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Due to family persuasion, the 63 project is about to start again. I have a 63 coupe, LT4, SRIII chassis, and some other parts and pieces. I need to buy a transmission and have been debating between a five or six speed manual. The LT4 is a dry-sump crate engine with about 650 horse and 650 pounds of torque. It is probable the engine may be chipped to bring those numbers up a bit. Though the intent is to not race, it would be nice not to blow the transmission if someone should get more enthused than normal. While I would prefer to keep the costs under control, between Tremec Magnum or RPM Magnum what is the better choice or is there another transmission that would be a better candidate? Is the idea of a six speed a waste vs. a five speed? The six speed seems to necessitate modification of the tunnel but would the five speed also require modification to the tunnel? I would like to use powered Recaro seats, would I be limiting my ability to install those seats with the modifications to the tunnel needed? I intend to drive this car and would like it to be as trouble free as possible.
Due to family persuasion, the 63 project is about to start again. I have a 63 coupe, LT4, SRIII chassis, and some other parts and pieces. I need to buy a transmission and have been debating between a five or six speed manual. The LT4 is a dry-sump crate engine with about 650 horse and 650 pounds of torque. It is probable the engine may be chipped to bring those numbers up a bit. Though the intent is to not race, it would be nice not to blow the transmission if someone should get more enthused than normal. While I would prefer to keep the costs under control, between Tremec Magnum or RPM Magnum what is the better choice or is there another transmission that would be a better candidate? Is the idea of a six speed a waste vs. a five speed? The six speed seems to necessitate modification of the tunnel but would the five speed also require modification to the tunnel? I would like to use powered Recaro seats, would I be limiting my ability to install those seats with the modifications to the tunnel needed? I intend to drive this car and would like it to be as trouble free as possible.
You only have to ask yourself how fast (top end) is it ever going to be driven? For MOST people the answer because of this would be a 5 speed. You only need the 5th gear for cruising at freeway speeds and above.
You asked two different questions that are at odds with each other looking for one answer. If you need a 6 speed, you will modify the tunnel which cascades into other fitment challenges (center console, seats, etc.). Torque is the killer of transmissions (differentials, drive shafts half shafts, and rear spindles, also so don’t forget about the downstream components), particularly when applied suddenly and violently. Depending on the 5 speed selected, you may not need to modify the tunnel. A TKO or new TKX will not require modifications or the tunnel, but they will not meet your torque requirements at the upper end. I suggest you call Silver Sport for advice. They are one of the top experts in this area for C2 Corvettes. Good luck!
I believe you to raise the tunnel if you go with a 6 speed. That means you will have to trim the bottom of your dash to accommodate for the extra height of the tunnel.
That was a deal killer for me. I went with a TKO 5 speed. However, it is only rated for 600 lbs of torque. So, as a pp said give the manufacture a call.
If you want the best go with the t56 magnum 6 speed all gears are evenly spaced.I f you want to save a few bucks get 5 .I have both .The t56 with out a doubt is hands down the best.
When I purchased my 65 coupe it was outfitted with a 427 out of a SS-427 Impala. The car was set up with a Richmond Six speed trans with a removable crossmember. No modification was done to the tunnel. It was constructed by a NASCAR team owner back in the early 2003 time frame and done extremely well. The car runs out nicely and the transmission shifting is gated and smooth.
You asked two different questions that are at odds with each other looking for one answer. If you need a 6 speed, you will modify the tunnel which cascades into other fitment challenges (center console, seats, etc.). Torque is the killer of transmissions (differentials, drive shafts half shafts, and rear spindles, also so don’t forget about the downstream components), particularly when applied suddenly and violently. Depending on the 5 speed selected, you may not need to modify the tunnel. A TKO or new TKX will not require modifications or the tunnel, but they will not meet your torque requirements at the upper end. I suggest you call Silver Sport for advice. They are one of the top experts in this area for C2 Corvettes. Good luck!
I have had the T56 Magnum since 2017 and like it a lot. I live in south Texas and even with the 75 mph speed limits and open roads I only use 6th gear sparingly. However, I only have a 3.55 rear end gear ratio. I have had a TKO 600 5 speed in a 1970 Chevelle and I did not like the way the TKO shifted, it shifts like an old truck. The T56 is a lot better but it will take a lot more work to install. If I were you I would look into the new TKX 5 speed. I haven't heard much about it though.
All things considered, the new TKX will present the fewest fit challenges. American Powertrain advertises an extreme duty upgrade that includes all of the usual sort of gear cryo-treatment and other upgrades to bring it up to a 900HP rating. They don't advertise the price for that on their site, but you can call sales and find out. I know the TKX's are on backorder because I'm waiting for mine. Last update was that AP expected to receive some on 1 March. Time to do the extreme upgrades would add a couple of weeks to that, I expect.
Do MPH calculations using your tire size, rear gear, final gear of transmission,
and find what RPM the engine will turn at those MPH calculations.
What you want is a highway cruise around 1500rpm or less for large displacement engines.
Once you dial in the correct cruise rpm:mph ratio it will guide you to the ideal final gear ratio of whatever transmission that happens to be.
You will have to raise the tunnel approx. 1-2 inches. Which will result in the dash (below the radio) being cut to fit. Additionally you will not be able to use Vintage Air evaporator for the C2, if that is a concern. Ask me how I know?
Back to the trans itself, the T56 is certainly a more stout transmission however the true benefit is the close ratio between gears. As you can see both transmissions are at ~.63 in top gear so top speed is not the motive, keeping the motor in a desired RPM range is the motive.
You will have to raise the tunnel approx. 1-2 inches. Which will result in the dash (below the radio) being cut to fit. Additionally you will not be able to use Vintage Air evaporator for the C2, if that is a concern. Ask me how I know?
Back to the trans itself, the T56 is certainly a more stout transmission however the true benefit is the close ratio between gears. As you can see both transmissions are at ~.63 in top gear so top speed is not the motive, keeping the motor in a desired RPM range is the motive.
Wait, I had no problems with the Vintage Air Evaporator in my 66 when I had the T56 Magnum installed.
Do MPH calculations using your tire size, rear gear, final gear of transmission,
and find what RPM the engine will turn at those MPH calculations.
What you want is a highway cruise around 1500rpm or less for large displacement engines.
Once you dial in the correct cruise rpm:mph ratio it will guide you to the ideal final gear ratio of whatever transmission that happens to be.
1500 rpms is ridiculously low for any kind of passing other traffic.
1500 rpms is ridiculously low for any kind of passing other traffic.
Right because, your car does not have a transmission so obviously overdrive is the only gear choice
I'm not sure what you are saying. It sounds like you want your overdrive to cruise the vehicle at 5000rpm cruise since 5000rpm is where the horsepower just begins to peak out.
Right because, your car does not have a transmission so obviously overdrive is the only gear choice
I'm not sure what you are saying. It sounds like you want your overdrive to cruise the vehicle at 5000rpm cruise since 5000rpm is where the horsepower just begins to peak out.
What you are saying makes no sense? My car doesn’t have a transmission? First of all I have a 4 speed not a 5 OR 6 speed but anyone knows that you are well below the power band of the OPs engine and if you needed to pass someone and stomped on it at 1500 rpms it would fall on it’s face. You would have to gear down to be effective. BTW, new car manufacturers want an engine to run a minimum of 1800 rpms for proper A/C compressor performance. You don’t want to be cruising at 1500 rpms with Luke warm air coming out of your A/C ducts.
02-14-2021, 11:32 PM
Restomod transmission choice
