L26 block options

[Justinp551]

What are the options of using a L26 block for overbore opportunities?   I know the L28’s go up to 89mm but what is the reasonable overbore range?  I have a L26 bottom end and looking to

build up a high comp 2.8 or 3.1 build.  Also with the same stroke as a l28 are the cranks relatively the same for a 26 and 28?  

[A to Z]

There are a lot more options than you will hear about.

 

Dave Rebello has built several big bore engines from L24 and L26 blocks.  Some racing classes in England require it, so it has to say it on the side of the block.  Both blocks carry a "P30" casting, and have an 83mm stock bore.  Also most guys see an L26 block as a throwaway....so get it for next to nothing, and if it passes Maganaflux its good to go.

 

From Dave, I learned that you can safely take one out 2.5mm to 85.5mm on the bore.  That's .020 under stock L28 bore.

 

Sleeving the block.  YES it can be done.  An L26 block can have all 6 bores sleeved, and costwise it can be done for about $150 per cylinder INSTALLED.  Sleeves can be custom made if necessary to meet the need.  Melling makes sleeves in 3/32 or 1/8" wall thickness AFTER final bore size.  So you order 90mm internal bore sizing with a 1/8" wall.  It IS possible that at some point, the sides of the bores may need to be milled flat so they can sit next to each other properly in the block.

 

Granted, some sleeves have a larger diameter stepped neck to support them, but it isn't necessary in an L6.  What the machinist has to do is simply bore it out for the sleeve but stop short....say 3/8's of an inch or 1/2 of an inch.  This leaves a "step" for the sleeve to sit on.  If needed they can simply machine off the length off the sleeve but leave it a tad long, so that once inserted, the block can receive a quick clean up mill.  Once done, you can't even tell it's been done.  If necessary the boring maching can then be taken back in and machine the step flush with the internal bore of the sleeve.....although it should be noted the pistons doesn't come down that far.  So the step and the head hold the sleeve in tight.  If someone wanted to be anal, they could weld the bottom of the sleeve in, but the press fit should be strong enough to hold it.  You could always bore the step almost flush, weld the sleeve, and then bore the step flush with the weld making it one piece.

 

In short, if the block has been magnafluxed and is free of racks....use it.  YES F54 280ZX blocks are said to have more ribbing between the bores, but they are also more common than not to be too thin to do any boring much past stock.  The sleeve gives you the thickness for good ring seal.  Whether the larger sleeve affects cooling to a degree that would be conerning, I do not know.  F54 is more expensive, and if you are going to sleeve it, is it still worth it?  I suppose if the extra webbing it still there after boring for the sleeve, then it would be nice....but I am a street car guy, and so, I would go with the P30 and feel great about it..

 

My L26 block, I took to 85.5.  I would not hesitate personally to sleeve all 6 and go with a 90mm pistons if I did it over again.  Just make sure you have the head gasket that will accept the bore you go with.

 

Peace.