chassis dyno fact or fiction

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steve cowan
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chassis dyno fact or fiction

Post by steve cowan » Sat Jun 23, 2018 5:55 pm

can you guys enlighten me on chassis dyno results please
here is the scenario,
my brother in law has a 2012 VE GTS commodore (pontiac) 4270 pounds with driver stock auto trans and rear gear, they put a vortec blower on the stock LS3 with a cam change chassis dyno says 600hp at the rear wheels,done approx 10 passes 11.14 @ 127mph on drag radial and pumpgas and street driving then kicked rods due to detonation everything junk start again.
buys new LS9 block (i think ) top dollar rotating assembly ,new stock heads,new blower etc everything brand new $ 40000 AU chassis dyno @ 630 hp at the rears now i dont have all the specs on everything about the car but i have my own opinion on the chassis dyno results.
raced at track last night (i was not there) but the guy who built the engine was there to check plugs etc,11.10 @ 126mph it has picked up a tenth in the 60 compared to the other engine.
now me thinks,
my own car runs 11.10 @ 121mph @ 3650 with me,sbc 383 that make 510 hp on pump never dynoed yes i have good converter 8'' 5600 and 4.1:1 rear gear on 255/60 drag radial.
NOW MY QUESTION IS - would the 630 rear wheel horsepower really be at the flywheel ??
i am only using the MOROSO slide rule as a guestiment,
i do remember him saying it is only around 8 psi boost and i am sure they will switch to E85 soon,
i am more interested in the chassis dyno theory as i am aware i am not comparing apples to apples here,any idea on what % of hp loss in drive train 20-30% ???
thanks for any input
steve c

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Re: chassis dyno fact or fiction

Post by user-23911 » Sat Jun 23, 2018 6:38 pm

My take on adding boost, you start off with 270KW (362HP) according to wiki.

Lets say you give it half a bar of boost or about 7 PSI.
That's not going to increase the power by more than 50%.
So you might see 540HP but it'll blow up of course because you didn't drop the CR.
That's at the flywheel.
At 100MPH road speed on a dyno you might lose 60 or 70 HP (or even less), it's never a fixed % but dynos aren't very smart to figure it out.

It takes 30 to 40 HP to push a car on the flat at about 70 MPH and it takes a bit over 100 HP to push a car on the flat at 100MPH, that's having to move the air out of the way as well as turn the wheels.


There's always lots and lots of threads about dynos....the only accurate way is with an engine dyno.
A torque converter makes measuring things really difficult due to the slippage and therefore a varying gear ratio.


The smart way is to do a before then an after on the same machine and see the difference.
Ignore the actual numbers.

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Re: chassis dyno fact or fiction

Post by RW TECH » Sun Jun 24, 2018 11:39 am

joe 90 wrote:
Sat Jun 23, 2018 6:38 pm



There's always lots and lots of threads about dynos....the only accurate way is with an engine dyno.


The smart way is to do a before then an after on the same machine and see the difference.
Ignore the actual numbers.
On the 1st point, you may experience 3%-5% power difference (on paper) between engine dynos....I see that all the time.

The 2nd point is one to take to heart & move forward with. It's not a chase the number on paper game unless you are working on one project & looking for gains/losses.

Outside of gain/loss recognition, the numbers (dyno output) are irrelevant and probably wrong anyways, if you compare them to what you would get if you tested in an OEM DV lab that uses current SAE correction factors & conditions inlet air so that no more than 2% correction can be applied.

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