redline?

[bonvo]

what is a safe redline to keep in mind my set up is

stock internal l20b with a stock cam

L16 intake mani with a weber 32/36 on a tall 1 peice adapter

header and 2 1/4 in exhaust all the way back to the muffler

new timing chain and head gasket

140 psi of compression all the way across

 

i have never run it past 5 grand but when im driving it and i shift at 5k it feels like im cutting it off early likeit still has more to give so my question is what is a safe redline with this setup?

[DanielC]

The most highly stressed pars of your engine are the connecting rod piston assembly. The highest stress occurs at the end of the exhaust stroke, and into the beginning of the intake stroke. At around 75 degrees before and after TDC, the piston velocity is the greatest. At TDC, the piston has stopped, and changes direction. The parts that physically limit the RPM of an engine you have not changed. So I would think your redline is basically what the stock redline is.

 

I wanted to know what a safe RPM for my L-16 was, when my 521 was running. I talked to a service manager at the local Datsun dealer, and we came to the conclusion that for a L-16 anything below 6500 was "safe" 6500 to 7000 was a "yellow" zone, and 7000 was the red line. This was based on the RPM limits on a 240Z car tachometer, since a L-24 has basically the same bottom end components a L-16, and the L-16 has the advantage of being shorter by two cylinders. 6500 RPM is about 1100 RPM above the peak horsepower RPM of the L-16

 

I would expect thet the L-20-B engine would have a slightly lower redline, because it was used as a truck engine. A good place to start is to find out what the peak horsepower RPM of the stock engine was, and consider about 750 to 1000 RPM above that, as a redline.

[]2eDeYe]

My 620 tach says 7000 rpm ;)

 

If your shifting at 5000 when driving hard, your shifting to early.

[KPGC10]

You don't need to turn a stock cammed L20B anywhere over 6000 RPM.

[datzenmike]

Only difference between a truck and car L20B is the larger clutch size. There's nothing internal that makes it a truck motor. A stock L20B peaks around 5,600.

 

The Z24 IS a truck motor. Only available in the 720 truck.

Edited November 21, 2009 by datzenmike

[bonvo]

thans for the input guys i was just wondering because according to the plate on the firewall it makes 110 hp at 6200 i know these are exagerated thats why i asked :D

[izzo]

oh come on bonvo, just keep the pedal to the floor until you hear the valve train starting to rattle, then shift :lol:

[ggzilla]

It's not exagerated. 110 HP comes from the high RPM that the L-series overhead so easily turns.

[datzenmike]

thans for the input guys i was just wondering because according to the plate on the firewall it makes 110 hp at 6200 i know these are exagerated thats why i asked :D

 

This is from an engine dyno probably. No alternator, water pump, air filter, air pump or fans, no muffler. Knock off about 15% for transmission losses, maybe a hair more for RWHP.

[lynchfourtwenty]

my engine stops turning (or seems like it) around 5800-6000 rpms.. almost like a rev limiter.. altho at those rpms it seems like its lost its power.. so i usualy shift at like 5500 if im "gettin on it".. maybe shes gettin tired..

[RoadRace]

its funny when people seemingly impose performance limits on a motor based on a certain application or installation for that motor, IE, the L20 is a truck motor. well, the L18 and L16 are also truck motors, so are the 350 and 454 chev, 302, 351 and 460 Ford V8's. the list is very long.

 

the L20b has a forged crank and rods, like the other L-motors. airflow limits RPM, nothing else. You can argue that wieght and harmonics or balance are also factors on the rev capabilities of a motor and you would be correct, but for this application, airflow is the limiting factor. The internals of this motor are safe for 8000 rpm when prepared for it. That being said, there is no way a DGV can flow enough air for a 2 liter motor to make power above 5500, and thats being generous. if you leave your foot in it long enough, you'll get the motor to spin higher, but you aren't making any power, you're revving off momentum - the vehicle is in motion, and tends to stay in motion, allowing the motor to turn a couple hundred revs more than it should. when you do this you're keeping the motor spinning at increased loads for long durations, not determining the motors rev limit.

 

the best way to determine any motors 'redline' (is on the dyno...) is use your eyes and your butt. put it in 2nd or 3rd gear and nail it, watch the tach, feel when it stops pulling or noses over, thats it. when it noses over, its done, stopped making power, this won't change. in 4th or 5th it'll be a lower rev count because you have aero forces pushing the vehicle back at higher speeds. first gear goes by too quickly for most people to get a feel for whats going on.

[datzenmike]

The Z24 is a truck motor. :D

[RoadRace]

The Z24 is a truck motor. :D

 

 

except the Z24, of course...:D

Edited November 25, 2009 by RoadRace
i'm an idiot

[datsunaholic]

For every engine and application there's a practical redline and an absolute redline.

 

The practical redline is the RPM thet the engine cannot exceed at normal full load. With a stock L20B it's somewhere around 6500-7500, but gearing, vehicle weight, tire size, and drag coefficient all change that. As the engine ages the practical redline changes as the valve springs get weaker (and they do) becuase you'll start getting valve float and that acts as a rev limiter of sorts. If the springs become too weak then that becomes an absolute (fail-mode) redline as the pistons may suddenly find valve heads.

 

The absolute redline is component based. Every moving part on the engine (and some stationary parts) has a maximum load. The first part to fail is usually the connecting rod bolts, and all else being equal the longer the stroke the lower the absolute redline (usually, not always). Longer stroke means faster piston travel at the same RPMs, and more strain on the rods and rod bolts . Stock rod bolts are probably OK **NEW** to around 9000-9500 in a L16, but they don't get better with age, and the same bolts aren't going to be nearly as good in a L20B.

 

There are also failure loads of the piston, the piston pin, the timing chain, the connecting rods, and even the crankshaft. One big factor is how well the entire assembly is balanced. From the factory they did a pretty good job of making sure stuff weas balanced, but it's not a blueprinted engine. Generally a blueprinted engine can handle more load and RPMs than a factory assembled engine, mainly because a proper dynamic balancing eliminates many of the harmonic vibrations that cause crankshaft whipping and the resultant crank cracking. But you won't get them all. Heck, back when I worked in medium-sized Diesels, we had what were known as "critical speeds" where we were to at no time to ever run an engine at. These speeds were usually well BELOW redline (or our set maximum non-emergency RPM which was 10-20% under manufacturer redline). We had one engine that ran all day at 1700 RPM. But never, ever run it between 1250-1350 RPM. You had to just rev it through that range as fast as practical. The non-moving parts that have fail rates are things like cylinder walls, head gaskets. that are pressure-related.

 

There are also limits on how fast you can spin accessories like the water pump and alternator. The belts have a limit, the fan blades. The clutch disc and flywheel can't exceed a certain RPM or they'll explode. Transmission gears and bearings. Usually these all can handle far higher speeds than the engine, but not always.

[1978dat620]

i have read how to modify your datsun and it states that the dstributor is a key factor it is stable to around 6000 to 6500 after that they need to be modified . pleas add to this ther are other factors like oil starvation ext

 

 

ps i love this site lots of info

Edited December 8, 2009 by 1978dat620

[lynchfourtwenty]

i can see that, since mine stops spinning around 6k or so.. well it doesnt stop, it just doesnt spin any faster.. its almost like hittin a soft rev limiter..

[b210in]

rev it until it stops accerlating.

[MicroMachinery]

I've always just gone by the stock tach in my 510. It redlines at 6500, and so I figure that with the L20b being a larger, heavier, more low end engine, I wouldn't push it past 6k. I've heard that somewhere else before, but that all depends on what you're using the engine for. But on stock internals, I think you'd be wise to keep it under 6k. Keeps things healthy :)

[lynchfourtwenty]

well when im sideways foot planted i have no intentions of letting off or shifting until im pointed straight.. lol.. the truck SINGS at high rpms :)

[MicroMachinery]

well when im sideways foot planted i have no intentions of letting off or shifting until im pointed straight.. lol.. the truck SINGS at high rpms :)

 

Death metal? Hehe:fu:

[lynchfourtwenty]

lol its hard to explain, you'd have to go for a ride w/ me :lol:

[datsunfish]

i have read how to modify your datsun and it states that the dstributor is a key factor it is stable to around 6000 to 6500 after that they need to be modified . pleas add to this ther are other factors like oil starvation ext

 

 

ps i love this site lots of info

 

The stability he refers to is the points bounce and flutter of a stock points type distributor and that if you are gonna spin that high,get a more accurate electronic distributor. The L20b can survive revs well above 6500. It has a fully counter balanced crank and all but like they have said it stops making useable power before its actual limit. The more mods you do the more power you will see in the top end but give and take. Oh,and the L20b is probably close to the same actual size and weight as all other l and z 4 cylinders.

[scooter]

my last datsun had a stock L16 with a weber on it and i'd shift it when it stopped pullin around 6500-6800..

 

it just laughed at that, these motors are built like brick shit houses.

 

 

later on i took the tach out cus i got sick of seeing what it said...

[motavated]

My truck has the same set up as your and also stops there... I think its because of the head Bonvo. I read somewhere on Ratsun that a a87 peanut head non sss cant suck so much air... So it kind of stops the engine around 5-6k. If it was an sss or the head was ported... It can rev higher????

[Guest kamakazi620]

My truck has the same set up as your and also stops there... I think its because of the head Bonvo. I read somewhere on Ratsun that a a87 peanut head non sss cant suck so much air... So it kind of stops the engine around 5-6k. If it was an sss or the head was ported... It can rev higher????

 

 

Like stated previously airflow will let the engine "breathe" if you have bigger vavles and ports + a carb that matches everything yah you can spin some rpms compression plays a key role as well,If you do everything above you would also need a cam to "wake up" the motor,a stock cam can only open the valve so much + for so long.A high lift cam will push the valve in more for more volume a long duration cam keeps the valve open longer for more air/fuel to fill the cylinder,a long duration cam generally lowers your compression by 1/2- 1% (for reasons the intake starts to close when piston is traveling up and pushes some of the air/fuel back in intake reduseing the volume)and works well with higher compression,Don't forget to "balance" the engine if above mods are being preformed,it'd be a shame to hop the motor up to spin 7000+rpms and throw a rod!!!!