Headers make bad MPG'S?

**kensz28** · 11-28-2008, 07:34 PM

Hey all. I have not been on the site in a while and thought I'd drop in and say hi. Anyway my question is regarding my 95 LT1 buick roadmaster. It sports a .030 overbore, aluminum heads, hooker headers, cold-air intake and 40 series mufflers. I have all new knock sensors, idle air control motor, o2 sensors and all the usual stuff, plugs and wires etc. Anyway, I've had the headers on about 6months and all seems well. I have 20's on the car and I lost 3-4 hwy mpg putting these rims and tires on the car. I got 26 going to ATL once with the factory 15's on it once. And after the rim/tire pkg I was getting 22 tops. Now it seems like even with all the new stuff (yes fuel filter is new) I can't get over 15mpg mixed driving. I know you LS1 guys get a pcm retune after headers and other mods and was wondering should I look into this? It actually seems like the mileage went downhill after the new o2 sensors if that makes any sense. The car runs awesome and idles smooth and shifts out perfect. It runs better than my 98 M6 Z28. Any thoughts? Thanks again.

**JaycenK** · 11-29-2008, 01:01 PM

what gear do you have in the rear end?
What profile tires on the 20's?
A tune may help because I just did long tubes on my Camaro with no cats and no tune and it is using more fuel.
Tire size may have you way down on your final drive ratio as well.

**SS02** · 11-29-2008, 01:14 PM

Originally Posted by kensz28

Hey all. I have not been on the site in a while and thought I'd drop in and say hi. Anyway my question is regarding my 95 LT1 buick roadmaster. It sports a .030 overbore, aluminum heads, hooker headers, cold-air intake and 40 series mufflers. I have all new knock sensors, idle air control motor, o2 sensors and all the usual stuff, plugs and wires etc. Anyway, I've had the headers on about 6months and all seems well. I have 20's on the car and I lost 3-4 hwy mpg putting these rims and tires on the car. I got 26 going to ATL once with the factory 15's on it once. And after the rim/tire pkg I was getting 22 tops. Now it seems like even with all the new stuff (yes fuel filter is new) I can't get over 15mpg mixed driving. I know you LS1 guys get a pcm retune after headers and other mods and was wondering should I look into this? It actually seems like the mileage went downhill after the new o2 sensors if that makes any sense. The car runs awesome and idles smooth and shifts out perfect. It runs better than my 98 M6 Z28. Any thoughts? Thanks again.

My Long Tubes were dynd in with a tune and a bit of other stuff... but after the tune I was better gas miles... alittle bit better on the highway and more in the city!

**kensz28** · 11-29-2008, 05:51 PM

Stock 2:56 open rear. 255/35/zr20 tires. Side by side they are exactly as tall as the 235/70/15 or whatever was on it before. Just a bit wider. 20x9 rim. I had a chance to score a 9C1 rear from pull-a-part for $74.99 w/exchange and didn't do it cause I don't own a truck. DANG DANG DANG!!!!!! That would be at least a 3:08 or 3:23's and posi to boot.

**c5z28** · 11-29-2008, 06:27 PM

If you haven't gotten a tune since the rims ands performance parts you need to get one. Headers help the car breathe easier and will help mpgs if your good.

**LT1 > LS1** · 11-29-2008, 06:59 PM

tune will fix your mpg's for sure. the o2 sensors arent used to whats going on. they have been relocated, and have much more air around em.

I noticed a gain in power, and overall engine behavior after the tune. a good dyno tune is totally worth the money

**kensz28** · 11-30-2008, 06:40 AM

Originally Posted by LT1 > LS1

tune will fix your mpg's for sure. the o2 sensors arent used to whats going on. they have been relocated, and have much more air around em.

I noticed a gain in power, and overall engine behavior after the tune. a good dyno tune is totally worth the money

That does make sense. The increased airflow alone probably makes o2 sensors think it's running lean. Thanks.

**hot93rod** · 12-27-2008, 04:41 PM

One more thing I'd say is that with heavier wheels/tires I'm sure that is hurting your mpg. I had a v6 mustang when I was younger w/stock 15's, went to the cobra 17's, and the car was noticeably more sluggish... never watched mpg on that, but I know that it took a toll w/much more rotating mass. Hope this helps too...

**t-rock** · 12-28-2008, 05:58 AM

talk to ed wright at fast chips in tulsa he will tell what you need to do.

**grandkodiak** · 01-12-2009, 01:15 PM

check the gaskets and bolts, aftermarket header bolts walk out like they dont belong! check to see if they are tight, and put some soapy water bubbles on the outisde of the gasket check for leaks... if the headers are suckin in air it will also confuse the o2s into pushin more fuel to compensate thinking you are lean.

**kensz28** · 01-12-2009, 07:27 PM

Originally Posted by grandkodiak

check the gaskets and bolts, aftermarket header bolts walk out like they dont belong! check to see if they are tight, and put some soapy water bubbles on the outisde of the gasket check for leaks... if the headers are suckin in air it will also confuse the o2s into pushin more fuel to compensate thinking you are lean.

I did find my nice Mr Gasket Ultra Seal gaskets leaking on the driver side. I have a set of o-ringed copper gaskets on the way.