It has been over five years since we first tuned and supercharged the Lexus RCF, and we are very grateful for all the support we received from the Lexus RCF community over the years! This month PPE shipped us prototype of their catted racing headers for Lexus RCF (using 400 cel GESI EPA cats) for our testing and development. We decided to use this opportunity to perform the most transparent and thorough testing of RCF mods. This was especially revealing given the recent trend with some tuners who have released grandiose claims (of up 20-30 hp gains!) by playing tricks with Dyno testing, showing unrealistically low baseline dyno results, and in general advertising dyno results with very little clarity or transparency in what was done.
If you are interested in understanding true RCF performance, you will read carefully this article.
Overall Approach
Our RCF Dyno Comparison tested a variety of bolt on mods, both with and without tuning. We used our in-house DynoJet 424X (located in a climate-controlled facility) for testing. The great thing about a DynoJet dyno versus a Dynapack, Dyno Dynamics, or Mustang dyno is that the results on one DynoJet should be essentially the same as on another DynoJet. This is because all DynoJets use the same exact specification rollers, and power is calculated based on your car’s ability to accelerate the rollers. Just about the only variability you can expect on a DynoJet is cooling variability (strength of the fans), or intentional tampering (messing with the air temperature sensor). With other dynos, all sorts of calibration factors, loading, and run speeds can be manipulated by the user, not so with DynoJet.
That said, we did our best to minimize all variability, using the same 100,000-mile RCF for all testing, on the same dyno, on the same tank of gasoline, with roughly same air temps (+/-5 degrees), and managed to compete all testing in one week.
This is what we tested in our approximately 100 dyno runs:
- Bone stock RCF
- Stock exhaust manifolds with 2.5” dual cat back exhaust
- PPE catted headers (featuring GESI GSport 400 cell catalytic converters) with 2.5” dual cat back exhaust with X-pipe
- PPE race headers with 2.5” dual cat back exhaust with X-pipe
- PPE race headers with 2.5” dual cat back exhaust with X-pipe (featuring GESI GSport 300 cell catalytic converters)
- Exxon 93 pump gas VS Sunoco 93 pump gas VS e30/93 octane ethanol blend
Testing Methodology
- All dyno runs in 4th gear. Using higher gear theoretically yields higher numbers, but we find that 4th gear pulls give the least run-to-run variability which is critical when testing sometimes subtle power gains from different modifications.
- For each mod, we typically do 6-8 runs. Our observation is that it usually takes a minimum of 3-4 runs to reach peak power numbers, and we continue running the car until we start to see a slight power decrease. We then choose a representative dyno run from among the top 2-3 runs.
- Our DynoJet 424X AWD dyno is equipped with 6 fans, each 1hp. The fans are directed at the transmission and oil coolers, radiator, and towards the engine bay/airbox.
Testing Results
Test 1: Stock RCF vs. Exhaust vs. Exhaust + Tune
Our baseline dyno runs netted nearly 419whp and 381wtq, great numbers for a healthy 100,000 mile RCF, so certainly we managed to extract the maximum possible numbers out of bone stock car – no sandbagging here!
Bolting on a dual 2.5” free flowing exhaust netted 16whp and 11wtq gain, not bad for just an exhaust.
Tuning gains were subtle, but noticeable for an additional gain of 5whp and 5wtq with stock exhaust manifolds and just an exhaust.
Test 2: Stock RCF exhaust manifold vs. PPE Catted Headers with 400cel GESI cats
Comparing tuned stock manifold to tuned PPE 400 cel headers netted an 8whp peak with up to 13wtq gains in the upper powerband.
While these gains seem mild, keep in mind that the placement of the catalytic converter close to the engine ensures maximum effectiveness of the catalytic converter. Additionally, for those considering forced induction mods, the GSport catalytic converters will offer much greater durability compared to stock ceramic core converters.
Test 3: PPE Catted Headers with 400cel GESI cats vs. PPE unequal length race headers
Race headers netted an additional 12whp and 17wtq gain over catted headers throughout the powerband. The full bolt on race configuration car with race headers, exhaust and tune netted 459whp on 93 pump gasoline, for a total gain of 41whp over stock, not too shabby for mostly bolt on mods on a normally aspirated v8!
Test 4: PPE Race headers and full exhaust: Testing effect of fuel quality
After completing our full bolt on testing and making 459whp on 93 octane Sunoco pump gas, we ran out of fuel and hopped over to the local Exxon station to fill a 5-gallon jug. We often use this station and have never had any issues, nevertheless, when we filled the RCF with the new fuel, we immediately lost 7whp and 10-13wtq! Pretty shocking for just a change of gas, with runs conducted within 15 minutes of one another.
Datalogs indicated that the ECU was cutting back timing a bit throughout the powerband. We are not sure if the octane at our Exxon station is lower than indicated, or if this has to do with a specific winter gas blend that Exxon uses, but the results speak for themselves – gasoline can be a huge variable, on par with gains/losses from a tune or exhaust mods.
Test 5: Testing the Ethanol blend
After observing the power loss with Exxon 93 octane gasoline (vs baseline Sunoco 93), we decided to add e85 to our 93 octane Exxon gasoline to bring the mixture up to approximately 30% ethanol content. The higher octane allowed the tuned ECU to self-adjust and yielded an impressive 8hp gain on the top end of the powerband. Adding additional ethanol did not yield additional power, as 30-40% ethanol seems to be the sweet spot.
Of course, for boosted applications, additional octane will make a huge difference, but normally aspirated engines are typically not knock-limited on 93 pump gasoline, so gains on race gas, e85, or ethanol blends are limited.
Our peak tuned power numbers of 467whp and 422wtq represent gains of 50whp and 40wtq over stock!
Test 6: Race headers and exhaust VERSUS Race headers and catted midpipe
Previously we tested catted headers with race exhaust, in this test we are testing race headers with catted exhaust. Please note that we do not have a direct comparison between catted headers vs catted exhaust. The PPE catted headers shipped to us with ultra-efficient 400 cel GESI catalytic converters, whereas our exhaust was equipped with 300 cel GESI converters welded to the midpipe. In the future we hope to test a 300 cel header. For now, we can come to the conclusion that 300 cel GESI cats result in a minimal 10wtq decrease in the mid-range.
Conclusion
What did we learn from conducting 100 dyno runs and spending many hours installing and un-installing parts? First and foremost, the basic formula for modding the RCF is as relevant today as it was 5 years ago. Race headers, uncatted exhaust and tune will net you around 40-50hp — this is very respectable gain for a normally aspirated car.
The new PPE 400 cel catted headers delivered 8whp and 13wtq gains over stock. This product may be an effective complement to a supercharged RCF. RR Racing and PPE will continue working closely in optimizing and developing this product (more tests with different cat options are planned for the near future).
Those of us looking for miracles or magic custom tunes that net 20-30hp gains should look elsewhere. Bottom line is, if such tunes existed, we would be looking at RCF’s consistently making 480+whp on a DynoJet, and that clearly hasn’t happened. Full bolt on mods without question transform the RCF, but if you are looking for huge gains, there is no substitute for SUPERCHARGING!