Hi, I was wondering if the often-used 3.08 posi unit can provide some good off-the-line punch? Can you expect a strong runner with a good 350sb and a higher yet still streetable stall converter? Any experience with 3.08 posi on the track? I`m still thinking about investing in the transmission/gears-department or better start with the engine and would be interested in your opinion! And it should be quarter mile, sorry, school`s been some time.... Jens
I think a switch pitch would be the only way to get both street manners and a decent launch out of tall gears via a converter.
Tranny is a TH350, gears are 3.08 posi, engine is a totally stock 71`350 low comp. Is there a chance to get the car going off the line faster and still keep it 3.08 and steetable? If I`d built the engine with the usually mods and change to a higher stalling converter would this give me decent off the line performance with actual gears? What about the switch pitch idea?
The switch pitch trans is good because you can have a nice high stall converter as well as having another low stall setting which gives you low slipage onthe highway. The modern 200R4 trans is an easier swap for a th350 car and offers a lockup torque converter and an overdrive gear. I like to use these 200R4 because they are an easy swap and you can add an aftermarket torque converter with a nice high stall and then on the highway lock up the torque converter 100%. If going with an overdrive a 3.73 or 4.11 gear is best to set your highway rpms at a decent rpm. If you used an overdrive trans with a highway gear you would "Lug" the engine unless you like to drive 100 mph LOL. If you have lots of low rpm torque then you can get a good launch with a highway gear... If you have a high rpm engine then the 3.08 gears would feel slow off the line. 3.08 is a pretty mild gear ratio and it gives great fuel milage on the highway, however a 3.73 gear would get better milage in the city and suck fuel on the highway. The key is matching the 3.08 gear with a roughly 2800 stall converter and a cam that makes power from 2800 and higher. Use a TA 212 cam if your 350 is stock. Get a nice quality torque converter that stalls high and also has a low amount of power loss when at speed. A high performance torque converter can save a half second off a car with a cheep high stall converter that slips 10% through the traps. Lastly some people use a 3.42 or 3.73 gear with a tall street tire and then use a shorter slick at the track to effectively have the best of both worlds.
Re: 3.08 and fast quarter mile? Thanks for your comments. Thinking back and forth I always end up with the idea of the OD-transmission. Just a matter of interest: when were the first documented convertions from TH350 to OD done, early 80ies? The switch pitch does sound like an alternative though, I`ll go get some more infomation about it. Thank you guys
Re: 3.08 and fast quarter mile? I can't comment directly to your question, but my buddy has a stock 70 455 in his 4500 lbs 69 Sportwagon with a 3.08 posi from a 71 LeMans. The car has a Switch-Pitch with the high stall being 3000. His best quater is 13.5. I think its quite respectible.
Re: 3.08 and fast quarter mile? A 200r4 Turbo Hydramatic with a dual pattern bell housing is a drop in conversion. As well as having OD first gear is a lower rartio than a TH350. 3.42 to 3.73 rear gears & you'll be laughin'.
Re: 3.08 and fast quarter mile? I think unless you want to change gears and a trans, going with a 2600-2800 converter, and run as aggressive a timing curve as you can will get you some decent punch. Match the converter to a cam and it should work together nicely.
Re: 3.08 and fast quarter mile? TH2004R would be my choice. If it`s not going to work, I guess I could live with a good converter and my 3.08 out back. The 455 Sportswagon with the 13.5 sec sure seems like a nice ride! Thanks for your help, still undecided but getting closer... Jens
I went to a 200-4R with a stock D5 converter out of a GN and I love it. I later went with a 3.73 gear and then to a 4.10. You would be amazed at the step up in performance even with a bone stock engine. Probably even better gas mileage because your engine will work less to get the car moving because of the 2.75 1st gear and the final drive with a 67% OD will equal a 2.50 gear with the 3.73 or 2.75 with a 4.10.
Re: 3.08 and fast quarter mile? The only thing keeping me from jumping on the trans right away is a tech inspection every street driven car has to go through every 2 years. I don`t know if these boneheads over here will accept a TH2004R instead of a TH350, that`s why I keep swinging back and forth. Can I "block" the overdrive mode for the tech inspection and release it again afterwards, you know something about such a "feature"? Jens
