The Money Pit

I just went to get a wheel alignment, and the mechanic found my stub axle has too much play to get a good alignment ,.. along with a worn front control arm bushing,....

Anyway, the fix for the rear means dropping the whole housing, so ......while it's down, I might be thinking about a gear swap.

Currently I have 3.70 gears, and yes it does run 3000- 3500 on the highway, depending on traffic speed. But,....I hardly use the vette for commuting anymore, just once in a while for a treat. Most of my tooling around is on back roads, I'd say driving 45-55 mph tops.

The 406 has a flat tappet solid cam that pulls hard to 7000. It's actually a 7500 rpm cam, but I guess that is rated in a 350. Has that choppy idle, kind of what you would expect from an L88,...but mines a small block. In looking at L88 options, I see that a 4.56 gear was available, so I guess my crazy thinking is if GM offered it,....it might be something to ponder for my next attempt at a performance upgrade.

I'd like to hear opinions from guys running 4.56 gears, or even L88 owners, as to just how unbearable 4.56 gears are. Or is it really "fun", and worth the trade off.................

thegazman

That stub axle problem is probably just a clip. Pull the cover off the differential, install a new stub axle and clip then you are good to go unless you have $1000 you are wanting to get rid of.

keithinspace

I also have 3.70 gears in a solid-lifter small block and I have to say...I think its pretty unbearable already.

I have put together a spreadsheet comparing different transmission options and gear ratios. I've used it to compare transmission ratios, rear end ratios, 5 speeds, and 6 speeds.

Based on my calculations, a straight-drive (4th gear) 3.70 rear at 2,500 RPM does 60 MPH. With 4.56 gears, you'd be turning about 3,100 RPM.

3,100 RPM with 3.70 gears gets you to about 74 MPH. You need to get over 3,400 RPM just to make it to 70. 74 happens at 3,800 RPM. That's a lot of RPM if sustained.

In 1st at 6,300 RPM (where a 3.70 car with an M20 would achieve 60 MPH), you're doing about 49 MPH. I guess that's what you'd be going for in the swap.

I'm certain you'd pick up a HEALTHY amount of bottom end. But personally, I wouldn't consider the change to 4.56 without also putting a 5 speed in the car. That's just me, though.

gerry72

You have enough motor for the gear. The biggest issue with using a really short gear is not having enough motor to pull it off. Meaning the engine rpms so fast that you shoot through the power band and you're out of the peak and on the down slope of the horsepower curve in nothing flat. The other issue pertains to automatic transmissions and that is just changing the rear gear has an affect on torque converter stall speed. If you were on the edge on stall speed with a 3.70, then you might find issues with the converter being too tight with a 4.56 and things like having a hard time holding the car at idle -wanting to pull through the brakes- and take-off characteristics.

I drove a lightweight, 4.57-geared, Four speed, big cammed street car and it completely changes the characteristics of the car and driving experience. It's not so good in low-traction situations but when it's dry, you'll be rowing gears like a Can Am car. It wasn't so sweet on the highway, but around town it was a blast.

One other addition: get a shift light. The tach is really useless with that much gear because the needle sweeps too fast for you to react to it.

The Money Pit

One of the reasons I am considering this swap is the fact the 3000 stall converter feels a little loose at low speed. I was hoping the gear swap would tighten that up some. As it is now I can idle at 1000 in gear with no problems at the lights.

I just looked at the prices of stub axles and an over haul kit. That's half the cost of a completely overhauled diff,...with a gear swap.

427Hotrod

4.56's are a heck of a lot of fun if you're not on the highway a lot. They are REAL fun in a Vette. The sensation in the first few gears is incredible with your butt so close to the ground and looking out over that long hood!

I ran them for years in my old 427 Camaro. Even used 4.88's for years with the same engine in a '57.

4000-4500 RPM on the highway kept you from getting run over...but you weren't out in the fast lane. But I did make 300+ mile highway trips with them regularly and the engine never whimpered or wore out.

A buddy ran them in his '73 Nova with a hot little 350 and a four speed. He had a 80 mile commute and did it for years. He surprised a lot of folks with that thing on the street.

As mentioned...you'll want to make sure it's got enough Wheaties to pull hard through 7000 RPM.

JIM

Little Mouse

something is really wrong with your calculation. I had three new cars two with 3.73 camaro's and one vette 3.70 and at 60 mph they were turning 3000 rpm not 2500.

I had friends yrs ago the only car they had to drive to work or anything else. one had 4.88 the other 5.13. I don't understand this new breed of folks if your car turns more then 1800/2000 rpm on the freeway its some how miserable lol. I guess part of it is the low rpm cams used today that do not have as high a cruise rpm where the engine is relaxed.

keithinspace

There may be. Dunno.

I created the spreadsheet out of curiosity to verify if I had a M20 or M21 transmission.

I ran through the gears and took basepoints comparing speed (measured by GPS) to RPM.

After tinkering with the data I collected, I satisfied myself that I had and M20.

Knowing that I measured 60 MPH on my GPS at 2,500 RPM, I went backward through the given gear ratios for an M20 and came up with "MPH per RPM" information and started extrapolating scenarios from that.

So...dunno. I just use it as a matter of comparison, really, not as something I'd take to court. Apologies if I'm spreading around non-factual information.

Point is that a 3.70 gear is tough on the interstate and a 4.56 would be just that much tougher. I couldn't conceive of it being enjoyable much over 50 MPH other than very short bursts, but that's me. As I said, a 5 speed would make it more sensible.

To your point about turning RPMs on the interstate: At least in my car, it's pretty loud. And pretty hot. Sidepipes wailing at 3,000 RPM about 18 inches from your ear can get a little tiring. The argument could be made that boat engines run along all day long at high RPMs and don't care. Valid point, I guess. Perhaps the ENGINE doesn't care, but the exhaust to those things points out the back into oblivion and doesn't get reflected back to you by every other car, tree, wall, and other thing you pass. I just know where my comfort level lies. For some reason, my tolerance of running the engine at high RPM for extended periods from a noise and heat perspective is not particularly high.

tektrans

Unless you are going to be at the dragstrip I would stay away from such a steep gear. It would be fun down low but it would get old real fast imo.

The Money Pit

Years back I drove the vette daily with P295 50 15's and the 3.70 rear, and never gave it much thought when I had the 355. Got 17 mpg commuting 400 miles a week. Rain, snow, and an occasional nice day........

I found a gear ratio calculator online, and plugged in a few numbers. http://www.grimmjeeper.com/gears.html

So this calculator allowed me to compare my old set up to whatever combination I wanted. I found if I put 4.10 gears in, with my P295 55 15 drag radials the rpms at highway speed is only about 100 more. The old street tires were 26.5 inches tall, the new MTs are 28 inches. Meaning I could go to 4.33 gears for a little edge,...but I'm not sure what to do just yet.

TheSkunkWorks

My former ZR1 had 4.56 gears behind a M22.

Fun? Very much, up until topping out. Max speed RPM limited well before aero becomes the primary factor.

Drivability? Around town, OK. Highway, forget about it.

Would I recommend it? No, unless use is limited to the strip or AX duty (too deep for RR) and you don't intend on doing any road trips. An overdrive trans would change this, but you certainly don't want one with a deep 1st ratio or you'll end up with a granny low.

My $.02

DZRick

My '69 Z/28 had 4:56 gears, thing was quick but it got old fast. I ended up putting 3:73 gears in it.
With 4:56s you'd want to stick to back roads with lots of gas stations too.

keithl1967

I had 4.56 in my camaro for a short time--had a mechanical roller 383...

Not that much fun to dirve on the street...great for the light to light, but really not a good cruising gear at all...

Think how much the car screams RPM-wise with the 3.70's at 70 on the highway...

Now imagine that all the time, even when cruisng down the road at 45...

and if you do ever actually get on a highway, you'll be getting passed by every grandma on the rod, all while the car is SCREAMING down the road at 60 (below the speed limit)!

unless it is a drag car, you'll get tired of the 4.56's pretty quickly, i'd bet

cv67

big fan of gearing the car so the cam can "work".

Not enough gear it might sound good at an idle but will be a bit of a dog and never really "hit" unless you got sheer CI.

Get a M/T drag radial and go have some fun I say.

called time to buy a brand new car thats stock.

Love running mine down the fwy not using OD and cruise it in its sweet spot. Plus it sounds great how often do you hear that on the interstate today not often. Good stuff

7t9l82

had a vega with a 377 that had 5:38 gears with 14-32w slicks on the street and was unbeatable, but cruising around i was looking for streets with no more than 45 M.p.h speed limits.
if you enjoy going cruising in your Vette i would recommend against that big a gear. it was fine and lots of fun back then but it will never make sense for a nice driver, a vega with a 12 point cage and slicks was never meant to be a nice cruiser. oh and gas was under a buck a gallon.

try driving your car in second gear and cruising a couple miles that will give you a pretty good idea what it would cruise like.

TheSkunkWorks

Glad to see that I'm not the only CF'er who occasioned to run 14x32w's on the street back in the day. ...w/ 5.13's, BTW.

Ironcross

I have always had stiff gears in my toys....most are either 4.1 and 4.56`s....Speeds with the 4.1`s was double the tach RPM...ie, 3500 was 70 MPH and this 61 315 FI Vette got 20 MPG at freeway speeds and higher......My 62 with the 4.56 spins 4000 at 70 MPH......I can and have just for the hell of it {or plain lazy} started off in 4 th gear........

I have 3 BB SS Camaros, 2 with Turbo 400`s and one a LS7 454 , with the 4.56, another is a L72 427 that I installed a 4,1 gear and also a 4 speed L78 396 car..... But after over a decade of using this forum and reading some sad stories I would never recommend bench racers change ratios/gears especially if they have to ask for opinions......

71454Chevelle

Love my 4.56's.
As others have said, I love a little deeper gear. It makes low speed driving with a lumpy cam that much easier, but without an overdrive, anything above about 60mph could get old.
I'm running a T-56 Magnum coupled with 4.56 rear gears and 30 inch tires, it works very well with my engine combo (see sig below). The motor peaks about 6500 and pulls hard to 7k. It launches hard and I have plenty of power in the upper rpm range to utilize the lower gears. The 6th gear ratio is .63, which translates to a 70 mph cruise rpm at a little over 2200 rpm. The best of both worlds.

ezobens

4.56 with an AUTOMATIC?!
No thanks.. Even with an OD, the thing would be unbearable above 45MPH.
I have a 409 SBC with a 3.70 gear and went to a 5-speed to keep my sanity on the highway. I have more than enough torque to break the tires loose as it is, why would I want even LESS traction?

To each his own but I don't think you'd be happy.
Just my .02

Jamess411

Remember the tire diameter has a bit to do with drivability as well as the gear, engine, and final drive gear in the trans. Also the gear vendor option is always there for someone with a little adventure and some pocket change to get the best of both worlds. All depends on what your goal is. Just my .02 )