dpiatkin

assuming all of the normal acessories (ie: alt., a/c, pwr steering etc..... what is the approximate loss of horse power percentage wise, from these acessories..?
Would like to more acurately judge HP of these GM crate motors once they have all of the goodies and smog B.S. installed...?? :jester :jester :cheers: :hat


[Modified by dpiatkin, 9:24 AM 9/12/2001]

dpiatkin

I guess that we do not have spell check as a default anymore..?? bummer... God my spelling is bad !! sorry folks... :cry :confused: :rolleyes:

65Z01

I'm not sure of the exact percentage but we can get some idea from the '71 to '72 HP ratings change when they went from "gross" to "net" HP. Net HP was measured with air cleaners, exhaust and all accessories installed.


In '71 the CGT 350cid motor was rated at 270 HP; in '72 the CDJ 350cid motor was rated at 200 HP. This is a drop of 70 HP or 35% of the net value.

My motor was rated at 240 HP new so I might expect about 325 HP gross. Based on my mods and track data I think I gained no more than 40 HP from intake & exhaust work. That would bring the value down to 285 HP, semi-gross. That leaves ~45hp to drive the accessories.

So, as an aside, if you're adding a 22% reduction underdrive crank pulley you should expect to see about 10 HP gain. Hmm, thanks for the inspiration to do the math on this one.

dpiatkin

With the assumed 325 HP gross and an approximate 45 HP used to drive the accessories...........
that works out to 45 hp divided by the 325 hp gross works out around 14%
reduction in gross horsepower from the accessories parasitic drag...?? is my math kind of correct here...? :confused:


[Modified by dpiatkin, 2:53 PM 9/7/2001]

65Z01

That's the number I get too.

I worked the percentages from the Net HP, since that's what was known for my L98. But for your purposes 14% off the crate should be good if my assumptions here are valid.

dpiatkin

So, with a 18% loss for an automatic transmission and 14% for the accessories.... I should factor in around a 30% to 35% loss between the bolt and rear wheels for a GM or any other crate motor HP numbers.
(estimation purposes only)
Does the Torque value work out the same way ?? :confused: :jester :cheers: :jester

mackeyred96

:confused: :confused: :confused: :confused: :confused: :confused: :confused: :blueangel:

65Z01

Now you have me wondering what my car would have dynoed if I had removed the serpentine! Could my VE even now be very close to 1.00??

dpiatkin

this is of course assuming that the crate motors are rated without the accessories.... since they are not sold with any accessories... they should not be rated with any...we should be getting a gross HP rating without anything at all as far as accessories.

correct....???

65Z01

I never thought of it before but it raises a serious question when you're looking at $$/HP of those motors.

There must be some authority that can come with a difinitive answer here.

dpiatkin

Ya no kidding.... when you figure that to get 300 HP @ the rear wheels. I need to get an engine around 450 HP !! so I need alot more crate for the Bang I am looking for....
I was always assuming that the normal 18% reduction due to drive train loss... but then I thought about this..?!?!!
I always was thinking that a 450 HP crate would get me around 350 to 370 HP not 300 HP OUCH !!! :eek: :eek: :cry :confused:

65Z01

Actually, now that I'm thinking more about it, shouldn't it take nearly the same HP to drive accessories like water pump, PS, A/C, Alt, etc on any motor?? In that case the % loss on say a 450hp crate would be less than on say a 300hp motor.

Guess I'm so accustomed to hearing about "drive train loss" as a % that I wasn't thinking about the physics of the situation. So now I wonder is even this "loss" a true percentage?? Or is it again just a certain HP required to run the drive train that only depends on RPM?

If so, that crate 450 monster would indeed deliver more like 350 or more usable HP.

This is a challenging thread, it's making me think about things that I had formerly just accepted and it seems like misunderstood.

dpiatkin

a required level of horse power to drive the accessories sounds more reasonable than a "Percentage"..... why would it take 63 horsepower on a 450 HP motor and only 49 HP on a 350 HP motor to drive the same accessories...? I dont believe it would..... so I guess the 14% theory is out.
Does any body know or have a semi experienced guess at how many HP it take to drive the stock accessories including A/C etc..... :confused:

Zpeedstr

Turning on the AC unit used 10 hp at 3000 rpm during a dyno test.
Rik

dpiatkin

well that helps but it is not quite what I was looking for.... what I really would like is to better rate the HP for these crate motors once I get all of my normal accessories installed... not necessarily with everything running.
Just an average number that I can use to represent all of the accessories mounted on the block.... there must be an average loss for these accessories ??
I just want to have a closer more accurate idea on what these crate motors will actually produce when installed in the car...??
:confused:

dpiatkin

anyone got a guess ?? :jester :cheers: :jester

Red Rocket

Hot Rod magazine disconnected the Power Steering Pump on an LS1 Camaro and dropped .3 in the 1/4 mile. FWIW.