znod

I have edited only my original posts in this thread to keep them updated for new information. While the details have changed, no discussions have been affected significantly in any way.

Hi Friends:

There is much controversy over whether typical bolt on mods produce significant or noticeable gains on 545i's and other cars. Previously, I have attempted several mod assessments (go here--post #37--for the most recent one). The results looked good (i.e., up to a 44 flywheel equivalent horse power (FEHP) gain), but the assessment method was subject to much estimation error. Given grogan?s fabulous formula (go here--post #38), a new method and more accurate method of estimating gains from mods is available. I use this method below.

Given the HP values from my GT2 G-meter tests (Edit: now 343 @ 57 MPH and 293 ave), the implication is that my modest mods have made a FEHP difference of 18 to 25 FEHP depending on the weight of my car--4,100 lbs. or 4,180 lbs.). Still, as indicated above, my most recent mod assessment implies that my mods do yield significant gains. In this regard, an independent calculation implies that my mods may have produced a FEHP increase of:

28.2 = 17.2 (lighter wheels/tires, spare tire removal, etc.) + 5 (Dinan throttle body) + 6 (B&B exhaust).

Conventionally, it is common to think of a 10 FHP equivalent increase on medium HP cars as translating into a .1 second improvement in the 1/4 mile time. So, we might equate my 28.2 value with about a .282 time reduction in ? mile time compared to a well-driven (WD) stock car. Now, given a WD stock car 1/4 mile of 13.7 [the average of the fastest times (i.e., conservatively ingnoring the slower time of 13.8) recorded by the US auto mags for Steptronics?(13.7 + 13.7) / 2)] and the most likely ? mile result for my Steptronic using grogan?s formula (13.467), then we might expect my car to win a quarter mile race, versus a WD stock car, by .233 = 13.7 ? 13.467. The .233 value implies an hp increase of 23.3 FEHP as compared to the 28.2 FEHP value calculated above. Still, the values are calculated independently and, thus, tend to support each other. So, the implication is that my mods have produced a 23.3 FEHP to 28.2 FEHP increase--which is not bad. And, remember that, given one's leanings, mods improve the aesthetics too--e.g., better looking wheels/tires and better sounding exhaust. Finally, I think that I can improve my prior test results--which will imply a greater FEHP gain from my mods.

Next, given the calculation from above,

28.2 = 17.2 (lighter wheels/tires, spare tire removal, etc.) + 5 (Dinan throttle body) + 6 (B&B exhaust),

regardless of which value we assume (23.3 or 28.2), the obvious estimate is that my Dinan throttle body and my B&B exhaust produce about 39 % (11 / 28.2) of my FEHP increase?or a savings of .11 in the ? mile. My conclusion is that if one is to get a significant and noticeable difference from a 545i (or a 550i), then he or she is likely to need to do a combination of mods including especially wheels and tires. And, one other factor is worth noting. My best average 3-run zero to 60 time is 5.09. The average for the big 3 US auto mags is 5.37--which yields a difference of .28 (or 28 FEHP). Thus, this calculation is highly consistent with the FEHP gain from my mods being in the range of 23.3 to 28.2.

Note that my car and grogan?s car are very likely to run neck and neck in the quarter mile (see the results of grogan's virtual race between our cars--here--post #54). His car is stock. But, note that grogan has 16? wheels on his non-sport-package car (thus, negating much, or all, of my aftermarket wheel/tire advantage over stock via his wheels/tires and other possible weight savings). In addition, I have comfort seats--which are quite heavy. And, grogan?s car is well broken in (i.e., my car has only about 6k miles). In sum, in terms of FEHP, grogan?s car very well may be the, or close to the, equivalent of mine. In sum, it would not be surprising for our cars to run neck and neck.

Finally, ignoring FEHP gains that might accrue to a CAI or programming, the very best gain probably would be produced using very light aftermarket wheels (I would use BBS wheels) of size 16? (non-sport package) or size 16? or 17? (sport package) along with drag radials. Neither Nitto nor BFG drag radials are available in the appropriate size for 18? wheels. So, if I had it to do over again, I probably would go with a 17,? rather than an 18,? wheel upgrade--thus, allowing me to go back and forth between "normal" tires and drag radials or to run drag radials all the time.

Happy additional "Mind-Candy" 545i mind candy to all interested.

Peter530i

znod

Hi Peter:

There is a lot there, and the prelude goes back a long way. grogan and I have been yaking for quite a while now. The linked thread provides the background.

stream

So let me play devil's advocate.

Unless you strap a supercharger on your engine, just about any other mods--including performance enhancements ("free flow" exhausts, "cold air" intakes, throttle bodies, etc.--short of NOS ) or weight reduction (removing spare tire, lighter exhaust, vacuuming regularly to reduce heavy dirt in the carpet , even lighter wheels with the obvious benefit of reducing unsprung weight--short of stripping the entire interior out )--even when taken cumulatively--will not produce enough speed increase for a person to notice. Perhaps with a GPS timer you might record a 0.1 or 0.2 or even a 0.3 sec. improvement in 0 - 60 MPH or 1/4 mile times, but would you really notice that without the timer? Sure, the engine sound might be more aggressive (making the car...sound...faster ), but at the end of the day I truly believe it's all psychological.

And this comes from a guy who has been a car nut for decades, and loves to mod his cars, but I realize that a 5% or even a 10% power increase just isn't noticeable, and not economically justifiable. That's not to say that I haven't loved the sport exhaust systems I've installed in my Porsches, or the various other mods I've done to numerous other cars, but I've never had any illusions that they would make my car noticeably faster.

For a normally aspirated engine, the one way to noticeably increase the engine's power is to supercharge, but then you run the risk of pushing the engine beyond it's technical limits...and good luck with any warranty claims!

znod

Hi S:

OK, I'll be the angel's (my own) avocate. You old you. The gist of your devilish arguments, I think, are (1) bolt-on mods may not be economical and (2) one may not be able to feel, for example, the additional HP needed to produce a .3 sec. difference in the 1/4.

With respect to (1), the mods are worth it to me; they may not be worth it to some; and they may be worth it to some others. So, there is no way to judge mods to be economical, or not, in some universal sense. I explored the issue of the economy of my mods in the first "Mind Candy" thread linked in my sig. I liked what I came up with as cost per HP; some others might too; and some others might not. Check the thread out if you haven't.

Also, as I mentioned, mods offer aesthetic value to offset their costs in addition to performance value. And, a value I have not mentioned before is provided by mods--psychic value--the same sort of value that might make one perfer a 550i to a 545i--i.e., more power even if he or she can't feel it. With respect to (2), I believe that I can feel the addition of the HP needed to take about 2.5 to .3 sec. off the 1/4. But, that's not what is important to me. What is important to me is that I have taken time that is significant to me off all distances up to 1/4 mile (and more). I don't have to feel the differences to know and to appreciate that they are there and that I have accomplished what I set out to do. Indeed, I was hoping to get about a 2.5 to .3 improvement in the 1/4th at this point.

The issue of a supercharger is something of a strawman since I am talking about "typical" bolt on mods and have no intention of getting a supercharger (or the cheap bolt-one supercharger--nitrous). I would not get a supercharger even if Dinan offered one--which would take care of the warranty issue satisfactorily because of Dinan's outstanding after-market warranty. And, if one did all the things you mentioned above (especially vacuuming ), except for a supercharger, and did them well, then I am absolutely positive that most could feel the difference.

Thank you for playing you old .

EuroCarFan

Just to add quickly to Znod's comments above.

1) A .3 sec difference might not be felt by seat-of-the-pants but IF you're going up against another car at a stoplight, it would make a noticeable difference.
2) Besides for aesthetic improvements, good mods should also improve the car's responsiveness and driveability. There's a fine line here though, too much modifications and your car is thrashed.

znod

I agree on both counts. My car definitely feels more agile and responsive. But, a streetie?

EuroCarFan

A hypotethical streetie...

znod

Oh sure, I'd do one of those. It's getting to be beddy bye time in London. Back in the US tomorrow. Later.

EuroCarFan

Have a safe trip back!