4 or 5 speed
Le Mans Master
Joined: Mar 2001
Posts: 6,237
Likes: 1,009
From: Watkinsville, GA and Glen Cove, NY
It's not so much having enough low end torque when you have "issues" in overdrive, but more about camshaft overlap. large camshafts don't like tall gears and overdrives. 
I have some surging issues with my 496 if I get much below 2k rpm (around 1800) in 5th or 6th gears (.80 and .63 ratios). I have more than enough torque down there, its just not smooth operation.
I have some surging issues with my 496 if I get much below 2k rpm (around 1800) in 5th or 6th gears (.80 and .63 ratios). I have more than enough torque down there, its just not smooth operation.
Drifting
Joined: Oct 2005
Posts: 1,527
Likes: 148
From: East London/SW Essex UK
Don't forget the 1st gear ratio of the 5 speed trans. You might end up with a 1st gear so low that it's never used. IMO, purchasing a 5 speed seems like an expensive solution to a rarely experienced problem. Most of my driving was done at speeds below 50 MPH around town. On the highway I kept to the speed limit and let the wanabe NASCAR drivers weave in and out of lanes far away from me. I had too much work invested in my cars to chance having a wreck.
My 606 ft/lb 489 cu in uses 27" dia rear rubber, a 3.08 rear end and M21 transmission. UK legal speed limit of 70 mph means approx. 2500 rpm cruise. With a usable power band starting at 1500 rpm I would be interested in how well a .60 5th ratio would work - .70 would be better I guess.
Last edited by roscobbc; Oct 11, 2016 at 06:06 PM.
Instructor
Joined: Apr 2007
Posts: 142
Likes: 6
From: Indianapolis, Indiana
496
SRP Forged pistons, Scat 4340 Forged crank, Eagle H-Beam rods L19 bolts
CFM Performance ported Stage 5 Brodix Race-Rites 294cc (now 310cc) Flowed 387 intake, 275 exhaust
10.5 scr
Ultradyne Solid Roller 256/264 .660/.660 108 lsa, Isky EZX lifters, Crower SS rockers
CFM Performance ported Victor Jr, Pro Systems 1000HP
T-56 Magnum 6 Speed, 12 Bolt TrueTrac, 4.56 gear 33 spline Mosier axles
SRP Forged pistons, Scat 4340 Forged crank, Eagle H-Beam rods L19 bolts
CFM Performance ported Stage 5 Brodix Race-Rites 294cc (now 310cc) Flowed 387 intake, 275 exhaust
10.5 scr
Ultradyne Solid Roller 256/264 .660/.660 108 lsa, Isky EZX lifters, Crower SS rockers
CFM Performance ported Victor Jr, Pro Systems 1000HP
T-56 Magnum 6 Speed, 12 Bolt TrueTrac, 4.56 gear 33 spline Mosier axles
Le Mans Master
Joined: Oct 2007
Posts: 7,444
Likes: 970
From: Tennessee/Rhode Island
It's not so much having enough low end torque when you have "issues" in overdrive, but more about camshaft overlap. large camshafts don't like tall gears and overdrives.
I have some surging issues with my 496 if I get much below 2k rpm (around 1800) in 5th or 6th gears (.80 and .63 ratios). I have more than enough torque down there, its just not smooth operation.
I have some surging issues with my 496 if I get much below 2k rpm (around 1800) in 5th or 6th gears (.80 and .63 ratios). I have more than enough torque down there, its just not smooth operation.
Last edited by jb78L-82; Oct 12, 2016 at 07:11 AM.
Le Mans Master
Joined: Mar 2001
Posts: 6,237
Likes: 1,009
From: Watkinsville, GA and Glen Cove, NY
496
SRP Forged pistons, Scat 4340 Forged crank, Eagle H-Beam rods L19 bolts
CFM Performance ported Stage 5 Brodix Race-Rites 294cc (now 310cc) Flowed 387 intake, 275 exhaust
10.5 scr
Ultradyne Solid Roller 256/264 .660/.660 108 lsa, Isky EZX lifters, Crower SS rockers
CFM Performance ported Victor Jr, Pro Systems 1000HP
T-56 Magnum 6 Speed, 12 Bolt TrueTrac, 4.56 gear 33 spline Mosier axles
SRP Forged pistons, Scat 4340 Forged crank, Eagle H-Beam rods L19 bolts
CFM Performance ported Stage 5 Brodix Race-Rites 294cc (now 310cc) Flowed 387 intake, 275 exhaust
10.5 scr
Ultradyne Solid Roller 256/264 .660/.660 108 lsa, Isky EZX lifters, Crower SS rockers
CFM Performance ported Victor Jr, Pro Systems 1000HP
T-56 Magnum 6 Speed, 12 Bolt TrueTrac, 4.56 gear 33 spline Mosier axles
Last edited by 69ttop502; Oct 12, 2016 at 10:05 PM.
Instructor
Joined: Apr 2007
Posts: 142
Likes: 6
From: Indianapolis, Indiana
We have very similar builds and parts. My cam is a little bigger solid roller than yours and as such I was worried about the overdrive issue with a big cam. My cam peaked at 6500. I opted for 3.08 gears and a Richmond 5 speed with 1 to 1 5th. Figure 70 mph will be 2500- 2600. Haven't driven it yet with this combo but hoping..... Love your car!
I was following your thread on Team Chevelle and looks like a real nice setup.
At the 70 mph highway speed, you should be fine at 2500-2600 rpms. With my .63 ratio 6th gear, 4.56 rear gears and 30 inch diameter tires, @70 I'm turning a little over 2200rpm and have no issues. My engine has cleaned up by 2k but if I go much less it starts surging a little but not too bad. 1700-1800 is about the minimum in OD I can run.
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Instructor
Joined: Aug 2003
Posts: 167
Likes: 2
From: BLACKSBURG VA
4 or 5 speed
roscobbc:
Hook your M 21 up to a GVO and you get the gearing you want with overdrive. Actually you can have overdrive in any or all gears plus 1 clutch less shift. Cost about the same as 5 speed a little tunnel work on a vette and a little machine work.
I have 2 73 BB 496 full roller vettes with Muncie /GVO transmissions and they are a blast to drive. Check out Gear Vendors Overdrive you will be glad you did.
Hook your M 21 up to a GVO and you get the gearing you want with overdrive. Actually you can have overdrive in any or all gears plus 1 clutch less shift. Cost about the same as 5 speed a little tunnel work on a vette and a little machine work.
I have 2 73 BB 496 full roller vettes with Muncie /GVO transmissions and they are a blast to drive. Check out Gear Vendors Overdrive you will be glad you did.
Tech Contributor
Joined: Jun 2004
Posts: 20,850
Likes: 959
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Ran the Doug Nash five speed in my car for several years, but I found out during track days that I was almost always just using the top two gears. I noticed those two gears in the five speed weren't that much different in ratio from the top two gears in the original M21 four speed, and the M21 was about 30# lighter. Swapped out the five speed about two years ago. I've taken enough weight out of the car in the last few years where I don't need the extra torque multiplication of additional gearing to move the car's mass from a stop. The car runs fine with my M21 and a 3.08 rear gear.
Race Director
Joined: Mar 2016
Posts: 14,321
Likes: 8,125
From: Napa Valley California
roscobbc:
Hook your M 21 up to a GVO and you get the gearing you want with overdrive. Actually you can have overdrive in any or all gears plus 1 clutch less shift. Cost about the same as 5 speed a little tunnel work on a vette and a little machine work.
I have 2 73 BB 496 full roller vettes with Muncie /GVO transmissions and they are a blast to drive. Check out Gear Vendors Overdrive you will be glad you did.
Hook your M 21 up to a GVO and you get the gearing you want with overdrive. Actually you can have overdrive in any or all gears plus 1 clutch less shift. Cost about the same as 5 speed a little tunnel work on a vette and a little machine work.
I have 2 73 BB 496 full roller vettes with Muncie /GVO transmissions and they are a blast to drive. Check out Gear Vendors Overdrive you will be glad you did.
Ok I checked out the Gear Vendors Overdrive website and I am interested to get more information from you regarding any installation problems you had installing the units in you corvette. I'll start a new thread and ask.
Instructor
Joined: Mar 2009
Posts: 157
Likes: 16
From: Yorktown VA
how does the process of getting the drive shaft go? does the Hurst and SST lines already have the measured out length for different vehicles or do you have to go and measure it after the trans is installed in the vehicle to then order the length you need?
Instructor
Joined: Sep 2015
Posts: 216
Likes: 16
From: Haverfordwest Pembrokeshire
Graham
Burning Brakes
Joined: Apr 2013
Posts: 1,194
Likes: 109
From: Las Vegas NV
If the trans has a slip yoke then you have some wiggle room. The u joint should be as close to the trans as possible but if the yoke is out a little bit it isn't the end of the world. The differential stays stationary relative to the trans unlike a truck or other live axle vehicle where every time you hit a bump or anything the driveshaft slides in and out of the trans.
Last edited by AboveTheLogic; Oct 23, 2016 at 01:15 PM.
Melting Slicks
Joined: Dec 2015
Posts: 3,181
Likes: 732
From: Texas City, TX Texas
I did.
Ran the Doug Nash five speed in my car for several years, but I found out during track days that I was almost always just using the top two gears. I noticed those two gears in the five speed weren't that much different in ratio from the top two gears in the original M21 four speed, and the M21 was about 30# lighter. Swapped out the five speed about two years ago. I've taken enough weight out of the car in the last few years where I don't need the extra torque multiplication of additional gearing to move the car's mass from a stop. The car runs fine with my M21 and a 3.08 rear gear.
Ran the Doug Nash five speed in my car for several years, but I found out during track days that I was almost always just using the top two gears. I noticed those two gears in the five speed weren't that much different in ratio from the top two gears in the original M21 four speed, and the M21 was about 30# lighter. Swapped out the five speed about two years ago. I've taken enough weight out of the car in the last few years where I don't need the extra torque multiplication of additional gearing to move the car's mass from a stop. The car runs fine with my M21 and a 3.08 rear gear.
Tech Contributor
Joined: Jun 2004
Posts: 20,850
Likes: 959
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Yup.
First gear is a (IIRC) 3.27, which gave the car a lot of torque multiplication for the 2.73 and 3.08 rear gears that I alternated in the drivetrain. That's the same over all torque multiplication as running a 4.11 or 4.56 rear gear with the old Muncie, but with the highway gearing of the 2.73 and 3.08 gears.
I've got the car at 2780# now (and close to 2750# without the tops and rear window during autocross, compared to the 3400# when I installed the DN transmission) and I don't need much gearing to get the car moving from a stop anymore.
First gear is a (IIRC) 3.27, which gave the car a lot of torque multiplication for the 2.73 and 3.08 rear gears that I alternated in the drivetrain. That's the same over all torque multiplication as running a 4.11 or 4.56 rear gear with the old Muncie, but with the highway gearing of the 2.73 and 3.08 gears.
I've got the car at 2780# now (and close to 2750# without the tops and rear window during autocross, compared to the 3400# when I installed the DN transmission) and I don't need much gearing to get the car moving from a stop anymore.
Tech Contributor
Joined: Jun 2004
Posts: 20,850
Likes: 959
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
I can send you a list of stuff by PM if you're interested. Just let me know.
Drifting
Joined: Aug 2015
Posts: 1,939
Likes: 477
From: NSW, Australia
C3 of Year Finalist (track prepared) 2019
I've got bits and pieces in several threads over the years, but quite a few of them involve aluminum welding, and there didn't seem to be much general interest in that topic, so I never bothered to try to consolidate the threads.
I can send you a list of stuff by PM if you're interested. Just let me know.
I can send you a list of stuff by PM if you're interested. Just let me know.