So continue ramping boost up with rpm?
I know this is an ls board and i keep bringing up stupid evos, but an ICE engine is an ICE engine, right? It seems like all the evo dyno graphs ive seen will peak boost near torque peak and then it tapers down from there. I rarely see completely level or increasing boost curves, and its not due to lack of turbo, even big 66mm stuff is setup like that, and it never made sense to me at all.
I have mine setup to go flat or increase boost with rpms and its been working, and the way you describe why makes a lot of sense. I think im going to start experimenting with that concept on both of my cars.

 

You turning up the boost will make it harder to light off the combustion than a couple tenths of a point of AFR lol. And no, anything in the 11s shouldn't blow black smoke unless its hella under timed.

Seth I agree with what you said and should have clarified my initial comment about cubes/CR/turbo size/rpms. My head immediately went to SBE and stock CR setups since that's all the rage now. If you're building a forged setup and have the ability to mess with CR, hell yes you can make a crap load of power on pump like Sonny much easier. Seems nowadays everyone wants to boost the crap out of their stock motors or junkyard stuff.

 

Whether you want...need to increase boost with rpm really just depends on the setup.

If you had small turbos etc there really wouldnt be any point trying to do that. If you rarely use higher rpm's...again, why bother pushing boost up. If charge cooling isnt as good as it could be...again, why bother ?

4v engines will tend to want to rev harder from the outset, so you might be more inclined to use boost to help them go further vs a lower revving V8, if of course you even need to be using those rpm's

Again, it's just building it right for your specific needs, then there is no mucking about needed.

 

Yeah, like I mentioned, the OP didn't specify, so I just treated the question as a generic hypothetical inquisition, within the LS architecture and no other limitations or requirements. Nothing wrong with either side of that coin.

I love the "boosting the crap out of a stock motor" stuff. It's so bad *** what we can get away with now-a-days. It wasn't all too long ago that even a pro built blown big block wasn't able to make what can be made, nor match the relative reliability we're able to get with a 200.000 mile junk yard engine, valve spring upgrade, and cheepo turbos. It's just insane when when I really think about it. Flipping crazy insane!

 

I'm pretty much with stevieturbo on this one.

To add to this, or put it into my own words.

You could very well blow your junk up! It's the complete combination of parts that make it a sensible option or not. And I'm not going to tell you, over the internet or in person, that it's something you should do blindly, without having researched theory, figured out the physics/math, and without having some sort of dialed in idea, a very keen sense, intuition, and written plan of what to expect with every slight change in the tune and boost map.

That's how I do things anyway. Some jump right in and blow stuff up, learn, blow stuff up, learn... Ultimately up to you.

I just brought it up as a point of discussion.

Try it at your own risk

 

yeah and I'm thankful we have decent tuning SW now like HPT and EFILive compared to the Tuner Cat and Maf T stuff that Harlem and them had to use when LS stuff was new. Even LT stuff is like WTF lol

 

Spider, thanks for sharing your experience.

StevieT, I'm a fan of 427 air flow by way of 323 spun 25% higher rpm than a 427. With the right cam and spring setup, crank up the boost past peak torque and watch the power climb.

Lots of good info on wise fuel target, timing adjustment around peak torque and reading plugs so no surprises.

 

I reread my previous reply to this and wanted to expand a little more on the points you made.

I couldn't say why any particular setup may have a decay of boost. Every setup is different. It'd does seem like most people shoot for a single target boost number and hold and maintain it as a static figure. And I can't think of any reason to intentionally decrease it after peak torque. So, I assume it's a limitation somewhere in a setup that would cause that kind of observed boost curve.

If I were to implement the tuning strategy of increasing boost to make up for decaying volumetric efficiency, I think I'd largely base it on the VE tables in the tuning software instead of observed torque numbers.

There's a lot of stuff going on. Peak Torque isn't necessarily peak VE. If you consider peak VE to be anything within a few % of the actual peak VE figure, it can span a relatively wide RPM range. Where peak Torque is the result of many things, but primarily the relationship between VE and the exponentially increasing parasitic losses of friction with increased RPM. There are other contributing factors (ignition timing, flame propagation, etc.), and even the two I mentioned could be expanded upon at great length.

All that to say... VE tables is where I'd look. Where they start to decay is the beginning of the rpm range I'd try to start making up for, slowly bringing them up toward the same values as the peak region by adding boost. And, I'd rather do it on an engine dyno, where I could more reliably hold or sweep particular RPM's or regions. I'd certainly pull timing and add a little fuel to create a safe environment to play in, then slowly add/subtract them back in after a round of boost table and VE table massaging and note any performance gains indicated.

And all that assumes the whole engine combination is cooperative and does what I want it to do. It could be that certain parts selections need to be evaluated and replaced. Compressors, turbines, waste gate size,waste gate location, boost solenoid configuration... Something's bound to require some attention and modification to get everything just right.

Anyway, I don't have the time right now, but later, I'll see if I can't find one of the Steve Morris videos that demonstrates the strategy... as a reference to chat about.

 

Thanks for taking the time to post all of that tuning info in this thread, it's been helpful and informative.

 

I have never been on a dyno, and probably wont anytime soon. What are your thoughts on using fuel pressure, ipw and AFR (basically fuel consumption) as an indicator for peak torque/peak ve?

as for the evo boost taper, it is a limitation of the internal wastegate design that they use and i think those curves are so ingrained in the community that they tend to tune in that curve even when moving to externally gated standalone stuff. or im completely misinterpreting the whole thing. Im a foreigner in the mitsu world.

 

That has to be the funniest thing i have heard all month... where do you get your info?

 

thanks for the kind words.

 

better off tracking g/cyl. Red hard Supra on efilive wrote a white​ paper using dyncylair and cylair to plot hp and torque. It comes from an accurate ve and or maf curves.

 

his blog is all links to a dead url. if you have that paper saved i would like to read it.

 

It may be funny to you but it's the truth. The smaller turbo can make to much boost down low and fold the rods, where as large turbo will spool a little slower making peak boost past the point of peak torque. At least that's the way I see it.

 

Been awhile, I think his blog had some info http://redhardsupra.blogspot.nl/
Also see here for rough estimates relating g/cyl to torque

https://www.hptuners.com/forum/showt...ue-Measurement

 

I'm pretty sure he isnt looking to build a 1000lbft at 2000rpm torque monster anyway...nor use cheap **** rods that might do what you suggest.

 

I saw an LS setup on here that broke 1000whp on 93 only. Search the forums. But yes, it was a large cube motor with very low compression.

 

Only a moron would use very low....of course people will have different perceptions as to what very low means.

 

+50 to this 4l60 comment. I'd rather try to tune a 4.8 to 1khp on 87 octane than try to get a 4l60 to hook a solid 700hp. At least the motors make more entertaining noises when they blow.