Jump to content
ErickwithnoK

Rebuilding my L20B

Recommended Posts

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 ???

Share this post


Link to post

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...

Share this post


Link to post

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.

Share this post


Link to post

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?

Share this post


Link to post

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.

  • Like 1

Share this post


Link to post

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.

Share this post


Link to post

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...

Share this post


Link to post

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.

  • Like 1

Share this post


Link to post

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 ...

Share this post


Link to post

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.

Share this post


Link to post

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.  

Share this post


Link to post

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.  

  • Like 1

Share this post


Link to post

reliable is close to stock

 

personally I like the 38/38 and they are new

 

question really is do you have at least $ 3 K in the Bank. if yes then go with the bigger better stuff.

If NOOOOOOOOOOO your living on the edge in a apt with no garage and tools

then go 38/38 on a L 20 get e Elelctric ignition. call it good.  Its a L motor.  spending $2000 on a L motor might get you 15hp. $800 on block and then rest on carbs cam valavle train misc....

  • Like 1

Share this post


Link to post

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.  

 

I'm interested in tuning, I'm not interested in bolting on a 38/38. I want side drafts so I have a toy to play with. I understand that the 38/38 is simpler to deal with, cheaper, and probably would even perform better since it would be better tuned. I am not interested in a 32/36, 38/38 or hitachi. They just aren't very interesting. 

 

If I do end up buying someone else's problems, I will not "give up" tuning, I will enjoy it! That's the plan at least. I have a company vehicle for work, so my datsun is a fun project and not my daily, so it's OK if I get a pair of side drafts and tune them for months before it's drivable. That being said, I'll wait till after Canby so I can show up in my 620.

 

In what way does a dcoe carb cause timing issues?

Share this post


Link to post

reliable is close to stock

 

personally I like the 38/38 and they are new

 

question really is do you have at least $ 3 K in the Bank. if yes then go with the bigger better stuff.

If NOOOOOOOOOOO your living on the edge in a apt with no garage and tools

then go 38/38 on a L 20 get e Elelctric ignition. call it good.  Its a L motor.  spending $2000 on a L motor might get you 15hp. $800 on block and then rest on carbs cam valavle train misc....

 

I love a lot of stuff to be stock, but stock-ish is even better.

 

I am not gonna spend 3k on my motor, but I'm not living on the edge in an apartment with no garage or tools. I think I'll go somewhere in between and risk side drafts (weber or dellorto or solex). At the same time I'll go electronic distributor. I'm glad you all are keeping me from going completely overboard, I don't expect to spend money and gain 50HP. I just want a driveable modified l20 that has some interest and is a fun project. 

Share this post


Link to post

From horror stories I have heard/read...don't buy used side drafts.

 

 

If they worked properly...they probably wouldn't be for sale.

  • Like 3

Share this post


Link to post

And they call the Hitachi a complex carb. 

  • Like 1

Share this post


Link to post

From horror stories I have heard/read...don't buy used side drafts.

 

 

If they worked properly...they probably wouldn't be for sale.

 

Exactly!!!

Share this post


Link to post

From horror stories I have heard/read...don't buy used side drafts.

 

 

If they worked properly...they probably wouldn't be for sale.

 

Maybe I'll shell out the cash for some new 40 dcoe's if that's really true. Is it an extra $600 true or just a caution? 

 

And they call the Hitachi a complex carb. 

 

The hitachi seems complex but it's also a stock downdraft carb which makes it boring to me

Share this post


Link to post

New carbs kick ass. Nothing quite like minimal fuss when you're dying to get your car running.

Share this post


Link to post

New carbs kick ass. Nothing quite like minimal fuss when you're dying to get your car running.

 

Are you enabling me to spend a lot of money right now?

Share this post


Link to post

You have my permission.

 

Might as well get a new manifold too.

Share this post


Link to post

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×

Important Information

By using this site, you agree to our Terms of Use.