I am setting up my 1970 Buick Skylark to be a daily driver with occasional weekend track time. I am running a Buick 350 / TH350 with 3500 BTE stall convertor. My question is will a 3.42 gear be enough for what I am using the car for? Thanks Maurice
What are you running for cam and compression? Head work? No sense keeping the rpm up if it's already running out of steam. I'm guessing the engine must be cammed up and be breathing pretty well to have chosen that stall speed. Devon
Yes I have a Jim Bell Buick 350 running KB 118 cam with 10:1 comp, head work, headers, ignition... it comes on like a rocket at 2500 rpm and pulls very hard up to 6000. I though about replacing the stall to 2500 but the a 3000 to 3500 stall was recommended for this engine set up.
3.73's are kind of high for cruising at 65mph or higher for any length of time (and suck for gas mileage). By "everyday" car what do you mean as far as weekly mileage ?
By "everyday" I mean this is going to be my daily driver around town. Say 20 to 30 miles a day if that. Maybe an occasional road trip. An yes I would like to keep the r's down. I did the math and was figuring on keeping the rpm's at 60 around 2500-2600. Just inside the torque curve that way I would get fairly decent mileage but am unsure to the gearing as the motor is a dog below 2000 rpms.
Maurice, steady cruising at 1000 rpm below the converter's actual stall will ruin your day, I'm afraid. The inefficiency of the converter is going to raise transmission heat big time and drain the gas tank in a hurry. Who recommended that stall speed for any kind of highway driving? Sorry, but a 3500 rpm stall and wanting to make road trips at 2500 rpm are mutually exclusive unless you have a lockup or variable pitch torque converter. Devon
336/tire diameter X gear ratio X MPH = RPM. That is without converter slip. If you want to keep the RPM down around 2600 RPM @ 60 MPH, then the 3.42's are your logical choice. 3.42's are an excellent gear ratio for performance. The torque converter will have more to do with the drive ability and performance you get out of the engine. I would be more concerned about that then the gearing, 3.42's will be more than OK. There is a lot of confusion about torque converters. Let me start off saying there is no such thing as a torque converter that will stall at 3500, or any other RPM in every combination. Unless the converter was custom built for YOUR COMBINATION, you probably have no idea where it stalls. With the current state of converter technology, you can have a converter that is built relatively tight for cruising and driving around town, and it will stall where you need it to when you get on it. That does not come cheap though, and odds are, if you bought an off the shelf converter, or bought it used from someone else, it may be too tight, or too loose. There are lots of factors that determine where a converter stalls in a particular combination. Engine torque, car weight, and gearing are the most important. Using the formula I gave you above, with 3.42 gears, and a 27" tire, RPM at 60 MPH without figuring in converter slip, will be 336/27 X 3.42 X 60 = 2553 RPM. With a good efficient converter, add 100-150 RPM to that. Figure 2700 RPM @ 60. If you converter is too loose, RPM could be considerably higher. Hope that helps.
hey maurice, just noticed your from lawton, im not to far from you (2 hours) if its not snowing sunday im going to thunder valley in noble. if you want to build a 455 i can help you out.
The converter I have is specifically built for my engine by BTE after I sent them all the information. It was not cheap by any means. It does flash up to 3500 when I punch it and seems fairly tight while driving around but loose due to the 2.56 gears I am currently running. I am figuring I will be spinning close to 2800 at 60 with my 26.6 inch tires with a 3.42. I am hoping that the 3.42s will help with the loose or sloppy feeling I am currently experiencing at low rpms and get into the cams operating range while driving around town.
Hey Lonnie, I thought about putting a 455 in my 1968 Buick Skylark but I have decided to retire it from racing and put it back on the street. I am going to build up a Buick 350 for the street with all the goodies + fuel injection and may be turbocharge it sometime this coming fall. I would like to get up to Noble this weekend but I have other obligations plus isn't it snowing there? Maurice
Hey Maurice, Another Idea you could put a lower gear set in the trans for launching at the track and have 3.42 for high way use you'll best of both worlds !
That is good that you had the converter built for the combination. Yes, the 3.42's should help with the loose feeling at low RPM. I don't know BTE, but I'm sure they could tighten it up for you if it still feels loose after the gear change. See what your actual RPM is at 60 and you will be able to tell whether the converter is slipping too much.
For that much street driving I would get the 9.5" (2500) converter sold by JW and be happy with a 3.08 rear ratio. You are not going to be happy on the street with a 3500.
opening day was postponed until this sunday. im going with my buick chevelle and my buddies sbc vega. should be interesting. if you need any 350 stuff hollar at me i dont need the brackets or anything since im going to put a 455 in my suncoupe.
I say keep the converter you have in there.... I suggest you go with a 3.42 gear, like the others are saying this is a good setup! ON the highway the 3.08 is a great gear!!! At the track with twin turbos it might actually run quick! NA maybe not much gain over the 2.56 you have. I am using 285/70/15 which are 30.5" in diameter on 15X10 wheels for the street on my twin turbocharged Skylark 350. I will drive to the track and swap on some lighter wheels and 12.5 X 26.5" drag radials. This way I have a good gearing at the track and no need for overdrive on the highway.
Sure sounds like you picked too much cam for a everyday driver... I run into this all the time with customers - They keep band aiding the rear converters tires everything but the real problem...the heart...The cam shaft. 2 cents more. Do the best you can as i doubt your replacing the camshaft. change the gear and see how it goes. It will be the cheapest way put at this time. Jim J D
Thank you All for the input. I have decided to remove the 3500 stall convertor for a stock stall convertor and will be running 3.42 gears.
