ddn

My new engine dyno'ed last week at 575tq and 545HP. Yesterday, first pull on the dyno, it did 283HP. What???? The only difference was 1000cfm EFI throttle body vs 850 Holley and my car has Hooker sidepipe headers with JCL baffles.

Pulling out the JCL spiral baffles netted 75HP with no other changes (slight map adjustment).

I'm still pretty disappointed with how bad the Hooker supercomps are, but losing 75HP to the baffles is unacceptable. I am still missing at least 100HP from where it should be.

GrandSportC3

THe STS baffles only work good if uncapped but they are almost as loud as open if you uncap them. There is no miracle muffler.. Mufflers will cost you top end horsepower.. There's no way around that..

Dyno numbers with automatic transmission are generally in the 30 - 35% range (from gross HP numbers) as accessory losses have to be put into account..
Manual transmission losses are usually between 25 and 30% total loss.
5 - 13% of that loss is usually from accessories. (i.e. alternator, mech. fans, mech. fuel pump). So, based on my calculation, you should have around 380 RWHP with a automatic +/- 15 HP and about 405 RWHP +/- 15 with manual transmission.. If you have a big stall converter, you will lose extra HP.
If you run a TH400, your losses will be worst as it eats up most HP. A TH350 will cost you noticeably less HP. Stick shift trannys usually cost you 15% + 10% accessory loss..
PLEASE DO NOT CONFUSE HP LOSSES OF FACTORY RATED HP NUMBERS THAN THE ONES FROM ENGINE DYNOS!!! Factory HP ratings of engines for new cars are obtained by dynoing the engine with all accessories and a full exhaust system attached. Dyno testing on a regular engine dyno is done with open headers or race mufflers attached and no accessories.. Accessories attribute usually for 10 - 15% additional loss..
I always see those threads where people don't know where the power went when they chassis dyno. They expect a 12 - 20% loss as it is for example on late model cars. For example, a 405 HP C5 Z06 would dyno in at around 350 HP which would mean about a 13% loss. However, the 405 HP are obtained with all accessories and full exhaust attached and your regular engine dyno run does not have the accessories and full exhaust attached.. Big Difference!!

ddn

My STS baffles were uncapped.

I've got a 4-speed manual, and the only accessory I'm running is the alternator. Nothing else. And I'm not talking about factory numbers, my 575/545 number came directly from the engine dyno. Of course you're correct that is with open race headers and no accessory.

Also it's worth mentioning that the baffles didn't cost top-end power, they cost power all the way through the curve. I'll get the dyno printouts posted later.

kellyr073

"Manual transmission losses are usually between 25 and 30% total loss.
5 - 13% of that loss is usually from accessories. (i.e. alternator, mech. fans, mech. fuel pump).

"Stick shift trannys usually cost you 15% + 10% accessory loss.."


Please clarify, the 2 statements from your post. I have a 383 with 405HP on the dyno, stock MT with a Centerforce Dual clutch assy.

From the first statement, my RWHP would be @260. From the 2nd, its a little over 300RWHP. Its only 40HP, but I paid good money for for that 40HP, and would like to preserve it.

BTW, is there any torque loss?

DRIVESHAFT

Horsepower and torque are always tied together.
You cant lose one without also losing the other.

GrandSportC3

There is really no exact number.. 5% accessory loss is the lowest that I have seen and 12% transmission/drivetrain loss is the lowest for a manual transmission that I have seen. However, that 12% was on a MODERN drivetrain with many lightweight components. ON a C3, the normal loss from transmission, driveshaft, rear end, half shafts etc. is usually about 15%. That's the drivetrain loss. Then comes accessory loss.. If you only run a alternator and you DON'T have mechanical fans and the electric fans are OFF during the dyno run and you do run a low draw electric fuel and water pump AND you run open exhaust, your total accessory loss might only be 5%. However, if you run a mech. water pump, mech. fans, mech. fuel pump and a alternator, your accessory losses might be even over 10%.. Depending on the exhaust used, it can be even 20% or more. Exhaust is the MAIN horsepower reducer.
So, in a IDEAL scenario with all electronic low draw accessories and fans turned off, the minimum loss from dyno numbers on a engine dyno WITHOUT accessories to RWHP numbers would be about 20% on a C3. When I had my TKO transmission in my '68 and the old 383 engine, my loss was 22.5% and I was running OPEN 4 inch exhaust, electric fans (off at dyno test), electric fuel pump and a mechanical water pump. So, my accessory loss was about 7.5% and my transmission loss was about 15%. However, the main reason for my low power losses was my OPEN EXHAUST with LARGE TUBE HEADERS and 4 inch OPEN exhaust.
Small tube headers or mufflers etc. on the chassis dyno will cost you SIGNIFICANTLY more power.
However, if you runn all electronic low draw accessories and open exhaust with large tube headers, you should not lose more than 20 - 25% total loss.. If you don't your power loss might be well over 30%, even with manual transmission.. There is no rule of thumb. If you let me know what exhaust and accessories you run, I can give you a rule of thumb idea on what HP I'd expect you to lose. I've dynoed my car many times and tried many accessory/exhaust combinations for the dyno and I have some idea what accessories cost you how much power.. #1 power killer is of course exhaust and #2 power killer are mechanical fans (it doesn't matter what type they are, even clutch fans will cost you noticeable power)

FRSTR90

You can not calculate RWHP by taking away a percentage of HP... If you have a 350 producing 350HP and you calculate a 20% loss the amount of HP loss would be 70 HP. Now if you put a 572 behind the same set up that was behind the 350 and the 572 is producing 700 HP and you calculate a 20% losee then the amount of HP loss woule be 140HP. Now if they engine was the only thing changed why would the accessories and tranny use up another 70 HP?

Each accessory takes up a certain number of HP and so does the tranny. When you know eactly how much HP your accessories and tranny take up then you can subtract that from flywheel horsepower. The percentage thing IMHO is the most ridiculous thing I've ever heard..

GrandSportC3

That's just the way it is.. Losses are in % and not specific Horsepower.

The worst dyno loss that I had on a engine was on a engine that dynoed on the engine dyno at 435 HP (approx.) and I got 285 RWHP or so on the chassis dyno.. Even though I ran open exhaust, I was running mechanical fans, water pump, fuel pump and alternator AND I was runnint a TH400 transmission which eats up quite some HP by itself.. Total loss was about 35% even though I ran open exhaust.. Mechanical accessories will eat up Horsepower!!

On another Vette, I had a 383 with 465 HP and the best dyno run was 365 RWHP which was about a 22% loss.. I had all electric accesssories on that test.

FRSTR90

Im very well ware of that.. What I am saying is why would bigger engine producing more HP and more torque lose more horsepower and torque? If a 350 lost around 70 HP through the drivetrain why wouldn't a 454 lose roughly 70 HP through the same drivetrain with the same amount of acccessories?

GrandSportC3

More power = more friction. More friction = more horsepower loss..
Especially when it comes to exhaust, the power loss can even increase in % by a huge amount. A engine has a certain flow requirement for intake and exhaust. If the exhaust is too small for the engine, you'll SIGNIFICANTLY drop horsepower.. Try running a GEO Metro sized exhaust on a 1000 HP drag engine and see how much horsepower the engine will lose..

GrandSportC3

Just thought of another example to illustrate..
Let's say that you have 2 remote controlled cars. One car goes 50 yards in 30 seconds and the other one goes 50 yards in 15 seconds.
Now, make each car drag a 1 lbs bag of sand. You will see that the faster car will slow down more seconds than the slower car..

mtcraigco

OK exhaust out of the equation, I understand that fairly well and the more you choke something that needs to flow the worse the loss will be.

But answer me this.

Will an AC unit cost the same HP to turn at 3500RPM on a small block with 180HP as it will on a BB with 500HP at the crank? How can that AC unit actually use more HP to turn just because the engine is different? Same question for a water pump and a power steering pump.

The power steering pump and the AC unit are exactly the same from one engine to another, how can it possibly cost more HP to turn those accessories on a SB or BB?? The accessories do not know what engine they are on, they only know it requires a certain amount of energy to turn at a specific RPM under a specific load.



I call BS on the % thing with the exception of the exhaust example. That makes sense as obviously you cant run the same system on a 500HP engine as on a 180HP engine. But then the exhaust is DIFFERENT!! The AC PS and ALT don't change! The water pump does a little but not that much.



With the above info in mind please explain how any of those accessories will draw different amounts of HP simply because the are on a different engine???

I say far more of the RWHP loss is attributable to dyno differences and trans/exhaust loss than accessories. Accessories should use a specifc amoun of HP regardless of what engine turns them.

BTW Not trying to be an azz, I just can't get around accessories costing different HP on different engines. Exhaust, sure, it needs to be sized to the engine/HP

Trans, sure, OK I can by that too.

Accessories, nope, can't see it.

To the OP, I'd toss that thing on a different dyno and I bet $50 you see different numbers.

That loss seems extreme to me as well.

toddalin

Wow, my 331 CI makes 293 RWHP and 293 ft-lb torque (with 9.5:1 CR and a Holley 600 dp). But I really doubt that I am making 550 hp at the crank. (I figure it is more on the order of 350-375 hp at the crank. )

shft22

I can see where the loss due to accessories, Water pump, etc is provided as a % loss for that engine, but this % number can not be use on a different engine....for example if the accessory loss on a 350 is 10% it does not mean that on a different engine lets say a 502 it will be also 10%, it most probably be like 6 or 7% since the engine has more power and the accessories will use the same amount of power so the % must be lower.....

ddn

Then it's not a % loss, it's fixed. It's only % relative.

mtcraigco is right on, the exhaust can be % loss, as well as drivetrain, but accessories are fixed.

My *** dyno is going to tell me how much I've really lost in a few hours. I didn't consider the water pump or the mechanical clutch-less fan either, but I still am blown away by the difference. 545 to 375 is a pretty massive loss. 22% to drivetrain (4spd man) and accessories?? Seems extreme. Guess I should have built it for 750 flywheel HP

panic

They work only wide open...and I'd still prefer a good custom undercarriage exhaust.

The Hooker side pipes robbed a good few ponies on my dinoed SB at 570hp engine as well...I could only go NEAR its full potential if with open through race muffler.

Otherwise they were a pain in that place.

FRSTR90

That is what I was trying to say all along.

As for the more power = more friction, that is not necessarily true on all circumstances. However, when comparing a SB to a BB or a 350 to a383 that would be true, but it is irrelevant. Power loss due to friction is already taken into account when you put the engine on a dyno.

As for the exhaust, I never mentioned anything about it, but I agree with you there.

FRSTR90

You'll be surprised how much HP is taken up by that clutch fan. I believe it was somewhere between 10-20 HP. One reason why electric fans is not only considered as a cooling upgrade but also as a performance upgrade. As for a waterpump, I personally prefer to run a mechanical. Yeah it will cost 10-15 HP maybe, but I believe they are more reliable and you do not have to go through the hassle of rerouting belts. Not to mention if the belt pulleys aren't perfectly lined up, you'll be constantly throwing them off.

C3 Stroker

I wasn't going to comment on this thread, but it is very interesting, reviving an old argument and I personally have verified the results.

GrandsportC3 is absolutely right....more friction is created by the higher horsepower motor trying to move everthing faster (fans, trans, etc. as well as air through the exhaust). True, the accessories each have a fixed resistance which would remain constant to the motor if the motor was not accelerating as on a dyno. A 30 HP motor can maintain your car at a constant 100 mph, but it takes much more than that to go from 0 to 100 in 12 seconds.

My own motor produced 628 HP on the engine dyno. On the chassis dyno the number was 490 RWHP.......a 22% loss. No, it doesn't take 138 HP to power the accessories; they work just as well at idle.....but it does take more effort from the motor to constantly accelerate them. Each RPM increase changes the constant.

Just my .02

MotorHead

Ok this has been batted around for years here. My 406ci made 550HP on an engine dyno and 430HP on a chassis dyno. Roughly 23% loss from gross HP to net HP on standard C3, more for an automatic.

If the OP got the numbers he says then one of the dynos wasn't working properly or calibrated incorrectly or the numbers were fudged buy someone who had an interest in the motor.

As for you guys who think a 400HP loses 70HP so an 800HP will lose 70HP you are dead wrong. The loses are friction/heat, it is all physics.

An 800HP will spin the dyno drum and all parts behind the motor at a faster rate (rate of change of rpm / time ) thereby producing more friction and heat and will lose much much more than 70HP. While not exactly the same percentage it would be pretty close.

If 400HP motor loses 20% that would be 80HP and would get 320HP on an engine dyno. The 800HP motor would lose a little less that 20% but the rear wheel numbers if in the same car would be about 650-670HP