exponential, not linear. So yes, a stronger engine will try to spin everything quicker, and it takes exponentially more force to do that.
70 Sport Fury 68 Charger 69 Coronet 72 RR
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Re: Chassis dyno...
[Re: Cab_Burge]
#1098537
10/21/11 10:09 PM
10/21/11 10:09 PM
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Joined: Oct 2003
Posts: 21,345 Marysville, O-H-I-O
70Cuda383
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yea, I know 6,000 is child's play for the guys with serious racer engines. but with this cam, 6,000 is all she's got! I need more head, more exhaust, and probably more intake to spin more than 6,000 anyway!
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Re: Chassis dyno...
[Re: turbobitt]
#1098539
10/21/11 11:24 PM
10/21/11 11:24 PM
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Joined: Feb 2004
Posts: 4,501 Gainesville,FL
goldmember
master
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master
Joined: Feb 2004
Posts: 4,501
Gainesville,FL
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Quote:
Quote:
I know that hp at the wheels is typically 20-25% lower than at the crank due to driveline losses... What about torque? Does the drive line also consume 20-25% of the torque?
There is no possible way that there is a 20-25% loss. I would say closer to 10% and 15% on the extreame high side. I had my Turbo Buick on the rollers(dynojet) a few weeks ago and made 840 HP @ 26# boost and ran out of fuel pump. Going back tomorrow and hoping for 1000HP. At this level, If you assumed 20% then something would be melting off the car assuming the loss would be due to friction.
Allan G.
I pretty much agree with this. With a torque converter the numbers can be a mess,but a manual trans is more accurate. I use 18% loss for my best guess,your % lost may be less. We have a Dakota,with an automatic,similar cam specs,4bbl carb,junkyard 360 magnum,etc,makes 315 at the tire,runs 12.20's 107mph @3550lbs. It's dead above 5200rpm as well. I can fix it but my buddy isn't ready for that yet.
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Re: Chassis dyno...
[Re: goldmember]
#1098540
10/22/11 04:38 AM
10/22/11 04:38 AM
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Joined: Aug 2004
Posts: 2,128 sweden
sshemi
top fuel
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top fuel
Joined: Aug 2004
Posts: 2,128
sweden
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if ti took all this much power woudnt it "engine brake" with as much force? newtons law? so a 1000hp motor would brake with 250 hp?
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Re: Chassis dyno...
[Re: sshemi]
#1098541
10/23/11 03:34 AM
10/23/11 03:34 AM
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Joined: Aug 2005
Posts: 5,999 Salem
Grizzly
Moparts Proctologist
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Moparts Proctologist
Joined: Aug 2005
Posts: 5,999
Salem
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I'm no expert, but by the looks of it 5000rpm. The torque is starting to fall off and so is the hp. With your 5 speed gear spreads, the next gear shift should be keeping you in the fat part of the curve. Won't hurt to wind it out in 4th though. Love that Dakota, by the way. Nice job on the engine build too.
Mo' Farts
Moderated by "tbagger".
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Re: Chassis dyno...
[Re: Grizzly]
#1098542
10/23/11 10:03 AM
10/23/11 10:03 AM
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Joined: Dec 2005
Posts: 1,495 Shelby mi.
JAKE68
pro stock
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pro stock
Joined: Dec 2005
Posts: 1,495
Shelby mi.
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We have a chassis dyno that we use to tune, On motors that we have engine dynoed and then chassis dynoed depending on the converter have been from 21-28% loss difference. With a stick it has been 18-20% loss This is not something i live by but just reference. The chassis dyno should only be for tuning and not see what THE NUMBER IS. I dont care what the number is I tune to see if there is any more. We also determine if converter is right for the outcome.
JAKES AUTOMOTIVE
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