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ratios

S

slugger89

New member
Joined
Apr 7, 2003
i heard that you can change your ratios and get big gains in hp if this is true can someone explain how to do it or where and how much it costs
 
ok i want to know can you get hp by changing gear ratios and if you can do that how would you do it and how much would it cost?
 
Thanks for the funnies Rob. That was a hilarious exchange you two just went through there. Ok, Slugger, if you want more 'power' from changing something that has nothing to do with the engine, follow these steps:

1: Stop talking to anyone who owns a riced out car, is under 25, and claims to know what they're talking about.

2: Understand that you can only get more 'power' from changing something which is attached to the engine.

3: Find out what rear end ratio you have before asking a question about how changing the rear end ratio will give you more 'power'.

4: Switch to a rear end which has a numerically higher ratio. If you have a 3.31 gear, you might want a 3.73. If you have a 3.73, try a 3.91. If you have a 3.91, try a 4.10 (rare).

Changing rear end gear ratios helps your car have more 'power' by multiplying the engine's output torque by a higher factor. This in turn makes the car accelerate more quickly, but also reduces the amount of speed in which each gear operates. If you have a 3.31 rear and switch to a 3.73, you will have to shift up at a lower speed in every gear. If your car redlined at 30mph in first gear before the swap, you'll have to shift at around 25mph now. If your can ran 2,000rpm @ 60mph before, it may run at 2,400rpm now. This reduces gas mileage by a couple mpg.

To accomplish this, you remove the rear end by unbolting the driveshaft, all the rear suspension linkages, and the brake lines and cables. You pull out one rearend, and swap in another. It'll vary widely in cost based on where you can get the parts, and how reasonable the seller is. Figure anywhere between $50 and $200 for a bare rearend in good condition. Labor will probably be a good 6 hours. If you're having this done by a shop, I have no idea how much it costs because I've never had a shop do anything but align my front wheels before. Be sure to bring some astroglide with you though. I heard it helps.
 
You should also know that switching to a higher ratio rear end will decrease your gas mileage the higher the ratio. This is because a rear end with a higher ratio will cause the engine to revolve faster at the same speed than a lower ratio rear end.
 
isaac said:
4: Switch to a rear end which has a numerically higher ratio. If you have a 3.31 gear, you might want a 3.73. If you have a 3.73, try a 3.91. If you have a 3.91, try a 4.10 (rare).
Click to expand...

4.10's are rare? I've blown two and didnt pay anything for the second one.. Every 740 GLE (8v) i've seen has had a 4.10, and there are a shitload of them around
 
where are the marking that will help us determin what ratio we are running?

Is there a serial plate on the pumkin or something, is it some other place, and will it actually say "3.73 ratio" "4.10 ratio" or is there a code that we will need to referance to find out the actual rear end ratio.


thanks,
Toby
 
Infector 944 said:
where are the marking that will help us determin what ratio we are running?

Is there a serial plate on the pumkin or something, is it some other place, and will it actually say "3.73 ratio" "4.10 ratio" or is there a code that we will need to referance to find out the actual rear end ratio.


thanks,
Toby
Click to expand...

yes, theres a sticker on the driver's side axle tube, about half way (you will wanna take some carb cleaner or something of that nature to clear the undercoating off) and the ratio will be on there. you gotta be careful not to nuke the sticker :)

I wanna say most 760 turbo autos have 3.73s (well, at least my two did, and the 740 turbo manual had a 373 in it as well.. wish i'd kept it..) the 84 760 gle had a 3.54 in it (thats on its way out... that'll be diff #3 i've killed in the 740). mechanic had a 331 in a 240 diesel.
 
It seems most, in fact probably all V6 auto 200 and 700 series had 3.54 rear ends.

On '79 and later rear ends there will be a sticker on the rear of the left axle tube as others have said.

On earlier axles there is a small brass plate on the left bracing rib of the diff housing, the ratio is on this.

I can't speak for 700 or 900 series, but 4.10's for 200 series cars can be found in early 240's. I've seen one in a '75 244DL auto, and one in a '78 245GL auto. These were Australian cars, so don't assume that US cars of that vintage and spec will necessarily be the same.

4.30's can be found in some 100 series, those with M41's I think.

Apparently a 4.56 is available for the 200 series as well, don't ask me what it was used in though.
 
linuxman51 said:
4.10's are rare? I've blown two and didnt pay anything for the second one.. Every 740 GLE (8v) i've seen has had a 4.10, and there are a shitload of them around
Click to expand...

They're much less common on 240s, which is what I think Isaac was referring to.

NA 940s (8V & 16V) all had 4.10s, probably most NA 740s as well.

Only a few of the earliest 240s got 4.10 gears.
 
isaac said:
4: Switch to a rear end which has a numerically higher ratio. If you have a 3.31 gear, you might want a 3.73. If you have a 3.73, try a 3.91. If you have a 3.91, try a 4.10 (rare).
Click to expand...

Hi Isaac!

Do U have idea which ratio is on an '89 765 ti? I know, I'd throw my fat ass under the car/rear end, but this is easier.
My understanding is that if the ratio is modified, then one will have to deal with the following problem: at the same hwy speed, you'll have increased rpm.
point in fact: let's say now I do 70mph at 3K rpm; changing the rear to a higher ratio would probably give me a faster start in benchracing :badboy: , BUT I'd do 70mph at (let's say) at 3,300rpm, which in turn would decrease my gas mileage. Is my assumption correct?

TNX,
Mark
 
turbotrance said:
[quote:b91c6f2ef1="Angus242"]Apparently a 4.56 is available for the 200 series as well, don't ask me what it was used in though.
Click to expand...

240s Diesels with the VW straight-six engine?[/quote:b91c6f2ef1]

heh no, thats the one we found the 3.31 in... and people wonder why they're so horribly slow... :)
 
Do U have idea which ratio is on an '89 765 ti? I know, I'd throw my fat ass under the car/rear end, but this is easier.
My understanding is that if the ratio is modified, then one will have to deal with the following problem: at the same hwy speed, you'll have increased rpm.
point in fact: let's say now I do 70mph at 3K rpm; changing the rear to a higher ratio would probably give me a faster start in benchracing :badboy: , BUT I'd do 70mph at (let's say) at 3,300rpm, which in turn would decrease my gas mileage. Is my assumption correct?


yes. a 4.10 with the m46 makes for a car thats fast off the line and pasted in most roll on. case in point: I raced a friends RSX from a roll a couple of times, varrying speeds, and every time he pulled on away (slowly, and i did have a passenger). when we went from a stop light tho, it was all over..we had near identical launches, but by the end of 2nd i was about 3 carlengths ahead of him. In the long run, he would have caught and passed me. I personally like my 3.54 for driving around, the car lost a little off the line (but the gears are longer, which is better for a turbo car), but my top speed has yet to be determined, I've been quoted at doing around 140 with 800-1000 rpms to go. An ideal rearend tho would probably be the abundant 3.73 imho.
 
Great thread. Of these can anyone tell me which models routinely came with the factory limited slip and what the usual ratios for those were? Tired of being a one legged wonder - can't launch with more that 8 lbs of boost :badboy:


Thanks
Renny
 
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