Expanding cylinder capacity to lower compression?

[ErbieG]

I'd just like to say Hi to everyone, and it's nice to meet you

I'd like to know if rather then changing to lower compression pistons and short throw rods I could expand the cylinder capacity by way of using two head gaskets with a sheet of steel in between laser cut out with the same hole configuration as the gaskets would almost do the same thing?

I'd also have to change to longer bolts, which is a smaller matter but nothing to really worry about.

The reason for the idea is that I cannot find anyone in the UK with shorter rods and lower compression pistons for a mk1 golf. I'd also like to say the reason for this is so I can modify the engine to accept a turbo charger without having to do some major work to the engine. I'm also not looking for a 150% rise in compression just something around the 80% mark over the standard 60 odd %.

On another note, this ideas seems a bit out there but say if I added 10mm-12mm or even 25odd mm, this would push the 1.8cc engine up to nearer the 2.0litre or above, how far could I go with how much?

Thanks in advance

[TheEnd]

http://www.ferriday.co.uk/cnc/decompression_plates...

Just the people to sort you out.

[cptsideways]

Better get back to skool for some maths me thinks

Adding h/g height does not equal larger capacity, that is derived from bore & stroke only. Capacity into squish area = compression ratio & its a very fine balance to get it right.

Then you have the issue of standard parts not designed for boosted applications & melting things very quickly.

[ErbieG]

Cheers fellas,

You've been very helpful, I'm not a car nut by any chance so I'm really quite new to this

Thanks again

[anonymous-user]

Also be aware, that by increasing your headgasket thickness you are increasing the "squish" distance, that is the distance for how close the piston crown gets to the cylinder head. On a 2 valve engine which often have significant squish features in the head (4valves do to, but there is simple less room for them due to the extra valve area), if you increase this distance you can dramatically reduce the turbulence and mixing of the aircharge mixture. This as a result slows down the burn rate of that charge and leads to great heat loss to the combustion chamber and piston. And on a turbo engine, where you are burning much more fuel per cylinder, the last thing you want to do is have a greater proportion of that heat pushed into your combustion chamber walls etc !

[stevieturbo]

ErbieG said:

I'd just like to say Hi to everyone, and it's nice to meet you

I'd like to know if rather then changing to lower compression pistons and short throw rods I could expand the cylinder capacity by way of using two head gaskets with a sheet of steel in between laser cut out with the same hole configuration as the gaskets would almost do the same thing?

I'd also have to change to longer bolts, which is a smaller matter but nothing to really worry about.

The reason for the idea is that I cannot find anyone in the UK with shorter rods and lower compression pistons for a mk1 golf. I'd also like to say the reason for this is so I can modify the engine to accept a turbo charger without having to do some major work to the engine. I'm also not looking for a 150% rise in compression just something around the 80% mark over the standard 60 odd %.

On another note, this ideas seems a bit out there but say if I added 10mm-12mm or even 25odd mm, this would push the 1.8cc engine up to nearer the 2.0litre or above, how far could I go with how much?

Thanks in advance

Whilst using shorter rods would in effect reduce the CR. What a totally and utterly mental way of doing it !! I'm glad to hear nobody makes shorter rods !!

And given you can easily get pistons made to whatever size and spec you need, I think you just need to try harder.

And as with the shorter rods idea, using 2 head gaskets and a spacer would be an absolute last resort.

And can you explain what this means ?

[quote]I'm also not looking for a 150% rise in compression just something around the 80% mark over the standard 60 odd %.

You sound confused about raising or lowering the compression.

But much more importantly...what exactly are you trying to achieve with this build ?
With proper design and implementation, you could run low boost levels without changing the CR from standard.

Either way, your ideas seem to be making a straightforward process complicated.

[Marquis Rex]

Someone (previous owner] had a similiar idea with my car and this was the result


They used a spacer plate and two fel pro gaskets to make up a thickness of 3.81mm rather than the 1mm stock thickness

Mid cylinders were 'swapping spit'.

[stevieturbo]

Marquis Rex said:

Someone (previous owner] had a similiar idea with my car and this was the result


They used a spacer plate and two fel pro gaskets to make up a thickness of 3.81mm rather than the 1mm stock thickness

Mid cylinders were 'swapping spit'.

That's detonation damage. Not a fault of the head gasket.

[eliot]

How much boost do you intend to run? As stevie says, you should be able to creep up to around 8 psi if you take your time and tune correctly. However if you believe that adding gaskets will increase your engine size, then i feel you are probably best leavig the diy path alone.

[Marquis Rex]

stevieturbo said:

Marquis Rex said:

Someone (previous owner] had a similiar idea with my car and this was the result


They used a spacer plate and two fel pro gaskets to make up a thickness of 3.81mm rather than the 1mm stock thickness

Mid cylinders were 'swapping spit'.

That's detonation damage. Not a fault of the head gasket.

It was running a very low CR (8-9 :1) using racing 114 octane petrol so I'm not so sure. The pistons were carboned up with very little breaking of the carbon that you typically get with detonation

[stevieturbo]

If it wasnt detonation, then you'd need to have driven flat out for a very long time to erode the metal like that.

Detonation like a plasma torch will do it in a split second.

[tristancliffe]

2 head gaskets = 4 sealing faces that can fail. So you double (probably more than double) your chance of a head gasket failure.

Only consider it as an experiment, and then get pistons made with the new found compression ratio, and revert to a single head gasket.

[CNHSS1]

[quote=stevieturboWhilst using shorter rods would in effect reduce the CR. What a totally and utterly mental way of doing it !! .
[/quote]

i agree, but im sure thats what Noble did on the 2.5 and 3L versions of the ford Dura V6 when they strapped a pr of turbos to them. Im pretty sure they used std V6 pistons, but shorter ford parts bin rods, one of the Noble gurus will be a long in a mo to fill in the details

[stevieturbo]

CNHSS1 said:

i agree, but im sure thats what Noble did on the 2.5 and 3L versions of the ford Dura V6 when they strapped a pr of turbos to them. Im pretty sure they used std V6 pistons, but shorter ford parts bin rods, one of the Noble gurus will be a long in a mo to fill in the details

If they did, sounds like a reason to avoid them if that's the sort of engineering they put into such an expensive car.

[davepoth]

I'd guess they used a shorter throw crank rather than shorter rods - you would get some fairly mad angles with very short rods at a time when you really don't want them.

[stevieturbo]

davepoth said:

I'd guess they used a shorter throw crank rather than shorter rods - you would get some fairly mad angles with very short rods at a time when you really don't want them.

If they did that, it would have made the engine smaller.

The only correct and sensible ways for them to change the CR, would be with pistons, or combustion chamber re-working

[Nick3point2]

Max_Torque said:

Also be aware, that by increasing your headgasket thickness you are increasing the "squish" distance, that is the distance for how close the piston crown gets to the cylinder head. On a 2 valve engine which often have significant squish features in the head (4valves do to, but there is simple less room for them due to the extra valve area), if you increase this distance you can dramatically reduce the turbulence and mixing of the aircharge mixture. This as a result slows down the burn rate of that charge and leads to great heat loss to the combustion chamber and piston. And on a turbo engine, where you are burning much more fuel per cylinder, the last thing you want to do is have a greater proportion of that heat pushed into your combustion chamber walls etc !

I was always told with spacer plates (within reason) any gains had with lower comp are offset by the issues you have described.


Do it properly, get low comp pistons or have the head worked.

[Marquis Rex]

stevieturbo said:

CNHSS1 said:

i agree, but im sure thats what Noble did on the 2.5 and 3L versions of the ford Dura V6 when they strapped a pr of turbos to them. Im pretty sure they used std V6 pistons, but shorter ford parts bin rods, one of the Noble gurus will be a long in a mo to fill in the details

If they did, sounds like a reason to avoid them if that's the sort of engineering they put into such an expensive car.

I know on PH people tend to worship the Noble, and mention it in the same breath as Porsches, but that's exactly the sort of engineering we're talking about: I saw the intake manifold, it was a carry over one from the Ford Naturally aspirated engine but simply boosted relying on all of the Ford corporate safety factors of design and not taking into account any of the transient issues that arise out of using N/A components on a boosted car. The engine is NOT an 'engineered solution'.
It was then I realise the Noble is seriously over priced, but most folks on here don't care and still worship at the alter so from a business point of view it's succesful.

[eliot]

Marquis Rex said:

: I saw the intake manifold, it was a carry over one from the Ford Naturally aspirated engine but simply boosted relying on all of the Ford corporate safety factors of design and not taking into account any of the transient issues that arise out of using N/A components on a boosted car. The engine is NOT an 'engineered solution'.

I know someone with a noble who's inlet manifold split apart (exploded in his words)

[CNHSS1]

i wasnt intending my comments to be Noble bashing or inflammatory in any way, just trying to assist the OP