If going to 79mm diameter pistons does the block need to be offset bored ?

no need usually for offset boring but walls could be porous from rust as is usually the case with some older A series donks. Im not sure what the prices are in Thailand Thai frog but I would say not so high that I would sleeve for 81mm and grout the bottom end up to the welsch plugs.

mmm interesting... whats involved in going to 81mm ?
The machine shop in my town is good at general rebores etc and spend most of their time sorting out truck and tractor engines..
They put liners in quite regularly and have a large stock.
There is also a guy in Bangkok that makes custom headgaskets....

could use this piston ? from a mitsubishi...

81mm pistons with 82mm A15 crank makes it 1690cc
i have a spare block if it goes wrong.....

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That is actually the piston I had in mind
HG could use reworked jp performance 80mm but Id rather
use custom hg with your needs with O-ring.
Lemonhead went to 82mm with liners just have
to make sure you grout the bottom end to have
better rigidity to suit rpm.

On further research I remember there were some audi/volkswagen 140kw and over engines using an 81mm flat top of CP 30.17 mm, which can be taken down to 28.5, 29, 29.5 depending on your deck height.

http://www.ebay.co.uk/itm/AUDI-VW-SKO ... AQD-ATX-BBG-/301445227459

http://www.ebay.com/itm/Audi-A4-TT-Qu ... :wUgAAOSwgQ9VnCJt&vxp=mtr

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  audi vw slugs.GIF (19.91 KB)

Hi D,
Thanks for your advice, but after a long think and based on my relative inexperiance (i have only rebuilt one engine before) i have decided on the following plan.

I have an A14 running nicely, but hanker after more power and torque.
I have an A15 stripped down in box's and a H89 head.
I have a Camtech 621 cam ready to be used and a set of A12T carbs.

Car is for the road, not drag racing or motorsports.

I would like to keep the same A14 block as it reduces the aggravation of changing documents.

Option 1. Strip down A14 and insert A15 crank/conrods/pistons together with new rings and bearings. Use new camshaft and twin carbs and gasket match to the H89 head.
This is the cheapest option and will give me some good power gains . However only possible if the A15 pistons are the same diameter as the ones in my A14 now (the A14 ones may be oversized from the last rebore.)

Option 2, If the A14 pistons currently in use are bigger than the A15 ones, then go for the 79mm option as i would have to buy new pistons anyway.


Filing the block with cement is a bit advanced for me at the moment and keeping it cool is also a worry ...

grout filling has no cooling issues as the top of the bores pistons is where all the heat is. Tk from PForums an experienced well known builder fills most of the high HP holden v8s he builds with over 500hp for the street and track and mostly all have cast iron heads with no cooling issues.

81mm is a breeze for the engine shop for an A14 with A15 crank rods and vw slugs. The cement filling is not really cement but a 2 pack polymer that matches the cast iron properties for heat dissipation and other factors.

Unfortunately a 1690 cc engine will make about the same peak power as an A14 with the same cylinder head. To make more power it will either need a higher flowing head, or to rev higher (different camshaft, intake & exhaust).

But it will make considerably more low-rpm HP (torque).

* 90HP: A14 with Camtech 621, H89 head, and Hitachi Twin Carbs, should make peak HP at 6800 rpm
* 90HP: A17 with Camtech 621, H89 head, and Hitachi Twin Carbs, perhaps will make peak HP from 6000 rpm.

Rear-wheel HP will be lower than the engine dyno figures estimated above.

Yes understand.
After the carb has been replaced with the twin hitachi's the cyl head becomes the bottleneck and increasing engine capacity will only move the peak torque/power further to the left due to the maximum gas flow being reached at a lower RPM.

The camtech 621 spec says:

Fair idle, good bottom end
and mid range power designed for engines with limited modifications. Min 9:1 comp ratio.
RPM RANGE 2600-6800

So if i end up just using the A15 parts or going to the A16 then i should still be getting a nice streetable engine with power for overtaking?
I tried a top speed test a few weeks ago, the fastest i could get was 146kmh (frogeyes are not very aerodynamic) but i found it faster in 4th gear , putting it in 5th lowered the revs to the point where there wasnt enough power to continue accelerating.

Also last weekend i got out dragged by an isuzu diesel pickup... very embarrassing..

I should be able to get on this in about 2 weeks time, once built and run in i can get it on the dyno and compare with my current engines figures....

Edit: another question for you more experianced guys... will it be nescessary to degree the cam ? or just use the standard set-up ?

did you lose to the diesel isuzu with the mini engine? even a peppy A13 with good induction, comp, pipes and mild cam will scream more than most women out of control. Capacity even with a max flowing A15 head with the right cam will make sure you have drive-ability than just peak and nothing below.

I had a 1608cc highly cammed A15 that was way more enjoyable with detuned gx style grind, high comp and alot of other go fast bits and mods. The thing would punch hard in any gear as opposed to race cammed pig of a thing. Capacity allows you to run more aggressive cams but at more enjoyable rpm for a daily. Also help with top speed as torque is fatter lower for more of the mid range as well