Top Speed & Fuel Economy

[ljbprrfmof]

I have had a CSX-T for about 10 years now. It had 33,000 miles on it when I got it and now it is at 62,000. My question is what kind of top speed can I expect from it. When I first started driving it, I was only able to get about 101 mph, down hill on the Interstate, with a tail wind. I added a MOPAR Performance computer and a K&N filter element, increased the injectors one size and now she tops out at around 110. After replacing the head gasket and radiator, lol - love boost, the performance is still the same.

The second question is about fuel economy. I consistently average 17-18 mpg with the car. I get kind of jealous reading the posts here about TD's with all kinds of horsepower, able to do 10 to 20 mph more than me, and still realize plus 20 city mpg. I have a short 5 mile commute, so I know the engine is not getting all the way up to operating tempurature until I am over half way to work/home.

I also feel that injectors have the car running rich. It was my understanding that it would lean out if I installed a better breathing exhaust, which should help mpg and mph.

Last night I was on researching this and found my way to Donovan's Dodge Garage. There I discovered the turbo on my car is the mitsu which he does not reccomend using.

I have toyed with the idea of intercooling, but I am not sure what all I need to change after adding the intercooler and its plumbing, and of course the exhaust system upgrade.

What should I expect for mph and mpg? What are the ideas out there to improve my CSX-T's performance?

[tryingbe]

5mile drives is what kills your gasmilage, not much you can do about that.

[ljbprrfmof]

Yeah, I know that. I tell my customers that all the time, especially the fact I can never get the rated fuel economy on the new cars, then I show them my big foot. But even when I concentrate on economy for a tank full it rarely comes back at more than 18 to 19 mpg. On a rare occassion, if I do a lot more driving on the highway, it will sneak into the 20 - 21 mpg. Maybe I need to, ugh, install cruise control.

[tryingbe]

Have you done stage 0 yet? Plugs, cap, rotor, wires, cam timing, spark timing, good tires pressure, etc...

I usually get 23-25 mpg city in my Daytona Shelby, but my commute is 14 miles one way.

[bfarroo]

The exhaust will help quite a bit on fuel mileage. Also the larger injectors are probably killing your mileage. I'd definitely open up the exhaust and get a cal to optimize the injectors along with a IC of some sort even if it's a stock rad/IC combo. Also a lazy O2 will kill mileage along with a plugged cat. You should definitely be getting better mileage than that especially with a 5spd. Should be around 30hwy if your just cruising.

[The Pope]

so you added a mopar computer and +20s then? You dropped your AF ratio instead of slightly leaning it for more power. You are now too rich and the engine isn't making much power at the same boost levels. First take out the bigger injectors and run the stockers and try it. I've driven stock CSX-Ts at 125 MPH and at part throttle stock. They easily have the power to go 150, they are gear limited. More power just gets you there faster.

[ljbprrfmof]

Quote:

Originally Posted by tryingbe Have you done stage 0 yet? Plugs, cap, rotor, wires, cam timing, spark timing, good tires pressure, etc... I usually get 23-25 mpg city in my Daytona Shelby, but my commute is 14 miles one way.

Yes I have done this stuff. New timing belt a couple years ago when the original broke. Thank god for non-interference engines.

[ljbprrfmof]

Quote:

Originally Posted by The Pope so you added a mopar computer and +20s then? You dropped your AF ratio instead of slightly leaning it for more power. You are now too rich and the engine isn't making much power at the same boost levels. First take out the bigger injectors and run the stockers and try it. I've driven stock CSX-Ts at 125 MPH and at part throttle stock. They easily have the power to go 150, they are gear limited. More power just gets you there faster.

When I put in the injectors and the computer, the car was burning out map sensors like it was eating candy. This solved that problem.

So I think you have answered both questions for me. Stock injectors, more exhaust flow. Would you go with a 2 1/2" or 3" exhaust?

And what is the solution for the gearing?

[mattsnewcell]

To get a more top end gearing you can either A. a new transmisson or B. rebuilt tranny with new gears, dont know which would be easyier. Maybe im wrong, If so someone else will know hope i helped

[ljbprrfmof]

That is what I figured too matt. I was hoping for advice for the specific tranny/differential combo. I believe the general rule of thumb when considering just the gearing, is you give up top end for acceleration and vice versa. My GTX stick shift has 3:55 rear gears for a nice blend of acceleration and top end.

[mattsnewcell]

What trans came in your car stock? And yes you'd lose some power off the line for sure

[ljbprrfmof]

When I pull the build sheet up on the Chrysler dealer service link, I get sales codes only now. It was code DDF. I am guessing it is the 520.

[crazymadbastard]

Yeah your car is not running right for sure, I used to get to 120+ on my t1 mitsu 88 lebaron. Are you sure you did not mean o2 sensors burning out instead of map sensors?

[The Pope]

you have to run a 3.05 gear A525 or a A520 with 3.50 gears. The A520 is most likely what you have and you should hit 140, 160 with IC. Also with a A520 the OBX posi is a drop in, very nice. I would run a Konig feather wheel like mine with the same size tire. I run 17X7 feather with a 40 degree offset. Then the best tire and the only one in the size is a 225 40 17 Nitto 555. The tire will slightly raise the gearing and will make the car safer at those speeds. Handling is unreal, I have them on my 89 CSX now.

The car runs too rich under boost stock, the MP computer leans it for more power. You went the other direction and killed power with fuel. Your computer was no dout toast, any excuse for a performance computer is good enough. Burning up maps and you already have +20 injectors I would buy a FWD stage 5 computer for 18 PSI for use with your +20s, then add a 3 bar map and an intercooler.

3" exhaust rules but is costly, you no dout have the tiny Mitsu turbo as well. Get a T2 Garret or a new S60 before you buy 3". Top speed will get hurt by the turbo someday, consider the Garret type upgrade. With the miles the car could be pretty nice and worthy of a new S60 from turbonetics.

Your car stock is a 30 MPG car, something isn't right. The MPH is way off, stock they cruize at 125 with no effort at all, like a high idle. Plugged cat? 02 sensor is toast? If your computer was sending out the wrong voltage and eating maps what else did it eat? Like home computers when the board goes it eats everything plugged into it normally. I would look at the cat and look into new sensors.

[ZoskalonMPI]

I made it to about 105mph in my TBI Daytona until it just coudn't suck any more air. Once I stuck the MPI manifold, I made it to 110mph once before I hut a curve. Hahaha, nothing like doing 130 in my R/T until the pisspants-limiter kicks in.

Make an adapter and a 2 foot spacer for your lugs so you could put rear tracker wheels on the front. Then you'd be hauling ass at 300+mph