NV 3500 5 speed for LSR

[ROCKET HEADS]

Hello racers.
Jeff here, with the 1952 XO / GCC 52 Buick # 1503
I'm building a better, faster, LSR Buick this year.Still XO class, Buick straight 8. I'll introduce the body build class soon. It is going to be a bit controversial, for sure.
... but first,  I have a 'time sensitive' question for review.
I have an opportunity to use a fresh, rebuilt NV 3500. I know this transmission has a front bearing failure reputation, but my first sponsor / supplier / re-builder is confident of it's capabilities.
Key word being "sponsored" transmission .  
325 c.i., under 300 h.p. , under 6000 rpm.
Any thoughts, lsr experiences or advice?

Thanks

www.rocketheadsracing.com

[jacksoni]

I don't know anything about this trans but a bit of research said the precursor trans was the one with the front bearing issue so "maybe" you are ok on that front. Also commented you have to use either GM or equivalent syncromesh trans fluid and that regular gear oils will ruin it. Torque rating to 300. Being "sponsored" is real plus, you should be OK.

[panic]

1991-* transmissions had the bearing fixed.
Which ratio set is it, wide or close?
They both have the same RPM recovery on the 3-4 shift (71%) and 4-5 shift (73%). The actual question: shifting normally, does 71% recovery drop you in a hole (below torque range)? E.g., 5,000 RPM shift drops to 3,571.
Is the .73 OD compatible with your axle ratio?

[Rex Schimmer]

If the step from 4th to 5th is 27% that is way to big, you want something around 10-15% no more. Also if it is rated at 300 lb-ft torque your straight 8 might be able to break it.

Rex

[ROCKET HEADS]

I've requested the close ratio from Bob Bendtsen, Speed Gems Adaptors, although I have not seen the ratio specs.
I figured on a re-gear for the od.

Panic, that rpm calc. is scary, with this engine, as I'm looking to improve from last World Finals, Muncie close ratio. Too big a gap from 3rd. to 4th, she couldn't recover in time, even with  NO mercy and speed shifting.

[ROCKET HEADS]

If the step from 4th to 5th is 27% that is way to big, you want something around 10-15% no more. Also if it is rated at 300 lb-ft torque your straight 8 might be able to break it.

Rex

Thanks Rex, I agree,  am looking into both these issues before proceeding

[38flattie]

I'll introduce the body build class soon. It is going to be a bit controversial, for sure.

Hi Jeff.

Has this new class been approved, or are you running time only?

[Stan Back]

Leave the back window out for better aero and you'll be just fine.

Stan

(or maybe bigger Dagmars.)

[panic]

I know zilch about these boxes, but there may be some alternate internal choices (mix-n-match) that improve the recovery.
I'd like to see less than 20% loss going into final gear (which may not be OD), even more if the engine is flat at mid range.
Before you pass/fail on a specific gear set:
1. the start ratio (1st, whatever) should work at your push speed, or whatever your clutch will take
2. intermediate ratios that shift below 100 mph relatively unimportant
3. if you have a dyno plot, look at how far down you have good power - that's got to be the recovery point going into 4th and high, even if you must over-speed it a bit (i.e., safe, but no power advantage).
E.g.: Low power below 4,300, max RPM for shift 5,500: needs 78.2% recovery (.78 OD, or 1.28:1 4th gear)

[jacksoni]

From Wikipedia:
Single shift rail unlike the HM290 and 5LM60[2]
Distance between the centerline of the mainshaft and the countershaft is 85mm.[1][7]
Fully synchronized forward and reverse gears.
A two piece aluminum housing with no access plates.
A shift tower mounted shift leaver.
GM RPO codes;
Wide-ratio MG5
Close-ratio M50
Dodge order code DDC
Rated for 300 ft·lbf of torque
Weight 110 lb with oil
Wide Ratio Gearing Option in Dodge 1500 & GM Fullsize Light Trucks:[1]

1 2 3 4 5 R
4.02 2.32 1.40 1.00 0.73 3.55

Close Ratio GM S/T Small Trucks[1] & 2500 Light Duty Dodge Ram Truck Gearing:

1 2 3 4 5 R
3.49 2.16 1.40 1.00 0.73 3.55

Looks like the 3-4-5 gears are same on wide and close ratio. Are there custom gear sets for this? You mentioned Muncie prior- can get T-10 with 1.23 3rd gear. You mentioned sponsored and cost is always an issue.  Richmond 5 speeds can be had with many gear sets, also the high buck stuff like Jerico. We have one with a 1.09 3rd ( but first too high in this trans. Anyway, many gear sets. )

[38flattie]

Heck Jeff, the close ratio Muncie gear ratio is better than this tranny, unless you replace all the gears!

Muncie- 1st. 2.20, 2nd 1.64, 3rd 1.28

If your going to go to a 5 speed, why not have 5th be direct( 1:1), and get less rpm drop across the board?

Takes a lot of power to pull OD! Also, didn't you tell me you trashed two Muncies? I don't believe this tranny is nearly as tough as the Muncie, is it?

I'm going to run the Muncie, because I can't afford the 5 speed, but the 1:1 5 speed would be my first choice.

[Rex Schimmer]

One of the things that make most 5 speeds, with OD, differ from the old Muncie and T10 is the path that the power take through the transmission. Most if not all of the trannys that we look at have a main shaft and a counter shaft (cluster shaft if you are an old fart like me) and the path of the power through the tranny is: In the input shaft,(again "main drive" for us old farts) down to the counter shaft then from the counter shaft back to the main shaft through what ever gear is selected, so you have two sets of gears that are transmitting power. Now the old 3 and 4 speeds when you got to high gear the main shaft was locked to the input shaft and the power went straight through, no gear lashes, very efficient. If your tranny has an over drive 5th then it again requires that the power goes through 2 gear sets, and as each gear set is only at best 98% efficient you will have an over all drive path efficiency of 96%, this does not include the power required to spin the gears through the oil and the bearing friction. Now this makes a 4 speed with a direct connection high gear is at least 4-5% more efficient in top gear than an over drive style gear box. So if some one sells you a 5 or 6 speed gear box and says they can make high gear 1:1 then it is going to have the same efficiency losses as any of the gear boxes that require two gear sets to get power to the output shaft.

Rex

[38flattie]

Rex, that is exactly why I love this board- I'm constantly being educated!

So, not only is this a weaker tranny, but it's less efficient.

Jeff, JMHO, but this sponsorship may actually end up costing you performance, unless I'm missing something here.

[ROCKET HEADS]

Thanks for the input guys.

It is under review.

@ Buddy: I'm going to introduce this build in the "general chat" category soon. I wanted to submit the idea to Dan Warner and theSCTA rules comity first. {your Cadi is looking good}
@ Stan: bigger dagmars = 5.5% increased peek speed.

[jimmy six]

Rocket: All the tranny info is good. My concern with your problem comes from not being able to "recover" as you say on the last shift. Your Buick engine has a long flat torque curve line and I believe your real problem is pushing the "aero" of a 52 Buick thru the air and the 3 miles you are working with when you put it in high gear.

Have you changed your rear gear to help in this? I had this type of problem in the 70's with my 40 Chevrolet with GMC power. I added 10 MPH by changing the gear ratio by .22 letting engine move up in the horsepower band.

I too am against OD's but have one in my roadster at a .96. It's there just in case and and we have actually slowed down twice by using it. There are also very low drag resistant oils you can use when all else fails...............Good Luck