Grand Prix MPG/RPM

[troy1]

99 3800 S II
23/24.5 MPG @ 80 turning 2400

Whats everyone else getting

Also how may people have replaced thier MAP sensor?

[tobster1911]

On the highway my '98 GTP gets 30+mpg (best of 34.5mpg) while doing 80 @ 2300rpm. Sounds to me like you have a problem (unless you are upgraded heavily).

[Langning]

Originally Posted by tobster1911

On the highway my '98 GTP gets 30+mpg (best of 34.5mpg) while doing 80 @ 2300rpm. Sounds to me like you have a problem (unless you are upgraded heavily).

Is this what's displayed on your DIC or you actually got over 500 miles on a full tank?

For my 01 GT, the best I did was 390 miles on 15 gals (or about 26mpg) of 2/3 highway driving @75mph...

[BNaylor]

This is just my two cents worth but you guys with GTPs have to realize that the GT and GTP will get different gas mileage especially highway. The supercharger becomes almost irrelevant at cruising speeds. It only has the load equivalent of 1 horsepower.

The main reason why is the GT has 3.29:1 final drive ratio gearing and we GTP owners have 2.93:1. If you don't get around 30 mpg highway on a GTP there is something wrong. I've made it from El Paso to Phoenix which is 475 miles one way on one tank of gas and that was hauling a%$.

I can't speak for the GT owners because I don't have one.

[troy1]

huh that sucks might have to sell me GT and get a GTP. I would of figured that GM would of made the GT with the 2.93-1 and the GTP with the 3.29-1. The GTP is more of the high performace of the two. cant believe that that small of a gearing change can make the MPG suck like that. Personally I still think something a little wacked on my GT I think it should get 26-28 atleast. Does GM want you to use anything other than iridium plugs or can you use platinium?

[apkcobra]

I have an 01 GT and my console dealie shows that i get about 30 highway, and thats going at least 75.

[BLKCOMPG]

I drive a 04 CompG GTP and I only get about 23 MPG @ 75MPH, but for some reason I get about 36 going about 50-55 MPH?

[Langning]

Originally Posted by BLKCOMPG

I drive a 04 CompG GTP and I only get about 23 MPG @ 75MPH, but for some reason I get about 36 going about 50-55 MPH?

That might have explained why I am consistantly getting 25-26mpg as I alwys drive @70-75mph. On my interstate where every car is doing 65 to 80 mph or more, doing 55 is too unsafe...

BTW, my RPM is 2200-2300 @65mph and reach 2500 @75-80mph... I was trying to pass a slow car (55-60mph) this morning, my car couldn't get pass 3000 rpm when I pressed down my gas; it accerated very slowly and eventually dropped back to <2500 after it reached 75mph... Is this an engine (low compression) problem?

[BNaylor]

Originally Posted by BLKCOMPG

I drive a 04 CompG GTP and I only get about 23 MPG @ 75MPH, but for some reason I get about 36 going about 50-55 MPH?

The '04 GTP Comp G is supposed to get better gas mileage than it's predecessor but I don't know if that really is the case. As usual too many variables. Pontiac went with differerent final drive gearing for your model. If you check your regular production codes (RPO), I believe you will find that you have 3.29:1 gearing unlike the 2.93:1 of the '97 - '03 L67 GTPs.

[richtazz]

To put things in perspective, if you take the difference in gear ratio's (3.29/2.93), you get a difference of 1.12, or 12%. So with everything else being equal, a GTP should get better mileage (taking Bnaylor's [Bob's] figure of 1hp parasitic draw at cruising speed as the gospel). Don't forget that GTP uses premium, and our GT's use regular, so the cost is less per mile for the GT when you factor in the more expensive fuel cost for the GTP. Your 23-24 is way low, as I took a trip with my 99 GT to Tennessee (from Michigan) and got better than 32mpg on the highway @75mph(including some mountain hills). I would suspect a tune-up is warranted,(plugs wires, fuel filter, PCV) and don't forget the PCV valve, as the MAP sensor get's it's vacuum thru the PCV, so if i't mucked up, mileage will suffer. As we've discussed on here before, stick with OEM Delco plugs and wires, as there is no reason to use gimmicky, multi-electrode plugs and "spiral core" fancy-schmancy wires. The only reason to change from stock is if you're modded.

[BNaylor]

Originally Posted by richtazz

To put things in perspective, if you take the difference in gear ratio's (3.29/2.93), you get a difference of 1.12, or 12%. So with everything else being equal, a GTP should get better mileage (taking Bnaylor's [Bob's] figure of 1hp parasitic draw at cruising speed as the gospel).

CAUTION: Don't take everything I say as the Gospel..lol.

However, the spec for the M90 Gen3 does come from the horses mouth Eaton.

But based on my experience a GT should get better in city only and overall combined city/highway fuel economy over a GTP. In city only I am lucky to see 18 mpg. And that was before mods so I don't even consider fuel economy on it anymore.

[troy1]

I went with the NGK G power plat. 3 bucks a plug I didnt want to spend 7 bucks for delcos. I've done a tune up, Delco wires delco FF NGK Platinium plugs (just switched from NGK TR55 Copper I hope this will help) I have not changed the PVC yet. Tires all aired up new purolator AF 10W30 Havoline and a Delco oil Filter. Had it hooked up to the Snapon scanner at work just dont see anything wrong??? Oh threw a Borg O2 sensor at it for shits and giggles. Engine is good and strong uses no oil only got 79K tranny works like it suppose too.

[ericn1300]

i just bought my 96 GP SE 3.1 late this summer with 183,000 miles on it. checked my freeway mileage by fueling up at the on ramp and doing a round trip of over 250 miles with only about 6 on city streets at the turnaround. I got over 27 mpg with the cruise control set at 80 most of the way. high desert driving, the speed limit here is 75 but the state police report that the average speed is now 79.6 mph. with 20% driving at 60 mph i guess another 20% must be doing near 100. i even got passed twice by an H2 while doing 80 on that trip. i think he had to pull off for fuel and got behind me again.

[Niq]

I have a stock 02 GTP engine. Except for a K&N (square) filter. I can routinely get over 30 mpg on the highway, with cruise control at 75mph. I have 30k miles on the car. And I measure gas mileage with the trip odometer, and re-filling the tank full. I'm not sure if I trust the dic... But it looks close.

Without doing a cost analysis (boring), isn’t cheap gas and premium gas the same in terms of highway mileage. With cheap gas, you pay less, but get less power from it, and with premium just the opposite. I wonder if you put premium in a GT, you would be much closer to the 30 mpg mark? <Shrug?>

[BNaylor]

Originally Posted by Niq

I wonder if you put premium in a GT, you would be much closer to the 30 mpg mark? <Shrug?>

I don't know about using premium but it wouldn't hurt to experiment but in the end will the extra cost be justified as pointed out. The closest thing I have to a GT is my wife's '99 Regal LS. Same NA engine/tranny but with 3.05:1 gearing. When we use regular the combined city/highway mileage was around 24 mpg. When we use mid-grade it averages 25 - 26 mpg. Haven't taken a road trip in a long time in it so I don't have any highway data. That is a difference of 34 extra miles per 17 gallon tank but it's a $1.70 more for the full tank of mid-grade.

Here's a current pic of my DIC on my GTP with in city only. Anyone else care to fess up?