Dyno HP vs driving feel

[Casper393W]

I know that I have seen a engine develop good power on the engine dyno, but wouldn't accelerate down the drag strip... Nothing like having a 650hp 406ci SBC and the best the car could run was 6.80's in the 1/8th. The owner of the car chased his tail Forever because he didn't want to accept the fact his new $15k engine was the culprit. He changed rear gear, Converter (2 times) and borrowed a known good PG Trans...

He took the engine to my buddies shop...we swapped the heads/and cam went back to the track and ran a 5.92 on his first pass.....

My take away

The biggest head and cam "might" make big power....but it doesn't mean it will be fastest

As long as the tesing is being performed correctly, and it is in the correct span, the one that makes the most power on the dyno will ALWAYS win! Fact!
Look elsewhere.......

To be honest...I believe the company fed him some bogus numbers...he was there when they dynoed the engine... The curve looked good to me, I will try to get a copy of his readout....you guys might be able to see something I don't!

[F-BIRD'88]

Getting the time of day and date and location of the dyno session is very usefull.
as well as the correction factor used at that time. Compare against NWS archived historical weather data.

[Tuner]

I know that I have seen a engine develop good power on the engine dyno, but wouldn't accelerate down the drag strip... Nothing like having a 650hp 406ci SBC and the best the car could run was 6.80's in the 1/8th. The owner of the car chased his tail Forever because he didn't want to accept the fact his new $15k engine was the culprit. He changed rear gear, Converter (2 times) and borrowed a known good PG Trans...

He took the engine to my buddies shop...we swapped the heads/and cam went back to the track and ran a 5.92 on his first pass.....

My take away

The biggest head and cam "might" make big power....but it doesn't mean it will be fastest

As long as the tesing is being performed correctly, and it is in the correct span, the one that makes the most power on the dyno will ALWAYS win! Fact!
Look elsewhere.......

Absolutely right ^^ !! The poor performance has something to do with the tuneup, probably too much timing.

In recent years (decades) the improvement in cylinder head port and "fast burn" combustion chamber design has resulted in engines needing significantly less spark advance than was common in the good old dayze. I know of several incidents in the lase several years in which, in spite of 28 degrees giving best dyno numbers, "Chevy Smallblocks run best at 36 degrees" and performance suffered or engine damage occurred.

Some goobers I know racing a streetstock dirt car had a 350 SBC with the corkscrew heads that only use 25 degrees advance. They were using 36 degrees and overheating oil and water and were blaming the "bad racing fuel". I told them, then showed them, set the timing to 25 total for them and that night the car moved forward through the pack instead of falling back. However, because the distributor curve was wrong for the 25 degree total, the engine didn't idle or run well in the pits or free-rev as snappy as it did with 36 total. You can guess what happened next week when they put the timing back to 36 because their engine builder said 25 was crazy, nevermind the driver says it made more power at 25, Chevys all need 36.

I have a few same stories about 18 degree 434 SBC's that were a lot more expensive than the iron 350.

You can fix the engine but you can't fix stupid.

[Scotthatch]

There are load dyno's ... PME has one that runs the engine like it is on the track ...they have a program for each track ... you can hear and see the changes as it goes into corners and revs up on long straights

[Tuner]

There are load dyno's ... PME has one that runs the engine like it is on the track ...they have a program for each track ... you can hear and see the changes as it goes into corners and revs up on long straights

This is still the situation. The load is different than the real world on the track.

On an engine dyno the load is released to allow RPM to climb, so the engine accelerates into a decreasing load as RPM goes up.

In a vehicle, the load of the mass of the vehicle is constant and aerodynamic drag increases to the square of the speed, so the engine accelerates into an increasing load.

An inertia dyno, like a Dynojet chassis dyno, or the engine dyno at BLP they did the Carb Shootout on, is a constant inertia load but obviously has no aerodynamic drag. Most dyno rollers weigh significantly less than the car being tested, so again the load is less than on the racetrack (or street) unless the car being tested is the same or less weight than the dyno roller.

This difference of load is one reason the ignition timing for best power on a dyno is usually too far advanced for best performance on the racetrack. I don't know where the idea comes from that timing should be advanced at the track beyond the amount that gave best dyno numbers. Because of the difference in load, the tune for best dyno numbers is usually too far advanced and too lean for best numbers on the track.

(As always, your mileage may vary. )

[Steve.k]

Im wondering if there are just things to look for on dyno. How the tq curve comes in and how long it stays in. That likely affects how car moves. The dyno is a useful tool to have, i dont believe that because it made a certain amount of power on dyno it wont move car. Its where the curve is at. The engine in dyno gets more load than it ever sees in vehicle.

On an engine dyno the load is released to allow RPM to climb, so the engine accelerates into a decreasing load as RPM goes up.

In a vehicle, the load of the mass of the vehicle is constant and aerodynamic drag increases to the square of the speed, so the engine accelerates into an increasing load.

An inertia dyno, like a Dynojet chassis dyno, or the engine dyno at BLP they did the Carb Shootout on, is a constant inertia load but obviously has no aerodynamic drag. Most dyno rollers weigh significantly less than the car being tested, so again the load is less than on the racetrack (or street) unless the car being tested is the same or less weight than the dyno roller.

This difference of load is one reason the ignition timing for best power on a dyno is usually too far advanced for best performance on the racetrack. I don't know where the idea comes from that timing should be advanced at the track beyond the amount that gave best dyno numbers. Because of the difference in load, the tune for best dyno numbers is usually too far advanced and too lean for best numbers on the track.

(As always, your mileage may vary. )

All very true but in car you have gears and transmissions to shorten the pull on engine. Ask most dyno operators and they will say this is the toughest work your engine will ever see. I beleive its a essential to to use to set car up. If you have no numbers to start with it's basically a crap shoot setting car. Knowledgeable tuners will get close but it still a guessing game.

[Truckedup]

For a street engine ,90 percent of driving is at part throttle with moderate acceleration...Throttle response is far more important than all out power.A well tuned manual transmission vehicle can accelerate briskly by short shifting and not having to rev the snot out of the engine..On the other hand, an engine with a very flat power band won't feel as lively when reved up..
You all remember guys who defeated the vacuum secondaries on Holleys or the air velocity "flaps" on AFB's or Q jets....push the pedal to the floor and there was a big bog followed by a rush of acceleration.. Many thought this was faster than a smooth linear rise of power...But it wasn't faster...

[Warp Speed]

There are load dyno's ... PME has one that runs the engine like it is on the track ...they have a program for each track ... you can hear and see the changes as it goes into corners and revs up on long straights

Are you talking about an inertia dyno?

[Scotthatch]

No ... they test a car on the track and can change the load on the dyno to mimic it ... it let's them test the engine as it will work in the car ... computer even controls the throttle so they can see how it works as they get on and off the throttle in a turn ... if the driver blurbs the throttle in the test due to traction it does the same on the dyno

[Steve.k]

Ford did that in the lemans days of the 427 oiler.

[SchmidtMotorWorks]

2009 Porsche 911 Engine Running Simulated Nurburgring on Active Dynamometer

https://www.youtube.com/watch?v=mfuleS9rnzc

[Warp Speed]

No ... they test a car on the track and can change the load on the dyno to mimic it ... it let's them test the engine as it will work in the car ... computer even controls the throttle so they can see how it works as they get on and off the throttle in a turn ... if the driver blurbs the throttle in the test due to traction it does the same on the dyno

Interesting, I didn't know they had an AVL?!?

[Steve.k]

https://m.youtube.com/watch?v=NxP__UPj7L8. Likley all started here.Barry R posted this before.

[Casper393W]

That old film is wild! Hard to believe they could do that back then....

[427dart]

You all remember guys who defeated the vacuum secondaries on Holleys or the air velocity "flaps" on AFB's or Q jets....push the pedal to the floor and there was a big bog followed by a rush of acceleration.. Many thought this was faster than a smooth linear rise of power...But it wasn't faster...

Well it sounded and felt great on the street since we didn't get to a track that often to tell whether it was fast or not.
Remember we were cruising the streets and burger joints 7 nights a week back then!!