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Does anyone one have detailed data for the gear ratios inside the four speed I might find in a typical F5?
I'm n in the final research stage for my F5 build and have been trying to work out which way to go.
Due to the "Nightmare on Widow maker St" and the associated grief of finding wheels and tyres to suit, I'm taking a different route with my project and am going to upgrade the front and rear axles with something more modern to allow better, safer and more comfortable use on the roads at 60mph as I plan to haul my race car on regular 400 mile round trips to the drag strip etc.
I plan on using the original flathead - electronic ignition, Fi and all the cooling mods to make it more reliable, but don't want it screaming it's nuts off at 60mph - especially as I'll be running approx 30" tires on the rear.
In order for me to work out what rear axle to go for from a suitable UK donor van/truck, I could do with working out a target 60pmh motor cruising rpm which I'm guessing on a flattie wants to be about 2,000 rpm for best blend of torque and economy? (Please advise if different)
I know the axle I'll be removing has a very low 5.83 ratio, but in order for me to work out the rest, I need to know the ratios in the standard gear box.
Can anyone kindly furnish me with this information?
That's a pretty tall order trying to achieve that kind of speed by only changing the rear end. To get 60 mph @2000 RPM with a 1.0 tranny would require about a 2.95 rear, which would most likely require a tow truck to get started from a stop with any kind of load. My F5 with the 5.14 rear, 33.5" tires and stock tranny will hit 57 MPH @2900 RPM
That's a pretty tall order trying to achieve that kind of speed by only changing the rear end. To get 60 mph @2000 RPM with a 1.0 tranny would require about a 2.95 rear, which would most likely require a tow truck to get started from a stop with any kind of load. My F5 with the 5.14 rear, 33.5" tires and stock tranny will hit 57 MPH @2900 RPM
Thanks.
Is 'spur' just the name of the tranny used?
What is an optimum rpm for a flattie to cruise at?
IMO, get rid of the spur gear if you intend to use it for anything but farm use.
Best cruising RPM for an F-1 (lighter and lower, less wind resistance than your F-5) is generally 2200 @ 55. If it's flat land where you are, you can go lower. You need to look at where you'd be RPM-wise if you have to drop down a gear, and where you'd be in 2nd gear going around corners. You don't want to have to burn up your clutch to get around. It won't hurt a flatty to spin at higher RPMs but obviously for long trips that is unnecessary extra wear. Climbing hills takes HP and the curve is pretty steep above 2200, you may need to be there with your extra weight. This is for the earlier models, but is very similar to 8BA engines (and is easier to read than the scans of 8BA curves I have).
IMO, get rid of the spur gear if you intend to use it for anything but farm use.
Best cruising RPM for an F-1 (lighter and lower, less wind resistance than your F-5) is generally 2200 @ 55. If it's flat land where you are, you can go lower. You need to look at where you'd be RPM-wise if you have to drop down a gear, and where you'd be in 2nd gear going around corners. You don't want to have to burn up your clutch to get around. It won't hurt a flatty to spin at higher RPMs but obviously for long trips that is unnecessary extra wear. Climbing hills takes HP and the curve is pretty steep above 2200, you may need to be there with your extra weight. This is for the earlier models, but is very similar to 8BA engines (and is easier to read than the scans of 8BA curves I have).
Thanks.
It's a balancing act between being tall enough for highway speeds, yet not too tall that first gear becomes an issue.
I have to find a suitable transmission to hook up to the flattie, yet a rear axle that works with it and my rear tyre size.
I was thinking of maybe a 6 speed from a 3 series BMW etc which I could use with a fairly low rear axle - say a 4.63 or a 5.12 etc but with my 30" tire will give me the best of both worlds. Plenty of gears to choose from to keep the revs in the right area, and a tall 6th for cruising?
From my calculations, there's no way of achieving the equivalent first gear ratio of standard. it's end up somewhere in between the stock first and second.
The most the entire vehicle will weight with my (lightweight) race car on the back will be about 7,750lbs so not massively heavy and only just over half it's capacity.
1st gear in the crashbox 4-sp is not really needed in normal driving, it is super-low. The 3-sp's used in F-1's have a 2.78 1st, with a stock axle at 3.92, overall ratio is 10.9 and with ~29" tires. Your stock 1st gearing is 32:1 overall but with taller tires and a lot more weight than an F-1. Still, I think you could live with quite a bit taller 1st gear. Note that many folks start in 2nd with the crashbox when driving unladen, that is around 15:1 overall.
1st gear in the crashbox 4-sp is not really needed in normal driving, it is super-low. The 3-sp's used in F-1's have a 2.78 1st, with a stock axle at 3.92, overall ratio is 10.9 and with ~29" tires. Your stock 1st gearing is 32:1 overall but with taller tires and a lot more weight than an F-1. Still, I think you could live with quite a bit taller 1st gear. Note that many folks start in 2nd with the crashbox when driving unladen, that is around 15:1 overall.
It tells me that the 1st gear on a bone stock F5 at say a max rpm of 4000 equates to 13mph and second gear of 21mph
If 2nd gear is a bit tall to pull away in (but not impossible) and first is very low, would it be a good compromise to have a first gear that equated to say 18mph which is just over half way to 2nd from 1st?
I feel the way to tackle this is to start at the motor and work backwards.
Firstly I'd need to find a top loading transmission with at least 5 speeds that can be mated to a flathead V8. I believe the Tremec (Borg Warner) T5 is such a transmission.
I'm know that my rear tyres will be 30", so using that table I could then work out what my rear end ratio would need to be get my first gear roughly where I want it at say 17-18mph at 4k, and see if that brings the 60mph rpm somewhere around say 2,500?
I think you're on the right track. Hard to say what 1st should be at 7500 GVW. Flatheads don't lack for torque, a fairly tall 1st shouldn't be a problem. The stock spur gear 1st was designed mostly for farm work, driving alongside a combine or whatever. In terms of driveability, I think I'd want a 1st that could give 20 mph at more like 3,000 RPM.
Just a thought on EFI; I was leaning towards a hydrid throttle-body injection system, until I talked to a friend who is a very knowledgable flathead guru and fellow engineer. I mentioned I was looking at EFI and he said "Why?". I said "driveability and economy". He said he has built them both ways, and he can get the same results with carbs, for both power and economy, as he can with EFI. I was skeptical, but have come to believe he's exactly right. He has published many flathead books, his name is Joe Abbin.
I think you're on the right track. Hard to say what 1st should be at 7500 GVW. Flatheads don't lack for torque, a fairly tall 1st shouldn't be a problem. The stock spur gear 1st was designed mostly for farm work, driving alongside a combine or whatever. In terms of driveability, I think I'd want a 1st that could give 20 mph at more like 3,000 RPM.
Just a thought on EFI; I was leaning towards a hydrid throttle-body injection system, until I talked to a friend who is a very knowledgable flathead guru and fellow engineer. I mentioned I was looking at EFI and he said "Why?". I said "driveability and economy". He said he has built them both ways, and he can get the same results with carbs, for both power and economy, as he can with EFI. I was skeptical, but have come to believe he's exactly right. He has published many flathead books, his name is Joe Abbin.
That's good to hear about FI - one less complication and expense. The reliability appeals, but I guess electronic ignition rather than points could help there?
Is there any point or need to 'tune' the flat head for my application? I have no interest in speed or performance. All I want is the best gas mileage possible from it and some low end torque. As long as it can get me to 60mph and take on the odd hill at that speed, I'm good.
A weak point on flatties is the distributor, specifically the spark advance. Ford went cheap and used a system that mimic mechanical advance and vacuum advance, using only vacuum. When in perfect shape, it works fine, but leaves significant economy on the table.
I elected to buy an MSD "Ready-to-Run" distributor, which is essentially the same thing but with MSD components. Not sure I'd do it again, and they have gone WAY up in price since I bought mine. But it has been totally trouble-free in over 10 years of use. Contrary to their name, they are not ready for flathead service as shipped. I had to buy an adjustable vacuum advance unit to make it complete and ready for my truck, among other bits.
A weak point on flatties is the distributor, specifically the spark advance. Ford went cheap and used a system that mimic mechanical advance and vacuum advance, using only vacuum. When in perfect shape, it works fine, but leaves significant economy on the table.
I elected to buy an MSD "Ready-to-Run" distributor, which is essentially the same thing but with MSD components. Not sure I'd do it again, and they have gone WAY up in price since I bought mine. But it has been totally trouble-free in over 10 years of use. Contrary to their name, they are not ready for flathead service as shipped. I had to buy an adjustable vacuum advance unit to make it complete and ready for my truck, among other bits.
Thanks - again!
My first point of call is to find my truck. I've based all this on the theory of a F5, but in reality, I'll be happy with any cab over Ford from '52 or earlier with a Flathead V8.
The tricky thing seems to be finding them on their original chassis AND with a title - both essential for me to export to the UK.
Prices seem to vary a lot from $2,000 - $7,000 from what I've seen and not always reflecting the quality of truck.
The vintage solution (the one used back when the trucks were used) was to install an auxiliary transmission. The typical three speed auxiliary combined with the four speed main box would give you around seven usable gear ratios. The top ratio would be good for 60 or so.
If you are always running unloaded or with a light load the stock "high speed" 5.14 ratio common in the F-4 trucks is a good place to start. One of our members with an F-4 purchased an auxiliary transmission. Before he installed it he rebuilt the engine. After the rebuild the truck was smooth enough to run 60 without the auxiliary. He has decided not to install the extra transmission since he is happy with the stock running gear.
The vintage solution (the one used back when the trucks were used) was to install an auxiliary transmission. The typical three speed auxiliary combined with the four speed main box would give you around seven usable gear ratios. The top ratio would be good for 60 or so.
If you are always running unloaded or with a light load the stock "high speed" 5.14 ratio common in the F-4 trucks is a good place to start. One of our members with an F-4 purchased an auxiliary transmission. Before he installed it he rebuilt the engine. After the rebuild the truck was smooth enough to run 60 without the auxiliary. He has decided not to install the extra transmission since he is happy with the stock running gear.
Fred, the 5.14 was also available in the F5, that is the gear in Edith.
08-19-2015, 05:07 AM
