L24 performance upgrades.

[tabrinn]

I'm about to dive into my my L24 engine to rebuild it. I was considering dropping in a L28 crank basically turning it into an L26. How much power/ torque is this mod worth? I'm getting the E-88 head sent to Rebello for the royal treatment, I have tripple 40 DCOE webers, MSA headers with dual exhaust. I also have the stock 4 speed and rear gearing. This is my first Z car, I've never driven one, so I'm not too sure what to expect. Will the 2.4 be under powered with the current gearing? Will the 2.6 hybrid mod be worth the effort? Has anyone here done this before? HybridZ gave me the duntz hat for not wanting to go with the obvious L28 turbo or NA.

[ktm]

The 2.6 will give you an approximate (2.6-2.4)/2.4 x 100 = 8.3% bump in power. Assuming 120 FWHP, this equates to 120 * 0.083 = 10 hp increase.

This increase is simply related to increase in displacement. Rebello's headwork will (most likely) result in a significant increase over stock, much more than the increase associated with the small bump in displacement.

If this is a numbers matching car and you do not want to swap parts, then you are stuck with the 3.36 gearing in your stock differential. If you are not opposed to swapping out the differential but want to keep it in the 240z family, you could opt for the automatic differential with its 3.545 gearing. This will help with acceleration.

Hybridz is not about trying to keep it stock. By modifying the crank as you are, you are not keeping the car stock, so why stick with the L24?

[ConchZ]

if you are going to calculate horsepower gains by directly relating it to gains in displacement, then you have to think about what his other modifications do to horsepower. Suppose the Webers, headers and headwork net him 40 extra horsepower, giving him 160 horse at the wheels, without the change in displacement. Increase the displacement by 8.3% with the L28 crank....

160 * 0.083 = 13 hp increase. While not a huge difference, its an interesting to think that the extra displacement will add roughly 8% more to each subsequent modification. The real story might be in the longer stroke increasing your torque.

As for keeping it stock, you would be using the same old numbers matching L24 block and E88 head. From the outside, that engine would look stock, except for the headers and triple Webers attached to it. You could go back to a numbers matching car fairly easy, if you think that's important. It its not important, then the hybridz guys are right, get the L28.

Of course, I'm not an expert at any of this. I'm just keeping the discussion going, I guess.

[tabrinn]

I wouldn't think it would be so linear?!? There is more going on than just adding displacement. As ConchZ said there should be a noticable improvement in torque from the longer stroke. If I use the L24 rods with custom pistons I'd have a better rod ratio (than stock L26) which is good for revs, less wear, maybe a couple of HP due to less friction, etc. Rebello Racing builds a similar "crate" motor. http://www.rebelloracing.com/enginebuild.htm

Any car show snob who snoops around, regardless of how thorough they are would never know there is an L28 crank in there. Besides, this way I don't have to scrounge up a new motor, no one wants these motors and I'd hate to toss this one to the scrap people, and L28 cranks are fairly easy to come by with all the people doing the L31 stroker.

[xray]

If you're going to go through so much effort (and expense) with custom pistons, you may as well do an 0.080 or 0.120 overbore and convert it to a 2.7 or 2.8l displacement as your link dictates above.

The hybridz folks say to turbo the motor because the cost associated with NA builds is disporportional to the benefit. Given the DIY/grassroots vibe of most members there, it makes sense. I like your ideas though--someone here went that route a couple years back. Search for "rebello" and see what turns up.

Good luck, and post dyno numbers when you get finished!

[Zs-ondabrain]

And not one of you mentioned ELECTRICAL. So let me say electrical, electrical, electrical.. Non of the upgrades will matter if the electrical or Ignition system sucks.

Don't get me wrong, I'm not knocking any advice, just pointing out the obvious. The headwork, intake and exhaust upgrades are awesome but you need Spark and lots of it. Make sure to stick with NGK plugs and wires. I'd suggest an infra-red / optical ignition system. It will stay true at higher RPM's and not peeter out or float like points do.

It's more expensive but I'd go with a Mallory Unilite Distributor. Great solid distributor that's right up there with the other top names in Datsun Upgrades (Rebello, Tokico, Eiback, MSA and Weber) And on top of that distributor, you can go with an MSD 6A to multiply that spark and a Mallory Promaster Coil to increase that spark.

I have this set-up in my Z and my NGK BP6ES plugs are gapped at 0.70 This set-up throws a 6+ inch white hot spark that'll make you think you're having a fricken heart attack. Take my word for it, it hurt, a lot. And I could go with a full 0.10 gap if I wanted.

Look into different options, or cheaper ones but Do Not Skip the ignition system. And increase the size of your stock battery cables to no less than 4 gauge and make sure the ground points are optimum.

Dave.

[tabrinn]

Yes, the ignition definatly needs upgraded as well. It still has the old points. I just haven't gotten around to fully researching all my options. I apreciate your recommendations.

[jmortensen]

I wouldn't think it would be so linear?!? There is more going on than just adding displacement. As ConchZ said there should be a noticable improvement in torque from the longer stroke. If I use the L24 rods with custom pistons I'd have a better rod ratio (than stock L26) which is good for revs, less wear, maybe a couple of HP due to less friction, etc. Rebello Racing builds a similar "crate" motor. http://www.rebelloracing.com/enginebuild.htm

Any car show snob who snoops around, regardless of how thorough they are would never know there is an L28 crank in there. Besides, this way I don't have to scrounge up a new motor, no one wants these motors and I'd hate to toss this one to the scrap people, and L28 cranks are fairly easy to come by with all the people doing the L31 stroker.

I'm not trying to follow you around from forum to forum being a ****. But I think the more you look at these issues, the less important they become. Some questions to ask yourself:

The rod ratio would still be worse than the L24, so then are you "giving up" hp to go with the worse rod ratio? What rod ratio would you have if you used L24 rods with a custom piston in an L28 block? What displacement?

Higher rod ratio allows for slower piston acceleration and deceleration. At what point do L engine pistons tend to fail due to piston speed? Are you going to spin your engine anywhere near those speeds with any combination of crank and rods?

Are you a car show snob? Do you care what car show snobs think? If you're going to "fool" a car show snob with your stroker L24, is there any other way you could trick them? Maybe sanding off the L24 and block number stamp and restamping it L28 and N42? I've never seen it done, but it just occured to me that it could be.

As to how linear displacement vs hp is, look again at Rebello's website. 2.7 makes 270 hp. 3.0 makes 300 hp. 3.2 makes 320 hp. Seems pretty damn linear to me...

Edited September 19, 2008 by jmortensen

[doradox]

As to how linear displacement vs hp is, look again at Rebello's website. 2.7 makes 270 hp. 3.0 makes 300 hp. 3.2 makes 320 hp. Seems pretty damn linear to me...

I think ktm was making a generalization, he did say approximate, about the hp gained by displacement change. As your example shows that generalization is fairly accurate for the small displacement changes. One could nit pick about rod length, port size, etc but the basic premise is valid unless you go crazy on the displacement change. It's unlikely the l24 head could flow enough to keep up if say you could go to 4.0 liters. But that's just speculation.

Steve

[Oiluj]

I just did the Rebello 2.7 liter upgrade on my L24. Dyno results are 212 HP and 197 ft-lbs of torque. I went with a milder cam to get a smooth idle at the expense of the additional HP.

Dave indicated that it peaks at 6200 rpm and revs nicely to 7000. I can recommend Rebello. Dave is great to work with and runs a first class shop.

[Diseazd]

Julio-What did Dave do to get that much out of your L-24? What cam,valves,shaving and shimming, etc. etc.? How much overbore and stroke? Guy

[Oiluj]

Julio-What did Dave do to get that much out of your L-24? What cam,valves,shaving and shimming, etc. etc.? How much overbore and stroke? Guy

First, it's really not an L24 anymore, it's a L27...Anybody got a 270Z exterior badges? *grin*

I really don't know the specifics of what they did. I provided Dave with a descripton of my budget, intended usage, and that I wanted more torque for drivability and the A/C. He discussed a few options, but after meeting with him, I was comfortable enough to just say "do what you do".

I know that they reworked the combustion chambers, ported & polished the head, installed an upgraded cam, followers, etc. My guess is that it includes larger valves as well. I don't know if they shaved/shimmed the head. I do know the only original part on the head is the casting.

The block was bored-out with new, (260/280?), crank. All external gear replaced, (water pump, fuel pump, etc). Carbs were re-jetted, (larger). I'm sure they also advanced the ignition a bit.

One nice thing, unless you are racing or abuse the engine, they warranty their work. I have to call Dave this week and ask hm for some more info. Some of what they do is "proprietary", so don't expect too much.