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tfrasca's 142 Turbo Project

Duder said:
Radial turbines generate shaft power via momentum transfer from the exhaust gas, but expansion ratio (inlet pressure/outlet pressure) plays an important part. By allowing the outlet flow to expand in a diverging nozzle you can reduce the expansion ratio needed to produce the required amount of shaft power at a given mass flow rate. Lower post-turbine pressure then results in lower pre-turbine exhaust backpressure. Helps improve engine VE reducing restriction, allows for more timing advance before the knock threshold, gets your exhaust manifold pressure down closer to intake manifold pressure; all good stuff.
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thanks for taking the time to explain it, learn something new every day!
 
Tfrasca said:
AGP offers a T3 housings in .63, I think. I was just super scared of lag, so I went with the tiny .48. The .63 T3 housing has a 3" v-band outlet option, too.
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gsellstr said:
Hell, I'm running a .63 on my 2871R with no issues with lag whatsoever (especially with a good tune, cold temps, and E85...lol).
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Careful with comparing the same numerical A/R across different turbo frame sizes. A/R is just a ratio, and within a frame size there will be a family of several different A/Rs. But as you go up in turbine wheel diameter (from GT28 to T3) the "R" (centroid radius) of the housing scroll will grow and therefore the A (flow area) also has to get bigger to maintain the same numerical A/R.

TL/DR: 0.63 A/R housing designed for a T3 turbine wheel (likely 65mm wheel inducer diameter) will flow more than a 0.63 A/R on a GT28 (54mm inducer diameter).

Edit: I just looked up the S252 sx-e turbine specs; it has a 70mm inducer so the difference in housing flow would be even more pronounced.
 
I don't have too much to update, other than to say I solved my high rpm/high boost misfire. It always seemed to coincide with a 10.0 reading on my AFR gauge, so I thought LH was just going rich enough under load to give me a rich misfire. It happened with the 19t at 18+ psi, and the s252 around 12+ psi.

I don't know why I never thought about spark blowout, but that was the issue. My BPR7ES plugs were gapped at .030. Set them at .021 and the issue is completely gone. This turbo feels strong all the way to redline at 20 psi!
 
Tfrasca said:
I don't have too much to update, other than to say I solved my high rpm/high boost misfire. It always seemed to coincide with a 10.0 reading on my AFR gauge, so I thought LH was just going rich enough under load to give me a rich misfire. It happened with the 19t at 18+ psi, and the s252 around 12+ psi.

I don't know why I never thought about spark blowout, but that was the issue. My BPR7ES plugs were gapped at .030. Set them at .021 and the issue is completely gone. This turbo feels strong all the way to redline at 20 psi!
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Interesting, I also never thought about closing the gap and always ran my BPR7ES at .028
Glad you found something so simple to fix the issue!
 
Uncleknucklez said:
Interesting, I also never thought about closing the gap and always ran my BPR7ES at .028
Glad you found something so simple to fix the issue!
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Yeah I can't believe I never thought to do that before. It's been an issue since day one.

Now I want to improve my ignition set up so I can run more than .021 and get some more power out of it without blow out.
 
Tfrasca said:
Yeah I can't believe I never thought to do that before. It's been an issue since day one.

Now I want to improve my ignition set up so I can run more than .021 and get some more power out of it without blow out.
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I know you wanna get away from lh2.4 but go the wasted spark route if you end up staying with it. I had to close my spark plug gap to somewhere around that with higher boost, even out of my 16t, before doing it.
 
soclosenotnear said:
I know you wanna get away from lh2.4 but go the wasted spark route if you end up staying with it. I had to close my spark plug gap to somewhere around that with higher boost, even out of my 16t, before doing it.
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I've actually been messaging Duder about wasted spark on LH. It seems like a decent stop gap until I have more time to do MS, and I can keep using the wasted spark Bosch coil even after I ditch LH.
 
I'm still sitting at around .025 or so with no blowout issues even when boost spiked to 26psi. BlasterSS and MSD6A though. The Blaster alone did make a noticeable difference. Next time you're up this way Tyler...
 
vwbusman66 said:
bump
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That's funny, I was just looking at your thread. Nice car.

I have no real updates. I took the car on another organized drive, and hammered on it for 1200 miles. My wastegate setup isn't ideal, and it'll creep to 25 psi around 5k rpm. I suspect the dump into the downpipe is a restriction. I also need a better cooling fan and either a bigger overflow tank or a proper expansion chamber, as it'll run hot on sustained hill climbs.

Other than that, nothing is happening. House projects and preparing for a baby in August have fully eclipsed car stuff for the time being.
 
We can talk radiator stuff at Davis Tyler. This setup I am doing is looking straight up legit and should have the capacity to cool even with boost. Should have it on the road this weekend.
 
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