I've had my Magnum R/T for a month now, and I love the car, but naturally I have already started thinking about making it better! I have a few questions I hope you can help me with; I searched some Chrysler LX car forums on the net but I found the answers to questions similar to mine are all over the map! I've come to trust the input I get on Moparts while building my Mopar-powered Javelin, so here are my questions about my daily driver Magnum R/T

-The owners manual says 89 octane preferred, 87 ok. The previous owner says he has used 87 for years with no problem, so I have been doing the same. I don't notice any pinging or drivabilty issues. My question is, if I switch to higher octane fuel will the computer adjust ignition and fuel curves accordingly, or will it stay at the lower octane settings? I can see how it could retard timing if it detects detonation, but if it does not detect detonation will it keep bumping things back up? Or do I need to reset the computer manually somehow?

-I have already modified the airbox after looking at the small size of the air inlet and seeing how the SRT8 and aftermarket Cold Air Intakes work. That seemed to help a little...or maybe my car now just sounds less asthmatic when I lean on it! After looking at the exhaust it seems to me the giant 'suitcase' mid-muffler is restrictive, but the factory X pipe before the suitcase looks to be even more restrictive! I know X pipes are supposed to help low end torque, but the factory one just looks like the pipes are pinched together in the cheesiest way possible. Does it actually help or hinder performance? My gut tells me Chrysler did it just to make the car quieter by forcing each exhaust pulse to exit through 2 mufflers and 2 resonators instead of one of each. My thinking is to run a straight pair of 2.5" pipes from the junction where the factory x pipe hooks up to the downpipes/catalytic converters, eliminating the factory x-pipe and mid-muffler altogether and attaching the new straight exhaust pipes to the factory tailpipes and resonators. Does this make sense, and do you think the car will be too loud or sound crummy or throw weird computer codes?

Thanks in advance for your input!

I drive a 2007 Magnum R/T and I like it a lot. I have run 87 octane 99% of the time and have no problems. However I don't race it. Of course around here most of the 87 has ethanol and is probably closer to 89.
Bill

The X pipe works just fine... it doesnt flow like your
thinking.. it shuddles a PULSE back and fore when
they is a low on each side... that reduces the back
pressure.. the engine puter will try to increase timing
to get the max performance out of it.. if it sees
any detonation it pulls it back.... we spend a lot
of time on the exhaust to get the best performance
out of it for a reasonable cost and there isnt a lot
of stuff that is better without getting noisey or
sound weird
EDIT
Its not a race car by any means.. that thing is a tank

One thing to wonder about when changing the exhaust. What will it sound like in MDS mode when it has 4 cylinder shut off?

That is the only reason my 08 Ram still has the stock exhaust, i am afraid it will sound like a tugboat when in MDS mode.

Thanks, I am also worried about the sound with exhaust mods when the engine is in mds mode. Since the x-pipe is actually helping then I should probably just leave the exhaust alone. I am glad to hear the computer will self adjust back up for higher octane fuel after running 87...so my next question, how far will it go to take advantage of higher octane fuel? Will it actually take advantage of 91 or 93, or is anything beyond 89 a waste of money in my Magnum R/T?

Thanks. I will try a tank of 89, and if that shows improvement I will try 91. My gut tells me the single most cost effective thing I can buy for my Magnum is an electronic tuner.

Your car has mufflers in the middle of the exhaust and "resonators" at the back right before the tail pipes.

You can get more sound by changing the middle mufflers to something more performance oriented, but leave the reso's at the back as they cover up drone and MDS 4cyl noise too.

Think of the resonators at the back as your friend lol. Although they could possibly be replaced by something that flows better and still muffles drone/mds, but I have no idea what.

You can search for this stuff all over YouTube for sound clips.

I picked up .3 in the 1/8 mile with a diablo preditor. It can also hold custom tunes if you decide to change stuff later.

You hear a lot about custom tunes from this guy or that guy but the tunes preloaded in the preditor are as good as you can get. I ran the 91 octane/cold air tune and loved it.

I since added TTI headers and a Procharger and have had a few of the "custom tunes" from diffrent guys and there no better then the tune you get from Procharger that you upload into the preditor.

I wish i had the controll over the engine like the FAST systems I run on my hot rods. That would be nice!

Did you try Johan for a tune,about the only guy I trust for an email tune.

The 5.7 can gain a lot from a cam change but I can tell you that a cam change is a pain on these but should you do this swap out the timing chain with one from a 6.1.


And just an FYI,Johan works for diablosport,if I could ever get to Florida with my car I would have him dyno tune it instead of an email tune.

Thank you for your help guys! Nice to know the mid 'suitcase' muffler is straight thru. I would think other than sound volume and weight loss there is little to gain from removing it...though it would be nice if the car did sound a little more muscular.

I ran the tank of 87 fuel nearly empty today and refilled the car with 91. I did notice after a few minutes of drivng slow around town with 91 the car ran and idled a little more smoothly. I have been keeping track of my gas mileage since I bought the car; first tank got 21.17mpg and second tank was 20.54mpg. Compared to my Jeep this thing is an economy car! I will look into the tuner you suggested, it sounds like the hot ticket and likely the best value per dollar modification I can make to my magnum.

I aim to make my magnum run as well as it can without spending a fortune. I plan to take it to the track soon just to see how it actually goes...but mostly to learn more about drag racing before our '74 Javelin is ready. Are there some basic drag prep things you can suggest I do to my magnum before or at the track?

I aim to make my magnum run as well as it can without spending a fortune. I plan to take it to the track soon just to see how it actually goes...but mostly to learn more about drag racing before our '74 Javelin is ready. Are there some basic drag prep things you can suggest I do to my magnum before or at the track?

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Don't do a thing to it before taking it to the track for the first time, this way you can get a good baseline. Then once that is determined you can add things like a diablo tuner or cold air intake. You might want to play with tire pressure while you are there also and make note of each change. Also if better times are your goal, make note of the weather conditions, this has a big impact on what you run. The hemi is pretty sensitive to heat in the intake, so even a bag of ice between runs can make a difference (of course you will have to remove the intake cover for that).
What part of ontario are you in?

Good advice, thanks. I live in Niagara, so my closest tracks are in Cayuga and Lancaster NY. I might get to cayuga sunday if the weather holds up...