Maybe Chassis Dyno vs. engine dyno?

 

I was expecting to get 480hp or more from it since I had corsa exhaust 3 inch x pipe it should added another 20hp.

The stock LT1 often dynos at around 410 HP at the rear wheels.
http://www.edmunds.com/car-reviews/track-tests/2014-chevrolet-corvette-stingray-z51-dyno-test.html
http://www.motortrend.com/news/2014-chevrolet-corvette-stingray-z51-dyno-test/

When you had the exhaust system components added, was a tune done? If so, I'd say you got a bad tune.

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As greggshare alludes, the stock 460 HP is ENGINE HP, at the end of the crankshaft. What you're seeing is HP at the end of the drivetrain, after passing through the driveshaft, transmission, differential, wheel bearings, etc. All of those things add drag and weight, so rear wheel HP will always be less than crankshaft HP.

 

Actually that reading is right. Count on a 20 percent drop off from the claimed 460 HP. 460-92 HP is the proper dyno reading.

 

I see you're using a dynopack. They measure load hp and will consistently read lower than a dynojet. My old track car would tune out to 341 hp on a dynopack and 379 on a dynojet. From a tuning standpoint I was always able to get a better tune off the dynopack. Both dynos are reading rwhp not crank hp. One takes drag into consideration and one does not.

Regarding exhausts, sometimes a little back pressure is a good thing.

fltsfshr

 

Correction, If said Dynojet is calibrated correctly the DynaPack reads higher.
We own both machines.

I agree something is definitely wrong with this car/dyno.

 

Manuals are reduced by 12% and automatics 17%. Then u take into consideration dynojet vs mustang. Mustang dynos will always register much less HP than dynojet!

 

......given the previous, your C7 is still faster than 96% of the vehicles on the street. Smile. Be happy. Enjoy.

 

curious why the SS reads more HP on a Dyno? for 2016 vs vette

 

There is something seriously wrong! Sorry to say. My car stock with a green filter only got 417 on a mustang dyno. However it's not even your hp number that concerns me because that could be changed by many factors but if I read the chart correctly then you are making peak hp at around 5300 rpm! That should be between 5900 to 6100. Did you get a tune? If so they ffed up.

 

only had the aftermarket exhaust done and 3 inch x pipe, but i'm not sure if the guy did a good job or not cus the engine light lit and i found a way killing the light by using AFM disable. no tune or other mod have done to my c7, but i recall once the dealer where i purchased my c7 he used the wrong engine flush with diesel one, after that the car feels very tame and sluggish but now it's fine i guess....
the dyno project i got it from Armytrix Taiwan, they offer me a stage 2 tune , hopefully they will figure out where the problem is and perhaps beef up the performance too

 

Thanks for mentioning the check engine light. It's not unusual for aftermarket exhaust mods to cause this, since the exhaust flow around the O2 sensors can be modified, and the heating rate of the O2 sensors can also be altered. The car's computer (PCM) looks at this information to confirm the O2 sensors are working per factory specs. If the O2 sensors don't respond as expected, due to aftermarket exhaust mods in this case, an error is caused along with a corresponding check engine light.

Because of the above items, there is the possibility that a car would remain operating "open loop" using a default timing and fuel map, which could have a significant penalty on performance. The O2 sensors are a key part of closed loop operation, and if the car's computer thinks the O2 sensor(s) are faulty, the car may remain in open loop.

It's interesting that the error was associated with V4 (AFM) operation, and I'd say that's an indication of how complex modern engines are.

An experienced tuner will be able to address this common issue correctly (or you could simply go back to your factory X-pipe).
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You can skip ahead in the video to 1:30 for the open loop vs closed loop discussion.
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Regarding the engine flush, why was an engine flush done?

 

it was advised by the dealer who sold me the vehicle, he suggest to use one bottle of engine flush oil mix with gasoline every 5000 km to help the engine run clean...

 

If the new exhaust system has significantly reduced back pressure you're unlikely to get optimal performance without a tune. Hopefully a good tune will resolve any remaining issues. To do a tune "right," though, the tuner really needs a dyno. If they're proposing to send you a tune without actually testing it on the car, it's going to be approximate, at best.

You said an AFM disabler resolved the CEL. If the new exhaust system removed the AFM valves, you'll get a code for that reason alone, even if nothing else is wrong.

I also wouldn't use any sort of "oil" in the gas, or a commercial gas treatment, unless you know you have poor quality gas where you are. GM specifically recommends against using any gas treatment (check the owner's manual).

 

I had my c7 (11000 mi) dyno couple days ago, I was expecting to get 480hp or more from it since I had corsa exhaust 3 inch x pipe it should added another 20hp. but when I see the result I was shocked:upset: ...what might the problems for loosing so much power? View attachment 51290

Sorry but C7 already has a merge of the 2 pipes so buying for X-pipe will not get any real gains
I suspect the 2 AFM exhaust valves were taken off, if so then of course it would trip AFM DTCs and by turning OFF AFM will also have the valves in off state

As to dyno, really not done, or reported correctly

1. look at the left results as to Torque
They report it as in Kgm,
if we convert that to foot/lb, at around 2,000 RPMs it shows about 433 ft/lbs at 77 Km/h ( 47 MPH)

2. right results for HP,
reports 350 HP at 125 MPH ( 5235 RPMs) should be been able to be more closely to 6,400 RPMS ( unless at higher elevations and if so then there is HP loss because of that)

You can suspect
1. they did not correct for elevation, temp, pressure or dewpoint
2. person doing the graphs did not graph correctly
3. dyno not calibrated for proper weight
4. Used wrong tranny gear

As to tuning, mostly cyberspace chatter has people believing the only way to have a PCM tuned is via a chassis dyno
Not a fact or correct, I have tuned countless GM vehicles since the 1990s and 99% of them were not done on a dyno but real world street and track data collected realtime via OBD-II

A non load bearing dyno ( just a drum) cannot even be driven as on street and hence can only see the limited WOT a engine sees in real world, hence cannot obtain all the other realworld engine conditions
to assure that is tuned correctly and ONLY then tune for WOT

A load bearing dyno would allow for all driven conditions but any time the PCM and TCM is flashed, all it has relearned and adjusted for is erased and needs a good 20-30 miles of different engine conditions to relearn again
and most shops are not going to tie up a $70-100K load bearing dyno to spend a good 2 plus hours to get a base tune, relearn, tweak the tune and then another testrun of that amount of miles

As we all know the car has the ability to calculate the Torque ( torque management) and from that what the HP is thus street or track live data will ALWAYS give a complete and full tune a dyno cannot do in most cases

 

I had corsa exhaust 3 inch x pipe it should added another 20hp. but when I see the result I was shocked:upset: ...what might the problems for loosing so much power?

why do you expect an aftermarket exhaust to create any real power; is it due to claims made by the mfgr?

The C7 factory exhaust it pertty-damn-good as-is; the aftermarket exhaust will give you a different sounding exhaust note... consider that the real advantage. Granted, if you add a blower or H/C packeae - where you'd then go beyond the capacity of the factory exhaust... that I can see why it would be needed.

Aftermarket "anything" that claims a power gain... their claims are generally after a tune. What they don't do in their testing is a full two tunes; one with the car pre-"new gizmo" added... and then one after the upgrade. A tune on a 100% factory car can yield 6-10hp increase.

 

I agree with you until the last paragraph. From my own experience with two different cars that I owned. I had both stock beside a greenfilter with the stock box and with a Camara ss manual I had an increase of 25hp/28tq and on my stingray z51 manual i had an increase of 40hp and 47tq. This was verified on two different mustang dynos. I do have to say that found the best custom tuner out there.

 

Here's a short dyno comparison - another data point for consideration.

 

i just found out from the tuning shop that hp is measured at wheel which i need to /0.85 to convert into bhp .. so first dyno run without tuning i got 351 whp (412bhp). after ecu tune now i have 384.5 whp (452bhp) :very_drunk:

what a relief ! i thought something went wrong

 

ALLRIGHT!!!!

fltsfshr