Sorry if I'm beating a dead horse with this, but I've recently discovered the joys of owning a F-150. I would like to put a true dual exhaust on my truck but a family friend told me that when he had put one on his (98 or 99 model) that he actually lost gas mileage. Has anyone else experienced this?

When he brought his truck back to the shop, he was told that the Fords use the backpressure to aid in the compression. Therefore when he freed up the exhaust, he lost compression along with gas mileage.

I'm not a mechanic by any means and still pretty new to the sport truck scene. Just looking for some input from other owners. Thanks guys.
Roush Racing Fan

 

Since you're new, I'll forgive you..... jk

Anyway, the theory is that if you lose too much backpressure, you will lose low end torque in these engines. The "extra" backpressure, somehow helps scavange the exhaust gases from the cylinders at low rpms, so the engine doesn't have to push it out or something like that.

I don't see how it would effect the actual compression ratio. The pistons, rings, heads make up total compression, as I understand it anyhow......

Since you now have less low end torque, it takes more gas to get you moving. True Duals should give you more high end power, but you have to be running at higher rpms all the time to really see it.

Some say the cats provide more then enough backpressure to maintain the low end, while others say it kills it...........

I had a muffler shop refuse to do the famous Flowmaster "Y" mod because he said you'll lose low end torque and you won't be very happy.........

This is just my understanding of it all. Other's will probably provide their own thoughts, which is what this whole forum is designed for. You'll just have to decide what's best for YOU!!

Again, welcome to the fun!!

Happy Trucking!!

 

I have true duals ran right off my headers. I did notice a little drop off on low end but if anything ive gained gas mileage, havent lost any. I ve had my true dual flowmaster 40 series for over a year now and noticed no loss in mileage. You will notice a little drop off the line , but you will gain more down the line. i would run true duals over a single exhaust.

 

Thanks for the input guys, I really appreciate it. In fact I just talked to a Ford mechanic yesterday about the matter and he says one of the main concerns is the placement of the oxygen sensors and having a cat to support a dual. If done improperly it can really screw up emissions. Of course all that may be a pitch to get the job done at a Ford dealership but it makes good sense.

I'm looking at putting a Borla system on my truck. My Dad has them on his Mustang and swears by them. For just pure free flow he says they can't be beat. Plus Borlas are stainless and I live pretty close to the beach, so that's a big advantage.

Good weekend all.

 

Did anyone use an X-pipe instead of an H-pipe for their dual exhaust?

 

Installed one about 3 months ago. No change in gas milage (it is still crap!!) 13/16. I have the 5.4.

One thing it did do was give my engine more power on the highway. It does not shift out of overdirve as much anymore. Plus it sounds cool ;-)

 

Your friend probally lost his gas mileage by laying his foot into that pedal that makes them pipes talk. Ive got true duels with 40 series flowmasters and thats what i lost my gas mileage to.Ive got a 4.6 and in town im getting around 11mpg on the road i got 18mpg in the mountains in north georgia.

 

Hello Dupre97,


If the install is done correctly you will not lose much low end torque. As MitchF150 stated, you need to have a good exhuast that will keep the pulse correct to help scavenge the exhaust gases out of the cylinders. What happens at low power is the pistons don't push the exhaust out of the cylinders, and a suction is created when the exhaust valve is open to help pull the expended gasses out. That is why you should install an x-pipe along with it to help even this pulse out. As the dealer said, having a good cat will help as well, but the cats on the newer trucks have much better flow from ones 5-6 years ago. Just don't go overboard on the diameter of pipe for the amount of power you are putting( or plan on) out or you will lose a lot on the low end. At 3000 rpm on up you will notice a large improvement on performance, and you will see the engine rev slightly quicker as well. When complimented with a good F.I.P.K. the performance will be even better.
There are serveral people on this board who have installed true dual systems and they may be able to help you with tips as to what worked on their trucks. Good luck on your decision.....