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turbo up grade help ..K27 ???

hello all fairly new to the forum
im a old 911 guy who spent the last 20 years dabbling with 356s and now im back playing with the 911's and 356's
I'm sure this has been asked many times in the past. But all the old threads i come across are close to 15 years old
I'm in the process of going through resealing / studding a low mile 76 row turbo . reusing most of the original engine parts as they are most all well within tolerances. and replacing the ones that are not with stock parts.

i was wondering what is the turbo of choice now a days. looking to stay pretty close to stock but would love a turbo that didn't have the lag like the original 3ldz. and a lower rpm spool preferably in the mid to upper 2k range. a direct drop in would be prefered but i am also quite handy with the welder not looking for extra hp more interested in driveability and less lag .. so what's the turbo of choice ?
Thanks in advance

Regards Ned


Last edited by gorskined; 11-22-2019 at 09:01 AM..
Old 11-20-2019, 11:43 AM
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Crotchety Old Bastard
 
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Welcome!
My opinion is for your application the K27-7200 is a perfect fit. It is as close to a direct bolt-in as it gets and performs MUCH better than the 3LDZ. The ones we have rebuilt are also machined to fit with no bracket modification making them a true bolt-on for the 930, both early and late. Of course there are many other brands/types that perform well but all require some sort of mod and don't really perform significantly better than the K27 when mounted on a stock engine.
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Old 11-20-2019, 01:52 PM
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How does the k27 7200 differ from the k27 4180 ???

Last edited by gorskined; 11-21-2019 at 04:36 AM..
Old 11-20-2019, 03:16 PM
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I have a k27 7200 (with a hooligan muffler) on my 77 930 that was rebuilt and modified by Evergreen Turbo. It certainly is a lot better than the 3LDZ. Pulls much nicer.
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Old 11-20-2019, 06:05 PM
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I also have a K27 7200 on my 85 930. I am very satisfied, it is much better than the 3ldz.
@ Brian, I'm looking forward to the 7006, I'll replace it with the 7200.
Old 11-20-2019, 08:41 PM
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evergreen is THE PLACE to send it.
let him do all his mods to it.
he just rebuilt mine and surprisingly it was not that much.
nice guy and loves to talk turbos.
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Old 11-21-2019, 03:57 AM
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I have two K27 7006 rebuild on my shelf. One of them fresh never driven, like new (incl. new flanges, bolts etc.). They are for sale fairly cheap if someone is interested. Location Europe. I have tested one of them on one of my 930's for a very short period, and it is a nice turbo but I am not satisfied. Others tend to use models like the GTX35 etc. and simular BorgWarner models. I am now building my own upgrade turbo. Specs. below.

K27's do fit the OEM headers, inlet etc., but from thereon the advantages are no longer visible to me anymore compared to the options we have today
K27's are too much downsized on the compressor inducer vs. turbine exducer for my taste.
Turbine is 12 blades....12 blades are now days mostly used for very small turbines to spool-up very fast with high back pressure. The K27 is not small, it is 64,5mm exducer - heavy for 12 blades
The compressor is 7+7 blades with appr. 53mm inducer, such smaller inducer (compared to turbine) increases the turbo shaft speed requirements dramatically resulting in later flow capacity/spool compared to a larger sized compr. inducer in same compr. housing on same turbine configuration.
Most people know the reference to Garrett, so in that term it's closest match is like old style GT28 compressor wheel (53mm) in a bigger compr. housing, paired with a GT37 turbine (64,5mm), i.e. it still need the shaft speed requirements of the GT28 in a larger compressor housing to get on boost with a 64,5mm exducer 12 blade turbine wheel. That is a recipe for moderate spool "ketchup" turbo IMO running too high shaft rpm's (due to small compressor inducer) to come on boost. Fits better on a large displacement diesel truck compared to an upgraded 930 IMO
Having said that, many are obvious really happy about these K27's as an improving over 70/80's OEM design. And they are nice upgrades on OEM turbo. It is nice to go one- or two steps up the ladder to the later K27's 70/80's design, but I believe it can be done better

Improvement to K27's IMO...

1) Larger compressor inducer dramatically lower the turbo shaft speed requirements for same air flow, which results in lower turbine speed/back-pressure (less shaft speed), quicker spool (due to much higher air flow per shaft turn) / with increased luxury problem/risk of early surge. K27 is 53/64 (compr. ind. vs. turb. exd), I would rather go 62/62 on modern design wheels.

2) Less turbine blades AND reduced turbine exducer diameter would stay on same back-pressure levels and save weight, this result again in quicker spool (due to less weight and higher exducer force on turbine blades from reduces exd. radius) and +/- same back-pressure depending on turbine wheel down sizing/less blade count due to same free-float exhaust air area between turbine blades (everything else equal). I would much rather go 10 blades 62mm exducer instead of 12 blades 64,5mm exducer in turbine and reduce weight and diameter for +/- same free exhaust flow.

Overall we all want a boost-map (i-map) vs. exhaust back-pressure map (e-map) as close to 1:1 all the way to red line. But we dont need to over compensate with too big turbine wheels to accomplish this. There are many ways to keep back pressure on target others than just turbine wheel exducer diameter alone.

My upgrade winter project ...

I am currently building my own custom "500hp turbo" for a 3.0L 930, it will be close to bolt-on. I want much sooner and smooth boost build-up compared to K27, more power and same low back-pressure
Compressor housing will be somewhat same size compressor volute volume compared to the K27, still 2' outlet, but two options: 3 inch inlet (as close to K27 70mm), and 4 inch anti surged inlet, with included turbo shaft speed sensor on compressor housing
Compressor wheel size: 7+7 billet blades, 62mm inducer / 90mm exducer
Turbine wheel size: 10 blade 62mm exducer / 70mm inducer
Turbine housings: 13cm2 area T3 Twin scroll, and 16,3cm2 T4 twin scroll, total 4 options, two of them in same 4 bolt turbine flanges (as K27/OEM), and two options with V-flange outlet in 3' outlet (T3) twin scroll, and 3.5' outlet (T4) twin scroll
Core: Dual ball bearings (not for spool-up, but mostly for reliability)
This will be a small targeted quick spooling turbo in center/save compressor map of crank 300-600hp on pump gas, and 300-650+hp on E85 :-) Choke line/max hp of course higher, but never target a turbo for choke line/max hp.
I will be testing this unit in January and looking forward to it
Old 11-22-2019, 09:14 AM
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Check out this thread:

K 27 & gt35r

I went from stock to K27 and then to GT35R. I am still very very happy with my GT35 turbo - provides the smoother onset and wider range and lower rpm power creation that you mention you are seeking. just my two cents. Never had a second thought about the swap. Was not a drop in but was not hard to accomplish, either.
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Old 11-29-2019, 05:35 AM
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Quote:
looking to stay pretty close to stock but would love a turbo that didn't have the lag like the original 3ldz
This describes the application of the K27-7200 perfectly. A GT35 is way too big, if insisting on Garrett a GT30 is a better match. You're talking about a low boost 300hp engine not a 500hp engine. For even quicker spool the K27 can be modified with custom wheels, still plug and play.
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Old 11-29-2019, 06:31 AM
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Who does the k27 mods?
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Old 11-29-2019, 06:44 AM
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Brian, do it (Rarly8)
Old 11-29-2019, 07:32 AM
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I agree with s5uewf. I have had the k27 turbos. They are very nice but will never give you the performance of the Garrett GT35. The k27 are such old technology. You can get all the adapters and the turbo from turbo kraft to install it on your car. Just my 2 cents. John
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Old 11-29-2019, 08:32 AM
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Let's remember he's doing a light refesh on a 1976 3.0L Turbo Carrera -- only 3 liters, and just 6.5:1 compression.
A GT35R would be too large for this low compression with CIS, and a GT30R would be a much better match. We build a GT30R that's very close to a direct bolt-in upgrade for the 3.0L Turbo, and they're popular with the owners who aren't stuck on the "only use factory parts" mindset. Overall, maybe 2 additional hours to install vs. a factory turbocharger.

A K27-7200 can be a bolt-in upgrade for the 1976-77 930, provided the turbine housing outlet is machined to get the same offset as the stock 3LDZ, and to clear the stock turbo/muffler support bracket.
But if you use our stainless turbo/muffler hanger bracket, then you don't have to machine the turbine housing.

IF he had a K27-7200, it could be upgraded with lightweight, high-flow internals -- 9-blade turbine wheel, 6+6 billet compressor wheel -- but that's more airflow than an all-stock 3.0L Turbo Carrera engine can utilize.
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Old 11-29-2019, 04:38 PM
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Quote:
Originally Posted by gumba View Post
Who does the k27 mods?
Charlie at Evergreen Turbo
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Old 11-30-2019, 08:51 AM
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If you need a intercooler I have a half bay garettson for the 3.0 liter motor.. I sell it at a good price if interested. John
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Old 11-30-2019, 12:08 PM
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Thanks for the info i just spoke with evergreen turbo . nice guy knows his stuff .i explained my situation and he had some great recommendations to lower the lag and the max boost rpm now all i need is a 970-7200 or a 988-7200 core so they can mod it ..
Regards Ned

Last edited by gorskined; 12-09-2019 at 11:47 AM..
Old 12-09-2019, 11:45 AM
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Quote:
Originally Posted by gorskined View Post
Thanks for the info i just spoke with evergreen turbo . nice guy knows his stuff .i explained my situation and he had some great recommendations to lower the lag and the max boost rpm now all i need is a 970-7200 or a 988-7200 core so they can mod it ..
Regards Ned
What is the K27 upgrade? What compressor inducer? what turbine exducer?
Down sizing turbine diameter???

The K27 has massive size turbine exducer to beginn with - it is bigger than GTX35 !! and certainly much bigger than a GTX30.... People are making close to 1000hp on K27 sized turbine wheels diameters in race applications. I dont understand why using K27 is such important with such an old diesel mismatch on the compr. vs. turbine IMO

What is the upgrade wheel specs?
Old 12-09-2019, 12:02 PM
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I would think that the GTX35 would be right at home on a 3L, the Subaru and EVO guys use them on 2L engines all the time.
Old 12-09-2019, 12:08 PM
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^^^ Most of those guys behave like teenagers.
They just bolt the biggest of everything on and go blow the thing up.


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Old 12-09-2019, 12:14 PM
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^^^ Most of those guys behave like teenagers.
They just bolt the biggest of everything on and go blow the thing up.


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What are you refering to?

K27 is bigger than GTX35
K27 is bigger than GTX30
K27 spool-up slower than both
Why?
K27 has larger turbine exducer than GTX35 and more mass (heavier due to more blades)
K27 has smaller compressor i.e. smaller compressor = later spool due to the psychics/fact that smaller compressor inducer require much more turbo shaft rpm in an equal sized turbine scenario to deliver same air flow (just look at compressor map shaft speeds in comparison)

I am very curious to the K27 spec upgrades

Old 12-09-2019, 12:17 PM
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