3.2 Turbo Build - Garrett G30-660

[Coultl]

I'm wondering if anyone has experience or insights on a Garrett G30-660 in a 930. I'm building a turbo 3.2 (NA motor converted to turbo) with pretty modest power goals (320 crank hp).

The G30-660 is definitely overkill but I can get an unused one from a friend (project that never happened) for a very reasonable price. I plotted the expected flow rate / pressure ratios on the compressor map and it actually looks great...even though I'm running less boost than this turbo is optimized for. Also seems like the 30 sized turbine and the smaller 660 compressor should make boost come on early.

Some details on the build:
- rebuilt 3.2 engine (915 trans)
- Piston tops shaved to lower compression ratio to 9:1 (plan to run 7-8 psi boost)
- APR rod bolt and head studs
- G30-660 turbo, 46mm wastegate
- Standalone engine management (ECUMaster Black)
- Twin spark, coil on plug
- Drive by wire throttle

Thanks in advance for any thoughts!

[Axel84]

I Feel really sorry for that 915 box ..

[Coultl]

Ha, I have mechanical sympathy... The nice thing about running standalone is that I can keep boost low in lower rpms to limit peak torque. I 'should' be able to have a flat torque curve at 275 ftlb up to redline. From what I've read the 915 should be okay with that torque level.

That said, any advice on beefing up the box? These CNC diff covers and bearing retainer plates look really nice, but I have no info on how much they actually help: https://californiamotorsports.net/collections/porsche-915-transmission-parts

[pocv0]

Avoid burnouts and launches and it will be fine. Sticky tires, LSD, and you cold break 1st gear on the input shaft. JMO
The later 915 aluminum gearboxes are pretty bullet proof. Billet side cover could help, not sure of the benefit of the billet steel bearing retainer.

[quattrorunner]

If you can keep the tq at or below 300lbft you should be fine........good luck with THAT tho.
Set the boost and run away from that knob or switch is my suggestion. Problem is late at night, while still reeling from the amazing night drive you just had, your bird brain takes over and certain scheming begins.

[mikedsilva]

Originally Posted by quattrorunner

Problem is late at night, while still reeling from the amazing night drive you just had, your bird brain takes over and certain scheming begins.

haha, that made me smile


Fyi, I'm also using the ecumaster EMU Black and have had nothing but smooth sailing.
What are you going to use for your crank and cam sensor pickup?

Do turbos, with "low" compression, really need twin plugging? My understanding is it was required with high compression pistons especially when the high dome would split the flame front.....

Looking forward to hearing more of your build.
Here is mine but I suspect you're more advanced than me.

https://www.youtube.com/playlist?list=PL33XrsdrT6VOkbWiZb8hCuhPfcYZbBQUr

[Coultl]

Mikedsilva your videos are great! I’ve commented on a bunch of them. Awesome build. Ha, so cool to run into you here. I have so many questions. What turbo are you running? What boost pressure? What RPM does boost come on? How does it feel?

I recently ‘finished’ a 1995 Audi S6 build using an ECUMaster Black. That car has fully built 5 cylinder running 30 psi of boost. It was a great project to learn ECU tuning. It took me a while to get everything dialed.

[Coultl]

That’s escalated quickly…

[Bucketlist]

Originally Posted by quattrorunner

If you can keep the tq at or below 300lbft you should be fine........good luck with THAT tho.
Set the boost and run away from that knob or switch is my suggestion. Problem is late at night, while still reeling from the amazing night drive you just had, your bird brain takes over and certain scheming begins.

Yea, or you pull out of the car show and this really nice 40 Ford coupe with the blown Big Block pulls up next to you at the light. You say "i'm not going to do it" then the light changes and all animal instincts take over. You let him blow his tires away off the line but somehow pull on him in second gear, then get out of it hoping you didn't hurt anything. I couldn't run a 915.

[g12314]

I’m in year 2 of ownership with a 3.2 GT30R setup. Lots of wrenching and tuning and have a very streetable 1 bar setup that has been on two 1000 mile plus rally’s with mountain road driving.

Definitely need to show some respect to the 915, but (knock on wood) it’s been solid. Those full throttle 3rd, 4th, 5th gear runs have surprised a lot of folks who thought that had something under their hoods .

[Coultl]

G12314 awesome. A full bar of boost is serious. What supporting mods did you do? 915 trans? Did you lower the compression ratio? Twin spark or single?

Learning as much as I can before the build!

[quattrorunner]

Originally Posted by g12314

I’m in year 2 of ownership with a 3.2 GT30R setup. Lots of wrenching and tuning and have a very streetable 1 bar setup that has been on two 1000 mile plus rally’s with mountain road driving.

Definitely need to show some respect to the 915, but (knock on wood) it’s been solid. Those full throttle 3rd, 4th, 5th gear runs have surprised a lot of folks who thought that had something under their hoods .

That’s cool. I too love 3rd 4th and 5th in a turbo with 915. I couldn’t afford a g-50 but that transaxle has very similar ratios to the 915.
I didn’t like the highway higher rpm’s at our higher freeway speeds these days but that ratio is awesome in a turbo 911 car. I miss mine. I had three 915 gearboxes. lol. It was getting kind of pricey and full of hassle breaking 2nd gears so I got me a short 930. I love it except the tall 4th gear. I should say the gap between 3rd and 4th. But I do like the lower rpm’s on the freeway.
I will say you can soften the blow of boost with clutch tuning. But that also gets expensive. I remember using a 225mm sport clutch, a 225mm center force and something else in 915 size. The center force broke at least two 915 gearboxes if memory serves but the sport clutch have just enough slip to maybe soften the blow at .7 bar. .8 bar would wreck the sport clutch.
My engine back then was a real 3.0 turbo 930 engine with an andial Intercooler. Really fun engine. Very revy. I also used a Garrett gt30r it was amazing. The spool and thrust of that turbo is so strong. I’m using a gt35r now but using a 3.3 engine.
Your setup will be really fun but possibly expensive. I’ve seen others with great results with wevo 915 supported parts. Also guard makes good gear sets. Good luck and have fun.

[g12314]

The original build is documented here: https://forums.pelicanparts.com/911-engine-rebuilding-forum/383835-ricks-engine-rebuild-starts-cleveland.html

I rescued it from the owner that had purchased it from Rick and have working away on it to fix issues.

[Tippy]

Originally Posted by Coultl

I'm wondering if anyone has experience or insights on a Garrett G30-660 in a 930. I'm building a turbo 3.2 (NA motor converted to turbo) with pretty modest power goals (320 crank hp).

The G30-660 is definitely overkill but I can get an unused one from a friend (project that never happened) for a very reasonable price. I plotted the expected flow rate / pressure ratios on the compressor map and it actually looks great...even though I'm running less boost than this turbo is optimized for. Also seems like the 30 sized turbine and the smaller 660 compressor should make boost come on early.

Some details on the build:
- rebuilt 3.2 engine (915 trans)
- Piston tops shaved to lower compression ratio to 9:1 (plan to run 7-8 psi boost)
- APR rod bolt and head studs
- G30-660 turbo, 46mm wastegate
- Standalone engine management (ECUMaster Black)
- Twin spark, coil on plug
- Drive by wire throttle

Thanks in advance for any thoughts!

So many thoughts here. If sticking with a 915, I feel the GT30 is probably the best bet and match. Literally perfect IMO.

These modern turbos like big boost, so running it at 7-8 PSI will be perfect from capitalizing on the inefficiency of the compressor at low boost. What am I saying? I’ve experienced firsthand how old turbos perform vs modern. Old turbos were in their sweet spots in the lower boost ranges. They hit hard at lower boost pressures while delivering all the CFM possible. This made for an on/off feeling. No boost then BAM!, 7-8 PSI and those old compressors were delivering the goods and you and riding partner would be grinning ear to ear.

That really doesn’t happen on the newer units from experience. They feel much more linear and only wake up approaching 25-30 PSI or higher.

So with all that rambling, your best bet for that 915 to survive is capitalizing off the inefficiency of the GT30 compressor at lower boost levels. I suspect your car will feel very naturally aspirated vs an old school 930 wallop of the past.

Here’s the downside. It’s easy to get more boost and turn that 915 into metal soup.

Have fun, but I’d try to get a 930 box or G50 to really let that GT30 eat. It’s addicting.

Lastly, you have a high flowing engine with the strength of a 930 low end. These 3.2’s make good power at a bar and above and can take it.

[Tippy]

Here I am using a stock 3.2 outside of 98mm cylinders and 7.5:1 compression ratio pistons with a Holset HX-35 that has a 58mm 8-vane wheel. This turbo is the smallest, lowest horsepower output from the HX-35 family (there are 60mm 6-vane wheels that flow much more IIRC). Running 1.4 bar boost at peak here (let off in 2nd due to wheel hop - non-LSD, cutting out at top end, and tiny restrictive air filter I've since remedied):

[Coultl]

Wow, that’s quick! I’m going to assume you’re not running a 915 trans…

[Tippy]

Originally Posted by Coultl

Wow, that’s quick! I’m going to assume you’re not running a 915 trans…

It’s the factory non-LSD G50 that came with the car

[stownsen914]

To beef up a 915, you’d want to do a side cover and the bearing retainer plate. Late 915s are beefier in general than early ones. Sounds like you should have a later one.
Another thing is that most 915s need attention I.e. rebuild unless that’s been properly done in the relatively recent past. That can get expensive quickly. Something to consider.
With advice mentioned above like no launches, slam shifting, or punching it in the lower gears, it could be made to live if you limit torque.

[Coultl]

Yes, this is an ‘84 so a newer 915. It does need a rebuild. Shifts terribly…

I started another thread that I’ll use to document the engine build. All the feedback here has been invaluable.