LZ24 build

[novita1021]

Hello everyone.

 

I'm building a lz24 for my 620 king cab. as of right now i have everything but I'm trying to figure out what head I want to put in. I currently have a u60 head i got from a friend. Head has work done to it I just don't know what. it has shims under the cam towers, a port job on the intake, Crane Cams cam # DA-272-2-10 NC and it also has 162-17-9. I also noticed that the head lash pad retainers are taller on the intake valve and shorter or sunken in on the exhaust side. Its open chamber but also looks like its been milled down quite a bit. i wanna run the head but my friend says that i might bend the valves. Z24 bottom end has dished pistons. Any help or info would be greatly appreciated thanks guys.

[datzenmike]

If this U60 head was used or intended for use on an L20B it will more than clear a Z24 piston.  Z24 pistons have a large 15cc piston dish, L20Bs are 11.3cc. The only time the intake and exhaust are open when the piston is at the top of it's stroke is at the end of the exhaust stroke and beginning of the intake stroke TDC. Neither valve is anywhere near full open. The intake is just beginning to lift off the seat and the exhaust is almost closed.

 

Set the cam dowel at 12 o'clock as viewed from the front. Now look at the two valves on #1. I doubt very much they are above the combustion chamber surface.

 

If curious about piston top clearance, place the #1 piston at TDC. Set the cam dowel at 12 o'clock. Place a small lump of clay on the piston top and gently lower the head into place on the dowels without a gasket. Check that the head is firmly on the top of the block and then lift it off. The clay will now have an imprint of the two valves in it. Measure the clay at it's thinnest point in the impression. Keep in mind that a head gasket will add another 0.050" to that.

 

 

 

* Under no conditions must you rotate the cam in the head with the piston at TDC

* Under no conditions place the head on an engine set to TDC with the cam dowel pin other than at 12 o'clock or 6 o'clock as viewed from the front.  

 

* this will cause the valve to strike the piston top.

[novita1021]

Good info Mike I'll  be trying that out tomorrow when I get a chance. I'll update when i get it done.

[Icehouse]

I just helped my buddy dave on his "LZ22" and it turned out to have a Z24 crank in it!   It was also bored out to 89mm, so it was a destroked 2.4L!  Kinda cool.  We lowered the compression to something like 7.8 to 1 since it's boosted.  Before it was over 10 to 1 and he was sick of buying race gas.  I thought it was a interesting way to get a 2.4L L series engine without messing with the front cover.  

[DISLEXICDIME]

Now Dave can turn the boost up !

[datzenmike]

The down side to this is the 2cm shorter block. Piston is so close to the crank throws that the rod is pulling more sideways. 

 

The L16 has a rod/stroke ratio of 1.8

The L20B is 1.69

The Z22 is 1.58

The LZ24 is 1.51 ..... I mean it's really getting down there. Build for mid range torque and power, you have the displacement.

[novita1021]

I would like a 7k rpm motor. My friend says it's possible with the right cam and carb set up. It's gonna be in a 620. I want the low end torque but when I'm over the 5k rpm mark I want that power I might even shoot a small shot of nitrous.

 

Carb for now would be a 38/38 weber till I get my mikuni 44s rebuilt.

[datzenmike]

The red line is the point below which and engine can safely be run continuously without risk of damage. The piston and rods have to accelerate and decelerate under terrific strain. Stock rods and pistons can sustain 4,000 feet per minute, and above this the metal parts begin to stretch or break.  Red line for a Z24 is 6,350 RPM. This is at the 4,000 FPM (feet per minute) max limit for piston speed. Anything over this and you are straining the metallurgical properties of the connecting rods and bolts of a stock engine and they will fail. It's also rough on the piston rings. (yes everyone knows someone who revs to 6,500 all the time, and you can, briefly, but sooner than later it will let go)

 

To exceed this limit safely you will need things like forged rods and studs/bolts. Forged pistons would be good also.... mandatory if boosting or NO_x

 

 

 

 Imagine rolling a Z24 crankshaft along the ground behind your car. 6,350 RPMs would be 45.45 MPH!!! That's 4,000 FPM. Piston and rod going up and down 105 times a second.