Turbo upgrade, which one.

[GEE-BEE]

It's a 2008 997Tt with dymag wheels

euro suspension

Tubi exhaust & headers , No cat's
6500.00 Mod

38k in Int option's

132K base

Wheel's were 11K

ECU to 680 hp 3500.00

2011 GT2 RS coming

GB

[bugnut]

I'm pretty sure his is white!!! I'm sure if you ask him nicely he will email you pictures 

bugnut I'm still rocking a K14 I have been eyeing the VNT-17/22 hybrid, but they are like $1800. I'm thinking maybe I should just find another hairdryer and compound them. It seems like that would be the cheapest way to reduce lag and make tons of boost. Since you can fabricate I bet twins would be even cheaper for you.

 Jack,
 I am going with the compound setup.  I have a k14 on the way.  Now I am just looking for the hx30.  I emailed gpopshop if they had any and they said I need a part number off the hx30.  I guess there are dozens of hx30's out there. 

 Which hx30 am I looking for?  The one's off a cummins 4bt?

[bugnut]

It's a 2008 997Tt with dymag wheels

euro suspension

Tubi exhaust & headers , No cat's
6500.00 Mod

38k in Int option's

132K base

Wheel's were 11K

ECU to 680 hp 3500.00

2011 GT2 RS coming

GB

Gee-Bee,

 I got to say that is one heck of a car.  What are your plans for the GT2

[jack's lack]

 Jack,
 I am going with the compound setup.  I have a k14 on the way.  Now I am just looking for the hx30.  I emailed gpopshop if they had any and they said I need a part number off the hx30.  I guess there are dozens of hx30's out there. 

 Which hx30 am I looking for?  The one's off a cummins 4bt?

I'm sorry I must have missed that part. Maybe you can help me understand these systems better. I guess I'm curious as to why if you run the turbos sequentially why you couldn't make 30 psi with two K14's? If the LP one makes 8psi and the HP one multiplies that to the 30psi range. I am basing this on the understanding that the increase in boost is not the sum, but rather the product of the two turbos. To ask another way why do I usually see a large LP turbo on these setups? Please forgive my ignorance I don't have any experience with compound turbo engines and they are my latest fascination. I am trying to understand to decide if this it the route I should go.

[bugnut]

I am sure if you ran 2 k14's you can make 30psi but you will be hot.  From my understanding of twin turbos is you are going for cooler egt's.  the primary turbo makes boost quick and then the secondary will kick in later. Then the primary will be bypassed to a certain point and it will mostly be ran off the secondary in the top end.  Just need to make sure to get a big enough gate on the primary turbo.  The primary will always be making boost and the secondary will add to that and that is when the boost numbers start to climb.  It's the pressure ratio thing going on. 

 I still have a lot more reading to do on twin setups.  So far that is the jist of what I know.  I am trying to lower my egt's down by using twins.  I can use a larger single but then again there is the lag that I don't want.   I just cooked my new engine buy running the egt's in the 1600+ range for a few short runs.  Compression in cyl 1 went down to 330 while the others are at 370.  Hopefully I just need new rings and not new pistons. 

[gldgti]

[/quote]
I am basing this on the understanding that the increase in boost is not the sum, but rather the product of the two turbos.
[/quote]

No. You roughly add them together (the sum) although the actual gauge boost pressure should be a little less still than the exact sum.

The reason you see a large low pressure compressor/turbine is because you want to extract the most work from the system (most boost) and the least cost (less exhaust pressure at the valves). If you compound 2 small turbos, you will surely be able to make plenty of boost, but you will see much greater exhaust pressure and hence high EGT's ant less power.

If you only have 1 small turbine and 1 large, the larger low pressure turbine imposes practically far less "restriction" in the exhaust flow and as such you get more boost at less "cost".

In practical terms, most people (with an old diesel IDI) don't want more than 12-15psi under 2500rpm anyway, so it doesn't matter if it takes until 3000rpm for the larger turbo to really get going. hence, you can use quite a large LP turbine and get maximum benefit.

[jack's lack]

I am basing this on the understanding that the increase in boost is not the sum, but rather the product of the two turbos.
[/quote]

No. You roughly add them together (the sum) although the actual gauge boost pressure should be a little less still than the exact sum.

The reason you see a large low pressure compressor/turbine is because you want to extract the most work from the system (most boost) and the least cost (less exhaust pressure at the valves). If you compound 2 small turbos, you will surely be able to make plenty of boost, but you will see much greater exhaust pressure and hence high EGT's ant less power.

If you only have 1 small turbine and 1 large, the larger low pressure turbine imposes practically far less "restriction" in the exhaust flow and as such you get more boost at less "cost".

In practical terms, most people (with an old diesel IDI) don't want more than 12-15psi under 2500rpm anyway, so it doesn't matter if it takes until 3000rpm for the larger turbo to really get going. hence, you can use quite a large LP turbine and get maximum benefit.
[/quote]

Thanks for clearing that up. That all makes perfect sense. It also clarifies the nomenclature of hp and lp turbo a little I thought they were referring to boost rather than exhaust pressure. This also helps me understand why my K14 is causing such high egt's at higher rpm's. Learning this I assume the vanes on a VNT are accomplishing the same task of providing the more boost at lower "restriction" across a wider range as well. Not to threadjack, but what would be a good large LP turbo for me to run with the K14 to achieve 25-30 psi with this type of system? Instinct tells me the Holset that bugnut is going for would be overkill for my goals.


I found this schematic. I think this illustrates the type of system we are talking about. I'm visual so this really helps me out.

[RadoTD]

While compounding boost makes small boost differentials multiply into head twisting boost, don't forget that you still need to flow the same amount of air through both turbo's. Look where 25+lb/min (.156 m^3/s) of air sits on a K14 compressor map, regardless of pressure differential.
Now, take a look at the ambient pressure that the compressor map is done at. Usually just shy of 1bar. Obviously in the schematic above, your HP turbo's inlet isn't exactly 1bar.... I'm not sure exactly how that would affect the compressor map, so I just tend to not worry about that compressor map so much, as long as the turbo can push decent air through the engine on it's own. Just don't expect it to be multiplying the boost by a whole lot. What I've been doing is assuming that the LP turbo is going to be compounding around 3/4 of the final boost on it's own and having the full flow.

That compound schematic posted is basically the most common design, except that with a good wastegate (possibly internal wastegate + and external wastegate), the check valve and exhaust flap are unneeded. On the intake side, your HP turbo is there to spool up quick and just squish the air a bit further for those nice high boost pressures. Some compunds have been done with the HP first, then the LP on the intake side. That spools them up a bit quicker, but you risk overspeeding the HP turbo. A check valve might be a good idea if you're going that route

Right now, I'm tentatively looking for a K24 or K26 to compound with my K14, hoping for a reliable ~30psi on my AAZ

[bugnut]

I just ordered up my HX30.  Should be here next week along with the k14.   So far what I got planned out is to run two gates on the k14.  The internal and put an external on it.  The external gate is a 44mm version.  So with bolth gates working I should be able to bypass the k14 when I am in the upper scale of the rpm range if I need to be.   What I am thinking is to have both gates setup to dump at different pressures.  Have the internal dump at 4 to 6 on the lp side and the external to dump at 20 on the hp side.  That way I know after 20 I am pretty much bypassing the hp turbo and running on the lp to keep my egts in check.  It sounds good right now, we'll see when tires hit the pavement.  If the k14 is too small and still getting high egt I can always swap it out for the t3 I have on the car right now.  I am shooting for max boost around 30 to 32psi. 

All this should come together in about a month or so.  Depends on how bad I messed the engine up the first go around. 

[myvolkswagen]

you should definatly start a build thread on this. I seen that your from hayden. I have a place in Coeur d alene. I'd like to come see what your doing next summer if thats alright

[bugnut]

you should definatly start a build thread on this. I seen that your from hayden. I have a place in Coeur d alene. I'd like to come see what your doing next summer if thats alright

 Once I get the turbos I will start a build thread.  Next time you are in town let me know.  Hopefully I will have the engine running again by summer.

 I see that andy2 had a thread going back in '05 about compound turbos but all the pictures don't work now. 

 I first need to figure out why my piston in cylinder 1 now sits .005" below the deck.  I am thinking I bent the rod. Cylinder #4 is at .016 above deck. 

[zukgod1]

Anything new to report on this?

[bugnut]

I just got most of the parts in to start the build.  The k14 just showed up about a week ago.  Still waiting for some pipe and flanges then the fab work starts while I am waiting for the rods to show up.  I'll have to take a picture of the hx30 next to the k14.  From the looks of it the k14 is super small but we will see when the time comes around. 

[bugnut]

A few pics of the build


and my new rods

[Smokey Eddy]

The hx35 is too big. nuff said. I have one on my table. It's too big even for a heavily ported, fueled up 1.9. Glad you went with the 30. VERY nice work. I'm envious.
How did you get involved with the diesel dubs? Usually people dont start insanity of this caliber until they've had a few years with the moderately sane debauchery that IS IDI VWs