1988 grand marquis mpg

[99grandmarquis]

hey i have have a question if i stright pipe my 88 grand marquis with cats on will i get better mpg

[DuceAnAHalf]

nothing that you will notice

[Nathan in MI]

The money that you save in gas will end up getting spent on ear plugs. :p

[gadget73]

no, actually you'll probably lose some mileage since you'll lose the backpressure and reduce the low end torque

[99grandmarquis]

The money that you save in gas will end up getting spent on ear plugs. :p

good thing ear plugs r cheep but i think it should be a little bit better because of less restriction

[Archangel]

no, actually you'll probably lose some mileage since you'll lose the backpressure and reduce the low end torque

Then would you care to explain what is it that you achieve with upgrading to bigger pipes? Cause you can't persuade me that a set of dual 2.25s flows less than a stock 2" setup... Now if he was removing the cats as well, and the tails while he's at it, then yes, he'll be a bit low on the low-end torque, but he's keeping the cats on, and all the kinky-bent tails as well, so methinks he'll be good. And FWIW, when I was running cats and dumps car actually accelerated better than the stock single exhaust, when I removed the dumps and cut off after the cats torque went to shit, but the fuel economy didn't change noticeable, if at all. Also, it was with the glasspacks and dual 2" pipes that I got those few 26-28 mpg freeway runs, tho that's more of a freak of nature than anything else...

[mrltd]

It'll just sound like crap and run a hair better. Probably not any gain in milage though.

[Brandon]

I had took the cats off my car, and ran dual exuast out the bumper with Fowmasters, and I can feel the difference in power than before. If you run straight pipes you better check and see if there's a limit on how loud your car can be.

[88Vic]

I used to have a Magnaflow muffler and tailpipes (cat also removed) but they have since been removed so I have nothing but a 3" straight single exhaust. It's loud and untoned (I still think it sounds decent, better then any loud 4banger and most 6cyls) and i'm pretty sure my mileage dropped an mpg or two. I'm putting the tails back on with a Flowmaster 40 to get some backpressure for more power and mileage.

Do you want to put in piping where the muffler(s) used to be and keep the rest stock or remove everything from the muffler(s) back?

[99grandmarquis]

basicly what im doing changing the y pipe to a h pipe so ill have duel im gunna leave the cats on and get rid of the muffler and pipes out the back or buy 2 flowmasters off my brother but he doesnt know what ones they r they just say flowmaster on it off his part car 86 mustang and doing that it not on the road yet so i half to do it after i get it cert and e tested in sept

[Archangel]

If you run straight pipes you better check and see if there's a limit on how loud your car can be.

I wouldn't worry about the noise levels too much - when I wind it up my engine screams more than my exhaust roars. Besides if the car sounds good even if tis a bit too loud the cool factor plays in your favor - don't drive like an asshole, and cops will leave you alone.

[Mr. Land Yacht]

you would feel some difference in mid range-top end but you will lose low end due to less backpressure(like gadget73 said).

I had totally straight duals on my Magna...shorty headers, no cats, duals with no mufflers(except glasspacks up front) gas mpg wasn't any better than before. When I put on some chambered mufflers to restrict it a tad I noticed a BIG jump in low end power..off the line it was quicker for sure.

[Tiggie]

The factory says you'll gain 10 horses and 10 ft-lbs with duals over single exhaust. I'd say that's close to accurate.

I just put full duals with Cherry Bomb Glasspacks on my wagon (cats still intact). I can tell you it doesn't run noticeable better on the highway. It does a burnout much easier now, though. I haven't checked MPG, but I doubt it will be anymore than 0.5 MPG increase, if anything.

The car wasn't really loud straight out of the cats. Loud, but nothing that would get you a ticket around here. Throttle response seemed improved with it running without the rest of the exhaust, though. Here's a link to a video of it: http://videos.streetfire.net/video/1...ria_178194.htm

[gadget73]

Factory also mentions that the torque and horsepower peak move upward by a couple hundred rpm, mostly due to the change in exhaust flow. Its not a negative thing though, the stock cam makes torque at such a low RPM that moving the peak upward by 200 rpm is not really noticeable.

In a general way. small exhaust is good for torque at the low end, big flow is good for high RPM horsepower. The smaller pipes create more exhaust velocity, which will actually pull a very slight vacuum in the cylnder due to exhaust gas momentum. Unfortunately the small pipe diameter begins to cause a restriction when you start trying to move more air through the motor at higher rpms. Big pipes don't give that low rpm scavenging effect, but they aren't a bottleneck for performance either. The stock duals do fairly well for a stock motor, but if you want to go beyond that, you really need more exhaust. The stock tails have a lot of twists in them, so it really screws up the flow. The stock mufflers are quite frankly awful, they're about an inch diameter internally.

[Archangel]

Yeps, that's why you step down the piping, to keep the velocity up as the gases cool down. For a 350/351 engine I'd go with headers, then 2.5" pipes, 2.5"in-2.25"out mufflers, then 2.25" tails. For the 305/302 engines I'd probably go 1/4" down in diameter in all pipes. Best-torque-wise mild-small-block exhaust seems to be the one with the headers, 2.5" midpipes, Flowmaster Y-collector, single 3" pipe, high-flow muffler, and finish the system to your liking - that's a setup very popular among the Bronco crowd, not so much with the halfton F-series and Chevy trucks, not sure exactly why...