stock 745i turbo research, some interesting findings....

papajetta · Post by **papajetta** » Feb 22, 2006 5:12 PM

i've been doing some research on the k27 turbo from a stock 745.
the one i have the compressor wheel measures 48mm/76mm. which turns out to be the same size of a
t04b super s and a t04e 40 trim. on the compressor maps at 15psi both of these are totally UNSUITABLE
for our cars. our engines run completely off the maq at about 3500 rpm, thats why the drop in power.
the compressor housing definetly has to be changed for something bigger like something in size like a t58 or t61

T_C_D · Post by **T_C_D** » Feb 22, 2006 5:41 PM

[QUOTE="papajetta"]i've been doing some research on the k27 turbo from a stock 745.
the one i have the compressor wheel measures 48mm/76mm. which turns out to be the same size of a
t04b super s and a t04e 40 trim. on the compressor maps at 15psi both of these are totally UNSUITABLE
for our cars. our engines run completely off the maq at about 3500 rpm, thats why the drop in power.
the compressor housing definetly has to be changed for something bigger like something in size like a t58 or t61[/QUOTE]

Wow, that sucks! Now we know why they make big torque and no HP.

Todd

Tjn182 · Post by **Tjn182** » Feb 22, 2006 7:10 PM

The 745i actually was equipped with 2 different K27s over its life. I think anything before 84 (?) used a smaller K27 -- basically a k26, while the later K27's were slightly larger with a 52mm//XXmm wheel. You really can't tell without measuring... and nobody really makes a big deal out of it.

But yes, we've all come to the conclusion that the K27 isn't suitable for our engines. 15 psi (my target) is about the most boost you want to run with one. Miller performance is pooping out an adaptor kit to mate up newer turbos to the 745i manifold.

If you want to try a different route, you can do some heavy research and try to uncover what garrett guts will mate in the K27.

Turbo Exchange Inc
501 Pitts School Rd # A, Concord, NC
(704) 721-6661

Todd used to use these guys a bunch. I called them up and they know what's up with the K27's. They told me last time I called they knew what wheels to use to upgrade the 745i K27 - I might hit them up a few months from now when the turbo is removed, a rebuild would be a good idea since everything else is getting a fresh start. But yeah - give them a call before 5p(est) and ask them if they can help.

HTH :p

russc · Post by **russc** » Feb 22, 2006 7:25 PM

Hey,
TJN182, I posted this a while ago under the Dan Milller nitrous thread with your post in it:

"In some looking for a K27 turbo map, I came across this thread from TJ in Boone.

K27 compressor map thread

It has a map and some calculations from TJ on the air flow of a 3.0l engine to the map. Couldn't have done it better myself. Thanks TJ. It appears that that map for a k27/2 with a reported .72trim wheel(?) will make 400hp at 22psi pretty easy and still be on a 70% efficency island. Just interesting and relavent to this converstion K27 compressor map "

That map goes out to 400hp of air flow(0.3 cubic meter/s). Not sure it if means anything. In looking at a TO4E 40 some trim, theire ~300-350hp compressors.

Not sure if any of this helps or not.

RussC

Tjn182 · Post by **Tjn182** » Feb 22, 2006 8:00 PM

Russ,
Those were the only compressor maps I found for the K27. You have no idea how long I searched to find them :p

I believe that chart is for the K27, just not the 745i K27. My thoughts are that it's for the 7200 model, which is much higher flowing than the 745i model. Many speculate the all 745i K27's are actually K26s in a K27 shell. But yet again... speculation.

Now if that chart reflects the 745i K27 properly, then we have all been wrong. Me and Todd looked at this a while ago and found that chart similar to the T60-1 chart, which means that the K27 is sized perfectly for the M30.

But really... there's so much "ifs" and "maybes" in this subject...

edit: look at the bottom right corner -- it says "911 turbo" and "91' M3" -- also says K27/2 on it. The 911 did use the same turbo as us... so... this might be the right chart! Right?

here's the map to save ya'll the hassle of opening another window:

[Edit by Tjn182 on [TIME]1140656814[/TIME]]

Post by **Jeremy** » Feb 23, 2006 12:05 AM

From what I've heard (and I can't remember the source, sorry), the k27 in a BMW 745i is different from the k27 used in the Porshe 911. I don't remember the exact difference, but the version used by Porsche flowed much better.

Jeremy

russc · Post by **russc** » Feb 23, 2006 12:18 AM

Well,
The date on that map is 1984. So it's in the right time frame. It does seem big, but I always thought the K27 was big turbo with a small wheel. putting a bigger wheel in it will definately give it some more flow. But you can still get some good power with a large turbo and small inducer wheels.

Can someone measure the A/R of the turbine?

RussC

papajetta · Post by **papajetta** » Feb 23, 2006 6:15 AM

definetly not the same one on the porsche:
- the collocter is too small for the hp levels that are developed on a "upgrade turbo" for a 911.
- i've been snooping around the porsche forums, and i've found out that they had a couple of choices for the k27, from quick spooling to high power.
where i got confused is that when people say a k27 it sounds like 1 turbo size, but its really like saying t4, theres not really a t4 turbocharger theres about 20 t4's.
i saw a compressor map for a k27 that was identical to a to4e 60 trim, but now i see that it was definetly not a "745i k27"

russc · Post by **russc** » Feb 23, 2006 2:10 PM

[QUOTE="papajetta"]definetly not the same one on the porsche:
- the collocter is too small for the hp levels that are developed on a "upgrade turbo" for a 911.
- i've been snooping around the porsche forums, and i've found out that they had a couple of choices for the k27, from quick spooling to high power.
where i got confused is that when people say a k27 it sounds like 1 turbo size, but its really like saying t4, theres not really a t4 turbocharger theres about 20 t4's.
i saw a compressor map for a k27 that was identical to a to4e 60 trim, but now i see that it was definetly not a "745i k27"[/QUOTE]

Hey papajetta,

Can you give us a turbine A/R on that one you have?

RussC

papajetta · Post by **papajetta** » Feb 23, 2006 2:27 PM

i dont have the right equipment to measure that, but i'm pretty sure its undersized. i'd guess its the smallest posible maybe .46 or less
its soo undersized, i'm starting to believe that it is a k26 in a k27 housing.
the turbine inlet port is 2 inches round in diameter.

Damon in STL · Post by **Damon in STL** » Feb 23, 2006 2:37 PM

I thought I read something a while back saying the 930 guys want the K27 from the '85 on 745 as it was an upgrade. I may be totally wrong, too.

I've got a loose replacement center section for my K27. What/where would I measure?

Also, when we did a group buy on the center sections, there were at least two different part numbers on the K27 turbos. This may be for the 3.2 liter vs. the 3.4 liter.

Damon in STL

russc · Post by **russc** » Feb 23, 2006 3:28 PM

[QUOTE="papajetta"]i dont have the right equipment to measure that, but i'm pretty sure its undersized. i'd guess its the smallest posible maybe .46 or less
its soo undersized, i'm starting to believe that it is a k26 in a k27 housing.
the turbine inlet port is 2 inches round in diameter.[/QUOTE]

papajetta,
you can figure the A/R easily.
Measure from center of the shaft to the inlet rim. thats the R in A/R.
We know the size of the inlet is 2", so the radius is 1", area of the inlet circle is Area = pi x radius^2(radius squared and pi is 3.14).
Then divide the area by radius. While it may not be exact, its close enough? keep all the unit the same, do if in inches, all measurement should be in inces.

RussC

altus22 · Post by **altus22** » Feb 23, 2006 6:39 PM

There's too many radiuses in there. The R in A/R is the radius from the center of the shaft to the center of the inlet rim, as russ said. The A is the area at that radius, which is the radius of the inlet squared times pi. I know everyone knew that, I'm just clarifying.

[QUOTE="russc"]papajetta,
you can figure the A/R easily.
Measure from center of the shaft to the inlet rim. thats the R in A/R.
We know the size of the inlet is 2", so the radius is 1", area of the inlet circle is Area = pi x radius^2(radius squared and pi is 3.14).
Then divide the area by radius. While it may not be exact, its close enough? keep all the unit the same, do if in inches, all measurement should be in inces.

RussC[/QUOTE]

papajetta · Post by **papajetta** » Mar 21, 2006 7:07 AM

just to update everyone on my research....
i got my k27 back, i fit a new compressor wheel instead of the stock 48mm/76mm, new wheel is 58mm/82, machined the housing.
that was the solution.
i used to run 12-13 psi and the car was always very unstable on the top end.
with this i can only run 10 psi because i dont have enough fuel ( 30lb injectors )
the engine power is smooth and constant up to 6200 rpm, in all gears under full load.
this is the best that the car has ever run, and the most powerful it has ever felt.

next upgrade will be the clutch, injectors, and MS ( which has been in the backburner for a year already )

Yellow2 · Post by **Yellow2** » Mar 21, 2006 12:35 PM

interesting. i wonder how much fast it would run if you were running a TCD or tubular manifld !

papajetta · Post by **papajetta** » Mar 21, 2006 1:24 PM

if i had to do this all over again i would go the TCD route, but i am way past the point of no return.
i'm trying to get the most out of this set up.
but i think i figured out the main problem with the 745 bolt on.
the compressor wheel on the stock k27 is just too small.

russc · Post by **russc** » Mar 21, 2006 2:22 PM

Ya,
A bigger wheel will give you more air flow per rpm.

Nice job, look forward to dynos.

RussC

Velocewest · Post by **Velocewest** » Mar 23, 2006 3:51 PM

papajetta wrote:just to update everyone on my research....
i got my k27 back, i fit a new compressor wheel instead of the stock 48mm/76mm, new wheel is 58mm/82, machined the housing.
that was the solution.
i used to run 12-13 psi and the car was always very unstable on the top end.
with this i can only run 10 psi because i dont have enough fuel ( 30lb injectors )
the engine power is smooth and constant up to 6200 rpm, in all gears under full load.
this is the best that the car has ever run, and the most powerful it has ever felt.

next upgrade will be the clutch, injectors, and MS ( which has been in the backburner for a year already )

Did you have the larger compressor wheel fitted by a shop, or did you machine and install it yourself? And where did you source the compressor wheel?

Thanks.

Tjn182 · Post by **Tjn182** » Mar 23, 2006 5:05 PM

Turbo Exchange Inc
501 Pitts School Rd # A, Concord, NC
(704) 721-6661

I got their name from TCD.

They should know all about the 745i k27 and how to upgrade it. This is where I'll be taking mine when it's time to rebuild.

You say your inlet is only 2" on your k27? Mine is 2 3/4"!!
The outlet is 2" though.

papajetta · Post by **papajetta** » Mar 24, 2006 6:12 AM

i had mine done at majestic turbo, they know about k27's from the porsche crew.
i did try the turbo exchange but they didn't have any info on the upgrade, plus delayed too much to do the research.

the outside diameter of the compressor housing inlet is 2.75 in.
but its a velocity stack and the inside diameter is less than 2 in.

my housing now does not look like a velocity stack but more like a cylinder.

Tjn182 · Post by **Tjn182** » Mar 24, 2006 8:09 AM

How much did majestic charge?

papajetta · Post by **papajetta** » Mar 24, 2006 10:01 PM

for full rebuild and , wheel and machine housing 700
i think they would only charge 300 for the wheel only

jimbixjr · Post by **jimbixjr** » Apr 04, 2006 2:37 AM

how much would it cost on average to get a k27 balanced.

papajetta · Post by **papajetta** » Apr 06, 2006 1:31 PM

i think about 125

chaste420 · Post by **chaste420** » Apr 12, 2006 8:21 PM

would this fit on the 745i manifold?

http://cgi.ebay.com/ebaymotors/PORSCHE- ... dZViewItem

russc · Post by **russc** » Apr 12, 2006 9:45 PM

Not sure if it fits, but thats one small looking turbine for out application? Its noticeable smaller than the compressor!

RussC

Velocewest · Post by **Velocewest** » Apr 13, 2006 7:31 PM

chaste420 wrote:would this fit on the 745i manifold?

http://cgi.ebay.com/ebaymotors/PORSCHE- ... dZViewItem

Ouch! For that money, you could buy Dan Miller's adaptor to the 745i manifold (which comes with a T3/04) and have access to every Garrett-style turbo on the market. Or a TCD manifold, which also opens up your wastegate options.

Velocewest · Post by **Velocewest** » Apr 14, 2006 2:06 AM

On the subject of Garrett adaptation... I was doing a little googling for examples of mount adaptors. Found a few, all basically a plate that bolts to the manifold and gets sandwiched between the manifold and the turbo. Then I looked for prefab T3 flanges. Then I wandered out to the garage and stared at the BMW turbo manifold for a while. Looks to me like fabbing an adaptor for a T3 base would be pretty damn simple and cheap.

Given the price of K27 mods vs. the price of T3/T4's, I'm thinking it makes a lot of sense ot free myself from the K27. Even with my determination to go low budget, this pencils out. I can sell my good K27 for close to enough to buy a T04e. Down the road, modding a Garrett-style turbo is much cheaper than modding a K27.

papajetta · Post by **papajetta** » Apr 14, 2006 6:37 AM

i was considering the t3 adapter for a while and almost went that route but:
- t3 is smaller housing than a k27 turbine. ( would make more sense if it was a k27/t4 adapter )
- a trip to the muffler shop and hack the downpipe.....
- a good turbonetics t3/t4 is 600+ ( not a knock off )

at the end i calculated that $/hp would be more beneficial to invest in a k27 upgrade.

papajetta · Post by **papajetta** » Apr 14, 2006 7:13 AM

not to mention as previous post :
TCD w t04e much better combo than $950 k27.....
unles your tapped your cyl head for 745 studs

MyE28.com

MyE28.com

stock 745i turbo research, some interesting findings....