Hello all. I am in the middle of making a new video for tuning on boost. I have *some* experience with it, as I have tuned boosted cars with great success, but I'm no expert either, and I certainly have not tired everything that could be tried. Unicorns aside, in an effort to be a thorough as possible I would like some input from the community on a number of things that I am trying to get a consensus on. Clearly, since I am making a video intended for use by both beginners and experienced tuners, I cannot recommend to folks to push their engines to the limits right from the start. That's a great way to get some folks in trouble.

So in having said all that, I want to stick to the generally accepted "rules of thumb" for this. Problem with that is, they all seem to vary, enough to be an issue and confusing, especially for beginners.

So here are some of the questions I have for the community:

1. What is an acceptable Effective Compression Ratio for pump gas? (I've found it vary from 7.5-8.5 DCR no boost, and up to 12.5:1 with boost with aluminum heads). Looking for what you guys think from your experience. Remember other factors here are not being considered, like methanol, intercooler, race fuel, and variable valves. Just think stock bolt on kit, with maybe heads/cam. Again, keeping it general as possible.

2. Recommended Static Compression. I know, this isn't nearly as important as the effective or dynamic numbers (since nothing compresses until IVC) but it still dictates total displacement, which has a big effect on boost and power. I typically go with the rule, less static, more boost, but nailing down a number is subjective. 7.5-9 ish is what seems to be the range most recommend, tell me if you have another idea.

3. Timing. For this I have used the 28 rule, as in start with 28 and subtract boost. What's left is the timing. Any other methods out there?

4. VE table setup. Typically I set this to 1.3 for 2 bar and interpolate, or 1.6 for 3 bar and same. Never had an issue with that, but I'm sure someone will disagree, as there is little consensus on this number as well. I think between 1.3 and 1.5 is plenty. However, technically I know it's physically "incorrect" since it should be double the last row (per bar), theoretically. But not everything that works on paper works in the real world.

5. Formula for finding final compression ratio. I have used this one here a number of times: ((Boost + 14.7)/14.7) * SCR another version is: ((Boost/14.7) + 1) * SCR
Those are actually the exact same formula, however the agreed upon result is the question. 12.4 seems to be the highest recommended. I know some will say that's low. Think stock here. I've seen it much higher, but I'd like to see what the community thinks on that one. I've seen others say it's too high.

So that I think is about all I have for ideas floating around in my head right now. I might think of more stuff as I progress into this video, which sounds simple enough, but just isn't if you really think about it. I would be remiss if I did a boost tuning video and left out SCR, DCR, and ECR and the other associated physics.

Open for debate here, and please let me know if you want something in particular added to the video. I also want to cover MAP offsets and so forth. Trust me when I say I'm being thorough, as I am covering basically everything I can think of here in one spot. People seem to like my approach, so hopefully I can get another home run with this video.

Oh and here is a nice little free compression calculator I made in excel. Way easier than entering your information repeatedly in the online calculators. This lines up with most of them, and it is fairly comprehensive. I left out altitude, and a few other small factors like piston crown and ring depth, but this is pretty good if you don't care about that stuff.

 

My 0.02 on a couple items above...
For 93 stuff only, anything 11:1 or south is ok assuming reasonable boost. Centrifugal blowers have more head room due to linear boost/power curve.

Start at 10-12* timing and dial in the AFR. Then start adding timing and read plugs/watch for boost.

 

Good stuff. Like the input. Type of boost is something I'll cover as well. With a procharger, it can be a bit higher as I've seen and tuned them, and research confirms that they support much more actually. Stock LS1 can get away with nearly 8 PSI without blowing up, that I know lol. Roots style is much, much lower on tolerance for DCR.

I also saw somewhere the absolute DCR limit (no boost) is 8.63, but I cannot confirm this anywhere.

 

Your equation in point 5 is for boost pressure ratio, not compression ratio.

 

Splitting hairs aren't we? It is called a number of things depending on who you ask. I used "final" in this one as it seems more appropriate than the often misused "dynamic compression ratio" which is technically theoretical only, but shows up even on the calculators as "dynamic". The only way to get that for real is with special equipment, similar to how IMEP and other tests are done, on special heads and all that good stuff.

 

I think you may be taking a good idea too far. Your intention is apparently to provide a comprehensive tutorial for people in need of legitimate info. However, unlike your government specced helicopter parts that have to fit within a certain tolerance, your potential audience will have access to a completely unknown list of parts from all over the globe. The exact same person who could really use the info you provide may very well be the one who does not even come close to understanding why one mismatched parts tosses all of your theoretical advice out the window. Think of some ls1 motors where 28* of timing at high rpm may be too much, then some BBC motors need 56*. The best I think you can hope to achieve is to give ballpark estimates with known part combos, then hope people are smart enough to look up the rest for themselves.

 

This is the reason I am sticking to "general" rules of thumb, in addition to adding known methods to increase success. I am not putting up parts lists or anything like that, only the factors and considerations involved, as I normally do. I will probably include ways to help reduce charge temps, and cover types of boost, but I'm not getting all that deep on that topic since, as you said, there are a million combos out there. I however cannot ignore talking about detonation, because all of these things must be talked about in a true guide to tuning for boost. Heat, compression, fuel, and timing all directly relate to detonation, therefore, cannot be left out.

Please don't misunderstand me when I say, I am tying to keep it Barney here. Last thing I need is someone getting in trouble with their combo because they failed to research for themselves, and then blaming me for it. This is why I intend to error on the low side, as I am well aware other combinations that could potentially be built. It also has nothing to do with helicopters or my other job. This is strictly based on my knowledge of cars, which after this many years of building stuff and researching everything to an anatomical level, has left me with valuable insight into many things besides just helicopters. If you want to know something about Hawks or Hueys though, I can also make you ears bleed with that topic and take it to the bottom of the rabbit hole lol. Some of those things still apply to cars though, like torque and gyroscopic precession, since those relate to physics, physics relates to everything, and physics are cool.

For your example though (for ***** and giggles), as a guess, I'm going to say that the BBC can have more timing than the LS1 probably because the chambers are close to double the size on the BBC. 118cc wouldn't be a uncommon thing to see on an old big block. LS series see numbers nearly half that size (70cc on LS3). Might be wrong there, but as a guess, I'd say that's probably why you can get away with more ignition timing. Carbs also allow for more as well, since the state of the fuel is still liquid, which draws additional heat away as it atomizes. Two reasons why spark could be higher right there.

Anyway, I'm just looking for some consensus from some of you guys on how you set up for boost. I have my ways, and I know my way around it, but in an effort to keep it understandable and simple, I am simply looking for the general rules you guys go by, or if the ones I listed are adequate. I've never had an issue with my methods, but it don't mean they work for everyone either. This is basically combining all the research into one spot, since I've spent literally years learning these things, sometimes the hard way. Consolidated knowledge isn't a bad thing, so long as it does work for everyone, hence "general".

 

I see what happened!

 

It's also often called "effective compression ratio" after plugging boost into the formula lol. I guess I can add "boost compression" to the list of things its called? Might as well if you felt the need to point that out. I'll make sure and include that on the "list" of things it "might" be called, though all mean the same thing lol.

 

From my experience and thinking about what has been important to me that doesn't get a lot of attention in tuning discussions is...plug choice, plug gap, and plug reading. Some times we want to focus too much on things that don't really matter especially on a less than max effort build while ignoring the most important things.

 

I will definitely include this. Great idea. Think the general rule for heat range, as I know it, is go down one for every 100 hp over stock, ish. Plug reading is also a key fundamental, for obvious reasons. Tells the truth better than any sensor can. Important for this topic since N/A builds are pretty forgiving. Under boost though, all factors are exaggerated, particularly heat. Thanks for the idea.

I know spider already mentioned this too, but I'll take it as two votes for putting in some plug reading and explanation of terms and general rules.

 

Stock ls1 here. BEEN running more than 8psi for over a year. It sees 12 psi on the regular.

Something of NOTABLE MENTION. Make sure you disable LTFT, if you dont have your fuel table dialed in 100% perfect, whatever your long term fuel trim sees last when you go wot will carry over to your full throttle....which could cause you to go rich or lean and not have consistent fueling. Even if your LTFT is dialed in perfect and something changes, and it uses the LTFT last seen before going into boost, it can cause you issues. My point is dont chance it. Theres many different things that could happen causing your fuel trims to change. I found this out just recently and have been chasing my tail with tuning my car under boost.

 

I think it's great you're doing this. It will come especially in handy for me, as I'm getting ready to bolt on the F1x within the next 2 months at most.

* +1 to plug reading/gapping tutorial
* Tutorial on how to switch to 3 bar map and adjust parameters for offset accordingly in HPTuners
* More detail on timing
* Simple stuff like Target AFR on Lean Cruise, Target AFR on WOT depending on fuel type

Thanks,
Andy

 

As mentioned, I am well aware that other setups can exceed the "general rules" but I am simply unwilling to offer advice telling folks to push it lol. This is focused as a beginners guide, and something to build from, as are most of my videos. That part with LTFT's is HIGHLY interesting. I did not know that, but now I do. Very good info. Are you running a MAF then? I know spider loves his MAF stuff and I know he has build stuff to at least 700 whp with a scaled MAF. Just curious.

I'm starting to think this video might turn into several. At least two minimum. One to cover boost basics, and a second going over tune setup. I'm tempted to leave them together, but it's quite long so far already lol. It's a complicated subject after all, if you really want to know what you're doing and why. I do want folks to understand the physics behind it all, and not just pick numbers because that's what so and so said or what not. That's not going to help you if those numbers don't work on your car, so you need to know why you are doing something before you do it, if that makes sense.

A lot of it is mathematical, unfortunately for those who hate math lol. If you are tuning though, I suggest getting familiar with your common formulas and so forth. One of those is how to do the linear offsets on your MAP sensor. You will need a new one, but sometimes you have to adjust the offset to get them to match your boost level. Seen lots of people have that issue in the forums through the years. Most of the time it works from the data provided though.

Really glad you appreciate the work going into this, as so far my entire day has been dedicated to powerpoint and surprising myself on how well I know this ****. Haven't had to google much lol. So all definitions used are my version, mostly in layman's terms, with a few jokes thrown in because I can't help it. This is me taking a break after about 6 hours so far, and I've got through 19 slides, and still not done getting through the basics. Left off at pre-ignition, which also correlates to spark plugs believe it or not. The wrong plug can cause that, and trust me that's about the last thing you ever want to have happen to a motor. This is why it might turn into two videos lol. I highly suggest watching them both when they are done, if I do split it up. Setting up the tune is actually the easy part. Understanding why you're doing it, well, that's another story lol.

 

Great stuff and the plugs are a MUST in a boosted application. Awhile ago Chief and Shawn did a video that included a little about plugs. It was Super funny! The datalog was called the "news" and what it reported, and the plugs were the "boots on the ground soldiers" and the differences they actually seen.