'81 A15s all economy models?

[deerio]

Hey all, based on the small amount of reading I've done,I was just wondering if all '81 A15s were high mpg low power models? I'm totally lost on the different types of A14/15 models.

 

I'm looking at an '81 PLB310RFU with a FS5W60A tranny and would like to know more info on the motor and tranny... Thanks!

[flatcat19]

Dogleg. That's all I got. 

[ggzilla]

60A is non-dogleg

 

The FU engine is the lowest power A15. But all 1981-1982 A15s have the low RPM cam (make Max power at 5600 rpm).

 

It is a great engine for fuel economy.

[deerio]

Thanks Ggzilla, that's the info I was looking for. How would you compare this A15 to an E1? I was debating in swapping it for future use but wasn't sure if performance would be significantly better.

[ggzilla]

A15: lighter, more power

E1: heavier, less power

[az_rat210]

A15 has a longer stroke so more low end torque.  I am running an A15 with A14 oval port head, weber 32/36 through a 2" exhaust bolted to an FS5W60A and 3.9 differential. I won't say its a racer but it does have a bit of get up and go. 

[deerio]

A15 has a longer stroke so more low end torque. I am running an A15 with A14 oval port head, weber 32/36 through a 2" exhaust bolted to an FS5W60A and 3.9 differential. I won't say its a racer but it does have a bit of get up and go.

That's the gist I got from what Ive read. I guess I just needed personal confirmation. Would it be safe to say it can cruise easy at 65mph with a little more to go? I plan on ultimately sticking it into an L320 pickup. I don't really need high top speed, I just didn't want to be pegging it around 60-65mph.

[az_rat210]

In 5th gear at 65-70 I am running around 2800 rpm maybe 3k. 85 is no issue for me if I want to run it that high but I do not remember what rpm I am running at that speed.

 

The rear end ratio will make quite a bit of difference. The 3.9 came in automatics, if your car came originally with a manual its most likely running a 3.7 rear end so you actually do better on the highway than myself.  One year of the 210 actually came out with a 3.5:1 ratio which IF you locate one would make for even better top end and mpg.

[ggzilla]

Ratios not based on year, but on engine, transmission and model. The FU engine came sometimes with the 3.54, which is the slowest-accelerating ratio and has the slowest top speed. But is absolutely the best ratio for fuel economy at highway speeds.

 

The ratio is listed on the same ID plate where you found the model number.

 

To get the highest top speed, the ratio needs to put the engine at the max HP rpm at the max speed. The 65 HP engine you have can only push a B310 to around 95 HP, and it only makes that much HP at 5600 rpm. In 5th gear it won't rev high enough to make 56 HP. With 3.54 gears it won't either. Shift down to 4th and it can accelerate to top speed with the 3.9 gears and stock 155SR-13 tires.

[datsunfreak]

The 3.9 came in automatics, if your car came originally with a manual its most likely running a 3.7 rear end so you actually do better on the highway than myself.  

 

He's got an L320 truck, not a 210 car. Which probably has some stupidly low rear gear ratio. Most of the older trucks seem to top out at around 55 because of the rear gear ratio. 

 

With the A15 swap you're also going to want to swap to a different diff or at least a different ratio.

[datsunfreak]

Quick Google search says his diff is a 4.875. 

 

That is why it revs so high on the freeway, not the engine. A gear swap and engine swap will be a night and day difference. 

[datzenmike]

Quick Google search says his diff is a 4.875. 

 

That is why it revs so high on the freeway, not the engine. A gear swap and engine swap will be a night and day difference. 

 

The E1 is very small in size (i liter?) and makes very little power and why it needs a 4.875 diff. The A15 should easily twist to over 5K in 5th gear with this. Assuming the 320 had 6:00 x 14 tires which would be about 23.5" tall.

 

You could go 100MPH at 5,722 RPMs in 5th.

80MPH in 4th at 5,500RPMs and

65MPH at 4,500RPMs.

 

The A series are revving engines and this won't hurt anything but for a bit more mileage you could lower the diff ratio to 4.375 and get 65MPH at 4,000RPMs in 4th

 

Don't forget that the engine has to be revving high enough to make enough power to push through the air, plus a reserve for climbing an incline and passing. Too low a differential and you won't be able to run in 5th and will have to down shift on every hill or use forth on windy days.