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L20B with v912 Head Build


Floyd

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Hey guys, got a L20b bottom end, and a v912 head. Just starting to get some stuff together to start the build and chasing a few opinions and measurements.

 

Planning on a high comp, big cam, high revving deal. Probably 150hp or so. Will be street driven but will definitely see track days 

 

what sort of restrictions are there with standard rods?

 

what flat tops/rod combo work best

 

Tips for closed chamber head and flat tops?

 

standard head thickness (trying to see if mines been done before)

 

Feel free to add anything else 

 

thank you 

 

 

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Nissan rods and cranks are forged and are fine. The L20B crankshaft is fully counter weighted and smooth revving. Engine red line is 7,000 on stock parts. To go higher you'll need stronger after market rods, specialty rod bolts and forged pistons. Way too much expense for a street engine.

 

For the closed chamber 219 or V912 to work the way it was intended, yes, flattop pistons are needed. The Z20E or S engines from the '80-'81 S110 200sx the '80-'81 A10 HL510 or the '83-'86.5 Mileage Option 720 truck all had the same 85mm bore and 86mm stroke as the L20B, are flattop, (with small eyebrows for valve clearance) and have a shorter pin height to use with a longer 152.5mm (6") rod. The Z20 also uses the L20B crank so very compatible making the L20B a long rod engine. In comparison the L20B uses a 145.9mm rod and longer piston pin height.

 

A V912 closed combustion chamber head and flattop pistons in a stock bore and stroke L20B would give you 10.68 compression.

 

Measure the head thickness between the head gasket and valve cover surfaces. An uncut head should be 4.24" but I would cc the combustion chambers to be sure. The combustion chambers on a V912 head should be 41cc if not re surfaced.

 

 

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Stock rods can be shot peened, cryo treated, , metal-laxed, deburred, lightened and polished. All of these treatments relieve stress and remove stress risers which can lead to fractures. Proper sizing and balancing is obviously important too.

 

If you want to float the pins, you will need to drill (and chamfer) an oiling hole on the top of the rod before the machinist hones the pin bore. You will also want to use ARP rod bolts.

 

If your budget allows, get some N85 rods and custom forged pistons (with proper pin height). If you want to dare take the L20B block to 89mm, machine the tops off of some dished KA24DE pistons. .010" out of deck is ok, so account for that before machining. Since there is not a complex shape in the piston, you can simply cut them in a lathe, but a piston vice on a mill is what most guys use now. If you are going to float the rods, you will need to find a piston with retaining clips.

 

I don't know how far down the rabbit hole you want to go, but there are a few dozen other little mods that can be done in the name of performance and reliability.

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Sweet thank you @Stoffregen Motorsports and @datzenmike. Also going to run 98 octane @wayno.  I was aiming to rev past 7k so probably have to go forged pistons and different rods. I assume I can source new pistons from other motors (ie z20e, other l series). How much would I be looking at for n85 rods? And I assume they’re strong enough to hit 8-9k. Also I’m aiming for 150whp, is this achievable with twin Weber’s and this set up? Probably will end up floating pin aswell. If you want to list any other tips more then welcome too @Stoffregen Motorsports. Chances are I’ll end up trying to do them. 

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since you in Quennsland Aussie

How about a L18 4cc dish pistons(stewardsMotorsports???) with that head head you have. would be cheap on that side. least stock bottom end

rest is head , cam valve train stuff sidedrafts  and think you could but 125-135 to the ground with that

 

after that ask Baz at Datsport if he is still alive for the magic stuff like Distributor

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20 hours ago, Floyd said:

Sweet thank you @Stoffregen Motorsports and @datzenmike. Also going to run 98 octane @wayno.  I was aiming to rev past 7k so probably have to go forged pistons and different rods. I assume I can source new pistons from other motors (ie z20e, other l series). How much would I be looking at for n85 rods? And I assume they’re strong enough to hit 8-9k. Also I’m aiming for 150whp, is this achievable with twin Weber’s and this set up? Probably will end up floating pin aswell. If you want to list any other tips more then welcome too @Stoffregen Motorsports. Chances are I’ll end up trying to do them. 

Unfortunately, even the strongest street motor with this bore and stroke will only rev just past 8000 and live to tell about it. Frequent valvetrain maintenance and the occasional broken valve spring will happen if driven this hard. To be able to run consistenly high rpms you are now venturing into the full race motor category and the price goes way up because of all the custom pieces. Not only strong parts, like Carillo rods and forged pistons, but also super light valves and durable valve springs. Then there's the modifying of the crank to sustain the abuse, nitriding, shot peening, cryo treating, knife edging, etc.

 

And to feed that motor at rpms higher than the occasional 8000 rpms, you would need 50mm carbs (Solex) or 48mm Webers. That carb and manifold setup alone will run you about $3000. We haven't even gotten to the ignition or exhaust systems yet...

 

A reliable street engine can run N85 rods and dual 44mm Solex/Mikuni or 45mm Weber carbs and mostly stock rotating/reciprocating parts (rods, crank) and still run 7000+ rpms and make 240hp. The price for an engine like this is roughly $6000 for the motor and $1500-$2500 for the carb/intake setup. Reliability is still a concern and a sturdy valvetrain set up by a seasoned engine builder is key to longevity.

 

I've built dozens of engines like this, and if driven really hard (like track days and redline shifting every gear), you will still break valvesprings or at least need to replace them every so often. The bottom end will last a few years and will only fail if detonation occurs or if there is a problem with oiling.

 

Oiling is another subject. Most of what you need to know there is outlined in the Datsun/Nissan racing engine books. Basically, you need to enlarge the #2 and #4 main bearing feed galleys (1/4" drill), chamfer every hole and deburr the bearing saddles, then get or make a set of full groove bearings. In the old days, the main bearing sets were all full groove, but then they started coming with only half of the bearing shells grooved. So you can either buy two sets or you can make a fixture to hold them in a lathe and groove them yourself. Even then, the grooves need to be made wider and smoother and the #2 and #4 feed holes need to be drilled to match the feed holes in the block. The bearing thrust also needs to be accurately set, as this controls oil pressure. A turbo/KA oil pump will be needed, unless you want to go drastic and dry sump it. Most vintage race guys run a wide sump oil pan and a turbo pump.

 

The top of the block could be o-ringed for added security (street engine) or as a matter of course for a race engine.

 

 

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