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Hi Guys...Maybe its just the way the shaft angle looks coming out of the stuffing box, but the guy who is going to install my engines thinks that I will need down angle gears for my 496 Strokers?? Didn't most of these boats come with straight Velvet Drive gears?? The ZF 63As are certainly much shorter and lighter than the Velvets, but not cheap...Any advice would be appreciated...Thanks, John

my 454's had straight drives, velvet i think

Had three sets of Merc Cruiser 454’s in the EarleyBird over the years. Transmissions were Borg Warner Velvet Drives. Upgraded to 1 3/8” Shafts turning 18 x 19 3 blades. All History now.

Straight transmissions, motors are mounted at an angle to meet coupling with wedges on the carbs.

my personal opinion is ALL the yesteryear 61,62,63 series velvet drives will not be rated for 496" at 525 pounds of torque. you will need to up- grade to ZF 63 A . they have an 8 degree down angle which will allow you to LOWER the engines and place further back toward cockpit. Carl will explain all about the huge advantages of stability.

John,
My1997 454 TBFI Mercruisers had 63A ZF Hurth 8 degree down angle 1:5:1 gears the coupling was located at the bulkhead aft of the motors. My shafts were 1-1/4" Monel shafts with a 96" shaft length with intermediate strut bearings just aft of the shaft log exit, the main struts were low profile measuring 9-1/2" from the hull bottom to the center of the strut barrel. You have to have the 63A Hurths for the torque that the 454 /496 CID motors produce. Don't waste your time with the older 71 series Borg Warner trannies, they will destruct very quickly.
Pete Fallon

John

Go with the down angle otherwise you will have the engine that angled down. My father always ran our with an extra quart of oil in them since he was always afraid that the forward bearing would starve for oil.

By the way, never had an issue doing that.

I would follow everyone's advice and go down angle ZF's.

Thanks for all the excellent feedback...ZF 63A it is 8 degree down!

thanks for the back -up Pete your "spot on". we all know manufacturers sometimes make quick fix gadgets that don`t do the job,An case in point is using a wedge under the carburetor in a inboard boat engine installation at a acute angle.What makes you think cylinder 1 and opposing 2 are going to get the same fuel as 7 & 8 DUH !!!! BAD,BAD DESIGN. The 8 degree down angle gears will help out in more ways than one.

Uh OH Bad News.....Told that I cannot use ZF 63As on Reverse Rotation Engines.....The stats say that Velvet 72C Gears will handle the Strokers...Thoughts????

ok listen up rather confusing. ZF has no dedicated forward and reverse move the shift lever one way and output shaft moves clockwise and move shift lever opposite direction and output moves counterclockwise. SO buy ZF- 220 IRM then bring 33C shift cables down to gears turn front shaft and watch OUTPUT shaft you want starboard to turn clockwise and port to turn counterclockwise. i hope i have not confused you .just think the transmission does not have a forward and reverse like a car the shift lever can go either way.
the added benefit is the ZF- IRM 220A will have a 10 degree down angle ------------nice

What Bob said. Don't be concerned about the gear ratios in 'forward' vs 'reverse'. Yes, they will be SLIGHTLY different. Yes, one will be slightly louder than the other at dead idle. Not a problem.

the 72c-BW velvet drive will not hold up to 525 pounds of torque .what i should have said in the above post is ZF-220 IRM ---clockwise and counter clockwise depending which direction you push shift lever,make sure you check BEFORE hand you do not want to PUSH shift lever for forward you have to PULL with 33 C red cable, no cheap knock offs.

I am pretty sure John is correct.

I believe standard ZF gears need Standard Rotation from the Motor going into the transmissions input shaft.

With standard rotation going in...the transmission runs equally well up to full power in either output direction.

John has counter rotating motors...


Think back to the velvet drive where you had to flip the pump going from a LH motor to a RH motor.
It accepted input in either direction, but only spun in direction of the motor up to full power.

Now almost all motor are standard rotating

carl are you saying john had a 496 big block built in counter rotating ? i have no knowledge of a roller cam or any performance camshaft for a counter rotation big block.that is really old school i doubt any engine builder would recommend one.

bob lico wrote:carl are you saying john had a 496 big block built in counter rotating ?

that is really old school i doubt any engine builder would recommend one.

Bob- I'm not saying anything. That is what I understood when John said the ZF could not be used on Reverse Rotation Engines.

Maybe they were built standard and John didn't realize...or maybe he just went "custom" counter rotating...OR we ask John to verify.

If it is reverse, yes its old school and he'll need an old school solution...or a new cam...


...or less reduction to really spin those props. Hmm that I guess is one of the the old school solutions.

John Nardi wrote:Uh OH Bad News.....Told that I cannot use ZF 63As on Reverse Rotation Engines .....The stats say that Velvet 72C Gears will handle the Strokers...Thoughts????

John- I guess the first thought is...are you sure your motors were built counter rotating?

If so...is changing that on the table?

Whats cost of installing and loosing the trans compared to changing over.
Or cost to find a trans that will handle. I think ZF used to have a reverse input package.
Or Less to No reduction - - means smaller wheel, less pitch spinning faster...less efficient but gets you on the water.

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