So here is the drivetrain: 300 I6 (325hp/425 ft-lb. usable torque to 5,200RPM) T56 six speed trans. Now I need to figure out what rear end gears to go with. (I intend to use a Detriot Locker differential) Im just nost sure what rear end gearing to go with. 3.80? or 3.55? The car had a stock 2.83 (!!!) gearing and a c4 for its little 200 six.
Rear end gears?
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restomoded66
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Hi! All depend on what gear ratio you got in the t56, is it 2.97 first gear and 0.62 sixth gear or 2.66 first and .50 sixth. the first one is like a t5z first and fith gear and most people recomand 3.70 gear and if you got the second you could go with 4.10 gears.
Hack
15 Year Member
What are your goals for the car? All out performance? Cruiser with an occasional trip to the strip? Will never see a drag strip? Road racing?
Your 300 6 sounds built to the 9s. I frankly wouldn't have thought it possible to get the power you describe, unless I'm misunderstanding your post. Maybe you're running 13:1 compression and E85; I don't know.
Anyhoo, knowing your goals will help people to recommend gears. I had a 250 6 in my convertible at one time and I think that engine liked tall gears (like 2.80 or so), because it wouldn't wind out. It had a lot of low grunt but nothing up top. If your 6 really makes over 300 hp it must be winding up to a higher rpm than the sixes Ford built in the 60s!
It would probably be good to post your power band too. For instance, if it's a drag car you might want to go through the traps at the top of your power band in fourth gear. We would want to know what rpm and what size tire to calculate the number.
Too much info?
Your 300 6 sounds built to the 9s. I frankly wouldn't have thought it possible to get the power you describe, unless I'm misunderstanding your post. Maybe you're running 13:1 compression and E85; I don't know.
Anyhoo, knowing your goals will help people to recommend gears. I had a 250 6 in my convertible at one time and I think that engine liked tall gears (like 2.80 or so), because it wouldn't wind out. It had a lot of low grunt but nothing up top. If your 6 really makes over 300 hp it must be winding up to a higher rpm than the sixes Ford built in the 60s!
It would probably be good to post your power band too. For instance, if it's a drag car you might want to go through the traps at the top of your power band in fourth gear. We would want to know what rpm and what size tire to calculate the number.
Too much info?
What are your goals for the car? All out performance? Cruiser with an occasional trip to the strip? Will never see a drag strip? Road racing?
Your 300 6 sounds built to the 9s. I frankly wouldn't have thought it possible to get the power you describe, unless I'm misunderstanding your post. Maybe you're running 13:1 compression and E85; I don't know.
Anyhoo, knowing your goals will help people to recommend gears. I had a 250 6 in my convertible at one time and I think that engine liked tall gears (like 2.80 or so), because it wouldn't wind out. It had a lot of low grunt but nothing up top. If your 6 really makes over 300 hp it must be winding up to a higher rpm than the sixes Ford built in the 60s!
It would probably be good to post your power band too. For instance, if it's a drag car you might want to go through the traps at the top of your power band in fourth gear. We would want to know what rpm and what size tire to calculate the number.
Too much info?
Well the 300 is based on performance achieved by the engineers at Clifford inline performance. Fairly radical cam (the wildest off the shelf cam, may end up going to a custom grind later) , ported polished head with larger valves (1.94/1.60) dual intake manifold with 2 webers, shorty headers, compression should be 10:1 at least. Forged 351 pistons with early 300 forged rods, forged crank. At this point its speculation, I intend to have it dynoed when its done. I do know that a much less radical build achieve 400 ft lbs of torque and 300hp. The engine its self needs to stay under 6,000 rpm, but usable torque will end at 5,200. With a turbo 550hp and 850 ft-lb of torque have been achieved with the 300. in a streetable form. Do not underestimate the 300.
This is a street car that I would like to road race if I got a chance, ad an occational drag run.
I know
I simply cant wait to push the pedal and feel the power surge, unfortunately the price of the project is great and it will take several long years to finish 
I really hope to reach these goals, I know its more than possible. Hopefully this fall i will return to college in pursuit of a mechanical engineering degree, hopefully that will help with such calculations.Good info, but I'll add that you're bottom end torque combined with the transmissions 1st gear ratio should determine the rear gear ratio. What I'm getting at is making sure you don't end up with a 1st gear thats really useless in a street car. My 06 GT is nearly there now. With a 3.55 ratio rear & 27" tires, I can take off in second gear from a dead stop. In a rolling stop, I almost never go down into 1st. Ford new what it was doing in replacing the 3.55 ratio in the later GT's with a 3.27 ratio. I wish mine had it. Going to anything deeper (numerically higher) than 3.50's is a waste of time for you. Unless you want to compete in tractor pulling.
This is something you're not going to learn from a book or calculations, but only from real world experience.
Hack
15 Year Member
Actually if it makes the power you think it will make it's going to be far superior to a 289 HiPo. I know Ford said a HP number back in the day, but you can use any HP calculator based on the Mustang's quarter mile speed to debunk that number. I think it was common back in the day to over-rate engine HP. Now there are regulations about how to test the engine and the dyno runs are double-checked before the car company can make some wild claim.
Im very anxious to see what the 1/4 mile times are. I know that i wont be at all disappointed with the top end. should be at least 160mph, possibly more. I am hoping for a 13sec ET.
I haven't taken the car to the strip. Since it is a convertible if I run faster than 13.49 IIRC I have to put a 4 pt roll bar in. I am not interested in doing that. I know how I am. My run would look like this ......... spin like crazy off the line then get it hooked up. Run through the traps at 13.48. I would then get pissed at myself and feel that I could do much better. End us installing a 4 pt bar and ruin the looks of my car.
I often wonder what the car is capable of. I would hope in the 11's but I have no idea.
Thats why im not installing a turbo, or going with a higher outpus. I know how i am, I will push, and I would make myself install a roll cage because i dont feel my life is a fair price for a few seconds of heart pounding thrill.
Right now im working on finding an oil pan so I can get started on making my motor mounts, after that Im going to fit the engine to gauge how much clearance I need my hood to give.
Right now im working on finding an oil pan so I can get started on making my motor mounts, after that Im going to fit the engine to gauge how much clearance I need my hood to give.
I started looking at 3.80s................ now im looking at 3.55s with trac-lok. With 400ft-lbs torque at 3,000 RPM in builds similar to mine, ant is fades to just under 350 at 5,000 RPM. Hp is 240 at 3,000 and 300 at 5,000. I feel I will have enough low end power to roll the 3.55s fine, the top speed at 5,000 RPM is insane, but I really like the 1,300 rpm 65mph cruising. Idle should be between 600-700 rpm.
Of course this may differ with my engine. This is based on a previous 300 build. I will be using a more radical cam, Com Cams hottest cam for the 300, (still streetable though, but with a nice lope) and 2x2bbl carbs where a 600 holley was used for this build. The cam for this build was so mild that the owner stated he could sit a quarter on the valve cover and it would stay with the engine idling. Im hoping that that will give me some extra ponies.
Of course this may differ with my engine. This is based on a previous 300 build. I will be using a more radical cam, Com Cams hottest cam for the 300, (still streetable though, but with a nice lope) and 2x2bbl carbs where a 600 holley was used for this build. The cam for this build was so mild that the owner stated he could sit a quarter on the valve cover and it would stay with the engine idling. Im hoping that that will give me some extra ponies.
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