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Home > Technical Chat > turbo and piston questions

Lsurt95

3 Posts
Member #: 10943
Junior Member

So after months of toying with the idea of a supercharger I have finally decided to go turbo since the car will be used regularly and will be driven long distance to shows and i really dont fancy 25mpg everywhere.

So my question is, would AE 21251 pistons be suitable for a low boost build? And if so what sort of power would they withstand?

Im wanting to use one of fusion fabrications gt1752 manifold with a freshly machined 1293 gt engine with a GT close ratio box. The plan is to have about 120bhp. Can any advise anything to make a nice reliable engine?

Liam


TurboDave16V
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***16***

SouthPark, Colorado

Reliability is hard to quantify really; but doing certain things like on the undercrown cooling jets definitely will make a difference in the longevity of pistons; especially those at the cheaper end of the market.
I would totally recommend to install a wideband O2 sensor, a clean burning fuel mixture will definitely increase reliability over something running lean or excessively rich...

On 17th Nov, 2014 Tom Fenton said:
Sorry to say My Herpes are no better


Ready to feel Ancient ??? This is 26 years old as of 2022 https://youtu.be/YQQokcoOzeY



Lsurt95

3 Posts
Member #: 10943
Junior Member

Hi thank you for the reply.

I didnt think the A series had anything like cooling jets? Or is this a straight forward modification?

I was planning on getting a wideband sensor as I know bore wash will ruin a fresh engine very quickly.

Liam


Rob Gavin

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6729 Posts
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Glasgow

there is a thread somewhere for installation of the under crown jets. I think the current jet of choice is the bmw one (or 4 to be precise!)


Yo-Han

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North of the Netherlands

From what I have seen posted earlier the 21521 pistons are not that suitable for boosted applications...
Not sure how much undercrown cooling will help though..

Dazed and Confused....


stevieturbo

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Northern Ireland

Unless you're making a lot of power and for long duration then oil jets really are not needed.

In general yes they are nice to have...but when you consider how uncommon they are on day to day cars, it just highlights they are not essential.

But the more power you make and even more so if you were racing it etc...then if you can do them then yes they will help.

The biggest weak link for a turbo piston is if there is a large slot behind the oil control ring. That is the last design you'd want to use.

Always use a piston with oil drillings behind the ring

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will


tadge44

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Buckinghamshire

As said many times before on here the standard Metro turbo piston is pretty good and will stand a lot of abuse.


minimole23

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Wiltshire

I would save the under crown cooling jets unless taking to the track and just use a decent set of omega pistons. Given the cost of preparing a block 100 quid extra for the pistons will have little impact on the overall budget but be a fit and forget option.

On 7th Oct, 2010 5haneJ said:
yeah I gave it all a good prodding


stevieturbo

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Northern Ireland




On 25th Mar, 2017 tadge44 said:
As said many times before on here the standard Metro turbo piston is pretty good and will stand a lot of abuse.


Yep, they might be big and ugly...but they're very robust !

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will


Lsurt95

3 Posts
Member #: 10943
Junior Member

Okay guys it looks like better pistons are on the list haha. Thanks for everyones input im sure ill be asking alot more as the build goes on :)


Vegard

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21251 are the worst aftermarket pistons out there.

On 13th Jul, 2012 Ben H said:
Mine gets in the way a bit, but only when it is up. If it is down it does not cause a problem.



JT

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Hertfordshire

I've always thought you get enough oil splashing up from the gearbox to not warrant under crown jets?

My build thread..

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=542985


stevieturbo

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Northern Ireland




On 26th Mar, 2017 JT said:
I've always thought you get enough oil splashing up from the gearbox to not warrant under crown jets?


Again depends on the application.

For low powered and light-moderate use builds...then they are in no way needed at all.

For something pushing very hard, or that sees track use etc, then they can be useful. Or perhaps setups with fuel/charge cooling limitations where combustion temps might be higher for those reasons.

Ultimately they are a piston cooling feature, although the huge chunky mini pistons would absorb a fair bit of heat anyway, and the big skirts should also allow it to dissipate well even without oil jets.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will


Joe C

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Carlos Fandango

Burnham-on-Crouch, Essex

bare in mind that the box will only really throw oil up at bores 2,3 & 4, plus the crank is in the way, and the oil can have a few bits in from the box,



On 26th Mar, 2017 JT said:
I've always thought you get enough oil splashing up from the gearbox to not warrant under crown jets?

On 28th Aug, 2011 Kean said:
At the risk of being sigged...

Joe, do you have a photo of your tool?



http://www.turbominis.co.uk/forums/index.p...9064&lastpost=1

https://joe1977.imgbb.com/



stevieturbo

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Northern Ireland




On 29th Mar, 2017 Joe C said:
bare in mind that the box will only really throw oil up at bores 2,3 & 4, plus the crank is in the way, and the oil can have a few bits in from the box,



On 26th Mar, 2017 JT said:
I've always thought you get enough oil splashing up from the gearbox to not warrant under crown jets?


But oil will always be splashing from the rod journal for each cylinder.

I've seen some rods and people modify some rods wit a little cut on the side face which they claim can allow some oil from the journal to make it's way to the piston underside too.

Either way, no big deal.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

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