Ok guys. Looking for some opinions on what gear ratio to run. I’m building a 51 “Shoebox “. The car will mainly see Highway miles and general cruising. A lot of “Sunday” drives....taking the family out to eat. Attending shows...as far away as TX (I live in east TN) I will be running a 302 sbf. The engine has a stock bottom end. A Motorsport Roller B cam, GT40P heads with comp cam valve springs, Motorsport 1.6 roller rockers, a dual plane intake and a set of Shorty headers. I will be running a SROD transmission. The srod is a 3 speed with overdrive. The gear ratios are 1st 3.25:1 2nd 1.92:1 3rd 1.00:1 OD 0.78:1 I have a Ford 8” in the back. I currently have a 3.08 gear in it. I’m going to go ahead and rebuild the center section...so if I decide to change gears now is the time. ...currently I’m leaning towards keeping the 3.08 Tires. I’m running 205/75R15’s Tire diameter is 27.1” Using a “Speed Calculator “ with the 3.08 gear, 27.1 tire.... at 2400 rpm in O.D. To run 80mph, 1800rpm would be 60mph Changing to a 3.55 gear at 2400rpm = 70mph, 2050rpm = 60mph , 1700rpm =50mph Im open to opinions. I don’t have any intentions of switching transmission....unless I just come a cross a great deal on a T5. I already have the SROD mocked up. So I’m looking for the best option to run with what I currently have.
3.73 ish since you have a ohv and overdrive. You'll love it on the street and can still cruise on the Hwy. The SBF likes higher rpms and honestly it would do fine with a 1 to 1 in the mid 3s to 3.73.
A lot of 5 speed fox stangs were born with 273s and 308s. Most here ended up with 373s That 3sp OD you have has a long distance between 1st and 2nd
Ford Performance M-6250-B303 camshaft has a 224° intake duration at.050", and a 224° exhaust duration at .050". This B Cam also features a 0.480" intake lift with 1.6 rockers.
I think 3.55's would be closer to what you want. Question...if that motor/trans combination was in a Mustang. What gear would it have come with??
Take your 1st gear 3.25 x the rear, 3.55 and it comes up as 11.53, with a performance cam anything around 10 will let you take off and not have it bog down. If this is the cam you'll need a higher stall TC, as a WAG I'd say a 2600-3000 RPM converter. https://performanceparts.ford.com/part/M-6250-E303
Specs show operating RPM range for that came to be between 3000-6000. It will drive poorly at 1800rpm, and you will not be getting the mileage from your overdrive like you would think you should. I would listen to the advice and lean towards 3:90, 4:11 OR switch cams. At some point you have to decide on building a hot rod or cruiser. Brand:Ford Performance Parts Manufacturer's Part Number:M-6250-B303 Part Type:Camshafts Product Line:Ford Performance Parts Camshafts Summit Racing Part Number:FMS-M-6250-B303 UPC:756122625026 Cam Style:Hydraulic roller tappet Basic Operating RPM Range:3,000-6,000 Intake Duration at 050 inch Lift:224 Exhaust Duration at 050 inch Lift:224 Duration at 050 inch Lift:224 int./224 exh. Advertised Intake Duration:284 Advertised Exhaust Duration:284 Advertised Duration:284 int./284 exh. Intake Valve Lift with Factory Rocker Arm Ratio:0.480 in. Exhaust Valve Lift with Factory Rocker Arm Ratio:0.480 in. Valve Lift with Factory Rocker Arm Ratio:0.480 int./0.480 exh. Lobe Separation (degrees):112 Computer-Controlled Compatible:Yes Grind Number:M-6250-B303 Valve Springs Required:Yes Quantity:Sold individually. Notes:Will not work with Speed Density applications. A modified computer chip may be required.
The “Advice “ is why I made this thread. I’m taking everything I can into consideration. The engine is all ready built. I have the SROD transmission out of an early 80’s F150 already. The rear gear is the only thing left to decide...after reading what everyone has posted I’m leaning toward a 3.73
I had an '84 Mustang GT 5.0 T5. First gear was 2.95, 5th was OD so the spread was similar to your SROD. The 8.8 had 2.79 gears. The 302 had no problems pulling highway speeds in OD. Cruising was fine at 70 but I could easily stay in 4th up to 55 or 60 if i wanted to. I think you will be fine with what you have.
Honestly it just depends on how ya want to drive it, cam and tire size That steep 1st gear would work with the 308s. The srod is designed for a truck. The car 5spd has better gearing and would probably like the 355s and 373s or lower better. I think 323s or maybe 355s with the srod Had a f150 with that srod and 355s. Loved it. Then bought another manual f150 with 273s. Hated it. Replaced with 355s.
The sbf in my '40 coupe is just about the same as yours, and I'm running a T5 and 3.73:1 8.8" rear, along with 2.35X15 75R tires about 29" tall. It's a cruiser, not a racer, and is happy at any speed you want to drive it within reason, and are willing to get caught running GA has a "super speeder law" that kicks in above 80 mph on 4 lanes and 75 on 2 lanes, so my Xway cruising is about 79 mph, and the rpm is approx 2300. It doesn't like getting much below 45 mph in 5th. I think you'll be happy with 3.73 as that shoebox should be a bit heavier than a '40 coupe
The Key is looking up the power specs for your cam. Find out when the cam starts to make power. IE 2000 to 5000. Gear it so that when you are running down the road you are just into the power band. 2100 or so.
I am a Fox Mustang guy. The 3.73 gears will work great in your application. My Daily driver Mustang has 3.73's 650 Holley D.P. Motorsport E- cam. with all the bolt ons known to man. Gets driven 400 miles a week and gets 18 mpg. Crusing RPM's at 70 mph with a T-5 trans and 26" tires is 2200 rpm.
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