BOOOOOOOOST

I took the check ball out. Boost control is much better now, it only spikes a little bit on upshift.

I noticed something interesting, though. If I set it for 150kpa at 3000rpm, it still holds 150kpa at 5000. If I set it for 170kpa at 3000rpm... it sags down to 150kpa at 5000. Either I'm at the limit of the turbo, or I'm at the limit of the exhaust system, or I'm at the limit of the 1.5" inlet hole in the airbox

All the above.

Knurled wrote:

nokincy wrote: Gotcha, why/how would one measure absolute instead of gauge pressure with a car?

The correct question is, why would one measure gauge pressure? 4psi boost is a very different thing at sea level versus 5,000 feet, but 125-130kpa absolute is the same pressure everywhere.

Mechanical wastegate cans (and most manual boost controllers) will regulate manifold pressure to a gauge value because they are atmo-referenced.

Electronic boost control can regulate the manifold to an absolute value, if it's driven with a MAP sensor (as most are).

Note that the compressor map for the turbo has as its two axes the air flow and the pressure ratio across the compressor. Since one side of that is atmospheric, the turbo may not be able to deliver a given MAP at altitude if it's starting with a lower pressure. So both gauge and absolute pressure values are of interest when talking about turbo cars.

In reply to codrus:

Good points, but as alfadriver pointed out, the engine doesn't care. All it cares about is absolute pressure, whether the outside is at 29in-hg or 20 in-hg or 8 in-hg (airplanes donchaknow). Or as I'm trying to make my brain work with better, grams of air per cylinder per cycle, which not only defines how much fuel you need but also how much pressure there will be in the cylinder and thus what the optimal ignition timing will be.

If you're worried about overspeeding the turbo at high altitude, cut the max boost to a level where you aren't hurting the turbo. I don't know about my Volvo, but Audi and Porsche worked in absolute pressure for just this reason... heck the old Audi boost gauges read in absolute pressure. "2.1 bar boost" was really 2.1 bar absolute.

Knurled wrote: I took the check ball out. Boost control is much better now, it only spikes a little bit on upshift. I noticed something interesting, though. If I set it for 150kpa at 3000rpm, it still holds 150kpa at 5000. If I set it for 170kpa at 3000rpm... it sags down to 150kpa at 5000. Either I'm at the limit of the turbo, or I'm at the limit of the exhaust system, or I'm at the limit of the 1.5" inlet hole in the airbox

I'd start with the air box. That's a heck of a restriction.

Yeahhh... this is why i never turned down the boost on the MX6 despite a blown head gasket, blown turbo, and blown clutch.

DOESN'T MATTER MADE 24PSI. (gauge)

You haven't lived until you see a boost gauge rapping the needle off of the stop at 30psi. Then again the engine doesn't live when you do that :(

You know you're serious about boost when your gauge reading is higher than your tire pressure.

ok, so since I am now lusting after a lotus 7, LBC, and boost, does this mean that I need to build a lotus 7 with mg knockoff wheels and three wipers, with a boosted v6 making more gauge pressure than tire pressure? is this what the voices are telling me?

In reply to Keith Tanner:

Big slicks need only like 8psi to drive on the street. Just sayin'.

Well, if you're running big slicks, then you're obviously serious!

moparman76_69 wrote: You haven't lived until you see a boost gauge rapping the needle off of the stop at 30psi. Then again the engine doesn't live when you do that :(

CHALLENGE ACCEPTED

Knurled wrote: I noticed something interesting, though. If I set it for 150kpa at 3000rpm, it still holds 150kpa at 5000. If I set it for 170kpa at 3000rpm... it sags down to 150kpa at 5000. Either I'm at the limit of the turbo, or I'm at the limit of the exhaust system, or I'm at the limit of the 1.5" inlet hole in the airbox

Update. Finally had a little time today to replace the front muffler and first bend with a piece of 2 1/4" pipe and a mandrel bend. OE exhaust is 60mm so the 2 1/4 stuff just needed a slight touch on the expander, and a little slit on each end, and it slipped over and clamped down with clamshell style clamps, which I love for the way they don't pinch pipes.

Of course it rained after work. A lot. But from what I have been able to see, it now holds 170-175kpa all the way to 5000rpm, at which point I lift because that is rather above the speed limit and I couldn't test in lower gears because it was all just wheelspin. Need to check to make sure it isn't TOO much over 175kpa at the bottom end.

The funny thing is, the exhaust isn't any louder. (There ARE two cats and two other mufflers in the exhaust) I mainly removed that muffler because the pipe ahead of it was rusted out, and the muffler had a hellacious rattle when warm that no amount of stereo volume could fix.

Awesome! When the weather clears you should take video and post it

chiodos wrote: In reply to nokincy: 21 psi absolute so its about 7psi

Depends upon the context. Every forum discussion I've see always states boost as a gauge value - above ambient. While 10 psi is technically 15 + 10, or "25 psi", AFAIK, no one pulls the "+15" trick. If I did that, I could claim 32 psi boost... The right way to do it is to measure boost in kpa units, then there's no confusing what value is being discussed.

i ran the 2.3t ford at 16psi, apparently anymore then that and the tiny turbo becomes the cork. i sold my turbo dodge because i knew i wouldnt be able to leave it alone and they seem to not be built as well as a 2.3 lima.

kb58 wrote:

chiodos wrote: In reply to nokincy: 21 psi absolute so its about 7psi

Depends upon the context. Every forum discussion I've see always states boost as a gauge value - above ambient. While 10 psi is technically 15 + 10, or "25 psi", AFAIK, no one pulls the "+15" trick. If I did that, I could claim 32 psi boost... The right way to do it is to measure boost in kpa units, then there's no confusing what value is being discussed.

kpa is just a pressure unit, it can be gauge or absolute, just like psi. The right way to do is to indicate things as 'psig' or 'psis' (or 'kpag' and 'kpaa') where the 'g' and 'a' suffixes mean gauge and absolute. But yes, many people will use psi for boost (and thus implicitly gauge) and kpa for MAP (explicitly absolute).

Replying to knurled's comment from July (that I didn't see until now), there are a number of reasons why the ECU cares about barometric pressure. Many newer fuel pressure regulators are atmosphere-referenced, rather than manifold-referenced, for example, so as the altitude goes up the effective fuel delivery against a manifold that's been EBC'd to a constant MAP will go down. Also, the VE of the engine will change with the barometric pressure, because the absolute back pressure through the exhaust system will drop.

Grams of air per cylinder per cycle also isn't the complete story, you need to know temperature to get the pressure. PV=NRT and all that.

clutchsmoke wrote: Awesome! When the weather clears you should take video and post it

I'm going to turn the boost down to 10psi or so. It's too much for the tires. Today, I found myself taking a 270 degree interchange spinning the tires the whole way around. In the dry. Couldn't do that before.

If it's too much for the hoops, then all the extra boost does is needlessly shorten the life of the engine, you know?

THOSE shenanigans are for my Quantum. I drove my old one today for the first time since... well since I got the Volvo a year ago. It's extremely rusty and has a lot of wiring issues but THAT HOWL and the short and close gearbox that has you shifting into FOURTH gear before 60mph makes it intensely fun to drive. And the new engine should be good for close to 30psi boost on pump gas with the right turbo...

Jay_W wrote: "Criminy. How do you people who live with turbocars not go for all the BOOOOOOOST all the time?" We don't. We're kinda stoopid that way. If our ECU has a map sensor that's only good to 2 bar, we boooost it to 2 bar and to hell with margins. Duty cycle on injectors at 100%? Pshaw. Turn up the duel pressure. She'll be fine. I'm amazed it ran like it did as long as it did. It took getting run into to stop it...

4G63s and DSMs warpped a lot of people in the 90s.

Every turbo guy on their morning commute be like "I'ma stay out of boost, get some decent MPGs." (elevator music playing in the background)...

Pulls up to red light. Smiles at the other car waiting there

Enters highway on-ramp "Well maybe just a-" BRAAAAAAAAAAAAAAAAAPAPAPAPAPA-CHOOOOOOOSHHHHHH!!!

And then you boost the rest of the way there because life is too short not to.

dropstep wrote: i ran the 2.3t ford at 16psi, apparently anymore then that and the tiny turbo becomes the cork. i sold my turbo dodge because i knew i wouldnt be able to leave it alone and they seem to not be built as well as a 2.3 lima.

My eariler post about 30 psi was on a stock 2.5 with a stock garret turbo. They can hold 20+ as long as you keep your fuel in check. I didn't kill that engine until I ran it with the knock sensor unplugged and 20 psi.

Knurled wrote: But from what I have been able to see, it now holds 170-175kpa all the way to 5000rpm, at which point I lift because that is rather above the speed limit and I couldn't test in lower gears because it was all just wheelspin. Need to check to make sure it isn't TOO much over 175kpa at the bottom end.

189kpa isn't too much, is it? That's a tad over 13psi boost... 10psi is safe, 15psi the computer screams bloody murder.

Interesting: The brakes can't hold the car at a standstill at 150kpa. It will build that much boost very easily. I suspect that it can build 13psi+ if I didn't mind the car creeping forward and dragging the rear wheels. This is the polar opposite of my friend's automatic WRX, which won't hardly build any boost at a standstill. Volvo saw fit to put a MUCH looser converter in my car! And a smaller turbo.

I'll probably turn it down. Or maybe I'll get port water injection installed and put Zener diodes on both MAP sensors so the computer never sees 200kpa. What I NEED to do is put our Genisys Touch on the car so I can read injector duty cycle. My personal scantool only reads generic PIDs.