Safe RPM

[Socalman]

What is the safe RPM on a l16 521 to cruise/sustain on the highway? I seem to be at 3500 60mph and I am not sure if that is safe to sustain for long periods? Stock 4 speed trans and rear end gears with a locker.

Edited February 23 by Socalman

[datzenmike]

Did you think a car maker would gear a truck so that it would damage the engine driving on the highway??? You couldn't possibly drive fast enough in 4th to do any damage. You might get it to 80 MPH and that's only 4,700 RPMs, but lets just say that you little 70 HP (on a good day) L16 could manage 90 MPH that is still only 5,300 RPMs. As long as in good shape, in tune and full of oil and water it could run like this all day.

 

A 73.7mm stroke engine can rev to 8,300 RPMs before there is sufficient stress on the metal parts to cause worry. That's just over 140 MPH

 

I think your problem here is the seemingly high screaming engine on the highway, but no worries, the engine is fine revving up and needs to, to make enough power to push through the air at those speeds.

[Socalman]

That's good to know, it just sounds like it's screaming for mercy, just didn't want to hurt anything, I finally got it to road worthy and drove it for the 1st time in 3 years of working on it (I bought it not running). I think it's about 72 HP with the few addons I did to it. LOL

 

 

[datzenmike]

The fact is you just can't drive them hard enough to hurt them.

[Socalman]

52 minutes ago, datzenmike said:

The fact is you just can't drive them hard enough to hurt them.

I'll let you know if I break it.

 

Edited February 23 by Socalman

[Socalman]

18 hours ago, datzenmike said:

The fact is you just can't drive them hard enough to hurt them.

Mike, why do some bolt in a 5 speed if there is no problem with RPMs at highway speeds? 

[Stoffregen Motorsports]

People think they need to run it at a lower RPM or they just want the comfort of less engine noise and vibers. That's all.

 

Cruising at 3500 rpms won't hurt it, but it may be annoying.

 

FWIW - even the tallest overdrive will only drop the revs by about 600 rpms.

[thisismatt]

I regularly run mine to 4000 to keep up on the highway.  Yeah, it sounds like a box of rocks

[datzenmike]

For a small L16 it has to rev to make enough HP to maintain highway speeds. You don't absolutely need a 5 speed but to might gain a tiny amount of mileage. Larger L20Bs have way more torque at lower speeds so a 5 speed is better.

 

At 4,000 on the highway in 4th in a 521 or 620 with a 4.375 differential and 25" tire you are going about 68 MPH.

 

A common swap for the L16 is the dogleg with a 14.6% over drive. In 5th the RPMs would be -584 or 3,416 RPMs.  A mid range 71B 5 speed would be 13.6% over drive with a -544 or 3,456 RPMs But a close ratio from the 280zx has a massive 25.5% over drive dropping RPM by -1020 RPMs down to 2,980. 

[banzai510(hainz)]

sidedrafts!!!!!!!!!!!!! cool.

 

60mph starts to get buzzy for me (my 521)but around town 45-50 is fine.  Long haul on freeway get another vehicle.

with my weber DGV in in 3rd gear at 25mph!!!!!!!

[datzenmike]

Hell the side drafts are making all the noise. Music to my ears!!!!

 

[Socalman]

It’s just a toy to have fun with. I like the sound of the side drafts as well. Really fun around town, I do think they need some adjustments past of just turning of a flathead screwdriver. They don’t have the snappy crisp response I had with a 20R and holly 350 carb once. Not sure if that’s a thing with these but would need a side draft professional to look at them someday. Right now I am happy to be driving her, finally. 

[Socalman]

BTW, what 5 speed would bolt right up without any modifications or dealing with driveshaft swapping? Just a straight up bolt in. 

[Crashtd420]

19 minutes ago, Socalman said:

BTW, what 5 speed would bolt right up without any modifications or dealing with driveshaft swapping? Just a straight up bolt in. 

the dogleg 5spd... but hard to find and not that strong apparently...

 

The closes one is a stumpy 71b from the mid 80s 720... but it would need a bell housing swap to L series and a new rear mount.. redeye on here makes the mount ... I have one in my 521....

Edited February 24 by Crashtd420

[NC85ST]

If you can find a parts truck 620 standard cab with a 5-speed, you’re set. Good luck with that. Take the 5-speed and the driveshaft, the only thing left is the mount. If I remember right, I used a piece of angle iron for the mount. 

[datzenmike]

 

Any L series five speed from:

'77-'79 620 op.

'77-'78 280z op.

'79-'83 non turbo standard after '79

'78-'84 810/Maxima standard

'80 720 2wd. op.

 

Shorten your front half of your driveshaft 5.5"

 

Modify transmission mount to match.

 

 

 

Remove rear flange by removing large nut.

 

 

Cover hole with 40mm engine core plug, and use sealer to keep oil in.

 

[Socalman]

3 steps, not bad, I am guessing the big nut is not needed for the flange on any of this transmissions mentioned? 

[datzenmike]

Nope only the 521 used the bolt in spline but it leaves an uncovered hole that must be sealed.

 

The speedometer cable is now on the right and more to the rear. I replaced the same 4 speed in my 710 with the longer 71B and pulled the entire cable up into the engine compartment then fed it down behind the head and diagonally across the top of the transmission and connected it. There is just enough cable for this.

[Socalman]

When you say longer 71B does that mean this particular transmission will require more than 5” removed from front driveshaft? Or are they all longer in the list you provided? She’s so pretty. 😂 

[Socalman]

[KELMO]

Dang I like that truck.

Is that a Ranchero behind it?

[Socalman]

46 minutes ago, KELMO said:

Dang I like that truck.

Is that a Ranchero behind it?

Thanks! I like it too. LOL. that is a '61 Ranchero W/ a 302 4 barrel. 3 speed, so it also doesn't like the highway speed, but can do a mean burnout... LOL

[datzenmike]

Around '62 Falcon Ranchero. Good eye

 

Ah there's the answer.

[banzai510(hainz)]

sidedrafts work better when you rev them up. but since you have a 521 they should rev up fine with the low gearing in the truck.

 

try retiming your motor. say 14btc with a light

 

are they mikunis or webers? thats a difference.  Some socalled carbs guys are just not going to get it better unless they really in the know. 44mm would be best for the street.

Edited February 26 by banzai510(hainz)

[Socalman]

17 minutes ago, banzai510(hainz) said:

sidedrafts work better when you rev them up. but since you have a 521 they should rev up fine with the low gearing in the truck.

 

try retiming your motor. say 14btc with a light

 

are they mikunis or webers? thats a difference.  Some socalled carbs guys are just not going to get it better unless they really in the know. 44mm would be best for the street.

They are Weber DCOE 40s. I plan on retiming after I run a couple of fuel tanks through it.