240z Performance Mods

[72ZDave]

I have a 72 240z that I'm redoing and after getting feedback on the carb forum, I'm going to stay with the Stock SU's. As I redoing the car, I'd like to get a little more performance out of it, but do not want to negatively impact reliability as this will be a daily driver. I was thinking mild cam and headers, but haven't seen much on mods and what results to expect. For a daily driver, could I get 175 horse out of the 2.4 with these mods or more? I appreciate your input!

[John Coffey]

I was thinking mild cam and headers, but haven't seen much on mods and what results to expect. For a daily driver, could I get 175 horse out of the 2.4 with these mods or more?

First, spend your time and money making sure your stock engine is running perfectly. Compression test, tune up, valve adjust, carb sync, etc. If your compression numbers are good (170 or above on all 6 cylinders) then you might be able to get a 15% power increase using the following:

Nissan Motorsports 1 5/8" headers.

2 into 1 merge collector.

2.5 " mandrel bent exhaust

Electronic ignition

Good plug wires (Magnecore, NGK)

Medium cam (L7 or L9)

Intake and exhaust port matching

SM needles

ITG air filters

[ktm]

A nice 'performance' increase for a stock 240z is to swap out the stock 3.36 differential for a 3.70 or 3.90. You will certainly rev higher on the freeway and your gas mileage will suffer, however, you will certainly notice an increase in acceleration.

[DaveN]

Good performance tips can be found here, especially re cam swaps.

http://www.geocities.com/zgarage2001/engine.html

In a daily driver go for as much lift as valve-piston clearance allows and only a little more duration than stock (to preserve midrange torque). A strong midrange is the key to lively street performance because it's used a lot more than the extreme top end.

Re SU's and air filters -- The stock air filter housing is very good, actually better that most aftermarket replacements. The stock element is good, too, (until it gets clogged by dirt), but an oil wetted foam replacement element can flow a bit more air and hold more dirt. Avoid any aftermarket filter that doesn't have both a radiused inlet air horn similar to the stock housing and a connector for the float bowl vent hose. You need the streamlined inlet for good air flow and float bowls vented to the clean side of the air filter for proper mixture control.

I have tried stock, 70-71 spec (N-27) and SM needles in a mildly tweaked 72daily driver. N-27's (slightly richer than stock) worked best. Had to lean out the SM's as much as I could with set up adjustments (low float levels, no water to the carbs) to make them tolerable, and they were still richer than optimum for performance or street driving.

Re headers and exhaust systems -- Well made headers add a little power above 4000-4500 RPM, but aren't quite as good as the stock manifold up to 4000. A free flowing 2.25" or 2.5" exhaust pipe and muffler are a must, headers are optional. (How deep are your pockets?) If you keep the stock manifold either remove the air injection tubes and plug the holes or cut the tubes off flush with the exhaust ports. (The air pump takes about 6 HP at the redline, 2-4 HP in the midrange. With tubes cut flush and a good 2.25+ inch exhaust system the air injection doesn't add enough back pressure to be noticed.)

Re ignition -- L24's perform best with lots more spark advance than the original spec. How much more depends on what's been done to the engine and the fuel being used. All the engine will tolerate without pinging is likely to give the best performance. Electronic ignition gives better timing control, less misfiring, and usually a better advance curve. Lot's of posts here & in other forums about which works best.

If you have deep pockets buy a book titled "How to Modify Datsun 510, 610, 240Z Engines and Chassis" (I may not have it word for word, but that's close) and find a reliable performance shop to do the valve pocket relieving and block eyebrowing it describes. An E31 (70-71) head is best for this mod because the stock compression ratio was higher, and you lose a bit of compression when the valve pockets are opened up. These head mods done right add at least as much performance as a high lift cam and 2.5" exhaust, and you can still do those things to get even more power.