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

[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

[Jake Raby]

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.

[jaykay]

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?

[Jake Raby]

Originally Posted by jaykay

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.

[Gilles]

Originally Posted by Jake Raby

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.,
.

[Jake Raby]

Originally Posted by Gilles

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.

[jaykay]

Originally Posted by Jake Raby

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.

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?

[Jake Raby]

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.