I am working on a 1960 Willys delivery that has a 1967 Buick 300 V8 installed in it by a previous owner. Need to swap out some bad axles (Found the rear housing bent and front is cracked). Since I am looking for new axles anyway might as well set things up to optimize engine RPM at highway speeds. (I will be taking it camping) Electronic ignition with a MAP sensor is already in the plan. So the question is what RPM range on a stock 300 is best for fuel economy at highway speeds? Thanks,
I would say that for best power up hills you would want to be at the peak of the torque curve which is about 3400 rpms. On the flats it would be happy in the 2200-2500 rpm range.
I have the "wimpy" (lot better than the stock 4 cyl that came in the willy) two-barrel with 9 to 1 comp. ratio rated at 220 hp (160 kW) at 4000 rpm and 340 lbft (460 Nm) at 2400 rpm So if I am reading your info above correctly I want to be at the torque peek (2.4k) when on cruse. If I go 3.73 gears (OD = 0.75 overdrive engaged) I get the following RPM to MPH points gear - rpm - speed 1st - 2k - 15mph 1st - 3.5k - 29mph 1st OD - 2.3k - 25mph 2ed - 2k - 30mph 2ed - 2.4k - 36mph 2ed - 3.5k - 52mph 2ed OD - 2.3k - 46mph 3ed - 2k - 46mph 3ed - 2.4k - 56mph 3ed - 2.8k - 65mph 3ed - 3.5k - 81mph 3ed OD - 2.1k - 65mph 3ed OD - 2.3k - 71mph 3ed OD - 2.6k - 80mph 3.92 Looks better at 65 and 70 in od @2.2k and 2.4k but 55 sits a little high at 2.5k (non od) all other common speeds sit slightly closer to 2.4k so better in that respect. But I give up the selectable 65 (2.8k or 2.1k) which would get the most used on roads over 45 around here. (also forces me to a D44 front since 3.92 is not offered on a D30 front axle) I think that is about the best match if I go up or down from there things seem to get farther off sweet. 3.54 just looks bad... @2.4k I get 58 non od and 78 od (65 is over 3.5k or under 2k) and 4.09 top end is lower and RPMs are higher on the common speeds. Any recommendations? Also what is the top recommended RPM for a Buick 300 for normal daily driving? (3.4k?)
3.73 looks ok, I do not see any reason why that would not work for you. You are factoring in the tire diameter right?
Yea I am going to stick with 29" on 15" rims since they are easy to find and don't cost a arm and a leg. If I go any bigger I need to start looking a body lifts / mega springs and this thing is tipsy enough stock. So if you had the choice between 3.73 and 3.92 with all things equal where would you go? More I think about it it seems like the 3.92 is the better option....
3.92 would likely be a little better if you do not have to pay a bunch extra to go that route. In the long run the D44 would be a better axle compared to the D30 IMHO. What kind of overdrive setup is this anyway?
Warn PTO overdrive. www hermtheoverdriveguy com/id21 htm (replace spaces with .) So current drivetrain Buick 300 Dana T90 3 speed Dana 18 transfer case Warn overdrive Yea just running into snags finding a D44 of the right width and caster angle. Scouts are close but caster angle of 0. Wagoneers are the right caster angle but 4.5" wider and not sure if the fenders will cover...
Here is your link: http://www.hermtheoverdriveguy.com/id21.htm So are there any other ratio options for the D30?
Standard D30 (standard rotation) ratios are 2.73 3.07 3.31 3.54 3.73 4.10 Aftermarket you can find 4.27 4.56 4.88 5.38 I have seen rumors that 3.92 exists but tried all the aftermarket sites I can think of and so far no hits.
Ok found them needed to search for 3.91 not 3.92 (my bad) So looks like 3.91 is a valid option as well. But there is a slight miss match at 3.9x (D44 = 47/12 where D30 = 43/11) 3.73 are dead on 41/11 for both the D30 and D44. Will 00.2% speed mismatch cause major issues? (front faster) 90% of the time front will not be engaged. Only real use will be for getting out of fields and or deep snow. rest of the time the axles will be unlocked and a non issue...
I tend to agree, as long as you are on a slippery surface it should not be an issue especially since it is very close. Only on the dry pavement for a long distance would cause things to bind up possibly.
One of the most important factors to good fuel economy is engine RPM. Lower is better. The stock 300 Buick makes good low end torque so slowing the engine down to 2000RPM or less at desired cruising/highway speed will work for you. If you tow at times, tow out of overdrive if neccesary and reap the benefits of low cruising RPM when not towing.
The slight difference in ratio won't matter. On "Xtreme 4X4" on "Power Block TV" they had a larger difference on one of their builds and said it wouldn't hurt anything. If you are towing very often or have lots of hills then I'd go with the 3.91 otherwise the 3.73 shuld be OK. "One of the most important factors to good fuel economy is engine RPM. Lower is better. " Only if the engine is not labouring, or you're not having to constantly down shift. Don't forget, that Jeep is about as areodynamic as a barn so the higher ratio might even get better milage.
RPM is not the only factor. You'll need the carb calibrated for the vehicle, including but not limited to proper idle fuel and air bleed passages; and proper power valve tuning so that you're not enrichening the mixture at cruise. Similar issues with spark timing--tuning the initial, centrifugal, and vacuum advance to optimize the ignition system will be among the most productive use of your time and effort. By the way, what good is a MAP sensor if you don't have the full computer-controlled timing curve? If you have the full computer-controlled timing curve, why wouldn't you use the rest of the sensors 'n' solenoids to provide feedback for the fuel mixture? Computer control of fuel mixture will NOT get you the best possible mileage, but it's going to be close and will also help with emissions and driveability. Far as I know, if you're within 3% front to rear on effective gearing (including tire size/rolling radius) you're fine.
The stock Buick 300 shouldn't have any problem with laboring at 1700 RPM in an old Jeep truck at 60MPH. I wouldn't be afraid of turning it that slow under those conditions.
