dkersten

I know that most of the answers I am looking for can be found here, but after hours of browsing, I am still unsure, so I figured I would ask my questions in one post, and hope that people with experience could help point the way.

I just purchased a 2006 Mustang GT convertible. It is on its way, and I am starting to put together my game plan as to what modifications I would like to make.

First, let me start by explaining what I am after. I purchased this car as a toy that will probably see less than 1000 miles per year. I live in Montana, at about 4000 feet of elevation, and here the winters are totally out for driving a car like this, and the early spring and late fall are pretty much out as well. Mid summer is usually brutally hot with 100+ degree days and because of the relatively clean air and high elevation, the sun is very intense on days like this. So my window for enjoying this car is limited to the milder days between 65 and 95 degrees, free of rain and snow, usually restricted to late spring to early summer, then late summer to early fall.
I will likely take short road trips (mountainous highway roads) where I could spend hours cruising at ~80ish mph. I will probably never race (well, maybe to put some ricer kid in his place) so I am not looking for race oriented mods (ie nitrous). I do love horsepower though, so I will probably always be looking for another power upgrade.

That being said, here is what I am after:
First thing I will do when the car arrives is hit the wheel/tire shop. I will probably put 19's on with a tire diameter that is similar to stock. Likely I will be looking for an 8 or 9" tire width in front, perhaps a little wider in back.. not gonna put many miles on so I dont worry about having to rotate tires.. Any recommendations on tires? I do plan to bump the rwhp a bit and I have read over and over that traction is an issue.. keep in mind occasional highway use where it is possible I would hit inclement weather.

Next, I would like to upgrade exhaust, but purely for a performance boost. I like the sound of the factory system, and dont mind a little more mean sounding, but when cruising either in city (30-40mph) or on highway (70-80mph) I absolutely do NOT want loud resonating exhaust. Can anyone recommend equipment based on this? I was thinking cat-back and maybe headers.. I want to keep it smog legal.

Next, I want to think about basic bolt ons, starting with CAI. I am not opposed to using a tuner, but once again, purely for performance increase.. I want the convenience of the factory tune (smooth idle, regular fuel) but with a little boost in performance. Up here regular fuel is 85 octane because of the thinner air. I assume that tuners either have elevation options or you just base it on 87 octane for my regular fuel? Any recommendations in this regard?

Finally, I am thinking that I would like to change the gear ratio. Keeping in mind its a 5 speed and I want to be able to cruise on the highway, is 4:10 gears way too aggressive? I don't want to end up at 5k rpm at 80 mph with the exhaust booming in my ears.. There is a good likelyhood of a pleasant 2000 mile trip to the coast this summer, and I don't want to end up miserable the whole time, or worse, getting 2 mpg because I have to redline the engine to make 80 mph.. Any idea what kind of rpms this car is at with 4:10's or 3:73's at 80mph?

I appreciate any feedback at all, and when my new toy arrives I will get some pics up.

Thanks
Dave

thejack

i have 373's in my 98 gt with a five speed, and i cruise at i believe right around 2200 rpms at 65 mph....i dont if that helps ..i was conserned about the same thing, i know they make 390s now for the 8.8. ull be fine with either choice.

Argonaut

Since you want summer only tires, Nitto 555 or BFG KDWs are popular. If you want a really sticky low treadwear street tire the Falken RT-615 is a great tire for the price, popular in AutoX. TireRack.com has lots of reviews and research.

To be totally safe about emissions stick with shorty headers...long tubes can be iffy. My violators are probably to loud. Flowmasters maybe. YouTube.com has tones of videos of the different cat backs.

The stock tune is very conservative and has horrible throttle lag IMO. An aftermarket tune and CAI combo, even if the tune is for 87, is far superior - more HP, better throttle response. Good question about the altitude, got me there.

Check out the following link, it has many calculators where you can determine the RPMs for a given tire and speed. See for yourself its not that bad. 4.10s are a kick, for your stated usage they would be great. http://www.wallaceracing.com/Calculators.htm

mynameismike65

Based on what you said this is what I would do.....
(You sound like you want to keep the mods relatively simple and not going overboard.)

1) Intake/tune.......go on Brenspeed.com and check out the JLT intake/tuner package. I would Email them and see what they can do about 85 octane in your area tune wise.....but like posted above 87 tune or any tune for that matter will be a world of improvement.
2) Axleback exhaust system. You dont want any drone and like the level of the stock system go with Corsa's. More expensive but no drone and not obnoxious. swapping out headers/midpipes will yield you more HP but make you emmisions illegal/alot louder/ect.
3)4.10's or 3.73's. either ones will be an upgrade. Your RPMs dont run much higher on the HWY with 4.10s. You will go from about 2000 in 5th to 2300 or something.
4) Tint.....it will look good and keep your car much cooler in the summer

dkersten

Thanks for the feedback!

I did a little looking, and with the help of the calculator Argonaut linked (thanks!), with a 27" tire (about standard far as I could find), 5th gear on the 5 speed at .67 (tremec website says .64 but that might have changed), with 4.10's I would be at about 2700 rpm at 80mph, with 3.73's about 2500 rpm at 80mph.. Now I just need to find out how different exhaust systems sound at those rpms to see if its acceptable.. Since this will mostly be in town driving, I will probably go the 4.10's.

I think I am limited to shorty headers on the convertible. Like I said, I want a little performance gain if I modify exhaust, but I dont want it to resonate and drone real bad at that magic 2700 rpm.. If I decide to take a 2000 mile road trip, I would go crazy if the exhaust was resonating at that RPM.. My brother's vette is as quiet as a cadillac at 2300 rpm, which is where he is at when travelling at 85 mph in top gear.. That is my big concern.. the exhaust can be loud as hell when accellerating, louder the better really, but at cruise speed I want quiet.

Thanks for the advice on tires, I will see what my local tire shop carries and try to stick with one of those brand/models.. Once again, I don't want to be cruising at 80 mph and have to put up with excessive tire whine either.. shouldnt be a problem with any street tread, but I don't want any surprises.. As far as tire width, so far I have read that you can easily do an 8.5" front, and a 10" rear.. Does anyone know if the 10" rear is possible without making the wheel/tire stick out further? I don't want this to look like an old firebird with big mags on the back hehe.. I would like the wider tire in the back but only if the exterior profile remains the same..

The CAI and tuner are something I will have to contact the various manufacturers about to get specifics on the elevation issue. If I keep it naturally aspirated would bigger injectors make a difference? If you put in bigger injectors do you have to upgrade the fuel pump? And if I go with underdrive pullies, am I going to have problems with like AC and power steering at a stop light?

Way back (20 years ago ugh) when I was a teen, I was into building motors and such. I loved building a 351 windsor that I dropped in my 75 mustang 2 coupe. I put a big ole cam in, built some crazy heads using 289 heads with tiny chambers that I had big 1.5" valves machined into and then ported the intakes and polished the exhaust, forged flat top pistons, 4bbl carb, etc. The combination put me at 13.5:1 compression, and with the big cam it barely idled at 900rpm. I could turn 9k rpm without floating the valves, and estimated (no money for dyno back then) the output at around 400hp, which was really fun in that 2300lb chassis. Back then I had no problem dealing with constant tuning, finding fuel that would run at that compression ratio (8 gallons premium + 8 bottles isopropyl alcohol to get to around 100 octane hehe), or dealing with extremely rough idling, but these days I prefer to not have to deal with those issues. I want performance without the hassle.

Of course, I need the car to get here first.. haha.

okbfd

I have the Flaken 452s on mine in a 19 and have been very pleased with them. Good luck with your build!

dkersten

What width tire are you running? 215? Same size front and back?