Twin turbo configuration questions: Theory & Application

[Natchamp]

Ok, here is where I'm currently at. I've been trying to find a better turbo spec for my motor to get faster spool up. Below is my current top choice (subject to change at any given moment). The dots reflect the corresponding flow rates I need to obtain the following boost at rpm points. According to my calculations, this map is the best fit and provides the quickest spool up without going past the surge line while still providing efficeint and adequate flow at top end.

rpm boost
2500 5lbs
3000 12lbs
3500 18lbs
4000 20lbs
5000 20lbs
6000 20lbs
7000 20lbs

[Natchamp]

whoops, here it is:

[dean]

Mark,
I would think that is too close to the surge line. What map is that for?

[Mr Beau]

Mark,

As I mentioed before, the exhaust A/R probably has a bigger effect on spool than messing with the compressor at this point. Is there anything you can do to change it easily?

Is the airflow map per turbo? If so, it's pushing 600 HP. Pretty impressive... ;-)

[Natchamp]

Dean, it's a GT28RS. I realize the points are close to the surge line but it is the best map I have seen were the points are not over the line. If you can find a map that will support those flow numbers I'd love to see it.

Beau, I agree the turbine section has a big role to play in spool up. But a particular turbo's spool characteristics are also relative to the compressor, wheels, trim. I hope you aren’t trying to make an argument to the contrary. Otherwise, we would all have T60 compressors with tiny little turbines. My current turbines are K16’s and even trying to find specs on them is impossible, let alone having options. Yes, the map is per turbo.

cheers.

[Mr Beau]

Hey Mark,

You might be surprised at how much of an impact the exhaust has. For instance, the Garrett T3 that everyone knows and loves was used on engines from 2.0L (and maybe even smaller), all the way up to 3.8L. Common vehicles include Chrysler 2.2L, Ford 2.3L (Merkur and Mustang), Datsun 280ZX, Nissan 300ZX, and Buick 3.8L.

Surprisingly the compressor size isn't that different between them. You will find a big difference in exhaust sizing, namely A/R ratio. For instance, on Ford 2.3L with auto tranny's, they used a 0.48. On the manuals, they used a 0.63. The Nissan's also used a 0.63. I think Chrysler used a 0.40. The compressors also changed, but not as much.

The flow map you show is missing one important item: wheel speed. If the exhaust can't spin the wheel fast enough, you're not going to make the boost you require.

With the old Garrett technology, a different exhaust A/R was <$100 housing that was relatively easy to swap. Unfortunately I don't think it would be same thing for your turbos.

BTW, we chatted quite some time ago when I talked about running a Haltech on a 2.8L. Sounds like you're still having fun. :-)

[Natchamp]

Hey Matt, thanks for the input. I don’t think we are in disagreement. My point is that I have no options at all with my current kkk turbos and they aren’t properly matched to my configuration in the first place. So, that’s why I’m contemplating the switch to Garrett. The GT28RS comes in a .86 and a .64 turbine AR, I would go with the .64. I too wish the map showed wheel speed. Like I indicated earlier, even if the GT28RS doesn’t quite flow (given all the other un-calculateable variables) these specific boost points, it is still the best map so far I have found. 18lbs of boost at 3,500 rpm would be classified as very respectable in my book. I talked to Turbonetics also, even though they don’t currently run the newer GT series. They recommended the T360 or T3S60. The flow plots for the 60 is below. The points are even closer to the surge line and I’m past the efficiency island on top end with no room to grow at all (compared to the GT28RS). If there are other maps comparable, lets see them. I am still having fun, just wish I had more time to “have fun”. Cheers.

[Natchamp]

just curious, am I the only one that's been having trouble posting pics?


T3-60

[Lukesportsman]

Who are most of you going with for headers on the dual turbo installs? Is everyone going with custom one off's or is there anyone with a "off the shelf" header design? Who is willing to make these for a reasonable price? Are most of you going SS or mild with coating?

Luke

still dreaming of turbos!

[RarlyL8]

Hey Luke - My home town is about 45min from you on the IL border.

The answer to your question depends on turbo placement. If you wish to place the turbos on the sides of the engine, such as Mark has, then custom fab may be you're only choice. If you place the turbos at the rear, such as the old race cars, then you can use a set of stock early heat echangers, SSIs, or headers. You would still need adapter tubing for the final placement but nothing like the effort to fab custom headers.

I am contemplating this right now. What I am leaning twards is a rear mount system that completely frees up the space on the sides of the engine for easy access during servicing (read valve adjustments).

[Lukesportsman]

Wouldn't you want to go to a full race header to reduce turbo lag and prevent excessive heat loss before the turbo? I'm not looking for a 600hp beast, but yet a 400+ hp driveable machine. So your thinking something like RSR headers with flanges converted to turbo flanges and then custom fab up from there...

[RarlyL8]

Optimally, yes you would want the headers to be very short.
My car is strictly street. That means I need the heater to work and the one-off fab stuff at a minimum for long term proven durability.
The stock 930 exhaust is terribly long and the Euro version works very well as is or with engine mods to 400+ HP. This length is greatly reduce simply by the fact that with twins each bank will be separate.
There will be compromise of form and function.

[WydRyd]

Why not use a set of 993 headers for a rear mount configuration?

[RarlyL8]

'Cause I'm a cheap bastard who just happens to have a set of early exchangers laying around. HA!

Actually, I've never priced 993tt exchangers. I figured they would be expensive and probably wouldn't fit very well. The car's are too different.

Noone has answered the question about 993tt TURBOS. Would they be a reasonable choice to use on my 930 engine?

[BURN-BROS]

I'm going to run some off of a 996 on my 3.3L. I don't believe that there any difference besides part #s. They are not installed so I couldn't comment on if they are the right ones for your engine. I am taking the chance on them anyway. Why the interest in the 993 turbos? From what I am learning, the garretts have a great deal of info on them and parts are easier to come by. In the end I may switch to them.

[WydRyd]

RarlyL8, I was referriing to second hand NA 993 headers, not the TT headers. The NA headers would be ideal for a rear-mount configuration. They'd just need to be modified to mount the turbo's higher up for gravity drain

I believe these are the headers Mike Rombotis is using on his TT conversion.

Agree with Burn-bros. Go with a pair of Garretts.

[ttucker6]

RickM,

I've just started researching the Protomotive Stage I kit. I don't really want to drop down $7k so I'm really interested in what you come up with regarding used parts and fabricating your own plumbing. I have a '77 911S body (w/ '84 3.2L) so I was going to go non-intercooled so I didn't have to change the tail.
Good luck!

[RickM]

ttucker,

I have to take pics of the pieces I have. I think the real benefit is showing the 3.2 plumbing installed with the engine out of the car.

[Lukesportsman]

*Rick, please post pics

*Would there be a significant or substantial port misalignment of a 993 header on a SC or Carrera head? Would you want to (after verifying a working system) port match the exh ports to the ?larger? 993 header primaries?

[RickM]

OK, I promise to take pics by next week.

I can't help on the 993 stuff.....