7A block to turbo spec rebuild

[Azman]

Hi guys.

Getting my hands on a 7A block to start an engine build. What are the main differences between this and the 3B/ABY????
Are the pistons larger?
If so I take it I will need custom pistons to reduce the CR or are the sizes the same and I will just need stock 3B/Aby pistons to reduce the CR to where it is needed at stock 3b/Aby levels???

Cheers

Right then.
To balance the bottom end what needs to be in place?

Crank, Pistons, Rods, shells etc.....

Cheers

[volcano rs]

no the bores are bigger on 7a so you will need custom pistons

[Azman]

Ahhh, So custom pistons due to size difference... right that will be expensive then!!!!

Thinking of scat rods to keep the price down.

Best place to get pistons??? JE

[caterpillar]

7a have 82,5 mm bore and 2,2 turbo have 81,00 mm bore..... custom pistons,
JE or CP or WOESSNER

[Azman]

Take it an ABY head still fits ?

[S2central.net]

Azman - I hate to say it, but I think you are starting on the wrong page there... Unless your budget expectations were for custom rods and pistons from the outset.

Does the 7A block have oil squirters ? I can't remember... They are mandatory.

They share the same crank, but all the main and b/e bearings are heavier duty on 3B/ABY/AAN/ADU

[Azman]

IIRC CR on the 7A is 10:1 isn't it.
So that would need lowering to 9.4:1 or is it 9.2:1

Also would it be easier to use stock pistons (new ones of course) and just use a pressure dropping gasket ala 034?

[Azman]

Was planing a full build up of the engine inc all shells bearings etc. I thought all the parts were transferable so I could use the 7A block for the bigger bore and was hoping stock pistons but obviously now not.

Can anyone answer the oil squirter question???
Thought it would have had them considering it is not that far behing the 3B is it?

[volcano rs]

yes they do have oil squirters

[Azman]

Cool
Cheers Bud

[Azman]

Those CR ratio's right? Or am I wrong again

[S2central.net]

Azman - you are best to accomodate the CR corrections into your instructions to JE (or whoever) for the custom pistons.

Let me know if you need help with the maths on that - a search for this subject should locate useful old threads when MarkH (and others) discussed it for their engine builds and custom requirements.

You NEED to get the volume of the chambers in the head measured before you tell JE what to do with pistons. Pretty sure MarkH shared some numbers he got when buretting his ABY head - I'll be doing same on a 7A head later in the year for comparison.

Paul

[Azman]

Cheers Paul. Surely it would not be that difficult though given that the stock piston size is 10:1 CR to reduce it should be simple for them (as they do it all the time)
Would it save hassle going for a pressure dropping gasket and just getting stock pistons

[GazzaG60]

7a is same as avw 16v. oil squirters etc. id go with 83mm pistons. JE or wiseco. they are good for not a lot of cash. think the oil squirter is on the oposite side so piston skirt needs to be different to 9a/6a piston. bout 550 for pistons and rods uk proce if you get a good deal in the states.

heas is cut same as 16v head so 16v spec dish is good. all 16vs 6a/9a/pl/kr/abf/ace have the same head combustion chamber cc

[Jamo]

Azman head over to motorgeeks it's all covered there as this is a common conversion for the yanks.

83 mm is the max you can run at personally i wouldn't as your at the limit.

You can't go beyond 83mm with another rebore down the line. Stick with 82.5 and then you have 82.75 and then 83 as rebore in the future.