Track Report & Powerflex Bushings - The Unofficial BMW M5 Messageboard (m5board.com)

RRoberts · 3rd May 2004, 16:28

I had the M5 out at Road America this past weekend. Conditions were cool and dry, and the track was great. I have the Dinan S2 package (except the mufflers), Stoptech front brakes, Sachs Race clutch on a lightened stock flywheel, and Michelin Sport Cups (265-35) on 9 1/2 in. Fikses all around.

The principal item to report is that the Powerflex front end bushings did not work out well. I had installed Powerflex PFF5-501 (thrust arm-large bushing under door leading edge) and PFF5-502 (control arm- smaller bushing directly inboard from struts) polyurethane bushings about 6 weeks ago, with the aim of improving toe change under hard braking and cornering. By the end of the first day (about 90 track miles), the control arm bushings had failed due to excessive compressive force, with one bushing segment having split and been extruded out of place. This caused excessive toe out and interesting handling braking down from 130-140 mph. Saturday night I drove back to the shop with the poly bushing elements wedged carefully back in place (the failed bushing popped out again when I had to brake heavily to avoid a !@#!! instant-on radar cop, and I had to jack it up and replace the pieces once again !@#!!), and re-installed the factory bushings into the control arms. All was well in the bushing department on Sunday, and the car performed flawlessly. I still have the Powerflex bushings in the thrust arm positions, and these appear from the outside to still be ok. These bushings are ~4x larger, so the unit stress is lower, and are probably still an improvement over the stock parts which have large void areas. I will pull them out to check condition when I get the chance. I guess the basic polyurethane material is simply not strong enough to handle the loads placed on the control arm. Close examination of the failed bushing elements reveals permanent deformation on the side closest to the centerline of the car, with little cracks similar to a brittle fracture, similar on all parts. On the one that came out, a complete fracture occurred in the deformed area. Needless to say, I am no longer a believer in polyurethane bushings for high performance suspension applications and likely will never use them again.

Now the good news:

- Replacement of the stock (organic) power steering with Redline ATF D4 synthetic completely eliminated fluid expulsion at the reservoir; only 2-3 tiny drops on the crew sock over the reservoir vs. 1/2 cup in previous outings. No other changes were made.

- The combination of PF01 pads in the front (Stoptech) and Porterfield R4 pads in the rear (stock) worked extremely well. Due to the cool weather - mid 40s - the brakes needed a few laps to get fully up to temperature, and were a little "grabby" under light braking until warm.

- The Michelin Pilot Sport Cups performed pretty well, but perhaps not fully up to fresh Hoosiers. Users are advised to run them relatively low on pressure (compared to other racing tires), mid-to-high 20s hot for best results. This was ok in the rear, but not enough in the front. I found that 32-34 hot worked best in the front. Breakaway is a little less abrupt than with Hoosiers, which is a good thing since I have a habit left over from lower powered cars to re-apply power at the apex.

- The Sachs race clutch performed very well. Slippage experienced in the past with the stock clutch is completely eliminated. No further issues here. This is the one place where an even lighter flywheel would be nice, but I keep reminding myself that this is a street car.

- There has been a lot of space on the Board addressed to the Dinan S2 package, whether it's worth the price, and whether it performs as advertised. Well let me tell you that I am one happy customer. Acceleration is awesome. While prepared E36 and E46 M3s, Porsches, etc., had more corner speed than my car, they were generally left for dead on the straights. I don't know what the actual power is, but it's alot more than stock.

All in all, I'm tired but the outing was a great success. The car is exactly where I want it, so it's time to stop modding (?)

Regards, Dick Roberts

Teutonaddict · 3rd May 2004, 16:34

Quote:

Originally Posted by RRoberts

Now the good news:

- Replacement of the stock (organic) power steering with Redline ATF D4 synthetic completely eliminated fluid expulsion at the reservoir; only 2-3 tiny drops on the crew sock over the reservoir vs. 1/2 cup in previous outings. No other changes were made.

- The combination of PF01 pads in the front (Stoptech) and Porterfield R4 pads in the rear (stock) worked extremely well. Due to the cool weather - mid 40s - the brakes needed a few laps to get fully up to temperature, and were a little "grabby" under light braking until warm.

- The Sachs race clutch performed very well. Slippage experienced in the past with the stock clutch is completely eliminated. No further issues here. This is the one place where an even lighter flywheel would be nice, but I keep reminding myself that this is a street car.

- There has been a lot of space on the Board addressed to the Dinan S2 package, whether it's worth the price, and whether it performs as advertised. Well let me tell you that I am one happy customer. Acceleration is awesome. While prepared E36 and E46 M3s, Porsches, etc., had more corner speed than my car, they were generally left for dead on the straights. I don't know what the actual power is, but it's alot more than stock.

All in all, I'm tired but the outing was a great success. The car is exactly where I want it, so it's time to stop modding (?)

Thanks for the write-up, Dick! Glad to hear that Sunday was a better day, and happy you escaped the instant-on revenue generator!!

Did you flush your P/S system when going from organic to synthetic? While this hasn't been a tremendous concern of mine (it's done it every track outing since new), it would be great to eliminate altogether.

I've had similar success with the PF01s up front on my StopTechs and a less aggressive (Axxis Deluxe Plus) on the stock rear calipers. Just gotta be more rigorous about washing the brake dust after each day.

Your Sachs race clutch as intrigued me from the day I learned it was possible with a little machine work. When my warranty replacement unit fails, I am certain to go that route. While I am duly impressed by the UUC unit, I'm also a bit of a tightwad, so would first pursue the 60% cost option.

Also glad to read another real-world testimonial to the S2's impact. I was pretty skeptical re: Steve Dinan's earlier response to S2 owners getting unusually low dyno numbers, but after I read the related article in last month's C&D, I'm giving creedence to the fact that you can't just strap one of these complicated Beasts on a chassis dyno and expect real-world extrapolations of BHP at the crank... Also in light of all the tuner horror stories, you don't hear similar tales about Dinan; even the Z8 fiasco was dealt with in a manner that demonstrates they're a stand-up outfit.

Finally, congrats on finding the "satisfaction point" with your mods. It's a pretty gratifying place to be!! Once I installed my StopTechs, I finally said "this might be it!" And in the last year I haven't felt the need to upgrade. Enjoy your ultimate, ultimate driving machine.

-Dave

TCM · 3rd May 2004, 16:34

Thanks for the report Dick. I am glad to see you elimanated the power steering problem by switching to redline. I am thinking baout doing the same even though I am not a heavy track person. How much fluid was required for the change?

RRoberts · 3rd May 2004, 16:40

Quote:

Originally Posted by TCM

Thanks for the report Dick. I am glad to see you elimanated the power steering problem by switching to redline. I am thinking baout doing the same even though I am not a heavy track person. How much fluid was required for the change?

Exactly one quart. Disconnect the lines at the PS pump, and work the steering back and forth a few times to expel the old fluid.

Regards, Dick Roberts

stever · 3rd May 2004, 17:21

thanks for the very helpful report

let us know what kind of life you get from the Cups - it seems like my first set fell off after 18 heat cycles on 4 very hot days last summer - i'm going to run them on the street for a while to even out the wear, then do a back-back test with street tires

i've talked to M3 and Porsche guys who've got great life from the cups, but also to a couple Porsche guys who've gotten mixed results - in any case, you need to be careful to switch tires front-rear and side-side depending on the track as the lack of camber in the M5 can eat up the outside very quickly - particularly on a track with a big sweeper

the problem may be that you've got to get in the range of 2 1/2 - 3 degrees negative (this is what the M3 guys run) at least in front to properly use the tires - i've been running as high as 36 psi in front and clearly need to be more diligent with the pyrometer to figure out what's going on

CSBM5 · 3rd May 2004, 17:21

Dick,

Thanks for the write-up on the bushings. Clearly, sub-par engineering (or none) went into the design of these for the M5. I'm glad no catastrophic outcome was experienced and that you were able to get things reset for Sunday. This sounds like a material like Delrin would be more appropriate for the loading levels encountered. It would much more solidly locate the components also; however, noise transmission to the chassis along with harshness and squeaking would come along for the ride with Delrin

Re the ATF fluid...is it possible that the temps in the 40's helped out a lot, or were you referring to previous experience at those temps also?

Can you give me a link to the wheels you are using? I've been looking at getting some track wheels, and the best I've found so far are the Dinan wheels. I will not run spacers, but I would like to run 9" or 9.5" all around and the 265/35 Pilot Cups.

Re Dinan S2:

Quote:

While prepared E36 and E46 M3s, Porsches, etc., had more corner speed than my car, they were generally left for dead on the straights.

Redshift · 3rd May 2004, 18:13

Good report, and thanks for sharing. We had our 3rd or 4th event in the M5 this past weekend and except for some corded tires

we ran great. My M5 is stock except for wider street tires up front, a short shift kit, and a Borla exhaust, and it still kills almost everything on the straights. Obviously not modified Z06s or highly modified C5 Corvettes, but this weekend I was actually slightly pulling on a Factory Five Cobra in the straights. He didn't seem to be going easy on it, and I was surprised. He left me in the corners (much wider, stickier tires, much lower weight) but I was keeping up well with lots of the cars.

I had a great time chasing down and staying even with an E30 325is on track tires, and a super lightweight Honda Civic hatchback (2100lb with driver I think) on race tires...neither could leave me, but I could also not catch up to either one of them. It was fun in such a large, heavy car on stock suspension and street tires. The E30 driver was shocked, and thought he should try to out-brake me going into turn 1, and ended up shooting right off the end of the track while I made the corner and went on. Now that was great!

You should see all the people looking at the M5 during track weekends to figure out the "secret" and they are usually shocked when they see a full interior and street tires. Makes me giggle with delight.

stever · 3rd May 2004, 19:22

i've had no problems running spacers with SSR comps (27mm offset - 3mm spacers in rear and custom 10mm in front)

the SSRs have a reputation for being soft and i have bent a couple, on the other hand if you go off in the wrong place you're probably going to bend anything

i love the Dinan wheels (my street wheels), but since you can buy 2 or 3 piece wheels for the same price, a Fikse or some such should be more economic in the long term on track - the one-piece Dinans are awfully expensive

Teutonaddict · 3rd May 2004, 20:55

Quote:

Originally Posted by stever

i love the Dinan wheels (my street wheels), but since you can buy 2 or 3 piece wheels for the same price, a Fikse or some such should be more economic in the long term on track - the one-piece Dinans are awfully expensive

You make a good point, Steve-

I have three-piece forged Kinesis wheels on my Beast. I had four bent halves replaced last year (two inners and two outers), plus a repolishing of the two original outers, plus a full polish of the formerly-painted-black centers, for the same price as retail on replacing one wheel ($1100). Since this was an insurance payment for some bloke boring into my Beast, it cost me nothing. But the realization that I could repair four wheels to as-new for less than the cost of replacing one was quite a pleasant surprise!

-Dave

Lscman · 4th May 2004, 04:25

Dick,

Sincere thanks for sharing such useful technical info.

It's amazing those poly bushings failed so quickly. Have to wonder if the mfr ever tried them on a car. It is increasingly apparent to me that all poly's are not equal. Some wear like iron (PST & Energy Suspension come to mind) while other's are total losers (Powerflex). I will not forget that mfr.

Your track test of Red Line P/S fluid is oh so timely. Please let us know if the seals begins weeping under street use from switching to synthetic. This has been my experience with two USA mfd vehicles after switching to Mobil 1 ATF and Valvoline syn in P/S. One of the vehicles literally poured it's fluid onto the ground...empty in 100 miles. Amaxzingly,...switching these vehicles back to conventional $1 ATF stopped these "gushing" leaks within a day. A third vehicle (another US domestic) converted to Valvoline showed no weeping issues even after 5 years of use. In my case, severe duty performance on synthetics was similarly improved.

Rick