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Discussion Starter · #1 ·
I just got my 2005 GTO 6 speed yesterday and have put about 90 miles on it so far. The car has a cam with the following specs, " 330/228 * 113 (including springs, pushrods, timing chain, crank bolt)". I have been babyin the car as the dealer filled it with midgrade gas; and with the cam I figure premium is a must so I havent got on it more than once or twice. I know cams hurt gas mileage but Im literally averaging about 12mph in a mix of city and highway and the highest I can get the instant econemy to go is about 25mpg and thats in 6th gear at 45mph! As far as I know the cam is just a moderate or modest hp adding cam, I dont know to much about them. I bought the car from the local Pontiac dealer and im contemplating trying 2 have them put the stock cam back in if this mileage continues. I cant see gettin more than 18mpg on the interstate with how its doing so far. Its guzzled down 1/2 a tank in about 90 miles! I cant imagine how bad the mileage would be if I got on it alot. The two times I did floor it so far I literally saw the needle drop as I accelerated! Its idling at 1000rpm which I figure could be part of my problem, what is the normal idle rmp for a stock GTO? The only other mods that I know of are x pipe and high flow cats. The dealer did note the rear end has been opened on the car so maybe gears are a possibility but my rpms are still very low in 6th gear. The previous owner posts on here tho and he didnt mention gears as being one of his mods. Any advice would be greatly appreciated.
Andrew
 

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Well my advice might not be something you want to hear but I would not have purchased a used GTO with mods only because you know the previous owner probably tore it up to say the least, but you really never know.

With that being said, the stock idle is between 750 and 800 rpms. I've heard some at 750, while my stock 06 idles just over 750, around the 800 mark. I only have 850 miles on her so far and am still adjusting to the differences between her and my 1990 5.0 Mustang that I modded to hell and back.

A cam will definitely lower your gas milage but I'm not sure how much exactly. You should get ALL of the details on your vehicle, any documentation you can so you know exactly what has been done to the car. You can't buy a high performance car like the GTO, especially after being modified and not know what you are getting into.

I'm not trying to be a jerk but you really should do some research about why the rear end was opened and so forth.

How many miles are on the Goat?
 

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It would also be interesting to see how many rpm's you're turning in 6th gear at 60mph- - -my guess is there may be something done to your car to improved the hole shot that's costing you in mileage.

Most people don't buy these cars for mileage anyhow. Buying a modded car and then wanting it to get advertised mileage (that from all mfg.'s is always a best case scenario) is not reasonable.

Premium gas may help you, or may not.

I can tell you my stock '05 M6 easily gets 25 mpg on all Interstate driving, and it has from the day I bought it. That's driving it conservatively tho- - and paying attention to what's going on up ahead to avoid hard braking, etc.

I try to drive conservatively on highways like this (although I do drive around 75 mph) and that let's me have more fun at the stop lights. I'm averaging 22 mpg per tankful.
 

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Discussion Starter · #4 ·
Thanks for the tips, I did do research on the car tho I found the previous owner on this forum and read all his posts etc so I know what was done to the car and its history. It has 8900 miles on it right now. Before it was traded it had long tubes, cold air intake and high flow cats, so the only mods still on it are the cam and the x pipe. It also has nitto 555's on the rear. I know it was traded for an automatic cause the previous owner injured there knee. I know where all the mods were installed and where it was tuned etc. Do you think it could be running really rich cause it was tuned for the mods and I need 2 have it re tuned? I know I shouldnt expect advertised mileage but I definatley wasnt expecting to lose 10mpg on the highway cause of a cam. I cant tell you for sure but the revs on the car at 60mph in 6th gear are probably around 1400 or so. The slowest I can go in 6th gear is about 40-42mph before it starts hesitiating at 1000rpm.
 
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