Garrett "Boost advisor" turbo selector.
 

Anyone try using that on their site? I tried it and it locks up, never gives me an answer. It looks pretty simple compared to the BW modeling tool but I thought I'd see what it says.

I have the mobile app version on my phone and its alright. It doesn't seem to like air cooled P cars though.. Does that same for me, locks up and just doesn't give an answer. I used it to ballpark some turbo options for an old Audi V8 Quattro build I'm starting soon and it was fine for that although I know it's numbers are a little off. For whatever reason it just doesn't think an old 911 is capable of making power. I even tried to use it to ballpark a 2.4 single turbo with a power target of 300hp... Nope... Wasn't having it

Chris at Turbo Kraft is your Garrett turbo selector.

:)

Yeah, but I want to know why the pros recommend what they do. I like to see a plot of the engine cfm on a compressor map to see where it is in relation to the surge line, where it will be at cruise rpm, efficiency islands at different rpms, etc. I can do it manually if necessary but it's a PITA when looking at several turbos. The BW modeling tool is very sophisticated, I wish Garrett had something similar. I shot an email to Garrett telling them it doesn't work, we'll see what happens, probably nothing..

The DSM guys get data logs from their MAF's (kg/s) to know exactly what compressor size they need. We can only go on hp and convert to CFM.

Chris at Turbokraft and these guys know everything about Garret turbos.

TurbosDirect.Com Web Site - Home
There's a phone number on their site.

One of the guys at Turbosdirect has owned several 930's and he likes their GSX 61 with billet compressor wheel. You can get it with a journal or ball bearing center cartridge.
I have one with the billet compressor wheel and ball bearings and it's great.

The Garret GT35R is another good choice. It's a little more expensive and may spool up a little faster because (I've been told) it has smaller ball bearings that weigh less.

^^ Oh cool, didn't know that. Good to know someone there knows our engines!

I can vouch for those working well in pairs. :D

The 35's just seem too big for a 3.3 CIS. Why do I want a turbo that will flow 60 lb/min @ 2 bar ratio ( ~ 600 hp) when I only have enough fuel for 400+ at the crank? Great for EFI but I question for CIS with a stock euro fuel head. I'm interested in maximizing area under the curve for the street, not just peak hp.

you dont pick a turbo to max it out - you pick a turbo to get in the sweet spot with your engine specs with highest efficiency on the map and for lowest backpressure. Key is to undestand the meaning of the turbo shaft rpm figures along the pressure/flow. Bigger compressors require LESS turbo shaft rpm than smaller compressors for same boost level ...lots of advantages to go big on compressor and never use full potential ... you dont get quicker spool-up by selecting a smaller compressor wheel on a fixed a/r setup and fixed size turbine setup.

As to the displacement question, well, they work amazingly well on 1.6-1.8 liter Hondas. They even work reasonably well on the 1.7 liters represented by 3 cylinders of my 911 they have to work with, you just have to wring the piss out of it. But trust me, when it starts pissing, it's a flood. As far as the "why do I want..." you answered your own question - area under the curve. A 35R on a single turbo 911 is unreal responsive and EXTREMELY efficient. Their compressor efficiency and ability to convert minimal drive pressure to usable boost over a fairly wide range of airflow levels just makes them fantastic turbos and very flexible. When the GT35R first came out, it was like the "jet age" of turbos had begun. It just really hit a sweet spot. Hard to believe that was way back in 2003 or so.

How much modification is required to install a GT35R?

OK, looks like I'll be spending some time with maps. Garrett doesn't show a map for the GT3476, it's got a 58 x 76 comp. vs. 61 x 82 on the 3582.

Speedfab, what rpm does it take to fully spool those twin gt35r's

It's not bad, you just have to cut off the muffler flange and weld on a new one.
Not really any more work than switching to a K-27

All of it. :D

Actually I haven't run it hard since putting it back together, and I honestly can't remember exactly where it was way back when, but it wasn't horrible. They have the smallest A/R turbine housings available. I do remember the fact that it gained nearly 500whp in the space of 1000RPM at some point when the boost was way up there around 2 bar, but reasonable boost makes a nice linear power curve. I don't recall where it peaked and broke over, but I never turned it past 8 grand, at least not intentionally.

When I put it back on the dyno I'll let you know and provide cool logs and graphs and all that happy horse manure, won't be long now. I only have a few things left to tidy up. Customers need to cut me some slack. ;)

You can get a "GT" style 4 bolt discharge turbine housing that will bolt almost directly in place of your factory 3LDZ other than moving the face of the turbine discharge flange (and consequently your muffler) a little toward the passenger side. The turbine inlet flange is identical, and I think the GT discharge bolt circle is 100mm just like the KKK. Places like ATP Turbo offer them with a T04E compressor cover which is 3" inlet and 2" outlet (the standard 35R cover is 4 in 2.5 out) making it fairly easy to adapt to the stock plumbing with minimal mods, the same basic stuff that is required when doing one of the "K27" upgrades, ie: no more O-ringed compressor discharge, etc. Then you only have the oiling to change - the 35R requires an inlet restrictor which you can get in either 3 or 4an connection, just change the feed line, and the oil outlet is MUCH smaller on the 35R - 3LDZ is 52mm bolt spacing with a huge drain hole, 35R is 40mm bolt spacing and hole much smaller... so your drain line, at least the flange, needs modding.

Simply put, Garrett's online calculator is essentially worthless in determining an optimal turbo for an air-cooled 911.
I've been using Garrett BB turbos since 2003, back when they were marketed under the "Ballistic turbochargers" line. Even back then, Garrett sized turbos too small for a 911, irrespective of CIS or EFI. Twin turbos they said would do over 600hp capped out at 540hp flywheel.

Sure, you can go smaller, but you'l find the turbine flow is too low and the turbo becomes the bottleneck.
Videos of essentially back to back testing: GTX3076R (ffwd to ~14:30) vs. GTX3582R
https://www.youtube.com/watch?v=hpPU7Y-VLno

FWIW, it's not a "2bar pressure ratio" -- it's a pressure ratio of 2, meaning 1.0bar boost.
TurboKraft has done 410whp at 1.0bar on a CIS 930 running a GT35R, SC cams, and typical headers-muffler-intercooler.

930s are usually fitted with too small a turbine. It's counter-intuitive, but often a larger one performs better at all RPMs.


911nut: we've been making all the pieces for 930 => GT35R conversion for years. Installation is not really that much harder than doing a K27, on par with a K29. A 930 sport muffler with adjustable tips usually bolts on with maybe the smallest tweaks. Rarely do you need to change the flange itself, but even that is easy.
Bolts to factory exhaust manifolds or aftermarket headers
New couplers & clamps for air inlet & outlet
New oil supply line assembly, restrictor; plus drain adapters as well as new aluminum drain cans
We even make a rugged stainless turbo hanger for 1984-94 models (almost done with 1976-83 version), as well as stainless heat shields


Maybe speedfab is getting different results, but in our experience, in order to truly take advantage of twin GT35Rs on an air-cooled 911, the engine needs to be developed to the max -- fully optimized heads, cams, intake, exhaust.
Otherwise sure, you have more flow potential, but the engine just cannot use it, and you introduce serious compressor surge despite ported shroud comp housings.
Case in point: 3.8TT with huge port work + cams + exhaust + intake making over 815hp to the wheels with twin GT35Rs, tested with 2 different turbine housings, always compressor surge.
Virtually identical engine with slightly smaller turbos, same A/R turbine housings, made slightly less peak HP but have *150lb-ft* more torque in the midrange.
Doesn't take a rocket scientist to figure out which of those two cars will be quicker in most race situations.

Chris, thanks for the input. Yes, PR of 2, not 2 bar, duh. I like the 410 whp with the same setup I'll have, SC cams, but cheapo used OBX headers that I got for a song and need some "attention" along with a custom long neck half bay IC that I will fab.

Nope, same results. I'll be the first one to say this is too far. Everything Turbokraft said is true. You had better have a hell of a lot of airflow potential, and even at that you'll be crowding the surge line at high pressure ratios. Would smaller turbos make more torque sooner? Absolutely... But like always, making it is one thing, applying it is another.

The only reason this ever happened is because the car had a single 35 on it the instant dealers could get their hands on them, which to the best of my memory was 2003 or so. That worked great, but the turbo ran out of airflow, then the twin stuff started and went through a couple smaller sets, kept getting stronger, and one day another 35R came off a car about the time the old one was taunting me from the shelf. It's one of those things that seemed like a good idea at the time back then, overkill everything (and end up with a dyno queen :rolleyes:). Having said all that, it's still pretty fun. Ideal, not so much.

A pair of 3071R's would probably be perfect, and if I continue playing with the car that's likely how it'll end up. Right now it is what it is... Those suckers ain't cheap, and these are already bolted to the car. ;)