7A with Aby head

[robo]

I am after bit of advise.
Can 7A complete bottom end be coupled with aby head with hybrid turbo?
I have all these parts ready and instead rebuilding my current engine I could have had another one build and just have it swapped.
I know our American friends should have most experience with this setup.

[steve briance]

Compression figures are different for sure. Research that and see what if anything people have done about it. The head will bolt on but, you might not last very long on boost..

[Error404]

7A block is 82.50 bore so you need a cooper ring type gasket e.g. Athena or custom MLS headgasket - think that PKM &/or Vidar had some 83mm MLS gaskets made recently - 7A paper gasket just won't cut it.
Above about 350hp,[around 450whp in American figures ] you will want to drop CR and put in some forged pistons and rods. Otheriwse block is nigh on the same as a 3B, [ a few small differences, turbo oil return will need drilling unless you have the return into the sump wing etc].

[robo]

Cheers, I have 83mm extra thick head gasket, would 7A pistons and stronger rods take 400 English bhp?. Second option would be stock aby pistons and stronger rods then have the 7a block sleeved to suit.
I would like to use the rs2 hybrid to its full potential which up to 400 bhp.

[steve briance]

Stock ABY pistons are not 82.5mm so won't go in 7a block.


Reducing the compression ratio would involve changing the pistons and then you have to ask yourself why you are doing that and not rebuilding your original engine as it would equal the same amount of work?...

[robo]

Stock ABY pistons are not 82.5mm so won't go in 7a block.


Reducing the compression ratio would involve changing the pistons and then you have to ask yourself why you are doing that and not rebuilding your original engine as it would equal the same amount of work?...

My current engine in UR has been build to racing spec and I have grown out of 1000bhp and I would like more or les standard reliable engine with rs2 spec. I have s2 with this spec and feels so good that's why I would like to use not tired 7A engine.

[steve briance]

I missed the bit where you said sleeve the 7a to suit aby pistons, that would work but that's not using the 7a as it stands now.

As it stands now your compression ratio will be wrong and if you did sleeving wouldn't that mean your 83mm metal head gasket is not right either?

Not many forum members are lucky enough to be able to do engine machining themselves so, I think you need to get some quotes to make your mind up for you.

Make a list of parts and prices to make them work for using a 7a block at 82.5mm (new pistons) vs using sleeved 7a block and aby pistons.

One other thing to throw into the mix is the question of whether your 7a is actually in good enough condition to spend the money on?... Have you done a compression check or measured bore wear? If it is worn to the upper limit in the manual, you may be disappointed when on boost you loose some of it past the rings. An 82.5mm 7a bore can (just) be machined to 83mm but then you are back to needing new pistons.

I looked at this a couple of years ago and could only find wiseco 83mm pistons for the 7a and they were £850 for the set + machining.

[Error404]

Sleeving the 7A block is an option, however I had a bad experience with a dropped liner and so I wouldn’t do it again using a straight liner, they’re just not stable enough for a boosted engine in my opinion - I am going to bore it out again and machine the deck to take a custom made flanged Ductile liner. The main issue with this is cost.
If I was you Id bore your 7A block out to 82.75 and buy some forged pistons and call it good

[robo]

Not many forum members are lucky enough to be able to do engine machining themselves so, I think you need to get some quotes to make your mind up for you.

I know things are not cheap, I had couple of engines build and one set me back close to 8k. Years ago money was no issue but not anymore that's why I am looking for advise.

I have not taken my current engine apart yet and can not say how bad it is. The spare 7A engine I have had very good head which is already machined to ABY spec so hopefully the block is in good nick too.