[GoinManta]

OK... I have three simple choices for my Opel swap.

The 240SX used a final ration 4.10:1

The simple choices I have are

I can either install a Impulse Rear end (3.90:1)

Manta Rallye - 3.67:1

Manta Std - 3.44:1

What are the pluses and minuses..?

The 240Sx wighed close to 2900 lbs.. the Manta 2200 lbs

Keeping tires equal, the 240sx did about a 8.9 in the 0-60

What would the Mnata do with the respective different ratios..

Also what about gas mileage.. The 240 got like 24mpg or something..

What do you think I can realizitically expect from the Nissan motor? Given the gears I have.

Charles

 

[GTJIM (R.I.P.)]

Over Drive 5th?

I guess the Nissan is fitted with an overdrive fifth in the gear box with about 0.8 - 0.85 :1 ratio??
The Manta is lighter so you can use a taller diff ratio to get similar performance. The Impulse gears would give you best acceleration but may be a bit harder on gas. The 3.44 gears may end up being a bit tall in overdrive and hurt gas milage by making the engine struggle. Maybe try the 3.67 gears for a compromise between accleration and economy in overdrive ......

HTH

 

[opelgt73]

With the weight of the Manta you should easily be able to get away with taller gearing. MPG will jump up too. Just a thought, is there any difference in the diameter of the tire on the Manta Vs. the 240?

 

[RallyBob]

Okay Charles, from what I could dig up on the 240SX with 4.10 final drive ratio
and 195/60-15 tires (24.21" tall), based on 6500 rpms.

1st gear: 3.321/13.616 final drive/36 mph
2nd gear: 1.902/7.798 final drive/63 mph
3rd gear: 1.308/5.3628 final drive/92 mph
4th gear: 1.00/4.10 final drive/120 mph
5th gear: .759/3.11 final drive/159 mph (theoretical, but not possible with current power levels)
5th gear cruise: 3000 rpms=73 mph

Now, if you have 205/60-13 tires (22.68" tall), here's the speed breakdown with the various Opel final gear ratios and the Nissan transmission:

3.90 axle: 35/62/91/118/156 mph-(very close to the Nissan overall ratios.)
5th gear cruise: 3000 rpms=72 mph

3.67 axle: 38/66/96/126/166 mph
5th gear cruise: 3000 rpms=77 mph

3.44 axle: 40/69/103/134/177 mph
5th gear cruise: 3000 rpms=82 mph

From this you can decide which is more important to you, acceleration or fuel economy. HTH.

Bob

 

[GoinManta]

Very cool.. thanks..

Now a few more ..

Obviously the 3.44 gives better overall top end and MPG. How much do you think accleration would suffer? Would it be noticeable on the street or just noticeable on the track? Could I assume about a 12% savings in fuel due to the gearing and add an extra 5% for wieght savings, maybe 2% for removal of the steering pump or about 18%..

City the 240sx got 22 and Hwy was 28.

The Manta I think would see in the 26 range City and 32 Highway...with the 3.44 Hmmm...

What effect would a LSD Isuzu rear have on acceleration with the 3.90? Obviously Gas Mileage would be a tad better than the 240sx, due to slightly different ratio and the power steering pump loss.

A 240sx does:

0-60 - 8.4
1/4 mile - 16.3

So in the Isuzu I would think close to teh same, maybe in the 7's (or 6s with the LSD?) 0-60 and 15's on the quarter due to wieght (and no power steering pump).

Wonder how much that would be affected by the going for MPG.. ?

Charles

 

[GoinManta]

With the weight of the Manta you should easily be able to get away with taller gearing. MPG will jump up too. Just a thought, is there any difference in the diameter of the tire on the Manta Vs. the 240?

I plan on using 195/60r14 tires. Can't find anyting in the 205/50 or 215/50 in a 14 that is a street tire. Not to mention its close to stock in size. Its 23.2 inches in diameter. Closer to the tires Bob used in his calculations than the 240sx.

Charles

 

[opelgt73]

City the 240sx got 22 and Hwy was 28.

The Manta I think would see in the 26 range City and 32 Highway...with the 3.44 Hmmm...

I don't think you can make a direct comparison like that. You need to include the difference in drag coefficient between the body of the Manta and the 240 in your calculations.

 

[RallyBob]

What effect would a LSD Isuzu rear have on acceleration with the 3.90?

Just to clarify, the 3.90 Isuzu (Opel type) rear axles never came with a limited slip in the US. I did a LOT of searching years ago to try to find a source for these, and while the original sales literature says they were available, there is no part number for this LSD in US parts books.

 

[GoinManta]

I don't think you can make a direct comparison like that. You need to include the difference in drag coefficient between the body of the Manta and the 240 in your calculations.

Actually I had checked at one time and the drag coeficent of the Manta is pretty low, Admittedly the 240sx is probably a little sleeker. But its not like I am comparing the mileage of the Manta to that of a Nissan Pickup (i.e. Brick w/ same motor). It got in the teens/low 20s. The motor was even detuned for the truck to improve MPG.

Charles

 

[GoinManta]

Just to clarify, the 3.90 Isuzu (Opel type) rear axles never came with a limited slip in the US. I did a LOT of searching years ago to try to find a source for these, and while the original sales literature says they were available, there is no part number for this LSD in US parts books.

While I have heard that too.. I have a junkyard with a axle in thier books from a 83 non-turbo with a supposed LSD. They even checked and the wheels both turn forward.

Charles