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how much HP loss from crank to rear axle

 
Old 06-02-2019, 06:30 PM
  #21  
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Originally Posted by bjankuski View Post
What are you running for exhaust, and air intake?
Hooker Super Comp Side Pipe Headers with high flow Hooker Muff inserts, factory tri-power (crank HP was with factory air cleaner installed, chassis Dyno had Air Cleaner removed and I went down one jet size on the outboard carbs as it was pretty rich during crank Dyno pull).
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Old 06-02-2019, 06:47 PM
  #22  
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I wouldn't get too hung up on Dyno numbers, I mean it's fun to know where you end up on a build but the correlation between Crank results and Chassis results will be an approximation at best. A simple example is tire air pressure differences from one day to the next and how much the operator cranks down on them affects the numbers.

I believe Chassis Dyno's have a lot more math involved to come up with the numbers, but they are a great tuning tool.
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Old 06-03-2019, 07:37 AM
  #23  
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Originally Posted by jim2527 View Post
As mentioned by jb I think our cars have a much higher drive train loss % than is typical. I remember from my C5 days that a GM power train engineer said the C5 was 13% for the M6 and 16% for the A4. If a C5 manual is 13% you can bet our cars are easily into the 20%+ range. Dig around on the 'net and you'll estimates up to 30%.
Guys, I don't know where this 10-15% lose comes from going from Gross to RWHP with our cars. It is no where near those numbers with these cars and their engines and drivetrains and I provided sufficient documentation earlier supporting the rationale. Gross HP has not been used for 45+years by engine manufacturers because it is totally misleading to the actual installed engine HP in car and thus, represents a HP number that can never be achieved in the car. A 10-15% Gross HP loss to Net HP makes perfect since Gross HP represents the power the engine makes with open exhaust, no AC, no power steering no alternator, no any thing. Add all that stuff and accessories back on a free standing engine and a COMPLETE closed exhaust, these engines will make 15% less NET HP.

Take another 10-15% off for the drivetrain frictional loses with a 4 speed and even more with an auto, and you get to at least 25% lose from Gross HP to RWHP...30% with an automatic. Those are the value and numbers but these are the facts!

A crate 383 450 Gross HP rated engine is no where near a real world 450 HP, not even close. The RWHP for this 383 engine numbers mentioned earlier by some are spot on...figure 300-320 RWHP, at best, on a great day with a tailwind at your back.

The other dirty little secret in our world, which makes everyone spitting mad, is because of the above math, a stout built 355 with top parts combination, can easily out power most CRATE 383's. The difference between IDENTICALLY built 355 versus 383's is about 15-18 RWHP/RWTQ....that's it folks! Sorry.

My 10C6Z06 with a modern LS7 and modern 6 speed tranny/drivetrain loses 10% HP on the dyno going from NET to RWHP....that is on a modern car!

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Old 06-03-2019, 09:07 AM
  #24  
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Originally Posted by gmcman52 View Post
Thanks for all the feed back , I was just thinking out load. I'm comparing my 2007 Trailblazer AWD that has 395 HP on the same dyno and it pulls 334 HP .
As for test driving before and after I think that the 355 was a little bit faster in and out of traffic. I'm going to call BluePrint and see what info they can provide then a call to Holley.

when on the dyno we adjusted the timing to 34 degrees total and the air/fuel ratio was at 11 and was change to 12.
Thanks to all that replied

Here's the some spec as stated by BluePrint .
heads- 64cc,2.02 intake/1.60 exhaust valves & 195cc intake/75 cc exhaust runners
Cam- roller .528 intake/.536 exhust,221 intake/226 exhaust duration @.050-110 degree lobe

auto trans 3.70 rear gear
are those Blue point vortec heads or something else?

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Old 06-03-2019, 01:14 PM
  #25  
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Originally Posted by jb78L-82 View Post
RWHP/RWTQ....that's it folks! Sorry.

My 10C6Z06 with a modern LS7 and modern 6 speed tranny/drivetrain loses 10% HP on the dyno going from NET to RWHP....that is on a modern car!
Exactly. So many variables the first being if the manufacturer accurately states the NET hp/tq. Case in point is the new Supra. Car and Driver ran one on the Livernois dyno, its rear wheel numbers where almost the same as the published NET number. Toyota is clearly understating the cars HP/TQ. It sure as heck doesn't have a 0% loss.

All said and done I think 300rwhp is nice target for a C3. My heavy Lexus with 305hp net hustles pretty good.
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Old 06-03-2019, 02:01 PM
  #26  
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Originally Posted by jim2527 View Post
Exactly. So many variables the first being if the manufacturer accurately states the NET hp/tq. Case in point is the new Supra. Car and Driver ran one on the Livernois dyno, its rear wheel numbers where almost the same as the published NET number. Toyota is clearly understating the cars HP/TQ. It sure as heck doesn't have a 0% loss.

All said and done I think 300rwhp is nice target for a C3. My heavy Lexus with 305hp net hustles pretty good.
Appreciate the confirmation!

BTW-my 2012 Lexus IS 350 F Sport weighing at 3,500 Lbs hustles really well to 60 mph (5.2 sec ) with its 306 Net HP 3.5L double overhead cam V6.........
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Old 06-03-2019, 08:24 PM
  #27  
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Originally Posted by jb78L-82 View Post
I figure my L-82 355 with AFR heads, Roller cam and 10.2 compression at 425+ Gross HP (RWHP 325 roughly) and that number is no way even close to the 450 RWHP LS7 HP from my Z06 ...not even close performance and you can see why when you look at the numbers and the losses. above^^^^^^^^^^^

BTW-A properly built 355 with top flowing heads (AFR/Dart etc) aggressively moderate roller cam with 10+ compression can easily match a crate 383's Gross HP numbers(410-430 Gross HP)....A max built 383 525+ Gross HP 383 is a different story.

So, do you have any actual dyno numbers for your l82 355?
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Old 06-04-2019, 06:35 AM
  #28  
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Originally Posted by 455230 View Post
So, do you have any actual dyno numbers for your l82 355?
Not for the 355 only when it was a stock engined L-82 with no emissions equipment, shorty headers with 2.5 inch duals on a dyno jet.

Numbers needed are gross engine on stand, net engine on a stand, and RWHP on a dyno in a car. My builder with a mustang dyno in his shop, confirms the percents and he has built and tested hundreds of engines, old and new. You can comb the literature like I have to confirm the percentages as well...there is no mystery here anymore....

There are literally dozens of engines with gross dyno sheets for that engine and then RWHP as installed in the these cars. The percent from Gross to RWHP is generally 22-25% with a 4 speed manual and up to 30% with certain automatics.

Again, a modern C6Z06 with modern drivetrain and modern LS7 427 looses 10% HP going from NET to RWHP, (NOT GROSS, no less). I can provide documentation for this if needed from my builder who does dyno runs all the time......

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Old 06-04-2019, 01:59 PM
  #29  
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Originally Posted by gmcman52 View Post
I'm not happy after my last Dyno. How much HP is losed from crank to the rear. I was thinking 15 -20%. I have a 75 that had a L48 / 355 mild cam alum intake and Holley
650 carb and headers with a 3:70 rear gear that posted 202HP at the rear. Currently It has a Blue{print 383 with 435 HP I changed the intake and replaced the carb to a 770 Holley. So I was thinking that I would lose about 20% (86 HP) and would have about 345-350 at the rear. Last week Dyno topped off at 286 WTF? I thought the carb might be too much and replaced the prim jets 2 sizes. it was over 6 grand to replace for only 84 more HP. I think I should have keeped the 355 put alum heads and bigger cam and maybe a bottle and what would have been about the same gains in HP. I don't know

285-300 rwhp on a dynojet sounds about right.
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Old 06-04-2019, 02:11 PM
  #30  
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Originally Posted by jb78L-82 View Post
Not for the 355 only when it was a stock engined L-82 with no emissions equipment, shorty headers with 2.5 inch duals on a dyno jet

There are literally dozens of engines with gross dyno sheets for that engine and then RWHP as installed in the these cars. The percent from Gross to RWHP is generally 22-25% with a 4 speed manual and up to 30% with certain automatics.

Again, a modern C6Z06 with modern drivetrain and modern LS7 427 looses 10% HP going from NET to RWHP, (NOT GROSS, no less). I can provide documentation for this if needed from my builder who does dyno runs all the time......

Iím not disputing your loss numbers.....Iíve seen
other dyno jet numbers for old school type engines and drivelines
and the numbers are low compared to modern set ups.
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Old 06-04-2019, 02:55 PM
  #31  
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There are a lot of things that can influence dyno numbers. The dynos themselves vary a great deal from one to another. I once tested this by bringing the same vehicle to multiple dynos after tuning and testing it on our dyno. To make a long story short, there was about a 20% difference in the numbers between the highest and the lowest dyno readouts. Our was in the middle of this spread.

Going from open headers and usually cooler running conditions of an engine dyno to warmer under the hood and a full exhaust will show loss, depending on the exhaust. Rear end gear ratio and the gear the vehicle is run in makes a huge difference. The type of transmission and the weight of the flywheel on a manual or the stall of a convertor make a difference too. Large sticky tires will cost you some horsepower on a chassis dyno. Low tire pressure will cost you too.

My Vette would be a good example of a car that would not test well on an inertia chassis dyno. I have a 700R4 with a 3800 stall convertor, 4.11 gears (taller gears test better), and big sticky tires.

Bottom line is; dynos are a testing and tuning tool and should be used as such as the variables are so vast that comparison from one vehicle and dyno cannot be compared to another vehicle and dyno. If you stick to one dyno, one operator, and make sure you test the same every time, it is an invaluable tool to see your progress.

Mike

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Old 06-04-2019, 09:07 PM
  #32  
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The formula for calculating the HP loss from the crankshaft to the rear wheels is:

HP Loss= Ax^2+Bx+C

Where A is the multiplier for exponential losses, B is the multiplier for linear losses, C represents constant losses, and x is the Net Crankshaft HP as measured by SAE J1349 that of course varies with the engine or any mods performed.

For HP to be a percentage, A and C would have to equal zero which is nowhere close to being correct. In fact, most driveline losses are a constant which means the C term is the dominant factor. If it takes 20 HP at 6000 RPM to drive the hydraulic pump in a Turbo 400, you could double the HP of the engine and that pump will still take 20 HP at 6000 RPM to drive...the pump HP Loss is a constant.

An example of linear losses would be gears. A well designed/machined helical gearset with an involute gear tooth has 1-2% loss which would contribute 0.01 to 0.02 to the B term. However, if you perform a chassis dyno test with an automatic or manual in the 1:1 ratio gear, thereís no relative motion between any gears because the input shaft and output shafts are locked together. The hypoid gears in the rear end arenít that efficient and will contribute about 0.04-0.05% to the B term. But if you add 100 HP to the engine, the HP loss increases just 5 HP.

An example of exponential losses is inertia like the wheel/tire and any other rotating driveline component. On a chassis dyno that controls the rate of RPM increase, the amount of HP going to inertia is small and any increase in HP from one run to another results in zero increase in HP going to inertia.

The HP Loss isnít a percentage and it isnít a constant, but youíll be a lot closer using a constant for a particular driveline assuming all is well with it including tire pressure as pointed out above. The only way to know is to remove the engine, dyno it, reinstall, then chassis dyno it. Anything else is pure guesswork which is why you see all sorts of numbers above.

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Old 06-05-2019, 05:53 AM
  #33  
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I am not saying (or others) that the percentage is a fixed number for any engine, transmission, or drivetrain???? It is a RANGE!

Calculating a range of HP lose for Gross to Net to RWHP is NOT a guess....it is a range based on thousands of examples of dyno testing various engines and configurations with these and any motor over hundreds of thousands of engine examples over the last 50 years through today. One can guesstimate fairly accurately the number of any one of Gross, Net, RWHP if you have some specific parameters as has been mentioned previously. Gross to Net HP is generally 10-15% depending on various factors with 10% being a modern engine and drivetrain. Net HP to RWHP generally is also 10-15%. Overall for our engines and cars, Gross HP to RWHP is a reduction of 22-30%, call it an average 25%......Not a shot in the dark, hardly!

This line of thinking is often communicated about building an engine with certain parts such as Cylinder heads, compression, and camshaft specs. One can very accurately predict the target Hp/TQ based on examples of the same engine using said parts within a range....not perfect but very close. Of course, you cannot say exactly what the HP would be, but one can, confidently, reasonable predict the outcome. It is this same reasoning and technique that is used by every major manufacturer when they publish HP numbers for their installed engines after being tested..they do not test every engine....Blueprint engines knows that a 383 with said parts will produce X HP/TQ...no guessing.

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Old 06-05-2019, 01:16 PM
  #34  
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Originally Posted by jb78L-82 View Post
I am not saying (or others) that the percentage is a fixed number for any engine, transmission, or drivetrain???? It is a RANGE!

Calculating a range of HP lose for Gross to Net to RWHP is NOT a guess....it is a range based on thousands of examples of dyno testing various engines and configurations with these and any motor over hundreds of thousands of engine examples over the last 50 years through today. One can guesstimate fairly accurately the number of any one of Gross, Net, RWHP if you have some specific parameters as has been mentioned previously. Gross to Net HP is generally 10-15% depending on various factors with 10% being a modern engine and drivetrain. Net HP to RWHP generally is also 10-15%. Overall for our engines and cars, Gross HP to RWHP is a reduction of 22-30%, call it an average 25%......Not a shot in the dark, hardly!

This line of thinking is often communicated about building an engine with certain parts such as Cylinder heads, compression, and camshaft specs. One can very accurately predict the target Hp/TQ based on examples of the same engine using said parts within a range....not perfect but very close. Of course, you cannot say exactly what the HP would be, but one can, confidently, reasonable predict the outcome. It is this same reasoning and technique that is used by every major manufacturer when they publish HP numbers for their installed engines after being tested..they do not test every engine....Blueprint engines knows that a 383 with said parts will produce X HP/TQ...no guessing.
Continuing to push the "percentage" theory means you're ignoring the constant and exponential portion of the equation which you can't arbitrarily do, any number you put out is automatically a shot in the dark. If an engine makes 500 [email protected] RPM and it takes 15 HP to drive a Turbo 400 hydraulic pump, it doesn't all of a sudden take 30 HP to drive the same pump because the engine makes 1000 [email protected] RPM.

You're way off on your Gross to Net number even if it was a percentage. My 1971 L48 had a Gross rating of 270 HP, in 1972 the exact same L48 had a Net rating of 200 HP...that's about 26%, not 10-15% as you stated above. But it isn't a percentage so it's a moot point.

I agree with you that you can reasonably estimate the HP of a certain parts combination when assembled correctly, but that has nothing to do with guessing HP loss through the drivetrain.

First you said HP loss isn't a guess, I bolded it in red above. Then you finally admit it's a guesstimate, also bolded in red above...so we agree in the end, it's a guess. It's impossible to assign a percentage for HP Loss and back calculate crankshaft HP. I'm fine if you think it's possible, I just wish you could explain how you ignore "constant" and "exponential" HP Losses when you do your calculation.
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Old 06-05-2019, 02:54 PM
  #35  
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Originally Posted by glass slipper View Post
Continuing to push the "percentage" theory means you're ignoring the constant and exponential portion of the equation which you can't arbitrarily do, any number you put out is automatically a shot in the dark. If an engine makes 500 [email protected] RPM and it takes 15 HP to drive a Turbo 400 hydraulic pump, it doesn't all of a sudden take 30 HP to drive the same pump because the engine makes 1000 [email protected] RPM.

You're way off on your Gross to Net number even if it was a percentage. My 1971 L48 had a Gross rating of 270 HP, in 1972 the exact same L48 had a Net rating of 200 HP...that's about 26%, not 10-15% as you stated above. But it isn't a percentage so it's a moot point.

I agree with you that you can reasonably estimate the HP of a certain parts combination when assembled correctly, but that has nothing to do with guessing HP loss through the drivetrain.

First you said HP loss isn't a guess, I bolded it in red above. Then you finally admit it's a guesstimate, also bolded in red above...so we agree in the end, it's a guess. It's impossible to assign a percentage for HP Loss and back calculate crankshaft HP. I'm fine if you think it's possible, I just wish you could explain how you ignore "constant" and "exponential" HP Losses when you do your calculation.
Following your logic then, does the pump require 20 hp at idle? Or does the power max out at a certain rpm?
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Old 06-05-2019, 04:05 PM
  #36  
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Originally Posted by glass slipper View Post
Continuing to push the "percentage" theory means you're ignoring the constant and exponential portion of the equation which you can't arbitrarily do, any number you put out is automatically a shot in the dark. If an engine makes 500 [email protected] RPM and it takes 15 HP to drive a Turbo 400 hydraulic pump, it doesn't all of a sudden take 30 HP to drive the same pump because the engine makes 1000 [email protected] RPM.

You're way off on your Gross to Net number even if it was a percentage. My 1971 L48 had a Gross rating of 270 HP, in 1972 the exact same L48 had a Net rating of 200 HP...that's about 26%, not 10-15% as you stated above. But it isn't a percentage so it's a moot point.

I agree with you that you can reasonably estimate the HP of a certain parts combination when assembled correctly, but that has nothing to do with guessing HP loss through the drivetrain.

First you said HP loss isn't a guess, I bolded it in red above. Then you finally admit it's a guesstimate, also bolded in red above...so we agree in the end, it's a guess. It's impossible to assign a percentage for HP Loss and back calculate crankshaft HP. I'm fine if you think it's possible, I just wish you could explain how you ignore "constant" and "exponential" HP Losses when you do your calculation.

I think you are missing the point.........I will leave it at that!

You are quoting a Gross HP from GM in 1971 and then citing the 1972 Net number to make your point......I would hardly base your case on those numbers..just saying.

How about a known BP 383 with 430 gross HP documented by BP with the engine and then a few examples of folks with said engine producing 300-325 RWHP on a dyno... 25% Gross to RWHP that I quoted earlier is 322 RWHP which folks have documented . 30% reduction is 300 RWHP which folks have documented which is magically and "guessing" 25-30%......Hmmmmmm

BTW-What I said is "Calculating a range of HP lose for Gross to Net to RWHP is NOT a guess....it is a range based on thousands of examples of dyno testing various engines and configurations with these and any motor over hundreds of thousands of engine examples over the last 50 years through today". You cannot cherry pick, sorry! Decent attempt at deception but no cigar......

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Old 06-05-2019, 06:04 PM
  #37  
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Originally Posted by resdoggie View Post
Following your logic then, does the pump require 20 hp at idle? Or does the power max out at a certain rpm?
Sorry, you didn't follow my logic. I specifically stated peak HP RPM for both engines as 6500 RPM to make it an apples to apples comparison. Your questions are a red herring. The logic you missed is: just because an engine makes twice the power doesn't mean the HP lost to the drivetrain doubles and that's what happens when you arbitrarily guess at a percentage. In this case, the pump is clearly a constant as are a majority of the things that cause HP loss.

If you really want to know what the pump requires at idle, you can find out how many cubic inches it pumps per revolution, install a gage to measure line pressure, and note at what RPM the engine idles at so you can determine the output in gallons per minute. With that data, the following formula to determine the HP required to drive the pump at idle applies:
Hydraulic HP= PSI*GPM*0.0007.

Modern transmissions typically have two pumps with one being unloaded when demand is low and the other being a variable displacement to reduce output/flow when demand is low. They also have proportional control valves to vary line pressure based on load. They're extremely efficient especially when compared to say a Turbo 400.

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Old 06-05-2019, 06:05 PM
  #38  
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Originally Posted by glass slipper View Post
The formula for calculating the HP loss from the crankshaft to the rear wheels is:

HP Loss= Ax^2+Bx+C

Where A is the multiplier for exponential losses, B is the multiplier for linear losses, C represents constant losses, and x is the Net Crankshaft HP as measured by SAE J1349 that of course varies with the engine or any mods performed.

For HP to be a percentage, A and C would have to equal zero which is nowhere close to being correct. In fact, most driveline losses are a constant which means the C term is the dominant factor. If it takes 20 HP at 6000 RPM to drive the hydraulic pump in a Turbo 400, you could double the HP of the engine and that pump will still take 20 HP at 6000 RPM to drive...the pump HP Loss is a constant.

An example of linear losses would be gears. A well designed/machined helical gearset with an involute gear tooth has 1-2% loss which would contribute 0.01 to 0.02 to the B term. However, if you perform a chassis dyno test with an automatic or manual in the 1:1 ratio gear, thereís no relative motion between any gears because the input shaft and output shafts are locked together. The hypoid gears in the rear end arenít that efficient and will contribute about 0.04-0.05% to the B term. But if you add 100 HP to the engine, the HP loss increases just 5 HP.

An example of exponential losses is inertia like the wheel/tire and any other rotating driveline component. On a chassis dyno that controls the rate of RPM increase, the amount of HP going to inertia is small and any increase in HP from one run to another results in zero increase in HP going to inertia.

The HP Loss isnít a percentage and it isnít a constant, but youíll be a lot closer using a constant for a particular driveline assuming all is well with it including tire pressure as pointed out above. The only way to know is to remove the engine, dyno it, reinstall, then chassis dyno it. Anything else is pure guesswork which is why you see all sorts of numbers above.
You may want to reword this section. In a muncie 4 speed which is very common in our vehicles all the gears are turning all the time,even if they arent locked in, the cluster gear is slaved to the input shaft and is never disconnected so I would assume a higher loss for that particular transmission. A super T 10 may be similar
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Old 06-05-2019, 06:20 PM
  #39  
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I think you guys are not presenting your sides well, Any loss of anything can be presented as a %. IF you give a range of percentages then you are covering your self for any changes in given values. If you have engine A with x number of HP then increase the HP and the set value of a given pump doesn't change,Your percentage will still be in a small range. And if that value stays within the given percentage it is obviously true. I could also say 10% to 25% and that covers a huge amount of loss. So yes starting with 350hp and loosing 5.7% gives you a loss of 20 hp. And gaining 100 HP from a cam change and losing 20 hp is still only a 4.4% change so you are arguing over a 1% difference that falls into his percentage range......

I've got a Dyno day this weekend and I asked the tuner what they normally see in their motors from crank to wheel differences on average, He asked me make amodel engine and tranny questions and said 13% to 15% is normal. I would say a professional that does it all the time would have a good idea since its his job, and his reputation. I hope I stay in that range.

My desktop dyno says I should have an easy 420 hp athe the crank gross, Hotrod says they got 450 hp gross with my setup. lets average that to 435HP, then take 15% of that for accessories 378.26 and another 15% for driveline and I should see 329HP at the wheels. I hope to get up to 350HP , but 329HP at the wheels would be pretty good for a stock bore 327.

Also remember that these lossses arent exponential. You cant add the 15% of the net lose and the 15% of the driveline loss and say you will loss 30% total because then I would end up down in the 315HP range. The output at the crankshaft is the amount you will loose the driveline percentage from.

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Old 06-05-2019, 06:44 PM
  #40  
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Originally Posted by jb78L-82 View Post
I think you are missing the point.........I will leave it at that!

You are quoting a Gross HP from GM in 1971 and then citing the 1972 Net number to make your point......I would hardly base your case on those numbers..just saying.

How about a known BP 383 with 430 gross HP documented by BP with the engine and then a few examples of folks with said engine producing 300-325 RWHP on a dyno... 25% Gross to RWHP that I quoted earlier is 322 RWHP which folks have documented . 30% reduction is 300 RWHP which folks have documented which is magically and "guessing" 25-30%......Hmmmmmm

BTW-What I said is "Calculating a range of HP lose for Gross to Net to RWHP is NOT a guess....it is a range based on thousands of examples of dyno testing various engines and configurations with these and any motor over hundreds of thousands of engine examples over the last 50 years through today". You cannot cherry pick, sorry! Decent attempt at deception but no cigar......
Seriously, I'm ok with you guessing at percentages if that makes you happy...and you did say "guesstimate" in your post above where you spoke the truth in your explanation. I'm really only trying to help you understand the linear portion is not only one of the three components but is also the smallest contributor to HP Loss, the constant portion is by far the largest.

Shame on BP for stating gross HP, in fact, shame on them for not telling which SAE test procedure they used. The gold standard is SAE J1349 (Net HP), do you know which one they use? Maybe SAE J1995 (Gross HP)? I'd be willing to bet they don't follow any of the requirements just from the looks of their dyno cell. I'm not seeing anything documented for their engine, you're just taking their word for it like you expect people to take your word for your guesses.

This really is an exercise in futility because the original HP number for the engine isn't even known. I based my Gross to Net HP comparison on actual numbers published by GM, they are certainly more accurate than the numbers you're guessing at.
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