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Old 10-09-2008, 10:48 PM   #1 (permalink)
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Princess - '08 Chevy HHR LSSR
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Best MECHANICAL Mods

I am looking for the best MECHANICAL modifications to improve mileage. I have a 2008 HHR Chevy with the 2.2 engine. I bought it for better gas mileage and it fits my needs perfectly in most other areas to.
My question is: What can I do mechanically to improve the mileage? My thoughts are:
1. Slightly taller tires to lower RPM. Done
2. Lower car 2 inches all the way around. Done
3. Better Cold Air Intake. Done
4. Large exhaust and muffler to get rid of restrictive stock system. Soon.
5. Underdrive pulleys. Soon.
6. Front air Dam. Done.
7. Trifecta tune to correct fuel and timing curves. Soon.


I feel that by doing these things I should be able to get better mileage and performance. Sure the driver can make more of a difference but this thread is about mechanical improvements.

Any other ideas? Thanks in advance. Curly

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Old 10-10-2008, 12:49 AM   #2 (permalink)
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You may find folks chiming in to say that opening up the exhaust may hurt your fuel efficiency. Search around for "back pressure" here to see the various theories.

The cold air intake may not help either, though it's debatable how much it will hurt, if at all.

Other than that, your list is decent.
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Old 10-10-2008, 02:09 AM   #3 (permalink)
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Curly1 -

Welcome to EM! I am interested in your lowering + taller tires. My paranoia is that my "one size up from stock" tires would rub on the inside of my wheel well. When you got your HHR, did you have the impression that the wheel well had plenty of "room to lower", or ?!?!?!?!?

As already said, items 3 and 4 are debatable for FE. Another alternative to the Trifecta tune is a fuel controller. Here is one example (I am assuming this is compatible, you'd have to ask someone on an HHR forum) :

Apexi Digital Super AFC II - air/fuel controller - Apexi - $400
Quote:
Apexi 401A911
The Super AFC II (Air Flow Converter) is the industry standard for sub computer fuel control. The S-AFC II is designed to fine tune and "squeeze" power out of existing engine setups by allowing the user to modify the fuel curve with precision accuracy. Since the act of simply bolting on performance products does not make maximum horsepower, the S-AFC II allows the user to calibrate the fuel system in accordance with performance upgrades as they are installed. The AFC modifies the air flow meter/ pressure sensor signal voltage going to the factory ECU (Engine Control Unit) to change the amount of fuel injected
Here are their latest goodies :

A'PEXi U.S.A. - Products: Electronics

If I were "starting from scratch", this would be a serious option for me because I think it can also double as a ScanGauge.

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Old 10-10-2008, 07:12 AM   #4 (permalink)
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See here: 50+ Vehicle modifications for better fuel economy - EcoModder.com

They are all sorted into catagories and relative effectiveness.
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Old 10-10-2008, 07:44 AM   #5 (permalink)
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Lowering

The car rides much better and handles better with the Goldline lowering springs. The stock HHR would get blown around badly in cross wind or at higher speeds (60 and up). Now it is much better.
I also went with taller tires at the same time and not sure how much it has helped. I was so amazed at how much better it rode that I put the stock wheels and tires back on to see if it handled and cornered better because of the lowering or the tires. I think most of the improvement in ride is due to lowering. The stock HHR sits up too high with too soft of springs so I do not know if you would get the same improvments from your vehicle.
The tires should have a 10% speedometer error but I have not been able to verify that with my GPS. Seems to be closer to 5%? and that does not make any sense. According to several tire web sites and it says a 10% error.
According to my DIC the mileage is about the same but if there is an actual 10% error then in reality I have a 10% improvement?
Bottom line is I like the lowering and tires but the improvements is hard to say exactly how much. Curly
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Old 10-10-2008, 07:45 AM   #6 (permalink)
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Princess - '08 Chevy HHR LSSR
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Quote:
Originally Posted by Daox View Post
See here: 50+ Vehicle modifications for better fuel economy - EcoModder.com

They are all sorted into catagories and relative effectiveness.
Thanks, I found that after I posted this. I will read it again and start making a list of things to try. Curly
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Old 10-10-2008, 11:56 AM   #7 (permalink)
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Don't forget to inflate tires to max sidewall pressure!

I bet some rear wheel well covers would look good if you were to go that route. I saw a "base" HHR the other day. White in color and Panel Van in nature with the fact that there were only windows in the rear, doors and windshield of the vehicle. That one would've looked neat with wheel well covers in white!
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Old 10-10-2008, 04:09 PM   #8 (permalink)
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Curly1 -

Quote:
Originally Posted by Curly1 View Post
The car rides much better and handles better with the Goldline lowering springs. The stock HHR would get blown around badly in cross wind or at higher speeds (60 and up). Now it is much better.
I also went with taller tires at the same time and not sure how much it has helped. I was so amazed at how much better it rode that I put the stock wheels and tires back on to see if it handled and cornered better because of the lowering or the tires. I think most of the improvement in ride is due to lowering. The stock HHR sits up too high with too soft of springs so I do not know if you would get the same improvments from your vehicle.
The tires should have a 10% speedometer error but I have not been able to verify that with my GPS. Seems to be closer to 5%? and that does not make any sense. According to several tire web sites and it says a 10% error.
According to my DIC the mileage is about the same but if there is an actual 10% error then in reality I have a 10% improvement?
Bottom line is I like the lowering and tires but the improvements is hard to say exactly how much. Curly
Thanks for the info. Some cars come with odometer error "built in", . That could be contributing to what you are seeing. If I had done things squeeky clean to begin with, I would have done a GPS check with my stock tires to have a baseline for my odometer. But, I wasn't as obsessed with MPG back then.

It's not a mechanical mod, but I agree with TomO regarding rear wheel/fender skirts. I know I have seen PT Cruisers with aftermarket fender skirts, so I would think the same would be available for the HHR.

CarloSW2
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Old 10-10-2008, 04:21 PM   #9 (permalink)
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nice list and even nicer lip. It goes well with the drop.
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Old 10-10-2008, 07:37 PM   #10 (permalink)
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Curly1:

Welcome to EM.

I'd recommend going back to the original diameter tires. That's one thing the factory generally gets right. Bigger diameter tires reduce MPG because oftheir higher rotational moment of inertia. Lots of pickup guys thouight bigger tires would help but once they correct their odometers, they find it got worse.

Smaller diameter wheels/tire aid the aerodynamics as well.

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