carx7

iTrader: (31)

At the risk of killing interest I will start by saying that I have not personally seen any of the above mentioned turbo setups. That said, all statements are based on pictures and individual conversations with people who own these setups.

A fellow worker showed me this site yesterday:
http://www.vishnutuning.com/exhaust101.htm

It has very interesting information about exhaust system design for a turbocharger. It was written by a designer for Garrett, so I figure he has a pretty good idea what he's talking about. It says basically what we all know, bigger is better, to an extent, when looking to turbo exhausts. He goes on to talk about exhaust sizing related to power and says that a 3" system is really too small for a 400+hp car. Interesting....

This made me think of the Magnus Gt42 that is so controversial. A huge benefit that Marco has pointed out is that it has a 4" DP to reduce backpressure thus making the car feel lighter on throttle. Couple that with a divided exhaust housing and a thoroughly researched manifold design and I don' t find it hard to believe that his turbo, despite being larger, could spool with the 35/40 given that it has been so tested.

I'll state now that I have never seen a 35/40 in person nor ridden in a car so equiped but... The pictures that I have seen appear that the manifold runners are not equal length. I could very well be wrong on this. I dont' think anyone will dispute the fact that equal is better.
The 35/40 (or 35r as I have been told the rest of the world calls this turbo) is essentially a T3 (more back pressure) undivided housing (not as good for spooling as divided) setup, and to me it doesn't look like the manifold has been thoroughly thought out. I say this mostly for the equal length issue and can't speak to the distance the air travels in the pipe. So yes, the 35/40 seems to work well but perhaps it could be made to work better.

Further after looking at a few Garrett compressor maps, it appears to me that the Gt42 is more efficient over the range of "street" boost levels and rotary air flow numbers than the 35r. This could also explain a better "feeling" turbo (I think that's how Marco compared it to a 35r)if the intake charge isn't heated as much during compression. Also, given the fact that the compressor is larger and capable of more airflow, it should make more power on the top end. Again, following Marco's observations and I think, to an extent, the observations of another lister (I can't remember who said it) butsomeone commented that their T78 felt like it had a 50shot of NOS over 6kRPM compared to the 35r. I would guess this is the T3 turbine housing becomming restrictive on the 35R.

So I think with this, the Magnus Gt42 seems like a great way to go. The new twins have the opportunity to flow exhaust wise and compressor wise like a larger turbo without the extra weight to spin. The questions will become what does the compressor efficiency look like in the usefull operating range and how well is the exhaust designed to reduce back pressure.

There is certainly the issue of the WG disrupting airflow and increasing back pressure if it is returned to the exhaust line close to the turbine. Which I think would be amplified by the internal WG used by the smaller GT turbos... but I wasn't planning to go there right now.

Thoughts? Opinions?

~Chris

M5150

what about for those of us who are looking for maximum spool and response? and not going down the drag strip as fast as we can, wouldnt the 35R make more sense?

carx7

iTrader: (31)

I'm not sure... I guess that's kind of what I'm poking at. The argument seems to be that just because the 35R is smaller it will spool better and make more power sooner. There are so many factors, I wish I could afford every option

Really the 35r has size going for it. The Gt42 (for example) has less back pressure, a divided housing, and a well thought out and tested, equal length manifold. I don't know exactly how these things could be weighted in a comparison but I'd bet that with a proper setup and sizing the 42 could spool equally as fast as a 35R.

If we assume both turbos to be operating on an ideal manifold (and I would argue that from the current offerings the 42's manifold is better matched to the Magnus turbo than the 35R is to it's manifold) the 42 has less back pressure and a divided housing compared to less rotating mass in the 35r. This should produce surprisingly similiar results.

Then add the extra efficiency of the 42 to the equation and you have the potential for a cooler intake charge, thus more power for a given boost level. So, even if it lagged slightly behind the 35r for response, the fact that it is operating more efficiently could very well mean equal power at a lesser level...

I certainly don't have all the answers, but I am thinking of making my own setup... it's mostly a questions of which turbo platform I shoudl start with.

I do think there is a very good chance the new twin setup will have maximum response, or at least the potential for that... provided the manifold/exhaust setup is well thought out and tested.

ZoomZoom

iTrader: (2)

I have the GT3540 with the 1.06 A/R. I was on the highway making boost adjustments and it comes on Very very fast. 16 psi was there by 3000-3200k RPMS. It was a very cold day as well. I would say I could easily afford a bit more lag as my boost response is vitually instantanious. I think a GT42 with the div exhaust housing and other mods to make it spool as fast as a 3540 but with more power would be the way to go. I am happy with my turbo but a GT42 would be MONEY!!

turbostreetfighter

nice post...it is good to see somenone with knowledge create a post like this. and your theory is exactly right,especially the part about twins being the ultimate setup ( which it is, i have them on my race car).


MWW

carx7

iTrader: (31)

Marcus, you are one of the people whom I hoped would reply. I was looking at your website, specifically the "custom" page where you have a few pics of turbo. The larger pic at the bottom shows the turbine housing/LIM and DP all in gold... some sort of thermal coating I assume? Care to share which one? Also, nice exit from turbine housing on the DP... just like the theory says huh

Do you by chance have any info for designing the manifolds? I think the website I mentioned above does an excellent job going over the exhaust side of things.

I know there are equations and such (theory) that go into the correct runner length and diameter based on the rotor pulses etc... I just haven't seen them for a rotary. Sure lots of testing will help, but the theory should give a nearly ideal starting point.

Also, as a total asside, I have no idea if you remember but I met you maybe 4 years ago at your shop in Houston. I drove down with my wife (GF at the time) in my 88 Anni to buy a set of Konig Monsoons from you. We bolted them on the car and away I went. I've since sold them. Anyway, glad to see things seem to be working out for you.

Heath

iTrader: (11)

Good thread! Now I wish I had a GT42 and a full 4" exhaust system instead of my T-78 and 3".

carx7

iTrader: (31)

I was actually leaning toward the Gt42 after talking to Marco and a few people who are running this setup. Then reading the post by the Garrett designer seemed to reaffirm all that I thought I knew and had read.

Now looking into the Apex twin setup that seems like it might be a really good setup for the reasons I mentioned previously. I'll be very curious to see pics of it and hear from people. I think I have a very good idea what is needed to build my own setup, the biggest thing is, without understanding the theory I'm left with guess work on the manifold, which I believe is a *major* player in the performance of the turbo. You could arrive at the right answer with enough experimenting though. I get the feeling this is how Marco arrived at his design... perhaps he'll chime in here.

While I firmly believe there is more to be had from these new Garrett BB turbos I also realize that my bank account is not sufficiently large to experiment every possible setup!

I am very glad that people have found this informative. My objectives were to be informative and to make sure I wasn't totally smoking something

Oh, and to ZoomZoom, thanks for the reply with some boost response info about the 35r setup. i'm filing that into my increase knowlege bank...