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Old 08-31-2015, 02:51 PM   #1
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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.

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Old 08-31-2015, 03:16 PM   #2
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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
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Old 08-31-2015, 03:32 PM   #3
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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...
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Old 08-31-2015, 04:10 PM   #4
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Wow - way above my head. Keep up the post! Tracking your progress will be very interesting. Lots to learn.
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Old 08-31-2015, 06:27 PM   #5
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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.

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Old 09-01-2015, 06:24 AM   #6
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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.

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Yep, that was me. Did anyone find any parts of my engine?
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Old 09-01-2015, 08:17 AM   #7
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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.

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Old 09-01-2015, 08:57 AM   #8
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Quote:
Originally Posted by Bigsmoothlee View Post
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.
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.
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Old 09-01-2015, 11:16 AM   #9
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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!
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Old 09-01-2015, 02:52 PM   #10
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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
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Old 09-01-2015, 02:56 PM   #11
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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.
Oh no does this mean my 3.2 cannot derive benefit from becoming 3.8 or 4.0 Ls?
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Old 09-01-2015, 03:31 PM   #12
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Jake Raby has a super-secret short stroke 3.6 brewing...
Calling Dr. Raby, Dr. Jake Raby....
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Old 09-03-2015, 03:55 AM   #13
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Originally Posted by BYprodriver View Post
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.
So scratch the idea on the 3.6 crank. So you're saying that boring to a 3.6 is the max?
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Old 09-03-2015, 05:36 AM   #14
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Originally Posted by BYprodriver View Post
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.
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!

Last edited by Gilles; 09-03-2015 at 05:50 AM.
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Old 09-03-2015, 09:35 AM   #15
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[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.
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Old 09-03-2015, 09:51 AM   #16
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So scratch the idea on the 3.6 crank. So you're saying that boring to a 3.6 is the max?
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.
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Old 09-03-2015, 11:03 AM   #17
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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.
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Old 09-03-2015, 12:32 PM   #18
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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.
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Old 09-03-2015, 01:10 PM   #19
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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.).
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Old 09-03-2015, 04:00 PM   #20
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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.
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.

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