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hp losses to running gear?
has anyone figured out how many ponies theyre losing to thier standard trans and rearend combo? does the jag rearend use more or less? and the ford toploader more than the tremec 5 speed? we all know the alt. and water pump #'s can vary depending on amps and volume. but out of curiosity. any thoughts?
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Numbers/rlosses may be dependent on dyno's used, so it may be hard to compare different cars tested on different dyno's.
An IRS will use more HP than a solid rear axle. You usually chassis dyno a car in a 1:1 gear, the gear to have the least hp loss, so that would be 4th gear on a toploader, and 4th gear in a tremec. Loss, I guess, would be about the same, maybe giving the advantage to the tremec since it runs a thinner tranny fluid. |
i guess the best way to tell is mph in the 1/4,i wish desktop dyno had this factor in it, it's been hard to get an accurate # like flywheel hp x .8 is considered by some to be a fair est. but i have seen 454 cobra replica's that dyno out more consistent with a flhp x .9 there aint much between the engine and the wheels in a cobra.i just wondered if any one had figured out what they were losing to trans and rearend. thanx anthony
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If you check the numbers posted by my name you'll see I experienced about a 16% variance between flywheel HP and rear wheel HP. There are a lot of variances that can make those numbers fluctuate but it might be a good starting point.
:3DSMILE::3DSMILE::3DSMILE::3DSMILE: |
15 to 18% is a common reference window. Jim's at 16%, I'm at 17%.
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great #s jim!!!! i assume these #s would be with open headers no alt or waterpump,and the usual 6inch velocity stack. that would be about right by my thinking i used a 32 amp alt. in hopes i'd save a pony or so, i know, whats a hp here or there with such a big motor. but i'm after every single hp i can get. i hate the thought of paying grands for all this gear and letting 1 slip away. lol maybe i'm just nuts!
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i guess some synthetic lubricants for the rear end and trans could help? anyone using these?
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The flywheel numbers were on an engine dyno at the builders shop, Keith Craft.
http://www.clubcobra.com/photopost/d...enesis_005.jpg The rear wheel numbers are with the car set up as I drive it on the street, i.e., alternator, water pump, headers and side pipes, etc. I wouldn't get too anal about one or two HP as I don't think you detect the difference.:eek: :3DSMILE::3DSMILE::3DSMILE: |
Several years ago a group of us got together for a chassis dyno day using a Dastek Eddy current chassis dyno. Two of us had SPF cars with similar motor builds. My car with a 418W pulled 478 HP at the wheels. The other car 468 HP at the wheels. His motor had a known flywheel HP of 550. Using a modest 15% gear and other parasitic losses on my pull would give you around 564 HP at the flywheel. I think a 20% loss with a an SPF car using an IRS rear axel, stock sidepipes etc. is a little too much as this would give a 590HP at the flywheel for my car, As mentioned earlier 15-17% loss seems reasonable.
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what an engine jim!!! and it sounds like you all are making appropriate hp to preserve the "cobra fearing" tradition out there on our streets and hiways!!! this sounds pretty agreeable to me. awsome feedback guys!! thanx
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Keith Craft told me that a 20% loss was average for Cobras. He had dyno'ed motors and then installed them it Cobras. Then dyno'ed the car.
I think because of the way they are made, sidepipes are the largest contributories to horsepower loss. Some have an 1 7/8" core with a lot of packing. Other have 3" core and little to no packing. Dwight |
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sounds like a mean powerplant,i'd like to hear what you get .ya, i've heard cobras lose a fair bit of steam to the sidepipes, i redid my heads(more porting big valves double springs and all that.gave her a windage tray and had some 5 inch od mufflers made up 3 inch id !! and its freakin loud. need some jet work to get it right. ive got a gtek module in the car but it looks like snow here any day now, so i don't know when i will get a chance to play. the last few shakedown run felt amazing but we'll see
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hey jim, 9.84@ 135? sound close give or take a couple of tenths
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The higher the rpm and the more your intake/heads/cam will flow the more h.p. you will loose through the sidepipes. My ERA 427 side oiler, 428 crank with solid roller cam, dual carbs, high rise heads, 12.5 to 1 compression lost 97 horse power with the sidepipes in place! I've run the car with and without the sidepipes and you can really "feel" the difference with open headers (but you need two sets of ear plugs, man that thing is loud)! :)
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97 hp that's criminal, what are you doing to handle detonation 12.5: 1 with open pipes. i bet it's loud but what a sound!!!!!!
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Simple solution, I rebuilt the motor with less compression, less cam, smaller carbs, cost a ton. 12.5 to 1 was a nightmare, that with IRON heads mind you!! :)
Yeah, it did sound great with the high compression, really really nasty. It's toned down considerably with the lower C.R. |
As others have already pointed out, on average, you can expect a 18-22% loss between flywheel HP ratings and HP ratings at the rear wheels. You can get those numbers down below 15% if you are willing to do a lot of extra work to your driveline. Headers/exhaust/tune......Everything from the types of fluids in your motor, transmission, and rear end to which bearings you have, how tight the tolerances are in your transmission/rear end just to name a few. I've watched some of the circle track guys spend days on chassis dyno's to wring out that extra 5-12hp as an advantage over their competition......
Bill S.; |
i bet!! what do you run for jets from mufflers to open headers?... 97 hp to mufflers?!? sheesh!! but thats what i mean i cant live with too much of these losses. not when i'm payin $$ for shiney parts that go in to the motor and i never see them unless sonething goes wrong! haha ..knock on wood
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now we're talkin, what lubricants are best for the toploader (synchro friendly) and the rear end w/posi?.... hp reclaimation therapy 101
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