Max bore 1.6 block

Hi all.

I wonder how much it is possible to bore the MK1 EG (GTI) block out to?

I have a 1.5 block here that i was about to cut open to measure,but was told that the 1.5 and 1.6 blocks are different.

My goal is to bore the 1.6 from 79,50 to 83,25mm
Has anyone done this before?

I think personally thats stretching it a bit far.

3.75mm is a lot of material.
Really you need to get the wall thickness of the cylinders tested with ultrasonics to determine what theyre currently at.
iirc VW blocks dont have a lot of material between the cylinders so you may run into a weakend cylinder that distorts as the engine runs ( and eventually cracks) or the gasket fire rings at the top could be compromised as the available support material is less than it would normally be.

Just out of interest, why do you want to go so big?
Its not likely youll gain a huge amount from it anyway, approx 166cc (if the stroke is 86.4).
Improve the breathing, optimise the tuning and itd work better and retain the rigidity of the block  (imho).
 8)

^^^ bingo. Saves the ballache of having to get custom head gaskets too, especially as they're more likely to go with less material between cylinders. I know the mini boys have a real problem with this when they bore out to 1410.

Overboost said

I think personally thats stretching it a bit far.

3.75mm is a lot of material.
Really you need to get the wall thickness of the cylinders tested with ultrasonics to determine what theyre currently at.
iirc VW blocks dont have a lot of material between the cylinders so you may run into a weakend cylinder that distorts as the engine runs ( and eventually cracks) or the gasket fire rings at the top could be compromised as the available support material is less than it would normally be.

Just out of interest, why do you want to go so big?
Its not likely youll gain a huge amount from it anyway, approx 166cc (if the stroke is 86.4).
Improve the breathing, optimise the tuning and itd work better and retain the rigidity of the block  (imho).
 8)

The reason why i want to bore the block that much,is because it will be used in a race car which rules allow max 1600cc.

I want to use the 1500 crank (which has 73,40mm stroke) and the 1.6 block which i "THINK" has aound the same wall thickness as the 1.8liter.

In my opinion,if this 1.6 block has the same wall thickness as the 1.8.
Then it is no problem to go with a 83,25mm bore,i have bored 1.8 blocks out to 84mm earlier without any problems.

The reason why i want to go with this bore instead of the original 79,50mm is simply because of valve shrouding,and the engine will be oversquare.

In theory,this will make more power.
But,i may be wrong.
It is only one way to find out though  

Head gasket issues is not a problem,i mean,the 2liter has 82,50mm standard bore without any sealing problems.

Oh,i forgot one thing.
This is a Normally aspirated engine.
So cylinder pressure won't get anywhere near a Turbocharged.

NORSK said

 
The reason why i want to bore the block that much,is because it will be used in a race car which rules allow max 1600cc.

I want to use the 1500 crank (which has 73,40mm stroke) and the 1.6 block which i "THINK" has aound the same wall thickness as the 1.8liter.

In my opinion,if this 1.6 block has the same wall thickness as the 1.8.
Then it is no problem to go with a 83,25mm bore,i have bored 1.8 blocks out to 84mm earlier without any problems.

The reason why i want to go with this bore instead of the original 79,50mm is simply because of valve shrouding,and the engine will be oversquare.

In theory,this will make more power.
But,i may be wrong.
It is only one way to find out though  

Head gasket issues is not a problem,i mean,the 2liter has 82,50mm standard bore without any sealing problems.

Oh,i forgot one thing.
This is a Normally aspirated engine.
So cylinder pressure won't get anywhere near a Turbocharged.

Ah ok, understood, its a maximum effort race unit rather than a road engine.

If ive read you right then, the solution ( to my mind) is to use the 1.8 litre block and the 1500 crank as youve already established its suitability for the boring out process.
Only way to know for sure what thickness the bores are is to get them ultrasonically tested because it can vary block to block.

Regarding the valve shrouding issue you mention, have you established that its a problem on these engines?
iirc, the chambers quite open on all sides of the intake valve bar the one, although there is a little scope to cut into the chamber wall at the closest side to the bore/valve itself and relieve it somewhat.
 8)

There is also some part of the rules that i must use a engine block that was used back in 1976 (it's for historic racing)
The 1.8 came later (around 1980 if i remember correct?)

So i am stuck with either a 1.5 or 1.6 block,and i have been told that the 1.5 is for sure thinner than the 1.6.

But,i guess you are right.
The only way to be 100% sure is to sonic test the block.

Yes,valve shrouding is a issue on these.

A golden rule is to have MINIMUM clearance from intake valve to cylwall equal to 12% of the valve diameter.
The exhaust valve distance is not so sensitive though

And with a 79,5mm bore,that is not possible.
So,a 83,25mm bore will make a huge difference there.

Ive not seen that golden rule before, i learn something new every day.

Looking at the way vw heads (youre using 8 valve i take it?) are made, the bore of 79.5 is approx 5mm from the periphery of the intake valve at its closest point.
However, its also at around that same distance for the duration of the valve lift ( are you going higher lift also?) because of its proximity to the vertical chamber wall.
If youre staying with stock lift, the only time the valve would be shrouded by the bore would be at or close to max lift.
Its shrouded by the chamber for the majority of its lift ( especially at all its low lift points) by the chamber wall.
I would think that if you can slope the chamber wall backward to meet the bore line ( even if you do decide to go oversize on the bore) that youd mostly eliminate any shrouding by that method.

Im lucky in that i built my own flowtest rig so i can check such things as bore shrouding, although id need to alter my head adaptor and do a set of lift tests with a stock bore and then a larger bore to see if it gives a gain by itself.
Probably about the only way to find out if shrouding actually exists on these, to what degree and how much it can be relieved by.

Let us know how you get on with the overbore! 8)

I will use a 8v head with higher lift cam.

Most probably i will use the EG (GTI  head) which don't have any combustion chamber.

Which mean that when the valve opens,the mixture is not flow restricted due to a tight combustion chamber,but this head use quite large intake valves,so distance to the cylinder wall will be too small (i think so anyway)
This is why i think it will be beneficial with a much bigger bore.

The downside of using the EG head,will be the piston design.
I planned to use JE FSR pistons (which is extremely light)with much longer custom length rods (around 152mm)
But i don't think the FSR pistons allow such a deep dish that using the EG head requires.

Anyway,i have just started to look at this project,so it will be some time before i start to build this engine  

Dont forget to update us with your progress, hope it all goes well.  8)

How did you get on with the max bore of the EG block? I am looking at rebuiling my EG at the moment. I am looking at the possibitlity of using 1.8 pistons due to the EG pistons not being available and certainly not at a rip off price?!! I would be looking at rebore to 81mm same as 1.8 block. It says in the article below, that you can bore both 1.6 and 1.8 blocks to 83mm! Obviously, I'm cautious and would love to hear how you or anybody as to how they have gone on.


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