5 spd Lenco gear ratio selection???

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5 spd Lenco gear ratio selection??? Empty 5 spd Lenco gear ratio selection???

Post  69BOSS on May 28th 2015, 6:04 pm

I am building a '69 Mustang fastback. I am planning on a 598 aluminum block with C and C hemi heads and a single 1150 carb. I am planning for the the shift points around 7000 rpm and about 1050 to 1100 hp at the crank. The car will be set up with ladder bars and coil overs with a small tire (28 to 29 inch). I can only guess at the total weight at this point, so I am guessing 3300 to 3400 lbs. The car will be raced just for fun (no competition) and driven to the local "cruise in" once in while. I am looking get between 8.50 and 9.0 second 1/4 miles at the strip. I put in an order for a Lenco 5 spd today but after talking with the sales rep I am rethinking the gear ratio. I was thinking a 2.44 first gear, 1.95 second, 1.56 third, 1.25 fourth and 1:1 5th with a 3.9 rear end. Lenco thinks I should be lower at around 2.9 to 3.2 first gear. I would appreciate advice from those of you that are experienced racers. Thanks.
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Post  bigblock t-bird on May 28th 2015, 8:02 pm

Yep 3.18 or 3.24 1st with a 3.90 rear gear, mite try a 4.56 rear gear? also bring your 2nd,3rd @ 4th up to. Give them a call back and ask them and give your car specs. You will love pulling all those sticks. Steve

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Post  69BOSS on May 28th 2015, 8:40 pm

I don't understand why I would need such low gear ratios in the trans and a 4.56 rear end would require around 8000 rpm at the 1/4 mi. The 2 spd powerglide's have a pretty high 1st gear and they get down the track, maybe it's more power and / or rpm thing.
I came up with the ratio's I listed by using 7000 rpm as a shift point and keeping the rpm drop around 1000rpm per gear and going thru the lights at 7000.
I figured the engine would have more than enough torque to get off the line with a 2.44 first. So far, you and Lenco seem to be on the same page.
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Post  cool40 on May 28th 2015, 10:58 pm

The glide has a converter to eat all that torque,unlike the Lenco with the clutch. Cool
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Post  69BOSS on May 28th 2015, 11:17 pm

Does that mean it would break parts with a clutch and not enough gear?
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Post  FalconEh on May 28th 2015, 11:48 pm

69BOSS wrote:Does that mean it would break parts with a clutch and not enough gear?

I will chime in with the pretense that I do not have a Lenco but I do run street strip setups... NO the non optimal gear will not break parts, but it will not perform the way you want, in order to run on the street you ideally want to keep the car out of the rpm power band to get it moving, on the track you want it near max rpm at the traps, you need more gear for the street to be friendly, not violent when the power comes on, however on the track you still want to hit the rpm number. the combinations to get the number at the track, can be made in numerous ways(ratios) with the desired outcome.
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Post  bigblock t-bird on June 11th 2015, 4:18 pm

So what did you go with???

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Post  69BOSS on June 11th 2015, 7:52 pm

Haven't made a decision yet. I put a deposit down to get the ball rolling but the guy at Lenco said they are about 8 to 10 weeks out, so I have a little time to figure it out.
Your recommendation was right in line with what Lenco said, but honestly, I am not grasping the need for such a low first gear. I have not built a car like this before so my only comparisons are to street cars. I have a mustang with a BB and a close ratio 4 spd (2.32 first gear) and it seems to start out pretty easy with a mostly stock CJ engine. I had a 2.78 first gear wide ratio toploader trans before, it sure rev'ed through first gear quick but I didn't much care for the spread between gears.
Maybe I am wrong (and I probably am), but it seems like with ton's of torque and horsepower it wouldn't need so much gearing to get going. My thought was to keep the rpm's in the torque curve through the gear shifts.
The quickest I have been in the 1/4 was an 11 second bike, that was a long time ago. It wheelied in 1st and 2nd but seemed so easy to ride. It was a lot of fun. This car I am building will be quite a bit quicker and because there is so much about race cars that I don't know, this is why I am looking for advice. If you could explain to me in terms of racing 101, or, racing for dummies, lol, maybe I could better understand why I need a very low first gear.
Thanks for your help!
Staci
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Post  the Coug on June 12th 2015, 1:22 pm

I am like you these engines have so much torque I am going with a 260 low gears lenco..... But I am also going to use a Bruno with it...
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Post  69BOSS on June 13th 2015, 2:50 am

I will most likely follow the recommendations of lower first gear, I just wish someone could explain it better.
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Post  DILLIGASDAVE on June 13th 2015, 5:11 am

69BOSS wrote:............ I just wish someone could explain it better.

Regardless of how much useable "at launch" torque numbers an engine might have I think it's a deal where you're using a little more 1st gear leverage to avoid lugging the engine so it doesn't fall on it's face at the hit. With an auto/converter trans the flash/stall speed helps reduce the chance lugging it, but you can also help it by allowing a little more wheel-speed to happen at the hit. With a clutch trans you can help it with either a little more 1st gear, or slip the clutch a little more at the hit, or allow a little more wheel-speed to happen at the hit.

The phrase I always heard was if at the hit it either falls on it's face, or climbs the ring gear, then you gotta "slip something somewhere" at the hit.
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Post  bigblock t-bird on August 21st 2015, 10:12 pm

Update???????????

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Post  69BOSS on August 21st 2015, 10:40 pm

Spoke with them yesterday, I had to provide the distance from the bellhousing to the pilot bearing. He said 3 transmissions ahead of me, so maybe I will have it next month.
Gear ratios are 2.85, 2.07,1.58, 1.25, 1.1
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Post  69BOSS on February 10th 2016, 8:08 pm

Finally got the trans just before Christmas. Had to cut most of the tunnel for it to fit. Building a new firewall and tunnel. I had to get it mocked up to determine where the shifter would mount. Talked to Kieth today to get the engine plates ordered. I need to get a flywheel and clutch set up. I am looking at a McLeod set up that Jegs has, part #43351-00-06. All I know about it is the description they give. They say it's good for street and strip, 1000-3000 hp depending on how any discs are used. Pretty expensive @ $2100. The other option might be Mcleod soft lock, it's about the same price but not recommended for street. They are both adjustable and both have aluminum flywheels.
If anyone here has helpful info on clutch/flywheel info I could sure use it.
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