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Rebuilding my L20B


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#21 wayno

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Posted 29 April 2017 - 08:56 AM

Pulling the head may be difficult to do in a junk yard, and getting someone to sell me just the block would be tough as well. I will do my best to investigate any z22 block I come upon, thanks for the photos those are super informative. I'll be sure to read through your thread.

 

 

Honestly when I think about spending more than 2k on my 620 it makes me feel like...it's just a 620. It has a lot of value to me, but I respect all of your opinions and would like to own a Z or a 510 some day and if I have a lot into my pickup it will be tough to get into anything else. So I'll just rebuild what I have. I didn't realize my U67 head already had larger valves than other L series, that's really interesting and seems like a good thing for my application. If I go with a rebuild on my l20 (possibly a mild bore for larger pistons like flatcat suggested, I'm sure the 38/38 would work great but I want side drafts, just for fun), what kind of costs should I be expecting? I would also be finding some dcoe's, after reading through the R1 thread I think it's a bit out of my league. Would I want to port my head?

Yes the U67 head has large valves and intake ports, the only reason it is not the sought after SSS 219 head is because it is an open chamber head design.

If you rebuild your block and choose the right pistons, that would basically turn your U67 head into a SSS 219 head, meaning if I build a LZ22 with stock type Z24 dished pistons and use a closed chamber head with big valves and ports I will have an 8.9 to 1 compression ratio, if you built a LZ22, use less dished pistons, and use your U67 head, you also can end up with 8.9 to 1 compression ratio, I have no advantage over you, your head is fine, it's all about information and choices.

Flatcat mentioned using 280zx flat top pistons, if they with your head work out to somewhere around 8.9 to 1 compression ratio that would be one way to go.

I personally run dual SUs on my L series builds, I also run stock cams as even using an RV cam robs one of torque, I like my torque and I am not on a circle track going around in circles at a steady 7000rpms, so the stock cam is a good choice for me.

I like SUs because I understand them, I don't like down drafts because I don't understand them and it seems the only way I can get a good one is if I buy it new.


 

 


#22 flatcat19

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Posted 29 April 2017 - 09:00 AM

I can attest to wayno's little 520 being a ripper. I followed him to Blue Lake last year.

That truck gets it.


I think the L20B with flat tops and an open head is right in the 9.0 to 1 ratio. Plenty of power.

Right rear end and a good transmission will make a reliable/quick engine without breaking the bank.

You can't hang if your nuts haven't dropped...it's physics


#23 datzenmike

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Posted 29 April 2017 - 09:07 AM

The L20B engines had U67 and W58 heads and all had the same 'large' valves compared to the L16 and L18s. Generally 35mm exhaust and 42mm intakes. These are the same size as the L16/18 SSS head.

 

The 280z and zx had 44mm intakes and seats.

 

There is only 0.2" or 5mm between the L20B valves in the combustion chamber so there are limits


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#24 banzai510(hainz)

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Posted 29 April 2017 - 12:07 PM

increasing valve size OAL of 2mm valves  and putting in new seats adds some cost. and hope the machine shop gets is right w/o throwing the valsh lash off.

cams need new rockers and retainers springs ect........

 

 

To me if you have a L20 b intake that's is matched to the l20 head just bolt a 38 38 weber  downdraft to it and call it good. its the cheapest power gain I have ever done

 

get a eleltric ignition conversion ot a matchbox distributor with the matching mount.

 

find a closed chamber head on side and build it up as learn and get parts(sidedrafts also

 

. so you can still drive the truck and when ready  do a swap. in a couple hours

 

 

 

read olddatsuns.com the tech section


Throw on some Weber sidedrafts, Rising Sun hood.... call it good

#25 wayno

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Posted 29 April 2017 - 12:11 PM

I can attest to wayno's little 520 being a ripper. I followed him to Blue Lake last year.

That truck gets it.


I think the L20B with flat tops and an open head is right in the 9.0 to 1 ratio. Plenty of power.

Right rear end and a good transmission will make a reliable/quick engine without breaking the bank.

The 520 has an L20b, and with the head that is on it it is a pig, it was really a pig with the Weber that was on it, it now has Dual SUs and it a lot better, but that W53 head with stock valves and that RV cam in it, it is a PIG, my work truck with a LZ23 with a good head and dual SUs will run  circles around that 520 and it is a way heavier truck, it weighs 3400lbs and will kick that 520s ass in every form from off the line to out running it, that is why I have built another LZ23 for the 520, once I put the dual SUs on the 520 and it started reliably, I lost my motivation, I have been considering just having the 219 head with a stock cam I have rebuilt/refreshed and then putting it on that engine, it don't smoke or use oil, so why make the effort and keep the LZ23 as a backup engine.


 

 


#26 ErickwithnoK

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Posted 29 April 2017 - 12:47 PM

So it's sounding like the general consensus is to run z24 pistons in my l20 block, leave my top end unmodified, and pick whatever carbs I'm comfortable with. The 38/38 was mentioned again but I don't find DGV carbs to be very interesting. I'd rather lose power and have a more interesting build than run a 32/36, 38/38 or a hitachi. 

 

 

I can attest to wayno's little 520 being a ripper. I followed him to Blue Lake last year.

That truck gets it.


I think the L20B with flat tops and an open head is right in the 9.0 to 1 ratio. Plenty of power.

Right rear end and a good transmission will make a reliable/quick engine without breaking the bank.

 

 Does higher compression, to a reasonable point = more power?

 

I thought I read that open chamber = lower compression, better for forced induction applications

                                closed chamber = higher compression, better for ???



#27 Crashtd420

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Posted 29 April 2017 - 01:07 PM

The down draft is only being suggested because of cost.... Side drafts get pricey and there are other concerns such as pcv and the distributor needs to go full mechanical... no vacuum provision on side drafts...
Compression does increase horsepower... I can't remember how much...
And I don't believe open vs closed matters as much as the piston it's paired with to achieve the right compression ratio...

#28 wayno

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Posted 29 April 2017 - 02:50 PM

So it's sounding like the general consensus is to run z24 pistons in my l20 block, leave my top end unmodified, and pick whatever carbs I'm comfortable with. The 38/38 was mentioned again but I don't find DGV carbs to be very interesting. I'd rather lose power and have a more interesting build than run a 32/36, 38/38 or a hitachi. 

 

 

 

 Does higher compression, to a reasonable point = more power?

 

I thought I read that open chamber = lower compression, better for forced induction applications

                                closed chamber = higher compression, better for ???

No, boring a L20b 89mm to put Z24 pistons in it is on the ragged edge, the cylinder walls may be too thin, I believe flatcat was saying bore it out to 86mm and use 280ZX non-turbo flat top pistons.

The Z22 block is larger and can be bored out to 89mm without being on the ragged edge, 

There is no substitute for displacement, but only race guys bore the L20b way out and run them for a season, the engine is disposable to them, if it blows up, put another one in before the next race or maybe next weekend if it is late in the night.

Personally I would just fix your engine if possible, and then start collecting everything needed for an LZ23, a 2.1 stroker, or whatever else catches your imagination, if the engine is not repairable with a new headgasket, then keep it simple this time, rebuild it and maybe use flat tops and make sure the compression ratio is at or below 9.0, get to understand what you have, then build the dream engine on the side.

My LZ23 engines are not fancy powerhouses, they are just a larger displacement engine that breaths good with the heads I normally use, I spend my money on the head and intake system, but it still is just a torque monster that likely any respectable KA will stomp on.


 

 


#29 ErickwithnoK

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Posted 29 April 2017 - 03:21 PM

The down draft is only being suggested because of cost.... Side drafts get pricey and there are other concerns such as pcv and the distributor needs to go full mechanical... no vacuum provision on side drafts...
Compression does increase horsepower... I can't remember how much...
And I don't believe open vs closed matters as much as the piston it's paired with to achieve the right compression ratio...

 

What is the PCV solution? Drilling out the manifold and putting in a fitting for it?



#30 flatcat19

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Posted 29 April 2017 - 03:40 PM

Where is Oregon are you located?

Draker and KO have reported there is a Datsun cylinder head guru in their neck of the woods; Eugene.


Side note: build your engine for strength/reliability. Build your head for horsepower.

You can't hang if your nuts haven't dropped...it's physics


#31 datzenmike

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Posted 29 April 2017 - 03:40 PM

To run Z24 pistons do some math. The L series pistons are 38.1mm tall the Z24 are 34mm. A difference of 4.1mm. The Z22 crank throw is 3mm longer so even with Z24 pistons they don't come to the top of the block at TDC by 1.1cc This volume above the piston (6.8cc) is added to the combustion chamber volume lowering the compression. Then there is the head gasket thickness and it's volume (7.46cc) the piston dish (15cc) and the U67 combustion chamber volume... 45.2cc

 

6.8cc + 7.46cc + 15cc + 45.2cc = 74.5cc total cylinder volume

 

The 89mm by 92mm stroke has a cylinder volume of 572cc

 

572 + 74.5 = 646.5cc divided by the above combustion chamber of 74.5cc = 8.677 compression.

 

 

 

 

The KA24E pistons are exactly the same as the Z24 pistons but a dish of 2.8cc. Reducing the combustion chamber by 12.2cc.

 

6.8cc + 7.46cc + 2.8cc + 45.2cc = 62.26 total cylinder volume

 

572 + 62.26 = 634cc divided by the above combustion chamber of 62.26cc = 10.18 compression.

 

 

 As wayno suggested get a Z22 block. You need a Z22 crank anyway and the cylinders are already 87mm and only need 1mm removed all the way round rather than 2mm to over bore an L20B.


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#32 Crashtd420

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Posted 29 April 2017 - 04:52 PM

What is the PCV solution? Drilling out the manifold and putting in a fitting for it?

Problem with that is you'd have to drill into all four runners.. I don't believe you'd can do just one.... I'm not really sure what to do... in my case I have a small filter on the crank case tube but that's only because I haven't figured out what i want to do yet...

#33 ErickwithnoK

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Posted 30 April 2017 - 07:04 AM

No, boring a L20b 89mm to put Z24 pistons in it is on the ragged edge, the cylinder walls may be too thin, I believe flatcat was saying bore it out to 86mm and use 280ZX non-turbo flat top pistons.

The Z22 block is larger and can be bored out to 89mm without being on the ragged edge, 

There is no substitute for displacement, but only race guys bore the L20b way out and run them for a season, the engine is disposable to them, if it blows up, put another one in before the next race or maybe next weekend if it is late in the night.

Personally I would just fix your engine if possible, and then start collecting everything needed for an LZ23, a 2.1 stroker, or whatever else catches your imagination, if the engine is not repairable with a new headgasket, then keep it simple this time, rebuild it and maybe use flat tops and make sure the compression ratio is at or below 9.0, get to understand what you have, then build the dream engine on the side.

My LZ23 engines are not fancy powerhouses, they are just a larger displacement engine that breaths good with the heads I normally use, I spend my money on the head and intake system, but it still is just a torque monster that likely any respectable KA will stomp on.

 

Is a stroker a motor where displacement was increased by increasing the distance between the top and bottom of the piston throw? 

 

I think you're right. I will fix my engine, and in the process take the advice of installing 280zx non turbo pistons, and focusing on my cash on the carbs and the correct rear end/transmission. I'm not looking for a race motor, I'm looking for something reliable, that is fun to drive, sounds nice and is interesting as a project. Since I have no experience building engines any modification I make is plenty interesting. 

 

 

 

Where is Oregon are you located?

Draker and KO have reported there is a Datsun cylinder head guru in their neck of the woods; Eugene.


Side note: build your engine for strength/reliability. Build your head for horsepower.

 

I'm in the scappoose area. If Eugene is where I need to go then thats where I'll go! I'm finding out people are the most reliable resource in cars. 

 

Thanks for the solid advice.

 

 

To run Z24 pistons do some math. The L series pistons are 38.1mm tall the Z24 are 34mm. A difference of 4.1mm. The Z22 crank throw is 3mm longer so even with Z24 pistons they don't come to the top of the block at TDC by 1.1cc This volume above the piston (6.8cc) is added to the combustion chamber volume lowering the compression. Then there is the head gasket thickness and it's volume (7.46cc) the piston dish (15cc) and the U67 combustion chamber volume... 45.2cc

 

6.8cc + 7.46cc + 15cc + 45.2cc = 74.5cc total cylinder volume

 

The 89mm by 92mm stroke has a cylinder volume of 572cc

 

572 + 74.5 = 646.5cc divided by the above combustion chamber of 74.5cc = 8.677 compression.

 

 

 

 

The KA24E pistons are exactly the same as the Z24 pistons but a dish of 2.8cc. Reducing the combustion chamber by 12.2cc.

 

6.8cc + 7.46cc + 2.8cc + 45.2cc = 62.26 total cylinder volume

 

572 + 62.26 = 634cc divided by the above combustion chamber of 62.26cc = 10.18 compression.

 

 

 As wayno suggested get a Z22 block. You need a Z22 crank anyway and the cylinders are already 87mm and only need 1mm removed all the way round rather than 2mm to over bore an L20B.

 

So compression is the cylinder volume with the piston at the bottom of its throw, divided by the cylinder volume with the piston at TDC? 

 

10.18 compression is too high correct? So in a Z22 the correct piston with a U67 head would be the z24 since it's closest to 9?

 

Thanks for the explanation, Mike.



#34 Crashtd420

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Posted 30 April 2017 - 07:14 AM

I dont think 10.18 cr is too bad.... you'll have to run atleast 91 octane... maybe 93...
My l16 is at 10.8 to 1 running on 93 without issues. (SO FAR)
I've read that over 11 to 1 you can start running issues with the head gaskets ...

#35 datzenmike

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Posted 30 April 2017 - 07:37 AM

Higher compressions make more efficient use of your gasoline energy. There is increased risk of detonation and you must run higher octane gas, possibly colder spark plugs and retard your timing to reduce this. The efficiency increase in mileage may offset the cost increase of the gas.

 

My old Ford work van gave more mileage on premium gas than regular. I tested this over several tank fulls on long trips and kept careful records. The increase in mileage was more than enough to pay for the more expensive gas. Go figure.


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#36 ErickwithnoK

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Posted 30 April 2017 - 08:06 AM

I don't mind buying more expensive gas



#37 distributorguy

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Posted 30 April 2017 - 08:46 AM

I run 11:1 on pump gas, so 10:1 is not that big of a deal.  Then again I tune cars for a living.  Can you get and keep yours in tune?

 

 38/38 will have synchronous throttle plates, not progressive linkage opening 1 barrel at a time.  Its basically a vertical DCOE, almost.  Its a solid "middle ground" carb choice between a SUs and 2 DCOEs.  I rate a DGV almost as low as the stock carb.  



#38 Crashtd420

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Posted 30 April 2017 - 09:20 AM

And when u say 11:1 on pump gas what octane?... 93?...

#39 ErickwithnoK

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Posted 30 April 2017 - 06:48 PM

I'm looking at dellorto DHLA 40H carbs, a redline manifold, and baseline jetting/linkage at roughly $700.



#40 distributorguy

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Posted 01 May 2017 - 07:33 AM

And when u say 11:1 on pump gas what octane?... 93?...

 

Depends on the gas station around here.  91-93.  at  roughly 1000' altitude.  Keep in mind I build distributors for a living, so timing setup is easy to avoid pinging.  The motor in our race truck is over 15:1.  

 

Erick, stop looking to buy someone else's problems.  By the time you give up tuning, you will have spent more than buying new.  The 38/38 won't give you timing issues like the 40's or 45's.