1970 240Z engine build options.......

[racer_z]

Ok, I have a 1970 240 that is ready to put an engine into and drive. The body has been stripped, media-blasted and primer baked before being painted. Transmission is a Nissan Competition FS5C71B Close-ratio overdrive, rear diff is an R200 with a 4.38:1 LSD. It has custom suspension and Wilwood brakes. This car will be street driven occasionally and taen to track days regularly. I have two different engine options I can go with...but which one?

 

OPTION 1-

 

Rebuild original L24 (E31 block) with Micropolished Crankshaft, Competition prepared rods, forged piston (not sure on brand or C/R yet), Slover- modified E31 head with 44mm intake and 38mm stainless competition valves, Isky Cam with .530" lift 264 degrees duration at .050, triple Mikuni Phh44's on a Datsun Competition manifold.

 

 

OPTION 2-

 

L28 built with F54 block, Micropolished and Knife-edged LD28 crankshaft, Forged 12:1 Venolia pistons, Slover-modified E-31 head with 44mm intake and 38mm exhaust valves, Isky cam with .595" lift 294 degrees duration at .050, Triple 44mm Mikuni's on Datsun competition manifold.

 

I am sure I am forgetting A LOT but this is what I can think of right now.

[Xnke]

L28.

 

Displacement, displacement, displacement.

[Tony D]

displacement displacement displacement

 

You, too, will understand how wrong the myth is with that combination.

[burninator]

Just ignore me if your already aware, but from what I've heard you might want to rethink the compression ratio on that second build unless your running race gas all the time, and even then it might be a challenge. I know newer engines can run that kind of compression, but with these old engine designs you might have a lot of trouble keeping it from detonating. I think race gas is a common requirement on anything over 9.5:1

[racer_z]

I'm not so concerned about what gas as it will be ran mostly on C16 anyway.

[Xnke]

I'm not explicitly wrong, so much as I didn't go on an excursion to explain my answer. I posted what I believe would be the best engine for a regularly street driven, regularly tracked car, and didn't back it up with anything.

 

The way I see it, you *can* make good power with the L24 warmed over, and still drive and track it, but if you are going to put the money into the engine, do it all at once and be done. The extra work for the extra half liter is minimal, and it has more potential. (about one half-liter more potential, actually.) The decision as to whether that extra potential is necessary is not an answer that anyone here can really give you.

 

For naturally aspirated track/hot street engines, given that the cylinder head will be the same for both of them, I see no reason, other than money to buy a block or a crank I didn't have, to NOT build the L28, whether I was building a stroker motor or not.

 

I'm not too new to the forums here, but I am new in the idea that I've only built five engines. I'm starting to pick up and read books a little closer, and more and more, I'm finding that Tony's comment about displacement being a myth is partially true. Many folks go for displacement on principle or ignorance; but almost as much gain, or in many cases a higher gain, can be had from tuning and careful parts selection, without the extra displacement. So, why not build the displacement, AND while you're at it, carefully select parts to work together, and then spend the time and money on tuning to bring in the best of both sides of the equation?

 

 

If you are going to build an L28, stroker or not, I wouldn't worry much over the block stamping. N42 and F54 blocks would both work just fine; because if you're going for a large overbore you should still have the block checked for wall thickness.

 

Running on C16 regularly? Have you spoken to Isky about what kind of compression ratio will work well with your chosen cam? (I'm thinking perhaps that's where the 12:1 number came from?) With the higher compression, a big camshaft will be able to run lower octane gas, due to dynamic compression, but there is still the question of timing advance; how much is optimal for power, and how much will your fuel grade and compression limit your advance curve?

[racer_z]

The only reason that i was considering staying with the 2.4 as opposed to the 2.8 is simply a matter of originality. The car has the original engine and transmission in it and I was concerned about that. However, I think that now i have decided to build an L28 and store the original engine and transmission away somewhere for a future "stock" rebuild.

 

lastly, I see where it was said that the cost of machining between an L24 and an L28 is about the same. Would this hold true if I were building a stroker?

[Xnke]

For a complete, ground up rebuild of the engine, including:

 

New pistons

Bored block

New bearings

New seals

New gaskets

Balanced crankshaft

 

Your extra costs will be:

 

LD28 crank = 150-450$

L24 9mm rods = 50-100$

ARP rod bolts = 75-85$

 

All other machine costs will be the same whether you are building a .20 thou overbore, or the various stroker configurations.