Mtchlcaney Posted August 5, 2019 Share Posted August 5, 2019 Hi I own a 1970 R685 model fire truck single axle with the 237 maxidyne, a 5 speed stick, 4.88 rear end, and 11 22.5 tires. Seems like my top speed is around 53 mph. I am looking at a 1969 R611 model fire truck single axle with a thermodyne, 5 speed stick, 5.14 rear end, and 10 20 tires. Any idea what its top speed would be? I never drove a thermodyne before. 1 Quote Link to comment Share on other sites More sharing options...
CaptainCrutch Posted August 5, 2019 Share Posted August 5, 2019 The old firetrucks typically has a top speed of either 55 or 65. I hope that answers your question... Quote Who needs a back yard when you could have a Yard?! Link to comment Share on other sites More sharing options...
Mtchlcaney Posted August 5, 2019 Author Share Posted August 5, 2019 Is there anything that can be done to bring it up closer to 70 mph? Change the rear end to a lower ratio? Or something like a different transmission with an overdrive maybe? Quote Link to comment Share on other sites More sharing options...
JoeH Posted August 5, 2019 Share Posted August 5, 2019 The 5 speeds top out at a direct 1:1 ratio I believe. Other transmissions have overdrive, sometimes in the range of .6:1 or .7:1. Quote Link to comment Share on other sites More sharing options...
j hancock Posted August 5, 2019 Share Posted August 5, 2019 The R611 will be a 50 mph truck. Either an OD trans. or new rear gear will up the mph. A 4.00 rear gear will get you in the range you want. Quote JimIt doesn't cost anything to pay attention. Link to comment Share on other sites More sharing options...
Mtchlcaney Posted August 5, 2019 Author Share Posted August 5, 2019 Awesome. I know the hp and torque are different between the maxidyne and thermo dyne will it drive drastically different? Quote Link to comment Share on other sites More sharing options...
AZB755V8 Posted August 5, 2019 Share Posted August 5, 2019 26 minutes ago, Mtchlcaney said: Is there anything that can be done to bring it up closer to 70 mph? Change the rear end to a lower ratio? Or something like a different transmission with an overdrive maybe? The easiest thing to do is change the pig in the rear. That is the differential portion of the rear end with a drop in from a rebuilder or take-out from a truck salvage yard. You what to get into the 3.7 range to do around 70mph with a direct in 5th transmission with all else being the same. Don't worry about winding it up quick to get to a fire for a hobby truck. Just worry about getting to a show before the show is over doing 50mph as is. Quote Link to comment Share on other sites More sharing options...
Mtchlcaney Posted August 5, 2019 Author Share Posted August 5, 2019 I dont mind going 50, but I get a lot of honking and hand gestures from those who are young and dont understand that 50 mph once was going fast. Lol 2 Quote Link to comment Share on other sites More sharing options...
j hancock Posted August 5, 2019 Share Posted August 5, 2019 41 minutes ago, Mtchlcaney said: Awesome. I know the hp and torque are different between the maxidyne and thermo dyne will it drive drastically different? The Maxidyne is OK lugging the motor along. The Thermodyne isn't really a lugging motor. It likes some rpm. For hobby use, a little lugging won't get you into too much trouble. Just keep it in mind when driving. In vocational activity, the R611 would have been mated to something like a duplex 10 speed transmission (two gear sticks) so there were more gear splits to keep the engine in the proper rpm range. Quote JimIt doesn't cost anything to pay attention. Link to comment Share on other sites More sharing options...
1965 Posted August 6, 2019 Share Posted August 6, 2019 1 hour ago, Mtchlcaney said: I dont mind going 50, but I get a lot of honking and hand gestures from those who are young and dont understand that 50 mph once was going fast. Lol If you don’t mind going 50, I wouldn’t fool with the expense or trouble in doing all that work. The way the world is now days your still subject to get the gestures! As long as your happy, I’d just smile 2 Quote Link to comment Share on other sites More sharing options...
Hayseed Posted August 6, 2019 Share Posted August 6, 2019 1 hour ago, 1965 said: If you don’t mind going 50, I wouldn’t fool with the expense or trouble in doing all that work. The way the world is now days your still subject to get the gestures! As long as your happy, I’d just smile ^^^^^^^ I second this ^^^^^^^^^^ Enjoy your Old Truck for what it Is.. Take all the back roads or old Highways, & enjoy the scenery... Quote "Be who you are and say what you feel...Because those that matter...don't mind...And those that mind....don't matter." - Link to comment Share on other sites More sharing options...
CaptainCrutch Posted August 6, 2019 Share Posted August 6, 2019 I love driving old i40 in the L, it can just about do the speed limit and it nice just to feel like you’re racing along through the back country! I can’t wait to get it back so we can go out for a drive in it again, luckily 40 is the route back towards home... 1 Quote Who needs a back yard when you could have a Yard?! Link to comment Share on other sites More sharing options...
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