Volvo Project - Part 2 [ February 7th, 2011 ] By: Mark Ozimek Posted in » Ramblings

I mentioned in part 1 that I have a hard time making up my mind. This is the story of how I came to decide what turbo should get bolted up to the engine to get me to where I want to go. Be forewarned: A lot of text lies ahead. I’ll do my best to be interesting as I tell the (not so) enthralling tale.

As a point of reference in all this, for those who are unfamiliar with the Volvo powertrain, the stock shortblock seems to be good for around 600hp without sleeving, assuming the engine tune is good and heat is managed properly. Beyond that, the cylinder liners have a tendency to crack where they touch the next cylinder. The 5 speed transmission, M56H, is reliable for around that much as well, and can handle more, although gear and bearing life is rapidly declining at that point.

Originally, I was aiming for around 350whp, maybe a bit more, with a 56 trim Garrett GT2871R tucked away behind the engine. Let’s take a look at how the engine matches up with the compressor map. I made some very basic and incorrect assumptions that will get me into a ballpark estimation, such as the pressure ratio across the turbine being equal to the pressure ratio across the compressor. That will give a rough feel for where the boost threshold lies.

This is at 21psi, with a 7000rpm rev limit. Because I am looking to make this last a reasonably long time, I am choosing to keep the shaft speed around 90% of the maximum listed on the compressor chart. For the GT2871R, this is a whopping 120,000rpm! This allows for some special circumstances, like driving up mountains, to avoid overspeeding the turbo to hit the higher PR needed to get target boost in thinner air.

Anyway, onto the actual graph. As you can see, this turbo looks pretty well matched to the engine I want to build, although it is just a bit on the small side for peak power. The spool-up is based on the 0.64 A/R turbine housing flow curve that Garrett provides. Volvo uses a T3 flanged manifold, so I would get this turbo with the T3 based 0.63 A/R turbine housing, but that shouldn’t noticeably change spool.

That is just about enough airflow for about 400bhp without pushing the turbo too hard, or around 340whp. Being a FWD car, that seemed pretty reasonable figure. More would only really be usable at very illegal speeds, or on a pretty high speed track. The real nice thing about the GT2871R was that it should be making as much boost as I wanted by around 3000rpm, which is perfect for the highway, where the engine sits at 3000rpm as the car cruises at 75mph in 5th gear. Stepping up to a GT3071R or GT3076R will bring the boost up to 3500-3750rpm, which may be a bit too late for my tastes, despite the possibility of a bit more power and a cooler running engine from less exhaust restriction on a small turbine wheel.

I thought I had my turbo picked out, and had everything picked out to support it; ATP ultimate internal wastegate, the actuator, an adapter flange, the hose kit needed to get all the fluids to and away from it, the whole nine yards.

Fast forward a few months, and Garrett announces the GTX3582R, 3076R and 3071R. With a redesigned compressor wheel, they give about a 20% boost in max airflow from each turbo over the GT turbos they replace. Curiously enough, they switched from 12 split blades to 11 equal height. That will certainly affect how the compressor wheel performs. Plus they added “extended tips”, which basically just makes the compressor wheel bigger than its advertised exducer size.

Older “GT” compressor wheels look like this:

Newer GTX:

The basic sizes of the wheels remained about the same, and overall efficiency didn’t change noticeably. The general operating window got pushed to higher PR and more flow, including shifting the surge line up. By by pushing the compressor map to the right with the same turbine wheel, the compressor will be operating in a slightly less efficient spot during spool-up. I suspect this will push the boost threshold up in the RPM range a bit, as there will be more energy required from the turbine to compress the same amount of air to the same PR.

Despite previously ruling it out because of the spool time, the GTX3071R seemed like more viable alternative. It suddenly offered a much higher power potential without a significant impact on spool from before. Despite being “slow” compared to the 2871R, I reasoned that having boost by 3500-3750rpm could be doable for a DD. That still left me with about half of my total RPM range in boost, which is far from being a spiky peak hp dyno monster.

Not long after that, I found out about BorgWarner’s EFR line. There were a couple things that I really liked about what BW did with them. First, they made a really light turbine wheel, and kept the size up. This improves the turbine efficiency, and increases the amount of torque the exhaust gas should be exerting on the turbo shaft. This, along with the reduced rotating mass compared to the typical Inconel turbine wheel, should greatly improve transient response, and reduce backpressure a lot while keeping a configuration that still allows a respectable boost threshold.

In playing around with Matchbot, it seems that the EFR7064 will spool around 2750-3000rpm, and the 7670 will spool around 3250-3500rpm. As far as turbo performance goes, the 7064 stacks up pretty well against the GT2871R; similar boost threshold, potentially faster transient response, and can supply a few extra lb/min of airflow at the top end. The Garrett is better than the BW at lower pressure ratios. The most pressure I want to run on the GT2871R is about 21psi, from what we saw on the chart before. The improved performance of the 7064 at higher PR and higher flow means that I could run about 25psi and get a reasonable improvement in power without compromising the spool.

In the end though, I ended up settling on the EFR 7670. Here are the operating points found through the matchbot program, targeting a peak boost of 30psi, the points are at 2750, 3000, 3250, 3500, 6000 and 8000rpm. As you can see if you can squint hard (or right click and open the image to see the original size), it can make 30psi by 3500rpm and hold it to 8000rpm without overspinning the turbo:

I decided that having full boost by 3500rpm, going through the peak efficiency islands of the compressor wheel, and a potential for 500+whp was a good compromise, despite being more power than I should really be trying to push out of the block, and even more than I should be trying to put down to the front wheels of a street car. Logic be damned, I’m gonna do what I want! Plus, the EFR series has the distinct advantage of having a built-in recirculating BOV, and a high-flow IWG with an actuator that comes with the turbo. Those two things save enough money to make the higher cost of the EFR worthwhile.

So, one step of the project out of the way! I know what turbo I’m going with now. It’s time to make the rest of the engine support my goals. I’ll save that for part 3, since this is already a tl;dr post.

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Performance Loss Hunt: Part 3 [ July 8th, 2008 ] By:Mark Ozimek

A while back, I made two posts about my car, and how there is a lack of power in the top end compared to what it used to feel like. I verified that the exhaust isn’t causing significant restriction and that the turbo is making about as much boost as it should be.

Since this is turning into a guess and check thing, mostly because my car is 10 years old and has almost 150,000 miles on it, and I don’t know how it was treated for the first 130,000 miles of its life, I said “To hell with it”, and ordered two things that I highly suspect to be contributing to the problem: Vacuum hoses and a CBV diaphragm.

Unfortunately, the vendor I’m getting the CBV diaphragm from does not have any in stock, nor does anyone else that I could find, replacing that part will sit on the back burner for now.

The silicon vacuum hoses from StylinMotors came in the other day, and sat in a corner of my apartment until I had the time to start ripping junk out of my engine compartment to get access to some of the hoses. Thanks to Independence Day being on Friday, I got a three day weekend to have fun. First order of business was figuring out what each hose does, and where it needs to attach to. Ideally, I would be able to just take one hose out, cut a new one to match and install. Knowing what everything does is something important to me, so I couldn’t make it that easy for myself.

After a couple minutes of fun wrestling with worm gear clamps and torx screws, the engine compartment of my S70 looked like this:

(click for larger image)

Although it looks like a disaster, all I really did there was take out the intake filter box and two intercooler pipes that were in the way of some hoses I needed to get to. Judging from the hose clamp style, the hoses are the original parts that were on the car when it rolled off the factory floor.

After prying the clamp off, I found something quite comical and frustrating at the same time. The hoses had rotted into place! I had to cut off every single hose I changed, since they would not come off any other way. Unfortunately, this meant that some of the hoses that are in tight spots did not get changed, since I couldn’t fit my knife into the area. I still plan on changing them though, I just need to remove more parts that get in the way.

Afterwards, the hoses in that picture had been replaced with silicone parts:

While changing out hoses, I found something very interesting. In the first engine picture, there is a small white thing on the very left edge in the center of the picture. This is a check valve that only allows air to flow in one direction. That hose comes from the intake manifold and leads downward to a T junction. The hose going to the right has another check valve, and connects to the intake hose just before the compressor inlet. The other hose goes to a solenoid that is part of the onboard fuel vapor recovery system.

Since the check valves are aligned in such a way to only allow air to be pulled out of the solenoid that is attached to a carbon filter, a broken valve from the intake manifold means that boost pressure can leak out of the intake manifold to before the compressor inlet or into the carbon filter. Both of these are things that should be avoided due to loss of efficiency and contamination of the fuel vapor recovery system.

Either way, I replaced the hoses I had relatively easy access to. Some will require the removal of the intake manifold, another is attached to the compressor housing, which the bottom part of the intake hose blocks, there is even a hose that runs over the top and back down to the back of the engine to the fuel pressure regulator. I’ll try to address the rest of these when the CBV diaphragm comes in.

So with all that said and done, did it fix the problem I’ve been seeing? Well, no. It actually did some things I didn’t really expect. Acceleration from a stop is now much smoother and more consistent as the engine speed increases. Fuel economy on the highway seems to have gone up by one or two MPG, but it is still too early to tell for sure. The most interesting is that the brakes feel much more responsive now. My suspicion is that there was a/some vacuum leak(s) that allowed air into the system causing minor problems, but not enough to make the ECU freak out. Knowing that is more motivation to go back and replace the rest of the hoses, since they surely have leaks too.

However, the top end power is still lacking, so the hunt to restore my engine to normal continues! I was joking with Charles earlier that I’m probably gonna replace everything under the hood short of the engine itself before I fix the problem.. I suppose time will tell. Until then, remember that preventative maintenance is the best thing to do to keep your car performing as it should.

July 8th, 2008 | 2 Comments

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