Shit happens - Rolling Road Piston Failure nearing start up (update 27 Nov 10)
Turbo Mini Forums

good to see you are cracking on with it again.

hi buddy, shit about the cam but at least the engine is an easy recovery

Yes i moved to the darkside

Instagram @jdm_brett

Is that near standard compression ratio for a standard 1275 turbo.

Own the day

I get 9.4:1 with a 0cc deck height. If I remember correctly the Omega's sit down the bores on a standard deck. So could be a bit less.

IMHO possibly a touch high for the boost/intercooler you were running Richard.

If something is worth doing, it's worth doing half of.

Yeah guys - crackin on but I'm well pissed off as I took it for granted that my man who sold me the Omega's had flogged me 10 cc pistons which they obviously are not.

When I ordered all my bits from Honeycrock (now closed down), I gave the guy a spec to achieve a static CR of 8.4:1 to run the kind of boost I wanted to.

I clearly took it at face value that the combination of chamber and piston volumes had achieved this.

The CR I have is most likely to have been the cause of det on this engine.

As you say John, 9.4 / 9.5 is WAY too much for this build and spec. I'm surprised it lasted as long to be honest !

In terms of the way forward, I clearly have the cam to sort out which I'm a bit fucked off over as it's only done about 2500 miles but, as you wanted the figures Robert, runs 240lb double springs with 1.5 Avonbar forged rockers - probably not a good combination in hindsight.

I'll change the springs for 180 lb jobs as I clearly dont need the 240's for the kind of revs I'm running (95% of time at less than 6000 rpm).

I'm assuming that despite me 'bedding the cam in for 20 minutes at 2500 rpm' when I first started the engine, the VR1 oil is not to blame ?

What cam choices are contenders ? - stick with the AP2 ? Or go for ST5, MG Metro ?

Oh - and I have a problem with the pistons.

Not only do I need to source a spare piston but they ALL need to be machined out from 8 cc to 14 cc to give me my 8.4 CR so does anyone know if there is enough material to survive the extra heat loading in the crown of what would have originally been a 6 cc cast +.020 Omega to take it to 14 cc ?

Or is the best option just to stump up and buy a set of +.020 14cc cast Omega's at, gulp, £300 (which I'd obviously like to avoid !) ?

Cheers guys.

Richard.

Edited by turbominivanman on 6th Sep, 2010.

Minivanless, but reluctantly happy living with the decision. There'll be another one day.
http://www.youtube.com/profile?user=minimadmotorman#p/u

If you are staying below 6000rpm I'd go for an MG Metro cam or if you want it new get the KC500, I'd also bin off the 1.5's in favour of some 1.3 rollers or some 1.27:1 pressed steel type rockers.

You may lose a bit of outright power but I reckon you will pick up on driveability.

Van will pull in top from 1500rpm with this combo.

As for the pistons I'd be tempted to stump up. As you say not the cheapest option but the safest!

IMHO go for the 14cc +20 Accralites as you will have the dish you need without having to get a set 10cc omega's opened up to 14cc.

If something is worth doing, it's worth doing half of.

id got my cast omegas machined out to 15cc richard ,theyve put up with a lot of abuse .

the 240 lbs springs are probalby what has wrecked the cam ,im running 180lbs up to 7200 no probs .

the mg cam seems to work well for little money . you could try it withn and without the 1.5's to see what you prefer .

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

You'll probably find that the 10cc cast Omegas sit about 40 thou down the bore on a standard block, so they give about 14cc generally.

Edited by Turbo Phil on 6th Sep, 2010.

WWW.TURBO-MINI.COM

Cheers guys.

Looks like there's some positive driveability reasons to go for an MG cam on 180 lb springs and pressed 1.27 rockers and then possibly change to the 1.5 forged as you've said Robert, to see what effect this has at a later date maybe.

As for pistons, Adam has a new set of 10 cc cast Omega's in the for sale area which I'm interested in but I'm not sure how far they'd come down the bore as I know my block deck has been skimmed but do not know how much by.

I'll need to measure where the current pistons come to from the deck but from what I can recall last night, it left the 8cc pistons about +.020 down which isn't enough for Adam's pistons which I'll need to get machined.

I'll need to make a decison on Adams 10cc pistons or a new set of 14cc Accralites as you suggest John.

Thanks for the help chaps.

Richard.

Minivanless, but reluctantly happy living with the decision. There'll be another one day.
http://www.youtube.com/profile?user=minimadmotorman#p/u

What about putting another couple of cc's in the cylinder head?

Edited by John on 6th Sep, 2010.

If something is worth doing, it's worth doing half of.

Minivanless, but reluctantly happy living with the decision. There'll be another one day.
http://www.youtube.com/profile?user=minimadmotorman#p/u

I would question the variance in ratios and the chances of you finding such a high ratio pressed steel rocker is probibly slim.

Don't think the mg cam is reduced as a drivable type, the phase two is just as drivable:
mg cam make more power before 4500 rpm, the phase 2 start to overtake it after, an 1.5 ramp on the mg will about equal a phase 2 with a trade under 4000 rpm.

The phase two is only a must have when you are using a bag of boost, his long exhaust timing help the lot of these exhaust gas outing, it is when the lost of power stroke (caused by a too early exhaust opening) is compensated by the lessening of power rob of exhaust gas thru this tiny exhaut valve.This also help to spool big turbines as there is more energy left in this exhaust gas charge, the mg cam bit this everywhere else (if only we had a larger exhaust valve.....32mm )

piston choice is depending of your boost target up to 12 psi engine dependant, the 10cc .02 down the bore and a cleaned head will go very well.
above and a nice set of forged bowls will be better, then you can work on your head heigh to compensate (this also decrease valve shroud and is very good,also allowing you to deck your pistons which is also very good combustion/detonation wise.
Then with a mgcam a set of std turbo springs will be enough to keep al this together.

fa&b

Why not utilise a cimetic headgasket or solid copper both reliable and widely used and a dmned sight cheaper than a set of pistons.

You can remove a fair fit of material from the chamber roof if you want to keep the chamber shape.

Own the day

he still needs to buy pistons as one has a hole in it...

Minivanless, but reluctantly happy living with the decision. There'll be another one day.
http://www.youtube.com/profile?user=minimadmotorman#p/u

Minivanless, but reluctantly happy living with the decision. There'll be another one day.
http://www.youtube.com/profile?user=minimadmotorman#p/u

You may be right with the 1.25:1 Richard. I believe Cooper S rockers were supposedly 1.27:1 but rarely achieved it.

All I can say is give it a go. You've seen the vids of our van on the strip with the MG Cam and pressed rockers.

I can also tell you it drives nicely on the road and still pulls to 6k+ with ease.

If something is worth doing, it's worth doing half of.

Edited by turbominivanman on 7th Sep, 2010.

Minivanless, but reluctantly happy living with the decision. There'll be another one day.
http://www.youtube.com/profile?user=minimadmotorman#p/u

it's around 8.4:1.

It's very drivable, but bearing mind the intercooler is half covered by the front panel and slam panel. It's probably only got a window of about 20cm x 15cm expossed to airflow...

It's actually nearer 8.15:1

If something is worth doing, it's worth doing half of.

though an mg cam with 1.27 (inno/1275gt rocks), will also just overtake a lot of thing on the road including subs/integras,
that start to open the can of worms.
I remember an cayman s driver just looking at his radio when we stopped at the red light ! Then we're just talking about 5/7 bhp against a phase2/mg and 1.5's. My aim as of today would to have a set of 1.3's titans...

Every day is a school day!

If something is worth doing, it's worth doing half of.

The first turbo motor that I built had a mg cam and 1.5:1 rockers, I ran turbo pistons machined with a bigger dish and a de beaked head. Im sure it was around 8.5:1. On 15psi it was a flyer and my favourite engine that I have built to drive on the road! Im sure it ran a low 14 up the strip as well!