DVB5150

Longtime lurker, first time poster. I'm the recent victim of what seems to be an increasingly common tale around these parts; I purchased a seemingly well-maintained 996 3.4L that unexpectedly requires a rebuild. The shortest version of my story is I bought 60k mile example of 2000 C2 with a 6-speed that came with a big stack of seemingly clean service records (all dealership or Pcar indy spots), bone stock other than an LN IMS retrofit which was installed at 39k miles and a heap of carbon interior parts, and a quiet, strong-running engine. No smoke, no ticking, no drips. The previous owner cared about the car deeply and owned it for 15 years, but was not mechanically inclined. The car went grenade mode about 7 days and 800 miles into my ownership.

The current diagnosis is that something went in the timing section and the car currently has low compression in cyls 1 and 2 and a dented piston and a bent valve in 3, along with some very early signs of bore scoring in 3 for good measure (separate issues from my understanding). I'll know how bad the damage is first week of Oct, but we believe the crank should be fine based on how/when the timing issue occurred. It's too nice a car to part out, clean CarFax, mint body work/paint/interior, and around $15k in carbon fiber in the cabin and I truly love the 996 platform (when it works). I was planning on keeping the thing for at least 10 years, so I've managed to get past the nausea the word "rebuild" and its associated costs and I've explored a lot of options for getting the car back on the road and optimized.

I've settled on doing the typical 3.8 conversion that most people seem to favor with the early cars. After some good chats with my local Pcar buds and Judd at LN/FSI, the build is being done by Automotive Associates of Canton in CT and we're having LN do the machining and Nickies install, bored out to a 3.8 with the upgraded Mahle pistons/rings/etc, and I'm going to do the full monty LN "Deluxe" rebuild kit with the Carillo connecting rods, an LN "Solution" IMS, and I'm sending the top to Len Hoffman to be cleaned up and optimized. The advice I've gotten from everyone involved is to run a new stock Sachs clutch and Luk dual mass flywheel, upgrade the radiators to CSF in both banks and forgo the third radiator install to start (the car won't be tracked and I live in the Northeast), do the low temp thermostat, a deep sump/baffled oil pan, new coolant expansion tank and a replace any parts that need it with new, and eventually I'll install an IPD plenum/GT3 throttle body/x-pipe/exhaust/tune to take full advantage of the increased bore and headwork. But for now, I just want the engine rebuilt in a way that makes it functional and and allows me to drive it through spring/summer 2024 and do those extra bits in Winter once I've recovered from the cost of the rebuild.

My goal here is to have the engine be as bullet proof and worry free as possible and to optimize the car as a spicy street/mountain road ripper. I have no plans to track it, but I'd love it to be that durable and have the option if I ever choose to convert it.

-Is there anything those of you with similar 3.8 builds would do differently if you had to do it again? Any parts you regret not installing when you had the chance?

-Has your ownership been pretty carefree (with proper maintenance and all that obv) since doing the rebuild?

-I'm fine with the cost of the rebuild and I'm fine with the time out of service (it's about to be winter either way), but I simply couldn't afford to do it twice and I'd love to hear about how your 3.8 rebuilds are fairing since completion. Good or bad -- let me have it. Show me some pics of your rebuilt cars with rebuilt engines living happy lives, though. I need the good vibes this week haha.

-Is there an upgraded oil cooler I should be looking at?

-I've read that the air box from a 997 Carrera S makes a decent difference and is an easy mod. Is this also something worth investing in now or just doing down the line with the plenum/throttle body/tune.

Thanks!
-DVB

De Jeeper

My story and better then a 3.8l.

https://rennlist.com/forums/996-foru...-the-dust.html

DVB5150

Sick solution! It looks like my core is salvageable and I’m really not hellbent on tracking it, but a GT3 swap would be incredibly fun.

996C438

I have a 3.6 FSI in my Boxster S since December of 2015 . Rock solid performance. I have a 3.8 in my 996 C4 for a little over a year now . Rock solid performance . Your plan is solid . Len Hoffman in my opinion is the best out there .

While the engine is out install the track version UAOS . Install a new oil filler tube . Replace every vacumn line and rubber hose . If your starter shows ANY signs of being iffy replace or rebuild . Install a brand new engine ground strap . Install a new Porsche OEM coolant tank .

LN/Jud/FSI/Len will do a great job for you . All very professional with hundreds of builds performed . Another thing the 3.8 factory air box flows very well . I have one in mine . Along with a GT3 throttle body they will flow more air than the intake plenums can handle . Good luck with your build and have fun .

amargari

Here's my story 3.6 -> 4.0, https://rennlist.com/forums/996-foru...e-project.html.
It now runs great and is bulletproof.

zbomb

Save money and keep the stock radiators, stock rods if no issue currently, low temp thermostat not needed, deep sump not needed. That stuff is going to add up to multiple thousands of dollars you can allocate to getting the car back on the road better than it was when it came off. Do they think the rods need to be replaced due to trauma when the pistons kissed the valves ?

I just don't see a value in the stuff above for a road car, even a road car that will see light track use ? If at a later point you decide it's needed, the only thing that you can't add back to the recipe are the rods and the only way I see you breaking a stock rod is to starve it of oil and watch it shoot to the moon - I don't see many reports of people having that issue on the road and the people we have seen have it on the track are generally pretty experienced running sticky tires.

These are just my opinions so take it FWIW - best of luck on the rebuild.

I didn't rebuild mine - I put 462WHP in it

wdb

If Jud says they’re good, they’re good. Only spend extra money on fancy internals if you really truly will build up. Extra power on these motors costs silly money. The 997 oil cooler fits. Nickies I assume! Nothing else is worth a tinkers damn.

Jmrjimbo

I just got done with my 3.8 LN build , K1 rods, Mahle, IMS Solution, new oil pump etc. Two things I would have done different; 1. Pin the IMS gear. I've done it on all my other builds but for some reason, I didn't think I needed it this time. Now having second thoughts. 2. Stage 1 or 2 clutch. I do a bunch of city driving and didn't want a heavier clutch feel but the stock clutch is prob just marginal given the HP gains. One thing I do recommend is to replace the oem RMS with one that has a spring incorporated in it. The oem style just doesn't seem robust enough. Have fun. This upgrade is amazing and honestly a vast improvement.

DVB5150

@996C438 Killer. I believe that "deluxe" rebuild kit includes all new lines/hoses/gasket sets/fasteners, but the plan is to absolutely replace anything like that, including the coolant tank. I've gotten mixed reviews on the track UAOS' importance for a street build for the cost, but I've also heard the same thing about the Carillo rods.

How would you describe the 3.8's feel? Everyone I've spoken to claims it takes the things I already enjoyed about the 3.4 and just gives it much more useable torque across the midrange.

Glad to hear you've had such longterm performance with your Boxster build.

DVB5150

@zbomb I'm on the fence about the deep sump as I live in NY and the car is definitely getting driven in NYC sometimes and I'm going to lower it slightly, but I've been told more oil means cooler oil and I'm really, really interested in reliability/durability/increased performance for street type stuff. Same for the radiator upgrade, though I might stage those in with the IPD plenum/GT3 throttle body/x-pipe after the initial build.

I'm opting for the Carillos at the suggestion of Scott at Auto Associates, but if there isn't a major performance gain or a proven durability gain in a build like this, I'd rather save the dough. My thing is just making sure I really put the right things in while I'm in there to set it up for success now if I do decided to throw more spicy parts at it down the line -- which very much might happen. I have no intentions of turning this into a proper track car ever (seems like the m96 is a mediocre starting point for a track toy in general unless you can afford a rebuild every few years).

Sounds like you built a real monster. How'd you pull those numbers out of it and how does it behave?

DVB5150

@Jmrjimbo Awesome. Yeah, I will be doing city driving with it sometimes and I do not want a heavier clutch if it isn't necessary. So you're saying you wish you had done the stage 1 or 2 clutch or had not?

996C438

My C4 is running stock radiators but I did add the center rad . Being in Georgia I thought that was $$ well spent . I actually added a used rad from a Boxster S . If the fans are working properly you will stay cool on the street . Short term I would say run stock rads and add better rads in the future if needed.

Extended oil sump . I was lucky and found one used for a great price ( thanks Jake ) . So I am adding it to my car . Not necessarily needed but extra oil in my mind is a good thing . My car also has aftermarket headers , catless x-pipe and Fister modified OEM mufflers . My car put down 318.5 hp and 290 lb ft of torque at the wheels when we dynoed it . That's aprox 385-388 crank hp vs the stock 296 .

Public disclosure : I worked for 5 years as the FSI break in driver . In that role I have driven aprox 180 various Porsche models with a variety of engines . Where do I rate my 3.8 ? It's right up there for enjoyment . Not the most powerful but not the weakest either . She pulls like a horse in the relatively light chassis. I have no qualms about my decisions for both cars .

Yes I am a fan of FSI/LN/Len Hoffman. I have seen in person their work over a 5 year period . Rock solid and repeatable due to solid processes used daily . Are there other quality builders out there ? Absolutely . Can you get quality results elsewhere ? Absolutely . Do your research , get advice and make the decisions right for you . Sorry for the long winded reply .

zbomb

I would not sacrifice the ground clearance for the maybe cooler oil from the capacity increase. From a durability and reliability standpoint, I think the lowered sump presents more risk than any perceived benefit from the oil temp change, especially if you're going to be driving it over NYC roads. The radiators are great bling and there is value there, I would just not get them expecting to see any tangible benefit for your use case. Same with the Carillos, nice to say you have them I just don't know what they are supposed to do for you that a stock rod doesn't for your setup and goals.

If it were me, I would take the money for all that stuff and put it to the intake mods you mentioned, I would add in exhaust mods with header, hi flow cats and a less restrictive muffler and the engine should make pretty good power. I would also get the ECU calibrated for all that stuff on a dyno to maximize the investment in the sum of the parts.This is something you will get to experience the benefit of far more frequently than the stuff I have suggested you hold off on.

Heres a thread with a bunch of dyno sheets, should give you a feel for what does what. https://rennlist.com/forums/996-foru...l#post19025102

I put an LS3 into mine. I have little experience with it, just finished'ish but so far the behavior is, violent.

ETA...

Whats the approx crank HP for 462HP at the wheels ? And, can you share your graph in the HP thread ?

168Sierra

Forged rods are recommended if going from 3.4 to 3.8. I have a 3.6 converted to 3.8 and two 3.6 converted to 4.0. I have used both Carillo and K1 rods and I think the K1s are fine for a street car. The increase in torque is what really makes them fun cars to drive.
LN / Jud will not steer you wrong.
Have the rotating assembly balanced (pressure plate, flywheel, crank, pistons, rods, front pulley). The better balanced these are the smoother the engine runs. I have a 4.0 baqlanced to .5 gram and a 4.0 balanced to .1 gram and you can tell the difference.
The UAOS with track drain back makes the system pretty much a “forget about it” system and you can easily change the diaphragm if it fails in the future.
Have Hoffman do the heads and ask for stage II porting. Like the rods, these are the hardest things to change in the future.
I used the deluxe kits on my engines and they are pretty complete except for coolant and vacuum hoses.
You can run the 997 oil cooler which is 1/4’ taller so it has a few more rows for increased capacity. If you use a 997 oil cooler you should be OK with stock sump plate but I would install an X-51 baffle with aluminum parts rather than stock plastic.
The 997 Carrera S 3.8 airbox is a good upgrade for a larger motor. The intake snorkel is larger and will flow better.
X-51 intakes flow better if you can find a set, but I found on my car they interfere with the AC suction pipe so you have to modify it. The AC suction pipe for the X-51 kit is NLA.
If you do not go to stage II porting the IPD and GT3 throttle body do not provide as much improvement.
Think hard about what is important to you and let that guide you. Make sure you do the internal things right the first time (rods, balancing and porting) because it is so expensive to re-do them later.
Good luck with your rebuild.
Mark

996C438

Zbomb I " think " the driveline loss is in the neighborhood of 20 - 22 % but I am far from an expert . Not sure if there is a difference between C2 vs C4 . There is no doubt you have a lot of power in yours .

I don't have a " soft copy " of my dyno sheets but I do have paper copies . I will see if I can take a pic and post . To be honest I thought I already did that .