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HP increase estimation?


Angela

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Hey there Ratsun family,

 

Could anyone give me a ballpark figure or opinion on HP increase with the following set up:

 

L20B with A87 peanut head

38mm SU's on a K-14 manifold

 

Thank you in advance & take care

 

-Angela 😊

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An L20b with a stock carb would be a big difference, it was the best upgrade I ever made to my Datsun 521 going from an L16 to an L20b(used), I soon after put the equivalent of a 219 head on it and a set of new dual SUs from Nissan and I drove it for almost 20 years that way, after that I built an LZ23, not as dramatic of a difference but I am happy that I did it.

I have beat the shit out of that 521 work truck for over 25 years, I fix it when it breaks, change the oil/filter every once in a while and I only have had to have it flatbeded home once because of a dogleg 5spd locking up, if all I ever had for a choice was an L16 I would have sold it as it was gutless and useless to me.

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Wow, I hope I'm as blessed. I good Datsun mechanic buddy of mine recently rebuilt a used (free) L20B I've been saving for a few years now. I had the A87 peanut head resurfaced by a local old timer machine shop. I was lucky enough to slowly source (over a few years) original Datsun timing chain, gaskets & linkage conversion kit so I can use the 38mm S.U's that came attached the the K14 manifold. He's almost done with the swap (also swapped in a 5 speed I've been saving) & I was just curious about the increase in power. I did a similar set up on my 510 wagon but with an L16, A87 peanut head & 38mm S.U's...it made a nice improvement & the power band makes for a fun drive. I just don't know what to expect with the L20B. Excited to find out though.

Edited by Angela
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15 minutes ago, wayno said:

An L20b with a stock carb would be a big difference, it was the best upgrade I ever made to my Datsun 521 going from an L16 to an L20b(used), I soon after put the equivalent of a 219 head on it and a set of new dual SUs from Nissan and I drove it for almost 20 years that way, after that I built an LZ23, not as dramatic of a difference but I am happy that I did it.

I have beat the shit out of that 521 work truck for over 25 years, I fix it when it breaks, change the oil/filter every once in a while and I only have had to have it flatbeded home once because of a dogleg 5spd locking up, if all I ever had for a choice was an L16 I would have sold it as it was gutless and useless to me.

 

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There is a really big difference in torque, the L20b has grunt, you do not need to worry about getting started when stopped on a hill, at least when the truck is empty, let me explain it this way, when my 521 had an L16 I was following my friends up a logging road to the top of the hill to go fly our hanggliders, they had big 4wd trucks with low range and they literally crawled up the hill, well the L16 could not drive up the hill that slow, I came to a grinding halt and could not get it going up the hill again, so we took the guys glider off my truck that was riding up the hill with me and put it on one of their trucks, they continued on and I backed down the hill till I found a spot to turn around I went down the hill till I came to a flatter area, I thought, well I could turn around and wait for a few minutes and try again, I made it up the hill going pretty fast, there was a hairpin turn with a cliff on the right, I took that corner as fast as I could and I did make it to the top.

That next week I found an L20b/stock carb at a local wrecking yard with a 5spd and I installed it in my truck that week, the next weekend I drove it to a hanggliding site 329 miles away from where I live and I drove up a much steeper hill in second gear driving slowly than I could get up in first gear with the L16.

Edited by wayno
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That's a great story...& illustration. My old L16 had low, uneven compression & made me a little nervous when navigating the local hills & climbing up the Cuesta Grade here where I live.. Having to stop for a signal light on a hill was awful. I'm stoked to know these are worries I can leave behind.

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The '71 Bluebird coupe with the optional L18SSS engine made 113hp. This is with dual SUs and a closed chamber head and a cam reputed to be the same used in the L20B. Now the L18SSS had flattop pistons so the compression is 9 to 1. This is a half point of compression and a full point would gain you in the neighborhood of 5-6% increase so 1/2 this would give it a 3%???. If we take away 3 HP this would be about the  same as an L18 dual SUs and 8.5 compression. So lets say an even 100hp. 

 

As the L20B has 11% more displacement it might make 11% more HP when scaled up. So 100 hp X 1.11 = 111HP. I would round down to an even 110 HP as the A87 will not have the larger ports of the Coupe's 219 head.

 

The regular L18 makes about 85 HP so a 100HP L18SSS minus the compression increase is a 17.6% increase, and so scaling it up to a stock 93HP L20B.... 93 X 17.6% = 109.42 (incredibly close!!!)  

 

I'll say 110hp or a 17 HP increase.

 

 

 

As mentioned the increased stroke will amaze you with it's torque at low and mid range speeds.

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Thx Mike!

 

I've got a hunch I'll enjoy the heck out of these upgrades. 

I was fortunate enough to find a speedometer guage that had just .9 miles on it so newly rebuilt engine, new, accurate mileage tracking. I'm gonna take good care of my baby so hopefully it'll last me for however long I'm on this earth & able to drive it! Having M.S sucks sometimes & is completely unpredictable but when I get in my wagon or 521 & just drive...nothing else matters & all is good. Nothing else compares. It's the best meditation & medication in my book😍

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Here is the mountain I used to drive up, this photo below was taken by me while I was flying my hangglider, you can see the tiny launch ramp on the top of that hill, you can also see that 90 degree gravel covered cliff corner I went around going way too fast in the bottom right of the photo, if you really look close you can also see a tiny hangglider where the road comes out from behind the trees on that corner.

img425.jpg

Edited by wayno
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I have two running and registered 521 trucks, Ratsun, and Dragon.  Ratsun has a 1980 720 L-20-B engine and five speed, 4.375 rear axle.  Dragon has a L-18, and also has a five speed, and the 4.375 rear axle, but Dragon's transmission has a 3.3 first gear, and closer gears than Ratsun.  I believe Ratsun has identical gear rations to a stock 521/L16 truck, but with a overdrive fifth gear.

 

In almost any driving situation, Ratsun can be in one gear higher than Dragon.  This may sound worse than it is, but to me the L-18 in Dragon just seems happier at a higher RPM than my  L-20-B does in Ratsun.  I actually think Dragon, with the smaller engine is more fun to drive.

 

Last weekend, I drove Dragon from slightly south of Portland, Or to north of Seattle, and back to get some engine parts.

But tomorrow, I need to get a load of hay, 20 bales, I am going to drive Ratsun.

 

In most cases, peak horsepower happens pretty close to peak RPM.   That counts when in a race.   But when driving on the street, the additional torque at low and mid range RPM of a L-20-B is way more usable.

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sBzw2v1.jpg

 

It's the same oil pump on the L, Z and KA series engines. The KA24E in the S13 and both KA24E and KA24DE in the D21 Hardbody trucks have 13% longer rotors inside and it moves more oil per turn.  This will boost low RPM oil pressure. The tired high mileage L20B I had in my 620 hot idled at 17 PSI. With no other change but a KA oil pump it rose to 29 PSI. These pumps are great if you have a cam spray bar or an oil feed for a turbo. I have always run them on my Datsuns.

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13 hours ago, datzenmike said:

sBzw2v1.jpg

 

It's the same oil pump on the L, Z and KA series engines. The KA24E in the S13 and both KA24E and KA24DE in the D21 Hardbody trucks have 13% longer rotors inside and it moves more oil per turn.  This will boost low RPM oil pressure. The tired high mileage L20B I had in my 620 hot idled at 17 PSI. With no other change but a KA oil pump it rose to 29 PSI. These pumps are great if you have a cam spray bar or an oil feed for a turbo. I have always run them on my Datsuns.

Well thanks for the advice & information (admittedly some of which is still above my pay grade...but I'm trying & learning).

 

Are these oil pumps fairly easy to source?

 

Anybody have leads?

 

Much appreciated as always guys. You rock 🎸 

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I just pull them from wrecking yards, after all they are well lubricated and low wear. lol.

 

This is a stock L series pump. If you look down inside you can just barely see the top of the rotor.

V2fckkS.jpg

 

This is a KA pump with the longer rotor that is obviously sticking up

7jkQ4Im.jpg

 

 

The 280zx turbo automatic cars all had oil coolers and had a similar oil pump.

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