L20a

[kp910 user]

hello L masters, I have a datsun bluebird KP910 with a L20a engine from a datsun Laurel c31, and I feel some lack of power, please can you give some advices with pistons, roads, and head work, etc to improve my engine power...

 

I want to keep it with carburettor and N/A configuration, and my budget is very small i will be happy with 170 whp...

 

soon I will buy SU carbs

 

But for now this is what i have:

stock L20a with single nikki carburettor

2.5 exhaust

msd blaster 2 coil

 

 

Edited September 20, 2012 by kp910 user

[DevilZX]

Sorry I don't have any contribution to helping you out with power but I just came to say I like your car! Saw it on the DATSMO fb page.

[Tony D]

Truthfully the easiest way to get to 170 with the L20A is Turbocharging.

The Japanese Magazines have been doing writeups this past year on hopping up the vintage L20A, but it's neither cheap, nor easy. Most stock examples spin a dyno below 100ps. Usually in the 75-85ps range depending on tune. The Bosch Dyno people were very surprised when my Twin SU 1975 Fairlady Z spun a 97ps reading. You effectively look to conservatively more than double what you likely realistically have, and while possible... it's far more economical to do with a turbo than N/A. (An L28 isn't an option, huh?)

 

Our Bonneville Engine made 175hp to the rear wheels at some rpm. Last build it was 205 at 9200 rpms (9500 shift points), and would pull beyond that if we needed gear spread.

 

If you want to stay N/A, and on a budget, you may want to consider lowering those expectations a bit. Our engine is not what I'd call 'streetable'!

Edited September 21, 2012 by Tony D

[kiwi303]

Get the L20ET intake and exhaust off a Skyline or other L20ET motor, and add an aftermarket EMS.

 

That would be your best bang for the buck.

[kp910 user]

Sorry I don't have any contribution to helping you out with power but I just came to say I like your car! Saw it on the DATSMO fb page.

 

thanks!!

 

Truthfully the easiest way to get to 170 with the L20A is Turbocharging.

The Japanese Magazines have been doing writeups this past year on hopping up the vintage L20A, but it's neither cheap, nor easy. Most stock examples spin a dyno below 100ps. Usually in the 75-85ps range depending on tune. The Bosch Dyno people were very surprised when my Twin SU 1975 Fairlady Z spun a 97ps reading. You effectively look to conservatively more than double what you likely realistically have, and while possible... it's far more economical to do with a turbo than N/A. (An L28 isn't an option, huh?)

 

Our Bonneville Engine made 175hp to the rear wheels at some rpm. Last build it was 205 at 9200 rpms (9500 shift points), and would pull beyond that if we needed gear spread.

 

If you want to stay N/A, and on a budget, you may want to consider lowering those expectations a bit. Our engine is not what I'd call 'streetable'!

 

 

so tony can you give me some advice please?? ... how can I make 120 whp?? maybe with high compression??

Edited September 24, 2012 by kp910 user

[Tony D]

Standard stuff, a good tuned twin SU L20A or L20E should be very close to 90-95ps, but average streeters will run about 75-85ps.There are no secrets: the power is in displacement, headwork, cam...

[ozconnection]

Standard stuff, a good tuned twin SU L20A or L20E should be very close to 90-95ps, but average streeters will run about 75-85ps.There are no secrets: the power is in displacement, headwork, cam...

 

Displacement...? It's the baby six and so the obvious choice would to increase the displacement but I get the idea from the original poster that he doesn't have enough mulla to do it or just doesn't want to. He might have a good reason for not increasing the size of the engine but that question could be asked of anyone who doesn't run an L28 or larger engine in their car.

 

As for the other bits, derr, but power isn't always the answer. Build torque instead and let the power fall where it falls. Big cams with big ports will kill low speed torque bro...derr! Great at 9.2K rpm though!

 

Turbo's are excellent torque generators. Superchargers even better for low down grunt, very linear. Think "street" engine, not "race" engine.

Edited September 26, 2012 by ozconnection

[kp910 user]

Displacement...? It's the baby six and so the obvious choice would to increase the displacement but I get the idea from the original poster that he doesn't have enough mulla to do it or just doesn't want to. He might have a good reason for not increasing the size of the engine but that question could be asked of anyone who doesn't run an L28 or larger engine in their car.

 

As for the other bits, derr, but power isn't always the answer. Build torque instead and let the power fall where it falls. Big cams with big ports will kill low speed torque bro...derr! Great at 9.2K rpm though!

 

Turbo's are excellent torque generators. Superchargers even better for low down grunt, very linear. Think "street" engine, not "race" engine.

 

thanks for the help guys!

 

In my country there are none L28 just L20a and L24 that is the reason why I don't buy an L28

 

maybe as all of you are saying a turbo set up would be the perfect choise, but will be reliably with standar internals....

[Tony D]

If you bore the L20A you can make a 2300cc using L24 pistons or 2500cc using L28 pistons.The 2300 was popular in Japan as you didn't have to do an engine swap each inspection.

Once the piston size is increased, you can use the larger valves from the L24 in the head.

Really though, a swap to an L24 would be easier if its allowable. That would put you near the 120 range if tuned to a "T" on all stock components.

Me? If I HAD to keep the L20A block for some sort of rule ompliance on displacement, I'd buy some Forged L24 Pistons, put them in the block for 2300cc's, then buy a ported and polished N42 head...make a call to Ron for a high RPM turbo grind, and build an 8500 rpm fuel injected street turbo motor with about 300HP

But that's just me. You can do what you want. With a 4.38 gear in that car, I'd go eating things...

[kp910 user]

If you bore the L20A you can make a 2300cc using L24 pistons or 2500cc using L28 pistons.The 2300 was popular in Japan as you didn't have to do an engine swap each inspection.

 

 

I´m really thanksfull with your help Tony, I have some more questions... when you put the L24 pistons in the L20 block with L20 conrod, without turbo, the compression would be lower than 180psi (stock numbers), how can I have a higher compression?? some like 200psi...

 

Do you have some more info about the 2300 CC?? I cant find anything....

Edited October 3, 2012 by kp910 user

[Tony D]

It was popular in the 80's in Japan. Chances are unless you read japanese, you won't find much other than what I recall, or what I can look up in my old Japanese magazines. I'd love to, but offhand don't know where the issue is I need, and don't recall right now if there was any specifics on the 2300.

 

 

I think you are incorrect about your CR, the increased bore size increases swept volume, and the L24 is a flat top piston, (the Pin height is the same L16/L20A as I recall) which means your compression will go UP not DOWN!

 

If you get L24 Pistons on L24 rods you would pop out the deck 3mm at least! With the 130mm rod, and same pin height... you should be golden.

[Gollum]

Seems to me that finding an imported L28 would be cheaper than any of these options. Is getting something through customs that hard in chile? Maybe I'm just being the ignorant american here, which I'm sorry if that's the case.

[Tony D]

South America is "difficult"....

 

His best bet is to convert to and L24.

Or as he notes, put some L24 Slugs on his L20A Rods with six new bores.

The CC on the L20A head will be high compression, best to port the head and lower it slightly, and take advantage of the larger bores by putting in at least L24 intake and exhaust port seats and valves for best breathing.

 

If he gets the 45mm SU's they will work fine on the 2300.

[ozconnection]

South America is "difficult"....

 

His best bet is to convert to and L24.

Or as he notes, put some L24 Slugs on his L20A Rods with six new bores.

The CC on the L20A head will be high compression, best to port the head and lower it slightly, and take advantage of the larger bores by putting in at least L24 intake and exhaust port seats and valves for best breathing.

 

If he gets the 45mm SU's they will work fine on the 2300.

 

No, I like this better. Leave the head, the Y70/O5L heads have beaut high velocity ports and small unshrouded valves. The Valve sizes in the L20A are actually the same size as in the low performance E30 heads which were also used on P30 L24 bottom ends. Inlets 1.5 inch. exhaust 1.3 inch. It was the late model L24's that had notched bores for the larger 1.65/1.38 valves.

 

My point is, leave the head and bang a big cam in it. Let the overlap and lift do the breathing, the ports will remain responsive at any engine speed, not just after 4000 rpm when anything below that will be useless for the street.

 

I currently have the 'ultimate' two litre 'street' L series. A Y70 head, stock sized ports and valves but with nearly 10 to one comp and a bigger than stock, stage two MSA turbo grind camshaft. Heck it still pulls 18 inches at idle. Midrange is very good and kickdown is very 'entertaining'. LOL. The sound of those high velocity ports is something else, too.

 

Everything else you mention Tony is spot on. The bigger bores will allow great valve unshrouding at maximum valve lift with the little valves.

 

I love my combination can you tell?

Edited October 3, 2012 by ozconnection

[Tony D]

People intent on lugging an engine ... What can you do?The design operational range is 2500 up on the L243500 up on the L20A...

You get the dual carb L20A cam... And that's what you get!

My L26 is at 3500 at highway commute to work, 3700-4000 when traveling long distances, like across the desert.The industrial applications for he LD used 2400 as operational rpm, the petrol versions 3500-4000 rpms.

[Gollum]

People intent on lugging an engine ... What can you do?The design operational range is 2500 up on the L243500 up on the L20A...

You get the dual carb L20A cam... And that's what you get!

My L26 is at 3500 at highway commute to work, 3700-4000 when traveling long distances, like across the desert.The industrial applications for he LD used 2400 as operational rpm, the petrol versions 3500-4000 rpms.

 

The 81-83 manual 280ZX (which I've owned 2 of) run their L28 at 3500 at 70mph... Quite high honestly considering that they run out of steam fairly soon for a L motor. Point being - Nissan never seemed afraid of winding their motors up.

[Tony D]

Thing is it's NOT 'winding it up'---the engine is HALF the displacement of a SB Chevy. To get similar HP, physics dictates 2X the engine speed.

 

They put a lot of nickel in the blocks to combat any sort of wear from the repetitions.... Simple Physics and metalurgy. That is where they are designed and geared to run.

 

If you look at the gearing overseas, the L24 with four speed got 3.7, five speed 3.9.

Put it in a 2+2 and you were 3.9/4.11 depending on trim level, and 4.11/4.38 with the five speed.

 

At this gearing, you find the top speed of the car comes almost exactly at power peak of the given engine.

 

My L20A S30S ran 6350rpms in fourth, "plenty of pedal" but it made no difference, it was all-in!

 

I drove from LA to Phoenix in 120F heat of summer running 4000rpms which had a 4.11 gearset in it.... it didn't overheat. I just sung the whole way there!

[Gollum]

I'm not going to argue with you Tony, but I am going to play devil's advocate here, just for the sake of those that simply don't know better...

 

...The best comparison I can see between the SBC and L-gata displacement specs is between the 2.4 L and a 302 SBC. Both are larger bore than the smaller siblings, both are slightly stroked, and it's about as close of a "double" as I can think of. There's a whopping .1" difference between stroke, or you could roughly say that the L24 is roughly 97% the stroke of a 5 liter SBC, or a 5 liter SBF (which are actually 4.9 liters in all honesty, hence the close comparison imo)

 

Why does this matter? Because if you TRULY rev'ed a L gata at TWICE the RPM, you'd be subjecting the piston to SUBSTANTIALLY more stress than the SBC. So your comparison, though getting the point across, isn't a fair one. When I used the term "winding it up" I didn't mean it to subjectively mean that it's stressful to the engine. Just the contrary, people think it's crazy I used to DD a CRX who's engine (stock but not to that chassis) would turn 4500 on the freeway... But when you consider the 8500 redline... I'd say it's pretty "reasonable".

 

I'm not exactly "surprised" at how Nissan decided to gear their L powered cars, but sometimes I do wish 5th was a further spread in my current '81. I can drive around at 25mph lugging it in 5th no problem. If you look at the pattern nissan made a VERY well spaced pattern that's extremely consistent with the later 5 speeds, with a "decent" overdrive to boot. But that said I, personally, would rather be on the freeway at 2,000-2,500 and have to downshift to accelerate than have a motor singing along at 3500 just so my top speed can match my peak power... But I also understand that's my preference and opinion, which doesn't change what I feel about what the factory did for the masses.

 

Oh, and also on the "needing to rev twice as much for a given power output", again, Tony, you know the gritty details. That's a broad statement. People routinely get 300bhp out of a 2.8-3 liter L motor, and that's on a factory head who's design goes WAY back, and to really give it less leverage, we'll "say" that the "preferred" heads are from the early 80's. How often do people make a 600bhp 5.7-6 liter SBC using 80's or older heads? Factory cranks? Factory rods? Maybe we don't see it often because there ARE such cheap aftermarket parts available, but I'd say it's safe to say the L motor "generally" spec for spec makes more torque per liter, able to flow better CFM, thus making more power per liter. GRANTED, RPM is a huge factor in that topic, and it's "generally speaking" easier to make a L gata rev up reliably, versus a SBC.

 

 

Maybe this is all just a pointless rant, and now Tony is going to come back and say I'm wrong. But you know what? I'm okay with that. At least now I've drawn it out to be much deeper than just "it needs to rev higher because it's so small". Have a ball Tony

[Xnke]

Even more, look at the FSM's fuel consumption curves. You'll get better milage, stock-for-stock, by cruising at 3000-3700RPM, than you will at 2500-2800RPM. Might also read around here on the "VE Valley" that stock engines map out with on megasquirt, even though we don't really know *why* it happens yet.

[Tony D]

Yes, I will agree there is more to it that my broad generalizations, but for the typical public consumption it gives them a 'general' idea.

 

As Xnke notes, what got me to change my gearing were the funky curves for fuel consumption. They are VERY peaky for the L20A and they ARE biased quite a bit higher than you would think.

 

I am adverse to 'lugging' because of my initial vehicles: Corvairs and VW's.... A VW has a very low mean piston speed, and will run around at 4,000 rpms all day long not overheating. Cut that in half with gearing and you melt the damn heads!

 

The world view of rpms is radically different from the US View of highway travel. Best I can explain it is why rednecks race pickups: a 70s Chevy Shortbed has 4.11's and it will SPANK most anything out there stock-for-stock if you can get traction.

Try running it against an Impala with the same spec engine and that 3.27 gearset, or even better those 2.72's! The Chevy is designed to run well below torque peak, and in fact likesto be geared high.

 

But you look at those fuel consumption curves for the Chevy and they are DRASTICALLY different in shape than the Datsun stuff!

 

I had my 73 geared with an 82 transmission and 3.36's. It worked, and got passable mileage. But it always seemed to be 'working'....

Changing to 3.70 gears, the car just seemed 'happier' all the way around and was a lot more sporting to drive. I didn't see any appreciable change in Fuel Economy.

I experimented with 4.11's in there, a lot of noise, quick acceleration but....meh, I went back to the 3.7's

 

There is a broad range of gears that "will work"---depending on what your definition of 'work' is.... Again, my preference due to the Air-Cooled Background is to keep R's higher, rather than lower, simply due to the fact that more oil flows across the bearings and the chance of catching a bearing when detonating is theoretically (and likely practically) less.

 

The smaller the engine, the more I tend to let them rev. My old A-Series 1,200 would just amaze me.... 4,200 rpms on the freeway.... sounded like it was SCREAMING with that open-element air cleaner... But 39-40mpg. It just seemed to love running along at those speeds. I find that the stock L26 in my Blue Turd LOVES 3500, and upping it to 4,000 makes me forget the speed I'm going is right near jail time... I'm often leaving the car in 4th trundling along with no throttle input at 4,000 before I go "oh" and upshift to 5th for 3,500.

 

I was in a Clio 1.3, carrying on a conversation outside Liverpool once.... Driver had left it in 2nd and we were going along at a steady speed for some distance at 5,000 rpms before I interrupted the animatedly-talking driver with "Andy?"

Yes?

"Change-Up?"

Oh, right, sorry!

 

And he shifted to 3rd, the rpms dropped to something like 4,200, and he continued back into conversation without another thought!

 

"Proper Gear For Speed" is something not really taught in the USA because big engines have so much torque you really don't need to 'drive' the engine. The L-Gata IS like them in this respect.

 

But damn, they are so much more fun when using the "proper gear for speed" method of driving!