Increasing Bore Size

[Chris Green]

As some of you may know, my engine needs to come out again, while I'm doing this, I want to increase the bore size.

Question time

1) Has anyone done this before?

2) What is a safe increase in mm?

3) What pistons were used?

4) Any further cooling upgrades required?

Thanks in advance

Edited May 9, 2013 by chrisgreen1993

[Jamie_VF22]

Yes mate many people do it when they go forged engine

Most people go for 74.5mm pal

I use Wossner forged pistons mate

Edited May 9, 2013 by Jamie_VF22

[AdamB]

You can increase the bore size but you'll need to use oversized pistons. Ie forged pistons as Jamie said.

There is a limit on how much you can hone the stock cylinders before a rebore to oversized pistons is needed but don't have it to hand atm.

You won't need any cooling upgrades, but proper maintenence of the cooling system is paramount.

Edit:

The largest bore size you can go to without having to rebore to suit oversize is 74.030mm.

The largest OEM piston size is 73.93mm.

Edited May 9, 2013 by AdamB

[morgey]

Dont toyota do oversized pistons? Im sure they do for 4ages. :/ might have a quick google about...

Yeah toyota do oversize pistons for 4age's so surely they would for 4e's?

Edited May 9, 2013 by morgey

[russ78]

for what you would pay for oversized Toyota pistons better off with forged ones for around the same price its a bit of a no brainer

[AdamB]

They do 3 sizes :

Size 1 - 73.91mm

Size 2 - 73.92mm

Size 3- 73.93mm

[morgey]

True but i think he's running a 5efe, find some forged n/a pistons lol

Edited May 9, 2013 by morgey

[morgey]

They do 3 sizes :

Size 1 - 73.91mm

Size 2 - 73.92mm

Size 3- 73.93mm

When i say oversize i mean 81mm stock an 81.5mm oversize. Like after a rebore piston. Do they not do this for 4efe's?

[morgey]

Not from toyota and not all that cheap buuuut....

http://www.precisionintl.com/Stock.aspx?Code=PTO4E40202E&EID=4356

Oversized 4efe pistons. Measurements are in imperial 0.020" is .5mm you can also get 0.040" or 1mm oversized from there

[AdamB]

When i say oversize i mean 81mm stock an 81.5mm oversize. Like after a rebore piston. Do they not do this for 4efe's?

Not OEM Toyota mate.

Think them pistons are pretty cheap but, but I not sure I would trust them.

[Chris Green]

Thanks for the input guys. Ive hear of people using Vitara pistons 75.5mm.

I couldn't go forged as that would lower the compression.

[morgey]

Vitara pistons are used on boosted engines as they handle it well. Also 75.5 is right on the limit of the block!

[AdamB]

I personally wouldn't opt to use that size piston. It wouldn't take much to buckle between the cylinders. Unless you spent a bit of money and ran a closed deck block to strengthen it.

[Taggy]

I think the point is why do you want to increase the bore size, is it because your bores are damaged already so you have to have a rebore to clean them up, or are you doing it just for a performance point of view?

Only wanted to check as the HP difference will be virtually nothing if your bore the block out to its limit and put oversize pistons in, the actual displacement increase is so small your barely adding anything. Unless your engine needs its because its scored, i would save your money and just put the same size pistons back in, use your money on other areas will be much easier/cheaper to get more performance i.e a good tune/map .

Someone did work it out before on TGTT, i think going to 75mm adds like 30cc or something with dished pistons lol its not much!

Edited May 9, 2013 by Taggy

[Chris Green]

I haven't checked if the block needs re-bored, by the looks of things there isn't much point getting it rebored.

I'll just re-hone the bores when doing the rings and spend the money else where.

Thanks again for the input guys.