Originally Posted by Frankenspyne
Question: If you only had $6,000 to spend on performance mods for your 2006 M5 with SMG what would you get done? Let's assume you don't care about exceeding 100 mph.
For example, CPU chip, exhaust and air induction
headers and exhaust
throttle bodies and a rear
If you could be brand specific that would also be helpful.
I really think it depends on what you're looking for.Your preferences will play a huge role in what mods will work best for your situation.
Assuming you're looking for straight line performance, your best bet would probably be:
Intake.(the RPi solution is $349 for the scoops & filter, $22.50 for the blockoff plates, plus free shipping locally, or up to 30 minutes for install elsewhere.Solutions from other companies vary).20+ hp possible, depending on dyno.
Pulley ($400-500, plus about 1-2 hour install).HP depends on what dyno, but all of the ones on the market with the same diameter will give you roughly the same hp.The difference between brands comes down to coating (regular anodized or hard anodized), weight, color (OE color, or totally different), and price.It's a nice " border="0" alt="" />At this point, it's probably time to look at exhaust (if you're ok with a sound increase), or software (if you're not).
Exhaust sound is a very personal thing. You really should listen to some and see what you like. Some add HP, some do not, and some even lose power. While all of this is important, if you can't live with the sound, it's a moot point anyway. If you want only a smaller increase in sound, doing just section 1 or 2 may be the way to go.
You may want some handling mods too. Eibach springs may be a nice choice, and aren't too expensive. A set of spacers/bolts can be used to give you a slightly wider stance.
In terms of weight savings, going with lighter weight wheels pays off both on the straight line, and through the curves. However, it's not cheap.
Take for instance, the ultra-light BBS magnesium wheels (Dymag, the producer of the carbon fiber/magnesium wheels went Chapter 11 earlier this year). These lightweight, relatively delicate wheels weigh only 15.4 lbs in 18 x 8.5" and 17 lbs in 18 x 9.5". A set of 4 will probably run you $10k or more. The OE wheel is 26.5 lbs front, and 29.1 lbs rear, so these save you roughly 46 lbs total.
For the rear:
285/40R18 tires puts you close to the same diameter as the original 28 lb 285/35R19 tires. However, they're not available in many of the most desirable makes/models. However, there's the Goodyear Eagle F1 Supercar (32 lbs in this size), BF Goodrich g-Force T/A KDW2 (31 lbs in this size), and Pirelli P-Zero Rosso (32 lbs in this size). In other words, about 3-4 lbs heavier per tire than the stock 28 lb tire.
In the same way, the correct sized front tires (255/45R18) weigh an average of 29 lbs, about 3+ lbs more than the 26 lbs the OE tires weigh.
So, you save 46 lbs in wheel, and add 14 lbs with correctly sized tires, putting you at about a 32 lb weight savings.
Because of the many MANY variables, it's impossible to pinpoint an exact relationship of effectiveness of rotating, unsprung weight vs sprung weight. However, most reputable places put it at upwards of 3-4x the benefit. So, a 32 lb weight savings from the wheels/tires MAY give up upwards of roughly the same benefit of dropping 128 lbs from sprung weight (ie. lightweight battery, CF hood, etc).
A stock M5 has 500hp and weighs 4012 lbs.
Dropping the equivalent of 128 lbs puts the car at 3884 lbs.
At 3884 lbs and 500hp, we're at 7.768 lbs per hp.
To reach the same power to weight ratio at the stock weight:
4012 lbs / 7.768 = 516.5 hp
In other words, dropping 128 lbs of weight will give you the approximate performance (at least straight line) of increasing your power by 16.5 hp.