More '03 Marquis Exhaustion

[VinnyG]

I'm starting to create a plan of attack for improving this car. I'm pretty conservative when it comes to such things - more a tweaker than customizer, I guess. Anyway, I'm considering a stock single to factory dual upgrade. 2", and I don't want to get into the relative merits of different pipe diameters, thanks, there is plenty of that debate for everybody in the "other" thread on this subject. I figure factory dual is a good, cost-effective way to make a small improvement in engine respiration and economy. My main question centers on that last assumption. I've read that factory single to factory dual in this car is worth about 11HP. Now, in my yoot, on carbureted, non-computerized cars, that would have also equated to a slight increase in MPG, with the variable being the scale of carb rejetting, if any. I'm not sure how that plays out with PCM tech. Would I see a (SWAG) 1 - 2 MPG increase, or would the 'puter just "see" the restriction reduction and perform the equivalent of rejetting by richening my A/F mixture accordingly? If that is how it works, is there a potential change in programming that could "redirect" some of the breathing improvement to better mileage, and what would that cost me? Second question - do I assume correctly that this conversion requires an additional rear cat, and if so is it included in the Ford parts assembly for this job? Thanks.

-VG

[mrltd]

The h/y-pipe bolts on behind the cats. No changes of the cats required.

Yes, the computer will adjust the A/F accordingly. They gains are in the ability for the car to not have to strain as much to push the air out. The extra HP helps the car move without as much load on the motor-less load equals less enrichment-which means less fuel.

You could get a tuner and lean it out, not sure that will really help though.

I found that making a hot air intake increased fuel economy a bit. I put an aluminum dryer vent hose on the header and put the other end into the air box inlet. Was good for 3-5 mpg on my mazda.

[VinnyG]

OK, so my decision on conversion to duals should be based on overall performance considerations, not one item in isolation. Can't really complain about that. Curious about the actual workings of your Mazda mod - did it "fool" the computer into thinking that the ambient air was warmer (less dense) that it actually was, resulting in a leaner mix than would otherwise have been supplied? If so, I'm surprised that the reduction in overall efficiency helped, rather than hurt your mileage (kind of the corollary to speculation about adding duals to my car).

-VG

[Leafsrule16]

I just cut off my back two cats, took off my reasonators and swapped out the mufflers off my factory duals and noticed more power and gas mileage, i can imagine having a single to start off with would make an even more noticable difference. Try and get 2.25 inch piping if you can, 2 inch is pretty small.

[SVT98t]

I did stock single to dual on the Tank. Economy and power improved. I replaced from the manifolds back. The newer designed cat pipe only had 1 per side as opposed to two.
I ran stock h-pipe to 2 cheap Thrush turbo mufflers. Then, two over axle tailpipes without resonators, and topped it off with a pair Marauder tips.
I do not run egr or O2 sensors and I still get 20-21 city & 28 highway.
And it sounds good.
Check readers ride page for pics and videos. I think its page 7. I dont know....

-ryan s.

Sent from my VM670 using Tapatalk

[VinnyG]

I've seen several interesting set-ups documented here. Unfortunately, emissions inspection is pretty rigorous where I am (Joisey), and the Authoritah don't seem to be very tolerant of mods to standard equipment. I suspect that eliminating cats and/or sensors could equate to failure to pass, regardless of the actual gases emitted. Seems like a potentially more expensive experiment than I'm willing to make.

-VG

I did stock single to dual on the Tank. Economy and power improved. I replaced from the manifolds back. The newer designed cat pipe only had 1 per side as opposed to two.
I ran stock h-pipe to 2 cheap Thrush turbo mufflers. Then, two over axle tailpipes without resonators, and topped it off with a pair Marauder tips.
I do not run egr or O2 sensors and I still get 20-21 city & 28 highway.
And it sounds good.
Check readers ride page for pics and videos. I think its page 7. I dont know....

-ryan s.

Sent from my VM670 using Tapatalk

[SVT98t]

Well,technology has progressed a little since 1993. The Walker setup I bought was brand new. It eliminated the pre-cats. The catalytic converter thats in there is as efficient as the system Ford installed 19 years ago.

Sent from my VM670 using Tapatalk

[sly]

as long as you have the equipment hooked up and cats (replacements or stock) putting some better flowing mufflers on and old car should pass no issues. If they ask about it... say the old ones rusted out and you got better ones. (would be truth from me about my 88... better ones included an H-pipe and driver side exhaust).