Blew my engine. Anyone here build a 3.8 or 4.0?
 

So 8/22-8/23 I drove my 3.4 equipped 986 from northern NJ to Devens, MA for the PCA Zone 1 AutoX.

My car was on 275mm wide Hankook Z214 DOT slicks on all 4 corners with a suspension and alignment to match, and it felt like a very fast combo.

Day two, without any warning, there was a sudden rattle ( hard to hear over a loud exhaust ), a boom, and a connecting rod went through the block and left both coolant and oil all over the pavement.

Being 220 miles away, I rented a U-Haul 10' box truck and a tow dolley and dragged it back home.

That being said, I'm now on a journey to build a bigger engine. Boring to 101mm and stroking it with a 3.6 crank will give me 4.0l, but is it safe? Should I use the 3.4 crank, bore the engine to 101mm, and have a 3.8? Or is it safer to gain 200cc from the 3.6 crank and bore enough to get a 3.8?

Im going to be autoXing and doing DE events.... this time with an Accusump and oil pan baffle.

Any input would be appreciated, thank you.

That sucks!

As a side note,

if you have AAA premier membership, you get one 200 mile tow per household per membership year, and three additional 100 mile tows to the destination of your choice

Ugh, that sucks. Sorry to hear.

Interestingly, in last month's issue of Panorama, the article on the 986/996 development stated that the Mezger motor was born for the 996 GT3 when the R&D team realized the M96 motor was not designed for sustained G loads above 0.8g...

Wow - way above my head. Keep up the post! Tracking your progress will be very interesting. Lots to learn.

You didn't happen to have your explosion on the taxiway nearest the police vehicle yard did you? I was at the SCCA autocross on 8/29 and there was a section back there that looked pretty messy.

Sent from my A0001 using Tapatalk

Yep, that was me. Did anyone find any parts of my engine?

We used a large broom to sweep as much as we could off the course, didn't see anything recognizable in the pile.

Sorry to hear about your engine, hopefully your build comes out badass.

Sent from my A0001 using Tapatalk

Increasing stroke increases load on the connecting rods & cylinder walls of a M96. If you have a 99-2001 3.4, the valve size is optimum for 3.6L & becomes a limiting factor for bigger displacements.

Hello BY,
Do you know if the 3.8 engine on the Carrera S (M97..?) also have the same issues as the M96 engine? Due to the longer stroke? Thank you!

Yes I believe they can suffer from scored cylinder walls in part due to increased heat load of a higher displacement

Oh no does this mean my 3.2 cannot derive benefit from becoming 3.8 or 4.0 Ls?

Jake Raby has a super-secret short stroke 3.6 brewing...
Calling Dr. Raby, Dr. Jake Raby....

So scratch the idea on the 3.6 crank. So you're saying that boring to a 3.6 is the max?

Do you know if this also applies to the later M97.21 3.4 engines? Or they also have the same valve sizes as the 99-2001 engines?
I assume that the increased load on the cylinder walls (w/longer stroke) applies as well, is this correct?

Do you know if the 3.8 engines on the Carrera S also have issues with their cylinder walls due to the longer stroke?

Thank you for your comments!

[QUOTE=Gilles;464483]Do you know if this also applies to the later M97.21 3.4 engines? Or they also have the same valve sizes as the 99-2001 engines?
I assume that the increased load on the cylinder walls (w/longer stroke) applies as well, is this correct?

Do you know if the 3.8 engines on the Carrera S also have issues with their cylinder walls due to the longer stroke?

The factory 3.8 engines can have increased cylinder wear, mostly from cold winter startups. I have a 2002 3.6 case with a scored cylinder.

Increasing stroke increases piston speed, which increases loads on the rods. At any RPM if the piston is moving further (longer stroke) it has to move faster to go from TDC to BDC at the same RPM. The longer the stroke, the stronger the rods have to be.

With the later engines you can bolt on bigger valve heads. The early 5-chain engines don't have that option.

No I'm saying step 1 is install LN 99mm "nickies" for 3.6L this step will cost $7,000 min.

To go bigger will cost alot more with rapidly diminishing returns power to $$ ratio, especially for high RPM DE racing.

I have a 2001 3.6L longblock I will sell for $15,000.

I don't think its that expensive, LN engineering lists the work for $3300, and $4600 if you want the pistons to go along with it.

Or, I can just have LN engineering bore the engine case I just bought from 93mm out to 96mm... but that wouldnt be much fun.

Diminishing returns after 3.6 noted. Im sure your 3.6 is a nice engine, but its out of my price range. Especially since I can handle all of the work.

I would have thought the difference in cost between between a 3.6 bore and 3.8, 4.0 would be minor compared to everything else and really attractive if you are doing the work yourself. Working with 3.2 heads (five chain) I would have also thought 3.8, 4.0 would have bumped up the torque significantly with at least another 100Hp peak with nice drive ability.

i think a 101 mm bore is the max (available to us common folk, anyway) so with a 3.2/3.4 bottom end the biggest you can go is 3.8. the m96 3.6 and the m97 3.6/3.8 got stroked, so they can go to 4.0 with a 101 mm bore. i don't think you can just drop the stroker crank in a 3.2/3.4 bottom end as the bearing races are different (possible, but lots of work?)? and, as stated, the longer stroke increases lateral load on cylinder walls = more scoring, which is the big failure mode on the m97 engines. fixed when Porsche went to a stronger liner with the dfi engnes. so, if you do go with a stroker crank, make sure you do the lne nikasil liner as well.

then there are the heads. there is some voodoo on the interchangeability of the various heads which jake has alluded to in the past, and perhaps if he reads this he'll add some content?

but by the time you've replaced the heads, paid $5k to bore the cylinders, and rebuilt the bottom end, i'd suggest you are well into the cost of a new engine (la dismantler has a 3.6 X51 Powerkit engine for $12k or something on ebay right now - X51 has hotter cams, better heads, dual oil pumps, improved oil baffle, etc.).

You need a 3.6 crankshaft & carrier & rods & LN pistons. For anything more stressful than auto crossing I would insist upon aftermarket rods. 3.8+ will have LOTS of low rpm torque, enough to increase autocross times.Peak HP I would guess would increase 8-12% depending on head work & bolt-on external parts.

Yes I should qualify 100hp as 100 over the stock 3.2.

And so we are talking 8 to 12% projected peak power increase for the 3.8 over the 3.6. This change in displacement will perhaps put us at 375 BHP peak while having to upgrade the crank, crank carrier, con rods...with no head options to fully realize the gains to be had. Now I see where the expense is for little result.

How is it that no crank, carrier, conrods are required for the 3.6?

Doesn't Eric at HRG have a 4.0 in his car.....5 chain? I guess with a race car and motec you can just load up a 3 chain in a car that originally had 5 chains.

Jeez I would hope that the result would be better than than the 944 turbo S and big aftermarket turbo I drove on the weekend

Size doesn't matter. When I found efficiency, I found power.


Bigger isn't better in most all cases. If It were I'd only be building my 4,2L engine, and nothing else.

To big build and optimize it, costs real money. Building it big without coefficient design, means it'll be a pig. I see people do this all the time, and the engine isn't good at anything.

Other than burning gas.

So this begs the question: What needs to be done for 3.2 to 3.8 to avoid piggish ness?

Will the 3.2 heads ported suffice?

The list would be a page long, if I were to post it. I won't, because I refuse to empower the band wagon pros.

3.2 heads can and will meet the demands, but all you'll end up using are the castings. 3 chain heads from an M96.24 are much better than 5 chain M96.21 heads, in every way.

All the work, and components for the heads alone are around 5,500.00-6,000.00

Timing alterations are required, too.

Jake: if you have a choice (similar cost) which route would you choose, BTW my car (CS '07) has a 3.4 M97.21

a) My 3.4 with 3.8 LN Nickies and forged rods. Q: Is the stock 3.4 crank strong enough? Would the cylinder walls be too thin & risk overheating?

b) A 3.8 from a Carrera S with LN Nickies and forged rods? But have to deal with the DME change and key programming etc.,
.

Loaded question, with way too many potential variables for a general answer.

The crankcase for the Carrera S is not special, its the same as your M97.21 in most every way. It has larger diameter cylinders from the factory, but we never care about that.

Now, if you use the Carrera S engine, you'll have front console issues, as the water necks and routing are different than the M97.21, AND you'll have to weld, drill and tap to fit your unit onto the case. You won't learn this until the engine is almost done with assembly.

If running Nickies, we can go clear to 104mm without overheating concerns, unless you misconfigure the engine combination, and CAUSE the engine to generate more heat. Lots of people are doing that with stock bore sizes these days, or going to some funky iron cylinder that causes problems, too.

You need to educate yourself separate from whats online, most of it is plain wrong, or being distributed by some clown that doesn't even change his own oil.

You have one chance to do this right. Learning curves are 90 degrees and margins of error are near zero. This is why I offer classes.

I always stick with the M# designation that the vehicle came with, unless its a crazy project with no budget or time constraints.

Jake,

I am sorry perhaps I was not clear enough, I was referring to the strength of the 3.4 crankshaft because I was considering going to the 3.8 Nickies with the forged rods and was not sure if the crank would be the weak point.

Regarding the learning curve, I have assembled a few aluminum (Italian and old VW) engines but by no means are an engine expert, but I am planning to attend your M96/97 rebuilt class, hopefully before this years end, thank you for your comments!
.

The only remaining enthusiast class is in December, and its mostly filled. I just finished the training site, so you can go there for details, and to sign up.
The Knowledge Gruppe

The factory crank is fine, just ensure it is magna flux tested, and that you do NOT use a lightweight/ single mass flywheel.

Its the little things that bite you with these engines. My classes are all about "silver bullets" that help avoid issues.

Yep understood, I just need to know what ballpark I will be working in. PM/email can work too if needed. The class will be in my future provided the engine build results warrant working with a 3.2 5 chain.

So some of my bounds/considerations:

3.6 bore for cost effective performance; stock crank, stock heads

3.8 bore for 8-10 % more performance; upgraded crank, upgraded heads at an additional 6K to realize output?

The 3.8 bore is much harder to build. You must set ring tensions (fish scale) yourself, and its not nearly as straight forward as a 99mm bore engine would be. The 101mm bore also requires a lot more port to keep from being a narrow power range pig.

The class is universally applicable, we work with 3 and 5 chain engines, and I even go over how to swap components between the engines.
Bigger isn't better. You won't believe me till you learn it first hand, though.

I am in the midst of having Jake build me a 3.6 SS engine from a 5 chain block from my 02 S. While we are on hold currently ( by me direction ) we will complete the engine this year. When I originally talked to Jake about what I wanted my head nearly exploded about all the combinations Jake offered. I quickly learned that these engines are finicky/difficult to hot rod CORRECTLY ! In my application basically the only Porsche OEM parts that are staying in the engine are the head and block castings. Everything else is being replaced either with LN Engineering items, aftermarket items or Jake Raby in house built items. This is NOT a small block Chevy rebuild ( no negative intent ) . My real point is there are engine builders out there like Jake that know how to build/hot rod correctly. There are DIYers that know how to build/hot rod these engines but keep in mind one tiny mistake can cost big $$$$$$ . Good luck with your build choice.

Its all in the combination. No matter the size.

I see DIY'ers doing a better job with these engines than most pros today. Why? Because they take the time to do research and they truly care about the project.

I see the shops that have jumped on this band wagon just building some bigger engine, and it ends up being misconfigured. They use a larger bore, but keep stock heads, don't alter cam timing, and etc. Most of the time they don't set ring tensions correctly, or even gap piston rings. They just assemble what comes in the box. The best (worst) one to dat was a 4.0 where the shop built up a 3.2 and they didn't even change the connecting rods. They just expected to hang a 101mm piston off the end of the stock rod, and figured it would work.

It did, for about 45 minutes. Thats when the guy's cheap, 9,995.00 big bore (off the shelf) engine ended up being a complete waste of money. I threw the whole core in the scrap bin.

Great information and direction....

I have had my 3.2 for a good spell and am looking for some added punch that is well worth the time and effort. The last thing I want is to end up with something that barely out does the 3.2 I have.....or is worse

Yes X51 is another route to consider for.....not sure about all the interface issues and any weak points in that engine.....I think you have one TRK how do you like it?+

The X51 shares the same bottom end and pistons as any other 3.6 engine. It has bigger ports, and larger cams, with a larger intake plenum.

I've never favored X51 engines, even to be built up into our platforms.

Curious as to why? The changes seems to fall into typical mods a engine builder would use to get more power out of a engine. Does it change the who power is delivered that you do not favor?

Its where and how the power is made. The engines make all their power so high in the RPM range that the hydraulic valve train is the determining factor. The engines don't really start to pull until 6K RPM, and before that they often make less torque than a standard care engine.

The big ports and big cams, with the huge plenums make for an engine that has a narrow power band.

The same characteristics follow the engines, even when they are made larger.

For a street driven car this doesn't make sense. Neither does what Porsche charges for it.