Schwitzer Turbo

Hey guys im Lloking for some Info, Mathermatical Formula's(Heavy Turbo Stuff)

Trying to work out If you compression is 12-1 at what Rpm will the Car start pinging at on 95 ocatane feul?

And if your dynamic compression is 8.5-1 and you boost 1 bar what is the real compression of your motor?

And how much can you boost before Destruction based on the Dynamic compression, perfect a/F ration and perfect octane rating..

Jcushing

magic formulas like those are a farse.... too many other factors that dont get considered.

E-b0la

Just turn the boost up 1 psi at a time until it blows up. Then back it off like 2 psi from there. That's how much boost your 12-1 C/R motor will be ale to handle safely.

On the other hand, theres no universal formula to say how much boost a motor can handle. It depends on two things mainly; The motor and the tune.

Tom-Guy

No, they aren't. It would just take longer to master the math and then crunch all the numbers that it would to work at McDonalds long enough to buy a sleeved block and GT35R.

samson

LOL.


JP

Schwitzer Turbo

Im just trying to understand a Few things ie: After a Certain Rpmthe car starts to ping?

If your Air/Feul Ratio is Perfect is it possible to ping/Detonate?

Tom-Guy

More like AT a certain rpm your car is most likely to ping. Take a look at a dyno graph sometime... where torque is highest, the cylinders are filling the most each cycle. While octane of the fuel, the ignition timing you feed the engine, AFRs, cam timing, intake manifold pressure vs exhaust manifold pressure (intake vs atmospheric pressure has little to do with anything), etcetera, all modify this it is the actual point of peak cylinder filling that is most significant. Think of it as either approaching or achieving a critical mass of air in the combustion chamber, much akin to a nuclear reaction.

While that analogy is somewhat exaggerated, if you breach a headgasket, break a ringland, have a bottom end come apart on you it's the emotional and sometimes financial equivalent of having the bomb dropped on your day.

If anything, in the upper rpms a car is less likely to detonate; the cylinders are less full each cycle, and with the really high rpm screamers sometimes the fuel literally doesn't have time to detonate. With the really high rpm screamers various frictions and the general treatment the vehicle recieves the vehicle is just as likely to come apart from non-detonation reasons, though, so unless you're dealing with a motorcycle built to handle those rpms don't go seeking them out. :P

LOL, where to begin?

AFRs are "indicated" by all these tuenarboi toolz we purchase and hook to cars; at no point in time is the actual air-fuel ratio calculated with any of the modern gear. The only way to do this is to meter the actual fuel entering the engine itself, which we at no time do. What we do is stick an oxygen sensor in the exhaust stream, and have a pile of microchips freaking GUESS what the AFRs are based on the amount of oxygen it detects in the exhaust stream.

- When everything works well, widebands are pretty damn accurate.
- Depending on how you log, if grounds or powers are substandard you log erroneous ----.
- If combustion is not efficient for whatever (usually mechanical) reason then all the air/all the fuel is not combusted and you read lean because of the extra oxygen in the stream. More fuel does not always help.
- If cam or ignition timing is off in one direction, it is possible to cause detonation because cylinder pressure builds and has no where to go because the exhaust valve is not open yet. If cam or ignition timing is off in the other direction, it is possible to cause detonation because the burn is still building pressure as it is ejected out the prematurely opened exhaust valve which super heats it on the way out the chamber and causes the exhaust valves to turn into hotspots which cause pre-ignition. AFRs read pretty close to "correct" in either case, because your problem is not fuel.
- ----------ing OCTANE is the measure of how detonation resistant a fuel is. To put it in the simplest, truest, most redneck terms I can muster, more octane is more coolant. 12:1 AFRs under boost is the almighty figure touted on HT and other pestholes riddled with incompetence.... yeah, that's great for a low boost Honduh on pump gas, or a moderate power drag Honduh on race gas, and a great number of other vehicles as well, but it's not always the best AFR for a given setup (aircooleds like it richer). I'm a big fan of going richer, but you have to understand that past 11.5:1 the cooling properties of fuel - the excess unburned fuel's ability to latch onto excess heat and carry it out of the combustion chamber - diminishes quickly and in higher power levels is more likely to either do nothing to hinder detonation, or causes a misfire which causes a false lean AFR reading on your wideband.

Joey is a big fan of using racegas before it's *really* required. All the bigger power cars that get pushed to the limit on pump gas end up lifting headgaskets, or occaisionally coming apart. All the bigger power cars that run racegas religiously last a subjective eternity. Coincidence? Not remotely.

Schwitzer Turbo

And if your dynamic compression is 8.5-1 and you boost 1 bar what is the real compression/in motion compression of your motor?(how much compression is your motor making?

Tom-Guy

Dynamic compression is the changing CR when the motor is in operation, I think you typo'd and meant static CR of 8.5:1, yes?

Measuring that sort of thing is difficult to do directly, but easy enough to deduce when you are making gains empirically. If torque goes up, cylinder filling/dynamic compression/volumetric efficiency goes up. Different cam profiles, cam timing, port and manifold dynamics, and a bunch of stuff all have an effect on this.

Really, most of the big name "I am an engineer I've done the math" Full----- types know little more than some general trends based off hands on experience. Vague, general theory expressed in big words sounds real good coming from a guy who knows from experience which turbo spools quick and makes great power on an engine, and most of that experience is based on being there for you and other's mistakes.

Here are the big points:

- Light cars rule the street and rule the track. Building a heavy family car chassis (Integra) and expecting a dinky four cylinder to make it fast is called mental retardation. Every car that rules the streets in ashEVILle is either an 88-89 CRX HF or a Civic STD, and there have been multiple ones. Welcome to weighing less than 2000 lbs, these laws of physics apply in your town, too.

- Small gains in VE have little to do with big gains in power from big gains in airmass ingested by the engine. Bottom line, cranking the boost **** like a ------- man with a pair of ***** is what makes power, not mincing around like a sissy ****** porting and polishing a generally excellent out of the box factory cylinder head and dropping thousands of dollars to make 15 more whp at some irrelevant psi level when your turbo is big enough to give you 100 more whp by cranking a $9 Grainger ball-spring MBC.

- A useable powerband means more than peak horseshit dyno toiletpaper. Unless the turbo is obviously too freaking small and therefore a restriction, ALWAYS trade spool for peak power and you won't go wrong. The fastest car I tune has an 84mm B18C, .60 T04E/T3 with stage 5 turbine wheel, and makes it's first psi at 2500 rpms. If you have 3500-4000 rpm powerband at full boost in your Honduh, with no big dips in power at the lower end of that range, your car ------- rules, end of story.

- Ball bearing turbos are completely worthless. Unless it's a hybrid unit with the compressor a LOT bigger than turbine you get a mere 400 rpm gain in spool for your +$650... mismatched compressor/turbine combos are the ones that get 1000 rpm gains in spool (GT2540R). Also, the ball bearing turbos freaking fail like clockwork as they are NOT a robust piece, and cost 85% what they run new to buy a new CHRA. It's what I call Magazine Technology - it looks good on paper, and sells well to magazine reading idiots who've never been in a fast car. Save the money and get a journal bearing turbo, you'll be really happy you did.

- Rich is safe until you max out the fuel's octane so it can't cool anymore, then it's time to run racegas. Make a point of tuning your timing, or your engine will blow, period. It's a pretty simple process. Start off with conservative timing and slowly advance it, power will come up if the timing really is conservative, and you will stop getting good gains in power right as you reach the 3-5 degree "flat spot" in power production before the engine starts detonating. Back things off a couple degrees from the flat spot and holy ---- your engine doesn't melt down.

- If you give up your life to pursue cars, you will learn.

CspecRun

^^^^ that should be stickied