R180 or r200

[78 280zcar]

What is the difference between these two differentials in overall performance. Thanks

[ChrisA]

R200 will handle more horsepower and had different ratios than the R180. Physically larger than R180 also.

[78 280zcar]

What about top end which one is better higher top speed. Thanks

[texasz]

Originally posted by ChrisA

R200 will handle more horsepower and had different ratios than the R180.

Not really the case. Here's a link to a thread from last year that provides all the info about the R180 and R200 ratio options: http://www.classiczcars.com/forums/showthread.php?s=&threadid=1568&perpage=15&pagenumber=2

Physically larger than R180 also.

And as such also heavier. I mention this because for some racers they try and cut weight anywhere they can.

[ChrisA]

A lower ratio like a 3:36 or a 3:54 will give you a higher top end speed if you have the horsepower to drive it.

Stop light drag racers like a higher ratio to get them out of the hole. 4:11 is typical in your Camaros and such but it does limit top speed. Friend of mine drag races a 57 Chevy with a 7:something rear end. He runs quarter miles in the 10's but the cars top speed is only 110 mph.

Depends on a lot of factors how fast you can ultimately go.

Chris

[ChrisA]

My repsonse to the R180 versus R200 horsepower issue is based on what Don Devendorf spoke about while building the Bob Sharp Z cars in the 70's. I recall him saying the R200's would handle more horsepower than the R180. With turbo'd injected L28's making over 800 horsepower he liked the R200 best.

Yes it is heavier because its built with stouter mechanicals than the R180.

Quaiffe diffs are an expensive option for most. I will stick with the R200 to handle the expected 460 crank horsepower from my L28 turbo motor I'm building.

I had a 327 Chevy powered 240 and I shredded the R180 with that motors 300 horsepower (its the torque that kills trannys and rear ends).

Chris

[78 280zcar]

The reason I ask, is because I have an automatic in my 280 and the r180 and my car will not go past 60 mph or it will but sounds like it needs to change gears, but it is already in third gear. Now if I put an r200 would that change top speed more or would I be better off getting the 5speed gearbox for it. Thanks for the help ya all

[ChrisA]

I have a 240Z with L28 engine and auto tranny, stock R180 rear end, my car will do well over 100 and motor is stock. I would say you have a mechanical issue. Tranny could be slipping if its really in third gear. Can you shift up from 1st to 3rd manually? That is a strange problem to not go over 60. You could have an engine problem also. Lack of fuel delivery at high rpm, bad timing, bad ignition spark at high rpm.

Changing to a 5 speed would help indeed. As long as your motor is working right.

You definitely have some work ahead of you.

Keep testing.

Chris

[78 280zcar]

The engine is in good working order, I havent tried manually shifting it though, I think I will try and see if I can. Yours does not sound like it needs to change to another gear when you get to 60 mph, I took it to a transmission shop and they told me it could be the lockup or something like and I do not know what that is, I asked him about changing it to a 4speed and he said it wouldnt make a difference because the 4speeds are geared the same way as an automatic, is this true. Thanks

[ChrisA]

That tranny shop guy fed you a line of bull. I have a 73 with a built L24 and stock 4 speed and it will go 135 (dont tell my wife). A four speed is better than the auto but not as good as the 5 speed.

My auto tranny will twist 5,000 rpm at serious speed. You may be right about the lockup. I dont know jack about auto trannys. The first one I had blew out second gear so I just swapped in a salvage yard unit.

I wonder how your fluid level is? Are the tranny cooler lines hooked up to the bottom of the radiator.

Keep digging man, you'll get it. That Z car out to do at least 120 in stock form.

Chris

[78 280zcar]

Well I just took it out and tried the manual shifting of it and it was fine, so I went ahead and took it on the freeway and went about 75, it was doing pretty good except for when I let off the gas just a little bit it would kinda jerk and drop rpms fast, and when I stepped on the gas a little it would take off like it was still in second or something, so it could be the lockup but I do not know much about auto trannys either so I am only assuming it is the lock up. does anybody know what lock up is suppose to do, from what I gather it is suppose to grab the engine when it is at a certain speed is this right or is it something else. Thanks

[texasz]

Honestly, if you're gonna have to do any tranny work just swap it to a 5-speed. You will probably spend a bit more money but IMHO a sports car deserves a stick not an automatic.

Also, earlier on you were talking about the car only going 60mph and asking if an R200 diff would help. The R180 or R200 does not affect this at all, what would affect this would be the ratio; that is if this was even your problem which it doesn't sound like it is. As it was already mentioned the lower ratio is good for top end and the higher ration is better of the hole shot, you must strike a balance with the ratio and the gear ratio of the tranny based upon the kind of driving you expect to do.

As for the weight vs. amount of HP it will handle the info is correct, the R200 does weigh more but this is a function of it being built to handle more HP...but if you are running a stock set up then you should not be in danger of damaging your R180 diff.