DiMarco Posted January 23, 2014 Share Posted January 23, 2014 (edited) Hello all, The V8 manta i am getting has a 3 speed auto set up running a camero rear axle. I have been told it is running 5000 RPM at 100 MPH but there is a way to change the ratio to make the car run at 4000 RPM at 100 MPH by changing the ring and pinion gear but i dont understand any of it lol. Please see below to what the owner sent me to change it i cant make heads or tails of it. Diff Ratio Calculations 4.1 = about 100 mph @ 5000 rpm mph @5000 rpm rpm @ 100 mph with various diff ratios with various diff ratios Ratio mph Ratio rpm 4.1 100 4.1 4914 3.9 105 3.9 4674 3.7 111 3.7 4434 3.5 117 3.5 4195 3.3 124 3.3 3955 3.1 132 3.1 3715 2.9 141 2.9 3476 2.7 152 2.7 3236 Wheel Diameter = 26” Pie x 26 = Circumference of 81.7” (81.679) 63360 “/mile 63360 / 81.679 = 775.7 Wheel rotations / mile = 77572 rotations / 100 mile 5000 rmp X 60 = 300 000 revs / hr therefore 100 mile @ 5000 rpm = 300 000 revs Engine Revs / Wheel Revs = 300 000 / 77572 = 3.8 ER / WR = ratio 3.8 / 1 But Diff Ratio is 4.1 / 1 Engine ---------------- 3.8 -------------------- Diff 3.8 / 4.1 Engine ----- 0.927 ----- GB ------ 4.1------- Diff So … ratio of 1 to 0.927 on final drive of Gear Box Using a 2.7 - 1 diff 0.927 x 2.7 = 2.5 ER / WR 2.5 x 77572 = 193939 ER 193939 / 60 = 3236 rpm @ 100 mph Using a 2.7 - 1 diff 0.927 x 2.7 = 2.5 ER / WR 2.5 x 77572 = 193939 ER 193939 / 60 = 3236 rpm @ 100 mph Edited January 23, 2014 by DiMarco Quote Link to comment Share on other sites More sharing options...
doveyte2800 Posted January 23, 2014 Share Posted January 23, 2014 Hi, Seems a bit complicated to me as well. Go onto www.math-prof.com and you can put all your info in easily and play with any figures u want till you get the right answer Quote Link to comment Share on other sites More sharing options...
DiMarco Posted January 23, 2014 Author Share Posted January 23, 2014 Thank you very much i think i have figured it out now thank you for the address. Quote Link to comment Share on other sites More sharing options...
tony g Posted January 23, 2014 Share Posted January 23, 2014 Just a reminder that with a torque converter you wont get exactly 1:1 drive, ie the converter will slip slightly so engine rpm will be a fraction higher than output of the gearbox so as a guess if the engine is at 5000 (under load) the "effective" rpm may be 4900 ish. Not sure how accurate you need to be re gearing at this point. My advice to you at this point is get everything up together and on the road and see how it feels. It seems odd that someone went to the trouble of fitting ford 351c and transmission then fitted a camaro axle. Most yank axles used are 9 inch ford and very common for many swaps and 4.11 is a ford ratio. There are plenty of aftermarket gears available for ford and gm axles though, in fact far cheaper than manta stuff lol. Get underneath the car and take pics of the diff housing and transmission and ill tell you what youve got (not the ratio tho lol) Tony Quote Link to comment Share on other sites More sharing options...
DiMarco Posted January 24, 2014 Author Share Posted January 24, 2014 Hi Tony, thank you very much i will do that when i get a chance i am very grateful. Nick Quote Link to comment Share on other sites More sharing options...
DiMarco Posted January 24, 2014 Author Share Posted January 24, 2014 I have just found out that the car has a General Motors; Ten Bolt Axle - 1971 Camaro with C-Clip Differential is 4.10 with Richmond Gears Locker. Quote Link to comment Share on other sites More sharing options...
tony g Posted January 24, 2014 Share Posted January 24, 2014 Ok it is a chevy axle then. Nothing wrong with them at your power level, also quite easy to buy different ratios for. The locker diff is quite an expensive part and will be good at speed on the road, but maybe a bit noisy/clonky at slow speeds. If your tyres are about 26" tall the 4.10 will be a "little" low geared but will be great for flooring it and hear the motor sing I would try it first and change it later if you cant get on with it. For cruising mileage a 3.7 (ish) would do for that but you will lose the urgency of the motor and a 3.9 (ish) would be a good compromise which would still launch quite hard and give a scary top speed but less likely to spin the wheels in top If you have a C4 transmission, its made of ally with a removable bellhousing (look for the join) . If its a C6 its also ally but bellhousing is part of the main case. The other option will be an FMX which is iron main body with an Ally bellhousing. If you need any advice with the box or the engine I can probably help. (Used to run a cleveland 450hp with FMX and C4 transmissions and am currently building a C4 to take 1000hp (like you do) Tony Quote Link to comment Share on other sites More sharing options...
tony g Posted January 25, 2014 Share Posted January 25, 2014 Found this online calculator, bear in mind they ask for tyre RADIUS not diameter, so 13" in your case. Looks like 3.1 will do 100mph at 4000rpm http://wahiduddin.net/calc/calc_speed_rpm.htm Tony Quote Link to comment Share on other sites More sharing options...
DiMarco Posted January 25, 2014 Author Share Posted January 25, 2014 Thank you very much tony that is a great help. She is Running a Cleveland 351 5.7 litre V8 with an FMX gearbox 3 speed with a 1971 camaro rear axle. She has 295 50 15 rear tires and 185 70 13 front tires. I am not sure what the Cleveland is running BHP wise as the chap told me it is hitting 320bhp but the engine online it says about 200 or something. Quote Link to comment Share on other sites More sharing options...
tony g Posted January 25, 2014 Share Posted January 25, 2014 the cleveland is actually classed as a 5.8l. There are a few variations on cylinder head and inlet manifold set ups. What inlet manifold and carb are on it do you know? Also are the heads 2v or 4v ? They can be 300 ish with few mods as long as its got a decent 4 barrel carb and manifold,but without knowing the full spec its hard to say. Tony Quote Link to comment Share on other sites More sharing options...
DiMarco Posted January 25, 2014 Author Share Posted January 25, 2014 Hi Tony, I am not sure if you can tell from the photos but this is the engine bay you might be able to tell something from the photos but I don't know that much about it. Quote Link to comment Share on other sites More sharing options...
tony g Posted January 26, 2014 Share Posted January 26, 2014 Ah good. I can see ally intake manifold so thats aftermarket. It has a Holley carb on there and some cheeky nitrous oxide solenoids The Mallory distributor is a nice piece too. Right now whip the cylinder heads off I want to see the pistons Tony Quote Link to comment Share on other sites More sharing options...
DiMarco Posted January 27, 2014 Author Share Posted January 27, 2014 I will have to see what it is like when I get the engine out as I need to get the manifolds shortened so that the new exhaust can fit nicely into the body. I will see what I can do when I get the engine out. I see from the cars you used to have the American muscle looks awesome. Quote Link to comment Share on other sites More sharing options...
tony g Posted January 27, 2014 Share Posted January 27, 2014 Yes the old tank had a cleveland in it, originally from my aussie falcon xb gt (mad max) god thats rare now and i scrapped it lol. Built a few clevos, good strong motors with the right bits and normal stuff like gaskets are quite cheap after buying jap stuff for years lol Tony Quote Link to comment Share on other sites More sharing options...
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