MyE28.com

Dyno fun at New England Dyno on a cold and rainy day....
#2/Blue - Baseline (5th Gear)
#4/Red - Fahey Track Pipe (5th Gear)
#5/Green - Fahey Track Pipe (4th Gear)


Car details:
- E28 M5 125k miles (~15k on refreshed engine)
- JC Chip
- Fahey crank hub
- Evo valve springs
- Al Flywheel
- Stebro Cat back

We dynoed, pulled the cat, told bad driver stories while John went to get new exhaust hardware, put on the track pipe, and then dynoed again so I think we got a pretty good A:B comparison. I'm not really sure how dyno's work in terms of gearing but John was convinced 5th was an overdrive gear (I thought it was 1:1 on our cars) so we did our last run in 4th and as you can see it made another ~10hp or so so I'm not sure which gear is a better/more accurate representation of power.

The good:
- The track pipe not only added 7 max hp but also added 8-15hp everywhere over 5800rpm.

The bad:
- Big torque dip max of -22ft/bls / -15hp @ 3300rpm. This was noticeable even as I was running the M on the dyno as the car was definitely slower to run through this rpm range. I can also notice the loss on the street however @ 3700rpm the track pipe takes over making the car feel faster as the torque comes in steeper from 3300-3700. I want my torque back! Is that hole something that can be tuned for?
- The car is also even louder now. It was slightly too loud with the cat in there thought it was just right at the track but now it is definitely too loud. I actually thought it was quieter with the pipe at first but once my ears adjusted back to normal after running the M all the way to 162mph inside the shop, the car is definitely boomier. Deeper, with a less tight more resonating bass to it.

The notable:
- The Fahey track pipe has an H pipe in it but the O2 sensor isn't on the H, rather it is after the H on one pipe. I don't know if that matters but I thought it was strange.
- John thinks there's more power to be made if we could adjust the A/F ratio and keep it closer to 13:1 everywhere. Any thoughts?
- My tach shows ~7600rpm before the limiter cuts in but as seen on the dyno the chip actually redlines @ ~7250rpm.

I'll keep the track pipe in for a while since there are a bunch of hpde's coming up and I don't think the car is so loud that I'll get flagged for exceeding db limits (off the street that is). I would like to make it a little quieter though so I can run the track pipe without even more evil stares from the neighbors than I already get. I loved the sound before but I was definitely on the line of my personal db limit. I'm thinking maybe just swapping the center resonator with a supersprint/stock item might do the trick.

I think it's best to have the O2 sensor aft of the H, this gives you a reading of the exhaust coming from all cylinders. Your AFRs could use a little tuning, though they aren't terrible.

What would be a more ideal A/F chart? I've heard that 12.8:1 is the theoretical ideal and that lean at low RPM and rich at high RPM is desirable but I don't know how these factors (rpm, load, etc.) actually play into what a good AFR chart should look like.

For WOT, ~13 is a good target. For light load/cruise/idle, you can be leaner (~14-14.5). You're definitely too rich above 6k and I'd say a little too lean below 4.5k. Good luck!

This is interesting...

I believe for an s38 engine you want the A/F below 13 at higher RPM. The engine likes it a little rich. When I ran the dyno I was around 12 to 1 at the top end. So I agree with leaning out your mixture a little...it may help that dip at 3300 RPM...

When we had a dyno day in Atlanta a few years back, my M5 had a dip at about 5000, happened both times. In addition, a nice puff of black smoke came out as the band took off again, so I am thinking it was rich as well. I could also feel this in driving unless I had" blown it out" in a previous run. Fast forward to recently, replaced the AFM, 5000 hiccup is gone.

Interesting,

I have a couple of custom track pipes I use with a B & B exhaust. One H-Pipe and one X-Pipe. I've never had the M5(s) on a dyno, but I don't notice the 3,000 rpm HP/Torque dip ... actually it feels the opposite. It feels like I lose midrange with the catalyst.

I'll totally agree on one point. Very LOUD with the track pipe and the B & B exhaust. Car alarms with motion dectectors don't have a chance!

I've used the exhaust on two M5s I've owned. One with 211,000 miles and my current M5 with 300,750 miles. Maybe that is the problem ... a catalyst with 300k! I've got another catalyst with about 150k ... I;ll have to try that and see if there is a difference. As far as I can tell the engine is still original. The head looks like its been off before. Compression is still near 150 psi on all six holes but leakdown was over 20% on number 5. All other holes less than 10%.

Regards

Eddie

Man,
I didn't see this initially.

Yes, your way rich in the upper end, I would expect to see 11:1 on a turbo S38, not NA. You'll gain ~10+hp if you can tune it to 12.5:1 easily. This may be due to lower test temps. What was the correction factor????

That torque dip may be from AFM issues. I would try to get a new/er one and see how it works. You car definately needs some custom tuning with the mods making that much power over stock.

Your overall #s are really healthy, 232whp is great for a S38b35, very good. Ive never seen #s that high for a NA S38b35, with mods or not.

RussC

Cool Russ! The dyno guy said the same thing that there was another 10hp if it didn't run so rich up high. I have no idea what the correction factor was, though I noticed in the software it listed correction factor as SAE? Is there something I can do to tune the stock AFM or is the only option to go to a MAF/Alpha N conversion to get the afr's right?

Thanks,
Andy

As a data point, there was a S38b35 dyno's this weekend at Edge Motorworks. It was stock with 177k miles and made 182whp. They stuck his Turner chip in(JimC software) and it made 211whp. Gee, thats what all the tuners claim with the chip!

Um, Id look at your AFM first. Mabye try a different one to see if the dip fixes. If not, then just adjust the AFM a few clicks tighter. Maybe 5 total if 3 isn't enough. If you don't want to do that, Id go adjustable FPR. You can knock off a few lbs of pressure at the top end. The ECU will compensate for the rest of the operating area.

RussC