I know this may sound stupid, but can you tell if the damage is fresh?

Could it possibly be from when you had first rebuilt the engine and were running it in unmapped?

I guess it could have been but I didn't go over 3k rpm and ran with zero boost.

How much advance was it running?

John

Seeing the car you're trapped. As you say the car would be useless, it's just too special (and probably rarer than a Ferrari or Lambo in N.America) not to put back on the road. Besides you promised me a ride if/when I come over to visit my lad

i would'nt put it all down to det yet to be honest

Alot of what look like det marks were more than likely caused by parts of the piston floating around

Looking at the piston the squish band is at least 30% smaller than standard as a result there is a lot less material holding that part of the crown to the rest of the piston, i am not sure why you would make it smaller TBH??

Also what squish clearence was you running

it would also be interesting to know the CR and what advance you was running plus boost levels



Ricky

The tuning issues including advance and boost levels were discussed in this thread.

John,

did the turbo come unharmed out of all that???
where did all the piston bits go, surely turbo blades must have been battered really badly...

Odd, v.odd!

V.

Yes the turbine blades were mangled, I sent the center section back to ATP and they sent me a replacement. I thought it was just the spark plug insulators going through the engine and now we were not seeing that problem any more I thought it was safe to put the turbo back on. Unfortunately the same thing happened again so I need another centre section. It costs me $80 to ship to ATP then ATP change me $550 for a new centre section and shipping back so it's not something I want to keep doing!!

On that subject it might not have been heat that had previously damaged the insulators, it could have been bits of the pistons hitting them!

any photos of the cylhead (combustion area...)?

It seems like parts of the piston have broken/sheared off I very much doubt it's anything else than mechanical. Mind you some of the "breaks" look rather shiny and untouched.

V.

No unfortuately I didn't take a picture.

The valves looked untouched except one exhaust valve which wasn't sitting quite right on the seat so that one is definately bent. The top of the combustion chamber was pitted in a similar way to the pistons but not as much. The head is being sent away to be cleaned up and made like new. I'll let you know what the report says.

John

No, detonation caused that damage. The piston might have been week in that area - like I said you need a drawing to see how thin that area will become. Det occurs most common on the inlet side which had the largest cut outs coupled with what maybe a weak design the det pressure mechanically failed the piston - but det would have been the root cause. For mechanical piston failure high rpm something like 8k would have to been seen and I doubt that in this case.

I agree with this, det has a caused a week piston design to fail and as a result the parts of the piston have caused alot of damage on top of the det damage.

Just look at a standard piston and you will see that the squish band is larger and as a result has more material holding it together

what brand are these pistons? the custom Barbz JE ones?

V.

They were the CP Racing ones from Barbz.

The link to the piston specification has been removed until I know who owns it.

Hi John, I will mail you seperately also. But for info the piston spec request sheet is not synonomous with a validated full CAD design, while the material and production methods maybe CP's high quality they do not validate the design as to do so they would have to do a full cad drawing. For instance I can show you a Guy Croft example piston design one of 3 pages; this enables not only calrification of weak points it gives a document to compare what is returned, in many cases you cannot assume what you get is actually what you asked for.

http://img.photobucket.com/albums/v74/sediciRich/D18lowcomppiston_example.jpg

Rich

thats exactly what is needed

Guy croft puts a lot of effort in to every little job in an engine such as this, he will not rely on anyone else to do the job for him

this is one of the reasons why he is one of the best engine tuners in the world

Thanks Rich. To be fair the spec sheet I showed was what I got supplied in the box from CP Racing. It's not necessarily what they used to build the pistons. For example there is nothing about the valve angles or sizes for them to know how big or where the cut outs would need to be.

I'll speak to the guys at Lightspeed to see what their piston design is going to be like.

is it OK to have these drawings on the forum guys?

V.

Very good point. I hadn't though about the intellectual property. I've removed the CP Racing piston drawing until I find out who owns it.

I wrote to Guy first, and obviously he's allowed to ask me to remove it. Notice there are a lack of dimensions as I asked for something for illistrative purposes.

Rich

Rich, you've got to remember John posted up the spec sheet that comes out of the manufacture not the design spec that went into the manufacture.
If there is an issue with the strength of the pistons then I would've had a problem by now. I ran 20k miles approx at 408BHP+ before Barbz even sold the kit to anyone to prove that it would last and that included TOTB 3 & 4. The head was then taken off for inspection.

I had a det issue with mine in 2006 but it was because I switched to race fuel and stupidly forgot to run out the tank internal swirl pot. But even then my pistons were not actually damaged to that extent just dropped the spark plug core and scored two of the bores. I actually still have all of those pistons in my car despite that & they are still fine with good compression at my level of tune

I think the issue is the canadian fuel, but to get det on all cylinders is pretty rough going. The piston has a weak spot but as Guy said to me something has to take up the detonation pressure either the pistons or the head gasket. I'd say for that fuel a lower comp and thicker - minimum thickness between 1st ring land and VR. Its not a weak piston per se but it has an area which sholud be beefed up or rather made to a different breif.

rich

The pistons did go through finite element analysis and simulation as part of the design process, so a visual comparison of the manufacturing spec isn't going to tell you a lot in terms of where the actual strength is. Neither frankly would a 2d cad model. The sheet that John has that came with the pistons is purely for the engine builders reference so that they get the bore right etc.
I didn't pay for consulting on the piston design for a laff, it was because given the constraints it is quite obviously a very complex job to get the piston right.

Fundamentally fitting a 2.4 stroke into a modern 2.0 block is not a simple task. It would be easy adding 15mm stroke if it had 80s design pistons like the 16vt but it doesn't. There is no additional space left at either the top or bottom of the bore as a result of the conversion so to make anything thicker you have to make something else thinner otherwise the CR will go up or something else will be stressed. You really cannot say beef that bit that broke up because as far as I recall the most stressed point on the crown was not where the piston has broken, so that is a result of det. And why should you make a piston take more det than that? why would you compromise the design for something that was so extreme in terms of being incorrect.

If you make that part stronger or at least have more material there will be somewhere else on the piston which will become weaker given the requirement to keep the CR the same. There is no more space.

The pistons aren't designed to take that much det any way you look at it. If the std pistons had have had that much det they would've been in pieces probably with a rod through the side of the block. It is a testament to the pistons strength that it was not obvious it had failed, and this is why I said to John's tuning guy look in the bore with an engineering endoscope.

Calm down. The weak part for such combustion pressure is at the VR, clearly, and no pistons can take sustained det. FEA is fine but I assume only looking at cyclical loading not the compressive force that det could cause thus the weak point location is only a function of the applied load. Sure something is going to give way, but I wonder why the det wasnt heard, sure a trace amount before such a significant event? To make anything thicker you have to make something thinner perhaps- Id say reduce the rod length and put the pin lower, not point chasing capacity if its going to fall apart. In this case lower the Pressures or temp for that fuel or watch it happen again. (this assume the RR operator did all he could to minimised such an occurrance)

I've heard some news from Lightspeed. The new 2.4 crank I fitted to the engine is now worn 5 thou. They want to regrind it to 10 thou. However I see on the FAQ section here that you can't regrind a 16VT crank due to loosing the nitride hardening. I presume the same is true for the 20VT crank and I need to buy a new one.

John

There was a thread about this in tuning just yesterday John. The outcome wasn't particularly decisive although I remember reading that they are nitrided and cant be re-ground in a previous thread.

If you do require a new one, I'd suggest speaking to Johnnybravoturbo as I think he has one no-longer required.

This is becomming an expensive rebuild. It turns out the head has 4 bent/damaged exhaust valves and 5 bent/damaged intake valves. Ouch.

No other news

John

Ouch.

Canadian fuel is a little unusual in that they use MMT (wiki entry) as a high octane additive as opposed to something like MTBE (methyl tertiary butyl ether) which is used in Europe and elsewhere but mostly banned in the US due to groundwater contamination from undergound storage (no problem outside the US, I blame poor housekeeping/maintenance). In the US they now use ethanol or the (similar to MTBE) compound TAME. I wonder if that is significant? Sorry to hear about the damage, but in the pic of the new piston it did strike me how little material there was between the bottom of the valve cut-out and the top ring

Few questions:
Who built the engine in the first place?
Are you sure it was built correctly?
Are you sure it’s det as it’s very strange to see det on all cylinders like that?

Engines don't go wrong if they are built and mapped correctly. I feel your pain as I had to rebuild my engine a second time due to poor workmanship (incorrect clearances to blame) however if you wanna do something right you do it yourself and that’s exactly what I did the second time round along with a trusty mate to be 100% sure.

There are many people who run the 2.4/2.5 conversion from Barbz and they don’t have problems so I wouldn’t blame engine components as they have already been proven. I wouldn’t blame fuel either as a good mapper should know the fuel their using. I hope you sort it out John it’s just another pain that you could do without.