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Perez620

Help! Rebuilding an L20 and what to do for most performance!

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Recently purchased a '74 620 and I just pulled the factory L18 from it with a factory 3-speed. A buddy of mine is doing a KA swap and he's pulling his L20B that he said I could have if I wanted. 

 

A few questions that I have since this recent opportunity came up. I was originally thinking about rebuilding my L18 but now pretty much set on his L20B. When rebuilding the L20B, what can I do to the engine to improve performance? Change bore, stroke, cam, crank? Will my 3 speed mate up directly to the L20B? 

 

I realize that the L18 is a 1.8L and the L20B is a 2.0L so my assumption is its be best to build the L20B and build it up. Any information to help with improving any performance for the engine to get the most power possible is what I'm planning to do! Pretty new to the 620 scene so trying to learn as I go. 

 

Thanks in advance everyone 

 

 

 

 

 

 

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That's why your buddy is doing ka swap. He will practically have 50 % more go with KA swap. To get that result with the L20, you will spend tons of money. Anything with L18? I would not a compression check on both before swapping. A lot will depend on your ability also. Will you have someone build your L20 or will you do it? Do you you have a place to work on your engine?

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Meant I would do a compression check on both engine

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I think the best way to decide is to find out what you have. Check the casting numbers on the L18 and the L20B. It's likely that the L18 is a good high compression motor, while it's also equally as likely that the L20B is a crappy low compression round port motor. If I had my choice, I'd rather have a high compression L18.

 

But yeah, if horsepower is really important to you, and you have a few grand to throw at it, go with a KA24 instead.

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3 speed.... automatic?

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That's why your buddy is doing ka swap. He will practically have 50 % more go with KA swap. To get that result with the L20, you will spend tons of money. Anything with L18? I would not a compression check on both before swapping. A lot will depend on your ability also. Will you have someone build your L20 or will you do it? Do you you have a place to work on your engine?

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Both motors have good compression after testing them. I’ve thought about doing a KA swap but it’s not in the budget currently. That’s why I’m just thinking about rebuilding an L motor with a little better performance. Not going for much bigger HP. If I was I realize a KA would be a better choice. Also, yes I have a shop to work on it at

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I think the best way to decide is to find out what you have. Check the casting numbers on the L18 and the L20B. It's likely that the L18 is a good high compression motor, while it's also equally as likely that the L20B is a crappy low compression round port motor. If I had my choice, I'd rather have a high compression L18.

 

But yeah, if horsepower is really important to you, and you have a few grand to throw at it, go with a KA24 instead.

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Makes sense about going with the L18. I’ll look into both motor and see what I have exactly.

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3 speed.... automatic?

Yes automatic. I realize now it was confusing how I stated it :(

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Makes sense about going with the L18. I’ll look into both motor and see what I have exactly.

Mostly I would see what heads you have.... that's where these L motors make there power...

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There is no replacement for displacement. The larger L20B will always outrun the L18 and produces much more bottom end torque. Torque is that shove in the ass when you floor it at low speeds. And the majority of driving is at lower RPM and speeds anyway. You have an automatic so you want all the torque you can get.

 

I've run both heads that came on the L20B '75-'77 U67 and later '78-'80 W58 and can't tell the difference stock.  Rather than a header, get the L16/18 square exhaust manifold and have a down pipe made for it.  It will also work on the round exhaust port W58 head and unlike a header... it fits, needs no attention and never needs replacing.

 

Get a moderate cam upgrade so the head breaths better. Too much cam and you will have to wait for the engine to rev higher to 'get going'. Bigger cam means the increased power is higher in the rev range.

 

Maybe a 32/36 replacement carb.

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Well the good thing is he has 2 L motors... decide which one you wanna build , put or leave the other motor in the truck and and keep the truck running.. easy weekend swap... no datsun down time....

 

I can say from experience plan the motor build.... all aspects....

I probably could have bought 2 ka motors for what I have invested in my L16... yes an L16.. keep the compression in the 9s and you should be ok....

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I could buy the best truck on the market for what I have into my race engine.  How much power do you want to make, and how much cash do you have to make it happen?  

 

Standard formula for a basic street engine:  regrind the cam, do whatever you can afford to raise compression, and buy a legit (expensive) Weber carb to put on it.  Get the distributor recurved for whatever engine setup you're building, and lighten the flywheel to make it more fun to drive (accelerates MUCH faster).  16 Lbs is a good weight to be at, and make sure it gets balanced after lightening it!!!   Some head work will also do wonders for hp. 

 

A basic rebuild with a cam will cost you $4k or more - depending on how well  or how sloppy its done.  Cut corners and do a $1500 rebuild and you'll be fighting problems until you sell it.  I'm guessing by your comment about affording a KA swap that a rebuild may not be in the budget either?  What compression values did you get on each engine?  

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Help! Rebuilding an L20 and what to do for most performance!

 

Well swap a KA24DE head and a turbo on it .... http://ozdat.com/membersites/zac510/

 

Or do you mean what simple cheap things can I do while re-building my L20B, to get the most performance bang for the buck out of it?

 

 

Engine strength is in the block, crankshaft, rods and pistons. This is what holds it together at high RPMs and HP.

 

Engine power is produced solely in the head and what you do to it.

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If doing a L20

going to need a to find a L20b flex plate(6bolt crank) and the adapter on end on the crank. find this first before tearing into anything otherwise youll have a junk truck in back yard

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I'm almost completely sure the flex plate to torque converter bolt patterns are the same for 5 or 6 bolt cranks. This would be for the '71 to about '82 3N71B JATCO automatics. Before this the Borg Warmer 35 were used and around '82/'83 the converter lock up was used and the torque converters were different size requiring a dished flex plate very similar to the L4N71B.

 

I have the measurements for the L20B 6 bolt crank torque converter bolt pattern.

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Where's the OP? You all scared him off.

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He's just absorbing....

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