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Precision 6870 dyno results and a study on VP Octanium
Hey all! My name is Leonard. I tune cars at Rotor REhab, alongside Brian, who is the head of the operation and master engine builder/technician. We recently finished the engine build on my personal FD and had some results we wanted to share. We also did a little experiment with VP Octanium that we thought was worth sharing.
Turbo:
Precision 6870 gen 2 turbo. 1.15 a/r exhaust and the "S" cover compressor housing.
Secondhand turbo manifold bought from another forum member a long time ago.
Tial 44mm wastegate.
Rotor REhab built engine with:
Large Rotor REhab streetport
S4 turbo rotors. Lightened, balanced, and clearanced by Chip Motorsports
Rxparts apex seals
Atkins cryo-treated solid corner seals and side seals
Rotor REhab resurfaced rotor housings
Rx8 E-shaft
Turblown stud kit
A few notes about the dyno session:
- The boost sensor on the dyno was down. It was stuck at reading 12 psi, so ignore that.
- We were having boost creep issues. I let off the throttle when boost creeped past 28 psi.
- I believe the RPM reading on the dyno sheet was about 500rpm off. The sheet shows me letting off at 6800rpm, but I was definitely letting off at about 7300 rpm when boost started creeping past 28 psi.
-Albuquerque's elevation is about 5200 ft. Humidity was around 17% in the dyno room (31% ambient) and the ambient temp was 36 deg F.
-All runs were done with 91 octane and water injection. Water is injected pre throttle body from a 500cc nozzle. Water starts getting injected at 10psi.
Here's the final chart from the day. We definitely felt like the car had more power in it by adding more revs and timing, but as stated above, we were running into boost creep issues and were letting off the throttle early. We didn't want to risk it too much, so we called it a day after a few runs.
Final and best chart from the day:
Our first run of the day netted 475 hp and 398 tq. That run was with no Octanium in the tank. Just 91 octane and water injection.
We did a second run with no adjustments, but that ended up being a throw away run. We got 450hp because the cooling system in the car works a little too well and it cooled the engine down so much that the Power FC started correcting timing and fuel. I didn't notice before doing the run.
The third run was with the vehicle warmed back up to operating temp and a bottle of Octanium added to a half gallon of 91 octane. Without any adjustments, we got 495 hp and 428 tq! Again, we let off right around 7300 when boost started creeping.
Our final run was with the Octanium still in the tank and 2 degrees of timing added in. The result was 512 hp and 433 tq. We called it quits there due to our boost creep issue.
Onto the knock logs. Here's our first run with no Octanium:
Knock was around 20 counts during peak torque.
Now, here is the log with Octanium in the tank and no timing adjustments:
Knock came down a few counts during peak torque! This confirmed that the Octanium was not only adding power, but also suppressing knock. We went ahead and added two degrees of timing. We ended with our final run of 512 hp and our knock log now looks like this:
After seeing this, we felt confident we could've gotten at least 530 hp with a few tweaks, but our pesky boost control issue was worrying us. The more power we made, the harder it was for me to let off around 28psi lol.
Final thoughts:
-The 6870 is NO joke. Thanks to Stephen at SMG Racing for convincing me to upgrade to that turbo from my old 6765. Spool is very good for a turbo this big. Again, the tach reading on the dyno is off, but we can gather that we have at least 400 ft lbs at 5500 rpm.
-VP Octanium looks to be an effective product. Because we just started using this stuff, we don't know its long term effect on rotor housings or anything of that nature. It does seem to mix well with TCW-3 two stroke oil, but we don't know what happens to the mixture after its pressurized and heated. I plan to keep running the stuff and will let everyone know if my opinion on it changes.
congrats on your accomplishment and also the quality of your post. really nice you shared so much detail. w that turbo even two 44s might have some difficulty corralling boost. knock looks good. boost dynamics look a bit lazy as you would like to see them head straight south rather than a 45 degree angle. of course you are at a high elevation which does cause an impediment.
congrats on your accomplishment and also the quality of your post. really nice you shared so much detail. w that turbo even two 44s might have some difficulty corralling boost. knock looks good. boost dynamics look a bit lazy as you would like to see them head straight south rather than a 45 degree angle. of course you are at a high elevation which does cause an impediment.
we look forward to further posts, good job
Thanks Howard! I really appreciate the kind words and everything you've done for the community over the many years. Although the turbo has a huge hotside, I do believe the issue has more to do with the elevation. I am currently tuning BW 8474 powered car and the log of that one shows a pretty similar angle. That turbo, however, does come online sooner and the angle is ever-so-slightly steeper. I've done a couple of s366 powered cars and those show a 45 degree angle as well.
Looks like a fun setup. 3" exhaust? Since you are running a power FC, do you have a failsafe for the water injection if it runs out of water or gets clogged? Also curious if you are injecting only water as opposed to boost juice or water/methanol mix?
Looks like a fun setup. 3" exhaust? Since you are running a power FC, do you have a failsafe for the water injection if it runs out of water or gets clogged? Also curious if you are injecting only water as opposed to boost juice or water/methanol mix?
Indeed a very fun setup! Yes it's a 3 inch exhaust. As of right now, I don't have any failsafe setup. I just have the AEM warning LED right in my line of sight to warn me of a system failure. It does seem possible to set up the "boost switch" setting in the Datalogit to trigger a lower boost setting when there is a failure in the W/M system. I am injecting 100% water in the system. With running over 25 psi on pump gas in a hot, dry climate, reducing the combustion temps is more important to me than the extra HP potential from methanol.
what do you have between your hotside housing and the LIM runners?
Nothing really. Just a block off plate and a silicone cap for a nipple that comes off of the water pump housing.
Originally Posted by Carlos Iglesias
The right pieces,effort, and thought rewarded... congrats!
Working through my new ECU and setting up knock control, I was hoping you might share what the knock frequency window you logged?
Thanks Carlos! It's just the stock knock sensor and settings in the PFC. Every knock sensor reads knock differently, especially with the age of these sensors. When I drive the car out of boost, the most knock count I see on my logs is 24. I like to add a 30% margin on top of whatever my highest knock count is when driving the car out of boost. Therefore, I consider anything above 31 a knock, or at least a reason to hook up a stethoscope and investigate. That's just what worked for me and kept me out of trouble when tuning PFC's. What ECU do you have?
Nothing really. Just a block off plate and a silicone cap for a nipple that comes off of the water pump housing.
Thanks Carlos! It's just the stock knock sensor and settings in the PFC. Every knock sensor reads knock differently, especially with the age of these sensors. When I drive the car out of boost, the most knock count I see on my logs is 24. I like to add a 30% margin on top of whatever my highest knock count is when driving the car out of boost. Therefore, I consider anything above 31 a knock or at least a reason to hook up a stethoscope and investigate. That's just what worked for me and kept me out of trouble when tuning PFC's. What ECU do you have?
Thanks for the comprehensive response. I'm still tuning my Motec M1 with dual (audio wideband) Bosch knock sensors (i.e. donut sensors). While all the adjustability and complexity have benefits once mapped, it's not an install-and-run like the stock one. Hence, my research and ask. That said, your knock threshold makes perfect sense and is similar to the Motec recommendations, though it also adds RPM and Load profiles to set the M1's knock thresholdsat. Sounds cool till you have to map it.
there should be of course a prioritized sequence, the first priority being focused on engine longevity. (not blowing it up)
there's a lot to like as to your bay. Precision is not the same animal it was 30+ years ago as a start up. i visited them in Hebron, Indiana about 10 years ago and had the opportunity to spend a few valuable hours w Dan Barlog, chief engineer. we toured the entire facility and examined every part going into the GEN 2 CEA turbos. at that time there was a war going on between tractor pulling (or something like that) competitors. it seemed some were not able to get there hands on the current Precision turbo... which as i recall were priced well over $40,000 per. be it tractors, or whatever, this is bigtime racing for bigtime money and Precision seemed to be the go to... it didn't quite work out for me but i have always been interested in a Precision Rotary match. so good for you not following the sheep.
love your Hellcat pump... love my Hellcat pump.
as in any setup there are missing links. your OE LIM needs to be replaced w a way better flowing Excessive. in addition to flow you can then check another box by adding two more secondary fuel injectors. you currently have comfortable delivery capacity (on gas) for 500 rw rotary hp and a turbo that can make more than 700. if you use ethanol your fuel gap becomes significantly wider. of course finding one ATM is a challenge since they seem to be back ordered.
the first two things i would do w your setup focus on heat.
topping the list is a barrier between the 1800 F heat of the turbine housing and the heat receptive aluminum LIM runners... in your case the front rotor LIM runners.
Cam Worth was dynoing a single turbo that wasn't quite doing the numbers. he noted the cherry yellow turbine housing being close to the LIM with no heat barrier. after finding something lying around the shop, a piece of SS plate, he placed it between the two and did another run w no tuning changes. the AFR dropped more than a full point from over 11 to just under ten. the rear LIM runner was only exposed to the wrapped DP so it did not change. the front rotor had to have dropped two full points! the motor had effectively been running above 12 in the front rotor and 10 in the rear. there is a simple relatively inexpensive FIX. a simple sheet of MICA. not as sexy as other XXXXX$ solutions but way better. refer to any materials properties list ... latent heat transfer.
visit the "System Design Section" of my site for all the info, and no, i don't sell Mica, i just use it. so does NASA for re-entry. i don't remember seeing any shiny metal on the bottom of the shuttle.
next item would be a turbo blanket.. the function of the blanket is not to solve the LIM runner heat problem, as it won't, but it WILL drop under hood temps 30 F. that would be the air your motor is using.
i recommend the PTP Lava Blanket as it contains a mica like substance.
you are making good power, especiially given your altitude. 5200' normal barometric pressure is 12.13 psi.
28 psi + 12.13 = 40.13 MAP
28 + 14.7 = 42.7 MAP at sea level
40.13 / 42.7 = .94
you are going to be down 6%, or around 30 hp due to elevation.
another altitude penalty is decreased turbo efficiency. the turbo sees 17.5% less pressure and will have to work significantly harder, heating the air.
making big power is challenging at sea level. . and it is all about heat.
the next system item to address is the location of your air filter. directly in the exhaust stream of both heat exchangers. this may not be a killer on the dyno for a few brief blasts w the hood open to 36 F air and a blower... but, close the hood, go for a sustained drive in 85 F and WITH a turbo blanket general underhood temps will be 130.F. what they will be directly downstream of your heat exchangers? charge air coming out of your turbo at 28 psi will be higher than 400 F. a really good IC generally removes 140 F. where does that torrent of heat go? out the back of the IC. no place for the air intake.
probably most of the above is not news and is on your to do list. i am very interested as to how your setup evolves. i do think you may in the future, at minimum, uprate your wastegate situation. now way does one 44 mm WG handle that turbo.
Glad I can offer at least some insight. Setting the knock threshold up is always a pain in the butt, but well worth the effort. I set up a Link ecu fairly recently and it was the same process, but I initially set that one up on the default RPM x throttle position table. I'm now revising it on an RPM x boost table like you are doing, because when we datalogged on a track day, that car would falsely breach the knock threshold and pull timing.
Howard,
Thanks for the great info and advice! That dyno story is downright shocking and its funny you should mention that...
So on my old setup, I ran a 6765 at 16 psi for 5 years. No heat shielding around the turbo or intake manifold. After rebuilding the engine and adding the water injection setup, I started to really crank that turbo up. Well wouldn't you know it, I reached 24 psi and blew a hole straight through the LIM right next to the turbo! It was perfectly fine at 16psi for many years, but that additional 8 psi was all it needed to call it quits lol. I looked for an Xcessive LIM for a couple of months, but got tired of not driving the car and threw on another stock LIM to get me by.
I grabbed some heat shield off of a junkyard BMW that I'm gonna shield my LIM with. The turbo blanket, better LIM, and wastegate setup revision are all on my to-do list and I will update this thread as I go. After installing the 6870, I was just so darn antsy to get the car on the dyno that everything else had to go on hold!
01-29-23, 01:35 PM
