L28, need a bigger turbo, which one?

[skirkland1980]

Drag racing (1/8 mile), my current garrett tc4305 has worn out. Would like something bigger. I'm leaning toward a borg warner because I can get a new one for less than $600. Car is a gutted 280zx. Ford explorer 8.8" rear with ladder bars. Drag radials, th350 trans with brake hughes 4500 stall converter. Engine is mostly stock internals. 7.4:1 compression, arp rod bolts, mild port cleanup on the p90a. Isky L6 cam .540" lift 236 duration @.050". Has a custom built intake manifold and header, intercooler, ms2,..etc. The car has ran 6.74@99mph @22psi. And somehow pulled out 115mph on a test run. 60ft averages 1.50 but has done 1.45. I was looking at part number 177281 or 177283. I know the compressor will make the power but will it spool up quickly. My current turbo is basically a 60-1 with .63 hot side. Launching at 16psi and hitting 25 psi in .6 seconds. I can post up some datalogs. I just need to make sure the bigger turbo will spool up quickly. Thanks.

Edited January 8, 2019 by skirkland1980
Added info

[skirkland1980]

a datalog and a screenshot of that datalog

2018-12-15_15.48.43.msl

[Gollum]

Well, if you're talking about the EFR line, and you can get one for $600, then that's a no-brainer.

 

As far as what to get, it's easy to say get the most modern design you can, as they promise the world when it comes to spool and power-per-diameter. And there's some truth there. But let's break out an exaggerated example to help show why some people end up unimpressed by dumping all their money for the latest model.

 

If a 65mm compressor is rated to flow 50lb/s with a peak efficiency of 70%, and the same company comes out with an updated version with a stronger billet wheel, and better aero and now makes a 55mm compressor that's rated to flow 50lb/s with a peak efficiency of 70%, which will spool better?

 

Everyone will say that the smaller one will, because it's smaller and will have less inertia to get going. But the problem with that assumption, is that the compressors are rated to the same efficiency. If "all things were equal" and the smaller turbine flowed the same air, then the efficiency WOULD GO UP. At the end of the day, the smaller wheel as better aero, and thus packs more air per rotation (or the same amount per second as the larger one) which means it takes MORE effort to spin the smaller one per MM of diameter per second.

 

Efficiency ratings on compressor maps take inertia into account, which is why on the compressor side of the turbo you should care a lot more about targeting a wheel that you'll not be way off the map with.

 

Now, the turbine side is where all the secret sauce is. A lot of people will go on and on about the material density/weight of the EFR turbos and point to that as the silver bullet as to why they spool so fast. Maybe they're right, but I have a feeling that just like the compressor, blade design is likely just as important. Garrett seems to be all about the temp ratings on the marketing side of the house, and it does indicate a form of reliability which scared EFR's early years with several shattered turbines with a material known to be brittle... Those reports seem to have calmed, and plenty of people run them in competition to prove they're not made of glass. So you be the judge.

 

Personally, instead of getting caught up in marketing hype, I try to find real world A/B tests comparing spool time and power. We're finally seeing some initial tests of the new Garrett G series which look promising. People are getting 400+whp out of the G-660, and I'd like to see the same power figures for the G-550 since the power rating seems slightly lofty for the compressor map max flow ratings, but time will tell. Sadly for you though, the G-660 is likely a touch small for where you're heading in power, but I'm betting it'd spool a TON faster.

 

Also, if you can get a few different housings to play around with, it's worth seeing if you ACTUALLY gain anything up top from a larger turbine AR housing. If not, then run the smallest AR you can, and if needed vent charge air to prevent surge. Could likely have a turbo at full RPM off the line if done right. No, putting that power down? I'll leave that up to you. You seem to have a lot of this stuff figured out already. Speaking of, I'm impressed all around by what you've put together.

 

And on that note, upgrading those injectors soon? Looks like you're touching 80% so more power will be rough on your duty.

[skirkland1980]

Thanks. The borg warner 177281 comes with an open .88ar turbine housing. I can't find one for that model any smaller. I had a .82ar on my tc4305 and spool was around 4500rpm which is a little late for 1/8 mile drag racing. The BG turbine wheel is bigger and would technically be heavier and harder to spin but it seems also that it would drive the compressor wheel more easily? I guess the L28 is too antiquated to find someone actually drag racing one with the BG turbo lol. So I guess I'll be the guinea pig. The 2jz and rb guys use them frequently but I don't think those engines compare. As for injectors yeah I just upgrade from 550cc to 750cc. Went from 95% duty cycle to around 85% so They may need upgraded again.

[Gollum]

Well, turbos don't really care about any details of the engine they're attached to. You can generally compare A turbo to B turbo and even if your engine input is different, you can compare the differences between turbos.

 

And now that I see you're looking at the SX line, specifically the S300SX3 the limitations become a bit more obvious. If you switched over to the SX-E BW turbos you'd likely be $200 or so high in price, but you'd have a lot more turbine housing options. That said, the S300SX3 should compare nicely to a GTX of similar size (likely a touch better transients actually). But it certainly won't be like the EFR series.

 

That said, switching to a twin scroll or maybe even a divided housing might see some meaningful gains in spool as well.

 

This is part of the challenge (fun?) of turbos. There's so many ways to improve the main drawbacks but they all take time/money/energy. I can see and understand why so many people just run "simplier" old school large turbos and feed it some nitrous. Works fine on a drag strip, just hard to maintain low bottle usage when on a circuit.

 

Looking at the data log again, you're losing boost in the last 1k or so RPM before shifting. You would probably make more peak power going to a larger AR turbine housing. So it's hard to recommend an even larger compressor wheel WITHOUT going up in turbine AR. I'd consider at least a simple hack like a quick spool valve to try to improve that low end response when stepping up to something larger.

[skirkland1980]

Well my current turbo is worn out. It has in-out shaft play as well as up-down. I've noticed max boost has been falling after nearly every run. I made several runs on 12-15-18, first pass max boost was 27psi, next two runs were 25psi. Then raced on saturday 1-5-19, max boost was 24psi. That's when i decided something must be wrong and gave the turbo shaft the wiggle test. Please explain the "quick spool valve". Thanks.

[Gollum]

A quick spool valve is when you have a divided entry or twin scroll (not necessarily the same thing btw) , turbine housing against a single exit manifold, and you put a butterfly valve between the turbo and manifold. Under no boost you close one side, so all exhaust gasses are directed to half of the divided entry to the turbine, which semi-fakes reducing the AR. Then at some set boost point you open the valve to open up the turbine fully. It's not ideal, but it's well documented to help in a measurable way.

 

What the valve looks like:

 

And an ideal improvement:

 

Obviously RPM improvement will be better in higher gears since it's a time-based improvement, not directly engine flow coupled/based. And if you're trying to spin a turbo that's not making full boost until 6k rpm anyway, this isn't going to magically get you to minimum boost in half the RPM off the line.

 

But what it WILL do, is dramatically improve initial boost response on a mild (less than 2 bar) when using a larger turbine AR when you're trying to get peak HP out of a turbo. This isn't of any real use when you're already on a smaller AR for a given turbo, or if you're running such huge amounts of boost you're in the borderline "should be running a compound to spool that sucker" territory.

 

 

Some argue that a proper twin scroll manifold paired with the quality twin scroll turbine wouldn't see any net benefit from this. But I'd argue that niether the quick spool valve or twin scroll design are essential to winning races, and I've seen plenty of record setting pro cars use neither. In the drag world especially, there seems to be little focus on the turbo itself when looking at how to get the turbo spooled up and on the stall.

[gregkring]

anytime I see boost falling with RPM I would check valve spring pressure as well. Especially if it is stock springs with that cam. A little play on a turbo is fine and won't cause dropping boost, but it is you doing the wiggling so I can't judge that. Feeling it move is one thing, but hearing it move by hand is definitely bad.