BOOOOOOOOST

Hey guys I found my boost problem.

Earlier somewhere on this very forum I was griping about how my car (whiteblock 4cyl Volvo) refused to make over 4psi boost, and that the bizarre thing was it would make 4psi at part throttle but absolutely no more except for a 1-2psi spike when the trans shifted.

Some from the peanut gallery mumbled something about "codes" as if that has anything to do with it, bearing in mind that I read boost with a scantool so I know what is going on. Others opined that boost was a manufactured value, nevermidn that Volvo uses not only a MAF but also two 2-bar MAP sensors, one in the intercooler and one in the intake manifold.

As it turns out, Volvo simply uses a very, very, very weak wastegate diaphragm, and they control boost by bleeding. Solenoid fails, boost is minimum boost or 4psi. I have no idea why it would not be linear with throttle position, but oh well. This is why turning the wastegate arm adjustment arm in two turns had no effect. 2 turns tighter against a lame weak spring is still lame and weak.

New solenoid is shockingly expensive and would get me only 7psi. There's a tune out but I think it's just the European T4 tune, which is why people with that tune have engine issues - the T4 had lower compression. Plus it is like $700. Screw that. $85 to Summit later and I had a Turbosmart manual boost controller, and I replace the (easily accessible) faulty solenoid with it. Manual says roughly every turn is 1psi boost. So, I count out 11 clicks per turn, and turn the dial 33 clicks from base. Well let's go to 36, that is a nice even number. Engine is warm, scan tool is graphing, let's go out onto the street and...

198KPa.

Okay let's turn it down to 24 clicks. 170kpa and accelerates fast enough in 1st gear to spike to 190 until it upshifts.

Okay let's turn it down to 16 clicks. 150kpa (stock boost when all working correctly) but it still spikes to 170.

Criminy. How do you people who live with turbocars not go for all the BOOOOOOOST all the time?

Who says we don't? BOOOOOOOST is the most addictive substance known to man.

We do, I built a manual boost controller for my first turbo car and 8 years later im still using a similar variant of homemade controller on my redblock. Boost is a glorious thing as long as you dont over do it.

I do suggest a wideband if you want to raise boost over stock pressures so you know whats going on. At least too much boost. That said bump it back up to 10psi!

I'd rather not... last month my front motor mount leaked all of its hydraulic juice out while I was out grabbing lunch. (Looked just like the water pump decided to throw up, a real nice thing to see) In 1st gear it comes against its stop hard and it sounds absolutely awful. With the boost turned up to 170, it does that in the first two gears and partway into third. Won't have the cash for new mounts for a few months and I will not abide by hokey fixes: this is a nice car and I want to maintain the things that make it nice, like the well-engineered hydraulic motor mounts. "No Cheap E36 M3" is my motto for this one. That is why I went with a nice well-engineered product instead of some ugly Home Depot monstrosity.

Allegedly the stock computer IS well-tuned all the way up to 15psi, at which point it throws a hissy fit because you are pegging the MAP sensor(s). I'll turn it back up to 10psi or so as soon as I replace the motor mounts and fix the spiking issue. That should be an easy fix, remove the check ball and spring, which is there for a fast boost rise. The turbo is the size of a thimble, it doesn't need help with spooling.

Keith Tanner wrote: Who says we don't? BOOOOOOOST is the most addictive substance known to man.

When Da Boss finally got a Grand National of his own, we did all of the usual inspection and new-acquisition maintenance. Then took it out and dipped into the throttle. 25psi instantly. WOAH NELLY. That's a lot of boost for a relatively stock GN. Turns out the wastegate arm was adjusted so tight that it was practically topped out at rest. He gestured like it had an inch of preload. A tiny bit of tension on the actuator (like a half diameter worth) is usually about 7psi and within sane preload ranges, every turn or two is about another pound of boost...

I think he has it set at 13psi, which is generally a nice safe number for those cars.

Blown hydraulic motor mount, GREAT reason not to turn up the boost, I had those retarded things in my old 740ti thank god this 245 has good old rubber ones. Yeah I know its a tiny turbo is it the 12t?

I'm kind of a fan of hydraulic mounts... the difference between this car and most other cars of this size and engine type is shocking. I like the smoothness and unobtrusiveness. It's way better than a generic rubber mount unless you're a fan of buzzy vibrations.

Yeah it's a 12t. Although if it ever dies I'll probably put a 14t in it because it bolts in and why not?

Yeah they work great until they dont..as you came to realize haha. Yeah I belive you there with the 14t ive got a 15g on a b230f and it way better that the measly 13g that would be on a b230ft but ive already got a big t3 on the shelf waiting. Yep thats the other part of this story, with turbo cars you get the boost addiction and keep adding boost until you start throwing on bigger and bigger turbos and follow the rabbit hole

I bought this car because my VW isn't finished yet. My VW has a bigvalve head 2.3l 5cyl with 7:1 compression. The plan was to run the K26 out to its efficiency limits (about 17-18psi) until I got bored, then swap in a Precision 5858 and see if I could break the North American 10vt power record (369whp, all wheel drive). Which should be eminently doable since HE had much higher compression and less good head/intake setup, and 10vts are airflow and detonation limited so less compression = more power...

"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...

Yeah, we don't. I'm running 24 psi on my Miata right now -- had some issues with fuel delivery the last time I tried turn ing it up to 27, so I need to finish sorting those out before trying for 30... :)

As for why it's not linear with the throttle, it's because the role of the waste gate is to limit turbine power (by diverting gas around it) whenever the manifold pressure is above the set point. Turbine power goes up non-linearly with gas flow, so in order to be able to spool up at a respectable RPM there's excess turbine power available at higher RPMs. As such, the waste gate has no trouble maintaing the set point at small throttle openings if the RPM is high enough.

This means that turbo engines are significantly less sensitive to the last 30-50% or so of available throttle travel than naturally aspirated ones. It'll probably make 80% of peak power at 50% throttle, for example. This is why I like electronic boost control -- if you set the boost target based upon throttle position, you can spread the available torque out over a wider range of throttle openings, which makes throttle modulation a lot easier.

I want boooooossssssst.

And knurled, You have a pm.

In reply to Jay_W, codrus:

Oh, I suppose it was a trick question. I KNOW you guys don't. I've seen enough bent rods and mains registers that look like coarse files and cracked ringlands and (my favorite) head gaskets literally blown out, as in 2" long chunk of gasket blown into the valley retained only by pushrods. People who battle the Boost Monster and lose paid for the Volvo. And the VW. And most of my RX-7...

Which is why I have the MBC set for 7psi. IF the car blows up, I will walk away. I will not concern myself with the fact that Darton makes MID sleeves for the whiteblocks, or the fact that a front drive 4G63 drivetrain is a bolt-in proposition for this chassis... Actually that one is easy to ignore. Mitsubishi didn't use hydraulic engine mounts

Screw a 4g63 just go all the way with the whitebock with an extra piston.

It'd be easier to just buy a NEWER S40, even though I don't like them because of how big they are.

I did see a Unicorn a few months ago on autotrader, though... the mythical AWD 6-speed turbo S40. One of about negative twenty sold in the US. Way outside my price range and besides, I don't like how big the '04-up S40s are. Really, the Volvo I have is probably the only one I would ever tolerate because it's just on the edge of how large a car I will put up with.

If the engine ever has to come out, I'll leave it to whatever junkyard gets the car The Plan is high quality maintenance but if major repairs are required, it's a new car and therefore disposable and it's best to just listen to The Humungus and just walk away. Walk away.

I love screwing around with older cars, but an '02 is a new car to me. No sense in putting Large Sums of Cash into it when that same money could get me any number of other cool new (therefore Bic-lighter disposable) cars. I mean, I lust after E46 M3s, but I wouldn't kick a cheap-o 330i out of the driveway. I'd love an STi but a 2.5i is half the power but twice the throttle response. So many things to choose from and only so many years to live and not enough time to have them all.

Do these things really make 21psi stock? I figured it would be more in the 5-7 range.

In reply to nokincy:

21 psi absolute so its about 7psi

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

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

http://www.enginelogics.com/read-a-turbo-compressor-map/

The more you know..

As for the how it is just gauge calibration to show the typical atmospheric pressure as 14.7psi (or whatever units you want). Then the vacuum can be seen when running out of boost. As for the why, the ecu uses the depression from ambient to help determine load on the engine, the same way it uses boost to figure out what is needed (fuel, ignition, valve timing etc.)

When you get past a 3 bar MAP sensor, come talk to me about MOAR BOOST!

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.

I went down that road with Midlana, the turbo Honda K24 is currently at around 240 kpa (~21 psi) on E85 - or 420-500 whp, depending on dyno. In a 1700 lb car it's enough for me - I'm mildly surprised that I'd ever say that.

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.

Plus, if you are using that to calculate the amount of fuel to inject, 130kPa will be the same fuel, too. Much easier physics that way.

Ran the wifeypoos 740 with no waste gate for years. MAXIMUM BOOST!

She loved it.