Understood.
3.08 gears with 2400 stall torque converter
- Thread starter pacem
- Start date
- Status
I have been where you are now, build something and then later think about MPG or longer trips and rpm's. The fact is right now with a HP cam even if its mild needs a higher rpm to run correctly and get the extra power it was designed for. With the overdrive and lockup converter with 3.73 gears you are set perfect for a street car. If you go to a 3.08 gear you will be happy on the road and might get a tad better mpg but the intown and takeoff performance will suffer greatly, not to mention the added stress of a higher gear and stall at takeoff and low rpms around town will tend to overheat the transmission fluid. All performance cars is a tradeoff but to me todays hotrods with fuel injection and overdrives they make driveability so much better.
Another thought if you want to change gears is to go to a scrap yard and buy a complete rearend out of another car and replace the whole assembly and then you will still have the 3.73 intact incase you dont like the higher gear or if you sell the car alot of perfromance folks like the 3.73.
In that case looks like the safest thing to do is to go with 3.23. It's a compromise gear, OK on both highway and in town. I had one before, although not with LT1.
pacem - You omitted the part when I said you SHOULD get an increase in gas mileage.
And 2.56 gears are not in the equation, anyway.
Arco is right - the lock up over rides the stall speed.
The stall speed is only used at it's maximum on hard throttle take off situations.
And 2.56 gears are not in the equation, anyway.
Arco is right - the lock up over rides the stall speed.
The stall speed is only used at it's maximum on hard throttle take off situations.
Found this interesting bit of info, makes sense?
http://www.camaros.net/forums/showthread.php?p=271539
Quote:
Ok the way it works is this. Say you have a 3000 stall convertor and you are going say 55MPH with your 3.73 gears. At this speed you would be turning around 2500 (depending on tire diameter). IF You now FLOOR the car, it would IMMEDIATELY feel like the car's transmission was slipping momentarily because the convertor has not gone beyond it's stall speed. A good rule of thumb is that the MAXIMUM stall you should run (assuming you are also running on the street) is 200-300 RPM LESS than whatever RPM you cruise at on the highway. For example I cruise @ 2800-2900 RPM so my suggested max. stall spped for my convertor should be roughly 2600 (which it is).
In the 496 example I cited earlier, if you pull away (say light throttle) away from a standing start and watch the tach, you can see that it momentarily goes to 3600 rpm not because the tires are slipping but because of the high stall convertor. On the highway the car feels as if you momentarily have it in neutral just prior to it "catching" in a sense.
Slippage does cause heat. Auxilary transmission coolers are more or less REQUIRED on cars with 2000 or more stall sooed convertors. Slippage also causes poor gas mileage. the 496 with the 3600 stall convertor gets maybe 6-7 MPG. My car with approximately 25 more HP gets 11-12 MPG. (yeah, I know guys it's apples and oranges but the point is high stall convertors KILL gas mileage for those of us interested).
I guess I would describe the effect of the convertor prior to reaching stall speed is the same feeling as if you were runnning a standard transmission with the clutch slipping. It is still engaged all right but you are not getting the full throughput of the motor.
Originally Posted By: pacem
In that case looks like the safest thing to do is to go with 3.23. It's a compromise gear, OK on both highway and in town. I had one before, although not with LT1.
http://www.camaros.net/forums/showthread.php?p=271539
Quote:
Ok the way it works is this. Say you have a 3000 stall convertor and you are going say 55MPH with your 3.73 gears. At this speed you would be turning around 2500 (depending on tire diameter). IF You now FLOOR the car, it would IMMEDIATELY feel like the car's transmission was slipping momentarily because the convertor has not gone beyond it's stall speed. A good rule of thumb is that the MAXIMUM stall you should run (assuming you are also running on the street) is 200-300 RPM LESS than whatever RPM you cruise at on the highway. For example I cruise @ 2800-2900 RPM so my suggested max. stall spped for my convertor should be roughly 2600 (which it is).
In the 496 example I cited earlier, if you pull away (say light throttle) away from a standing start and watch the tach, you can see that it momentarily goes to 3600 rpm not because the tires are slipping but because of the high stall convertor. On the highway the car feels as if you momentarily have it in neutral just prior to it "catching" in a sense.
Slippage does cause heat. Auxilary transmission coolers are more or less REQUIRED on cars with 2000 or more stall sooed convertors. Slippage also causes poor gas mileage. the 496 with the 3600 stall convertor gets maybe 6-7 MPG. My car with approximately 25 more HP gets 11-12 MPG. (yeah, I know guys it's apples and oranges but the point is high stall convertors KILL gas mileage for those of us interested).
I guess I would describe the effect of the convertor prior to reaching stall speed is the same feeling as if you were runnning a standard transmission with the clutch slipping. It is still engaged all right but you are not getting the full throughput of the motor.
Originally Posted By: pacem
In that case looks like the safest thing to do is to go with 3.23. It's a compromise gear, OK on both highway and in town. I had one before, although not with LT1.
Interesting stuff:
http://www.chevytalk.org/fusionbb/showtopic.php?tid/238783/
Quote:
every mod you make to your engine results in a compromise in some area of performance,the hot cam is designed to produce about as much power as you can reasonably expect to get from an otherwise un-modified, or basically stock tpi or lt1 type sbc,it raises the basic power band about 600-700rpm over the stock cam, in most applications and gains you about 30hp in most basically stock engines and while it can be used with the stock stall converter, its best when used with a manual transmission or a 2500-2600rpm stall converter, because that allows you to instantly access the higher power curve, with the slightly higher stall speed as theres noticeably less lag on the power curve when you stomp the throttle and matched to a 3.54:1-3.73:1 rear gear, its a great combo, for a basically stock engine.
now you can use your 2200 rpm stall converter but be aware its going to have a tendency to want to idle a bit higher and jump when you go from neutral to drive as its a bit marginal on daily driver characteristics with the stock stall speed.
I learned that the hard way when I installed one in my 1992 LT1 vette with the better springs and roller rockers, that come in the G.M. kit.
It made a BIG difference when I installed a 2800rpm stall converter , making the car a fine performer but it was also obvious that a 2500-2600rpm stall would have worked.
but I had plans for a larger cam , hence the higher stall, converter
http://www.chevytalk.org/fusionbb/showtopic.php?tid/238783/
Quote:
every mod you make to your engine results in a compromise in some area of performance,the hot cam is designed to produce about as much power as you can reasonably expect to get from an otherwise un-modified, or basically stock tpi or lt1 type sbc,it raises the basic power band about 600-700rpm over the stock cam, in most applications and gains you about 30hp in most basically stock engines and while it can be used with the stock stall converter, its best when used with a manual transmission or a 2500-2600rpm stall converter, because that allows you to instantly access the higher power curve, with the slightly higher stall speed as theres noticeably less lag on the power curve when you stomp the throttle and matched to a 3.54:1-3.73:1 rear gear, its a great combo, for a basically stock engine.
now you can use your 2200 rpm stall converter but be aware its going to have a tendency to want to idle a bit higher and jump when you go from neutral to drive as its a bit marginal on daily driver characteristics with the stock stall speed.
I learned that the hard way when I installed one in my 1992 LT1 vette with the better springs and roller rockers, that come in the G.M. kit.
It made a BIG difference when I installed a 2800rpm stall converter , making the car a fine performer but it was also obvious that a 2500-2600rpm stall would have worked.
but I had plans for a larger cam , hence the higher stall, converter
Cool stuff. I need to find out the specs for my Comp Cam.
http://www.chevytalk.org/fusionbb/showtopic.php?tid/189166/post/1430239/
Quote:
I went through this decision a while back and all the previous recomendatoins are good. I dont know what a zz4 has for a cam but this is what I found out. You do not want to cruise below the RPM the cam makes power. If your cam makes power 1500 to 5500 RPM, you want to calculate a gear ratio using your favorite cruise speed above 1500. Maybe 17 or 1800. That way you get into the efficient RPM of the cam. Below this you will get bogs and poor mileage. With my cam and 27 inch tires it was 3:70 ratio. I have a 700R4 with the low first gear so I should launch nicely and have a good cruise RPM.
http://www.chevytalk.org/fusionbb/showtopic.php?tid/189166/post/1430239/
Quote:
I went through this decision a while back and all the previous recomendatoins are good. I dont know what a zz4 has for a cam but this is what I found out. You do not want to cruise below the RPM the cam makes power. If your cam makes power 1500 to 5500 RPM, you want to calculate a gear ratio using your favorite cruise speed above 1500. Maybe 17 or 1800. That way you get into the efficient RPM of the cam. Below this you will get bogs and poor mileage. With my cam and 27 inch tires it was 3:70 ratio. I have a 700R4 with the low first gear so I should launch nicely and have a good cruise RPM.
How's your cam going to "get along" with those higher gears? I'd call Comp and get their advice. Cam/converter/gearing all go hand in hand. Personally, I'd keep the 3.73s and just drive slower than 80 on the highway if MPG is that imporant to you. And 2700 at 80 isn't that bad at all. lol
FWIW-When I was a "kid" I had a 77 Z28 with a 454, T10 4spd, 4.56 gears and 26" tall tires.......that thing spun around 4 grand at 70 or so mph on the highway....fuel economy was the last thing on my mind. lol
FWIW-When I was a "kid" I had a 77 Z28 with a 454, T10 4spd, 4.56 gears and 26" tall tires.......that thing spun around 4 grand at 70 or so mph on the highway....fuel economy was the last thing on my mind. lol
Been lucky, in that I've owned the same platform (1970s), in 1.9L 4 cylinder, 202ci. I6, 253 V-8, and 308 V-8.
Every single one of them got within a MPG or so of each other on the highway, and the 308 was turning just over 3 grand at 100km/h. Around town, there was a huge difference. Mixed mode, there was a significant difference.
If your converter is locked up, then your horsepower to drive at 80 is set.
The efficiency then is determined by your cam/carb set-up, and how wasteful they are at the RPM turned at that speed.
Just a guess, but if you've got a performance cam, it's going to be less happy as you pull RPM down.
Every single one of them got within a MPG or so of each other on the highway, and the 308 was turning just over 3 grand at 100km/h. Around town, there was a huge difference. Mixed mode, there was a significant difference.
If your converter is locked up, then your horsepower to drive at 80 is set.
The efficiency then is determined by your cam/carb set-up, and how wasteful they are at the RPM turned at that speed.
Just a guess, but if you've got a performance cam, it's going to be less happy as you pull RPM down.
- Joined
- Sep 28, 2002
- Messages
- 39,793
Quote:
I am not real sure if it has lock-up but I will confirm.
Unless you mod'd the computer OR it came without a lock up (rare, but possible. I've only read about it in NEON's) you would be throwing a code without lock up. The PCM would detect the wrong rpm vs. VSS output.
The best combo for what you're aiming for would be tall gears and a high stall with lock up. There you get to play without paying on the highway. The heat can be handled with an auxiliary cooler if it's really all that much.
..but...2700 @ 80 mph is hardly "high revving". I'd just drive 75 instead
I am not real sure if it has lock-up but I will confirm.
Unless you mod'd the computer OR it came without a lock up (rare, but possible. I've only read about it in NEON's) you would be throwing a code without lock up. The PCM would detect the wrong rpm vs. VSS output.
The best combo for what you're aiming for would be tall gears and a high stall with lock up. There you get to play without paying on the highway. The heat can be handled with an auxiliary cooler if it's really all that much.
..but...2700 @ 80 mph is hardly "high revving". I'd just drive 75 instead
I finally got the specs for the cam and the Torque Converter. Looks like it should work nicely with 3.23, they say it's the highest gear that can work with it. Anyway, the cam doesn't appear to be much different from the stock cam.
Competition Cams Comp cam LT-1 LT-4 Chevy 93-96
* Application 1993-1996 Chevy 350 LT-1 and LT-4 engines
* Power Range 1000-5000 RPM
* Idle Quality/special requirements-Best for original LT1 with stock computers
* Valve Lift 500/510
* Adv Duration 266/276
* Duration @.050 210/220
* Lobe Centerline 114
TC:
GM Big Shot 12LS
This converter is primarily used in Street Rods that are slightly modified and always street driven. The Big Shot 12LS is an excellent converter for long distance cruising with mild performance increases, good lockup, and minimal MPG loss. This slightly higher than stock converter produces good idling with mild street rod designed cam shafts. Rear ratios should be in the range of 3.23 to 3.73.
Stall speed range: 2000-2400 rpms.
Competition Cams Comp cam LT-1 LT-4 Chevy 93-96
* Application 1993-1996 Chevy 350 LT-1 and LT-4 engines
* Power Range 1000-5000 RPM
* Idle Quality/special requirements-Best for original LT1 with stock computers
* Valve Lift 500/510
* Adv Duration 266/276
* Duration @.050 210/220
* Lobe Centerline 114
TC:
GM Big Shot 12LS
This converter is primarily used in Street Rods that are slightly modified and always street driven. The Big Shot 12LS is an excellent converter for long distance cruising with mild performance increases, good lockup, and minimal MPG loss. This slightly higher than stock converter produces good idling with mild street rod designed cam shafts. Rear ratios should be in the range of 3.23 to 3.73.
Stall speed range: 2000-2400 rpms.
- Status