reverse rotation engine
 

Hello, Iknow that this more of a hi-perf site. but I got a lot of advise when building my Scorpion. I have 34 Searay with 2-340hp 454's. I know these are basically truck engines. thinking of replacing with 383 sb's. one engine is reverse rotation. question, if I use the 2-gear setup I assume the cam profile is the same only the rotation and firing order are different. Is this correct? I know about the different seals and possible piston offset. and thanks for any other imput. my goal is better fuel mileage and easier access to engine room About 1200 lbs lighter and 7" narrower on each engine demension

don't waste your time there...thats a heavy boat(had one) and you will have to run the crap out of the small blocks till you kill them...better off building a high torque big blocks...also what year ? after mid 80's the reversed the rotation in the trans(hurth) and engines were the same...you will not gain fuel milage doing this...I have known guys that tried and burned more trying to keep boats like that on plane...if it has prop pockets thats another killer along with sea rays deep V....takes a lot of power to just get those pigs on plane....be better off using a high torque 502

Some 34' Sea Rays use Bravo 1 and Bravo 3 drives - all of those have standard rotation engines.
Double check and make sure your boat actually has a reverse rotation ENGINE, and not two standard rotation engines with one reverse rotation prop.

with a 340hp its a inboard....

Thanks for the info, it's an 86 model. my plan was to use some good aluminum heads and intake a little hotter camshaft and upping the compression ratio with some good performance exhaust. figured I could shave about 1200lbs of weight off also it has closed cooling so I would not have to worry so much about corosion. and yes it is inboard (Velvet drives) maybe I'll go the 502 route hopefully won't have to repower until next year. Just kicking options arround

you would be way disappointed with the small blocks...been tried...you need torque....and tons of it !!!

Not to beat this post to death, but does anyone have the actual torque production specs for big block mercruiser and small mercruiser engines, they list Horsepower but not torque.which is funny to me as I have a Harley Davidson and they list torque production specs and no horsepower specs we always figured it was because they were ashamed as they surely could have done better, the metric bikes usually have better Hp lol

Dog, you better look at all your options before taking out a wrench. R/R motors are a strange beast. The cam is opposite in every way not just spun backward. Also there is only one flat cam available (if it still is) for BBC and it is a lame cam. So unless you plan on making the motor a roller motor and having a custom cam made by Bob you may want to think twice.

I run a 383 and it is great motor in a light boat, I have to go along with the BB thoughts. I had one of my clients switch from 454 330 to 502 415's in a 37 Silverton sedan, the comparison end result was as follows. Stock his cruise was 23kts at 3200 burning an average of 25 gph, the 502's matched the stock speed of 23kts turning 2600. The fuel consumption at the 2600 dropped to 20+, at 3200 it was almost identical to the 454 but speed was 27kts.

The weights of some of Chevy's past engines
Chevy Corvair flat 6........... 300
Chevy Sprint 993cc L4....... 147
Chevy 1.8-2.0 L4.............. 302
Chevy Chevette 1.6 SOHC.. 300
Chevy Vega L4 .................285
Chevy II 153 L4 ................350
Chevy L6 194-250 .............440
Chevy L6 216/235..............630
Chevy L6 216/235............. 615
Chevy V6-90 229, 4.3........ 425
Chevy V6-60 2.8, 3.1......... 350
Chevy small block V8.......... 575 <----------
Chevy LT-5 DOHC 5.7......... 600
Chevy L98 5.7 V8............... 600
Chevy V8 348/409.............. 620
Chevy V8 348/408 ............ 655
Chevy big block V8 ............ 685 <----------
Chevy 454........................ 675
Chevy 427 ZL-1................. 550

Think about 502's with aluminum heads/intakes which will narrow the margin by about 100 lbs per side, your 1200 lbs total reduction between SB & BB just does not ring true.

Thanks for all the responces, I'm convinced. now do they make a reverse rotation 502 and if not how dificult to get done and who would you recomend to purchase complete engine other than Mercruiser(they are proud of their prices)

Dave,
The R/R camshafts used in the marine applications are unlike the standard cam core in a number of respects. The use of a gear to gear setup (without an idler gear which changes the D.O.R. of the final gear) in a RR engine, the crankshaft is turning CCW (reverse) and the camshaft turns CW, or standard rotation. The cam core used for this type of application is designated a standard rotation/reverse fire core, meaning that while the cam is turning standard, the fire is reversed which alters the lobe orientation on the core. The face of the cam (front journal) is machined in a different configuration to accept the upper gear drive. (See photo)

These cores are unique and cannot be adapted from any existing core. After a number of requests for these cores we contracted with one of our vendors last year to produce a short run of roller cores. The process consists of the following steps:

• A bar/spool of aircraft certified, vacuum degassed, 8620 billet>

• Rough in spool on lathe

• Copper plate spool

• Hob gear

• Cut copper

• Rough mill lobes

• Carburize heat treat cores

• Straighten core 2x

• Grind main journals

• Grind lobes
Bob

clockwise (from the flywheel end) is a counter rotation motor. Standard rotation motor is left hand. I think you meant to say

When is velvet drive going to make a tranny that reverses rotation? A standard 71c or 72c that reverses would be so nice..

The merc 383 4v makes 429 lb torque @ 3800 rpm, you can get them for under 8K. Plug & Play.

key right there is 3800 RPM.... glad Bob chined in...he can do a reverse rotation cam for you...I went thru all this a few years ago..wise I would have bought to of the high torque 502's GM makes, and redid myself to marine engines and had Bob do a reverse cam for one...and yes if they did a 72c reverse would be great !!!!

502HT crate engine =512FT lbs at 2800RPM.

I know nothing about cruisers, but curious.....How hard would it be to adapt to a twin disc transmission? To reverse the rotation of prop, but be able to run two standard rotation engines?

The reference to CW and CCW, in the post, was intended to address the DOR of the crankshaft and camshaft at the drive interface, or gear stack (engine front) to illustrate the cam and crank rotate in opposite directions as compared to a chain/sprocket drive where the cam and crank rotate in the same direction.

When referencing the DOR of the crankshaft during operation, standard rotation or reverse rotation are terms which remain accurate from both the front and rear of engine point of reference. Hope that clarifies the post.
Bob

You can spin them either way by just flipping the pump over but output shaft spin is always determined buy the direction the input shaft is spinning.

wrong !!! you can on a hurth, not 71 or 72, the reverse clutch back is not the same as forward one...I went thru all this when I repowered my gibson...

Yes, unfortunately in the velvet drives that is all you can do.

What are the dimensions on the Hurth? Same as the VelvetDrive? What model?

Thanks

Just for info, does anyone know what the torque production figure at what rpm for the 454/340 I cannot find any figures anywhere on the net?

Or a V-Drive (which could reverse in the V Drive and not in the motor itself.

I still haven't seen the model of boat mentioned, which would eliminate a bunch of head scratching. Is it a Sundancer, an Express, a Bridge boat, a Center console, an Aft Cabin ?? Knowing this would help.

And some reverse rotation motors use a STANDARD rotation cam and a gear drive instead of a cam chain. This lets you use a standard distributor and standard oil pump. If you reverse your own motor, make sure the pistons are swapped to accomodate the backwards thrust angle, water pump is different. Alternator fan is different, starter is different (unless you use a reverse mount bellhousing). Raw pump is plumbed differently.

MC

the V drives used in these boats are NOT reversable...been down that road...V drives have nothing to do with prop direction...simple gear to gear...yes early reverse rotation engines used the gear drive set up, but after genVI engines they no longer do that...

Let me summarize

Inline Velvet drives (the 71 & 72 series – output is in line with input) will not change output rotation however they can be used on both standard and opposite rotation engines by changing pump mounting. Same thing for the old style Velvet V drives. However the V drives come in chain and gear versions, so it is possible to use a chain on one side and a gear on the other to reverse output. And there are a couple of the inline ratios where the output is opposite the input.

New Velvet 5000 Liberty series, Hurth & ZF all allow the reversal of the output rotation but can only be used on standard rotation engines. They are available in both down-angle (the output is offset and at an angle) and v drive.

The cam spins the normal way but the lobes on the cam are lined up different and unless you are going to use a roller there is only 1 cam available in RR in flat tappet and no others are being made.

There is no difference in pistons but if you are going to swap a motor over you do need to resurface the crank along with change the rear and front cover seals. If not oil will be pumped out of the motor.

No difference in the water pump. The veins on the wheel are straight and it don't matter what way it spins and the ALT fan also makes no difference what way it spins.

True and the raw water pump is as simple as putting the input hose on the out put side and vice versa.

I spent a year researching a RR motors and what could be done with them. My advice, run away as fast as you can.

It is an Express cruiser with straight velvet drives

more than likely have 72c trans...just work on the reverse engine, If I had it to do over I would but the high torque 502 truck engines strait from chevy have Bob match up a reverse roller cam, you will have to use the special reverse built GM EST dist from crusader with that...but should work very well in that boat...

Cam should spin the same way as normal. It's the crank that spins backward. That's why there is only 2 gears and not 2 gears and a chain timing set. The dist turns the same way you just put the plugs wires on it backward. If you spin the cam backward not only would you need a custom dist but you would also need a custom oil pump and unless someone builds it for you, you are not going to find them.

I have a reverse rotation Crane 741 cam and special cut distributor gear. This gear will mount on any .500 distributor shaft.
This drives the oil pump the same way. Yes the same way!
This works with a standard timing chain.
The firing order is just opposite.
This will make the Crank run in the reverse direction
I have never had to change the rear main seal. Yes same seal!
The pistons were the same exact Ross part number
for the counter as normal rotation.

I have detailed threads posted years ago on all this.

if anyone could use the cam just pm me.
KR

I don't know what the big hangup here about a reverse rotation engine is. They been around for DECADES. I know a few guys who were running 1000+hp reverse rotation engines in 39 Ocean express cats, 32 hustlers, with arneson 1600 series drives. Not to mention a million cruisers are still running reverse rotation engines.

http://www.marineengines4less.com/bu...neengines.html type ''502'' in the search box. New GM base engine, avail in reverse rotation also.

Another
http://affordablemarine.com/gm.htm

another
http://wolfiesenterprises.com/8200base.htm

another
http://www.miamimarina.com/frontend/...1D8A?id=217561

thats the old way they did with gear to gear, not with the gen VI engines, they use a timing chain, cam has a reverse cut gear along with the cam, now this is where the problems come up...when you pull down on the dist shaft by reversing it...there is no thrust load bushing to absorb the load..kills std dist in a very short time !!! I did 4 before I traced down the "special made with extra load bearing" EST dist..the old gear to gear to me was a better deal but was told the wider gears would not clear the newer timing covers.

What about the oil pump that runs off the dist also?

Anyone want to take a guess which is the counter?

http://i1293.photobucket.com/albums/...pse9c622d8.jpg

it continues to rotate in the normal direction.;)

the cam is running in reverse, but with the reverse cut gears on cam & dist, that runs correctly to make the oil pump work...

yes my boy!

http://i1293.photobucket.com/albums/...psfe341bc9.jpg

there will be a test on this later