How to: Put an L series head on a Z block

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How to: Put an L series head on a Z block

Postby PEZi » Wed Dec 30, 2009 7:36 pm

NOTE:the information in this thread has been borrowed from several other sources and no portion of it has been created by NICO.

To use the NAPS-Z block with an L series head, you need to use all the parts foreward of the block from an L20B. Use the front timing cover to match the L series head pattern as the NAPS-Z is slightly different shape where it seals to head around the timing chain. You also need the longer L20B timing chain and matching gears, guides, tensioner and longer L series distributrer drive spindle. The NAPS-Z blocks lack a chain oiler peg. You could drill the block and add a chain oiler peg but this is probably unnecessary since L series front cam tower and the chain tensioner both oil the chain. Im told the L28 6 cylinders didn't even use a oiler peg. Drill a dipstick hole on appropriate boss on right side of block and plug the left side dipstick hole since it will now be covered by exhust manifold. Use an L series dipstick and tube in the new hole, the NAPS-Z dipstick wrong length. Use an original 510 L16 oil pan and oil pickup, NAPS-Z or L20B oil pan wont clear the 510 crossmemember and steering. You will need a headgasket with larger bore if cylinders are over 86mm. The cheap but difficult solution is to use a NAPS-Z headgasket. The shape of the timing cover to cylinder head gasket surface is different between L series and NAPS-Z, headgasket modifications are necessary to seal front cover section if using the larger bore NAPS-Z head gasket (use an entire NAPS-Z gasket and seal the front cover with silicon or cut and splice the front segment of a L series gasket onto a cut NAPS-Z gasket.) The NAPS-Z gasket lacks the valve "eyebrows" so the gasket bore is a true circle, this would prohibit beneficial grinding of the head chamber and block to unshroud the valves, probably best to use the 89mm Z24 gasket even if on a 87mm Z22 block since it will allow the most unshrouding within cirular bore. The NAPS-Z block has all the water passages of the L series (plus a few extra) however the NAPS-Z gasket covers some of these coolant passages that should be open for an L series head, drill holes in the NAPS-Z gasket to match an L series gasket for correct coolant circulation. Even easier to assemble, buy the expensive Nissan Motorsports 88mm big bore L-series gasket. The opening of the cylinder head oil passage at the headgasket should be elongated to better match to the oil passage of NAPS-Z block.

The NAPS-Z20E block that I checked had headbolt threads same as L20B block but I have heard that some NAPS-Z blocks have the headbolts threads deeper in the block hole, you can obtain more clamping force for headbolt by using all long length headbolts (turbo 280zx headbolts part #11059-P7600). Countersink or mill down the upper face of cam tower by 0.5" where headbolt contacts camtower so the headbolt sits 0.5" lower into block. For headbolts that do not thread through camtowers, use .350" thick washers below the longer headbolts to keep them from bottoming out in hole.

For the taller NAPS-Z 2.4 block, do all the above modifications, lengthen the L20B timing chain by adding 4 extra links of datsun chain using 2 master links from a Mercedes-Benz timing chain (#000997-0598), lengthen the L20B timing cover to seal the extra 3/4" block height (welding and machining involved), and modify motor mounts/oil pan so engine sits low enough to close hood. (or use hood scoop!) Another method I have heard of is to space the entire front x-member downward from the chassie and then relocate the controll arm pick-up points upward. Ground clearance to oil pan will be minimal. Most used NAPS-Z 24 blocks will be cracked around at the headbolts, finding a good used core can be difficult.

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Re: How to: Put an L series head on a Z block

Postby AbleSmith » Mon Aug 30, 2010 5:28 am

The block heights listed in the Honzowetz book for the different L and NAPS-Z motors are the height from the oil pan surface to top deck. This is not a particularly useful number if you are trying to compute piston deck height at TDC. I researched a bit and came up with the more usefull measurements for height from crank centerline to top of block. With the crank centerline-to-deck measurements inhand, it was easy to see that there were some mistakes in the rod lengths in the Honzowetz data, especially among the NAPS-Z motors. I was able to double check some of the suspicious measurements in other sources. Knowing the crank stoke, deck height and piston pin height, I was able to make some reasonable guesses as to what rods Nissan actually used in different motor to achieve near zero deck height of the piston at TDC. (most of the L, Z series have the piston slightly below the block deck at TDC). With the corrected information, I experimented with a spreadsheet to design some hybrid crank, rod, piston, block combination. HOW TO MODIFY recommends not letting the top of the piston protrude further than 0.3mm above the block at TDC. The following is what I have come up with.

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