3.36 ratio & T-56?

[Fastzdriver]

I am building my 75' 280Z up with a modified GMPP HT383 motor with a modified TPI unit suppling fuel. With aprox 425-450 hp and 500 lbs of torque. It will be mated to a 94'-up BW T-56 with .5 final gear. My question is this: If i use a 3.36 diff gear set will my gas milage improve of suffer? I do a great deal of traveling and am looking to get the best gas milage as possible. I am not really worried about the lower gears because of the amount of torque i will be running. Any input will be greatly appreciated.

 

P.S. I have already searched the archives but was unable to find a clear answer. Once again thanks in advance for your help with this.

[Lone Star 1]

On the home page of this sight their is a gear ratio calculator. With 235/60 /15 tires it looks you would be turning about 1575 RPM at 70 MPH in 6th gear. That would probley get great gas milage.I running the 4L60E that has a .7 fourth gear with that tire and the 3.36 rear and I'm turning about 2100 RPM at 70 MPH. I'm getting about 22-23 MPG in highway driving. My LS1 is making about 300 RWHP.

[Guest greimann]

Depending on how modified your motor is, it may run more efficiently at a higher rpm than a lower one. In my setup with a T5 with a .62 overdrive and 3.7 rear gear, I get better mileage in 4th gear at 60 mph than in 5th gear. I know this from running data acquisition and doing tests. It becomes more econmical for me to shift into 5th at 65 mph and higher. This has a lot to do with keeping the engine in the "sweet spot" of its brake specific fuel consumption.

 

The basics specs on the motor are: Crane cam 216/228 @.050, 112 lsa. TFS heads 64cc, flat top pistons, Holley 4Di TBI, Performer manifold, cast iron exhaust.

 

With a .5 OD and 3.36 rear, you may not want to shift into 6th until way up in the MPH range, but only testing will tell you for sure.

[Mike C]

Greiman is correct. You also need to calculate tire height for actually overall gearing. If you are running a carbureted car, it may not work smoothly at the rpm the 5th gear puts you in. IMO, the 6 speed isn't as good a choice as a Tremec or BW as far as gear ratios go, but that would be max output and not economy minded.

[Brad-ManQ45]

Someone (Mike I think) has a T56 and 3.54's and he said he has to be doing 75 to get into 6th.

 

Now I do believe he has a pretty stout cam.

 

.5 final gear? I thought .72/.60 was stock and didn't know another was available - no diff....

 

Sounds like your cam isn't as wild as Mikes, and the EFI certainly makes a diff (he has a carb I believe).

 

All said and done though, if you DO have a .5 you'd probably be bettor off w/a 3.54 or 3.7. Even w/ a .60, unless you do a lot of high speed driving in an area that has few gendarmes, you'd still probably be better off w/the 3.54 or maybe higher.

 

Anyone think differently?

[Fastzdriver]

Once again thanks for all of your input thus far. As i stated before i will be running TPI for fuel delivery not carbs. And once again the BW T-56 does have 2 overdrive gears to work with. SO even if i rarely had to hit 6th aside from highway miles, the 3.36 could save me alot of money in the long run. Last year alone i put close to 40k miles on my other car and 15k on my motorcycle so the gas milage for me is quite important. And being that the motor is a torque monster the low gears shouldnt affect it but so much once i am simply maintaining highway speeds of 70 mph and up. Mainly i am just concerned about making a vehicle with as much of the best of both worlds as possible. Hell, modern corvets can pull 27 mpg on the highway. I just want to be able to compete with those numbers.

[Modern Motorsports Ltd]

"SO even if i rarely had to hit 6th aside from highway miles, the 3.36 could save me alot of money in the long run."

 

I don't see how a 3.36 is going to save you money when built to the power levels you mention? No offense. I wanted to reply earlier this week but I've been super busy.

 

Why build to your power level with a .5 6th gear and then put a 3.36 in? vs. a 3.7 you just gave up 9% torque in simple gearing and IMO that cam won't be that efficient at lower rpm levels anyhow so you'll likely be better off with a 3.7 or similar on the highway. OR build a slightly smaller cam which would have broader torque and somewhat less and then run 3.36's. To build that power and then just zap it with the 3.36's doesn't seem quite right to me. That gear will hit you most in upper gears IMO. You mention the lower gear losses d/2 3.36's won't be missed but it's higher up it'll be more prevalent IMO. Road racers don't swap up gears for their lower speeds (at least my buds haven't), it's their higher speeds/corner exits etc where it's been most beneficial......most all of us have lots of torque at lower speeds.

 

Perhaps if I understood how your power goals/plans fit your cars use/functions it might be more clear to me.

 

"Mainly i am just concerned about making a vehicle with as much of the best of both worlds as possible."

 

That's what I was looking at as well, a proper balance.

 

"Hell, modern corvets can pull 27 mpg on the highway. I just want to be able to compete with those numbers."

 

YOu want the 1320 times/mpg and....or...?

 

mpg is easily accomplished with similar motor in your lighter car......LT1 setups, even mildly modified in a Z can fetch that. But running a larger less efficient cam (less efficient at lower rmp's where it's overlap is most noticeable is what I mean) and then lower gears won't help hit the mark IMHO.

 

Just my .02c and worth what you paid for it

 

PS and I have 3.36's and 3.15's on the shelf so I must believe what I wrote

[Guest Anonymous]

I have a 90' Corvette and got great gas mileage with the stock 3.45's, however I hated not really using that 6th gear unless I was saving gas.

On my 6th gear at 60mph I was turning 1250 rpm..which is really laid back.

I slapped in some 4:10s and got a better acceleration, and really havent noticed the gas difference (I can't tell what RPM i am running on my 6th gear cause my shift light knocked out my tach, which explains why I got the z..another story for another time)

But regardless, with all that horsepower, I dont see anyway of saving gas anyhow? no?

So if you do have the option to swap any gear set, id go with a lower gear (higher numerically) cause later on your gonna be pissed that ya did'nt win that race and you gonna say "Damn I woulda won if I had some 3:73 or 4:10's"....hehe.

Nothing feels better than the awesome launch of good gears.....you wont regret it!

better yet, get a beater Honda so you can have you cake and eat it...but watchout for them "Fast and Furious boys", they might wanna challenge you to see who reaches 110 mph first...lololol.

Good luck!

[jeromio]

Well, now I am interested in this discussion. I'm putting in a A4 initially, because I am too poor to afford a T56 right now. I currently have 4.11 in the car. I figured I'd leave the 4.11 in there initially, but plan to drop in the 3.54 since I presume that with the torque of the LS1, the light weight of the 240 and the low gears, I'll be cording them rear tires quick fast.

 

But, I definately plan on getting a T56 asap. So, it sounds like I should hang on to the 4.11, or possibly not even pull it out.

 

Seems like there was other discussion here about people not even using 1st gear with the T56 though. Looks like that trans has ratios that are just too wide for real world use???

[Guest Anonymous]

Well in my opinion, matching a rearend gear to a transmission is crucuial to performance.

I have raced plenty of Mustangs in my Corvette that are somewhat overpowering my Vette, but they just lose every time, simply because they have bad engine-tranny-rearend combos!(Ok dumb driving has alot to do with it!)

So before you start hacking at your car, make sure you know where your sweetspot is and then figure the ratio to play with.

In my opinion 4:11s are a sweet gear for anything with at least a 4 speed.

Powerglides and Hydramatics need not apply unless your a straight shooter down the track!

Good luck!

[Guest Anonymous]

This topic has come up a time or two before, and as was mentioned above you need to match the rear to your state of tune.

 

If the motor's a torquer then you can probably pull that top gear just fine at 1600 revs, don't ask for a good pass without a downshift though.

 

If the motor doesn't like to pull cleanly until 2000 revs then of course it won't be suitable.

 

Both approaches (torque motor with tall gears or rpm motor with lower gearing) IMHO can work, I'd like to one day prove this by building a turbo SBC motor that makes fat mid-range power and doesn't rev to the skies, maybe 6k tops and run taller gearing. Can this work? Seems to work for Scottie in his Turbo Buick V6 and he's in the 10's now, although he does use an automatic.

 

The downside of course, torquier motors have lots of low end which makes traction more of a problem getting out of the gate, but on the other hand motor's that make HP at a higher RPM can experience the same problem only up the RPM scale a bit. Torque is still torque whether its spinning the wheels at 2500 rpm's or at 4500 rpm's IMHO and with 400-450 HP this will happen with frequency I can almost assure you.

 

Look into what you want the car to do, if its a highway car and the engine can pull the low revs without a problem then its feasable, if not, maybe 3.54's at least would be better suited. Just an opinion of course. Good luck with your decision.

 

Regards,

 

Lone

[fl327]

i would like to believe that a car is a car and some things about cars are universal. like running high gears with a radical combo to be able to use all that high end craziness. with a mild motor, mild gears. the z already has this crazy power to weight, you could improve on that even more by having some crazy butt gears and building the motor a little tougher. with a six speed you will comfortably cruise at just about any speed you want without breaking 2500rpm, it will make 4.11 turn into 2.05- in a 01 ss maro

ive done 145 at around 3k, it was great, thats the kind of top end you can get with 3.36, i think they have 3.42 gears or something. i wish i had t56 money right now, i would try to stick in some stump pullers and do some camming and all types of pump up to my motor then. economy? economy is when your 5-10k car stomps vipes!!

[pparaska]

Another thing to consider is the usefulness of a manual with a very high numerical first gear like the Tremec 5spd (3.27:1) with a numerically high rear gear and the typical 25-26" rear tire on a Z. With a 3.27:1 first, a 4.11:1 rear and that 26" tire, you'd have a pretty useless 1st gear.

 

BTW, the 93 F-body T-56 ("400 lbft capacity") has a 2.97:1 first gear, and the 94-2000 T-56 ("450 lbft capacity) has 2.66:1 first gear. The later 2.66:1 is pretty good for a 3.7:1 or higher numerical ratio, I'd think.

 

Hmm. But with a really steep first gear and a very tall 6th gear, you could go with 4.11:1 or something and just not use 1st gear.

[Guest Anonymous]

Well, I would have to say if you have the "choice" of gears, get around 4:10-4:30's because in reality, that first gear is whats going to get you out of the hole and into second gear within nanoseconds, not to mention a very good 60 foot time.

millions of racers wil tell you...4:11's over 3:36 or even 3:54's.

Its just common knowledge, unless your running a powerglide or something that will keep you hovering at 4k in 3rd gear, but your not, your running a six speed! so lets end this forum and just get the 4:11's!

If you must do more research go ahead, but your going to see that the minimum racing gear to use with a 6 speed is at least 3:73!

Take it form someone that already has the gears and a six speed...they work better on the launch and 60 foot times....as well as the gas!

Think of it as "Damn I will finally get to really use that 6th gear!"

Don't be scared damnit, its not like its permanent! and if you don't like the gears, im sure theres going to be plenty of people ready to gobble up those gears in trade for 3:56's!

(But im sure your gonna like them, unless your driving a minivan)

[Mike C]

I agree on the max gearing. I have 4.11 in my Camaro with 2.62 first and I think it is near optimum. I think the '93 trans and 3.73 would be perfect or the '94 and up with 4.11. Everyone I know with a modded 6 speed car went with 4.11 anyhow.

[geotek]

I'm convinced-

What year and model used the 4.11?

I guess the 3.90 would be a suitable alternative?

[Guest Anonymous]

Again by choice, only if you had the option.

The R200 came with 3:90 gears.

So alone you really would only need your stock rearend (granted it was a R200)

If again the rearend option was to come about.

I would go for the setup Scotty did to his Z and add a Vette® rearend.

I'd stick to the 3:90 rear if money was an object.

If Money was no object i'd prefer a ZO6 with 550hp on tap!

[Guest Anonymous]

If you went to a R230 I think you can get gears near 4.11. I don't think you can compare gearing on a Camaro to a Z, the Z doesn't have the weight of the Camaro and doesn't need that sort of mechanical advantage to get rolling. The only comparison is like the F-body's third gear is where the mechanical advantage really starts happening big time and the scenery rushes by big time once you shift to third in a Hybrid V8 Z. (the g forces are great in the first two gears, but third is where real speed starts happening at least in my car)

 

IMHO unless you use some pretty tall tires in the back you'll be shifting into second by the time you pass the tree. Thats why it was mentioned, it depends on your engines state of tune, if it rev's to 7k, that 4.11 might be just fine, if its more like a stock LT1 it'll run out of steam QUICK in first.

 

Second gear starts are easily done with the T56 and a 3.54 even, first is really optional in such a light car, I routinely pull away from lights if I get lazy, in 2nd in my Z. Just an opinion, but then again my car's a street car and not a full time drag racer. I guess in the end, its gear the car to its ability to pull 6th cleanly and just live with where 1st gear falls out as there isn't much you can about it. Of course the above is an opinion and we know what those are like, and no one elses will fit etc..

 

Regards,

 

Lone