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I went from 3.4 to 3.8 and basically did all the goodies you're doing. It's a lot of money for SOME noticeable gains. I don't track the car, so I can't say that it was "worth" it to spend all that money. Don't get me wrong, love the car, etc. and if your only sports car and you want to keep it forever, then MAYBE it's fine.
Overall, it'll be a fun car to rebuild and you'll learn a lot with the experience.
I'd recommend doing the UAOS to make that bulletproof. UIDS as well if you plan to track the car.
Some notables:
I didn't touch the radiators (and only have 2, not 3) and zero cooling issues
Stage 1 Hoffman heads
Stock intake
Stock throttle body
Underdrive pulley
Stock tune for now but that will change one day....
I'm about 4 months in to driving my 3.8, I did the full CSF radiator kit. (All 3) I have the low temp thermostat.
I swapped the radiators because the stock ones were 20 years old and the plastic tanks at that age are a problem on the way IMHO..
(Based on 3 BMW's with plastic tanks before the 911... )
The CSF rads are thicker than stock, the third radiator is probably mild overkill but I got a sale price on the whole set I couldn't pass up..
My temps all the way up to outside temps in the 105 range are rock solid 180.. Probably partly the bigger cooling but also the thermostat..
#1 recommendation is get LN or the builder to hook you up with a tuner, I had mine done and we did 4 revisions so far and each time you can tell.
The engine took about 3500 miles to really break in, now its amazing.. I'm nowhere near top of the list on HP but its a absolutely amazing drive.
The stock Mahle 3.4 pistons are very light weight, the bigger 101mm pistons are heavier and place more stress on the rods. So go with Forged H-beam rods unless you are "positive" you will never do a money shift, or run at near red-line for sustained periods..
UAOS is a no brainer, it is what should have been done from the factory. It uses the same diaphragm as the Mclaren Mp4 but is placed in a convenient location and can be changed in 10 min and the UAOS "system" is 4x more efficient than the Mclaren system or stock m96 system..
The only ones who have anything negative to say about the UAOS system are the ones who are so frugal they squeak when they walk or are newbies who have no clue what has happened in the last 20 years.. But you don't have to take my word for it, just look back in the archive here from the last 20 years, and that doesn't even tell the whole story because Porsche knew it and even lowered to oil level to help out the stock AOS..
Good luck with your build, I think you will make all the right choices and are in good hands..
Jason,
I know they say the stock rods are adequate if you only increase the bore by 3mm (99), but you do need to use ARP bolts which are much stronger than factory bolts.
I think the larger bore (101) just puts more stress on the rods and it may be due to the use of “cracked” rod big ends in the factory rods. Th K1 forged rods are about $600 less than the Carrillos.
End the end it is a how do you feel about the risks. I personally feel better about upgrading the rods due to the difficulty of doing it later and the consequence of a rod failure. Everyone needs to do their own risk tolerance and make their decision accordingly.
Mark
I suspect getting stock rods reconditioned is close to the same price as buying K1 forged rods. I put the K1’s in my 4l build and they have been very reliable for the last 900 miles 😉
I also popped for the IMS Solution and the UAOS because I want longevity.
I bought ARP carrier bolts because they were cheaper than stock. I also bought ARP head studs but later found out the stock head bolts can be reused. I would reuse the stock ones if were to do over again.
I bought new injectors, plugs, and cam bolts. And new gaskets, oil fill tube, 997 oil cooler…
Early on I thought the LN kits were too expensive. I was wrong. They are a good value.
Jason,
I know they say the stock rods are adequate if you only increase the bore by 3mm (99), but you do need to use ARP bolts which are much stronger than factory bolts.
I think the larger bore (101) just puts more stress on the rods and it may be due to the use of “cracked” rod big ends in the factory rods. Th K1 forged rods are about $600 less than the Carrillos.
End the end it is a how do you feel about the risks. I personally feel better about upgrading the rods due to the difficulty of doing it later and the consequence of a rod failure. Everyone needs to do their own risk tolerance and make their decision accordingly.
Mark
At this point, I have about as little tolerance for risk as anyone possibly could, maybe a hair short of the person that’d feel so burnt by the car blowing up after 7 days that they had to move it on as a roller or part it out. I simply cannot afford to do a rebuild twice. I can barely pull it off once, but I’d rather find a way to make it count now and invest in the most durable and high performance parts possible while it’s opened up than risk a second rebuild later. That said, I’m not just trying to throw money away and I do love the idea of the car and want to enjoy it for a very, very long time. I can totally commit to it if I feel confident in its longterm reliability after a rebuild of this nature. I also don’t hate the “bling” factor; those parts do look good on a build sheet if I ever DO want to unload the car and I still think the market for 996s is going to go up. No one ever thought 993s would cost what they do now and ppl are already swinging for the fences on low mileage 996s. I don’t expect to ever make a profit on the car with a rebuild, but break even…maybe in a decade? Who knows. I want to enjoy it that long regardless.
So I’m sticking with the fancy forged rods, prolly forgoing the deep sump oil pan, but getting a metal baffle for the stock one, upgraded oil cooler, upgraded AOS, and I’m gonna do the CSF units bc the car has its OGs installed now and I’d rather just swap ‘em for peace of mind.
@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?
Yes. The clutch and PP have wider surface area. Of course, it takes me less than 3 hrs to pull the motor and trans so its something I'll do in the future.
I did the stock clutch flywheel pressure plate on my 3.8 , if there were a pressure plate that was just a bit higher spring rate it would be a good thing,
Or I have used a centerforce dual friction disk in a stock clutch on other rides, to just make it tougher..
Once my clutch broke in its holds nice but I had to be careful the first 1500 miles or so.. Taking off in first you could tell it wanted to slip, once it broke in its fine.
I sent a perfect running 3.6 down south and it came back as a 4.0. Absolute night and day difference. Total animal. Gave my turbo a run for its money before that car got a tune.
10/10 would do it again.
Oh, I said perfectly running.....but let me tell you, on tear down at 29k, there was evidence of cyl 6 piston skirt failing.
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
Is the flow increase for the 997 airbox all due to the snorkel? If you use the 996 snorkel is there no benefit?
Answers for several comments/questions:
stock rods cannot be rebuilt because they use “cracked rod” technology. The rods are manufactured and then the big end is fractured and put back together. The fractured surface between the rod and end cap is rough. This makes them fit together perfectly. They do not use a dowel around the rod bolt.
When rods are rebuilt, the process is to grind down the mating surface of the rod and cap. Then they are bolted back together and bored to the proper diameter. This process shortens the rod so a new wrist pin bushing is installed and bored off center to re-establish the correct center to center distance between the big and small ends of the rod. With a cracked rod, you cannot grind the mating surface between the rod and the rod cap.
997 Carrera 3.8 and 996 air boxes both use the same filter element. I know the 3.8 Carrera S snorkel is large but I don’t know if there are other internal differences that allow it to flow more air
the 997 snorkel requires the use of the mating fitting that snaps into the deck lid but this requires no modification to switch. if you use the 997 3.8 airbox you do need to move the Swecondary air pump about a 1/4” to the left. I was able to order a modified bracket for the air pump from EVOMS.
Hope this helps explain a few things.
Mark
09-22-2023 | 12:21 PM
