pump gas - knock limited before MBT?
 

I am getting tuned on Thursday. 01, 92 E0 pump gas. Rotrex at about 10 psi at redline. The tuner (subie mostly shop) wants to go for MBT and is not worried about knock. This concerns me. I have read the dyno tuning thread. I am building hornetball's det can setup.

Is my concern justified? Aren't we knock limited at midrange RPM?

You probably wont be nearly as knock limited as the turbo guys since the failtrex builds pressure so gradually

I'd still be careful, so your nervousness is not unjustified

MBT or 3° shy of det onset (whichever is least advanced). Don't you dare let that tuner tune your car past det!

Vlad's got a point re: Rotrex, but there are a lot of variables.

Good luck. We want vid and charts.

Subscribed, I'd love to see some good information on this.

I have to think compression plays a big factor as well; tuning to MBT on a 94-97 car would have to be a lot safer than doing the same on an 01+ car with higher compression.

Rotrex on pump gas at 10psi should get MBT before det, but if the tuner "isn't worried about knock", he's an idiot. I would try and find another tuner based solely on that statement.

My words not his. Brevity due to phone posting. He went on at length about why we should hit mbt before det. I just don't know if our engines are similar enough to what he's used to tuning for his common practices to be applicable.

That's the other thing that makes me very nervous about this guy:

if he's a subaru tuner, he of all people should be the MOST careful around det/mbt because subaru's are THE MOST knock happy and finicky, and are det capped well before mbt 9 times outa 10

Sounds like you need to reconsider the tuner.

Who is it btw? You can PM me to keep it private.

I have called and spoken with 4 different dyno operators in the area now. None of them use anything specific for knock detection.

"You can feel it, or hear it, or see it in the power drop."

Therefore I'm taking my own. I will get my cable built and tested tomorrow and if for some reason it isn't working I'll postpone the tune.

I agree with you, but for a different reason. Less exhaust pressure means there is a lot more exhaust scavenging with the supercharger which helps get the heat out of the chamber.


OP,
Does this shop have experience tuning track cars, or just street and drag cars? Because there is quite a big difference in knock limitation between a car that runs hard for a few seconds and a car that runs hard on and off for 10 minutes or more.

NB has a knock sensor.
also det cans are your friend.

Also I wouldn't want to be anywhere near mbt if you plan to track this thing. I'd back it off a good few degrees. Maybe I'm just a wuss lol

Run E85 and give it all the boosts.

Ok the det cans are built. I'm getting alternator whine anyway, but I can live with that. I can hear the ticking of the engine at idle. Tomorrow I will put the clamp on a better bolt than the one I was using today for a test up by the EGR valve.

My April '13 GRM came today. In "starting line", Tim Suddard discusses a run of bad luck they've had recently. They tracked a Camry, and blew the engine. This is right and proper for a tracked Camry, so this is fine. They tracked a 200k mile WRX project car, and blew the engine.

Then he discusses the Subaru some more.

"We had the air/fuel ratio right, but again, we knew we were modifying a car that had a couple of hundred thousand miles on it -- and cranking the boost does add stress to an engine (they added 100hp). We'd even experienced an odd shutdown on the dyno a few weeks prior, and in retrospect, knowing that these engine computers back down boost when they sense knock, we should have stopped to study the problem. Yet again, though, we had deadlines to meet, so we quickly attributed the shutdown to a fluke and went on about our tuning. As they say, we paid our money and took our chances."

WTF? Why would anyone tune a modified boosted engine without some form of knock detection? I mean, it's like not wearing a condom on a casual hookup - it's not expensive, it's maybe a little inconvenient, but the consequences of not using it are many orders of magnitude higher.

E85 on a piggyback w/stock ECU - don't want to go there.

+1, this dude is a fucktard.

Because only MS3 and AEM do a good job of knock listening. I disable it on most cars, then tune ultra-conservative.

I was det limited on my OEM VVT tune, you are going to be limited as well. Most of these dyno operators are fully retarded. Back before I found Exatorq, I had two dyno operators make fun of me for using the det cans.

If this guy is happy tuning an engine with as much advance as possible and expecting knock-detection to do the hard work on his behalf, you need to walk away. When I tune cars I find MBT everywhere I want to, then I start the destruction testing. I load up the dyno heavy and run 1st, 2nd, 3rd, 4th, 6th (I skip 5th for the added rpm range. The header glows yellow people duck for cover, I get scared every time. I recently did this on Mini-P's car and had to pull 3-5 degrees from cells that previously did not knock.

It's important that you find a tuner who discusses his process with you and why he does what he does. If he's not putting extreme, sustained load through the engine and listening for detonation, you need to find a better tuner. It's about creating racetrack-like conditions for cars that go on the racetrack. Any tuner that would intentionally or unintentionally put an engine in a detonation-prone tune and expect the computer to pull spark, is an abject fool on many levels. First, he doesn't understand what he's doing. Second, he is relying on an imperfect system to protect several thousand dollars. Third, he's lazy.

Unfortunately, this seems to be the norm these days. I worked with the dyno guy at MER (adjacent to MSR-C). He was planning to rely upon OEM knock detection and was surprised when I told him that a 1990 Miata has no such animal. MER is supposed to be a dedicated Miata shop. He was fascinated by my det cans.

:facepalm:

MER is a shell of what it once was. They know nothing about tuning and they are balancing cars on axles, not diagonals.

A guy in Houston bought eMS2 and rather than use me for $300 decided to give the tuner at MSR-H $700 to tune his car because "he's a pro". I drank beer with this tuner once and he told me that steady-state tuning was a waste because he could guess the sub-100kpa spark angle values based upon experience...experience of guessing I suppose. He also had no understanding of transient-fuel characteristics. lol Oh, and he thinks max power is 14.7:1 at WOT.

I suspect that the statement is not fully in context. I think what was probably meant was that the tuner expected to find peak torque before the knock threshold. I would agree and expect the same, though frankly I have not tuned a Rotrex equipped Miata so I will only speak of expectations and not from direct experience.

If the tuner has a good dyno that properly controls the car and is very consistent, you will see a reduction in power before the onset of det. However dynos that are less repeatable and/or unable to load are a different story. IE, knowing the operator's equipment is also important for context. A $70k Dynapack creates a different environment than a $24k Dynojet.

I've been laughed-at for using det-cans and the peanut gallery of "professional tuners" comment that "detonation is what a knock sensor is for!"

I got money on lazy, almost every time.

I flat out disagree, but am aware that there are respected tuners that think like this for one reason or another.
A knock sensor is there to help save your butt if you get bad gas and should not be relied upon as a substitute for poor or lack of spark tuning.

But you can get a good tune in most cases without det cans *if* you have good equipment and the know how to operate it. That being said, there are some situations where they are helpful and sometimes are required.