Gilbert Han

Hi all,

As my previous post, my 2006 997.1 C2S engine failed on me and engine rebuilding is going on now.
https://rennlist.com/forums/997-foru...lt-engine.html

My mechanic said I have an option, whether rebuild as it is, 3.8L, or 4.0L conversion.
The benefit of 4.0 conversion is mere when it comes to HP gain (10 - 15 HP), but more mid-range torque + more reliable engine that can avoid known issues.
Con of this option is I have to spend few grand more to do so.

Could you share your thought, recommendation, experience or opinion?

Thanks in advance!

mcfisticuffs

cosm3os

You'll kick yourself.

SoCal C2S

platinum997

Spending all that money for the same motor seems silly. Spend a little more and every time you step on the gas you will know why you did.

Look at the hp/tq curves... Peak hp might not be much but the overall powerband improvement is significant.

Dripola

apperception

I'm trying to budget, just in case. I just hit 100K miles and so far, so good. Only using 1 quart of oil in 5K miles. I know this has no bearing (pun intended) on IMS issue, but...

Larry in Georgia

Dripola

srcn

Mine is a higher mileage car (87k), but so far so good. Oil consumption is present but within the acceptable range.

But if I decide to keep it long term rather than move up to a 991.2, I will definitely go for a 4.0 rebuild as a preventative measure.

Does anyone know if X51 cars have been bumped to 4 liters before? I'd be curious as to what the output would be.

TheBruce

Gilbert - sucks about the engine but a 4.0 sounds like a badass project. Go for it.

Any insights into what led to the rod bolt failure?

Fined

Would be interested in the answer to this too. I have a 9a1 engine with x51.. but even having some info from 997.1 x51 4.0 liter would be interesting to note.

DrJordan1911

Do it.

I did it to mine and could not be happier. I can tell you horsepower gain is more along the lines of 40-50 hp not 10-15. The torque is amazing. It definitely feels stronger than a 991.1 base power wise. I can say it feels as quick as a 991.1 S due to the lower curb weight. To pull of in 2nd without bogging I would have to feather the throttle before; now it leaves in 2nd with zero effort. My brother has a 991.2 GTS 4 Cabriolet and my good friend has a 991.2 4S coupe - I love those cars and I would love to get one...until I get behind the wheel of my 997 4.0. I literally lose the car buying bug because mine is so enjoyable to drive. Of course the 991.2 is ridiculously fast, gorgeous, and has all the tech features of today; but my 997.1 really cranks up the enjoyment factor.

CrossT

user 72902

I did the Flat 6 rebuild and the difference is so much more than extra HP; it is stronger and smoother. The torque comes on much earlier and holds - like from 4000 to 6000 rpms that there is no need to redline any longer. It is faster to shift prior to redline and stay in the power band. I imagine it is less stress on the engine as well. Good luck in whatever direction you choose to go.

JustinCase

As a result of a badly scored #6 cylinder, I had the M97 engine in my 2008 C2S Cab rebuilt as a 4.0 via the LN Engineering route including Nickies and matched JE pistons, IMS solution including pinning the sprocket (even though mine has the large bearing which showed no issues), replacement billet chain tensioner and guides (mine were pretty worn), new AOS (since the engine was apart, anyway), new water pump (mine was leaking), new clutch (just because), new coolant tank (cracking), new starter cable (cured hot start problems), etc., etc. I essentially checked all the boxes for known M97 engine issues and killed them all off at once.

The quotation for 3.8 was identical to 4.0, so it was a no-brainer for me -- went with the 4.0. Since the rework process is identical, I'm not sure I understand why there would be much difference. In my case there wasn't any.

I have not put it on an actual dyno yet, but I plan to in the next month. My butt dyno cannot detect any noticeable added power, but I agree that the power band is more than *noticeably* wider with lower end torque. One of the mechanics told me the engine would also be a little louder. I'm not sure, but one of my wife's first comments was, "That seems louder now."

I have absolutely no regrets about my decision. I'm very happy with the results. To sell my car (which I love) as a roller and purchase a similar used car with all these issues resolved would have cost at least twice as much. Instead, I have exactly the car I want starting with zero miles. Except it definitely has a bigger kick in my pants.