Anyone have the formula for converter efficiency? 30 X 9 Hoosier Radial 4.10 rear gear 6600 thru the traps 127.5 MPH Let me know if you need more info. Thanks for any help.:3gears:
Jim, To figure out the converter slippage we need to know the rear tire diameter. Use a piece of string and rap it around the tire,mark it where the string meets itself,then lay it out straight on the floor and measure the length you used. Need to know the length in inches. This will give you a more precise converter efficiency calculation than just going off the 30" tire measurement. Hope this helps and make sense.
Converter performance is very important, just as traction/chassis performance. Here is a converter slip calculator to evaluate your converter: http://www.wallaceracing.com/converter-slip.php
I would love to hear from some of you who have improved your efficiency numbers per the chart formula in post #1. Tell us what you did to gain efficiency. (If you'll have to "kill" us, keep those secrets to yourself)
AWSOME TRACTION and LAUNCH EFFICIENCY AT 110-111 mph in 1/4 mi.! Compaire these 60 ft and ET's The average good runner scores 184. So 170's is blastin' out of the hole. Car #1 Score 171 Here is a 1971 Skylark in the GSXTRA march/april 2011 page 5 that shows what efficency is about. Screamin' off the line. I realy like that 7.36 1/8 mi !!!!! Impressive for a 110 mph car. 1.55 60 ft, 7.36 1/8 mi, 90 mph, 11.78 1/4 mi, 110.4 mph ( score 171) Car # 2 Score 190 Here is a v8buick members GS with a switch pitch and 3.55 rear, basically stock stuff. This can be improved a bunch, yet it already runs great. 1.72 60FT, 7.70 1/8 MI, 89.6 mph, 12.10 1/4 mi, 111.4 mph (score 190) Multiplly your 60 ft X your 1/4 MPH and see what you score.
Hi to all - I'm currently running a stock 65 Gran Sport convertible, weighing about 4000 - 4100 with me in it. It has 3.23s, ltd slip, boxed arms and a factory sway bar (.975?). It has a SP 300, and goes to low stall about 3 seconds into a run. It also has stock springs and air bags, from when it was an open diff and I used to jack the rear. I have also been using coilover shocks in the rear for ride height as the springs are weak. t I'm running a best 60 ft of 2.171 (ave 2.20) and come up with a factor of 199 (@92 mph). From the chart I need to launch harder, and for that I need weight transfer. I have work to do on the front to let it rise, and need to change the shocks all around, I know. I could use a recommendation on the rear springs though.. reading through this thread I've seen 3 Moog numbers (5379, 5401 and 6321) thrown around. If I intend to use the bags for cruise night ride height, what would be the best application for my car? Please keep in mind that it's driven to the track, and to work and the kids school and all over the place.... Thanks,
The 64-66 A body used different springs on the rear than 67-72. Your best choice is a MOOG 5231 rear spring which is .531 wire diameter. This is a stock replacement for Skylarks will give a stock Skylark stance. These springs are not pigtailed on both ends and this will easily allow you to cut some off one end to get a lower stance if you like. 1965 GS factory springs were stiff as hell. They were not performance friendly at all. I love the small diameter springs, and they improved my traction dramatically. You can get firmness from big shocks and big swaybars if you want to stiffen things up a bit. Purchase from autozone using the same Moog 5231 part number but under their odd name brand, or get a good price from www.rockauto,com.
Oh, by the way, if you want to improve your 60 ft, install a 400 switch pitch tranny or just go with a th400 non s/p and use a 9.5 3200 stall converter. I put a 400 in my 65 GS & with the help of a 3.55 rear gear and good exhaust, I gained over a full second in the quarter (15.70's to 14.60's). I had to offset the transmition mount a little and alter the linkage to accept 3 speeds. Also welded angle iron for the crossmember to sit on and drilled holes for the hold down bolts. Some guys on this site can help you more as I did this mod 40 years ago. Huge gain in performance.
Gary - thanks for the feedback. I have so much work to do on this suspension, it rides for crap, but there's no shock rebound and still the front end bobs on bumps like a porpoise. Both ends have lost ride height and the springs are like stones in there...For the long run, a softer sping has a tremendous appeal, coupled with really good roll and shock control. I'll give those 5321's a try - I like a higher stance both front and rear, but need some movement and transfer. Sounds like that should do the trick. Any suggestions for the front? It's a non A/C car. Actually, the ST300 is dialed in pretty well at this point - I'd like to raise the shift point another 200-300 rpm and firm up the shift, but I cant complain as it sits..The converter does it's thing, I'm sold on the switch pitch with some sort of manual control. As it happens, the 73 4 spd came with a Kenne-Bell short shaft switch pitch TH400 in it. I dont know the stall speeds, but it seems pretty stout. When I put the 4 spd back in, I plan to at least try the 400 in the 65..I've been lurking on a couple 67 Console/shifter auctions, but cant justify the high bids...yet. What about the 400 made it better, in your opinion? Did it have a lower first, better gear spacing, etc? (My car drops like a stone between gears - 1500 rpm at least) I was concerned about the extra HP draw of a 400 cancelling out the benefits... Thanks again for all your input...
For the work involved, the extra weight, the higher HP draw, the extra cost, etc. you can usually gain about a tenth. Now you will really have a traction problem. The 400 has a 1st of 2.48, 2nd. of 1.48. Unless you are going all out, just MHO, it's not worth it. Problem is as you increase HP the 300 will have to come out more often for a freshen-up. There are NO High Perf. parts for the 300 that I know about. Can you increase the shift point about 500RPM's???? You'd be surprised at what that may do for you. Tom T.
Hey Tom - I think I can increase the shift points, I have an old article about how to modify the governor and also modify the valve body for firmer shifts..I'd like to pick up another governor if I'm going to experiment though, and keep one stock. If the weather breaks and I get the car back from the tranny shop (they're resealing it, it leaked from everywhere since the last time they did it for me), I plan on coming down to see you this week..I'll call ahead. Thanks again
SPRINGS..... Put some Moog 6204 front springs on that GS and WATCH IT DANCE !!! Good front end lift is a thrill. GEARS..... On the GEARS. Multiply the low gear of your tranny times the rear end ratio. I like a starting ratio between 8.00 to 9.00 range for street and strip. I like 10.0 or more for stick shifts. Tall tires will lower the starting ratio effect. * TH 300 with 3.08 Orig 65 GS...........1.77 X 3.08 = 5.45 starting ratio. * Th 400 with 3.08 Common.......... ...2.48 X 3.08 = 7.64 starting ratio. * Th 400 with 3.55 My 65 GS mod......2.45 x 3.55 = 8.80 starting ratio. * Th 400 with 3.73 Popular combo......2.45 x 3.73 = 9.25 starting ratio. To get the 60 ft below 2.0 sec.,you need to combine enough starting ratio, with a good stall converter, and have the power to shove that baby off the starting line. Oh, & traction of course.
Gary - How does the switch pitch figure into those equations? Road test back in the day took those figures (or figures like those) and multiplied them by 2.2 to account for the higher stall...so the starting ratio wound up being like 12-22 or so....Does that not translate to the real world, or is the benefit lost too quick? From Car Life Magazine: 65 Lesabre - ST400, 2.48 first, 3.08 gear = 16.96 67 GS 400 - TH400, 2.48 first, 3.90 gear = 21.8 65 Gran Sport, ST300, 1.76 first, 3.08 gear = 13.3 By that yardstick, I'm at 12.5 with my 3.23s
You're right, they referred to torque multiplication figures and added them to starting gear ratios. That is not common any more, probably due to converters having such a disparity in overall efficiency from one to another. It did reflect some aspects of driviability for the street driver of the good ole days when simple tech figures were good enough for Mom & Pop or Jr. Compare the overall efficiency of a Vega 3500 stall converter to a coan 3500 or ATI or JW's converter. The Vega converter would get beat. Yet they would all be honestly 3.5 to 1. Same thing would happen to an original 1970's L-88 Corvette converter. Same thing would happen to a large diameter and heavy Buick S/P converter. As for todays street car tech, the performance range is usually 3000 to 3500, and lockup efficency is gaining popularity over just "stall". Add to that...lighter weight and smaller diameters. Now we look at our ET & MPH to brag or complain. We're just more high tech dudes nowdays. Note to S/P guys. For street traction, try this: * Torque up about 1200 with the S/P off. * Hit the switch on and throttle down at the same time to launch. * Count off two seconds (or 60 ft) then turn the S/P off for the rest of the run. This worked very good on my car for street. The fraction of a second it takes to reach high stall, is just enough for the tires to turn and grip. Still may need sticky tires though. Depents on your power.
The greatness of this board is proven once again.:TU: Over the last few months I have been learning a lot about chassis tech. And have come to the obvious conclusion that I need to ditch my very stiff rear springs. :blast: They came with the car when I got it 25 years ago, so I don't know exactly what they are, but I do know they are very stiff. My Skylark has chassis dynoed at 410HP and 510TQ...but with 3.42 gears, 26X10 slicks and a fresh TH400 with a JW SP converter the best 60ft. time I have is 1.99 and best ET is 13.2 and MPH is 105.:af: I am definitely changing my springs. ou: I have been considering using a coil-over spring perch kit from TRZ Motorsports http://www.trzmotorsports.com/ but am not sure if it would be worth the trouble. You basically cut-out and replace your lower rear spring perch with a coil-over style perch which allows the use of coil-over springs and gives some ride-height (or pre-load) adjustability. Seems like a good idea.o No:
BirdDog, In case you haven't looked it up, the score card list I provided says that if you go 105 MPH, this is what you can do: 1.75 60 ft.....7.96 ET & 85 MPH 1/8 mi......12.62 ET & 105 MPH 1/4 mi Not hard to do with 3.42, good traction and a good 9.5" or 10" converter. Other heavy converters will usually require a lower rear gear, like 3.73 or 3.90. When I installed Moog 6204 front, and 5379 rear springs, along with my JW 9.5" converter, I had all my numbers on one line of the chart straight across. My compression was down a bit, but the numbers noted above (within .02 ET) are exactly what I ran at 105 MPH with a 3.42 rear and 3800 lb 67 GS.
Yeah Gary, I had looked at the chart and saw that my numbers were all over the place. ou: My rear was so stiff, it was like it was solid mounted, and the front of the lower arm was just over 3 inches higher than the back. ou: I have already received the 5379 springs and a Hellwig tubular rear sway-bar. I am waiting for some better fitting wheels and some new shocks. :Brow: I got some new urethane upper spring pads, but I'm not sure I am going to install them, at least not right away. I have always felt that my car should be a mid-to-high 12 second car...we'll see what happens.
Are the Moog 5230 and 6204 springs good for the 2nd gen A-bodies like my '72 or just the first generation...or both?
