piston size

[sub555]

whats the biggest piston size that you can use in a Q4 engine walkers only do a .4 oversize :? :?

[Brul(tm)]

I really don't know. It's funny you started this topic, today at the TT motor cycle track in Assen, the Netherlands i had a discussion about oversized pistons with a view Q4 quys (and former drivers). The discussion was about the 2.2 conversion and if a 2.4 conversion even excists. Nobody knew for sure.
So we didn't get any further.

Greetings,
Marc

[arjunior45]

I believe I saw somewhere the 0.6 oversize but I do not remember where.
Gozzoli {www.gozzoli.it} in Italy has even a 85mm dia for the 16v Integrale.

Cheers

Nick

[sub555]

ive been speaking to someone about 5mm over size for mine so the engine will be a 2.5 im just waiting to hear if this can definatly be done safely and what mods are need to the head and fueling :wink:

[Juan AR155Q4]

Standar oversize are 84,4mm and 84,6mm.
I really don't thing that boring to 89mm (5mm) is factible. The wall between cylinders, would be really thin (if any is left). I'll check with my old head gasket wich is the separation between cylinders.
I don't think that overboring would be a good way to get a higher volume because cylinder walls would get weaker. May be changing stroke (with a change of crankshaft) would be the way...

[sub555]

but if you have a bigger cylinder capacity surely that meens more horse power for less work and the total material lost would only be 2.5mm circumfrence ive heard that for every mm in piston size you gain a min of 20bhp :shock: any ideas on this :?:

[arjunior45]

"overboring" from 84mm to 84.6mm gives you just + 0.6mm in circuference and if it's correct that each 1mm corresponds to 20bhp, you'll have just a {20x0.6=12} 12bhp of "more power"! But you could have the same power increase just increasing the turbo boost for a +0.1bar.
Overboring to {84+5=}89mm, even if this would be possible, will give you {5x20bhp=}100bhp? Joeri {see http://members.lycos.nl/joerifiles/building_300_hp%20page%201.htm } has "just" 300bhp and his engine in just one piece.

cheers

Nick

[Juan AR155Q4]

Having a bigger cylinder capacity gives you more torque but no more power (really is just a little more).
Here are some pics that would correspond to a similiar engine except cylinder capacity. No overboring, just with a bigger stroke.
The first one is power and the second it´s torque.
Sorry but I´ve it only in spanish.

http://img329.imageshack.us/img329/2655/16wk.jpg

http://img140.imageshack.us/img140/912/25xo.jpg

[sub555]

well after havin advice from various intergrale spealist i decided to get the 1mm over size pistons because they dont take to much material out of the block also there forged pistons whish should be alot better than standard :wink:

[arjunior45]

well after havin advice from various intergrale spealist i decided to get the 1mm over size pistons because they dont take to much material out of the block also there forged pistons whish should be alot better than standard :wink:

make sure that they are forget type so that to encrease the boost with no fear!

Cheers

Nick

[sub555]

8) 8) 8) :wink: