Q: Bottom Mount Single Turbo Responsive Setup

finnporter

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Jan 9, 2021
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Hi there,

Vendor: Speedtech (I may consider DR700 but it locks you into Precision turbos)
WHP Goal: 450whp functional average, 500whp peak --> but close to 500whp average if possible. Hoping to spool before 4K rpm, like around 3.5k to 3.8k and I'll just bang gears if needed.
Fuel: 93 pump gas
Tuning: Potentially @Twisted Tuning since I'm local
Car Goal: HPDE and Autox

Turbo considerations: BW S362 SXE, BW S257 SXE, GTX3076r, GTX3576r

Borg Warner line: I like the idea of OEM durability (I mean... these are on the N55 lol), cheap turbos on the used market and even at retail, and the option to rebuild. I mean BW SXE are like $700 - $800 new and cheaper on the RX7 and Supra forums and FB Groups. Cheaper long term costs and more quality than eBay 17T or 19Ts lol.

Garrett GTX line: I like the idea of water cooling the turbos for better heat management and having 300 to 500rpm to spool a bit quicker. However, I'm not a professional racer, I'm most likely going to do 2 to 3 HPDE sessions, maybe 4 on a good year, and 2 or 3 autox sessions on a good year if budget/timing/other hobbies/family are aligned with the stars. I'm open minded to this option though if the GTX line is considerably light years ahead of the BW SXE line in terms of tech and reliability.

Precision: I've seen too many in-person during my 240sx days have reliability issues on SR20s and KA-Ts. I've heard my EVO and STI friends complain about them too. I know that's a small sample size and people have luck with them, but that's what's biasing my opinion to not step into this space.
 
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RuskiRacer

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You are definitely not married to precision long term with the dr700 xona rotor is always a good option if you don't like the precision
 

finnporter

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I saw a Speedtech kit user with a BW s257sxe with an .83 AR seeing spool around 3k, with full boost to redline from 3.5k onward with pump gas. The person hasn’t dyno’d his car. He mentioned he’s going port injection with E85 (don’t know the %). His IG is N54Bryan, he claims with virtual dyno it’s around 500whp. It’s probably more like 460 to 470whp, which seems functional to me.

I’ve seen a RB26 with a S257sxe with 1.on run 498whp with AC91 gas, but it’s fully built.

For the Garrett side, I see that Berns ran a GTX3076r with E30 and AC91 mix, around 500whp with fast spool. MDorphin (I think) on this forum runs a GTX3576r but his motor is fully built which runs 500whp according to dyno jet on 93 pump gas. I see cases where spool is in the early 3k range.

So I think my closest reference for baseline and my potential scenario for pump gas is the IG dude if I wanna to the BW SXE line, but I’m going to ask Jeff about the AR sizing unless you guys have an opinion

Edit: Jimbo on this forum posted a troubleshooting log with a S257, sees spool around the 3k range, with 20 PSI around 7k on 92 pump gas I think.

 
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finnporter

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I found this on reddit
, i'm not sure about the accuracy since I'm not well versed in this stuff and the turbo calculators offered by Garrett and Borg Warner blow over my head. However, if I follow that video's calculations, it looks like the S257sxe would be highly efficient for my usage (assuming my inputs are correct or if the input variables themselves are even correct). I just have to figure out the AR and if Jeff's kit works for a T3 or T4 divided since I saw this disclaimer and I have no idea what the hell this means lol: *PLEASE NOTE: The turbine housing on the S257 SX-E uses a T4 bolt pattern, but uses T3 port sizes. BorgWarner notes that it can be ported out to a true T4 port size.

If someone is able to ELI5 or provide video resources for future reference on this stuff, I would appreciate it. I know figuring out turbo sizing is one part of the equation because I'm assuming engine, fueling, and whatnot are up-to-spec for my goals, pretty cool to learn though, just hope I'm not being steered in the wrong direction. It also sucks that researching this stuff is a hassle now because data is hidden behind Google search, FB Groups, YouTube, reddit app, etc. nothing is cross-searchable now.

Edit: Jeff from Speedtech clarified what the T4 bolt and T3 port sizes meant on a S200 series, and I saw pictures from Jimbo's thread on this forum on how it's done.
 
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r0nd3L

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Picked a tad too small of a turbo initially, GTX3071R Gen 2 T3 Divided. Anything over 20PSI starts blowing hot air. Trapped around 120mph on Draggy running 93oct in 90F heat, with tune that was still being polished. Anyway, wouldn't mind picking up 5-10MPH, so looking at 3076 or 3576. No other input, but will be following this thread.

 

Torgus

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Picked a tad too small of a turbo initially, GTX3071R Gen 2 T3 Divided. Anything over 20PSI starts blowing hot air. Trapped around 120mph on Draggy running 93oct in 90F heat, with tune that was still being polished. Anyway, wouldn't mind picking up 5-10MPH, so looking at 3076 or 3576. No other input, but will be following this thread.

While I bet it spools well it is only a 60lb/min turbo. Especially on pump gas it will be limited. You might consider running meth injection if E85 is not an option.
 
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finnporter

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Picked a tad too small of a turbo initially, GTX3071R Gen 2 T3 Divided. Anything over 20PSI starts blowing hot air. Trapped around 120mph on Draggy running 93oct in 90F heat, with tune that was still being polished. Anyway, wouldn't mind picking up 5-10MPH, so looking at 3076 or 3576. No other input, but will be following this thread.

Wow, positive boost by 2.5k and 18 PSI by 3.5K. Jeff also reco'd me a GTX3576r, I really want to go that route due the cooling and spooling aspects of the turbo but I'm not baller enough for a GTX. Perhaps in the future.

I'm most likely going to do a S362 .91 ar with T4 divided and give up a few rpms. According to that YouTube video about calculations and looking at the S362 compressor maps, it's still in the efficiency path since I'm still up and to the right on the curves, just not as efficient as the S257 which seemed super efficient on the graphs. I'm guessing with a more restrictive AR, I'll see positive boost around 2.5K but hit 18 PSI around 4k -- probably 4.5k to give me realistic expectations lol.
 

r0nd3L

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While I bet it spools well it is only a 60lb/min turbo. Especially on pump gas it will be limited. You might consider running meth injection if E85 is not an option.
It's kind of a long story, but I had PTE6766 and ended up going completely opposite direction on this car to focus on response for mountain driving. Since previous turbo was so annoying laggy (duh), I went with much smaller one that did meet my initial goals, but now want just a tad more.

I do have E85 available and might explore that. I have PI mechanicals, but switched to DME/BoostBox setup from JB4. Looking to hear more reviews in regards to the new Motiv Reflex to see if PI and Flex-Fuel integration can be done in much cleaner fashion. Thanks for recommending that again.

Wow, positive boost by 2.5k and 18 PSI by 3.5K. Jeff also reco'd me a GTX3576r, I really want to go that route due the cooling and spooling aspects of the turbo but I'm not baller enough for a GTX. Perhaps in the future.

I'm most likely going to do a S362 .91 ar with T4 divided and give up a few rpms. According to that YouTube video about calculations and looking at the S362 compressor maps, it's still in the efficiency path since I'm still up and to the right on the curves, just not as efficient as the S257 which seemed super efficient on the graphs. I'm guessing with a more restrictive AR, I'll see positive boost around 2.5K but hit 18 PSI around 4k -- probably 4.5k to give me realistic expectations lol.

Even better, 19PSI @ 3100.... Yeah, this thing spools quick! This is with lower compression motor as well. It's awesome in lower gears, but lacking that pull in 3rd and higher. I think I'm narrowing down towards 3576 as well. What is not baller is spending additional $2K just to swap the damn turbo. Hopefully I can find a buyer for my 3071. Moral of the story, make sure the turbo you pick fits your goals as to not spend 2x :tearsofjoy:
 

finnporter

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It's kind of a long story, but I had PTE6766 and ended up going completely opposite direction on this car to focus on response for mountain driving. Since previous turbo was so annoying laggy (duh), I went with much smaller one that did meet my initial goals, but now want just a tad more.

I do have E85 available and might explore that. I have PI mechanicals, but switched to DME/BoostBox setup from JB4. Looking to hear more reviews in regards to the new Motiv Reflex to see if PI and Flex-Fuel integration can be done in much cleaner fashion. Thanks for recommending that again.



Even better, 19PSI @ 3100.... Yeah, this thing spools quick! This is with lower compression motor as well. It's awesome in lower gears, but lacking that pull in 3rd and higher. I think I'm narrowing down towards 3576 as well. What is not baller is spending additional $2K just to swap the damn turbo. Hopefully I can find a buyer for my 3071. Moral of the story, make sure the turbo you pick fits your goals as to not spend 2x :tearsofjoy:
Are you on a manual transmission? Maybe change the gearing if you have a stock manual transmission diff to maybe a 3.3ish or 3.4ish? Hopefully you could make more use of your 3rd and 4th gear for canyon carving, assuming that is the case haha.
 

r0nd3L

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Are you on a manual transmission? Maybe change the gearing if you have a stock manual transmission diff to maybe a 3.3ish or 3.4ish? Hopefully you could make more use of your 3rd and 4th gear for canyon carving, assuming that is the case haha.

Haha, yup, that's the goal of this car. I have 3.46 LSD, just need to get around installing it. Should help, I hope!
 
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finnporter

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Haha, yup, that's the goal of this car. I have 3.46 LSD, just need to get around installing it. Should help, I hope!

Yeah, I'd also second what @Torgus said too about E85. Jeff said the speedtech kit on E85 on equivalent 850whp rated turbo sees full boost by 3.5k. He does have port injection, so this could be the equivalent of having 1000cc injectors in addition to more tuning variables you can play with? Not sure, since it doesn't pertain to me I won't research into it unless I have to lol.

E85 with a LPFP could be one the variables why @berns sees pretty good top end as well on the same turbo, but his car also weighs slightly less than a 335i and his tire setup is different as well so that may affect the gearing too.
 
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RuskiRacer

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You'll Pull much harder on e85 up top, you'll have more knock resistance , burn cleaner and have more room to increase timing. Only drawback is you'll be burning through it pretty fast
 

doublespaces

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If saving every dollar isn't the top priority, I would go with the CES kit. Instead of a cast manifold you get a CNC steel unit. If getting a single turbo at the lowest price is your top priority, the SpeedTech kit definitely seems to hit that mark very well. However I have leaned toward the CES kit personally. I just really like the work that @JohnCES has done over there and some of the small details that someone anal like me seem to be covered. Not that the speedtech kit is bad, I just feel like the CES kit is a bit more my flavor and the price is very good compared to the other kits we used to consider the gold standard in the early days of single turbo conversions.

 

I am Jacks N54

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Totally agree on the CES and SpeedTech points.


I recently stumbled on this and was surprised to find out CES goes that extra step and includes a custom Wedge tune for MHD. It's expensive, but they really do cover all the bases. You get what you pay for.
 

WOT808

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I have a SpeedTech kit with a Borg 364. It's kinda laggy around town in comparison to stock turbos but nothing a downshift doesn't cure. I'm sure the 362 will be a little better.
One thing to keep in mind with the SpeedTech kit is you'll get wonky o2 readings unless you go with ADV o2s. Jeff may have come up with an alternative, may be worthwhile to reach out to him about it, ADVs were the only fix out when I was experiencing it.

Here's the dyno of my setup on E85 (I've gotten consistent high 68x on another dyno in the area)
https://www.spoolstreet.com/threads/speedtech-borg-sxe364-dyno-results.5012/

20psi (red)
Screenshot_20210427-112559_Gallery.jpg


If I were choose again, I'd go for the 64mm GTW in hopes of better transient response and more flow headroom

Here's a top mount GTW dyno (awesome tuner by the way):
https://www.spoolstreet.com/threads/n54-garrett-gtw-6465-3884r-dyno.5374/
 
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nahor

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I have a 0.83 AR GTX 3576 on a Speedtech kit. Unfortunately I don’t have any dyno numbers yet, but driving experience wise I think it (or anything similarly sized) would be ideal for what you’re looking at doing. Transient response above 3.5kish feels identical to stock turbos, the only time I really notice any extra lag is if I try to pass someone in 6th on the highway. Even then, it’s minimal.

It’s awesome in the canyons too, even in the tighter stuff leaving it in 3rd is no problem if I want to. One caveat though, I usually do run E85, but mostly because ACN91 is garbage. My $0.02 is whether you go Garrett, Borg Warner, or Precision, I definitely wouldn’t go smaller than a 3576 or it’s equivalents because spool is already fantastic, and you’d just be hurting your efficiency/power potential on pump gas
 

r0nd3L

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I have a 0.83 AR GTX 3576 on a Speedtech kit. Unfortunately I don’t have any dyno numbers yet, but driving experience wise I think it (or anything similarly sized) would be ideal for what you’re looking at doing. Transient response above 3.5kish feels identical to stock turbos, the only time I really notice any extra lag is if I try to pass someone in 6th on the highway. Even then, it’s minimal.

It’s awesome in the canyons too, even in the tighter stuff leaving it in 3rd is no problem if I want to. One caveat though, I usually do run E85, but mostly because ACN91 is garbage. My $0.02 is whether you go Garrett, Borg Warner, or Precision, I definitely wouldn’t go smaller than a 3576 or it’s equivalents because spool is already fantastic, and you’d just be hurting your efficiency/power potential on pump gas
Do you have any logs to share? Just want to compare to my 3071.
 

finnporter

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Yeah, the CES kit looks nice
I have a 0.83 AR GTX 3576 on a Speedtech kit. Unfortunately I don’t have any dyno numbers yet, but driving experience wise I think it (or anything similarly sized) would be ideal for what you’re looking at doing. Transient response above 3.5kish feels identical to stock turbos, the only time I really notice any extra lag is if I try to pass someone in 6th on the highway. Even then, it’s minimal.

It’s awesome in the canyons too, even in the tighter stuff leaving it in 3rd is no problem if I want to. One caveat though, I usually do run E85, but mostly because ACN91 is garbage. My $0.02 is whether you go Garrett, Borg Warner, or Precision, I definitely wouldn’t go smaller than a 3576 or it’s equivalents because spool is already fantastic, and you’d just be hurting your efficiency/power potential on pump gas

Makes sense, when I was doing the calculations. The BW S257 is on the edge of choke point on the compressor map but it’s very up top and to the right. I guess the choke point is why I chose the S362, and when I did the calculations for the horse power variable, I didn’t account for weight. I just made a guess.
 

nahor

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Do you have any logs to share? Just want to compare to my 3071.
Sure, here are a couple. They're not the cleanest, but they're the best I could find in my mountain of saved logs. I'd go out and grab a few better ones for you, but sadly my tires are showing cords, so it'll have to wait

3rd gear:


4th gear:
 
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CAA

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Picked a tad too small of a turbo initially, GTX3071R Gen 2 T3 Divided. Anything over 20PSI starts blowing hot air. Trapped around 120mph on Draggy running 93oct in 90F heat, with tune that was still being polished. Anyway, wouldn't mind picking up 5-10MPH, so looking at 3076 or 3576. No other input, but will be following this thread.


What AR were you running on that log? 18 psi at 3.1k rpm is absolutely awesome for a ST.