piston choice
Turbo Mini Forums

im currently in the process of collecting parts for a turbo engine. i was planning on buying the omega forged 18cc pistons but i was wondering if they might be a bit overkill for what i want? i plan on running 15psi with intercooler, phase 2 cam and standard mg head. so i suppose they have to withstand what, 140hp?? (or am i dreaming). will i get away with some cheaper pistons as at £420 they aint cheap.

thanks.

Loads of pistons that can take 140, but you get what you pay for suppose.

Back once again like a renegade master

i've been running on the same AE21253's for the past 3 years with no problems at all, simon machined them out to 11cc to help drop the CR.

And I have taken out 2 sets of Mega's cast pistons in the last year!

Total cost well over 500 quid, so 400 for the forged dont look so bad now!! I have now ordered some accralite forged from Avonbar. If you factor in the rebuild costs thats a cool thousand quid on pistons... Food for thought.

I have just done a quick search for piston failures on the site, all seem to be cast pistons....Wish I had thought of doing that a year ago...

Terry

website:- http://www.terryhunt.co.uk

ringland trouble IIRC.

Yup

Took the ring lands out both times. First one was explainable but the second time really worries me as the engine was not really out of tune as regards fuelling and advance. Though I was thrashing the ass off it at the time!! and BTW I heard NOTHING either time.

Before I run it again I am going over the engine with a jaundiced eye, my current suspicion is that the spark from MJ is not all it should be, I would expect to see a nice fat spark but it looked weedy last time I looked.

Terry

website:- http://www.terryhunt.co.uk

the Don has mega pistons , with eylets for the valves , so some pointy edges but no problems up to now,.
and well over 220 hp

carl

WWW.FORCE-RACING.CO.UK PLEASE CLICK HERE

you get what you pay for

Megas rule! I'm fitting them in my new engine aswell.

No doubt some people are having great results with mega's but an extra 150 quid or so for the Accralites... as was said you pays yer money..


Search TM and find a picture of a blown forged piston. --granted there are not as many out there but I cant find one


Now search for blown cast pistons (heres a starter for 5 sets)


http://www.turbominis.co.uk/forums/index.php?p=vt&tid=3623

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=175568

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=185154

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=161831

Edited by Turbo Tel on 29th Nov, 2007.

website:- http://www.terryhunt.co.uk

you have a valid point Tel

it seems the ring lands part company
usuall caused by incorrect fueling and ignition timing

i run acralites no bother todate
all the power the engine makes is ontop of the piston ..........................

Hopefully the Hypatec Pistons are going to prove them selves worthy of a good fight in my 1340! Granted i wont be running silly boosts like some of the guys on here, but the pistons and rings only cost me £90 plus import duties.

1/4 Mile 14.3secs 96Mph Terminal 10psi of boost.


Fibreglass Parts? - http://www.tdkracing.co.uk/
Split Rims? - http://www.force-racing.co.uk/

well tel i think my second set have gone the same way, this time i know its not over fueling as i have a afr gauge and the mega jolt has been on this engine all the time and i know that i spot on.

took her out for a spin today took her to 3500rpm then lifted of and yes what a suprise some nice blue smoke when depressing the throttle.

f@cking pistons wish i had gone acrillite the first time round.

always looking for them bigger bunches of bannanas

What pistons are you running hog?

1/4 Mile 14.3secs 96Mph Terminal 10psi of boost.


Fibreglass Parts? - http://www.tdkracing.co.uk/
Split Rims? - http://www.force-racing.co.uk/

Is it AE group who manufacture them, mabie a large box of scrapped pistons should be sent to them for analysis.

A lot of mega pistons seem to be going fuck at the moment, on this site anyway, I dont know elsewhere. Are they just being used outside the conditions they are designed for.

How many people have built engines with these in recent months that have actually survived. I think until this issue is sorted, or a reason for failure found, I will look for standard turbo pistons to build my engine.

Edited by minimole23 on 29th Nov, 2007.

mine were the mega turbo pistons times 2 sets, first set got sent off and they said it was loading from above eg to rich and to much ign.

what bugs me is my 1380 was running 9.8 and 9.4 cr with 10 and 12 psi max boost for ages, some times it was a bit rich and some times getting close to det, but did they ever fail NOPE.

i persoanly think these pistons aint that clever if they are to fragile then they may as well be binned before they get sold.

both mine went after 200 miles after rebuild so aint as if they were getting thrashed at all!!!!!!!!!!!!!!!!!!!!!!!.

also built quiet a few engines in my time and this is the first time i have had any trouble.

i no td and fast carl have used them with out any probs, but dave has had his for quiet a whilst so could be meterial problem.

how many people have used the minisport 4 pin diff before they found out they were crap.

always looking for them bigger bunches of bannanas

Yep - Mine are at least 5 years old - but I'm now sufficiently wary of the issues folks have had,,,

Someone (Tel?) questioned the accuraccy of Megasquirt/Jolt... I don't recall allan (first link above) having any more issues - but maybe he did?

There is one trait - that you guys (tel and hoggy) are using megawhatever. Sounds blatantly obvious, but a quick check with a decent timing gun on a known tdc might be judicious? Is the thing pulling out all the advance as the boost comes in for example??? It m ight say it is on the screen - but doing it is another?

This is still somewhat concerning however - I guess proof is in the pudding. If Tel and hoggy both build engines using the Avonbar pistons and don't have any more issues (without changing anything else) then that is the best proof of all.

Spending $800 on a set of pistons is still going to make me wince however LOL!

Edited by turbodave16v on 29th Nov, 2007.

oh - If i was Tel - I'd be teaming up with hoggy and sending all the failed pistons to whoever it is that supplies them to minispares...

If this is a problem, they need to know about it.

well i did get it checked on the rollers and the mega was 2deg more retarted than the fig eg mega running 26 actual was 24.

i think i will get miniwilliams put in my next set as they will be accrilites


atleast i can then blame him lol.

always looking for them bigger bunches of bannanas

But if it was another fault causing the failures (it probably isn't, it's a quiet change in piston material by the sounds of it) then the (more durable) accralites might just survive better making it look like the prob is the megas.

Jeeze Hoggy sorry to hear that... But I have to say that it makes me feel a bit better...maybe I didn't miss something after all. Did you hear any detonation?? I didn't.

Like you I cannot explain the failure, 24 degree advance, AFR at 12.5-13 full throttle, 9:1 CR and no leanouts or rich areas at any point of driving. What concerns me is that the top of the piston looked black, if anything rich, My latest thought is that I have a weak spark which is causing incomplete combustion so giving false leans... When I first tested the Megajolt before starting the engine for the first time I must say I was not impressed with the spark but as the engine ran fine never followed it up... I will this time!

And also only got a few hundred miles on each set..


Talking to Ian Avonbar, he said no Accralites have cracked a land as yet.. and after reading how RED850 pushed a likely lean engine and get away with it scott free I was convinced to go for the Accralites.

website:- http://www.terryhunt.co.uk

Tel - what coil pack are you running?

so basicly i should be safe with the forged omega ones.

EDIS is crap, lol. I supose its better than the dizzy though

Mega pistons are manufactured by AE, they come in an AE box and have AE stamped on the crown.

Detonation is the killer! and with the Megajolt, how many people have actualy had the igntion fully mapped on the dyno. Any engine suffers det limitation in some conditions where the advance needs backing off some what to prevent det in any atmospheric conditions likely to be experienced. Most of the map however should be tuned for MBT (Minimum advance for Best Torque) where there is a reasonably large band of ignition advance where no more torque is yielded, but det does not occur. High RPM detonation is difficult to hear without some sort of hearing device, and is extremely destructive.

You can reasonably get away with rule of thumb ignition advance figures in most of the map and fall within this MBT-Det band. The problem arises when there is an area of the map that is Det limited (low RPM high boost). Setting ignition advance to close to the det limit in cold atmosheric conditions is asking for trouble when these conditions change for warmer conditions

With tuned turbo engines and 'DIY' mappable ignition systems, i would be very cautious with ignition figures, until it was on the dyno being properly mapped, this also requires some way of detecting knock to find any areas of det limitation, the rest of the map is tuned so that when any more advance is applied it does not yield an improvement in torque figures

I agree that all the failed pistons should be analysed for failure modes, but you know that, from a manufacturers point of view, what the answer will be, so i would then say it would be better for an un biased, independant analysis to be done, but that will cost money. What about a university, maybe they could do this for free at the same time give the students something worth while to work on?

Edited by Sprocket on 30th Nov, 2007.