Looking for honest opinions from 4 speed guys with heavy cars. I am in the process of building the drivetrain for my 72' Chevelle SS 454 tribute car. Long story short, it was bought back in 05'. Most of the resto work was done in 2005-2006 by my father and I. Back then, didn't know about the PSMCDs. I believe it has a wide ratio M21 in the car now. I am going to pull it out soon to verify. All my father can tell me is that it was a good used muncie he bought from a friend of his. What is easier to drive on the repro polyglass tires? I have read people like both. With my LS1 car, (totally different animal than an LS5), the 6 speed cars have a 2.66 first gear and are easier to walk out on street tires with more gear. Say a 4.10 ring & pinion vs. the factory 3.42's I am at the point that I will be pulling the non-correct engine and trans out in a few weeks. I planned to have the trans rebuilt. But, need to decide if I want a wide ratio trans, or a close ratio. I am leaning towards the 2.20 ratio M21 because big blocks have gobs of low end TQ. Thanks in advance. :3gears:
An M-21 is a close ratio transmission. An M-20 is the wide ratio M-21- Ratio: 2.20 / 1.64 / 1.28 / 1.00 M-20 Ratio: 2.52 / 1.88 / 1.46 / 1.00 An M-21's ratios were designed for final drives of 3.42 and lower, while an M-20 was used for final drives higher than 3.42. A 21 with a 3.08 would be bog city out of fist gear.
With an LS-5 i would go 4.10 and wide ratio." USE THE TORQUE LUKE !" More low end and mid range to pull the car. :3gears:
If I would have listened to JJ and pete 2 years ago could have saved myself a ton of money. in the last year, I had the trans out 5 times, deciding on wide or close along with 3 different rear ends from 4.11, 4.33 and 4.56.they were right! The close ratio and 4.11 was 2-3/10ths and 3mph slower than the wide ratio, tested on the same day last year at Martin when I broke the wide ratio. The feel of the car was night and day. I ended up using the wide and 4.33, as the 4.56 was too much at the big end.for an ls5 chenille, Tim clary is right on, wide ratio, he knows as he tested both also. I would go either 4.30 or 4.56' as the 4.11 leaves some on the table. On the other hand, Jim Lerum swears by the close ratio as he revs it up and slips the clutch out of the hole with the 4.30 I have a real nice and new m21 if anybody wants one or wants to trade for a wide ratio
I am thinking 4.10's in my car for sure. I feel anymore and the engine will be out of steam. Optimistically, I am guessing around 104 MPH will be my trap speed. 104MPH X 4.10 X 336 /25.9" tire height = 5531 RPM at the stripe. I would guess my car to be around 3700lbs w/o driver. Buckets, console, PS, PB, A/C, stereo, full guages, etc. Am I off base? I just don't think it will trap any higher than that. Thank you for the replies gentlemen.
I think he means a lower (higher numerical) gear Look there are more experienced people here but this is my experience . I owned a 428 SCJ mach 1 and a coupe Boss 302 Mustangs/ The boss was a high winding engine and if you have the ability to spin a lot of RPM them go close ratio. This keeps the engine from dropping off the power band. On the other hand if you have a torque monster engine then a wide ratio is best to take advantage of the torque. A 70 Stage 1 with 364 gears probably has enough torque to use either. My Boss 302's had 390 and 430 gears from the factory
believe it or not my fastest ever @ 116mph was with the 4.10 and the wide ratio . The LS5 won't have the top end charge of the 6, but will have a brutal BUICK like 1/8 mile and finish around 108 mph .:TU:
Tim, if it traps 108 MPH - I will do cartwheels in the staging lanes. I just don't have high expectations with the weight, and the fact that it's a non-cowl induction car. (Just a domed hood with the single snorkel air cleaner) o No: If I was starting from scratch, a 70' LS6 car or a 69' COPO 427 Chevelle would be my first choices. Bench seat, TH400, manual steering, no radio. But, I have this car and want to enjoy it. Thus far, I have really enjoyed doing the research and hunting parts. I am in my early 30's, my folks bought a Mulsane Blue 72' LS5/Automatic Chevelle Coupe new in fall of 71'. My dad remebers it being a "dog", in his words. And said the 4 barrel wouldn't "honk" until he sawed holes in the air cleaner base. (I know, not a class legal mod.) Things like that have me worried, it's going to be an extremely steep learning curve. I truly appreciate everyone that has been willing to help me with free advice and links to answers along the way. And look forward to making at least one race in 2011 with my car. Hoping to have it done and do some testing at my home track in Orlando this spring.
Jensons 70 chevelle had the domed hood with dual snorkel -I actually forgot this was a 72 but still quite optamistic for the combo. New rules 9.3to 1 plus 1.5 compression = 10.80 same cam as a 70 LS5 = 461/480 lift semi open chamber heads = better flow than the 70 heads hard to beat cubes.
9.3:1 CR? I thought 72' was 8.5:1? I had planned on shooting for 10:1 SCR - per the rules. My block is .060" overbore. (.070" max allowable IIRC) I have a set of the correct 241 casting heads, haven't dealt with them yet. Trying to get a complete shortblock together first. Camshaft... not sure yet. The only thing I see available so far is a Crane "blueprint" camshaft.
I think it all depends how you drive the car as a driver off the line. I think it's that simple as to what the car likes for a trans.:TU: Jimo No:
Beautiful car, would love to have it... but I am sure it would financially drain me. I hope it finds a good home. (Or I win the lotto)
yeah, but they grow when you heat them <object width="640" height="385"><param name="movie" value="http://www.youtube.com/v/b5L575uS0jI?fs=1&hl=en_US"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/b5L575uS0jI?fs=1&hl=en_US" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="640" height="385"></embed></object>
True, but close-ratio gearsets were also available in the M22, which had the same ratios, but had spur-cut instead of helical cut gears- thus the noise and the nick-name "rock-crusher". I had the M21 in my '64 Impala convertible, with the special high performance 327 (300 HP, AFB, 2-1/2 exhaust stock head pipes). It'd smoke the 10" clutch instead of the 3.90 posi axle- fed 8.75"X14" bias plies. Bog city is right. I bought it with 100+k on it at 1/4 mile at a time, and third gear gave out. I seriously considered going wide ratio since I had to buy the cluster gear, anyway. I put a 3 speed in it until I rebuilt the 4-speed and I'll tell you that 2.73:1 first gear made for a nice launch on that barge.
