3N71B automatic heeeeeelp!!!!!

[Datsun fan]

Hi guys , I'm new to this forum but not to cars !

 

My car is Jeep-like Aro 4x4 spartana (modified) specs are as follows :

 

Weight : 1300 Kg

Engine : Nissan A15 OHV 1488 CC

Gearbox : Automatic (3N71B)

Diff ratio : 4.44 RWD

Wheels : 195/70/R14

 

The problem is the performance , acceleration is low and max speed is 120 KM/H @3200 RPM . Anyway the engine is well tuned and the autobox is OK ,

Local mechanic told me I have to replace 3N71B with an overdrive one in order to get better performance , top speed and milage too!!

Any ideas or seggestions are highly welcome ....

[Bleach]

welcome

 

Don't expect much from the J15.

 

People have done dual carb setup on that engine. As with any engine, you loose some torque to gain power at higher rpms.

 

A swap to a manual 5-speed transmission will do more for you than any engine mods can with that auto.

[datzenmike]

Купить ! Roooski made 4X4 with a Nissan motor?

 

It's an A15 ... 120 KPH pulling an un-aerodynamic 4X4 is probably it's top speed! What does the A15 make about 80 hp? Well 80 hp will only push so much air out of the way. If you can find a torque converter lock up 3N71B OR an L3N71B 4spd auto it will lower your RPMs at 120 KPH to the point where you will be making less hp... less hp means you will loose your top speed. This is called power limited top speed.

 

Nissan began using the torque converter lock up about '83 and the 4spd automatic a year or two later. The L4N71B 4th over drive gear is .686!!! that's a 31% drop in RPMs! This means that at 120KPH your engine will be turning what, ... 2200RPMs? How much hp does an A15 make at that RPM? 20-30 hp? I doubt if they were even used on the A series motors.

[datsunaholic]

You'll never get great acceleration with an A15 and an automatic, no matter what you do. Especially the old JATCO autos, which are stout transmissions but pretty slippy. If you can't get past 120KM/h @ 3200 RPMs (considering the max HP is over 5000 RPMs for that engine) you've pretty much maxxed out the torque available for that engine for the car's weight. An Overdrive will give you better mileage and freeway RPM, but it won't increase your top speed if you can't get the engine to pull the 1:1 ratio past 3200RPM. The reason is the transition from 3rd to 4th will drop the RPM, and if you don't have to torque to pull it up, it would have to downshift.

 

You should be able to hit 160KPH with that setup in a car, but in a ARO Spartana you're pushing a brick. Still, the RPM/speed seems about right so the transmission isn't slipping much. Sounds more like a lack of power. Almost like the engine is being strangled by too little carbeuration.

 

(for those who aren't familiar to what an ARO Spartana is, it's a Romanian SUV somewhat like a cross between a Jeep Wrangler and a Land Rover)

 

http://flickr.com/photos/daviddb/354651234/

[Datsun fan]

Hi

 

Thank you people for facts and ideas . Anyway I agree with Bleach almost 100% , i have seen a car just like mine but the gearbox is MANUAL 5-speed , and diff ratio is original ARO 4.3 the takeoff is very good and max speed is 160 km/h and milage economy is far better . considering gear ratios for my 3N71B are : 1st : 2.458 , 2nd : 1.458 , 3rd : 1.0 and the manual ( FS5w...) are :

3.460 , 2.153 , 1.53 , 4th : 1 , 5th : 0.748 I think the big share of the problem is gearbox ratios besides a role of torque converter . Anyway I found from a scrapyard an automatic gear box wih 5-speed with TIPTRONIC selector so I can choose gear manually !!!! and it came wih (mounting points) to be connected to front weels (4x4) ,a guy from that scrapyard old me that auto is out of '9x Maxima and it is in good condition and will fit great in my car, so I think it is good option to keep car auto , isn't ? Manual gearbox ratios i mentioned above isn't accurate and need citation ! waiting fo comments or ideas .........

[Datsun fan]

Hey people .................

 

I wrote updated info and wait for your comments .

 

Thnx in advance

[Guest jaimesix]

Get a manual transmission so you can maximize your RPM and torque. Otherwise the auto gear box will do it for you.

Unless you are rock crawling, a manual gear box is way better for off roading than an automatic.

Automatic have poorer mileage numbers , for all the reasons you are asking for ( torque, HP, efficiency, mileage ) use a manual.

Your engine is an A15. It is a good engine. I do not know how heavy your car is, but if it is a heavy car, you should consider an L series engine, L20B with a 5 speed. For off road, a 4 speed is great, better low ratios.

I would use the A15 with a 4 or 5 speed gear box. If the car is not a road driven vehicle but an off road one, I would stick to a 4 speed.

BTW, where are you located Datsun Fan??. You might be able to get better responses by posting your location, you might be very close to another Datsun fan.

 

Jaime.______________________________________________________

[Datsun fan]

thanks jaimesix for making it clear ..

 

Pls check the top of this thread to read more info about my car (1300 KG)

and you should know that my car is usually driven on highway/byway and I'm not intrested in offroading using this car . Also pls check another thread I wrote in ENGINE section ( Carb questions ??????????) I think it is part of the problem . Currently I live in an old-fashion state in the middle east called Syria , you need a microscope to see it on a school map !

 

Waiting updates ...............