L20b rebuild: what to look for

[cjzeppy]

If you haven't seen in this section, I have no clue what I want to swap into my '72 510. I was first thinking of swapping in a SR20, then a KA24de, and now I'm leaning towards rebuilding the L20b that's in it currently. I'm in contact with a gentleman who use to build and race 510s back in the 70s, and I would be honored if he would help me rebuild my engine. I'm not sure what parts are availible, but if someone could help me in the right direction. I guess I would need a new gasket set, new rings, bearings, timing chain, possible water pump, etc. Maybe try to find some aftermarket parts (pistons, rods, cams). Any help would be appreciated.

[fourfiveten]

http://community.ratsun.net/topic/46787-i-love/

[fourfiveten]

for parts check out http://www.rockauto.com/

[datzenmike]

A stock rebuild will be the easiest. Specially if you have limited experience with the L motor. Have the bores measured and if too worn you are going to have to bore and go oversize pistons. If doing this, go for the largest over bore size there is... probably 1mm. (it costs the same as .5mm so might as well get the bigger)

 

If you have rebuilt these motors yourself you can do much of the work and save labor.

[cjzeppy]

A stock rebuild will be the easiest. Specially if you have limited experience with the L motor. Have the bores measured and if too worn you are going to have to bore and go oversize pistons. If doing this, go for the largest over bore size there is... probably 1mm. (it costs the same as .5mm so might as well get the bigger)

 

If you have rebuilt these motors yourself you can do much of the work and save labor.

 

I think I have the capability to rebuild it, but I've gotten in contact with a older gentlemen whose says he use to build L20b engines and race 510s in the 1970s. Apparently he has a lot of spare parts for Z cars, and a couple L20b blocks. He said that he would rebuild my engine for me, and all I need to do is buy the parts (and pay him how ever much he wants). I'd rather let someone with experience do the job. I would like to know what should I buy just for a normal rebuild?

 

Here's what I'm already getting..

Gaskets

piston rings

timing chain

 

anything else?

[datzenmike]

Well first the bores may be too worn for a rebuild. If worn too much even with new rings the final clearances will be too much for the rings to seal properly and it either won't last or will simply burn oil. The cylinders must be measured for wear first before buying rings. If too worn the block will have to be bored out to the next oversize and new oversize pistons and rings fitted.

[cjzeppy]

So for right now I should get a gasket kit and a timing chain. Then when the block is torn apart I'll look into buying new parts to replace what is broken.

[tr8er]

Not sure what you are looking for, but when I put in an l20b, I made some easy mods. Flat top pistons, performance crank shaft, bored out the cylinders, changed out my valve seals. Love the engine!!! But I went from an L16, to this modified L20b, so was I stoked because of these mods, or just the bigger engine? Not sure, but they were all relatively cheap to do so I figured why not. The biggest performance mod I've ever done is the electronic dizzy. Getting points out of the mix was just amazing! Next was the carb. Just a downdraft Weber 38/38. This was a Massive upgrade from hitachi carb drivability. But I am very happy driving a L20b. Tons of power. And I'm about to put in my 5 speed. I'd say, buy the pair, just as mike suggested. You very well may wish you had another gear.

[cjzeppy]

Not sure what you are looking for, but when I put in an l20b, I made some easy mods. Flat top pistons, performance crank shaft, bored out the cylinders, changed out my valve seals. Love the engine!!! But I went from an L16, to this modified L20b, so was I stoked because of these mods, or just the bigger engine? Not sure, but they were all relatively cheap to do so I figured why not. The biggest performance mod I've ever done is the electronic dizzy. Getting points out of the mix was just amazing! Next was the carb. Just a downdraft Weber 38/38. This was a Massive upgrade from hitachi carb drivability. But I am very happy driving a L20b. Tons of power. And I'm about to put in my 5 speed. I'd say, buy the pair, just as mike suggested. You very well may wish you had another gear.

 

Where did you get the pistons and crank at?

[datzenmike]

The stock L20B crank is fine as is. It's fully counter weighted and vibration free.

 

For pistons you can use stock L18s which have a small 4.36cc dish that will bump the compression to almost 9.3. This is a stock 85mm piston... when rebuilding you may have to overbore the worn cylinders, so oversize pistons may be needed. If over boring you may want to keep going to +1 or 86mm, and in this case late 280z flattops will fit and give you 10.09 compression. Have a care as increased compression is a life time of higher octane gas and risk of detonation in hot weather. The gain is only about 4% per compression number. For example a 100 hp L20B at 8.5 will theoretically gain about 6 hp going to 10. Increased compression makes the motor more efficient at capturing and turning heat energy into motion.

 

I would build for longevity (or stock) and add a 32/36 weber. If over boring just get +1mm L20B pistons so the compression is reasonable. U-67 head, W58 intake with weber, L16 exhaust (these are cast iron headers) low resistance muffler. Try to find a lower ratio rear end even if you have to convert to R-180. Get the 4.375 or 4.11 front diff from a 720 and install. Go have some fun with it.

 

 

At a later date look into a cam for the head. Not something to jump lightly into, this will make a bit more power but it takes away from the bottom end where you drive most of the time.

[cjzeppy]

The stock L20B crank is fine as is. It's fully counter weighted and vibration free.

 

For pistons you can use stock L18s which have a small 4.36cc dish that will bump the compression to almost 9.3. This is a stock 85mm piston... when rebuilding you may have to overbore the worn cylinders, so oversize pistons may be needed. If over boring you may want to keep going to +1 or 86mm, and in this case late 280z flattops will fit and give you 10.09 compression. Have a care as increased compression is a life time of higher octane gas and risk of detonation in hot weather. The gain is only about 4% per compression number. For example a 100 hp L20B at 8.5 will theoretically gain about 6 hp going to 10. Increased compression makes the motor more efficient at capturing and turning heat energy into motion.

 

I would build for longevity (or stock) and add a 32/36 weber. If over boring just get +1mm L20B pistons so the compression is reasonable. U-67 head, W58 intake with weber, L16 exhaust (these are cast iron headers) low resistance muffler. Try to find a lower ratio rear end even if you have to convert to R-180. Get the 4.375 or 4.11 front diff from a 720 and install. Go have some fun with it.

 

 

At a later date look into a cam for the head. Not something to jump lightly into, this will make a bit more power but it takes away from the bottom end where you drive most of the time.

 

I would say I want to go for stock. I'm not sure how long I'll have this car, but I just want a dependible engine that I can drive outside of town to car shows. If I can keep the internals I will, but if parts look worn or scarred I'll replace them with new (if I can get new).

[datzenmike]

That's the plan.

[cjzeppy]

I might tear the engine at my house, order the parts, machine the block, and then let my person reinstall the parts.

[tr8er]

Stick with Mike. His advise is always best. I got my crank and Pistons from Oliver over at Z-Specialties North of Seattle. He has been an invaluable source of knowledge and equipment for me. The biggest thing is a new Carb. Get that in, and get it on the road.

[tr8er]

The stock L20B crank is fine as is. It's fully counter weighted and vibration free.

 

For pistons you can use stock L18s which have a small 4.36cc dish that will bump the compression to almost 9.3. This is a stock 85mm piston... when rebuilding you may have to overbore the worn cylinders, so oversize pistons may be needed. If over boring you may want to keep going to +1 or 86mm, and in this case late 280z flattops will fit and give you 10.09 compression. Have a care as increased compression is a life time of higher octane gas and risk of detonation in hot weather. The gain is only about 4% per compression number. For example a 100 hp L20B at 8.5 will theoretically gain about 6 hp going to 10. Increased compression makes the motor more efficient at capturing and turning heat energy into motion.

 

I would build for longevity (or stock) and add a 32/36 weber. If over boring just get +1mm L20B pistons so the compression is reasonable. U-67 head, W58 intake with weber, L16 exhaust (these are cast iron headers) low resistance muffler. Try to find a lower ratio rear end even if you have to convert to R-180. Get the 4.375 or 4.11 front diff from a 720 and install. Go have some fun with it.

 

 

At a later date look into a cam for the head. Not something to jump lightly into, this will make a bit more power but it takes away from the bottom end where you drive most of the time.

 

Mike, you recommend the L16 Exhaust Manifold over Headers? Please qualify.

[datzenmike]

For most all applications the only difference is the weight. Headers are over rated expensive bling that can extract a few hp at RPMs you never drive at.

 

L16 manifold...

 

May already be on car (cost nothing) or very cheap to get. (mine was $10) Will fit all square port heads.

Never never never will rust out or need replacing. (may be rusty though)

Fits without cutting your exhaust system or loosening motor mounts and jacking engine up. Clears steering box and seals without leaking. Doesn't come loose.

Quieter.

[tr8er]

Well, I'm rolling with an L16 manifold right now, and I have had my share of exhaust leaks. But none right now. Its that damn lower connection. It is crazy rusty and truly the ugliest sight on that engine. But I am less anxious to replace it now. My main motivation was the thought that this manifold is from a L16, and I am running it on a modified L20b. It must be limiting my performance. But sounds like not too much.

[ddrum]

What would be the compression ratio on an l20b with .20 oversized L18 pistons, and w58 closed chamber head shaved .003 inch? this is what my engine has right now, i was thinking around 9.6ish compression?

[datzenmike]

What would be the compression ratio on an l20b with .20 oversized L18 pistons, and w58 closed chamber head shaved .003 inch? this is what my engine has right now, i was thinking around 9.6ish compression?

 

9.948 without accounting for the 0.003" shave which would be negligible. It could be higher if the head was previously milled.

[ddrum]

Wow, that seems a bit high. Thanks for the info datzenmike.

[datzenmike]

Stock L20B with L18 pistons and closed chamber W-58 head.................................. 9.915

Stock L20B with L18 pistons and open chamber W-58, A87 or U-67........................ 9.279

 

Stock L20B with only W-58 closed chamber head..................................................... 8.903

Stock L20B with only W-58, A87 or U-67 open chamber head.................................. 8.4

[ddrum]

Good to know! I always wondered what were the numbers with L18 pistons. Thanks for sharing.

[80daterpillar]

Awesome thread, think I know what I want to do now! :thumbup:

[banzai510(hainz)]

Let us know if you find L18 pistons.

[cjzeppy]

bumping this thread. I've been trying to find a KA24, but have no luck. Guess I'm rebuilding the L20b.