[gtofreek]

I don't understand the whole 25% loss through the driveline thing. How can they rate that in a percentage? 25% of 300 HP is 75 HP. 25% of 1000 HP is 250 HP. You mean to tell me that a certain driveline will take 175 more HP to drive simply because the engine makes more HP? It just doesn't make sense. Seems to me the driveline will rob "X" amount of HP regardless of how much power the engine makes.

[Baron Von Zeppelin]

Sounds like it should be more in the 475hp range like the 408 with ported iron heads that gtofreek just built/dyno'ed .
It went through stock size R/A exhaust manifolds - no headers.
Just a wee little bit more cam - and a Qjet.

I would be PIZZED OFF .
Maybe that chassis dyno is REAL stingy

[dataway]

Originally Posted by gtofreek

I don't understand the whole 25% loss through the driveline thing. How can they rate that in a percentage? 25% of 300 HP is 75 HP. 25% of 1000 HP is 250 HP. You mean to tell me that a certain driveline will take 175 more HP to drive simply because the engine makes more HP? It just doesn't make sense. Seems to me the driveline will rob "X" amount of HP regardless of how much power the engine makes.

Yep, in the world of real life physics driveline loses will be relatively constant. Sure ... if you are sending twice as much HP through the driveline there may be an extra few HP in loses just because of greater friction loses under higher loads, but is it a straight percentage ... not even close.

With an engine of 350 crankshaft HP .... get 300+ at the rear wheels... I wouldn't be that disappointed. Either you are in the HP race or you are not, if you are building a street engine, throttle response and drivability mean way more than 30 hp on a dyno.

[1funride]

I was disappointed. I am trying to figure out where all my HP went?? Hahahaha. But seriously I was surprised, maybe even shocked. Good compression, good heads, port matched, ports aligned, the air fuel ratio is a little rich but overall it was good, timing I think is typical pontiac good (I am going to check that again), I degreed the cam, good spark, I expected more from the camshaft (with 1.65 rockers even) as it didn't make power past 5000 and we pushed it to 5700, Is it the exhaust is holding it back......and the cam does have a little more in it? Maybe the flex fan? Is it as simple as just an accumulation of drivetrain loss, flex fan, exhaust, and accessory loads?

Not that I am horsepower chasing, but when you have attention to detail and use parts that should perform a little better you want it to perform to its potential. As stated prior the car has very good throttle response and pulls through entire RPM range, easily breaks the Nitto tires loose when snapping the thrrottle in first gear half throttle driving speeds, spins them pretty good at 2nd gear shifts. The dyno runs shows it running smoothly with no hickups.

The TH400 is power hungry, I have read of real world tests where they take more than 25%, see article below for a real world test and the reality of big auto transmissions stealing your power.

https://www.hotrod.com/articles/ccrp...in-power-loss/

[Formulajones]

Originally Posted by 1funride

I was disappointed. I am trying to figure out where all my HP went?? Hahahaha. But seriously I was surprised, maybe even shocked. Good compression, good heads, port matched, ports aligned, the air fuel ratio is a little rich but overall it was good, timing I think is typical pontiac good (I am going to check that again), I degreed the cam, good spark, I expected more from the camshaft (with 1.65 rockers even) as it didn't make power past 5000 and we pushed it to 5700, Is it the exhaust is holding it back......and the cam does have a little more in it? Maybe the flex fan? Is it as simple as just an accumulation of drivetrain loss, flex fan, exhaust, and accessory loads?

Not that I am horsepower chasing, but when you have attention to detail and use parts that should perform a little better you want it to perform to its potential. As stated prior the car has very good throttle response and pulls through entire RPM range, easily breaks the Nitto tires loose when snapping the thrrottle in first gear half throttle driving speeds, spins them pretty good at 2nd gear shifts. The dyno runs shows it running smoothly with no hickups.

The TH400 is power hungry, I have read of real world tests where they take more than 25%, see article below for a real world test and the reality of big auto transmissions stealing your power.

https://www.hotrod.com/articles/ccrp...in-power-loss/

Those numbers aren't terrible at all for a 400 Pontiac. When we were at a dyno day there were a handful of mild 400 Pontiacs that were under 300 RWHP. I remember 2 of them were in the same 275hp range you are, one was in the 280's. I was the only 400 that day that hit 301 RWHP and 355 RWTQ. There was even a hopped up 455 with open headers that barely did 320RWHP.
I was running through a 400 turbo with a stock converter, and a 12 bolt rear, all accessories including Alt, PS, Water Pump, Fuel pump, stock clutch engine driven fan, and the factory 70 RA air cleaner in place. All that stuff drags down HP. If you run even the slightest stall converter, it really sucks down the power at the wheels, which I suspect that 455 had, because his RWHP didn't reflect how he was running at the track that day (mid 11's)
If you run steel wheels, steel driveshaft, bigger rearends like 12 bolts, 9 inch, it will all suck the power down. So don't get too worked up over it. They are fantastic tuning tools though.

[mchell]

Originally Posted by 1funride

I was disappointed. I am trying to figure out where all my HP went?? Hahahaha. But seriously I was surprised, maybe even shocked. Good compression, good heads, port matched, ports aligned, the air fuel ratio is a little rich but overall it was good, timing I think is typical pontiac good (I am going to check that again), I degreed the cam, good spark, I expected more from the camshaft (with 1.65 rockers even) as it didn't make power past 5000 and we pushed it to 5700, Is it the exhaust is holding it back......and the cam does have a little more in it? Maybe the flex fan? Is it as simple as just an accumulation of drivetrain loss, flex fan, exhaust, and accessory loads?

Not that I am horsepower chasing, but when you have attention to detail and use parts that should perform a little better you want it to perform to its potential. As stated prior the car has very good throttle response and pulls through entire RPM range, easily breaks the Nitto tires loose when snapping the thrrottle in first gear half throttle driving speeds, spins them pretty good at 2nd gear shifts. The dyno runs shows it running smoothly with no hickups.

The TH400 is power hungry, I have read of real world tests where they take more than 25%, see article below for a real world test and the reality of big auto transmissions stealing your power.

https://www.hotrod.com/articles/ccrp...in-power-loss/

Don’t get too into trying to compare your numbers with “what others” are getting .....it’s a dyno.......every single one will produce a different number....best to get it to the track if you want to judge your real world power... the guess will turn into reality.....and frankly, that may be a disappointment as well....sound like a decent build, have fun with it

[Skip Fix]

Originally Posted by mchell

Don’t get too into trying to compare your numbers with “what others” are getting .....it’s a dyno.......every single one will produce a different number....best to get it to the track if you want to judge your real world power... the guess will turn into reality.....and frankly, that may be a disappointment as well....sound like a decent build, have fun with it

What he said same goes for engine dynos. My RAIV 400 with a 288/296 UD made 385 engine HP on a very conservative dyno through headers and mufflers and ran mid 12s @ 109 weighing 3900 lbs. My 455 made 400 rwhp and with some tuning at the track ran 10.90s @124 weighing 3750. Current pump gas 455 made 525 HP on a Stuska engine dyno runs the same as previous 455 and formulas show more like 550-570 hp engine HP.

[Formulajones]

Originally Posted by gtofreek

I don't understand the whole 25% loss through the driveline thing. How can they rate that in a percentage? 25% of 300 HP is 75 HP. 25% of 1000 HP is 250 HP. You mean to tell me that a certain driveline will take 175 more HP to drive simply because the engine makes more HP? It just doesn't make sense. Seems to me the driveline will rob "X" amount of HP regardless of how much power the engine makes.

I'm in agreement, and have told people in the past trying to figure out flywheel numbers on a chassis dyno from a percentage is not that accurate. I've had an engine on the dyno, and the same car on the chassis dyno later. The percentage thing doesn't quite pan out.

[Lee]

Originally Posted by gtofreek

I don't understand the whole 25% loss through the driveline thing. How can they rate that in a percentage? 25% of 300 HP is 75 HP. 25% of 1000 HP is 250 HP. You mean to tell me that a certain driveline will take 175 more HP to drive simply because the engine makes more HP? It just doesn't make sense. Seems to me the driveline will rob "X" amount of HP regardless of how much power the engine makes.

TOTALLY correct. I've had a few rants on this previously. There are few people that have done more personal testing on chassis dynos than I have. I've seen 40+ hp differences JUST from changing torque converters. I've seen 35hp swings from air filter elements/housings.

The "25%" thing is horribly inaccurate. There are just TOO many variables.

[Steve C.]

And two interesting articles related to the subject.....

Dyno Thoughts and HP Losses

http://www.sdsefi.com/techdyno.htm


Comparing Chassis and Engine Dynos – Racing Dynos

https://www.hotrod.com/articles/1106...-engine-dynos/



.

[mchell]

Originally Posted by Steve C.

And two interesting articles related to the subject.....

Dyno Thoughts and HP Losses

http://www.sdsefi.com/techdyno.htm


Comparing Chassis and Engine Dynos – Racing Dynos

https://www.hotrod.com/articles/1106...-engine-dynos/



.

Bingo.......good reading