Fixed 1 prob. now lets figure out a gear

[BigBlockMonte]

okay heres the set-up again since this a new thread. what gear ratio will be best for the car. I do like to drive on the highway a good bit. If i can keep the car at 3k or lower at 65mph. that would be cool. but I don't want to be always on the converter either. so if more gear is required then so be it. don't wanna kill my tranny from all the heat.

 

okay

 

468

10.2 compression

aluminum heads (320cc intake runners) 119cc comb chamber

2.25 intake valves 1.88 exhuast ( rect port)

eddy air gap (rect port)

holley 850 vacuum secondary

comp cam XE284h 574/578 lift 240/246 duration @.50 110 Lobe seperation

holley 130gph pump w/ 3/8 line from tank to pump

hooker comp headers w/3" exhaust & flowmaster mufflers

28" tall tire

TH350 w/ shift kit

2.73 single spinner

 

71 chevelle weight is 3825 with me in it.

 

any more info needed just ask. thanks everyone.

 

 

[Montemedic]

3.31's will be exactly 3000 rpm @65mph. You will have much better acceleration and keep it at the RPM's as requested.

[CrazyDavey]

I'm not sure anyone makes a 3:31 anymore, a 3:42 with a 28" tire would be close...Dave

[Andy's Auto]

If you can't find a set of 3.31s let me know. I have several sets of niced used matched sets.

 

Andy

[Sam (Bones)]

if it was me I'd go with no less than a 3.55

[BigBlockMonte]

I just went to Richmonds website and did their street calculator. According to them it tells me a 3.73 gear will be 2909 @ 65mph, and a 3.90 will be 3042 @ 65mph with a 28" tall tire.

 

I'm curious with a lower numbered gear(3.55 to 3.31) and the weight(2800+lbs) of the car will I always be slpping the converte cruising around? Or could I get away with less gear.

 

I really dont know how to determine the gear and converter and engine combo.

 

I know I dont want to kill the trans

[wallaby]

When you're just keeping a steady speed on the highway, there isn't much load on the engine...you don't have to worry about much converter slippage. There will be some, but not much. If you had a shoebox-shaped RV going at speed, then there would be a genuine concern.

When I try to figure out gear ratios, I ask myself: "how fast will I need to go in the quarter mile?" , and "how high will my engine rev?"

The ideal gear for racing will have you crossing the line just as you reach the point that your engine starts to "lay down" or reach max revs, which ever comes first. [for example, your engine is safe to rev to 6500, but really doesn't make power over 5,000] Then you can figure what that gear will be like for normal highway driving. Chances are you will need to lean toward the comfort of daily driving and and sacrifice some dragstrip performance. Another thing to consider is whether you would really be happy cruising at 65, or if you want to keep up with traffic and cruise at 70 or maybe 75?

 

I used a different online calculator, and it provided different numbers than the Rockwell site you quoted.

Just for fun I plugged in Crazy Davey's quarter mile speeds with your 28" tire.

His Monte does 115 in the quarter; with a 4.11 gear that puts his rpm at just under 6,000. That's about perfect except that same 4.11 gear is a bit much for highway cruising (3,400 @65...3900 @75). You can see where we're going here. It might make more sense to tailor the gears for good daily manners, and live with the dragstrip results.

 

If it were me, I wouldn't want to cruise for any length of time with a gear with a number greater than 3.55. When you want to do the dragstrip, change to a 26" tire. That tire change will net you the equivalent of a gear somewhere between 3.70-3.90.

 

This is the calculator I used: it's pretty handy because it lets you calculate two columns so you can see results side-by-side.

Because the form is set up for 4WD vehicles, just put 1.0 when it asks for a transfer case ratio.

http://www.grimmjeeper.com/gears.html

[BigBlockMonte]

3.55 sounds to be the best gear to cruise around on. at the most a 3.73 gear, it raises the rpms a litle more than a 100 rpms from the 3.55 at the same speed.

 

I think the 3.55 will be the wineer. I'm ordering today, thanks you everyone for your help and suggestions on this. I always appreciate your help.

[kc8oye]

your stall speed can be an issue with an o.d trans

 

my 700r4 has a 2500 stall converter, and I run 2250 locked up in 4th, and around 2500 unlocked. it's even worse below 70mph because now I'm well below stall speed. it will also generate a lot of heat.

 

if you are running 3.55's with out an o.d you probably won't have too much of an issue with this tho.

[680HPStroker]

I agree with the most recommended 3.55 gear set, but unless I missed it you didn't list your converter stall speed. That also comes into play when selecting a gear ratio. If it were me I'd select my gear ratio first and then select a stall speed based on all the other driveline and weight variables to obtain the desired cruising/racing RPM. My converter is set at a tight 4,000rpm stall speed. With 28" tires and 4.11 gear I run at 33-3,400rpm's at 60mph. Not to conducive for cruising, but originally I was going to do some racing so it was a trade off. Now I wish I either had an overdrive, or a little less stall with a 3.55 gear(would require a series three carrier/even more money).

[BigBlockMonte]

i did forget to list the stall. my mistake. I have a trans specialties converter 2800-3200 stall.

 

TH350 trans

28" tall tire

2.73 gear ratio/ single wheel

 

I talked to ATI and told them my set-up & weight of the car. They suggested a 3.90 to 4.10 gear.

 

Those gears are a little steep for my cruising around on the highway that I like to do. So I decided to go with a 3.73 gear.

 

I know the converter will slip a little, but it shouldn't slip much. ATI was concerned with excessive heat on the trans, which is why he said a 3.90/4.10 gear.

 

I'm hoping a 3.73 will be good enough to cruise around town/highway & maybe a once or twice trip to the track.

[Andy's Auto]

Duder, if you going to put miles on that car a det of 3:31s or .55s will quell the regrets you might get from the 3:73's. I have 3.73s in my 71 with the new 3500 convertor gives me 3650@70mph. A little loose but the car does do a solid burnout.

 

Ondy

[CrazyDavey]

Duder, if you going to put miles on that car a det of 3:31s or .55s will quell the regrets you might get from the 3:73's. I have 3.73s in my 71 with the new 3500 convertor gives me 3650@70mph. A little loose but the car does do a solid burnout.

 

Ondy

 

Pizino....shouldn't you be heading for the track or something???

[Andy's Auto]

Originally Posted By: Andy's Auto

Duder, if you going to put miles on that car a det of 3:31s or .55s will quell the regrets you might get from the 3:73's. I have 3.73s in my 71 with the new 3500 convertor gives me 3650@70mph. A little loose but the car does do a solid burnout.

 

Ondy

 

 

Pizino....shouldn't you be heading for the track or something???

 

Oh Wise One, track opens at 6pm. And Allan pulled a Mikey. Just me and my LoverGirl.

[kc8oye]

yeah 3.73 is gonna be a little rough w/o over drive.

 

my o.d trans has issues and won't shift into o.d right now.. so I've been driving it in 3rd gear.. running somwhere around 2500 rpm in 3rd gear with 27" tires. while it doesn't HURT the engine.. it does make cruising at highway speeds a lot less pleasant. my engine isn't balanced so it vibrates a lot up there and just generally feels like it's really straining to pull the car along at those speeds. but it certainly has no lack of get up and go not waiting for the 4-3 downshift

[BigBlockMonte]

so you guys think I made a bad decision on the gear. I probably should have never called ATI on this. The tech kinda had me scared if I went with less than a 3.73. That I would always be on the converter, and burn the trans up with the excessive heat from the converter slipping.

 

He wanted me to do a 3.90/4.10 gear. I told him theres no way I would enjoy driving the car if I went that high. He then said well your only option in a gear is a 3.73. but no less.

 

So thats what I did. I may regret it. I hope not.

[CrazyDavey]

only if you plan on doing a fair amount of highway driving, then they can get on your nerves. If it's mostly around town the 73's are a blast.....or....get this...you don't have to go 70 mph.....you could always leave a little early, slow down, kick up the Ipod and enjoy the cruise...Davey

[wallaby]

The difference between a 3.72 and a 3.55 is minimal...does that help?

[Z204me]

Another opinion to help you out...

 

In August, me and Lisa put over 2000 miles on the 70 during the Western meet and the week afterwards. We did a mix of city and interstate driving throughout Oregon, Washington, and Montana. The 70 has 3.73 gears in it with a M22 4 speed. The only consideration is interstate driving - I don't drive the 70 as fast as I do the 73, which has 2.73 gears. As a result, I like to keep it (the 70) around 65 or so. I have Radial T/A's on all 4 corners...235/70/15's.

 

Here is what I came up with during the trip, both on the GPS and my speedo/tach gauges...

 

60 MPH...2800 RPM

70 MPH...3300 RPM

 

So, yes, on the open interstate, I keep it MOSTLY under 70...however...like Davey says...it is the ride/drive that I truly enjoy when in this car. Also, I wanted this car to be a streetlight screamer, so that is why I went with the 3.73's. Although with the dead first gear in the M22, I really should have went with 4.10's or higher. Eventually, I am going to buy a Gear Vendor's overdrive, so I will be able to enjoy the equivalent of a 2.91 in 4th over after it is installed.

 

Hope this helps "calm" you down regarding the 3.73's...

[BigBlockMonte]

yeah, you know what. i'll be fine with the 3.73. it may not as desirable as a 3.55 or 3.31. but it will be fine. They arrive tomm. Hopefully they arrive early enough, I can get it to my machine shop to press the bearings on and whatnot.

 

weather suppose to be okay this weekend, so if everything works out. I'll let you all know how the gear works out on the car. I am hoping it will wake it up abit. 2.73 gear kinda sucks.

[Heckeng]

How about 3.55, and a good tranny cooler? That is what I did but my cam is a little smaller than yours. I have a gauge on my tranny temp and I keep it around 170 degrees just with a B&M stacked plate cooler. My converter is an ATI 3000 rpm stall but is on the tight side which helps with the heat deal.