Max hp/tq safe for 3.6 N/A turbo?

[993Speedster]

So how much power (or probably more accurately how much torque) can a 964 3.6L N/A long block safely handle? I feel like most the forced induction 964 crowd is doing the TPC supercharger route and find themselves limited due to heat, octane, and tuning flexibility.

I’ve got stand-alone, e85 and water/meth injection on my side so I don’t think compression or detonation is going to be my limiting factor here... likely engine integrity. So what’s the difference between 964 n/a rods vs 964 3.6L turbo rods vs 993 turbo rods. Just different compression pistons or more at play?

Currently sitting at 0.6 bar peak tq. tapering to 0.8bar redline; 7-11 psi. Where’s the line drawn for “unsafe” given my spark plug readings look good and so do the AFR’s/ data logs

[993Speedster]

Well... I see a lot of people watching but no advice so I turned her up again! Added a boost controller. Instead of 7psi creeping to 11 it’s 14 right out the gate. 3rd gear rips my face off but once again blowing out the spark... now at 190ish kPa MAP. Looks like closing up the plugs another 4 thousandths and let her eat!

Before I go bonkers with coil on plug... are there any hotter coils I can bolt right in for twin plug 964 ignition?

[dannobee]

Aren't the 964 rods the same part number as the turbo con rods? If so, 600 hp is about max after replacing the rod bolts.

[993Speedster]

Originally Posted by dannobee

Aren't the 964 rods the same part number as the turbo con rods? If so, 600 hp is about max after replacing the rod bolts.

Searched the parts catalog and confirmed this. Same con rods and crank; different piston/cylinder set and ring pack. You're also not the first person I've heard the warning from about the rod bolts. More of an RPM related concern though, correct? Hopefully a non issue with a factory rev limit in place.

I did manage to get some pulls in tonight after removing plugs and tightening up the gaps once again - this time all the way down to 0.018" (0.45mm) which is the smallest I'd consider going as ultra high boost cars seem to get by. It appears I'm at the end of the road ignition-wise now which is maybe a good limit to hit as opposed to structural limit or fueling... which is also at 80% injector duty so I think I stop here

14-15lbs though feels every bit 400whp/500crank in this stripped down cabriolet though, my face got rearranged a few hours back.

[lite75]

Knock sensors dialed in? How do your plugs look?

[dannobee]

Get a dragy and the app. That, and a flat road, and see what she'll do. And if you know how much the car weighs, you can compare it against the hp/weight 1/4 mile mph calculators on the internet. The hp calculation is usually well within 2%, assuming your scales are accurate. The 1/4 mile trap speed doesn't lie.

[dannobee]

Re: rod bolts.
The issue with weaker rod bolts is that on the exhaust stroke, the rod is thrown up with more force than at any other time in the combustion cycle. Without compression forces acting to push the piston back down, it's when the rod will fail. The bolts stretch along the parting line, then the big end goes oval and the sides of the bearing pinch the crank. At that point the crank can exceed the rod's limit and it breaks somewhere along the beam. Better quality rod bolts are more resistant to stretching and help avoid this dilemma.

Turbocharged cars are usually easier on rods than higher revving NA engines. There's usually some backpressure in the exhaust to help push the piston back down, and the turbo obviates the need for higher RPM's to make power; just turn up the boost and away we go, whereas the NA engine needs higher speeds to make decent power.

[993Speedster]

Originally Posted by lite75

Knock sensors dialed in? How do your plugs look?

Still need to get knock detection enabled but e85 + water meth seemingly never knocks, it’ll run smooth over advanced losing power right until pre-ignition or mechanical failure. Plugs look great though and still planning on getting knock detection enabled though in case I need to fill up with pump gas one day.

Originally Posted by dannobee

Get a dragy and the app. That, and a flat road, and see what she'll do. And if you know how much the car weighs, you can compare it against the hp/weight 1/4 mile mph calculators on the internet. The hp calculation is usually well within 2%, assuming your scales are accurate. The 1/4 mile trap speed doesn't lie.

I’ve been doing just that! Loving VirtualDyno for comparing each subsequent raise of boost for sanity check. I’m unsure of the car’s weight but I know it’s low for a cabriolet so I’m estimating 3k

Originally Posted by dannobee

Re: rod bolts.
The issue with weaker rod bolts is that on the exhaust stroke, the rod is thrown up with more force than at any other time in the combustion cycle. Without compression forces acting to push the piston back down, it's when the rod will fail. The bolts stretch along the parting line, then the big end goes oval and the sides of the bearing pinch the crank. At that point the crank can exceed the rod's limit and it breaks somewhere along the beam. Better quality rod bolts are more resistant to stretching and help avoid this dilemma.

Turbocharged cars are usually easier on rods than higher revving NA engines. There's usually some backpressure in the exhaust to help push the piston back down, and the turbo obviates the need for higher RPM's to make power; just turn up the boost and away we go, whereas the NA engine needs higher speeds to make decent power.

I was wondering if EMAP vs IMAP on a turbo app would alleviate rod stretch and to what degree.

Here’s a plug from middle cylinder passenger bank





And a couple pulls, lower one is 11psi and 3rd gear, larger number is 14psi and 4th gear hence it was shut down early... starting to get dangerous on these trips to Mexico, LOL

[K24madness]

I ran 7psi on stock 993 NA block for a while. It made 390whp on a mustang dyno.Those rods are really weak compared to what you have.

When I tore it down for rebuilding I found the heads were starting to move around a bit. I think that’s gonna be your biggest issue not the rods.

[K24madness]

I had similar spark problems. Instead of COP I installed Crane CDI box. I can safely run 11-12 PSI with factory 11:2 compression without blowing out the flame at .030+ plug gaps. I run 100oct but hope to swap to E85 soon. That’s why I kept high CR. It’s magic with boost!

I have a fair amount of experience with the plug problem as I struggled with it in my turbo before. I suggest avoiding fancy plugs and run a cooler copper plug. I found the iridiums harder to fire and more likely to cause flame out problems.

Hit me up via email and I’ll give you more info than you’ll ever need. hogan.thomas@outlook.com

[dannobee]

Originally Posted by K24madness

When I tore it down for rebuilding I found the heads were starting to move around a bit. I think that’s gonna be your biggest issue not the rods.

Yeah, there's that, too. But at least it won't saw the case in half like a broken con rod.

[spuggy]

Originally Posted by 993Speedster

You're also not the first person I've heard the warning from about the rod bolts. More of an RPM related concern though, correct?

The issue with 3.2/3.3 rod bolts is because the factory reduced the diameter. They're more prone to stretch beyond the point of elasticity than either the earlier/later rod bolts. It all goes downhill quite quickly from there.

Missed shift can certainly cause it on a 3.2/3.3 bottom end. With a 915 and a turbo, it's astonishing how much the gate can move around under power with standard mounts. And the 915 is notorious for it - to the point that it has a name; "the money $hift".

Same week my car was finished after doing the money shift and spinning #6
bearing, customer had his 3.2 in for the same thing. The shop owner's (a full-time Porsche wrench since 1986) assessment? "He's owned the car for 20+ years. He almost certainly didn't over-rev it - and says he didn't. They just do that. Sometimes".

With ARP or Raceware rod bolts, the 3.2/3.3 bottom end is very strong. Juan on here was making well north of double stock power with his big nasty turbo I'm guessing - on a 3.2 bottom end, IIRC.

I've never really heard of any concerns with 964 and later - because the factory increased the rod bolt diameter back again; it's only the 3.2/3.3 that has the weak bolts. Although upgraded rod bolts (and even rods) couldn't hurt if you're going to make 2x, 3x stock power. Pauter or Carillo rods are stronger than stock and lighter (much, much, lighter if you go for the titanium option) - less reciprocating mass.

[Raceboy]

You can inrease dwell time of the coil a bit, like .3-.4 ms or better yet, add some coil charge MAP scale, then it adds some dwell on boost.

[Tippy]

Other's may disagree, but I don't think there is a HP/torque limit on stock rods, rather peak RPM limit as mentioned.

The amount of power I have seen from other engines that make usually double of the HP we make and some times 3 X's the torque, our rods should be plenty stout.

[TurboKraft]

Factory 3.2/3.3/3.6 rods with ARP rod bolts, 6500rpm: 752whp

Been running like that for 9 years.

[Tippy]

Originally Posted by TurboKraft

Factory 3.2/3.3/3.6 rods with ARP rod bolts, 6500rpm: 752whp

Been running like that for 9 years.

[993Speedster]

Originally Posted by spuggy

Missed shift can certainly cause it on a 3.2/3.3 bottom end. With a 915 and a turbo, it's astonishing how much the gate can move around under power with standard mounts. And the 915 is notorious for it - to the point that it has a name; "the money $hift".

I deal with gate movement to a decent degree with the G64 shift linkage being attached to the torque tube... it was real easy to tell my trans mount bolts were backing out again on the 1-2 shift. Already have solid rubber RS engine mounts and I welded in the gusset kit to reinforce the engine carrier, I noticed it had started to tweak just a little bit on low boost before the clutch job. I think it's time for an upgraded trans mount now too and maybe semi-solid engine mounts. Still has a bit of rubber-band like snap back and forth on really high power shifts. Flat-shifting seems to help though

Originally Posted by Raceboy

You can inrease dwell time of the coil a bit, like .3-.4 ms or better yet, add some coil charge MAP scale, then it adds some dwell on boost.

Sounds good, I'll give that a try when it's time to turn it up to 1.25bar; my methanol injection controller/gauge is being intermittent (Snow Performance Stage 2 for anyone curious) at the moment and the current plug-gap is holding up at 1.0bar til redline.

I think knock detection setup is in order past this point, especially since the meth kit is being weird... at least with the VEMS stand-alone you can setup some closed-loop feedback for when the water-meth doesn't engage.

I'll try and read the knock setup Wiki page a few times before I bother you though If any other VEMS users have any input or advice, I'm all ears.

Originally Posted by K24madness

I had similar spark problems. Instead of COP I installed Crane CDI box. I can safely run 11-12 PSI with factory 11:2 compression without blowing out the flame at .030+ plug gaps. I run 100oct but hope to swap to E85 soon. That’s why I kept high CR. It’s magic with boost!

I have a fair amount of experience with the plug problem as I struggled with it in my turbo before. I suggest avoiding fancy plugs and run a cooler copper plug. I found the iridiums harder to fire and more likely to cause flame out problems.

Hit me up via email and I’ll give you more info than you’ll ever need. hogan.thomas@outlook.com

Running standard NGK racing copper plug. 1 step colder, an 8 vs 7 and with a recessed tip vs projected as they're recommended for power adders and resist blow-out a bit more. Exact plug is a R5671a-8

I'm going to get what I can out this current ignition and fueling setup and then the next jump will be a big one. Car also kind of needs some body work and attention to interior so who knows when that'll be. It makes plenty power on 14/15lbs so I should just chill out with the boost knob

Originally Posted by Tippy

Other's may disagree, but I don't think there is a HP/torque limit on stock rods, rather peak RPM limit as mentioned.

The amount of power I have seen from other engines that make usually double of the HP we make and some times 3 X's the torque, our rods should be plenty stout.

Originally Posted by TurboKraft

Factory 3.2/3.3/3.6 rods with ARP rod bolts, 6500rpm: 752whp

Been running like that for 9 years.

Sounds like a decent end goal if I can keep my intake plenums together and attached to the engine, LOL. 3 times now they've popped off under full load and scared me to death thinking the engine let go. 15lbs seems to be the end of the line, at least for my current parts configuration.

Also worried about this G64/00 trans. Not to mention the 31/69% power split sucks... Too much power to front tires and an open diff; front gets real light under full tilt and torque steers over a lane in 2nd like an overpowered Civic. Understeers heavily coming out of corners in boost but at least its predictable and doesn't get you killed when you inevitably lift