foggy

Ok, so background: this fall I added Kooks LT ceramic headers w. Cats
Did the LS6 (by Dorman) Intake Manifold
Replaced Injectors with AUS new ones- same size as OEM
Did the Yella Terra 1.8 Rockers with new pushrods, Blue GM Springs,
Seals, & Ti retainers


MY DIC shows that after the tune- HP Tuners
that I gained some MPG - hwy avg is around 27-30 ..
which is about 1-2 better than with stock manifolds & stock LS1 intake and the hypertech tuner.
BUT MY DIC is SO Wrong Now !!! It used to be right on the money.
Doing fill up calculation over a 500 mile all highway road trip...
My Actual is only 21 MPG...

My numbers on Dyno were 367 & 362 HP/TQ
I told the Tuner I wasn't interested in trying for a dyno #, but wanted
good drive ability & efficiency.
SO, What the Hell Happened ?????

foggy

To ADD: 2000 Vert, A4, 3.15 Rear Ratio
I am the only one who has ever worked on this car, ever
I didn't really expect a MPG improvement, but this really sucks (the gas)

sirdano

Confused....
MY DIC shows that after the tune- HP Tuners
that I gained some MPG - hwy avg is around 27-30 ..
which is about 1-2 better than with stock manifolds & stock LS1 intake and the hypertech tuner.

These are two different things unless it was a keyboard slip? Do you connect a hypertuner after it got the HP tuner? This could have erased the HP tuner program?

foggy

NO, the old setup was all stock w hypertech 'box'. Cold air, catback .. Used to get
27 ish on hwy trips. And that's exactly what the DIC would read - accurate..
NOW, after LT Headers w HiFlow Cats, LS6 Intake, Yella Terras and HP Tuners Dyno
Tune, the DIC reads 28-30 So I "thought" I was getting Better MPG.. BUT,
the DIC is Very Wrong !!! I am really only getting 21 mpg
( I removed the hypertech tune after mods before going for Dyno Tune)

Gordy M

A dyno tune will give you numbers about acceleration, torque, HP, injector settings etc. but not under load. A load bearing dyno will give you better tuning characteristics because the engine is under a 1000 lb load. As a result, you will get lower hp/tq readings but a better all around tune. If you changed tire sizes, it can also change mileage. When I went from Stock C5 front tires to 255x40x17, my mileage went up but my spedo was also off.

Unless you are going to do a lot of drag racing, using NO or boost you get the best real world tunes by a 20-40 mile street log/tune. However, GI/GO still rules and in that case you are limited by the talents of the tuner. Also, do not rely on the dyno to give you real world numbers, take it to a drag strip and have before and after results. An auto trans usually dyno's about 295 +/- Hp in stock form, the 2000 C5 will give you better dyno numbers with cold air, headers, tune, injectors, etc because it is a higher lift cam than the rest of the C5 nonZ Corvettes but gaining 70 hp with you mods seems like a far reach, 35-40 Hp seams more realistic IMHO

insertclevername

What do you know about the tune, OL, CL or SD? Did the tuner adjust the VE table, or just the MAF?

When I purchased my Vette, the tuner did a simple OL MAF tune and I had error on the MPG DIC readings vs actual. Now that I have put it back in CL and been street tuning, getting the Dynamic air and MAF air very close all the errors are more narrow. If its a MAF adjustment I feel since the MAF gives sloppier air reading my MPG's were off and worse.

Ask the tuner what he tuned, I'm guessing it maybe a MAF only adjustment. Also ask whether it's OL or CL. Nothing wrong with a good OL tune, much easier to get what you want in the tune, but I prefer a CL tune for the street.

foggy

I have contacted the tuner w/o response yet..
I will take this info to him & find out.
He used HP Tuners on the Dyno

I figured with LT, High Flo Cats, LS6 intake, 1.8 Roller Rockers and New springs w TI retainers, along with the existing cat back, cold air, 180* Tstat, That I would
gain some engine efficiency. Maybe or maybe not any MPG since mine was so good before.
I figured about 30-40 hp gain with mods would be about right..
And it pulls alot harder especially over 3000 rpm now..
I just didn't want to sacrifice my 27+ ish MPG for HP

insertclevername

I hear ya, I'm not expecting a gas saver, but I don't want to be absent MPG's on a daily if I don't have to be.

Hopefully your tuner is cool and can help get you your mpg back some. I would think with that much mpg loss, it's not in CL. But maybe he had to add that much fuel for the rocker arm, I don't have any experience with those.

Good luck!

enoniam

Why did you change injectors if using the same size? Most likely the DIC error is due to issues with the tune in regards to the injector parameters. Those same issues aren't going to help your fuel mileage, but there's likely other issues causing that large of a mileage loss.

foggy

I just wanted NEW Injectors as couple of mine "broke apart" taking them out after
17 years. I was able to get the AUS injectors at a better price and local than even
the oem replacements.. The AUS brand is supposed to be very well made & balanced.

I don't really "care" that the DIC mileage is OFF,... It was right on for 17 years before..
I really just don't know how I could have lost that kind of mpg.
The car runs fantastic, but that's a big penalty..
The 1.8 rocker arms on the stock cam would have only brought the lift up to around .525 ish and only added 1-2 effectual degrees to the cam.. So that shouldn't affect too
much.

Tiggerwelder

I haven't modified or tuned my '01 convertible yet, I have ported 243's ready to go on with Kooks long tubes and catted xpipe and a cam. I am not done tuning my Suburban yet, but I went from a stock flex fuel 5.3 to a 6.0 with new rings and bearings, a BTR state 2 truck cam, Speed Engineering long tube headers and off road Y-pipe. NNBS intake with new flex fuel injectors and the stock NNBS throttle body. I used a Corvette fuel pressure regulator as the rail mounted would no longer be used. Initially the mix was 10-11 to one AFR and about 9-12 mpg highway. A good baseline got me to 14.5-15.0 cruise and 12 on overrun and WOT, so I have more to go, but I recently went for a 90 mile run on two lanes through the mountains and highway back going 75-80 pulling a trailer with a two post garage lift and got 18.5mpg. That is as good or better than I got with the 206000 mile 5.3 before.
With no change to the overlap on the cam, you should really be a little better with the tune.