Qwkswede's Red 740 Wagon. Part Deux aka Superfridge

Harlard said:

Chris,

He has a similar wastegate setup as I do, being a 38mm gate flange welded directly to the turbine housing. Currently it produces about 185 peak tapering to 175 kPa at redline, using an 8 psi spring. I think a smoother gate outlet and merge, paired with a different gate spring would be enough to resolve the creep issue.

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Those changes should help as well. I was speaking in general terms / best practices, but of course there’s always more than one way to make it work.

Keep in mind he’s at much higher elevation which means his turbo speeds are much higher for the same boost pressure, all else being equal. The turbine has to work harder to drive the increased power requirement from the compressor, and that drives increased turbine pressure ratio and so increased pre-turbine backpressure. In other words an identical wastegate hardware setup may not work as well in Denver as it does in Portland.

Hey Chris,
This is a different wagon than I drove to Davis. This one hasn't really been up for a road trip since I have owned it. I just barely got the black widows and hornets cleared out after it sat in a field for 10 years.

Thanks for the wastegate info. I was suspecting much the same stuff with the 90 degree angle into the gate tube. I copied Harald's design on that , and it is in a tight spot between the engine and frame rail. I might have room for a larger diameter gate, but not much. My wastegate spring starts opening about 10psi, I checked that on the bench. And you can see the deflection in the boost curve in the chart above. It just doesn't do much to control the boost and everything stabilizes somewhere between 18-22 psi depending on rpm, time, etc. I guess that's not the definition of "stabilizing". But it doesn't shoot to 40 psi with the gate wide open either. It is really a 6-10 psi overboost situation, if the wastegate was working as intended.

I'm going to pull it apart and see if I can do some flow path work. Maybe open the hole to a larger oval shape and rebuild the inlet with an elbow facing the incoming flow. There really isn't much room there with the turbo mounted to the factory 90+ manifold. I tried to make the most of it, and that's why the gate is welded into the turbine housing. Maybe some room for improvement though. I didn't anticipate this would be a problem with a smallish turbo. Thought there would be plenty of back pressure that cracking the gate open would get the job done.

Another thing I was thinking about, maybe I just vent the wastegate pipe to the atmosphere. Though I'm not really interested in making MORE noise. That might help control boost though. I do have a catalytic converter and one straight through muffler in the exhaust. Seems like an open dump wastegate might be immensely more effective than merging back into the downpipe.

Gotcha Ken!

I think a stiffer spring won't eliminate boost creep in the top end, going back to that idea. The problem is that once the wastegate is full open, it can't flow enough exhaust gas to control boost. A stiffer spring will delay the opening point and possibly help a bit in that it won't have as much time to creep to the same level as today, but it wouldn't fix the root issue.

Any porting work you can do around the wastegate plumbing should definitely help.

And yeah, I think an atmospheric WG dump tube would also potentially improve the situation, if there's a way to do that cleanly without introducing more restriction somewhere. Another thing that in general will help with boost creep is making the main exhaust system more restrictive (although not really desirable). There are many cases I've seen / heard of where boost creep started for someone after they enlarged the post-turbine exhaust system. Removing restriction from the system is a good thing for engine performance since it reduces both post-turbine and pre-turbine backpressure. But what it means is that the turbine wheel needs to flow even less to make the same shaft power and control boost. Meaning the wastegate has to flow more. If the wastegate valve & plumbing was right on before upgrading, then stepping up in exhaust diameter can make it marginal and sometimes induce boost creep.

Duder said:

Those changes should help as well. I was speaking in general terms / best practices, but of course there?s always more than one way to make it work.

Keep in mind he?s at much higher elevation which means his turbo speeds are much higher for the same boost pressure, all else being equal. The turbine has to work harder to drive the increased power requirement from the compressor, and that drives increased turbine pressure ratio and so increased pre-turbine backpressure. In other words an identical wastegate hardware setup may not work as well in Denver as it does in Portland.

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Big variable I was ignoring. Thank you for the clarification!

Harlard said:

Big variable I was ignoring. Thank you for the clarification!

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No worries! We talk colloquially in boost pressures of course, but that reduced ambient inlet air pressure at higher elevations makes it necessary to run at a higher pressure *ratio* to achieve the same outlet boost pressure. Speed is directly proportional to pressure ratio for the majority of a compressor map unless you're really far over to the right, approaching choke. It starts to get really interesting when you look at what's happening with a turbo system at Pikes Peak...

0-60 test runs

Despite a bad case of the boost creeps, I took it out to my secret test location in Mexico for some 0-60 test runs. I've been using this app, or a similar one like it for quite a while with my cars. I wish I had all the timeslips together somewhere, but phones change, apps deprecate. I do have a few screenshots like this from over the years.

A couple of 5 second 0-60 times. That probably puts me on track with modern Honda Accords and Toyota Camrys.


Here was one from my 244 that died and gave many parts to this red wagon. It was an 8v turbo with uSquirt and e85 tune. Baseline test when it was no-turbo.


And after the turbo e85 conversion.


This chunky Superfridge has got some moves. It looks promising, and it might have a little growing room still.

needs squeeze

Haha. Antilag juice, Indeed. It doesn't have enough traction today on the street tires. But that does help get these cars up on the converter. 1st gear is a fine pedaling exercise once the boost hits.

linuxman51 said:

needs squeeze

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Timeslips, datalogs, enjoying the car.

Following up months later.

I did pull the turbo off and open up the hole in the Turbine housing to the full diameter of the inlet to the wastegate. And that fixed my boost control problem. It's rock solid now. I have run as low as 12psi without any creep. And am now running 15psi. That is a 200kpa setting in closed loop boost control in megasquirt. It works bitchen. So docile and safe feeling. Just what I wanted for daily driving.

On a nice Wednesday in August I made my first disappointing trip to the drag strip. The car is making good power, and I did get some good datalogs to help the tune along. But F%*# me trying to launch this combination. I knew the lag was bad, but I didn't think it would be 3.32 seconds to the 60 foot mark bad.

9200' density altitude. + 16V engine with no low rpm torque + AW71 means 1800rpm and maybe .5psi boost leaving the line. GAG!!... Not entirely what I want from my street car.

The good news is that it ran 101-102mph through the speed traps!@! I'll take that and celebrate. But I wish I could figure out some happy medium to get it to leave a dead stop faster than an old person on a walker. I know I could do it with nitrous. I have done it before. But with the stock rods, and stock pistons in this 200k mile motor, I would rather have it just make some low end grunt ALL the time and not just when the bottle is full and activated.. I'm open to ideas. The 16V motor is super cool and gets alot of compliments. But this combination is a bit of a pig at altitude.

Anyway, enjoy the pictures from a gorgeous Summer night at the track in Colorado.









And the photo so I can watch myself age in a Volvo on Turbobricks.

Dang. Mine did 102 at about the same boost, but at 500' with bigger cams and intake. I must be doing something wrong

I hope your 60' times were better than mine.

Harlard said:

Dang. Mine did 102 at about the same boost, but at 500' with bigger cams and intake. I must be doing something wrong

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A bit…best was 2.1. Still ran a 14.2. Stupid car.

EDIT: I misread your slip as ET being 13.95 instead of 16.23. Feeling a little less stupid and a little more stupid on two separate dimensions now

Harlard said:

A bit?best was 2.1. Still ran a 14.2. Stupid car.

EDIT: I misread your slip as ET being 13.95 instead of 16.23. Feeling a little less stupid and a little more stupid on two separate dimensions now

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LOL. Yep. The car next to me went the same MPH, but 3 seconds faster ET.

I brought out my window tint connection to lay down some film today. A nice security upgrade for when I park the car and have stuff inside that I don't want people to see. Should keep things a little cooler inside on bright summer days too.

I'm old school and like cars with dark windows.

It is 5% in the rear and 15% on the front windows.

The drag bug bites and digs it's teeth in.

After seeing first hand how much lag this tiny 3071 turbo has I decided to do something about it and build myself an antilag device of sorts. Short of running a tiny TD04 turbo, I don't really see a way to improve the turbo response when launching from a dig at 6000' ASL. It's an AW71 problem as much as a turbo problem. Leaving the line at 1750rpm does NOTHING intersting at all! Who knows, maybe I'll circle back around to a tiny street turbo. But the top end power is just hard to deny...

So I picked up some fresh solenoids and a single WET fogger type nozzle for a turbo spooling 25hp shot. Jets are a measly .022" N2O and .014" Fuel.

I got everything installed and headed back to the track for a little redemption. Everything worked out great! 60 ft times are now below 3 seconds. Best was a 2.5xxx. Best ET 14.35, Best mph 104mph.

I was spraying in 1st gear until full boost hit and then just letting the turbo do the rest. A small success I think. I jumped right over the 15s and into the 14s. With some tuning I feel like I should be able to launch a more appropriate 2.0-2.2 60' and drop into the 13s. That's a goal before the end of 2021.

Math from some online calculator for a 3550lb car running 104mph trap speed: 307HP

I wanted to run 13s this summer in my full weight daily driver wagon. And I damn near drove it into the 12s in the 1/4...

Me and Superfridge made it to the Wednesday night test n tune at Bandimere speedway tonight. The weather is finally cooling off to more turbo friendly temps. I think it was mid 70s at the start and high 60s after the sun went down. My car was loving it. So much faster than the 100 degree days we had all summer. The car was really running great! A 25hp shot of nitrous helped my 60' times by over a second! The AW71 is holding up like a champ! I am somewhat surprised it's still alive, but there it is. Still kicking along like a youngster. The best ETs were done just leaving the stick in drive. It seems to shift between 6100 and 6200 rpm which is almost perfect for the 16V motor i think. And that lets me hit the nos button in first and watch the boost gauge. I usually let off when I see about 10psi and 5000rpm. Before the 1-2 shift happens. No need to push my luck on the AW71.

I'll start listing my excuses for slowness first...
Some of the best altitude readings all year...


I'll start listing my excuses for slowness first...
Some of the best altitude readings all year...



Timeslip:



Views out the windshield while waiting in that line up...


The car was really running great! A 25hp shot of nitrous helped my 60' times by over a second! The AW71 is holding up like a champ! I am somewhat surprised it's still alive. Best ETs were done just leaving the stick in drive. It seems to shift between 6100 and 6200 rpm which is almost perfect for the 16V motor i think.


I'm super stoked. I've been working hard and waiting for the car to surprise me with some good passes for a while...

Back to the track!

The drag strip closes mid October in Denver Colorado. I wanted to squeeze in one more night before things shut down for winter. I really wanted a 12 second timeslip after being so close last month. And so I turned the boost up to an even 20psi and I did a little bit of tuning on the fuel and spark maps to make sure the power increased with the new higher boost. The motor seemed really happy, hopefully the AW71 would take it. I also made sure the nitrous bottle was filled and ready for spooling the turbo on the starting line. I'm still running about 35-40hp shot from the wet kit. The car leaves with some authority on the bottle. Much better than my 3 second 60' times without nitrous.


And SuperFridge did not let me down.
Best pass was a 12.33 @ 114mph

It was super busy at the track last night. All 8 lanes full with about 30 cars each. I waited 2 hours to get my first pass done. The pressure was on. With a couple more practice runs I'm sure I could cut a better 60'. I accidentally pushed through the start lights while trying to power brake the car both times. Something to work on next season. Could I even run an 11 with that 114mph trap speed? Maybe maybe....

Timeslips attached.

Awesome Ken!!!! Great work!

Dang Ken, that's awesome!