whitetaco02

I have an 88 4runner, 22re, at, with a LC header, hi-flow cat, and a FM 60 series delta flow muffler. my gas mileage SUCKS!!!!!!!!!!!!!!

(I have changed out the fuel filter, PCV valve, 02 Sensor, etc..)

My question is: Is there such thing as having (not enough backpressure)? If that makes sense. Could this be my problem? I am thinking of getting my muffler guy to put a stock muffler back on. How will this affect my truck with the LC header and hi-flow cat? I can't stand the noise of the FM so I have to get rid of it. Will this help me out in the long run putting a stock muffler back on? Any advice would be greatly appreciated. Thanks!!

WATRD

Yes. Intake, engine and exhaust are a system. Changing the balance has an effect, sometimes that effect is something you are trying to do, sometimes its an unwanted side effect.

What you are describing is certainly possible. The only way to know for sure is to make the change and take measurements again.

X-AWDriver

Actually too much flow can hurt MPGs due to the engine (naturally aspirated engines are much more affected) not getting enough torque down low thus forcing you to use more skinny pedal to get up to speed.

rdharper

Basically back pressure is wasted energy. However there is the question of resonance, a sweet spot where pressure is minimum. This would be a "tuned" exhaust.

It is also possible you are taking advantage of additional power of course, without realizing it.

rdharper

Probably should have mentioned that resonance can actually improve power and mileage, ie: efficiency.

Here is a link for a pretty good explanation: http://microcarproject.tripod.com/ht...ust_system.htm

Also note that the opposite can be true. An improperly tuned exhaust can work against you.

4Runner1988

Sell me your bull bar and then you can buy more gas!!!

Could the AT also be a factor...?? Never been in an Auto 22RE.

trythis

If you open your exhaust too wide too fast, it will cool down too fast and get denser closer to the head. You want hot headers, (this is why they are wrapped by some people) to promote fast moving air. Cool air moves slower. The cast iron 22re manifold is a very well designed exhaust, and doesn't need replacing unless it is broken or you put a turbo, or a blower on it. Read this linked thread below at 4x4wire and you can see that the best setup for the 22re is stock manifold, 2" to cat and 2 1/4 cat back.
http://www.4x4wire.com/forums/showfl...&o=365&fpart=1

Once you are past the cat, the heat is going to be pretty ow and you want to open it up.

If you read all of EB's comments, you can see where I am coming from. If you are running your truck at ridiculous high rpm (as in racing) your exhaust is a good setup because so much air is moving through. Street driving it is probably creating more "back pressure" with the cold air at the header.

whitetaco02

ThanKs Rob for the reply. I am going to get it done as soon as my dang state tax comes in. lol I just hope it helps me out in the long run.

whitetaco02

that makes sense. I have to fill up every 170 miles or so. My gas mileage is horrible!!!!

whitetaco02

thanks for the link!!

whitetaco02

LOL I hear ya on the bull bar.

I do hear that the AT does suck as far as gas guzzling goes but I wouldn't think it would be that bad. The MAIN reason I want to put a stock muffler back on is due to the noise factor. It is annoying and embarrassingly too loud. If it helps out with the gas and HP issue than that is even better!!! I am just hoping I can "kill three birds with one stone" if you know what I mean.

whitetaco02

thanks for the link. The main reason i got headers was I had a pretty bad exhaust leak and i wanted to eliminate the problem all together. i still have the stock manifold but i spent WAY too much money on the headers to get rid of them.

will a stock muffler with the rest of my set up be a bad choice or is that just something that I am going to have to figure out once I do it?