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What would you do

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I got two engines. One is a L18 with Closed Chamber w53 other is L20b with u67.  Hoping to run a single side draft carb and l16 header.

 

One has more torque, one is a rev master.

 

Its going in my new '74 620.

 

 

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It really depends on how you want to drive it.

If you like revving the shit out of it then the L18 with the W53 head, but the intakes need to be ported, also with your foot that deep into the pedal you likely will have to install hardened seats as the valves will sink into the head if your lead footed.

The L20B with the U67 head is a torque monster compared to the L18, but it is not a rev happy engine, but it breaths way better and the intake ports are already big as well as it has big valves.

Does the L18 have flat top pistons, if it does I wonder what the compression ratio would be with the U67 head on it.

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L20 will better for driving all over the state going to Datsun shows, like you do. With taller gearing of course.

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Why not L20B with the CC head?

 

 

 

Id personally run the L18/W53...cuz I'm odd.

 

 

L20B with the W53 just seems like the better overall option.

Just add a 4.11 rear end and a 5 speed...happy traveler.

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Which one is in better shape?

Both looks to be in good shaped. L20b block matches Paint of truck

 

 

It really depends on how you want to drive it.

If you like revving the shit out of it then the L18 with the W53 head, but the intakes need to be ported, also with your foot that deep into the pedal you likely will have to install hardened seats as the valves will sink into the head if your lead footed.

The L20B with the U67 head is a torque monster compared to the L18, but it is not a rev happy engine, but it breaths way better and the intake ports are already big as well as it has big valves.

Does the L18 have flat top pistons, if it does I wonder what the compression ratio would be with the U67 head on it.

 

Not sure IF I want to open it up to see.   My last L20b build had  l20b block, bored .20 over with L18 semi dished pistons with CC head

L20 will better for driving all over the state going to Datsun shows, like you do. With taller gearing of course.

 

Gearing is a must

Why not L20B with the CC head?

 

 

 

Id personally run the L18/W53...cuz I'm odd.

 

 

L20B with the W53 just seems like the better overall option.

Just add a 4.11 rear end and a 5 speed...happy traveler.

I was going to post that question too, but not sure if I want to swap.

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Both looks to be in good shaped. L20b block matches Paint of truck

 

 

 

Not sure IF I want to open it up to see. My last L20b build had l20b block, bored .20 over with L18 semi dished pistons with CC head

 

Gearing is a must

I was going to post that question too, but not sure if I want to swap.

...L20b it is then...good luck.

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L20b w/cc.

 

It's a truck damnit. Needs torque to tow.

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L20B red line is 7,000, so just how much revving do you need????? Always go with displacement, always.

 

Closed chamber head is nothing without flattop pistons. L18 and L20B have dished pistons so no quench area. It will run the same as an open chamber that's been milled to the same 41cc volume. Besides the W53 has smaller intake ports than the U67.

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There is no substitute for displacement, if the L18 has dished pistons like the L20b, then it's a no brainer, L20b with the U67 head, the W53 will need a lot of work and money to breath like the U67 head.

The L20b runs out of poop at just under 5000rpms, it may make it to 7000rpms in the first 3 gears, but race cars on tracks have to rebuild their engines every year or every other year, them engines have hundreds of miles not tens of thousands of miles on them let alone a 100,000 miles, revving them like that is hard on them.

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My l20b runs out of breath at 5k but is a good cruiser. Torque is nice.. old probably go l20b, but never had an l18 to compare with.

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L18...4cc dish pistons.

L20B...11cc dish pistons.

 

Both 85mm.

 

 

 

Although not game-changing...L18 with the peanut will do more than putting an open head on it.

Same as putting a peanut head on the L20B.

 

One can't say that "nothing" will happen. A slight increase in CR is going to happen. It's math.

 

 

But...as already said...the U67 has bigger intake runners. Have to be able to suck in to be able to push out.

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new '74 620.

 

 

Have you shared pictures yet?

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Have you shared pictures yet

No

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It's been a long time since I had anything with high compression, the one I had was very fun to drive, but that was 37/38 years ago when gas was gas, not this shit they call gas they sell these days, I still am not sure if I should buy race fuel(103?) or try the 92 ethanol free stuff I can get locally to test run it.

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The L20b with the small chamber head will be your best bet by far.  I have one set up like that and it runs great on premium fuel.  Of course the head is ported or it would have really been choked.  Aluminum is easy to port, so that's no excuse.  And get a fresh valve job - it'll last you years.  The cam and distributor are what limits revs more than anything.  Both engines likely have the exact same cam, one with more wear than the other.  

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L20B with small chamber head would also be my choice. A compression ratio of 10:1 or thereabouts is ideal for a street car/truck, but I would ditch the single sidedraft Weber in favor of a single downdraft Weber. The progressive downdraft will give you better throttle response at partial throttle and the common plenum of the stock intake will give you better fuel atomization, resulting in better mileage and probably the same power as the sidedraft.

 

I would also consider a cam swap and a recurved distributor to make everything run right. A small cam (like a 27C) will give you more of everything, but isn't so big that it requires more than just new valve springs. The recurved distributor will allow you to run maximum timing without the worry of part throttle spikes in timing resulting in pinging and broken rings.

 

If you have the L18 exhaust manifold, run that. If not, try to find an early 4-2-1 manifold. They are much better preformers than the 4-1 L20B manifold.

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This was my first engine I built for my original 620. L20b with ported/polish w53 Peanut with aftermarket cam.  Bored .20 over running L18 4cc dished pistons. First was running SU but went went weber.  Ran great but had to sell it for rent payment.  Sold it to a guy in so Cal, then his car got stolen. So bye bye engine

 

p_007.jpg

 

p_027.jpg

 

 

Thanks for all the info guys

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L20B with closed chamber head is 8.9. Slightly more if it's been milled before.

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If L20 is together and running already just put the correct oil pan and pick up and install it. no porting has bigger intakes. just match port the intake if it isnt matching already. The head swap to a higher comp i say isnt worth the time to port out the head and have it done. yourll rolling in a day except say for the flywheel T/O bearing clutch issue

 

If your clutch is the same then go with the clutch beeing same issue.

 

But I think the L20 is a better choice for a truck.and u have the clutch set up already going by your avatar(78KC)

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Which would require a complete Z24 and everything from the L20B but the block, crank, rods and pistons. 

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I need to stop spending money, so im just going to get it running again.

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