I have a 1971 skylark with a BBB 430 and will be putting in a muncie m21 soon. It will be a street car that I may take to the track every now and then. I will probably be running a 255/60/15 tires(27" height). I need help on a few things: 1. what is the ideal rpm for cruizing at 65mph? 2. what gears would be best for cruizing and a little racing? Thanks
With a close ratio trans (2.20 first) and that big tire, at the very minimum, you'll want a 3.42. You might want to even get a 3.73. I cruise at 3000-3200 on the highway. The 70 has 3.64's and the 71 has a 3.73.
Is 3000 rpms good for cruizing with a BB? I always heard that 2200-2600 is best, ofcourse I guess if I slowed down to 55-60 that is where I would be.
As long as the cooling system is up to snuff, the engine wont break a sweat. Years ago I had a GS-400 with 4.10's in it. I would cruise at 4000-4200! :eek2: I wouldnt recommend that thoughp
1. For cruising (sorry, I'm not hip enough to use a "z") at 65, a 455 can run super-low RPM. I have a 2.56 ratio rearend, and there are times I wish I had an OD. I'll bet a stock motor would still be fine at 1600 RPM. 2. Figure that for cruising you want a 2.56, and for racing you want a 4.10 - your compromise will probably be somewhere in the middle. But I still run my 2.56 at the racetrack (13.3@108), but that's tricky for consistency in the brackets. 3.42 is a very popular ratio, however I do too much highway driving for that. -Bob C.
ALL this info is depending on how the motor is built. Is your 430 a stock motor? Or is the 430 rebuilt with a aftermarket cam? If stock then 2200 is the normal for a 65 cruise on the highway...THIS IS STOCK factory stuff. Gears were normally 2.93 3.08 3.23 AUTOmatic will be 2.56 2.73 gears. If your car engine is in good shape 3000 RPM should not hurt it a bit to cruise around at on the freeway. SOME TIMES it is just your choice and what YOU personally want or can handle listening to that RPM with aftermarket flow master etc... USUALLY.... remember you can order pretty much what you wanted but most V8 stock motors had tons of torque and lower horses which gave them very good drivability and snappy take off and the best gas mileage they could possibly get for that era....LOL GAs <ILEAGE...What a hoot!:3gears: :3gears: :3gears: Jim
I is a built 430(ta 280 cam, ta intake, ta headers, nodular iron crank, 430 heads with big valves). I am restoring the car. It still has original peg leg rearend with 2.56 gears. What would you do to make the car very streetable and at the same time decent off the line. Not looking for a 11 second car...Thanks
I have a stock 8.5 rear end(peg leg) with stock 2.56 gears. Should I just put in a posi and leave the stock gears to see if I like it? If not I could alway change the gear to 3.42. What are you running for horsepower and tranny? Thanks
The problem is that an M21 is made for use with ratios of 3.42 and lower. Leaving a dead gear like a 2.56 or even a 3.08 and the car will be doggy off the line. If you want to use a dead rear, then an M20 would be better.
lol. AGAIN it is stick shift so there really is no doggie gear. BUT to leave the 2.56 in the rear will NOT be good with the 280 cam have a good amount of duration for a street car. you will need to at least run a 3.08 3.23 3.42 gear. REMEMBER the 4 speed trans is STILL 1 to 1 at the end of the 4th gear. I would go with your 3.42 that duration cam will need to run close to 3000 RPMs for its sweet spot on the cam. I am sure it is 2500-6000 power band ish...BUT with the 430 cubes you will have a much better chance of over coming the duration lag that MIGHT occur. So there you go. I would say 3.42 gear ration with the 8.5. Lets see what other think. Take care, Jim If you need any rear diff parts or help setting up shoot a PM I will most certainly help you.
Yes, but what I was trying to get at was that the 2.20 first gear of the M21 might be a problem with 3.08's. That would give you a first gear ratio of 6.776. But we came to the same conclusion anyway- 3.42's :beer
I have no issue cruising mine at 3,000rpm for hours on end. I've now got 3.08 out back behind a TKO-600 trans, used to have 3.70's. Ran the 118 cam for a while with it and now the 212 cam. Even towed a trailer with an engine on it while the 118 cam was in. Made a slight difference taking off in first gear, but now that I'm used to it I don't even notice the 3.08's except for I'm not shifting .5 seconds after taking off from a stop. It won't make for the quickest 1/4 mile time, but the down low torque is more than adequate to pull a pretty low rear gear nicely on the street. At least as well as a 6-cylinder and 3.23's, lol.
I do not understand what your kind of getting at... 2.52 is 350th and 2.48 is the 400th...with a 430 cube motor...you will not enough feel a glitich with the 2.20 first gear...power glide is 1.76...try that tranny...lol 1st gear goesa forever and cars were hooked with 2.73 and 3.08?? second gear pull will more than make up for the lack of fist gear which you are not in that long anyway. A v8 and stickshift will have no problem with that first gear at all. If it were a High duration small block that first gear will make a big difference needed. Like you said all in all we agree about the ratio. He will be the ultimate chooser anyway no matter how much we go on about it... Jim That is what the sites are all about discussions like this....
I asked this exact question of Denny Manner at the GSX Reunion last year. I told him I had a stock 455 with a 4-speed in my GSX with stock 3:64 rear and I was concerned cruising at around 3200 RPM while cruising on the highway. He said "no worries" and that engine will run all day long at 70 mph in that configuration and there is nothing to worry about. I figure he would know better than anyone. FWIW... Rob
Ahh- I remember the 60s and 70s when we would go 3 grand 4 grand 5 grand etc even, and if we did'nt hear ticketee ticketee, hammer hammer, we were good to go, " Hey I dont mis that Hammer Hammer a bit LOL.
Yah I hear ya. The over drive fuel injection motors make everyone think motor is suppose to run at 2000 and lower rpms...FAR from the truth on a carburetor motor. You need at least 2200-2500 minimum for good fuel atomization in the intake for power and mileage. Injected motors have the advantage of the early spray from the injector head to atomize the fuel into the air coming in. This is why they can run at lower RPMS and still have fairly good drive-ability. 3000 RPM really is not out of normal drive RPM. It is just the older vehicles have such vibration issues because of sagging frames body mounts bushing drive line issues etc. Just one of the things you will usually have to deal with in a 40 + year old vehicle that WAS A MUSCLE CAR FROM DAY ONE... JIm
I'm running about 450HP NA plus a lot of nitrous (up to 250HP). But more importantly, the engine still creates a ton of torque. I am an unusual case- I do a LOT of highway driving, and I only go to the track for fun (just to see what it will run, never to compete). I drove about 10,000 miles in 2009. BTW, best time is 11.6@118 on a 150HP nitrous shot. I do agree that excessively tall gears (like my 2.56s) do present issues. Since I mostly travel at 70-75, I'm doing some decent RPMs (2400 or so). But I also believe that even a motor with a decently tuned Q-jet (or other carefully tuned spreadbore) and a relatively stock cam should be able to run fine at 1800 RPM. Should you run 2.56's for now? Totally up to you. I wouldn't bother putting a posi setup in it, though, instead I would try the 2.56's first and see how you like them. Most people don't, which is why you see so many people recommending the 3.42-ish ratios. But you can try them for a while if you want. If you fall in love with the 2.56s, then go ahead and look into a posi for it (if it is even possible). By the way, I also run Rhoades lifters. I know some people call them a "band-aid" but I like the way they really extend my low-end while still allowing me to shift at 5800 RPM. All opinions are strictly my own! -Bob C.
Try a little gear math here. A fair performance starting ratio is 10 to 1 (2.43 T10 low gear X 4.10 rear = 9.963 starting ratio) You have a 2.20 commonly used with 3.55 rears from the factory. (2.20X3.55=7.81 starting ratio)...not worth a hoot for serious performance. If you use a 3.42 rear: you will have a 7.52 starting gear and will do 68 MPH at 3000 RPM. Not too bad for cruising, but a clutch burner for drag racing. A T56 provides a 3.36 low and .62 OD. with a 3.73 rear = 3.36X3.73=12.533 starting ratio and .62X3.73=2.31 cruise gear. WOW!! 12.533 starting ratio will blurr your eyesight off the starting line. WOW!! 2.31 Cruise will get 1943 RPM at 65mph (26" tire) and 3886 rpm at 130 MPH. For racing, a 2.20 trans would have a starting ratio of exactly 10 to 1 with a 4.56 rear gear and do 4000 rpm at 68 mph. Holy crap. For racing, I hated those 4 speeds when they came out new in mid 60's. At least mopar made a strong 3.06 low for the slant 6 back then.
Wow, this is why I love this site! You guys have so much knowledge when it comes to this stuff. I am probably going to just do the muncie conversion first and do what Bob C. said, drive it around a while and set how I like it(even with the peg leg) and make a decision then. If I feel like I am not getting out of the hole well then put in the 3.42's with a posi and then have fun. I was just more concerned with running 3000rpms on the highway but according to you guys these motors have no problem doing that. Besides, I have no problem cruising at 60 unless some silly mustang pulls up next to me then the rpms will be running much higher! lol Thanks again guys! Your help is greatly appreciated... Lee
