The damage, what has caused this?
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So this is the piston that was obviously buggered and had zero compression for the obvious reason



Now here is another piston (the other 3 were in a similar condition of varying condition) this piston still gave good compression readings. It seems almost like the pistons were too tight in the bores; maybe caused by excessive heat?




Any thoughts? Engine is off to see if it can be rebored tomorrow.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

the top one looks like nitrous has done its worst , the bott looks like seisure.

so its got to be det! surely.

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DET!!!!

AlexF

Looks like det has taken out the first pictured piston, second one is odd though?

get the bores checked properly with a bore guage, i think sommat funnys up and i have a feeling i've seen it before. I wont go into detail here.

I've seen the future and tbh its Pie

http://www.hadmac.com/piston_%26liner.htm

No N2O, purely boost.

From that link I think it might be a combination of two things - Over heating (owing to it leaning out) and tight bores.

And yst Pete that damage is around the exhaust valve cut out. However, the damage is equal on both sides on all the pistons except the melted one.

It dosen't really make sense though as we are running less boost at a lower CR and same advance as the old engine, which proved bulit-proof.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

how many miles had they done - thats scary

They had done 3 events and a couple of RR sessions; so maybe 50 or 60 miles. But as I said, I still have the old pistons which are in perfect condition and had done 4 seasons. I don't think it's a piston problem, well it isn't.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

i would say that the top piston has got too hot from detonation ,possibly due to lower octane or extreme atmos temp we had at avon ,the first step is it get hot ,starts eating at the strength of the ring lands ,they then nip up and the piston as it rocks in the bore pushes the rings flush with the piston wall,at this point the combusting gases find a new path down past the 3 compression rings ,and out the oil control slots into the crankcase ,then this localised path gradually heats the top till its soft enough to be eaten away ,.
the second picture is a similar scenario ,but earlier on in the process , the heat effects the dimentional stability of the piston and subsequently it gows more across the pin where the mass of ally is greater ,so semi siezing in the bore ,as part of the same process .i have seen this sort of thing a lot in rover v8 engines .
the answer would be run cooler with more octane and poss less timing on boiling hot days ,run richer to keep piston cool ,and possibly increase bore clearance ,but this can raise its own probs if done too much with the trapped mixture between the top ring and the piston top being a possible source of det itself..best to run a correct clearance ,and keep it cooler .
best of luck
robert.

Edited by robert on 18th Jul, 2006.

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

All that sounds like a reasonable expination

We run 101 octane fuel, but I think a fuel filter blockage leaned it out causing the heat and det etc. we could easily retard the ignition a few deg.

Wil

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Did you have a fuel filter block?

If so that is sure as eggs the cause of det - you ran lean.

Hot air temps doesnt help DET but it does lower the density of the air so you end up running a little richer than usual - that usually helps reduce det!!

On 101 RON fuel it shouldnt have done that just because it was a hot day - you have an IC dont you? Do you know your Air Charge Temps?

How was the ignition mapped? Det cans? Rolling Road?

Alex

AlexF

The fuel filter was deffinately a restriction, but this has happend on many occasions, for various reasons, and nver resulted in this before.

Yes we have an IC.

And yes it was mapped using Det cans on a RR

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Cheers Peter.

What I am finding difficult to understand, as I have already said, is that the old engine running the same advance, fuel and cam timing, but a higher static CR and more boost never had a problem; even in similar temperatures.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Ahh. T2 running 65% T3 running 70%

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

From the logs taken on the day (not including inlet temp unfortunately, and the O2 sensor is not working either) it only ran 217KPa which is about 17psi, so even the boost was not silly.

http://www.twin-turbo.co.uk
http://www.hillclimbandsprint.co.uk/default.asp

A man without a project is like a like a woman without a shopping list.

something else that may have some relavency is that if you were running the t2 ,instead of the t3 ,your exhaust back pressure could have been higher ,the t2 r5 turbine is 47mm big dia 35.25 small dia,whereas the t3 is58.5 and 48.5 ,so could well create less back pressure ,this creates less exhaust reversion and hence less contamination of the incoming charge with hot exhaust gases, which is deff a detonation encourager!... did you record this bp on the rr compared to the t3 bp,wil?

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

superb post there peter!

I'd not thought that through as thorughly!

I'm going to re-do some calcuations for running 10psi on a t3 with no IC last year at avon - there was no sign of det on strip down.

Alex

AlexF

Great advice from Peter and Robert there.

Undercrown cooling jets for next year maybe?

Any chance you did get a bogus batch of fuel?

alex, what happened to you this year?

Team Racing

Jim,

I didnt go :p

I got pissed off getting so close to finishing my car only to be let down by a shoddy part (oil cooler take off), that I threw my toys out the pram and didnt go.

Actually - the real reason - I decided I couldnt stand the sight of all you lot being faster than me hehehe

Alex

AlexF

Oil cooler ? who needs an oil cooler ? lol

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[quote=mini1071s,18/07/2006 12:43:49]If insufficient octane is a cause of detonation, as I understand it then pulling timing only makes it worse in fact as you are starting the combustion process even earlier.


peter,pulling timing means retarding it,this would delay the burn not start it earlier.
the reason this works (up to a point) is that ,if you imagine lying on the piston looking up as it approaches tdc ,
the spark occurs and the combustible mixture lights up ,
but not explodes ,
it burns a bit like a forest fire in a wave ,moving faster or slower across the chamber towards you and sideways at different speed depending on the varing degrees of mixture homogeneaity and turbulence,
.all this time the piston ,with you on top of it ,is moving towards tdc ,
then ,at some point, peak cyl pressure occurs
and hopefully just at the right time past tdc to create the most shove on the piston and create the most torque,
all this time ,while the burn is passing through the chamber ,the mixture thats not burnt is experiencing a rise in pressure and temp,and if things go critical ,it explodes spontaneously ,
or detonates ..
if we start the burn a little later ,then that flame front is travelling through the chamber a little bit after the point of max compressive pressure ,and so the unburnt mix ,experiences a slightly lower max pressure and temp before it gets eaten by the flame front ,so is less likely to detonate ,and the engine lives . the downside is less total force and so less torque.

hope that made sense!
robert.

Edited by robert on 19th Jul, 2006.

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

it seem to be det for me, I think the t2 is on boost earlier, this making the "T3" ignition curve too agressive, making a big difference in events. about exhaust restriction T2 have a smaller turbine wheel , but a larger A/r (0.35 vs 0.25) this meaning that it is in fact more perméable than the T3 (less restricted) .
I think you should recurve your ignition to match the T2 boost curve.
cheers
fab