Re-Tapping 302 head bolts to 1/2 inch

[Kevin Box]

At topic that I am sure will raise a lot of discussion !!!

Recently at a car club meeting the discussion arose about drilling and re-tapping the 302 head bolts to 1/2 inch.

I had never headed down that track before so I had a look at the possibilities

It looks feasible .

Maybe you could get better tension (better sealing) as in 351W

Has anyone done this ???

I have attached the sizes for information.

It sounds like a good idea and there is only one TPI difference between them so maybe it would work ???

Appreciate any comments

regards kevin B

 

[Jac Mac]

Yep, it works, preferably only on the blind hole blocks though ( & you need to drill the holes slightly deeper ), have seen a couple of the later roller cam blocks that have been done, but thats just a waste of time since the main bearing bolt thread boss's in the webs on those have no meat around them. Not much point in saving the head gasket if the cranks gonna end up in the pan.
Also you can drill the 351 blocks to take the 385 series ( 429/460 ) 9/16" hardware if your keen, but for NA stuff thats a bit over the top...

 

[Kevin Box]

Thanks Jac Mac

I have always just stuck to 7/16 stud set from ARP and been particularly careful to minimse detonation on 302s I have built and to date had not had a drama.

I was wondering what all the hype was about so thought I would throw it open and see what comments came back.

I have always thought the Motorsport 9.2 block was best for 302 CuIns - A bit of buggering around but strong and cheap.

regards

Kevin B

 

[Jac Mac]

If there was to be an 'ideal' block for a 302 cu in it would be the Dart 8.7, that allows a 6" rod & 1.2" pin height, the 9.2 adds unnecessary weight & size, but the 8.7 has the cost issue of intake/spacers etc- horses for courses really & if your really trying hard & not in a class where there is a ( heavy ) minimum weight limit then light weight will always be a factor

 

[Kevin Box]

Jac Mac

One of the odd 305 cuin combos I saw in the US was 9.2 block (302 main size) with 6.2 in rods and pistons were 1.5 pin height design for C class jet boat.
I thought full height piston without pin in the oil gallery sounded like a cool idea.
All bits were custon including the Kinsler EFI on it
Heads were C302B I think

Always thought it was an excellent combo
6.2 inch rod is really out there.

regards

KB