[Mk2] [Turbo] Cracked blocks – should I be worried?

[androo007]

Hi chaps,

With the forged build on the way it’s got me thinking. Cracked blocks – should I be worried?

I’m sure that we’re all aware once the pistons are rods are in, the weak point is the actual block itself; something that was remedied with the 5S casting using much less brittle material for the blocks.

Peter mentioned that in all the time he’s built the 3S he has seen 7 crack – some at stock boost, some at big boost. Some on Rev1, some on Rev2, and and some Rev 3. Doesn’t seem to be a pattern or rhyme.

Therefore I think that we can all safely assume that there is an element of risk – every engine has its weak point afterall.

Goals are to hit 350-400bhp long term …. But how increased are those risks?

Interested to hear from people that have been running north of 350bhp long term and who has had cracks where.

[craig]

As Pete has correctly stated, there is no pattern with cracked blocks, it really is luck of the draw.

My revision 3 3sgte block cracked in 2014. I had that engine in the car since 2008 without issue. Started off on stock boost, raised it to 1.1 bar etc, with no problems.

It let go 6 years later.

So, revision, power etc, makes no difference. If it's gonna go, it's gonna go.

I was running around 300bhp on my block, before it cracked. Someone may be ok running 350+bhp without issue, but that shouldn't reassure you that your block will be fine at that power.

It really is luck of the draw.

[androo007]

Yeah, interesting that really. So many cars go for big power so I think that it is over exaggreated too - people wouldnt still be forging etc 10 years later if it was that common.

Where did your crack, Craig? Top near headbolt 1, water pump or between 2&3?

[craig]

Yeah, interesting that really. So many cars go for big power so I think that it is over exaggreated too - people wouldnt still be forging etc 10 years later if it was that common.

Where did your crack, Craig? Top near headbolt 1, water pump or between 2&3?

Mine went between 1 & 2. The combustion pressure and coolant steam cleaned the top of a piston!

Well narked at the time. Just had the car build finished, then engine goes pop.

[androo007]

Seems that is the weak point in them all unless you run 700 - then its the head bolt area.

A rich tune and concervative tune are the best things I've read so far to help keep pressures down - along with cool air I guess. (?)

[jimGTS]

find a rev4+ block

issues were addressed in those years and upwards.


late 5s block is the mc'daddy i believe.

[androo007]

I can't seem to find a genuine Gen 4 Turbo block..... if anyone knows where one is please let me know as i'm due to handover for building in a week.

Actually - I say that - are we even sure? Because i'm pretty sure even the REv 4/5's are EXACTLY the same castings as the Rev 3.

[jimGTS]

im not talking gen4, im talking rev4+

but yes "gen" 4 blocks are also good.

[androo007]

Yeah thats what i meant, sorry - Rev 4 being the same as Rev 1/2 in terms of likely to crack.

[SonicSW20]

Go all in, build a 5SGTE

[androo007]

Too late, all parts here and i'm maxing out my budget on the 3s

TBH I think the cracking may always subjective to external factors..... cooling, bad tunes etc.

[C35Rob]

I have no first hand experience of a cracked 3s block and while I know it does happen, the amount of high powered 3sgte engines around the world vs the amount of confirmed cases of cracked blocks kind of suggests it's rarer than people would have you believe.

I'm tempted to take the 'this rev/year is stronger than that' story lightly too, with the exception of the quite obvious additional meat around the water pump area on the later gen 3 blocks, I'm not aware of any actual testing to show the cyl walls are thicker or are a better quality material (genuinely interested in this if anyone has any links to blocks being cut up for testing, ultrasonic NDT or other metallurgy info on them)

the only way to see how much meat is on your block is to have it ultrasonically tested, which is prohibitively expensive, is it really necessary? probably not..

that said, if I was going to build a 500+ bhp mr2 I'd probably want to use the 5s block which has thicker cyl walls, but I'm not.[/u]

[gnzyza]

Even though the block is weaker, poorer casting something must cause them to crack at stock or high power.

Is it thermal cycling, cold coolant rushing in?

[androo007]

Definitely have to agree with Rob there. Speaking to Peter today, in 15 years he's seen 7 cracked blocks so not common at all.

HOWEVER he did explain - it may not be the block that's at fault, more so some contributing factors around it. I.e cooling issues, poor tunes etc - there are so many contributing factors other the just the block strength which may only be a parting factor.

Anyway I'm going to invest in cooling cooling cooling before cranking anything big on and make sure I keep the tune rich.

[mr2magic]

I too tend to believe it's less a case of certain gens being prone to cracking at least until such time as some of the known flaws become relevant.

As to cooling - i'm pretty certain that is a factor (there is a spot in the block where the waterpump mounts that could possibly lead to a disrupted flow and therefore a hot spot) along with pre-ignition and/or bad tuning.

It's funny how often the cracked block is cited but you only ever find 3 or 4 pics of damage on the interwebz

[craig]

It's funny how often the cracked block is cited but you only ever find 3 or 4 pics of damage on the interwebz

My rev 3 3SGTE block. Steam cleaned piston due to hairline crack between 1 & 2:

[Dale_V]

I cracked a totally standard (and well maintained may i add!!) rev2 NA block, around the waterpump area

[ashley]

Mikey cracked a rev2 turbo block a month or two ago- hairline crack running down one of the bores.

I cracked a rev3 turbo block- on the top of the block deck between no 2 & 3.

Yep- it's pretty rare to see these blocks crack

[androo007]

Hmm interesting. Although Craig were there leading factors to WHY yours cracked?


Seems rev 3 cracking appears more than others, that's undeniable.

For the Rev 2 - a cracking down the bore - now that's the first time I've heard of that type of cracking, must have been something pretty intense going on

Ashley, interesting to see it cracked on the deck. What power were you running at the time? Do you think there *could* have been another factor to it? We're you comfortable with the tune, have all the things in place for cooling that you in hindsight should have?

Don't get me wrong I accept that it is possible to happen....but just trying to identify any items that could be attributing to that event.

[craig]

Nothing obvious mate. Bought the car in 2008. Ran it as a stock engine/ecu with a boost increase to 1.1 bar and the block cracked 6 years later in 2014.