Rceron

Making a decision now on 3.6 engine rebuild vs. 3.8 upgrade. I did a search and it seems there are many folks that contemplated it but I didnt see anything with a post-rebuild update. The only downside I can see from doing the 3.8L is that my car would be hard to sell later (should I wish) to anyone who would race it. I suspect this car is a keeper so I'm heavily leaning toward the 3.8L for the torque. I believe the HP difference isn't that great. I assume the reliability is the same going forward. Thanks for any input.

Ramon

ScottArizona

I definitely would. The additional cost is so small compared to all the labor. It would kind of be a shame If you didn’t at least benefit from some increased horsepower and torque. That is, unless the car is some collector piece you’re gonna try to sell at a premium at some point soon. Otherwise, I say go for it. Also, I think member luisGt3 did a 3.8 in his and likes it.

Jim H.

Although it would be somewhat measurably "faster" with the 3.8...it seems that as of late many people appreciate the "character" of the 996.2 3.6 motor over its absolute output.

I've read comments on the forums and on BaT that the later 3.8s or 4.0s, although torquier and faster, don't have that "rush" of the 3.6.

No personal experience to verify but perhaps something to consider...

ScottArizona

This is a true statement. I don't love the stock 3.8 gt3's despite the additional torque. Even the sharkwerks guys have been known to comment that the "sweetness" of the free revving 3.6 is lost a bit with the stock 3.8. I think that's why they built a 3.9 kit that would actually rev faster than a stock 3.6 set up. With all that said, I think it comes down to what type of pistons you use and if you upgrade cams. It all has to work together to retain that charismatic engine character.

Rceron

Thanks for the comments thus far. Interesting. Would my R&P gear change the "feel" of the 3.8? I suspect it wouldn't as it would merely spend more time in the upper end of RPM spectrum. I didn't ask but I wonder if the rev limiter is reduced a bit?

ScottArizona

Do you already have a shorter R&P? 4.0? Or 997.2rs 3.89? I have the latter and love it, but truth be told, If I knew I was going to be doing a 3.9 I probably would have left the gearing alone. With the added power I don't feel like the shorter gearing was really necessary. With the stock 3.6 though, I freaking loved it and highly recommend it. Have you driven a 997.2 gt3 or rs? I drove a buddy's 997.2rs (with the 3.89 r&p) back to back with my 996 gt3 (which at the time had the rs flywheel, 3.89 r&p, and stock 3.6l engine), and the rs did not feel as "eager" to rev as my car. Hard to explain, but it was like you could feel the extra heft of the larger pistons (even though that sounds impossible). There is just something different about the character of the 3.8 cars. That's one reason I love the 3.6's (996 and 997) so much.

powdrhound

On my 996 I've had a 3.6 Mezger rebuilt into a 3.8 and later into a 4.0 with 106mm Mahle Motorsport pistons / liners. The 4.0 kit is much more trick from a tech standpoint. Having run both set ups under heavy track use for many hours at some high hp levels, I would 100% recommend the 4.0 Kit. There is simply no comparison in both power and smoothness over the 3.8 kit. The 4.0 kit uses the stock 76.4mm GT3 crank and does require minor machining of the case and water jackets but it's well worth it with the increased responsiveness of the engine with the larger displacement. The displacement actually works out to a 4.05L. Something to think about if considering an engine build. I was actually not very impressed with the 3.8 kit on my 996 and and my stock 7.2GT3 3.8L engine leaves a bit to be desired in smoothness as well compared to either a 3.6 or the 106mm 4.0.

air993

I hope this is not an off topic question. But how does a 3.9 rev better or more freely than a 3.8?

ScottArizona

not off topic at all. And I’m not sure the answer. All I know is this thing revs very very freely and more free than the oem 3.8’s I’ve driven and I’ve driven quite a few. Perhaps piston weight? I think the cp pistons are pretty light. Different cams? I’m not sure.

Edit: Got this from the sharkwerks site:

“ the character of the motor is amplified and even extended by an additional 400rpms. Utilizing our light-weight Piston kit we are also able to improve upon the already-quick throttle response and revs to an even more lively level”.

https://www.sharkwerks.com/engine/p4217-sharkwerks-3-9-liter-engine-upgrade-for-996-997-gt3-rs-SHAE230

powdrhound

Lots depends on the type of supporting hardware (i.e. MOI of the clutch assembly and the quality of tune more than just the small difference in displacement between a 3.8 or 3.9 which is relatively insignificant in the scheme of things.

Rceron

Great input from all. I seems to me that I need to evaluate the trade-off of a smooth revving 3.6L vs 3.8 with an additional 12 ft-lbs of torque. I may be leaning to keep the 3.6. A refreshed engine will already feel like I got a boost in performance. Although the 4.0 option sounds great, I'm not inclined to pursue such an expensive path.

ScottArizona

can’t go wrong. And I think you are right that you’ll feel a nice improvement with everything new. Plus, now cool that you will essentially be the first owner of the new engine!

smclaughlin

I've seen threads on 4.0 rebuilds but don't recall anybody talking about the "all in" cost of parts and labor, including all the "while you're in there" stuff. Anybody want to share?

-Scott

powdrhound

The cost difference between the 3.8 and 4.0 builds essentially boils down to the price difference between pistons and liners and that is minor. The Mahle 4.0 pistons/liners in my case were actually cheaper than the Mahle 3.8 parts they replaced, both being in the $8000 range. There is the added cost of slightly machining the case for the 4.0 parts that is really the only extra item and that cost is negligible in the scheme of things. Overall cost difference between the 3.8 and 4.0 is really a toss up. Knowing what I know now having done both, if you have a competent builder, doing the 4.0 is a no brainer.

Total out the door build cost on any build, a 3.6, 3.8, 3.9 or 4.0 will vary greatly depending on what all is done while the engine is out. To get an idea, speak with several builders and get quotes on what you are considering and that will give you a better picture of the final number depending on how crazy you want to go.

ScottArizona

interesting info above. I recall being told years ago that the jump in price to make a 3.6 into a 4.0 was fairly significant as opposed to a 3.8. I guess it would be if you use the 4.0 crank!