KAZ24 build thread / compression questions / cam / header / DONE!!

[HRH]

Heeeeeeey kids! If anyone has been following the post whoreness of my 510 and D21, you'll know I'm planning a build for the D21.

 

I went to all the trouble to source 240sx pistons for 89-90 according to wikipedia where the compression ratio was higher for the sohc those years than in the truck. I'm guessing it's all in the head as I have .050 pistons now for the car, and they are indeed a different part number than the truck pistons, but they look identical, except the car pistons have anodized heads, whereas the truck pistons do not. Wristpin, dish, etc. All the same. So seeing as I had the block prepared for those pistons, that's what I'm going to use.

 

I'm also using a Z24 block, instead of the KA block since I had a good donor motor and a bad KA. Already verified that will fit right in with the Z24 motor mounts. My curiosity is supposedly the truck sohc KA is an 8.6:1 compression ratio, and of course I'm going for a decent amount of power beyond the stock application.

 

I don't want to go the turbo route since that will require expensive efi software and turbo, etc. Just want at least 150-170 out of the truck versus the stock 134. But of course, I don't want it too high where I can't run 87 octane. So I'm thinking a 9.1 or 9.5 to 1 would be ideal.

 

 

Does anyone have any stock compression specs or know about how much .030 off a KA head will yield in increase? Just toying around with options at the moment.

[HRH]

No ideas all day? Ratsuners must be out partying! I was dealing with stupid people at work, oh joy! They really came out in Spokane today.

 

Anyway, the whole idea is not only to have more power, but enough power to sufficiently move the 4000 pound D21 down the road with minimal effort. So the NX2000 gets 27 pretty normally with mixed highway/city driving, not too deep into the throttle. I just did a simple power to weight ratio calculation. If 140 hp = 2600 pounds, then 4000 pounds (with me in truck) needs to have 215 horsepower to equal the same power to weight as the NX2000.

 

The other compounding factor is the lower gearing in the truck versus the high gearing in the car. However, I actually pull LOWER rpms at 60 mph in 5th gear in the truck, probably due to the truck motor vs. SR20 where power doesn't even begin to happen until 3000 rpm. Technically though, I should be able to move the weight better given the lower gears. So maybe I can get away with a little less than 215 hp.

 

I realize there are many unaccounted factors here, such as displacement, fuel mapping, torque vs. hp, and aerodynamics.

 

My goal though is to get the behemoth hardbody with mud tires into the 25 mpg category provided I keep it around 65. I don't mind going slow for good mileage. With that in mind, let's hear some input!!

[HRH]

Food for thought: The heater core I'm putting in my Datsun guru's beat to hell 1980 720 pickup has a Z24 with an L head, fuel injected, running 13:1 compression and 0 degrees of timing gets 30 mpg and has torque all day long. So it can be done, but I'd like to not have to make it 13:1. :)

[datzenmike]

Matt, this is the first I've seen this post.

 

The earliest KA24E in the 240sx was 9:1 compression. I believe the piston was lightly domed 1 or 2 cc.

 

Also the car pistons were used with fully floating pins. If you look in the pin holes you'll see a groove for the cir clip that holds the pin in. Here's my set of E floating rods/pistons. The pin slides through the rod end by hand.

 

 

The rod ends have a bronze bushing the pin turns in.

 

 

The D-21 pins are pressed into the rods. Now I see no reason the floating pistons won't work on rods with press fit pins. Check the pin length.

.

[HRH]

Now see, that's what I thought. But the pistons I have from the old KA truck motor I took apart are exactly the same. The only difference is the pins are pressed on, and the truck pistons are not anodized. The dish is the same. The only thing I can think of is the shop that did the motor rebuild (and fucked it up) used car pistons for the same reason I'm using car pistons. OR the pistons are the same except for the full floating pin options and the combustion chamber of the 240 head is different. With that in mind, they would still list the pistons as 9.1:1 since in that motor they would be.

 

Anyone have a set of truck sohc KA pistons handy they could throw some pics up? This is baffling me.

[datzenmike]

Two different car KA pistons were used, both with floating pins in the rods. The first 3 months of the '88 were (I think) a domed piston with 9:1 compression. # 12010 40F10 The Oct '88 through the end of '90, a 2.8cc dish piston was used. # 12010 30R10 Both will have a groove for the retaining C clip in either end of the piston pin hole.

 

The Hardbody pistons were a different part number # 12010 86G20 and different rods with press fit pins.

 

The Hardbody pistons likely don't have the C clip retaining grooves in them. Have a look.

[HRH]

But they do! That's one of the weird things. I would imagine though, since getting these aftermarket and having such a small run of the early 9.1:1 compression those are probably only available through Nissan, I'll bet all the rest went with the regular dish. These came from Altrom and are JCC pistons. Think those are Taiwan? Really nice quality and since I have them I'm going to use them. But they aren't domed.

[HRH]

Alright, since the truck has been making chain noises again, I've renewed my interest in using the Z24 block and spare KA head to make another motor to stick back in it. This led me to some revelations we were pondering on above.

 

Visited the ozdat forum and found out that yes, the early 240sx pistons are domed 2cc, whereas the stock are dished 2cc. This sucks for me because that means I have the nicer anodized pistons, but they are the stock 8.6:1 compression ratio.

 

So I got out my 2 cycle mixing syringe, which happens to have cc markings, and filled the spare cylinder head with water. The stock KA truck head has a 62 cc combustion chamber volume, which is horrible huge. At least when compared to L20B options.

 

EDIT: Check the post a few beneath, calculated incorrectly, rectified in said post.

 

 

OR, should I just get an entire Altima KA24DE and stick it in the truck? OR, should I rebuild the Z24 head and make an adapter for the KA fuel injection?

 

OR should I just accept it and build the motor? Block is already bored and ready to go besides having the pistons hung on the rods and main/rod bearings.

[datzenmike]

The KA-E chambers are 65cc (close enough) but the head has an oil drain back hole that conflicts with the Z block water passage, so this needs to be tig'ed up.

 

If the combustion chamber is about 88mm diameter then removing 0.060"? would remove 9.1cc Or were you removing 0.060mm??? 0.060" is 1.5mm

[HRH]

I wonder if they measure that accounting for the head gasket area as well? Any more than 62cc would have been way too much, but with a gasket .030 thick, I could see 3 ccs fitting in that pretty easily.

 

Wait a minute, I think I might have forgotten pi when I calculated that this morning. Should be v= pi times r squared time height. So I did f that up. I'll recalculate this mess when I get home. Maybe I will be able to shave enough off then.

[HRH]

Okay, did some checking.

 

Here's what I'm thinking. The head chamber is roughly 88mm in diameter. We need to figure out how many cc's disappear when we cut .060 or thereabouts off the head.

 

Going online, I found a math website with the formula for volume of a cylinder as V=pi*r2*h That should be r squared, not r*2. And I can't believe I just remembered some 12th grade math pnemonic device. (PEMDAS, parenthesis, exponent, multiplication, division, addition, subtraction)

 

So we have a radius of 44mm, or 4.4cm. So 4.4*4.4=19.36 cm.

 

So pi (3.14) multiplied by 19.36 multiplied by .060, but that's in thousands of an inch, so you have to multiply .060 by 2.54 (centimeters per inch), which comes out to .1524 cm.

 

So 3.14 * 19.36 * .1524 = 9.2644 cubic centimeters. Dammit, I never should have questioned your math Mike! :)

 

So now, that's good that I screwed up the calculation earlier, because apparently I CAN get the compression ratio I need by milling the head. And knowing .060 is 9.2 cc less, 4.6 would be half of that at .030, so basically a .030 mill would get me close to 9.1 compression ratio, actually a smidgen over that.

 

So figuring from the original, .060 off would get me 9.6:1 compression roughly. Hmmm, I like the sound of that. Wonder if I could run 87 octane with that if I backed the timing off a ways? I don't need it to wrap out, it's more for mileage and towing power.

[HRH]

I just went and read some threads on ozdat. Good info, but what is it about Aussies not providing oics!!!!? :D I searched the 21 page KA24E head conversion thread and found all of two pictures. I should join there to demand oics! (Pics, if you don't get the reference)

 

Anyway, think I know which head hole to weld up, have to go look at it again. Probably in the morning, I'm beat from today.

[HRH]

Okay, finally went back and found the original website in that head thread. This one shows clearly which head passage to weld up. I think this website is listed in the KA24E conversion thread, just didn't see any pictures in the main thread. Regardless, here it is!

 

http://www.ozdat.com/membersites/zac510/

[datzenmike]

Matt your 9.264 is spot on. I rounded 0.060" as 1.5mm but it's really 1.524mm. It would have been good for a rough estimate but yours is more correct.You do not want to mill that much off anyway. It will affect the chain length.

[HRH]

That's only if you don't shim the cam towers. They come in .015 thickness, so four shims will restore the chain length. Just like when I cut .030 off the current race car head, have two shims under the cam towers on that.

[HRH]

Okay, having finally exhausted most of my playing with the new computer I got for Christmas, I finally made myself go down into the basement and use my Christmas present to myself! A head off valve spring compressor! Yanked all the valves out of the head for inspection. It's amazing how much nicer the ports are on even the KA sohc head. I love the L head, but you can't deny progress.

[HRH]

So I just realized something that you might have already realized Datzenmike! You can't shim the cam towers on a KA sohc head because the cam towers are half and half bearings around the cam. Consequently I can cut .060 off the head, but I'll have to deal with chain slack at that point. Fortunately I'm using the Z24 bottom end, and I'm thinking I should have enough adjustment with the guide shoe to make up the difference in slack. Have to consort with the Datsun guru on that, but I'm still planning on going ahead with it. We shall see.

[mike]

random thought but might be in line... timing wise, can/could you redrill the chain sprocket to compensate for the milling of the head if you can get the slack out of the chain? Is it even necessary?

[datzenmike]

Each number on the sprocket adjusts 4 degrees of advance or retard. So if on #1 you can adjust a total of 8 degrees. On a really stretched chain or a well milled head that can't be adjusted, you could move the chain back one sprocket tooth. Each tooth represents 9 degrees so on an L20B cam which starts on #2 you only have 4 degrees to work with. You may move one tooth (9 degrees) ahead and move back one number -4 degrees to get +5 degrees. :lol:

 

Regardless, all you are doing is timing the cam to the crank TDC... any slack still ends up on the slack side and has to be dealt with over there with the tensioner and/or guide. On a truly custom set up a chain link could be removed?

[HRH]

I asked one of the guys at the machine shop and he said with .060, one link is probably going to be too much. But yes, the other issue is because the cam isn't moved up (smaller circle now), it will retard the timing. However, that is easily fixable since Joe made a copy of the Nismo cam gear years ago, and we can make any of the three retarded holes on the cam sprocket since we're using L series parts there. So the cam retardation is not a problem. I have 4 advanced holes in the L20B in the 510 and am using #4 for the rally cam.

 

Knowing if I can get rid of enough chain slack with the cam gear moved down .060 is another question. Doesn't seem like a lot, but it doesn't take much to make a chain loose. Think I may have to get the set, put it on a motor, then measure the distance, then take on a board and move .060 down, just doesn't seem accurate enough. I may just say fuck it, and mill the head anyway and figure out a way to git r dun! :)

[HRH]

Well, I got the head back from Joe and have decided to hold off on the milling for right now, in search of a better way to raise compression than just chopping stuff off the head. Played around with some VG30 pistons, couldn't seem to get the right rod height. I'm going to do some digging and see if there's another option before I chop the shit out of the head. I may put the motor together on the stand without the head gasket though and see how much slack that gets me as that's about .030, which I could then calculate slack for .060.

[datzenmike]

VG pistons are 2 1/4mm shorter so you would need a 2 1/4mm longer rod, not to mention they are only 87mm.

 

 

Weld some aluminum around and behind the spark plug. Grind close to flush and have the head lightly milled. A small quench area is always good.You only need to add 5-6ccs.

 

Check out these L heads that were welded up and milled down. Then some creative grinding...

 

 

 

.

[HRH]

Haha, holy shit Mike, are you my long lost twin brother, or do we just think alike? :) Already talked to Datsun guru about adding material. U $fortunately, that's going to be $100-$200 for him to spend the time welding, and that's with me cleaning up and making sure all the areas are the same. I can get 10.7:1 pistons from Arias, but they're $600.

 

I did however start going through other pistons and found that 80-85 318i bmws have 89mm pistons. Going to go by NAPA here in a second and see if they have a domed top. Might get a set in to measure and maybe if I'm really really lucky, they'll work as a high-compression substitute. We shall see. They also may be horribly dished and useless.

[datzenmike]

Center of piston pin to top of piston HAS to be 34mm. If less, it doesn't reach the top of the block and this space now becomes part of the combustion chamber... making it larger.

 

Matt. you got a mig or tig welder? Do-it-your-self.

 

BTW those were p-nut heads with the valve angles tilted over to better fit the ports and the valve seats and combustion chambers welded up and machined. Found the article years ago and saved the pictures. Looked later and it was gone. Naturally ............... it was from Oz.... figures eh?

[HRH]

I have an okay MIG. I'm still not that great on steel, and aluminum is even trickier, plus don't have the spool gun or the confidence to not fuck up the head. Porting and polishing is fine because it's just removal. On the other hand, I was just thinking the clearancing is going to cost near $100 with how much material they'd have to take off in quite a few passes. So maybe I will experiment with that. I was going to go get some plumber's putty, make my shape, then refill the combustion chamber to see how many less.

 

And I checked on Arias' website, they list the KA combustion chamber as 62cc also.