I decided to work with Partee Racing to spec an engine build. I really wanted to push the absolute edge of compression ratio, but there's just a limit to what can be done while retaining full Vanos range, or at least without getting into a ton of work with custom pistons that may take several iterations to nail down. Being that I planned to run E85 at least some of the time, I was looking to run 13:1 compression or higher, but it just isn't physically possible with a 288+ camshaft and full Vanos travel. Here's where we ended up:
Main engine details:
Mahle 12.5:1 pistons
Carrillo lightweight rods
WPC bottom end bearings
CNC ported head (exhaust, intake was also cleaned up)
Supertech full "high RPM" shimless valvetrain (lash cap conversion)
Shrick 288/280 all surfaces DLC'd
Other relevant mods:
BBRTuning Emtron plug-in standalone ECU tuned by myself
Bosch 550cc injectors, 5bar fuel pressure
Haimus V1.5 prototype airbox (see notes below)
Dinan 52mm throttles
VAC pulleys
SuperSprint V1 stepped oversize headers
SuperSprint oversize section I/II unresonated
SGT SCZA muffler
The combo of lightweight bottom end and lash cap dual-spring valvetrain is all designed to handle 9000RPM. I really wanted to find a combo that will make power to 8500+ RPM and be reliable at that range, yet run safely on 91 octane and retain full OE driveability with no quirks. Amazingly this combo is perfectly happy on 91 octane (California 91 that everyone says is so crappy - it's not) due to the 288/280 lowering the dynamic compression ratio, and an engine builder who knows what they're doing (proper combustion chamber preparation). I was able to reach MBT without knock with this combo. Having a standalone ECU where you can actually datalog raw knock sensor data at a very high frequency and set the ECU up accordingly goes a long way, as any aftermarket piston will be "louder" than a factory engine and the ECU needs to be adjusted to suit.
As a side note, one of the most shocking aspects of this build is how incredibly the oil temps are compared to the last engine. I used to see 265F+ oil temps (coolant was always 180-185) after 2-3 hot laps at Buttonwillow or Willow Springs, and this was shifting at 7600-8000. With the new engine, making considerably more power, shifting at 8000-8400 RPM, with very similar ambient temps, I wasn't able to get the oil temps over 215F even after a full 20 minute session. I was blown away. I'm actually going back to a stock oil cooler from CSF to pull some (apparently unnecessary now) weight off the nose.
Here's a comparison of my last setup (11.5:1, 288/280 with stock rockers) vs the new engine on a Dynapack dyno. Power gains everywhere, from a combination of the higher comp, head work, and just generally much less internal friction. You can see in both cases there's some sort of airflow limit at the top end that I need to figure out. At the time I still had SuperSprint HJS cats in section 1, so I figured the restriction was either the cats, the SCZA muffler (it's 2.5" but pretty quiet) or the airbox. I later swapped to a catless section 1 to replace the HJS and to my surprise made almost no difference, maybe 1-2HP max. However, the HJS cats are 100 cell so they certainly are not very restrictive. The top end power restriction remained.
I wanted to get actual SAE Dynojet numbers, since that seems to be the universal standard. I hit up Steve from EAS (European Auto Source) who was also interested in doing some testing with me. I wanted to try and find the restriction - the plan was to pull the air filter out, then swap airboxes (he was nice enough to steal his Turner airbox off his E36 S54 track car), and then remove the SCZA muffler completely as a test.
I've been dyno tuning engines for over 15 years now, and I tried to be as objective and scientific as possible. All tests were run multiple times until power stabilized, and the best of each were posted. I also made sure to keep air, water, and oil temps within a few degrees for all runs. ECU is set up to do closed-loop fueling at full throttle and knock control temporarily disabled (but monitored of course), so air/fuel ratios and ignition timing were identical for all runs (except E85 tests where a different ignition table is used). Here are the results.
91 Octane - Haimus Airbox - ITG filter vs. filter removed
Small gains but not worth looking into further. This ITG filter was also not freshly clean. This airbox has always had an interesting power bump around 7000-7500. Note the slight dip around 6400, some of this could probably be reduced some with more Vanos tuning but it was persisent with this combo.
91 Octane - Haimus Airbox vs. Turner Airbox (both with filters)
Alright, making some progress here. Keep in mind the Haimus box I have has an older design trumpet compared to the ones they're shipping now, so results may be different with their newest offering. Turner has an odd dip right where the Haimus comes on strong (may be able to tune out slightly with careful Vanos tuning) but the Turner does pull ahead up top. ~5whp gain is cool, but you wouldn't be able to feel it. I personally like to keep the snorkel which the Turner doesn't have, so I don't think I'll be switching. Power is starting to carry a bit closer to what I was originally hoping for, though..
91 octane - Turner Airbox - SCZA muffler vs Muffler Removed
Well, this was interesting. The old adage about "you need backpressure" has long since been debunked, so I can only assume this is due to some turbulence in the exhaust outlet ending at section II and blowing into the bumper or maybe the proximity of the two outlets right next to each other. It also sounded GODAWFUL. Bottom line, the SCZA muffler is pretty incredible for how quiet and nice it sounds. At this point, we can pretty safely assume the top end "restriction" is not in the exhaust system.
E70 Fuel - Turner Airbox - SAE and STD corrections shown
Next, added E85 to an almost empty tank but was only able to get up to E70. I then adjusted ignition timing for E70 to dial that in. Super stoked with ~383whp SAE on this setup and approaching 400whp STD. Stock engines made 280-290whp on this dyno, so literally +100whp gain is pretty cool! Also showed STD correction for comparison with some of the other dynos on here.
Where do we go from here? Well, I think it's safe to assume there isn't a restriction in the intake or exhaust systems. I really wanted to hit that 400whp mark, and if the power continued linearly to 8500, I'd be there easily. But I'm really quite happy and the car feels insane now especially with the 4.10 rear end. However, just because I've come this far already, I'm talking to Partee Racing about doing a 296/288 cam setup next. Unfortunately this would require limiting the Vanos slightly, but should definitely produce some gains at the top end. Realistically, the low end losses will be relatively small and only at 4500 and below, and of course only at full throttle, so this may be an OK tradeoff.
Here's another S54 race car I tuned, also running my Emtron ECU kit, with 12:1 compression and 296/288 cams (with limited Vanos). Notice how the power carries all the way to 8500! I'm making the same peak numbers as this car, but I think with the extra 0.5 compression and E70 fuel I should be able to beat it (this car was on 100 octane). Accidentally had Torque Y-axis scaling incorrect on this graph.
Dyno run:
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