HOW DO YOU KNOW WHEN TO STOP ADDING BOOST FOR A GIVEN FUEL? I have been pondering this a lot lately, and just can't come up with the answer. Some tuners won't go past 12 psi on pump gas on the dyno, while others go for 18 or more! I'm on pump gas, but for argument's sake and irrespective of fuel type...how do you know when to stop adding boost, at the same time trying for the most power possible? Is it just a personal comfort level thing? Does a tuner just try and take build factors into account, like sleeves, internals, etc to make this call?

I have heard of many guys running insane amounts of boost, and Ign. retard on pump gas to keep under the det. limit.

My story: Finally I have my fuel curve perfected at all IAT's and all ECTS. The comps are perfect, and keep my A/F in check and consistent regardless of external conditions, factors and boost levels. I have taken it slow, read my pugs, and guessed my way as far as I dare with the ignition maps and street tuning on pump gas up to about 13 psi safely.

The last thing to do before I close the book on my tune is a dyno session, which would be my first one ever. I have been present at the dyno before, and seen how it is done, overlaying pulls while adding timing to get the most torque out of your fuel, stopping where it peaks. So my question is not concerning Ign. tuning but when to stop adding boost. You guys are all great and always willing to help other so thanks in advance.

 

As you said it is all on build factors. If it is on a stock motor with pump gas I would rarely go above 8-11psi. Also take into account what type of motor you have as a GSR will have more compression than a LS motor. It is all in the factors of the build.

One thing to remember start off low in your boost map and work your way up. On some dynos for instance you build 13psi on the street which may not be the same on the dyno.

 

Thanks Rtype16 - Its a Godzilla sleeved, 9.5:1 comp fully built 84mm block. Pretty stout internals - Eagle rods, Arias pistons. Built by the guys at Golden Eagle. So removing the limitations of internals, what flag do you use during tuning that says to stop? Do you stop making power at some point, regardless of adding more boost given you have A/F and Ign. tables in check?

 

Implement and USE a Knock sensor. It is a good warning sign for fuel and ignition limitations when you are talking about how much boost you can run.

 

Any suggestions on good aftermarket knock sensors tuned for our motors? I keep hearing knocksense? Is that one still a good option?

 

First, you need to know that PSI doesn't mean ANYTHING. A huge turbo could outflow a small one 10x's as much CFM at the same PSI. So as long as you aren't lifting your cylinder head or blowing head gaskets the sky is the limit with a BUT.

The BUT is that every power adder has an efficiency window. Some are more broad that others. There are MANY ways to go about all this but most will add timing (and adjust fuel as necessary obviously) until it stops making power and back off 1* - 2* for safety.

In a round about way the same can be done with PSI. Eventually power will stop gaining or IATs will become dangerously high - the turbo is being pushed passed it's efficiency. This will also shorten the life of the turbo as well. You should do the calculations and plot the info on a compressor map to get an idea in the ballpark of your turbo's limitations. BUT since you have a Precision (LOL) I guess that's not possible.

KnockSense is a VERY viable options but it is very picky on its settings. Boris still ships them out. There are MANY threads on this system and implementation as well as adjusting.

 

Thanks very much for all the info so far this helps a lot. It sounds like the indicator for when to stop adding boost with a given fuel, is just when you get outside the efficiency range of the turbo, or conditions get dangerous, I.E. you start seeing high IAT's or det that no amount of Ing. retard will resolve.

I plan on getting a knock sensor, but here is my only heartburn with knock sensors: By the time you are seeing knock at the sensor, can't you sometimes be WAY past max power? Doesn't that make them a silly choice for street tuning Ign. maps solely using a knock sensor?

 

Anyone that tunes solely off a knock sensor is an idiot - plain and simple. The only time you will be able to go passed peak power without knock is when you run a fuel with a high detonation resistance. In almost every instance with pump gas (93 octane or less) you will detonate before max power. Depending on EMS you can actually use something like the KnockSenseMS to retard timing in the event of knock. If you have a later model AEM you can even do it per cylinder.

To street OR dyno tune you need, NeeD, NEED to master the art of reading plugs. With out EXPENSIVE cylinder pressure monitoring this is your ONLY way to know EXACTLY what is going on inside the engine. Ideally, for any setup you would want to run individual cylinder EGT and A/F Ratio combined with a knock sensor. Of course the more you monitor the better, but most people with independent monitoring find each cylinder can want very different fuel due to air flow into and through the intake manifold and head.

Fortunately for you, just about every turbo and combination imaginable has been done to Hondas and you can look up similar builds or call Precision (LOL) themselves.

 

Then what good is a dyno when tuning on pump gas? By this logic, you would never make it to max power on the dyno without detonation?

I only ask because a local tuner I have been watching and learning from never uses any sort of knock detection on any of his customers' cars. He only dyno tunes to max power according to the dyno, and stops there.

I don't and won't have individual cylinder monitoring. So you are suggesting that my best option is to get the knock sensor in place, and dyno tune in the DIRECTION of max power until I see knock, then back off 1 or 2 degrees? Checking plugs of course?

Then why don't I just tune till knock on the street w/reading plugs as I go?

 

Haha, you don't understand how it all works I see... Search and read up on Mean Brake Torque. The dyno is ONLY a tool, a great one, but still useless in the hands of people that can't extract the data. You keep adding timing until power drops off and then back it off. That is your maximum power with all the variables at that time in place.

If you had some fuel with high knock resistance you could actually put too much timing and still be hurting the engine but not detonating. This is where a dyno helps as well because you would be able to see the power dropping off. This is hard to see / feel on the street but can be done with datalogs and tools such as Virtual Dyno - although nowhere near as efficient as the real thing.

You don't actually WANT to tune for knock as even a short blip can blow your engine or have some other failure like a cracked ringland. The idea is to make power until it loses some (hopefully before detonation) and then back it off. This is the reason you go slow and easy when street tuning, but that means more pulls and more spark plug reading. All of this is very hard on the engine and leads to bad things - i.e. speeding tickets. A drag strip is also a great tool since power can be calculated with MPH gains. Most will dyno tune and still finish up the tune at the track.

 

Hey Will...you won't be disappointed if you get one, their inexpensive and once you get that and the knock sensor installed you can try setting up what we have in which I'll make you a small circuit that'll allow you to install this inline with the KSMS to listen for knock by means of an electronic det can....PM me if you got questions or you still got my email too

 

I personally never keep adding timing til it loses some power. As you start to increase timing in areas you will see big jumps in areas. The more timing you add however these increases can start to only climb by like 1-2 horsepower per degree. This is the point that I stop and back it down a degree or 2 just in case you get a batch of bad gas. A 1-2 horsepower increase can simply be dyno error on the run. Although Hondas are pretty consistent. I just dont find it useful to extract every last bit of power on the car(especially when it is not a dedicated track car). I rather it be safe.

 

I think what op is trying to say is when do you stop on a dyno.


Without a knock sensor and only a dyno how do you know if the motor is knocking before mbt


From what ive read you will see mbt 1-2 degrees before knock on 93. Im bot sure if this applies to 91

 

Another thing to keep in mind is volumetric efficiency

 

At what compression? Haha, there is no blanket statement here. If I am being vague then sorry, but it's on purpose. There are WAAAY too many variables to take into account on the inside and outside of the engine. This is the whole point of adding timing until power isn't being gained. An experienced dyno operator knows when to call it quits - it's all in the details.

 

Completely forgot about comp. i figure nowadays everyone is running 14:1 lol

 

Thanks guys for always being willing to help us lesser experienced guys. If there is anything I have learned in tuning my own car, its that any idiot can tune A/F ratio, but it takes a real man to tune Ign. maps.

Sounds like I had better get a KS hooked up and dialed in before going to the dyno in case there is any unexpected detonation pre-MBT. They seem like cheap & easy insurance against something so detrimental. My comp is a comfortable turbo spec - 9.5:1. I don't know what that means I can expect to see in terms of detonation threshold on the dyno though.

Heh, hey Kyle! I wondered when I'd be hearing from you on here about knock sensors man. I'm def. going to have questions for you...

Also, this thought by Rtype16 helped the most. I had a major ah-ha moment. I'm pretty sure this is going to be my on-dyno Ign. tuning approach -->

 

absolutely! that's why its called MBT since its the "Mean" avg figures that really are as far as one should go since the gains tend to drop off once you've made big leaps and bounds per each change till that point.

Hit me up for anything though! Lately I've pieced together a few listening modules for some on here so it all works fairly well with the KSMS....I've been listening to my ignition for the better half of a year now it seems and its helped me immensely

 

I think you guys were taking me WAY too literal haha. I don't know of anyone "in the know" that keeps going for every last 0.0001 horsepower. Like I said, keep adding timing until it drops off - it being the gain curve. I reread what I typed and I guess I didn't realize I had to spell every last detail out... A quick search of what MBT actually is (like I said previously) would have solved that issue. Oh well, at least you kinda hopefully have it figured out now.

 

idk if you stumbled across this yet but its a good read on mbt MBT (Minimum Best Timing ?) - Engine & fuel engineering - Eng-Tips

 

Thanks for all the replies so far! I'm amazed at how much help there is out there for tuning newbs like me.

Here is another wrench for you guys. How do you all deal with wastegate inconsistencies while tuning? Seems to me that if you had any kind of creep, then 2 back to back dyno pulls attempting to establish a baseline or even MBT, at a target boost level could fake you into thinking you are making more power when you are really just boosting higher. How do you deal with creepy wastegate on tuning day?

 

 

Haha to tell you the truth i was just glancing at most of the posts and completely missed the whole part of MBT and just saw keep going til it drops. haha. Sorry. Plus once you go past MBT and keep adding timing its not power that will drop it will be the motor in most cases. haha.