R200 questions. Best ratio for SBC w/ 5spd?

[Guest Anonymous]

I'll be most likely swapping in a 305 TPI with a 5 spd into my car. Right now it has a 3:54 ratio rear end (R200), but I also have a 4:11 R200 out of an '86 200SX Turbo. I picked this up because I was originally going to put the original motor back in with a T5 behind it. Right now I'm thinking that I'll use the 3:54 rear end with the SBC because it'll be great for the highways and it's still a lower ratio than what came in the IROCs (3:28's ???)

 

Also, didn't the '86 300ZX Turbo come with a 3:64 R200 with a posi?? I may be way wrong on this.

Thanks

[blueovalz]

Unless you spend a lot of time quarter miling the car, the 3.54 will be about the lowest ratio you will want to go with. The T5 5th gear allows this ratio to be tolerable on the highway, and with the increased torque from the SBC, you won't miss the 4.11 gears, even with taller than normal tires.

[V8ZRACER260Z]

I agree on the 3.45 R200. This is what I run in my Z. Trust me you don't need a 4.11 with the V-8. Z's are light cars and do not need a short gear to get them moving ask Scottie he has a 3.07 running 10's! My Z with a 83 T-5 turns about 2700 rpm @ 80mph on the freeway. Rick

[Guest Anonymous]

I'll take it to the strip on occasion, but I'm not looking for super low ET's. I've got my Grand National for that. I figured the 3:54's would be the best, but I just wanted another opinion. I was also wondering about what I'll have to do to get the speedometer calibrated or where to find speedo gears for the T5?

[V8ZRACER260Z]

I had to do some trial & error on this. Somebody else probably has a chart. I went to the dealer and changed out gears till I got close. Mine is still a couple % off but good enough for street driving. Another sugestion would be to get a electronic speedo from Autometer(only avail in 160mph) and set it by the touch of a button, This is what I would reccomend. I opted for the 200mph speedo which is only avail in a manual config. RICK

[V8ZRACER260Z]

By the way why go with the 305 when a 350 is the same price and has much more potential for HORSEPOWER!!

[Guest Anonymous]

Thanks for the replies. The reason I'm thinking of a 305 is because I would like to find a wrecked F Body that I can pull the TPI SBC and T5 out of. I don't want an Automatic and there are no F Bodies with a T5 behind a 350. If I get a T5 by itself, then I'll definately be looking for a TPI 350.

[Dan Juday]

Mike I planned to go with a 350tpi as well. I just couldn't find one in the yards that was not tons of miles or beat to shreads. I bought the 305 because it was cheap, $1250 complete, and low miles, 68K. The differance in power for '91 model year is 230hp/300tq for the 305, and 240hp/345tq for the 350. BTW, mine had an auto behind it, I changed it to the t5. Very little wiring to change.

[Modern Motorsports Ltd]

The largest numerical diff you can run that yields highway rpm's that you can tolerate is prefferred if 3rd/4th/5th gear power is important. Anything less just gives up all the other gears so 1 or 2 requires less driver input to control the traction. I do lots of highway so stopped at 3.7's with my .7 4th or I'd have gone 4.11's if I had a T56........having 3rd/4th/5th etc feel like 1st is kind'of a dream of mine

 

I can't see buying all the parts and building a mod'd car if power is part of the equation and then giving up 5 or 10% acceleration/torque by simply putting in a smaller than tolerable numerical gear. Both my V8 and L6 haven't sucked back fuel at a high rate during constant higher rpm times. Diff ratios are the easiest power/acceleration gain bang/buck for most cars on average. Comparing Scotties wicked inferno is a little off target IMO when his rwhp is 2-2.5x's that of those inquiring.

 

As well compare torque curves b/t setups, peak numbers rarely tell much of the story especially when comparing engines of differing design/CI's etc. Just my .02c CD and worth the .001c US you paid for it

 

Typically I've locally seen 4.11's used them in setups from 300-400+hp when the buyer could find them. When highway was important and no or limited overdrive then 3.7's and 3.54's typically in that order.

 

If 95% is around town and your highway cruising is moderate then I'd plan around that.

 

Good luck.

[Guest greimann]

When you select your rear gear, you will then need to calibrate your speedometer by putting in the correct driven gear. Typically the drive gear in a T5 is a 7 tooth unit so base your decision on that. Go to:

 

http://chris.kellnet.com/chambers/speedo_gears.htm

 

This will tell you how many teeth your speedo driven gear needs. Next, go to the GM parts counter and order the appropriate gear based on these GM part numbers (these gears are less than $4):

 

18 teeth #3987918

19 teeth #3987919

20 teeth #3987920

21 teeth #3987921

22 teeth #3987922

[Guest Anonymous]

Unless you have a motor that can RPM real well (this seems like Deja Vu this discussion... ), I doubt you'd want a 4.11 with a T56. IMHO even with the 3.54, the 1st gear in a T56 is pretty short, a 4.11 wouldn't improve that a bit. As it is I'm into 2nd even before getting through an intersection. Just a opinion though, and as I say it depends on your engines capabilities. *shrug*

 

Regards,

 

Lone

[Scottie-GNZ]

Lone, excellent point. One needs to look not just at diff ratio, but the overall ratio (trans * diff). You need to make sure as you move towards a lower diff ratio that you do not end up with an overall 1st gear ratio that makes that gear useless. In actually, you also have to consider tire diameter in the equation of the overall ratio and since most Zs typically tun a 24.5" tire, that makes it more critical to calculate it before making the change.

[Modern Motorsports Ltd]

"I doubt you'd want a 4.11 with a T56. IMHO even with the 3.54, the 1st gear in a T56 is pretty short"

 

OK, this is my point exactly. To build your gear ratio around 1st when an OEM LT1 with a T56 in a Z can start out fine in 2nd all day long (driven one) with a 3.7 ratio seems a little off IMO. You just gave up power in 4 OR 5 gears for the 1st one which is still a 'short' gear no matter how you gear it IMO. I generally sidestep out of 1st in my 700R4 and then floor it in 2nd unless it's the 1 in a 100 starts that I really want to shred thru the intersection or am concerned for my frontline rights. I guess I enjoy 1st and 2nd like everyone but really strive for the roadracing 3rd/4th/5th etc to be more maxed than enabling a little more function out of my 1st gear that still leaves a bit to be desired. I can see 1/4 mile planning as totally different but if the posters were dedicated quartermilers I think they'd have said as much. Not saying 4.11's is everyone's solution but I'd sure hesitate to drop to 3.54's in anything but a very strong build, just free power/acceleration IMO. The 10 or 11% from a 3.54 to a 3.9 is a noticeable torque difference. I recall the chang in my ZX when I went from OEM 3.36's to 3.9's and it was night and day. Same effect can be had with a V8 setup once you're accustomed to the new power level and are still wishing for more out of the bottom of the go pedal. Having driven various V8 rides from slower/moderate/ to quick I still believe the moderate to tame builds could very much benefit from higher numerical gears (again, as long as their highway manners are tolerable). Most T56 owners may not want 4.11's but as I've seen 1st being a sidebar already I think it'd be fun to try. Diff's aren't that hard to change so no decision is too final to not be altered.

 

I'm not involved in any late night/early morning or 1320 competitions at all and usual street fare is relatively tame so I'm not cruising with drag radials (although I did some 'hunting' each summer with the A032R's which was fun ). Event highway trips and roadracing events (lapping days) is usually where I really get to let it out besides my daily commutes and stoplight brigades.

[Guest Anonymous]

Thanks for all the replies

 

I was 95% sure that I should stay with the 3:54 rear end and now swap in the 4:11, but it's always good to get opinions from others before I start a project. The only reason I picked up the 4:11 R200 was incase I decided to drop the L28 back in with a 5 spd from an 80's 280ZX.

[Guest Anonymous]

I agree Ross, I don't think we're really talking all that different a language, just approaching it from different standpoints and different uses.

 

Your right second gear starts are no problem. I understand your view on loss of torque through mechanical advantage, but IMO (worth nothing to anyone but myself) lack of torque is not a problem in a V8 conversion, because your only a little right foot pressure from being in a huge world of torque at nearly anytime. Thats what attracts me to the V8z, abundant torque immediately available like any good 60's muscle car, not winding the crap out of it waiting for something to happen like the import racers.

 

Ironically, the stronger the build (raw horsepower wise) the less bottom end torque is generally available meaning your plan of 4.11's would be justified to pull 5th and 6th strongly in a T56, my very mild (stock) 350 pulls strongly from 1000 rpm's to about 4800 so it can actually pull the 3.54's with more authority at cruise rpm (which is not to say its a rocket in 6th at all, a downshift still has to happen to get a pass with authority) than say a engine that doesn't come alive till 2500 and would need a downshift to keep from loading up the motor.

 

Also ironically, the lower cruise RPM generally the better the MPG (which is why detroit started all this OD transmission stuff in the first place to improve its fleet mileage IMHO).

 

Given the gearing available, and the ratio's of the popular chev. trannies, its still all a compromise for either strongly pulling 4,5 and 6th, or rowing the tranny like crazy in the lower gears, whether its important or not depends on how the car is used and what you like and how much freeway gridlock you are stuck in and what your build likes to do RPM or torque (like Scotties).

 

Respectfully,

 

Lone

[Modern Motorsports Ltd]

"I don't think we're really talking all that different a language"

 

Me neither, just fielding good opinions which I enjoy so much on this board. I love how we don't get into a my dad's bigger than yours debate

 

"my name is Ross and I'm a torque addict....thanks for letting me join in your TAA meeting.....so what's my first step.... "

 

I'm sure yours has fine torque as do all V8 setups. Our perception of 'fine' varies amongst us and even though mine will spin my 245 Rcompounds from idle thru 1st and into 2nd I'd like to know and experience it doing that in 3rd 4th etc or come closer anyhow (was same with 327 or roller 350 and Victor Jr etc). I don't have any flat spots in my setup from idle to 6k but would always appreciate more kick and now that 1st and 2nd are adequate I'm going to see what I can stir up in 3rd and 4th. I want your 'huge' world of torque in 3rd and 4th etc. It'd be cheaper if I could accept differently but that's why I'm in Torqua Addicts Anonymous...oops public now;^)

 

I don't think lower rpm's for better mpg is surprising if the engine is under only light load at those lesser rpm's, just seems natural but I actually experienced no loss in mpg in my 280ZX from 3.36's to 3.9's even though my highway cruising rpm's at higher speeds on 900 mile trips went up to 3600 etc. And in going to California I saw similar results in my V8 setup (ie. no loss in mpg at higher travel speeds, was still around 20mpg). Surprised me but what I experienced anyhow.

[QWKDTSN]

I'm going to be running 3:90s... just because that's what I bought for my L24... we'll see what happens with the 350

[Guest Anonymous]

Lone Star 1,

Is your 3:36 rear end an R200? Since it's a posi, where did you get it from? I'm not too excited about running an open diff.

[Lone Star 1]

Yes Mike it is an R200. I bought from David Spillman on this board. I think he had it made from two different rear ends, but i'm not sure. I'm not sure if Datsun ever made any in there cars.

[Guest Anonymous]

A rumor has it that an option on the the '86 or '88 300ZXT was for a 3:64 R200 Limited Slip Diff. If I can find one I'm guessing the carrier is the same as my 3:54. Especially since that's most likely where the posi for your 3:36 came from and the 3:36 ratio came in the first of the R200's back in '76?? (Maybe it was '75) The funny thing about my '77 is that it has a 4 speed manual which called for the 3:36, but in fact has the 3:54 which was used in conjunction with the 5 spd in '77. Since the 5spd was an option I'm guessing that they just dropped a 3:54 in all the '77's. My Z was terrible on the freeway with the 4 spd, but it wasn't too shabby with acceleration.