Pelican Parts
Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   Pelican Parts Forums > 1- Porsche Technical Forums > 911 / 930 Turbo & Super Charging Forum


Reply
 
LinkBack Thread Tools Rate Thread
Author
Thread Post New Thread    Reply
Eye of the Toiger
 
matty74's Avatar
 
Join Date: Oct 2005
Location: Sydney, Australia
Posts: 1,204
Garage
anyone heard of a K27 witha k29 hot side?

I guy I know has a k27 turbo and he says that it has a k29 hot side.

he said that it kicks in at around 2200 and pulls strong all the the way to 5500 rpm.


Is this a model of k27 or a custom job?
__________________
http://www.aircooled.com.au

1973 911 RSR clone powered by 77 3.0 turbo
Old 03-17-2010, 08:24 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
Registered User
 
Join Date: Jul 2006
Location: Honolulu, HI
Posts: 5,191
I have a K29 with a K27 turbine.
__________________
Bryan O.
77 930
08 Boxster
14 535i M Sport
Old 03-17-2010, 11:41 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #2 (permalink)
Crotchety Old Bastard
 
RarlyL8's Avatar
 
Join Date: Jan 2000
Location: Huntsville, AL
Posts: 13,427
Garage
Custom
__________________
RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 03-18-2010, 04:02 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #3 (permalink)
Infidel
 
JBL930's Avatar
 
Join Date: May 2006
Location: UK
Posts: 1,172
Surely you'd have a larger cold side, K27 hot side and K29 compressor side. What would be the advantage of having a larger turbine and smaller compressor?
__________________
Jonathan.
87 930, 993 turbo engine, RS Tuning 520PS/515lbf-ft, Arrow Rods, ARP hardware, Solid lifters, G50-50, RS Flywheel, 890nm Sachs clutch, RSR coil overs all round, 993 C4 calipers front, 930 fronts on the rear, Ruf Speedlines.....
Old 540 BMW, XB12S Modified, for being a total hooligan
Old 03-18-2010, 04:11 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #4 (permalink)
Eye of the Toiger
 
matty74's Avatar
 
Join Date: Oct 2005
Location: Sydney, Australia
Posts: 1,204
Garage
Quote:
Originally Posted by JBL930 View Post
Surely you'd have a larger cold side, K27 hot side and K29 compressor side. What would be the advantage of having a larger turbine and smaller compressor?

yeah why what would that do
__________________
http://www.aircooled.com.au

1973 911 RSR clone powered by 77 3.0 turbo
Old 03-20-2010, 11:20 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #5 (permalink)
Max Sluiter
 
Flieger's Avatar
 
Join Date: Mar 2006
Location: So Cal
Posts: 19,573
Garage
Wouldn't that mean quicker spool-up and less restriction at the top end, at the cost of some ultimate boost pressure? Combine that with a moderate static compression ratio for a snappy Turbo engine with a strong mid-high range powerband.
__________________
911S
1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened

Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
http://www.flickr.com/photos/max_911_fahrer/
Old 03-20-2010, 11:26 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #6 (permalink)
 
Registered User
 
copbait73's Avatar
 
Join Date: Nov 2003
Location: Chesterfield IN
Posts: 1,314
Garage
The more power (exhaust flow) that goes through the turbine and not the wastegate the more efficient the match. This comes out as reduced backpressure. What is left not knowing is what is the turbine housing A/R (or area) of the "K29 hot side" being used.
As long as the compressor can provide adequate airflow at good efficiency throughout the engine rev range it is acceptable. Turbo framesize is usually defined by the turbine wheel size (and supporting bearing system). It's typical that the largest compressor of say the model K27 turbocharger framesize, is the smallest compressor option of the larger framesize, in this case the K29.
Old 03-21-2010, 05:24 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #7 (permalink)
Rocket Scientist
 
Join Date: Jun 2008
Location: Detroit
Posts: 881
It is technically true that high massflow through the turbine makes for the most efficient turbo match, but why do all high performance road cars have wastegates?

A typical turbine map is shown below. As the mass flow parameter (just think of it as exhaust gas flow) increases, the efficiency also increases (red line).

But look at the range of efficiency. The bad is around 60% and best is around 70%.



That is small potatos for a gasoline engine. What is more important is turbo response. Getting up to the maximum boost as quickly as possible is the name of the game; efficiency is secondary. For best response, the smallest turbine that can be fitted, along with a wastegate makes for the best overall package in a street car. A K27 turbine is 68mm in diameter. A K29 is 82mm in diameter. That it a very big chunk of iron to get spinning. A K29 is not going to give an increase in response. The 10% in efficiency is no way going to offset the rotational inertia of that much iron. It will make more power, once you get there, but it will be a loooong wait. Even the lightweight Formula 1 turbo cars of the 80's used wastegates

.


The only technical reason to increase the turbine size, is when response is secondary to another goal.

Very high power ratings for a two valve engine like ours can only be sustained when backpressure is as low as possible. In this regard, twin turbochargers are usually adopted because they allow for tuned exhaust plumbing. Efficiency is key. Above 800 HP on a two valve 930 motor the engine goes into a "death spiral". You have to add more and more boost just due to the breathing (volumetric efficiency) of the engine, but the backpressure is going up and up also due to the high exhaust flow and small turbine area needed to get that kind of boost. The only way to favorably impact this is to improve the volumetric efficiency (cams, and ports), and improve the turbine efficiency (big turbine). It will be a dog around town, but once it gets rolling, look out.

Botton line: a K29 is not going to be a good choice for most 930's on the street. If you are headed to the Texas mile, that's another story, but then you (hopefully)wouldn't be looking for advice in this forum!
Old 03-21-2010, 07:32 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #8 (permalink)
Registered User
 
copbait73's Avatar
 
Join Date: Nov 2003
Location: Chesterfield IN
Posts: 1,314
Garage
I don’t think the original poster was asking for advice, he was making an observation and everyone else including me was responding accordingly. I didn’t say use this turbo or that one. But since you often seem to take issue with almost everything I post, I’ll take you on, no problem.

The wastegate is a necessary evil and a cost effective compromise to attain boost response. The variable nozzle turbine (VNT) is a better compromise because they use the energy instead of dumping it overboard. VNT was not an option during the days of F1 however they are used on Porsches top of the line modern TURBO and on millions of diesel engines. The VNT uses the exhaust energy more efficiency and oh by the way can also be matched with a larger turbine and still provide better response.

Responding to your map, that is all good but what happens when the wastegate opens and dumps energy overboard? Your effective turbine efficiency is now poo-poo. Here’s Porsche own published data, P2 is intake pressure and P3 exhaust pressure. When you open the W/G you begin generating pumping losses in the engine system.



Everything about turbos and matching is a compromise. Relating to rotor inertia, what would you rather have? 1) a small turbine wheel that comes up to pressure a split second quicker but is restrictive and has poor efficiency from there on, 2) A larger turbine with less restriction and higher efficiency that can offset opening of the W/G to a higher engine speed. There is no set answer it’s a compromise for the conditions and intended use.

Manifold pressure does not = power. Positive pressure differential between the intake and exhaust manifold at a set manifold pressure = power. Yes, Eddy is out there making big power using known turbocharger principles
Oh, regarding your F1 motor. Marvelous piece of engineering those motors. I would consider those turbos to be quite large. I have an F1 turbocharger and it has a 65MM turbine that was fed by only 750CC.

Last edited by copbait73; 03-21-2010 at 09:50 AM..
Old 03-21-2010, 09:03 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #9 (permalink)
Rocket Scientist
 
Join Date: Jun 2008
Location: Detroit
Posts: 881
I think Flieger was suggesting that a big turbine would give better response and better efficiency. I think we are both saying it will do either, but not both. I've driven a K29. I thought it was aweful, but that was a fast car. The lag was something else. Your post was fine. I just wanted to add a bit more.
Old 03-21-2010, 10:21 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #10 (permalink)
Max Sluiter
 
Flieger's Avatar
 
Join Date: Mar 2006
Location: So Cal
Posts: 19,573
Garage
I do not have any hands-on Turbo experience but wanted to keep the discussion going. I found the above posts very informative. Thanks.

In regards to the K27 compressor/ K29 turbine hybrid being discussed, I was suggesting increased response compared to a K29/K29 due to the decrease in compressor inertia (until the compressor stalls).

__________________
911S
1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened

Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
http://www.flickr.com/photos/max_911_fahrer/
Old 03-21-2010, 12:53 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #11 (permalink)
Rocket Scientist
 
Join Date: Jun 2008
Location: Detroit
Posts: 881
It's a good point. A smaller compressor does have lower inertia. But the amount is pretty small because it is made from aluminum instead of Nickel/Iron. In the F1 days we did make some Magnesium compressor wheels though, for just the point you are asking about. They weighed like they were made of styrofoam. On a street car though, probably not noticable compared to switching from a 68mm turbine wheel to an 82mm one.
Old 03-21-2010, 01:55 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #12 (permalink)
Registered User
 
Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
In the past putting a K29 compressor wheel in a hybrid K27 frame was the best option for a motor that was going to make in the 400hp range. The stock LDZ just could not support over 300hp at any level of efficiency. The larger compressor wheel could move more air and heats the intake air less when doing it so more air and fuel can be packed into the motor and the ignition can be operated at a more ideal setting.

The K27-7006 and K27-7200 worked very well into the 360+hp range with modest sized compressor wheels. The 7006 has a larger hot side and makes better track HP. The 7200 has a smaller hot side and comes in faster.

Most of the newer K27 hybrid turbos do not use the old K29 compressor wheels anymore as there are a lot of other choices that might fit better, have less weight to them, and run more efficiently. They are often called HF or K29 quick spool turbos depending on who you get them from. Most are based on the small hot side K27-7200 which seems to hit a wall as to how much exhaust it can flow no mater what size compressor wheel you put with it.

The trend dose seem to be toward larger compressor wheel turbos with smaller turbine hot sides. This seems to make for a turbo that comes on earlier because of its smaller turbine and also can support more HP efficiently with its larger air flow potential.

This works well on a street oriented car. Just make sure you have the wastgate capacity to bled the increased volume so the boost dose not creep over your goal.

Also, thinking of how you can get the WG side to flow well just like we do at other parts of the exhaust system would probably be a good idea.

However, if you are building a track car, going to a larger hot side can reduce pressure in the headers add more HP to the part of the 4000-7000rpm power curve you would be using on the track. The cost is boost onset and full boost points being about 300rpm or so later.


Just a note, moving from say 60% to 70% efficiency is about a 17% increase in efficiency which is pretty significant.
Old 03-22-2010, 09:17 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #13 (permalink)
Wo ist die Rennstrecke?
 
DonE's Avatar
 
Join Date: Mar 2004
Location: Brooks, GA
Posts: 1,211
Quote:
Originally Posted by copbait73 View Post
I donít think the original poster was asking for advice, he was making an observation and everyone else including me was responding accordingly. I didnít say use this turbo or that one. But since you often seem to take issue with almost everything I post, Iíll take you on, no problem.
[snip]
Ouch - I didn't read it that way, but OK. In my opinion, I enjoy reading both of your posts because you use facts and data - two points sometimes lost in forums like this.

I appreciate both of your posts/input.
Old 03-23-2010, 06:20 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #14 (permalink)
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 


All times are GMT -8. The time now is 01:50 AM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page
 

DTO Garage Plus vBulletin Plugins by Drive Thru Online, Inc.