"building a motor" or "hybrid L-series!"

[e_racer1999]

okay, i'm trying to find a really god combination for a street/autox car. i want decent power, but i don't need buttloads of torque. i have a 1972 240z (all stock) with the E88 head. i have a complete N47 L28 (1979) and i already have some ideas. i wanna know what you think!

 

okay, i'm taking the 5 speed and i'm keeping the R180 (LSD comes later) and putting 4.11 gears in it (good idea?). i plan on getting flattop or slightly domed pistons and using the crank and rods from the L24 (i know you think this is going in the wrong direction, but i want revs!). will the L24 rods be good enough?

 

I also want to know which head i should use (E88 or N47). i know the E88 has better compression, but is limited by the ports/valves. is there a better head that i can get for not a lot of $$? any feedback is greatly appreciated!

 

-jason

 

btw - i plan on running stock SUs for the time being, until i go for a good camshaft (shoud i use L24 or L28 until i get a custom one?) and a good intake system.

[Dan Baldwin]

Here's why the destroked L28 idea sucks:

You want POWER. Power is TORQUE times RPM.

So you want TORQUE and RPM equally badly.

Destroking an L28 will LOSE you torque, but GAIN you rpm.

The PROBLEM with that is that it loses you MORE torque than it gains you rpm. The reason for this is that torque varies linearly with stroke, while rpm potential varies approximately with the SQUARE ROOT of stroke. Decrease the stroke by 7% and you lose 7% of your torque, EVERYWHERE, but only gain a theoretical 3.5% in redline rpm (only helps you at redline/rev limit). Actually, accounting for the "better" rod/stroke of the L24 crank/rod combination, you theoretically get 4.6% more redline. That doesn't make up for the 7% torque you lost, and again the torque is missing EVERYWHERE, while the rpm gained is only at the very top.

 

Put flat-top pistons in the L28 with the N47 head and you'll be doing fine.

Gearing will depend on which 5-speed you have. Go here:

http://www.geocities.com/z_design_studio/

[e_racer1999]

thanks for the info... i have the 79 260zx(a) 5-speed.....

 

i was just wondering b/c i know that destroking a chevy engine allows for longer rods, e.g. a better geometry within the engine... anyway, thanks for the info!

 

-jason

 

edit: i had to cut it short, but i also wanted to add that i plan on raising the compression, and i was thinking that higher revs at a higher compression was ideal.... anyway, i am willing to sacrifice some torque to get max horsepower (via revs) and i was hoping that the trade-off was worthehile..

[e_racer1999]

after doing some reading in other threads i decided on sticking with the N47 head and L28 crank (as per your recommendation)... alas, another idea swirling quietly down the drain,,,,

 

-jason

[z-ya]

I recently built a stock bore/stroke L28 with flat tops and an N47 head (~10:1 CR). The head is bone stock, with stock cam. Only mods are 6-1 header, 60mm throttle body, port matched intake, and Megasquirt fuel injection controller. 164HP and 175ft-lbs at the wheels. That's close to 200HP at the crank with an essentialy stock 2.8L. Thing is a ball to drive, with plenty of "spank".

 

Dan, how's married life treatin' ya?

 

Pete

[e_racer1999]

that sounds quite tasty! what do you think i can expect with the same mods w/ SUs?

 

-jason

[johnc]

Stop!

 

Before you decide what you're building, figure out the rules for the sanctioning body you intend to autox with. The engine build rules are very restrictive for SCCA's Stock, Street Prepared, Street Touring, and Prepared categories. The engine build you've described so far would only be legal in SCCA's Street Modified category, where you'll get your butt handed to you at any national level event by 300+ horsepower CRXs and Miatas.

 

If you just want to compete locally, then you might be competitive in Street Modofied or whatever the local "run whatcha brung" class is.

 

EDIT: Just saw that you're from San Diego. You won't have a chance in Street Modified unless you're a very, very good autox driver.

[z-ya]

John,

 

Not to hyjack the thread, but horsepower is really not that important in autocoss IMO. A great handling chassis is. I get my but handed to me by NA Miatas and Neons on a regular basis. Yes, I'm a good driver, and I've got close to 300HP in a well setup turbo 240Z. Now if you are talking road course, power makes a huge difference. But then again, those spec Miatas are pretty darn fast on a road course.

 

Also, the SCCA is not the only game in town for autocross. In fact, I avoid those events, because they are too big, with too many cars. You are lucky to get 3 runs for a whole day of work. The local clubs are a better bet, and don't have such anal rules regarding class. Typically, smaller local clubs will have stock, street mod, and race groups. Usually 6+ runs, and fun runs! So yes, a race 240Z can certainly get spanked by a stock S2000, but who cares. Are you having fun? YES!

 

Pete