997gr8

Hey all,

I have a 2006 997 C4S with 30k miles on it.
The engine (X51) runs great and I'm very happy with it.

Just like most though, I would like more power, and am considering upgrading to 4.0 as per Andrew930 https://rennlist.com/forums/997-foru...-to-4-0-a.html
I would likely want to do all the upgrades possible, including nikasil liners and LN IMS etc

I don't know the exact differences between an X51 and stock motor (not huge I'm guessing), and the question is whether I would be better off (financially) selling the X51 engine, and buying a non-running engine for the upgrade.

Your input would be greatly appreciated!

Thanks

Balr14

Sell your car and buy a Porsche turbo. Realistically, this is the most practical approach. You are going to spend a lot of money you will never recover if you do it your way. Used 997.1 engines are not worth as much as you would like. Do the math, the only time a swap is practical is if you have a blown engine.

997gr8

Balr14, if you had said buy a GT3, I would tend to agree, but a turbo doesn't do it for me at all, I really like the NA engine.
I do believe that a GT3 would cost me a lot more than this approach, so I'm inclined to stick with my car especially as it is pretty well perfect with very low miles.
Agreed on not getting my money back, just trying to see if I can save a few k that's all, thanks for your input!

Linnm

Go find a 2009 or later car and drive it!

Sneaky Pete

You might want to contact Jake at FSI.

Fined

I wouldn't trade my factory x51 for a 4.0 liter unless it was a Porsche factory 4.0 liter. I think the 997.1 and .2 x51 were similar (with both having head work). I read an article that detailed it at some point in the past but have no idea where I found it. Anyways.. perhaps spending more time about 6k RPM would sort you out.

qikqbn

I think I can relate to you in some ways. A 2007-2008 Turbo would be the easy way to go if you really want a huge power difference. Yet, as you said, a Turbo may not be what you are after and it is the N/A throttle response, predictable power delivery, and joy of revving it out to over 7000 rpm is what makes you happy.

I am seriously considering this upgrade as well at some point in time because I just love my car and the condition it is in. I have owned my 2006 C4S with some mods (Intake, plenum, GT3 Throttle body) for over 8 years now and purchased it with only 6000 miles on it. It currently has 75k miles and I have it so dialed in to the exact way I want it as far as looks, wheels, interior, and overall pristine condition, that I am finding it very difficult to find another 997 or even a 997.2 in nicer condition or with similar options. I have driven several 997.2 S and the power difference you feel is only from 6500-7500 rpm. The surge above 6500 rpm is noticeable, but It's just not enough of a power difference, considering my mods, to overall convince me to switch over. With your X51 power kit 381 hp, you already have a very desirable engine and power similar to a 997.2. For me, and what I guess is what you are after, I would need to feel GT3 power difference (415hp -450hp ) To make the decision to jump out of a car I already really love.

The 4.0 liter conversion , from what I have read and seen dynos, should make about 360-380 horsepower at the wheels, which is about 425-450 hp at the crank range. You should really try to drive a GT3 to get an idea of what that power feels like in a N/A motor. Although the GT3s are really all about top end power 8500 rpm, you still have to rev them out to get the full effect, but atleast you can feel what 435 n/a power feels like. The 4.0 should give a nice overall torque improvement and similar power, but not rev as high as a GT3. So in essence, more usable power around town. Just be aware, that you will get use to that power at some point too. Why do you think turbo guys have 700+ hp kits. Because at some point your body gets use to the power and you will always want more and more. Try to drive a 4.0 build if you can. It will be noticeably faster, but will it be enough to scratch that itch for years and years to come?? Or will you just want more after you get use to it?

Your X51 motor is a desirable engine for sure. All the great things Porsche did to that motor, will be meaningless if you do the 4.0 conversion. You may be on to something by thinking of selling it and getting a regular 3.8 engine to tear open for the conversion. I would contact the engine builders that are already doing the 4.0 conversion like Jake Raby, and get some feedback from Andrew930 and see what they say. Maybe you can work out an exchange with them. I have met Andrew930 and seen the shop they did his 4.0 motor at. Andrew is a great guy, super nice, all around helpful, knowledgeable car guy and very impressive workshop with knowledgeable mechanics specializing in Porsche/BMW. If you are in the area make an effort to contact him and see the shop.

The big question... Is it worth the Investment of $25k to do all those engine upgrades?? Do you plan on holding on to this car for a very long time? Then it may be worth it to you. You will have a special motor for sure and something bulletproof with nice power, but unless you hold on to it long term, I don't think it's an investment that you will see any kind of return on in the future. In fact, the Porsche community is very fickle about upgrades. Most buyers will want something that does not have upgrades like this. If you decide to sell it in the future you will need to find a special buyer for sure and that can be difficult.

keep us posted. I love the idea of the 4.0 liter and it is very tempting in so many ways, but also a very expensive decision to consider.

Balr14

The 997.2 (and newer) Porsche turbo does not have the sort of throttle response you may be accustomed to in other turbos. I had the same mindset as you until I drive a 2010 Turbo S PDK. Response is much better than my modded 997.2 C2S.If you haven't driven one, you really need to try one before you judge.

LexVan

This. Though technically, I think his is a 4.1l.

Sneaky Pete

Yes he has gone to 4.1L and other variations that he doesn't even advertise. The more I drive mine the better it gets........and I'm going on having it close to 3 years. When I'm on it in high rpms the rear wants kick out to the left...quite the feeling.

Dom991.1

DesmoSD

For 27K, you get this and is still smog legal in CA. That's not a bad upgrade given smog is very strict in CA.

4.0 Nickies
Case Halves modified by LN Engineering
Ported & Polished Cylinder Heads
Treated Springs
JE forged Pistons
ARP Fasteners
Carillo Rods
New Crankshaft from Porsche
LN Engineering 2 quart deep sump with with baffle
LN IMS Solution
IPD Plenum
Upgraded Throttle body

The factory X51 package was a nice premium and a bonus when it comes to selling. IMO, you have a perfectly running and low mileage 997. Why tear it down and have downtime when you can sell it and get a 997 GT3.

srcn

I don't think you'll get much for your motor because it still has lokasil heads and the original IMS bearing, even though it's an X51.

The cost for a 4 liter engine is roughly the difference between the value of your very low mileage C4S X51 and a good 997.1 GT3.

My advice is to either sell your X51 and get a GT3, or enjoy your X51 and only do that rebuild if the engine develops a problem and needs to be opened up.

The latter is the route I will be taking for my own '06 C4S X51 with much higher (88k) mileage.

Petza914

Not sure where you're located, but if in the Southeast would be happy to take you for a ride in my RUF supercharged 997 to show you what 500 HP feels like in a 997, and because its supercharged (boosted all the time) it feels normally aspirated, as there's no boost lag - it drives like a normally aspirated car, just with 125 more HP everywhere.

Fined

Nice one! This is the exact chart I was referring to.