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

[BYprodriver]

Originally Posted by Bigsmoothlee

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.

[Gilles]

Originally Posted by BYprodriver

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!

[jaykay]

Originally Posted by Gilles

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

[jaykay]

Originally Posted by BYprodriver

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?

[j.fro]

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

[Bigsmoothlee]

Originally Posted by BYprodriver

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?

[BYprodriver]

Originally Posted by Bigsmoothlee

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.

[Bigsmoothlee]

Originally Posted by BYprodriver

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.

[jaykay]

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.

[BYprodriver]

Originally Posted by jaykay

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.

[jaykay]

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

[Gilles]

Originally Posted by BYprodriver

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!

[BYprodriver]

[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.