L24 (Modest Upgrades)

[Weasel73240Z]

I've decided to rebuild the motor in my 73 240Z even though it has very low miles, and I'm just looking to build a nice, quick (but not a race car), mostly original, and (hopefully) very reliable 240. I'm gonna do the rebuild myself. I've rebuilt motors before, but this will be my first overhead cam motor. Previous experience was with American muscle cars.

I bought a set of round tops on eBay, and put the original flat tops and the smog stuff in storage. I'm just looking for a slight bump in performance (nothing extreme like a cam), and it seems like 2.5" exhaust, electronic ignition and a good carb rebuild should get me there.

I've only been on this site since I bought the car 2 weeks ago, but I think this question may open up some debate. Again thinking of reliability as the top priority and speed and HP as a somewhat distant second, what would you folks suggest as the best way to make modest performance gains, without sacrificing driveability or reliability? Just to set a budget, lets say I want to sink less than $1,000 into the engine.

[Arne]

Get a copy of the current (Nov. 2007) issue of Classic Motorsports. This issue outlines exactly what you have in mind. They did a rebuild and mild upgrade on an L24 and got 167 HP at the rear wheels. The main difference is that they used the early E31 head, that you don't have. But for street use you should be able to come pretty close to that even using the late E88 head your car came with.

[gogriz91]

How about a header with a bigger exhaust setup? I would recomend the Ztherapy rebuild kit for your carbs too.

[BRE-240Z]

How about a header with a bigger exhaust setup? I would recomend the Ztherapy rebuild kit for your carbs too.

I thought that conventional thinking was that a header doesn't add power on a 240Z. Weren't headers discussed and then rejected by the BRE team? Seems like I read that in the 'How to Modify' book.....

[Arne]

Summary of the Classic Motorsport build up:

• Bored 0.040"
  
• All rotating parts balanced
  
• 280ZX Turbo oil pump
  
• E31 head shaved 0.018", no port changes
  
• Good valve job (3 or 5 angle, can't remember which)
  
• Mild cam
  
• Rebuilt SUs
  
• Pertronix ignition in stock distributor
  
• MSA 6 into 1 header
  
• MSA 2 1/2" exhaust
  
• All the normal rebuild stuff, new guides, timing chain, etc.
  

They did a baseline pull of 137 RWHP before the rebuild, got 169 when they were done. Not bad for a totally streetable L24.

[ktm]

Unfortunately Arnie, that would not be considered a 'mild' build for an L24. The poster asked to keep the price under $1000. The headwork alone will exceed that (and nearly double it depending on who does the work). The engine has also been bored over and parts replaced such as the oil pump.

In all honesty, he would be better off buying a complete L28 or sourcing an F54 block/N42 head and slapping on the SUs. He will come out with money in his pocket and a peppy little car.

[Arne]

Oops! My bad! I totally missed the $1000 part. You're totally right, best bet for that budget is a good used L28.

[Goose52]

I agree with the L28 plan (have one myself). If you want to stick with the engine that you have, I think your carbs, exhaust, and ignition plans are a good starting point.

You might want to search the archives regarding carb needle selection for your application (N27s are a good starting point for your 2.4 liter - they were the original needle on the 70-71 cars). Good reading at the Datsun Garage in regards to typical, and streetable, NA mods - some may fit into your budget: http://www.geocities.com/zgarage2001/z.html

Also, re the 169 rwhp quoted from the Classic Motorsport article - check out the dyno results for the well built 2.8 liter on the Datsun Garage web site - 167 rwhp. There's dynos, and then there's other dynos ...

[Arne]

Also, re the 169 rwhp quoted from the Classic Motorsport article - check out the dyno results for the well built 2.8 liter on the Datsun Garage web site - 167 rwhp. There's dynos, and then there's other dynos ...

Very true, you always need to take those numbers with a grain of salt. Especially when the stock original pulled 137 RWHP on that same dyno. My thought was if the engine is still that strong, why bother?

But regardless, the 30+ HP gain would be nice.

[beandip]

Weasel. I did what KTM said however I am running the P-79 head that the F-54 engine comes with. If the 280 engine is in good running order it will have vary noticeable improvement in performance over the L-24 you are now running. When the time comes in the future, to do a valve grind have the head milled when the head is serviced. Mine is milled .030 and the compression is 9.5 to 1 . Not a high compression but you wont need to shim the towers. I have been using the middle grade of gas with no detonation problems. For street I would recommend a 2 1/4'' exhaust . I am running headers only because the engine came with them. The stock ZX manifold is fine for street use and the engine bay will stay cooler, and there is not much difference in performance. This will save some $. I am also running SUs but I found the 54 needles work the best for me, the 27s were way to rich. I also have the ZX ignition and this alone is a big improvement over the old points. The zx ignition will help your L-24 as well. I do have a question . You say that the L-24 is a low mileage engine. Why do you want to rebuild it if it doesn't need it? Especially since you need to keep the cost way down. Gary

[Weasel73240Z]

I'm taking the motor out and apart to diagnose the problem with the motor (i.e. coolant in the exhaust). I took the motor and tranny out yesterday, and spent today powerwashing the engine compartment. The reason I'm pulling the motor apart is because it has just sat idle for too long. The head gasket and valve cover gasket were both dry-rotted. It may not end up a true rebuild, more like a tear down, clean, re-gasket, and put it back in. True, the car has only 26K, but most of those miles came 20 years ago, and it has basically sat since.

[Walter Moore]

Good luck with the rebuild.

I took mine apart because it wouldn't start, and found that someone had driven it for a while with a leaking head gasket. It eroded the #6 cylinder head, and the head had to be welded to fill in the erosion. By the way, does the head still have brass seats on the intake valves? Those are expensive to replace as well.