Richard Tramell Posted January 26, 2021 Share Posted January 26, 2021 Hi everyone, My name is Richard and im a Bullnose fan. Working on a 83 Bronco 4.9 4speed 3.55 gears. Ive got her running good and just doing maintenance. Currently on the drive train. Seals ujoints ect. Hope to some day help others with there projects as I know I will need help with mine. Link to comment Share on other sites More sharing options...
Richard Tramell Posted January 26, 2021 Author Share Posted January 26, 2021 Good afternoon, I have a question. I have a 83 Bronco with 4.9 435 4speed 3.55 gears. 31/10.5R15 tires At 69Mph im almost running 3,000 RPM. Every calculator I’ve put my information in says im running 4.10’s. But I jacked up the truck and double checked. Its 3.55’s. Does this sound right to you? Running a factory tack but this truck has been rebuilt some time ago. Could the tack be off? Maybe from a V8? Tack runs smoothly. Nothing to say its off. Any information you could tell me would be appreciated. Link to comment Share on other sites More sharing options...
Gary Lewis Posted January 26, 2021 Share Posted January 26, 2021 Hi everyone, My name is Richard and im a Bullnose fan. I've never been to a "BA" meeting, but in my mind I always thought that's the way they'd open. Welcome! Glad you joined. Always room for one more. Where's home? We have a map (Bullnose Forum/Member's Map in the menu) and we could add you if we had a city or a zip. On your RPM, I used our calculator (Documentation/Driveline/Calculators) and dialed in 31" tires, 3.55 gears and 69 MPH. And that shows 2655 RPM. You asked about a tach from a V8, but the tachs are all the same with the V8's having a ground run to them from the ignition to tell the tach to divide the pulses by 4 instead of 3 for a 6 cylinder. And if your tach was in 8 cylinder mode with the engine turning 2655 the tach would read 3540. And, as you said, if I dial in 4.11 gears I get basically 3000 RPM at 69 MPH. So, maybe your tach is reading incorrectly? Link to comment Share on other sites More sharing options...
Richard Tramell Posted January 26, 2021 Author Share Posted January 26, 2021 Hi everyone, My name is Richard and im a Bullnose fan. I've never been to a "BA" meeting, but in my mind I always thought that's the way they'd open. Welcome! Glad you joined. Always room for one more. Where's home? We have a map (Bullnose Forum/Member's Map in the menu) and we could add you if we had a city or a zip. On your RPM, I used our calculator (Documentation/Driveline/Calculators) and dialed in 31" tires, 3.55 gears and 69 MPH. And that shows 2655 RPM. You asked about a tach from a V8, but the tachs are all the same with the V8's having a ground run to them from the ignition to tell the tach to divide the pulses by 4 instead of 3 for a 6 cylinder. And if your tach was in 8 cylinder mode with the engine turning 2655 the tach would read 3540. And, as you said, if I dial in 4.11 gears I get basically 3000 RPM at 69 MPH. So, maybe your tach is reading incorrectly? Thank you. I will get another tach and check it. My Home is 88240 Hobbs NM. Link to comment Share on other sites More sharing options...
Gary Lewis Posted January 26, 2021 Share Posted January 26, 2021 Thank you. I will get another tach and check it. My Home is 88240 Hobbs NM. You are now on the map. Link to comment Share on other sites More sharing options...
grumpin Posted January 26, 2021 Share Posted January 26, 2021 You are now on the map. Welcome! Link to comment Share on other sites More sharing options...
Rembrant Posted January 26, 2021 Share Posted January 26, 2021 Good afternoon, I have a question. I have a 83 Bronco with 4.9 435 4speed 3.55 gears. 31/10.5R15 tires At 69Mph im almost running 3,000 RPM. Every calculator I’ve put my information in says im running 4.10’s. But I jacked up the truck and double checked. Its 3.55’s. Does this sound right to you? Running a factory tack but this truck has been rebuilt some time ago. Could the tack be off? Maybe from a V8? Tack runs smoothly. Nothing to say its off. Any information you could tell me would be appreciated. Welcome aboard Richard. My questions would be: Have you verified your speed at 69 MPH? Are you going by the Bullnose speedo or GPS, or other? Have you verified the actual height or OD of the 31" tires? Often times 31" tires are more like 30" or 30.5" OD installed. If by chance your speedo is off by a few MPH...you would only have to hit about 72 MPH to be at almost 3000 RPM. Somebody can correct me on this, but I don't think that Broncos came with 31" tires until later on it in the 80's, like 1989 or so. Link to comment Share on other sites More sharing options...
kramttocs Posted January 26, 2021 Share Posted January 26, 2021 Good afternoon, I have a question. I have a 83 Bronco with 4.9 435 4speed 3.55 gears. 31/10.5R15 tires At 69Mph im almost running 3,000 RPM. Every calculator I’ve put my information in says im running 4.10’s. But I jacked up the truck and double checked. Its 3.55’s. Does this sound right to you? Running a factory tack but this truck has been rebuilt some time ago. Could the tack be off? Maybe from a V8? Tack runs smoothly. Nothing to say its off. Any information you could tell me would be appreciated. Welcome aboard Richard. My questions would be: Have you verified your speed at 69 MPH? Are you going by the Bullnose speedo or GPS, or other? Have you verified the actual height or OD of the 31" tires? Often times 31" tires are more like 30" or 30.5" OD installed. If by chance your speedo is off by a few MPH...you would only have to hit about 72 MPH to be at almost 3000 RPM. Somebody can correct me on this, but I don't think that Broncos came with 31" tires until later on it in the 80's, like 1989 or so. Welcome! Link to comment Share on other sites More sharing options...
Recommended Posts