3.2 Turbo Build

[Coultl]

I figured I'd start a thread on my upcoming engine build and standalone tuning. I REALLY appreciate any input along the way. Hoping to also hear from those who have boosted their 3.2.

First, HERE's the car, and HERE is the rust work that I need to finish before I do the fun stuff (engine build).

Build goals:
- Modest power goals (320hp crank)
- Highly responsive, boost should come on at ~3,250rpm...hopefully
- Reliable and drivable. Not trying to smoke everyone on the road. I just want my version of a 930.

Engine rebuild plan:
- Rebuild the 3.2 and (hopefully) keep the existing pistons and cylinders
- Shave off a small amount of the piston dome to get down to 9:1 compression (need to remove 3.5cc fo aluminum)
- ARP connecting rod bolts and head studs (bought already)
- Rebuild cylinder heads, twin spark
- Grind cams to 964 spec? Worth it?
- Thought about building the heads to redline at 7k rpm but it just doesn't seem needed.

Boost:
- Retain factory headers and heat
- Turbo: Garrett G30-660. Any ideas on turbine AR? 0.62?
- 46mm Precision wastegate
- Side mount turbo on drivers side. I just seems like this is a better spot for the turbo, but I need to CAD it all up and make sure I'm right.
- Turbo oil drain into lower cam cover. Hopefully I can get the turbo high enough for this to work. Not water cooling the turbo.
- Water to air intercooler. Intercooler from a BMW M3. It's compact and it's performance is known. Pretty good little unit.
- Various 3D printed parts to make it as factory looking as possible.

Management/Fuel:
- ECUMaster EMU Black (I used this this in a fully built Audi URS6. Great ECU.)
- DBW throttle body
- 60-2 crank sensor (Either on a new flywheel or a pulley mounted wheel. Not sure yet.)
- Clewett cam sensor
- Injectors? I've used ID1000's before. They are great but very expensive and overkill for this build. Will run a Walbro 255 external fuel pump.
- Flex fuel sensor and all fuel lines to support E85. I'll mostly run pump gas but it's nice to tune on E85 before going to gas.
- Coil on plug ignition

Trans:
- Rebuild 915 with factory LSD. I'll tune the boost curve to keep torque under 300ftlb through the rev range. That means something like 6 psi max at 4000 rpm. Do the billet diff covers actually help?
- Clutch? Sachs Power Clutch? How much torque can these handle. I'm not launching this car so I don't need anything crazy.

There's a few reasons for the water to air intercooler. I'm not running a whale tail and I don't really like the look of the intercooler covering the engine. I can remove the end tanks on this intercooler and and build custom 3D printed end tanks to integrate it into the overall setup. I should fit mostly out of sight in the engine bay.

What am I missing? Open to any input and criticism too!

[Coultl]

The Garrett G30-660 is a different choice, I know. I was able to buy it for $1k and couldn't pass that up. A few reasons why this could work well.

First, it has a smaller compressor wheel / faster spool than the GT3076R (the turbo I think most people run). That also makes it a little more compact and easier to fit in side mount.

It's true that these new turbos are optimized for high boost, but actually the compressor maps have a huge sweet spot. Here's a comparison:

GT3076R


G30-660


The red dots and line are from 3,000-6,000 rpm with boost building to keep peak torque low at lower RPMs. The yellow dots and line are the same except at 0ft elevation (I'm at 5,000 ft). The blue dot is a higher peak boost scenario

I don't have a turbine housing yet and I'm really not sure if I should go with a 0.83 or a 0.61 AR. Any thoughts?

[RarlyL8]

320HP at the crank is way too conservative if adding a turbo and EFI, even if using a 915.
The 915 can live just fine at 300HP at the wheels. With mods it can live at 350whp as long as you let the turbo do the work, no drag starts or speed shifting. A stock 915 can handle 320CHP no problem. Reinforcement for longevity and added strength would be a reinforced side cover and larger bearing retainer. LSD helps evenly distribute the load for even more strength. I ran that combo in front of a 3.3L 930 engine in an SC for 15 years that saw variations in output from 300whp to 350whp depending on what we were testing at the time.

Least expensive and problematic turbo install would be to use OE 930 parts. Install becomes plug and play with only the intercooler being custom at that point. This is assuming a standard flange pattern turbo is used. OE "Euro" heat exchangers and J-pipe would help keep the power level down closer to your target as well. Protomotive does a side mount turbo so they have those parts if going that route.

[Coultl]

You're probably right RaryL8. That blue point on the compressor charts is 12 psi boost. I'd guess that would be good for about 375-400 crank hp.

That said, I'm going to try to keep this build tame. My goal is to have similar power to weight ratio as a 993 Turbo.

Agreed that things would be more straightforward if I used 930 parts. Doing something a little different is part of the fun for me...but we'll see how things develop. I may need to pull it in a little!

Anyone know what A/R ratio you are running on your turbo?

[Tippy]

If you can locate a 930 or G50 box, you can relax and do wherever you want power wise. Someone will definitely scoop up your 915 to offset costs.

Hate to hear folks keeping power down due to the 915…

[scottrx7tt]

Originally Posted by Tippy

If you can locate a 930 or G50 box, you can relax and do wherever you want power wise. Someone will definitely scoop up your 915 to offset costs.

Hate to hear folks keeping power down due to the 915…

CMS bearing retainer really helps the 915 stay together. I had no problems after exploding 2nd gear after I installed the retainer(and new 2nd gear). I had 400hp and 360tq

[quattrorunner]

I'd definitely do 964 cam and 7k+rpm mods especially if your wanting to keep the 915 and lower power levels.

[Coultl]

Appreciate the input all.

Looks like people are asking for $20k for a rebuilt G50. Can’t do that. I also like the idea of the 915 being designed by Porsche and I’m good with torque staying around 325 lbft. If I build the engine to rev I could get 400 crank hp while keeping toque low. To that point…I agree…it’s probably worth the cost of a set of valve springs to allow the engine to rev to 7k+.

Good to know on the CMS. I think I’ll do the trans rebuild myself and have a lot to learn before I do so.

[Coultl]

Also, I’m going with a 0.83 AR for the turbine housing. The video below convinced me. In the video they compare the same turbo I’m using G30-660 with both a 0.62 and 0.82 turbine housing. The 2JZ is 3L 4 valve and is somewhat similar in flow to the 3.2 2 valve 911 engine.

Their tests show the 0.83 performs better across the entire rev range. I don’t quite understand why it also comes into boost sooner, but it’s enough evidence for me.

https://youtu.be/qvSibDP902k?si=WdRcsOBU8MywSmm4

[Coultl]

Question for any who have a turbo 3.2. What wastegate size are you running and do you get boost creep?

I’m planning to get a Precision 46mm but I’m concerned that it’s not big enough and I’m not going to be able to keep boost down at my target (7-8 psi) at redline. Any experience? Thanks!

[quattrorunner]

46 should be perfect.

[greglepore]

46 should be ok, I have a 40 and I do get creep, winter project is to go larger. I've lived with it a long time, it's a .5 bar spring but intercooled and it doesn't really creep above .7 the way that I use the car.
Your 915 will be fine if you drive it like a 915-be aware that 2nd is weakish, and no clutch drop starts. Mine lasted a long time even with 120k on it and a weak 2nd sychro before a guest driver
crunched up 2nd for good and I had it rebuilt. Not the fault of the turbo setup of the trans.

[Coultl]

Good to know. Thanks guys. The turbo I’m running is pretty large so creep might be more of an issue. I’ll stick with a 46mm and hopefully that will be enough. Tempting to just get a 50mm Garrett Wastegate now, but I did already order the Precision 46mm gate.

[g12314]

Running the Tial F46 with 1 bar spring, no boost creep.

[Dieter9]

Check up my tread .. your over thinking it .
If you have questions feel free to message me .
Btw, tial 46 mm over here.. no boost creep .
Good luck !

[Coultl]

Over thinking it is the best part! Ha.

Good to hear ~45mm is working for everyone here. I’ll stick with that.

Speaking of other thinking it, I’d really like to go with a side mount location for the turbo, similar to Protomotive’s stage 1 setup. There’s a couple photos online but I’d love to see what they do with the engine pan. Seems like they have the turbo right where it should be.

[Coultl]

Here’s a pic of Protomotive’s side turbo setup on a 3.2. Doesn’t seem like the engine pan would fit…

[greglepore]

No idea how that would fit. I have an early generation Protomotive kit on my car that uses the stock heat exchangers, it is "side mount" but the turbo is below the engine tin.

[Coultl]

Greg, is there any chance you could snap a few photos when convenient? I’d love to see how low it is and see how they routed the exhaust / wastegate. No rush, but would be great to see!

Do you have a scavenge pump for the turbo or does it just drain into the lower cam cover?

[greglepore]

Sure. Will do. The exhaust is not Protomotive, had a local shop do that when I changed to the gt35. Just a drain on the oil line.
The one exhaust feature that appears nice that I wouldn't do again is that the wastegate is routed into the tailpipe rather than having a zork tube. Makes changing out the wastegate a real project...