How much of a difference in hp between those engine dynos you see done on tv shows and those advertised in Summit, Jegs, etc catalogs and what happens once in a car?

Just so happens Super Chevy magazine tested theirs in a recent article. They built a 413 BB and first went with the engine stand dyno and then chassis. In their words "we were down 130hp and 150lb ft torque". They felt the loss was drivetrain loss from the powerglide and torq converter.

On the engine stand they pulled 411hp and 452lbs ft torq.
Chassis 282hp and 304lb ft torq.

When they put the engine in the car they did use the cast iron manifolds rather then the headers, also hooked up the alternator and fan so there was that loss of hp.

This article shows the drop to what actually hits the ground. This being a good reason to ask when someone wants to talk hp, how did they come up with their number.

 

Bill,

Those numbers look spot on for what I generally consider the percentage loss between gross to net and then net to RWHP for older cars like a C3 (modern cars have much less loss), which seems to be so debated. Based on the overall numbers posted by the magazine, there was a total percentage loss from gross HP 412 to the RWHP posted (282 HP) of 31.55%. I generally figure a 15% loss of HP from Gross to Net HP and 15-20% from Net Hp to RWHP. If you take the 15% figure for the loss from Gross HP to Net HP and an additional loss of 18% (off the Net HP) to RWHP, you end up with a total with a RWHP number for the engine above that is pretty close to what is reported.

Using the numbers posted:

412 Gross HP with a 15% loss to Net HP=350 Net HP

350 Net HP with an 18% loss installed in the car with all accessories, transmission hooked up/stock full exhaust (no Headers) =287 RWHP versus the actual reported RWHP of 282. Difference-5 HP.

These differences are meaningful when comparing motors. A C3 with a built engine like a 383 that claims to have 425 HP (which is properly Gross HP, Not NET) is actually probably producing about 350 Net HP, not too shabby but not the 425 HP claimed in the real world. As an example, Comparing a C3 with the 383 with "425" HP to a new Caddy CTS V-Sport with the twin turbo V6 making 420 NET HP without knowing the differences seem pretty close in HP. The 383 is at 350 Net HP versus the V Sports 420 Net HP. That is a big difference.

 

I would call that a poor comparison because the motors were radially different. You have to compare apples and apples to give meaningful information.

This is like these people posting (their) dyno runs here on the forum and it isn't the same motor or it is a stripped down motor with an electric water pump, uncapped dyno headers and a 900 CFM dialed in carb and intake. Then they gloat over their numbers

 

The Net and RWHP number is much more meaningful HP number representing the HP the engine will actually produce installed in a vehicle, not on a stand. You are correct that a Gross HP number compared to what actually the engine produces in the car are very different.

 

My engine dynoed 657hp on the local, well known dyno. In my car it dynoed 460 rwhp...(Superflo dyno but using the dynojet correction)

Differences:

DYNO
*Air turbine on the carb (the dyno velocity stack) adds 10-12hp over nothing at all on the carb.
*2" headers and no exhaust
*No water pump or any accessories
*Electric fuel pump
*Water temp at 120*/oil at 180*

IN CAR
*1 7/8" headers and 3" pipes/muffs all the way to the bumper
*Full accessories, (PS, AC, Water pump, Alt--although an electric fan/not the clutch fan)
*Mechanical fuel pump
*L88 air cleaner base only
*T400 w/tight 10" converter
*IRS with heavy drive shaft and 3" half shafts--all HD stuff)
*Pulls at 120-160* water temp, no oil temp
*Turning 255/60/15 BFG Radial TAs at 35 psi.

The air was way better when we dynoed the engine alone but... SAE correction factors on both should take the weather out of the equation...

That is the reality, roughly 200hp difference from dyno to car... Same tune up, AFR monitored on both setups..

Car runs 127-128 mph at 3662lbs on a -500' DA day.

Don't get too wrapped up in dyno numbers...

 

Super Chevy and CHP are two magazines I consider complete toilet paper, for exactly these types of "comparisons". I don't understand why they can't take the time to decide what they're doing and do it right.

I agree that it's a complete apples-and-oranges comparison, but it comes back to what engine and chassis dynos are for...which is not to make bragging numbers.

Engine dynos are for break-in and testing, chassis dynos are for tuning.

The important thing here is not to look at this as "drivetrain losses" or try to do the math - it's just not valuable or valid IMHO.

 

Your personal experience seems to validate the article's findings. Thanks for posting.

RWHP and Net HP eliminates the bragging that comes with "Gross" HP numbers. It is very valid. Typical Scenario #2:
Guy with a C5 corvette, asks the C3 guy with his built/crate 350, how much HP? C3 guys says 425 and the C5 guy with 350 Net HP walks away going wow! Problem is the C3 does not have 425 Installed Net HP, no where near. Not sure why folks insist on the gross HP ratings today.

 

As "gkull" mentioned....and I agree with...you can not dyno an engine on a stand..and then change components/conditions and expect it to produce anything remotely close to the initial test. It is stuff written like this article that can cause a person to "scratch their head" and get upset....because they are worried about a number....so they can talk about it constantly. Like it a badge of honor. Like it matters at all. I get impressed when the chassis dyno gets pegged....1000+hp.

It will drive you crazy.



[QUOTE=jb78L-82;1585962553Not sure why folks insist on the gross HP ratings today.[/QUOTE]

In my opinion:
Mainly because they MUST feel that because the engine can produce that power producing that gross rating....they can say that is has that much power ...regardless what it actually puts to the ground..and conveniently forget to mention it...or choose not to mention it...so they "feel" that they have the much stronger engine when the conversation is done.

I am all for "the numbers" being important data/information for people who race their cars. But I have stopped worrying about the numbers when it comes to a street car. Although they are important...and I pay attention to them...I do not get caught up in these "numbers" and have them make me loose sleep over them...when in 90% of the time...the engine will never/rarely reach its total potential on the city streets...and I am glad they do not see it.

Many people that I have worked on their cars in the past get seriously caught up in these "numbers" and for some odd reason...they feel that they have to have the most awesome engine that produces so much power/torque....and they talk about it with other customers...recite numbers left and right...and by their own admission....they rarely ever use it. It is really hard for me to get too excited any more....especially when I was lucky enough to work on a Nitro funny car team and experience power that is insane. I have been ruined for life. I still enjoy a powerful engine...but I just do not let the "numbers" get the best of me....I try to make sure the power and torque can get to the ground as best as all possible. Smoking tires just seems to be a waste.

DUB

 

though some will argue with me on this but the only reason i would use a dyno is as a tuning aid. i don't care much about arbitrary numbers. all i care about is E.T and M.P.H

 

Wow......a lot to read....good information too.

So, any guess what a brand new L48 (let's say 1974 like my car) would dyno at using the conditions crate engine manufacturers are using today?

That would be interesting so I could do an HONEST comparison between my L48 and a crate engine.

 

Billa, I have to take issue with this. The Engine dyno is the only tool I use to calibrate (tune) the engine. With the engine dyno, one can do a much better job characterizing performance vs all the variables involved at any instant of time. Fuel flow to each cylinder with individual temp and O2 sensors at all load and rpm conditions. Precise load setup. Input air temp control. Accurate rpm measurement, This list goes on.

The chassis dyno is good for characterizing losses due to drive train (which are not linear BTW) when accurate engine output HP is known. , etc. but is much harder to control all the variables that are needed for a precised tune.

Dyno's are tools. Not bragging rights generators.

 

We can respectfully agree to disagree - and definitely agree that it's not about the numbers and bragging rights.

In my experience regardless of the tuning on the engine dyno, the work will need to be done again once the engine is in the chassis, even if you're duplicating the entire setup (accessories, exhaust, etc.)

Having EGTs in every tube, metered airflow, etc. is great...except those won't be the headers or environment you have in the car. You'll have different headers, full exhaust, air cleaner, hood...you won't have a precise loading, but you'll have the REAL load...and finally, anything unique to the installation isn't replicated like linkages, etc. It's awesome for making sure everything's working before the installation work, but I don't spend any time if stuff is in the ballpark.

All this is just one guy's experience - I just have yet to see this not be the case in practice.

 

Ok, Peace. I will respectively disagree. Characterizing an engine is a engineering science that requires detailed understanding of all variables with respect to all other parameters at all operating conditions. The better one does that the better the tune. I just happen to believe that can be done easier on an engine dyno and not need to be re-done.

 

Wow...This is an emotional subject sometimes.

I love engine dyno's....and yep....I often dyno them with electric water pumps and open headers etc..I want to know exactly what the engine alone is capable of. If I just happened to use the headers that are in the car... might never know that they are too small...or too big...or too long etc etc.

Testing with various carbs, spacers etc let you know what the engine would like. Maybe you hit it dead on...maybe not. If you don't test you don't know. Same with engine temps...I test them with cold water and hot oil..because when I go the track..that's what I will replicate. I also test them at "normal" temps to see what effect it has on timing needs, fuel mixture etc. Some combos are very sensitive.. some aren't.

Anyway, dynoing with all accessories disconnected allows you to compare to every other engine out there..that's how they are done in the aftermarket. It is what it is.

Then dropping it in the car allows you to see what is actually getting to the ground. The wide open tune will be pretty close and you can play with other stuff on either dyno if you want to. Otherwise it's track time and street use.

I don't see anything really wrong with the testing except I'd have like to have seen the iron manifolds on the engine dyno so we could eliminate that variable.

Ajrothm did some extensive chassis dyno testing and showed everyone what did what....and at the end of the day the car still showed the power going down the track!


JIM

 

Funny that I should find this post. My 383 installation was just finished this past week and the final tuning was done on a Dynojet chassis dyno. Final numbers were 267 rwhp and 310 rwtq. Very pleased with the results for a street driven car. As has been said, lots of people like to quote gross numbers at cruise nights and such but numbers change once the rubber hits the road. For me, its all just for fun but it's interesting none the less to find out what the true numbers are. And even the chassis dyno numbers can't be compared from one shop to another.

 

 

Did you do the engine dyno also? What's the combination?

 

No, just the chassis dyno. Engine is an Eagle stroker kit, Patriot 190cc heads w/64cc chambers, 1.5 Roller tip rockers, Edelbrock 1806 carb and Edelbrock 7116 intake, DUI distributor, Hedman 1 5/8 headers. Comp 279TH7 cam. Tranny is a TH400 rebuilt with a 2400 stall speed and Transgo 400 1-2 kit. Running all accessories including PS, Air (A6 compressor), 7 blade fan. Still has the original 3.08 rear (for now). Also running true duals with cats on each side through Magnaflow mufflers.

Video of the dyno run.

 

Your comments are exactly what the point of article is. It's not about testing, tuning, breakin etc of engine stand dyno versus chassis dyno. The purpose of the article is to EDUCATE folks that Gross HP numbers are NOT the actual HP installed in the vehicle. Gross HP numbers are very misleading and why ALL the manufacturers were forced to switch to NET numbers in 1972. The purpose of the article is also to make folks aware when looking at crate engines/rebuilt engines etc that if you are quoted Gross HP (which is usually the case-ask to confirm) that will NOT be the installed HP-the difference can be quite large as illustrated in the article and by others who posted the Gross/RWHP numbers. The article specifically illustrates what happens to a Gross HP number when the engine is actually installed in a vehicle, which is the relevant number. It is very clear in its purpose and makes the point precisely. This topic has nothing to do with Apples to apples comparison-That is and was not the point.

 

The comparison chart is very similar to my mostly stock 70 L-46. Original heads were ported, xe262h cam installed, 10.4:1 CR.

Engine dyno (Stuska) - open headers, venturi stack, water pump.
341hp@5600
387tq@3400

Chassis dyno (Dynojet) - Alternator, PS pump, water pump, original air cleaner, original intake/exhaust manifolds, M21 3:70, 2.5" exhaust and mufflers.
243hp@5000
304tq@3750

About a 29% loss.