1362cc Turbo using 73mm Pistons
Turbo Mini Forums

Hi guys,

I have been thinking for absolutely ages now regarding the engine size i can stretch to on a turbo application. I already started a topic on the possibility of a 1430cc Turbo but that proved not to be such a great idea!

Obviously with a 1430 getting the compression ratio down would be difficult but my main concern was the wall thickness of cylinders if it was bored using 73.5mm pistons. I don't know how much strain it could take with such thin walls so i dont really want to risk it!

Then, i thought to myself, whats stopping me from achieving a large engine size by another means....using a stroked crankshaft?? this wouldn't affect the wall thickness of the bores at all therefore may prove to be a good way of having a bigger turbo engine? Would this work?? I just wondered why i haven't seen any stroked turbo engines before? is there a reason for this??

i have also come across these new 73mm EVO pistons and other similar 73mm pistons sold by a variety of companies. Does anyone have any experience with these??? they have an 11cc dish....is this big enough for a turbo application? It would take the engine to 1362cc, which is near enough a 1380cc engine but using smaller pistons and thus retaining strong bore walls. I'm going to be running high boost (20 psi) on this engine from time to time so want it to be very strong.

Also, if i combined these 73mm pistons with an 84.3mm stroked crankshaft from MED, what engine size would this give me???

Any help would be greatly appreciated,

Cheers,

Mike

oh and here is a link to the pistons:

http://www.7ent.com/detail.cfm?pageid=3166

You would get a 1411.32cc engine.

However I reckon that even with 30cc in the cylinder head you will struggle to get the compression down to around 8.5:1 depending on the deck height.

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

thanks for the reply!

Is there a way of calculating what the compression ratio would be with different combinations of pistons, deck height, combustion chambers, stroke etc???? Then i would know if its feasable or not

also how did you work out the engine size then??? i could play around with different combinations if i knew how to work it out..

i want to be able to work out how big it would be with the 73mm pistons and 82.3mm Crankshaft?

Cheers

Try this.

http://www.afracing.co.uk/CR.xls

My opinion if you are wanting a large capacity turbo is just jump in for a standard stroke 1380 using 18cc Accralites.

Edited by John on 15th Jul, 2009.

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

try this

http://www.afracing.co.uk/CR.xls

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

IMHO from my reading on here, it seems that the main failures have been pistons and head gaskets rather than the blocks.

heard of cranks breaking.

Own the day

cheers, but does anyone know if those 1362cc 73mm pistons can take the strain??? it will be running nitrous too! and what is +20, +40 and +60 thou in millimetres??? that program on excel needs the piston bore in "mm" and i can't work it out for a 1293????

cheers

Its listed over to the right hand side of the spreadsheet.

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

you're loosing your time in dreams,
put together a well built 1293/1310/1380engine with turbo mind designed piston (mine is a 1275 ), a good head on top of that,
then concentrate on turbocharging,ntercooling, the power is here, not on capacity.
Fab

Edited by fab on 15th Jul, 2009.

Personally, I have an irrational fear of going large overbore and doing all the fancy things you do to a block (centre main strap, general machining etc) then not having enough meat left for another rebore in the future. You'd have to start from scratch on a new block, that's what put me off going 1380.

Could always slap some liners in there.

I know, but that's more cost. Just another thing to consider.

Very true, and then to be fair you'd be going backwards, so might aswell start small and get bigger.

then why do bigger engines produce far more power on a N/A application?? Surely turbocharging a bigger (and more powerful) engine in the first place would allow you to extract more power from further turbocharging and intercooling???

the idea is to put together a well built engine anyway, so this is why i'm spending a lot of time deciding on the engine size! i don't want an average turbo engine, i want to go as powerful as possible thus why i'm interested in larger engine sizes.

thanks for the replies

If you want to go big capacity then do it. However I know of three proven 200bhp+ engines and if I'm not mistaken all are 1293cc. There is no comparison to NA engines.

N/A engines with bigger power, hit huge rpm, have wild cams etc

On the other hand turbo charged engines use lower revs, with mild cams, as the turbo comes on boost ealy on with in the rev range.

You can't directly compare the two engines as they both achieve their power outputs in different manners.

Also if you think about it in simplistic terms, if you take a bog standard 1275 engine and overbore it to 1380, and apart from that leave it standard, the power increase will be extremely small.

Its not just a case of more cc's means bigger bhp or torque, its a combination of specific components working together... this is what produces the results.

WWW.TURBO-MINI.COM

REALLY!?

fuckers.... i was going to get a set next year.

Apparantly so. Accralite quoted £155 per piston +VAT to make some one offs, & Avonbar don't stock them anymore.

WWW.TURBO-MINI.COM

uhh i just got a set of 73.5mm 18cc's from avonbar. they may still have a few about :p

WWW.TURBO-MINI.COM

Go direct to Accrlite. You'll get them acheeper. John had a set of them a few months a go.