There wasnt much talk of head gaskets...

is a copper gasket a replacement for the normal head gasket or is it just a spacer for lower compression and still requires head gaskets either side?

what other options are there if any?

Copper head gaskets are an alternative type of gasket, They are commonly used in conjunction with O rings.

A head gasket shim [spacer] is readily available from ACL, not many dollars either. From memory there is a couple of sizes [thickness] available.

Permaseal also make spacers, or "head saver shims" as they call them. They're actually intended for use when the head has had the bejesus machined out of it, and the CR has gone too high. I believe they are available in .75, and 1.5mm.
The upside for folk like us is, we can lower our CR's without a full motor teardown.
Have you ever lowered the CR of any of your motors? Too high a CR will be the kiss of death for a forced motor.
HOWEVER, the bloke who does my boring/honing etc has advised me that too low a deck height, can actually promote detonation!

I read a thread ages ago at a mopar site, where they were discussing minimum piston to head clearance. The general consensus was that the tighter the squish, (And therefore the higher the CR) the less likely a motor was to ping.
Of coarse a forced motor is a bit different.
If I could afford forgies I'd run them at zero deck, with a nice dished out bowl to keep the CR down. Take a look at datsun100A racer's photo of the pistons he hand machined out so the dish was offset to be under a closed chamber head.
On my latest engine I increased the dish in my pistons,( larger diameter dish, not alot deeper. And still kept the squish band around the periphery) and used a head saver shim. I never actually measured my CR, but the static comp is around 130psi.
As far as I can tell, (The zhorst is a bit loud) I don't have any detonation.
If you're building a new motor, I'd dish the pistons, and O-ring the block.

"mainly promoted a mind set, a way to work through problems and try to understand em"


I spose that was point in a way..originally although I lacked the verbal elagance to say it! its why I got annoyed with you asking the questions.

You've learnt how to work through problems...and here you were/are asking questions which you should have some idea how to solve!!

As for dishing pistons (A14force) wouldn't this weaken the piston??? take a piston from an atmo car, dish it, boost the engine....sounds like trouble????

surely head shim savers or a copper head gasket would be the way to go. a copper gasket might cost
around $150 so its not that expensive????

I've got an article on making a knock indicator (zoom mag) costs about $50 to make plus cost of knock sensor. If your keen can send you a copy.

Quote:

Corky Bell makes this comment in his book about supercharging...

But plenty of people use these shims and report good results.

I would be interested to hear about detonation problems from people who have used A14 cranks in A15 blocks to decrease compression (with the pistons many mm below deck) and the pulsar ET piston deck height and detonation characteristics.

im interested in the head shims...
do they completly replace the headgasket???
or do they work like a decompression plate needing a headgasket on both sides??
a mate who is running a a14turbo with et pulsar pistons(modified dish) recently cracked them on 12psi with an excellent tune.....
we later found out the pin let go and that caused it to crack.
he is now temporarily running his tubo setup on a dead stock a12 @ 8psi.. it has been alive for 3 weeks now and is starting to get very smokey under boost..
i wonder how much longer it will last.

Quote: Thats one hell of a statement. 1 bar of boost [all day, every day], stock pistons, no 'O' rings, as it isn't going to be serious. [15psi in an A series not serious ]

First thing, ... homework.

What kind of pistons do other engines that run 1 bar of boost use? What kind of rings do they use as well?
What about their head gasket design, is it significantly different around the fire ring than an A series gasket?

At the very least, I think that hypereutectic pistons would be needed [12% silicon content or more] if such things exist, while stock Datsun pistons are very likely to be of the money saving hypoeutectic type [less than 12% silicon content]
Hypoeutectic are just fine in low stress stock Datsun engines, but aren't real happy as the boost [& heat] start to rise.

Ignition timing seems to be critical & you need to be able to retard the spark more & more as the boost rises, & water injection is one of those things that helps to keep detonation under control. Think about it.

Personally, I would build the engine & run it at about 7psi for a while. Run it in at this lower figure.

Once you have it sorted, push it to about 10 psi & make sure there is no detonation. After that, it's up to you, but that would probably see the conservative little-old-me out. I like engines that live long [& prosper]

1200rallyman, the psi you run isn't as important as the volume you flow. A turbo off a 1 litre charade at 15psi isn't going to be anywhere near as good as a T3 at 7 psi. I run an A14 with a 3mm decompression plate. 7 psi boost with a T3 spec turbo. I drive it reasonably ( I still run a 56series box!) Don't know what pistons are in it, but it seems to go ok.

there have been a few very well made points that should steer you in the right direction. i tend to think that a hone and some stock rings and stock pistons will be fine, but its your tune and turbo system itself that need attention. When i look at the size of those little fellas and then hear 14 psi it just HAS to equal heat. detonation is nobody's friend.

for example the bloke who built my CA is a cylinder head specialist and engine builder. The first motor he ever built and still has is a STANDARD gemini motor bored out to accept VL turbo CAST (non forged) pistons. He runs a massive turbo (800hp roller), 38 psi (in the turbo's efficiency range, not producing undue heat) and nitrous oxide (as its an auto) and runs 10.5 quarter mile times. how?

its tuned properly (microtech)

the turbo flows massive amounts of air, but still produces it efficiently enough for a front mount intercooler to keep in check

it has enough fuel.

topgear has proven that with a well tuned setup, forged pistons fancy rings and decompression theories are all out the window as long as you don't overrun your turbo(s) and your motor is not detonating. a freshen up will be sufficient, investing in a more tunable ECU and sorting out your turbo's proper efficiency range will be your key to boosting bliss

Absolutely right on the money Lagwagon.
1200RC for Gods sake throw those stupid little windmills away and do it once and do it right.
If the setups good it will still go very hard at 8lbs boost without having to wind up to 1 bar. In fact I was always led to believe that 14 lbs was really IT for cast pistons.
FYI my A14 powered B110 set up 14 years ago ran a quarter mile in 14.3 on 8 lbs and the supercharger 1 ran 14.6, again on 8 lbs- all this on a standard engine that was driven daily.
You have been told.....