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Aiden’s 521 V.2


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Hello everyone, My name is Aiden you may have seen my truck on my dads thread a few years back titled sons first truck. since then I have used my 521 as a daily for the better part of 3 years and i definitely love it! it’s a 71 521 with a Z20b; u67 head 274f schneider cam i believe it has standard l20b pistons and rods and it’s paired to a zx 5-speed. the reason i’m starting this thread is because though it’s a great truck the low compression leaves some power to be desired and after driving it all the way through high school and into my first year of college i’m ready for a change. in the past months i’ve been stock piling parts to tear down and rebuild my truck with the goal of making it more fun to drive while keeping it period correct appearing and tastefully styled. so far i have n85 long rods, a spray bar, nismo head gasket dual dcoe45 weber carbs and long runner gooseneck manifold, arp connecting rod bolts and some other small items. i plan on pairing my long rods with flattops, a ka oil pump, bigger schneider cam along with resurfaced rockers, bigger intake valves at the minimum possibly exhaust, head porting and port matching, bore if needed, new valve guides, performance oriented clutch and possibly flywheel, and possibly the kameari gear tensioner. the reason for this thread is i’ve had trouble locating valves and bronze valve guides and was wondering if anyone had any recs or sources. other than that i’ll be periodically updating with pictures as my build progresses in the next few months and posting questions as i face problems. thanks i’m advance and here’s my truck as of currently!aF51QSk.jpgbrkSnqB.jpg7TAyayI.jpgexgf4xZ.jpg

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when it was put in the first time i believe it was .5 or 1 mm bored over with standard l20b dished pistons arp connecting rod bolts on a standard crank. the head has been decked because i have shims and still have some chain slap even after new tensioners which is a big reason i’m rebuilding as well, we installed schneiders street valve springs and retainers as well as the cam mentioned earlier that’s all that has been done to the current motor.

 

i got the motor in the bed of my truck when i got it, the previous owner was planning on a “turbo” lseries and because of that it has dished pistons and i’m pretty sure it has l rods but i’m not 100%. the guy who built it was a motor cycle guy and it never got passed the initial stages of planning. when me and my dad put my truck together he decided to leave the low compression set up to dum it down until a later date where i would either turbo or swap. problem is i’m picky and i don’t want to do either anymore hence the long rods for the new build. 

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Try here for the valves.... you have to email him... I bought a set of the valve from them and some other stuff... others here have as well without issue....

 

https://datnissparts.com/engine-mechanical/?sort=alphadesc&page=3

 

Valve guides can be found on rockauto,  if out of stock just search the part number on Ebay... they are out there....

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is there any reason that i shouldn’t go with 44mm intake and 38mm exhaust, i’ve read around a bit but i haven’t seen anyone confidently say 36 or 38 mm for exhaust. is there any problems with fitment with 44/38 and is that a good ratio for intake and exhaust? thanks

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1 hour ago, 521aiden said:

is there any reason that i shouldn’t go with 44mm intake and 38mm exhaust, i’ve read around a bit but i haven’t seen anyone confidently say 36 or 38 mm for exhaust. is there any problems with fitment with 44/38 and is that a good ratio for intake and exhaust? thanks

If mainer311 see this he might have a picture or 2... I believe i bought the same valves he did and they were 43 intake I believe 1mm oversize and a stock 35 exhaust . he was able to just recut his valve seats.... i think the 44 might need a bigger valve seat installed... this is just a guess....

The other thing is clearance to the sides of the combustion chamber and possibly the piston and bore, which may or may not be a factor depending on cam.....

I'm sure someone who knows more can elaborate.....

 

This is my head with stock valves, you can see how close things are...

I was opening up the combustion chamber to descroud the valves... 

Headgasket for reference of how far I can push the edge....

Edited by Crashtd420
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Look behind the dip stick just below the head on the top of the block. If an L series the displacement will be stamped there on a raised flat boss...

 

fb9yF51.jpg

 

 

What head???? U67 or W58???? The head ID is along the bottom edge of the head behind the fuel pump between plugs 1 and 2.

 

yp5uytu.jpg

 

 

Go larger on the intake rather than bother with the exhaust. Getting air into an engine is hard as ambient is only 14.7 PSI at sea level. Exhaust on the other hand is still a few hundred PSI and want's out in a hurry. I would replace the intake seats because you might get 44s in there but the opening below the valve face is still a choke point. Forty-four seats should be much wider below the face cut. Fit the 44s and look at the exhaust, got room???

 

There us a shrouded area on both valves. This is the side of the combustion chamber directly beside the the intake and the exhaust valves. Anywhere else around, the valve opens into the cylinder but to the chamber side air has to squeeze past to get out or in. A larger valve will increase the shrouding by being tighter to the wall. Over all a 44mm will gain though.

 

Shrouding...

Take a new head gasket and scratch the outline of the fire ring into the soft aluminum. Now you can see where metal can be carefully ground away to open up and reduce this shrouding. From the valve seat to the head surface try to round gradually and polish smooth. Think of this as a trumpet on a side draft that smooths the flow.

 

This is an L head that I'm having on a Z24 which is 89mm bore vs. the 85mm on a stock L20B. It's a little exaggerated but shows what's possible. If you are going to flattops you have tons of compression and removing some material to let it breath won't affect it.

 

fLTUVOI.jpg

 

While you are at it make sure the straight part of the seat going down into the head blends smoothly into the port wall and there is no ledge.

 

 

If you are going to try to use a cutter for the valve seats better make sure the valve guides are not worn or it will wobble.

 

 

15 hours ago, 521aiden said:

when it was put in the first time i believe it was .5 or 1 mm bored over with standard l20b dished pistons arp connecting rod bolts on a standard crank. the head has been decked because i have shims and still have some chain slap even after new tensioners which is a big reason i’m rebuilding as well, we installed schneiders street valve springs and retainers as well as the cam mentioned earlier that’s all that has been done to the current motor.

 

Stock L20B is 8.4 compression. There are only stock dished L20B pistons for it and only L20B rods will work with them. If a turbo application it might have forged pistons.  Milling the head won't cause chain slap, the tensioner corrects for slack, however milling the head and not using shims or just chain wear will affect cam timing. This is why the cam sprocket has a #3 hole. This will bring the cam back 4 degrees to correct for chain stretch. 'Chain slap' might be the rubber coating on the chain guides is worn off and the chain is metal on metal.  

 

 

 

 

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i just double checked, it’s a u67 head, i looked in the spot you mentioned to confirm but i wasn’t able to grab any numbers off those areas there was a scratch or two on one of them but nothing i could make out. also under the exhaust manifold there’s an outcropped spot that i was able to make out a Z on and last time i replaced my intake/exhaust gasket i distinctly remember a Z20 marking. already have 44mm si stainless intake valves thanks to crashtd420s recommendation and i plan on getting 36mm stainless si exhaust valves soon just waiting till i pull everything apart to make sure. if i do the head work myself it will be at work, my boss says he has all of the tools for it but i’d rather pay someone who knows what they are doing to do stuff like un shrouding and i’ll do the easy stuff like porting myself. what i meant by the chain slap thing is it was milled and when we put cam tower shims in i don’t think it was the right thickness so there is still slack in the chain, both tensioners were recently replaced no change in noise and all of my valves are regularly adjusted so it’s not valve train either my cam sprocket is on the number two spot and it could be due ti chain stretch.

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yes the engine is still in my truck, the reason I haven't pulled it yet is because i will have to use my 66 460 swapped f250 on 37"s to get around with a whopping 7mpg and i cant afford California gas prices as is so I'm waiting until I have as many parts as possible before I rip my Datsun apart.also the z20 block is exactly the same as a l20 block? for some reason I thought it was taller but that could just be the z22 and 24

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Slightly newer revision casting but otherwise absolutely identical, even uses the U60 L20B crankshaft.

 

There were two style of Z20 engines one for the '84-'86 720 truck and one for the '80-'81 A10 and the '80-'81 S110 200sx. The car Z20 had the 6" rods and flattop pistons. If a l head is used the snmaller combustion chamber brings the compression to a little over 10. You won't know till you get the head of. Might even have L20B rods and pistons.

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yeah last time it was apart I'm pretty sure it had l20b dished pistons so I'm assuming it also had l20b rods, my boss knows Dave Rebello and he recommended the 6 inch n85 rods and milled ka24de pistons I believe so that was my plan. I have the rods already so just waiting till the machine shop lets me know what size pistons to use. ill probably try and open up the chambers a decent amount so I can keep my pre detonation under control because it is going to continue being my daily after everything is said and done.

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One more thing, I have a truck flywheel and clutch and id like to replace my clutch and throw out bearing while I have everything apart. There's lots of people who sell clutches that mate up to these engines but what would be a good mid range performance oriented clutch I haven't seen much info about them outside of the z guys and the people who swear by 280zx stock clutches on everything.

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6 hours ago, 521aiden said:

One more thing, I have a truck flywheel and clutch and id like to replace my clutch and throw out bearing while I have everything apart. There's lots of people who sell clutches that mate up to these engines but what would be a good mid range performance oriented clutch I haven't seen much info about them outside of the z guys and the people who swear by 280zx stock clutches on everything.

clutch masters

exeddy

OS Giken

Stay away from center force.

 

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1 minute ago, wayno said:

When you get to the 44mm intakes the seats start combining, these photos are of photos I took of the screen of my old computer with these photos on it, detail sucks but you can see what I am talking about.

 

DSC00058.JPG.d81680a95afb72ab15f42f18dcb5e9bb.JPG

 

DSC00057.JPG.222aa3274ff4b625f101de81ed26ce1d.JPG

 

what size exhaust valve is that?

 

 

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It is pretty big, normally I go with 280Z valves so whatever the exhaust valve is on them cars is what it is, I am guessing 38mm, but it has been so long ago I do not remember anymore, that photo was taken 7/28/2013, I only remember that is the only head I had made with 44mm intakes, normally I use 42mm when I had a head made.

 

Compression is nice, but the pump gas they sell these days is crap, you will need to use special fuel with the stuff you are using, racing fuel, I limit myself to 9 to 1 CR.

Edited by wayno
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16 hours ago, 521aiden said:

yeah last time it was apart I'm pretty sure it had l20b dished pistons so I'm assuming it also had l20b rods, my boss knows Dave Rebello and he recommended the 6 inch n85 rods and milled ka24de pistons I believe so that was my plan. I have the rods already so just waiting till the machine shop lets me know what size pistons to use. ill probably try and open up the chambers a decent amount so I can keep my pre detonation under control because it is going to continue being my daily after everything is said and done.

 

There are dished Z20 pistons used on the 720 truck. Maybe what you saw.

 

N85 rods on an L20B/Z20 crankshaft only leaves 26.95mm for a pin height. Do you know the pin height on the DE pistons? I found 34mm which is the same as the KA24E. To fit you would need to mill 7mm from the tops. That's way over 1/4". Almost into the top ring land. Better check.

 

KA24E pistons on L20B/Z22 rods in bored to 89mm block works and makes a 2,300cc

 

 

 

 

 

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