would a bore of 3mm really make a difference? I was talking to someone who said a bore of 3mm would make it a 1500.45cc motor... is this correct? If it is, it barely sounds worth the trouble

Quote:

My figures tell me the 3mm overbore gives the A15 a 1608cc displacement.

how you figure that out? cause that sounds about right but im obviously doing something wrong.

PixR squared x stroke xnumber of cylinders.

BlownB310 looks to have it. My quackalator calls it 1607.74774cc. Thats close enough to 1608cc for me.

I use the formula... Radius squared x Pi x stroke x No. of cylinders divided by 1000.
All measurements in millimetres mean that the second last number is the displacement in cubic millimetres. Dividing by 1000 converts it to cubic centimetres.

With an original A15 displacement of 1488cc, the 3mm overbore will give you another 120cc, & thats an 8% increase. Is that enough to be worth it?

The 4mm bore job [to 77mm] with 77mm stroke in an A12 block yeilds a 22.5% increase. Thats not too bad when you remember that it's all stock parts with a small amount of lathe work on the crank being the only real modification.

So you use a lathe to make the crank fit, not just hack at it with a grinder?

i reckon ud have to use a lathe so its all smooth but what hapens with blanacing?

How much does it roughly cost to get it bored 3mm oversized to 79mm in Australia.

Any one done it in Australia? What pistons are people then using then for this rebore eg. car make, model and year and what pin mods and bore size to the conrod for the piston they used?

What was the comparisons on piston to deck height between standard A15 and mod A15 bored to 1608cc and pistons used?

How much of a performance gain did it give and how noticeable was it, what characteristics eg. torque-rpm?

This is also other important info needed if possible please as myself and others are interested in this mod.
Cheers

The capacity increase would be hardly worth it. If you are going to use forced induction I would advise against it. You are just asking for trouble. How much power is an A-series cabable of Handling? The more material you take away the weaker it becomes. It also makes the block a lot more expensive on the next rebuild if you need to sleeve it.

I don't know what it would cost to have a block bored in Australia, but I can tell you what parts to use for this modification. I first heard about it from a Yahoo 210 club message board post from a member named Carlos, from Costa Rica. He said they race the 1608 combination there, built with 79mm Subaru Justy pistons with A10 rods. I sourced four 79mm [1mm oversize] Subaru Justy pistons from my local Subaru dealer [remember: the Justy is a three cylinder engine- so I had to order four pistons and two three-cylinder ring sets]. Eddie Rattley was nice enought to sell me an NOS set of A10 rods, which I sent to my machine shop to have the small end bored and bronzed bushed to the Subaru's 18mm wrist pin. It turns out, that was all wrong, because upon the test assembly, the A10 rods were way too short. My fault, I shouldn't have taken Carlos' word for it about needing A10 rods for this combination. In any case the original A15 rods are all you need. I had them bronze bushed from their 19mm size down to the 18mm Subie size. Additionally, the small end of the rod needs to be narrowed as well, to fit properly in the Justy piston. We narrowed them on a surface grinder as shown:




After narrowing the rods looked like this:




When I put it together, the piston crowns were .070" below the deck at TDC. I then had the block decked .065". I haven't yet determined final compression ratio, but I am using the open chambered "H72" oval port head, so it will be around 10.25 to 1. Here's what the piston crown looks like. The Justy is a 3 valve per cylinder engine, hence the three valve reliefs:



In any case, there are advantages to boring these engines out 3mm. It is common knowledge that the larger the bore, the better a given cylinder head will flow. Boring an engine will also slightly raise the compression ratio as well. The downsides are that the engine may run a bit hotter. Personally, I wouldn't worry about needing to sleeve the block on its next rebuild. The A14's and A15's are easy to find here in the US for scrap prices.