Page 1 of 3 123 LastLast
Results 1 to 20 of 56
  1. #1
    CB750 Enthusiast KIRBY's Avatar
    Join Date
    Oct 2019
    Location
    Abilene, Texas
    Posts
    46

    Can a stock CB 750 bottom end handle an increase i power of 25%

    Will the transmission need beefing up?

  2. #2
    CB750 Guru amc49's Avatar
    Join Date
    Sep 2015
    Location
    Fort Worth TX.
    Posts
    2,598
    SOHC or DOHC? More than one kind of CB750...............

  3. #3
    CB750 Enthusiast KIRBY's Avatar
    Join Date
    Oct 2019
    Location
    Abilene, Texas
    Posts
    46
    Quote Originally Posted by amc49 View Post
    SOHC or DOHC? More than one kind of CB750...............
    Probably the SOHC. I'm still in the designing phase. I'm thinking of a reverse trike with two CB 750 motors tied together with a transfer shaft across the front to make essentially a 1500 cc straight eight, and the design of the chainsets will split the power, sometimes sending 120%of stock power through one engine while routing 80% through the other.

    This will become more clear in the diagrams to follow
    The fourth diagram is the overall layout.
    The second diagrams are more detailed.

    "A" shows the reverse differential I've devised to combine the power from the two fours.
    "C" is "A" with the final drive sprocket/bevel gear carrier "B" installed.
    "D" is "C" with the chains installed.
    When both motors' (which are locked together) transmissions are in the same gears (First/First, Second/Second, etc...), the center sprocket turns at the same RPM.
    When one motor's transmission is in another gear from the other motor's transmission (First/Second, for instance), the bevel gears in the center sprocket turn, and the center sprocket averages the two different RPMs of the left and right sprockets.
    These resulting ratios are seen in "E" in the column marked "Ratio".
    I have shown 9 close ratio combinations and their resulting ratios.
    This setup is essentially like putting in a gear between First and Second, Second and Third, Third and Fourth, and Fourth and Fifth.
    Shifting is simple, starting with both transmissions in First (1/1), and shifting one to Second (1/2), then the next shift, putting the other in Second (2/2), and own up (2/3, 3/3, 3/4, 4/4, 4/5, and finally 5/5).

    The differential will cause the power splits you see in"E" under "Left" and"Right". The biggest power shift is "1/2" causing 60% of the overall power (or 120% of factory power) to be routed through the left motor's transmission, while only 40% of the overall power (80% of factory power) goes through the right motor's transmission.

    This is the reason I ask if a CB 750' bottom end and transmission can handle the increased power.
    Last edited by KIRBY; 10-07-2019 at 03:58 AM.

  4. #4
    CB750 Enthusiast KIRBY's Avatar
    Join Date
    Oct 2019
    Location
    Abilene, Texas
    Posts
    46
    Click image for larger version. 

Name:	Twin CB 750 A.JPG 
Views:	11 
Size:	18.1 KB 
ID:	9147Click image for larger version. 

Name:	Twin CB 750 B and C.JPG 
Views:	9 
Size:	36.0 KB 
ID:	9148Click image for larger version. 

Name:	Twin CB 750 D E F and G.JPG 
Views:	13 
Size:	85.9 KB 
ID:	9149Click image for larger version. 

Name:	Twin CB 750 System.JPG 
Views:	7 
Size:	24.4 KB 
ID:	9150

  5. #5
    Moderator dirtdigger's Avatar
    Join Date
    Feb 2012
    Location
    Black Hawk SD
    Posts
    2,849
    The stock primary chains are your weak point. They last long time in stock form but wear quickly with increased power, why there are heavy duty aftermarket primary chains, even then the chains are still the weak point.

  6. #6
    CB750 Enthusiast KIRBY's Avatar
    Join Date
    Oct 2019
    Location
    Abilene, Texas
    Posts
    46
    Quote Originally Posted by dirtdigger View Post
    even then the chains are still the weak point.
    Thank you. The increased load would only be during the times when one transmission is in the next gear from the other. The trike can be used in matching gears (1/1, 2/2, 3/3, 4/4, 5/5) when quicker acceleration is not needed.
    Isn't the same transmission used with the CB 900 and CB 1100? Do builders have the breakage problems when they install oversized cylinders? I'm new to this.

  7. #7
    CB750 Enthusiast KIRBY's Avatar
    Join Date
    Oct 2019
    Location
    Abilene, Texas
    Posts
    46
    The heart of this system is the chain differential, giving the extra four rear wheel ratios. Is my thinking sound on this? Do you see a flaw?

  8. #8
    CB750 Enthusiast KIRBY's Avatar
    Join Date
    Oct 2019
    Location
    Abilene, Texas
    Posts
    46
    I really want the two motors to stay in phase with each other (well, 90 degrees out of phase with each other, so there is a firing every 90 degrees). Is there another way, besides joining the two mechanically at the crankshafts?

  9. #9
    Moderator dirtdigger's Avatar
    Join Date
    Feb 2012
    Location
    Black Hawk SD
    Posts
    2,849
    Quote Originally Posted by KIRBY View Post
    Isn't the same transmission used with the CB 900 and CB 1100? Do builders have the breakage problems when they install oversized cylinders? I'm new to this.
    No the sohc motor is completely different from the dohc motor. Yes breakage problems are still an issue...especially with big bores and racing/hard riding applications. The crank and cases can take large boosts in power but the transmission and primary chains are the weak points. Mostly the primary chains. They will run for a while with large power but its a ticking time bomb.

  10. #10
    CB750 Enthusiast KIRBY's Avatar
    Join Date
    Oct 2019
    Location
    Abilene, Texas
    Posts
    46
    How can I reduce the power of the motors to 55HP? I really want the straight eight idea, with it's four firings per revolution (every 90 degrees the howl at 9,000 RPM would sound like 18,000 RPM on a single four), and the 9 speed close ratio "virtual transmission". The trike doesn't really need 134 HP, and if the motors were only 55 HP each, the 120%/80% power split would only be 66HP/44HP, which stresses the first motor no more than stock.

  11. #11
    CB750 Guru amc49's Avatar
    Join Date
    Sep 2015
    Location
    Fort Worth TX.
    Posts
    2,598
    Whew..........where to start...............OK, the setup as proposed there cannot and never will work ever.

    A given, I seem to be seeing bearing pillow blocks in pics A and C between the outer individual drive sprockets and the center 'main' output sprocket.

    You will likely explode gears before the final vehicle even moves an inch.

    Why?

    You absolutely cannot link two engines together to stay in phase while expecting them to run at different rpms (in different gears from each other), it's impossible. You are then in two gears at once and what makes transmissions explode instantly at the racetrack, you cannot even be at idle speed and do it.

    You cannot either tie two different power levels/loads into the opposite ends of a differential spider setup to both work at different percentages like a true car differential does, the one engine in one gear will violently affect the other one in the other not same gear because they are locked together in the spider setup, never mind the overlaid transfer shaft from engine to engine that blows them up too. The difference in gearing would be modified as well by throttle levels on the two engines, they CANNOT be the same, they would then interfere even more.

    A differential splits power but it must match side for side and power cannot be applied INTO the OUTPUT sides, it CAN come out of two sides having been split though.

    More.............I've barely started.

    The two engines MUST switch gears electronically as any period of time while one is being shifted unloads the side gear on that side, the vehicle stops pulling instantly when the spiders then spin and the unloaded transmission goes apesh-t like with a missed shift. It will be very hard on clutches.

    Study a standard car differential....................why is it the main drive gears are so big and the spiders are so much smaller??? Because the main big gears carry the power and torque, putting that backwards through the unit then loads all that power onto the spiders instead and they break very quickly. Spiders are sized to be able to coast adjust, they only get used at power off cornering, they have to take little power and why they are so small. Make them the hardest loaded part and that changes instantly.

    I have to ask why does one need that many speeds if they are talking about limiting the overall power? A whopping better idea would be to use a first gen 900C engine that has the OEM 2 speed subtransmission to have 10 gears accessible at all times and with solid reliability. Then simply provide power takeoff off of a stock engine that works SO much easier.

    FYI, use a 4 cylinder header that pairs 1-4 and 2-3 in dual exhausts and you have the same sound as your 8 cylinder does.
    Last edited by amc49; 10-08-2019 at 01:24 AM.

  12. #12
    CB750 Enthusiast KIRBY's Avatar
    Join Date
    Oct 2019
    Location
    Abilene, Texas
    Posts
    46
    Quote Originally Posted by amc49 View Post
    Whew..........where to start...............OK, the setup as proposed there cannot and never will work ever.

    A given, I seem to be seeing bearing pillow blocks in pics A and C between the outer individual drive sprockets and the center 'main' output sprocket.
    Yes, those are bearing blocks, but the two outer sprockets are on separate shafts. The center output sprocket rides between the large bevel gears of a differential, and is not solidly attached to either half shafts.

    Quote Originally Posted by amc49 View Post
    You absolutely cannot link two engines together to stay in phase while expecting them to run at different rpms (in different gears from each other), it's impossible. You are then in two gears at once and what makes transmissions explode instantly at the racetrack, you cannot even be at idle speed and do it.
    The engines run at the same speed, 90 degrees out of phase from each other. when one transmission is in a different gear from the other, the differential spider carrying the center sprocket will rotate at the speed which is the average of the two input sprockets.

    Quote Originally Posted by amc49 View Post
    You cannot either tie two different power levels/loads into the opposite ends of a differential spider setup to both work at different percentages like a true car differential does, the one engine in one gear will violently affect the other one in the other not same gear because they are locked together in the spider setup,
    No, they are not locked together at the spider. Each has it's own shaft which ends at it's own large bevel gear. The center output sprocket is attached to the four small bevel gears, and rotates with them.

  13. #13
    CB750 Enthusiast KIRBY's Avatar
    Join Date
    Oct 2019
    Location
    Abilene, Texas
    Posts
    46
    Quote Originally Posted by amc49 View Post
    A differential splits power but it must match side for side and power cannot be applied INTO the OUTPUT sides, it CAN come out of two sides having been split though.
    have you tried it? where is it written?


    Quote Originally Posted by amc49 View Post
    The two engines MUST switch gears electronically as any period of time while one is being shifted unloads the side gear on that side, the vehicle stops pulling instantly when the spiders then spin and the unloaded transmission goes apesh-t like with a missed shift. It will be very hard on clutches.
    Yes, I plan to use paddle shifters, and not power shift.

    Quote Originally Posted by amc49 View Post
    Study a standard car differential....................why is it the main drive gears are so big and the spiders are so much smaller??? Because the main big gears carry the power and torque, putting that backwards through the unit then loads all that power onto the spiders instead and they break very quickly. Spiders are sized to be able to coast adjust, they only get used at power off cornering, they have to take little power and why they are so small. Make them the hardest loaded part and that changes instantly.
    That may be a good point
    Thanks for your advice.

  14. #14
    CB750 Enthusiast KIRBY's Avatar
    Join Date
    Oct 2019
    Location
    Abilene, Texas
    Posts
    46
    OK, I believe I addressed all your points except the differential. I will redesign it for greater lightness, and call it "The input averaging unit." Thanks for pointing out the weakness of the traditional bevel gear differential. I will try to draw more detail in so my design is more clear. To answer your question about the 900C this exercise is a novelty concept. I can phase the two engines 45 degrees apart and have the sound of a 90 degree V8.
    The problem with unloading one side will be solved with servos on both clutches, set to engage both clutches whenever either transmission is paddle shifted. There will be no time when one transmission is hooked up alone to the input averaging unit, therefor, no unloading problem. Thank you for bringing that up.

    Why not just use a 900C? I don't like the ratios. 3H (6.374) is too close to 4L (6.14), 5L (5.26) is actually a downshift from 4H (5.253), giving effectively 8 usable ratios, and some shifts require an upshift of the transmission AND a downshift of the sub transmission. 1H to 2L is wider (125.5%) than the widest shift in my design (1/2 to 2/2 - 123%) The shift width of my design is:119%, 123%, 112%, 114%, 110%, 111%, 108%, and 108%, compared tothe CB900C's 10 shift width: 117%, 125%, 117%, 109%, 117%, 104%, 117%, and 99.9%.

  15. #15
    CB750 Guru amc49's Avatar
    Join Date
    Sep 2015
    Location
    Fort Worth TX.
    Posts
    2,598
    'You absolutely cannot link two engines together to stay in phase while expecting them to run at different rpms (in different gears from each other), it's impossible. You are then in two gears at once and what makes transmissions explode instantly at the racetrack, you cannot even be at idle speed and do it.'

    You are right, I was not looking at that aspect correctly.

    The engines may be running at same rpm though, but they will NOT be happy, the differing required throttle amounts will make them act funny. Similar to when carbs are not synced, the engine acts weird. The two power levels argue with each other just like one cylinder opening carb faster does to the slower one. With a setup like that you have to drive everywhere with throttle mainly fully open or close to it, there is no fine low throttle ability and the driveability issue. Drive a mis-synced engine slowly and you will know what I'm talking about, it's ugly.

    I see no advantage to all this, the vehicle should be light enough to not need the extra ratios anyway. Unnecessary complication is what the Japanese do like the latest Nissan V variable compression engine that could have simply used the turbo more to decrease the engine parts by like 50% and now they are wearing out (TWO crankshafts and sets of rods in essence) faster than lightning. The unnecessary parts require like 40 more hp. just to overcome the parasitic drag too. Why we could use much lighter and smaller AMC V-8 engines to make cars that outpulled much bigger Mopar 426 and 440 engines in high gear drag racing. The extra reciprocating/rotating weight in those huge components required up to 100 more hp. to get them to 7000 rpm. Horsepower that could be put to the wheels instead.

    You actually do NOT want gear ratios evenly spaced either. You space them wider in lower gears and they should get closer together in higher gears, the difference in resistance to wind at slow and fast speeds and the dropoff in engine efficiency in higher gears and the increase of tire resistance. Engines tend to overrun easier in the low gears, you run them deeper in rpm in 1 and 2 and then begin to bring the gear ratios closer together the faster the vehicle gets. 4 to 5 should almost be the same ratio.

    You may likely be better served just ignition killing the engines at shift, simpler than servos on clutch packs.

    I suspect (the above) the differing loads issue is going to present driveability issues, even engine timing is going to be an issue, advancing one engine will be getting ahead of the other to promote preignition. They are tied together but not making the same degree of power, the same thing an engine wildly out of tune does. The engine running slower will be lugging or trying to and engine damage on these to do that. So you will lose some rpm range flexibility too. In normal use they go through that range so fast there is no harm but your setup will likely be making one engine stay there for a while.

    In the main, there is simply no advantage to all that complexity other than 'can it be done'.

    Of course, yours and do as you will.................

  16. #16
    CB750 Guru amc49's Avatar
    Join Date
    Sep 2015
    Location
    Fort Worth TX.
    Posts
    2,598
    Rethought it, it cannot work, you cannot have two variable INPUTS on a planetary with engines that are locked together. The smaller planets are positively mounted, when one side gear moves the other has to in the opposite direction the EXACT SAME AMOUNT to get any reduction. ANY planet movement itself is being in two gears at the same time, the positive locking together of the engines disagrees by creating a second different input. Can't work as proposed.

    'The center output sprocket rides between the large bevel gears of a differential, and is not solidly attached to either half shafts.'

    Actually it is or the car wouldn't move. Standard differential construction if you reverse the power flow.

    It works in a differential because the two tires are not geared together, they can slip equally and separately to equal the total distance traveled. Try pushing a race car with a spool rear end and the diff gone, you will know instantly why it can't work. With the spiders gone the two tires argue in the same way, the car acts like it's in two gears at one time, the tires literally jump off the ground due to the gearing lockup. The tire ratio is not the same as the other tire ratio.

    Again, yours and do what you will.
    Last edited by amc49; 10-08-2019 at 10:25 PM.

  17. #17
    CB750 Enthusiast KIRBY's Avatar
    Join Date
    Oct 2019
    Location
    Abilene, Texas
    Posts
    46
    amc, I appreciate you and Digger helping me think this out. I'm a novice, and I'm trying to understand all the ramifications of my design. I'd like to continue this after a night's sleep. Thank you, again.

  18. #18
    CB750 Enthusiast KIRBY's Avatar
    Join Date
    Oct 2019
    Location
    Abilene, Texas
    Posts
    46
    Let me address the differential situation.
    Let's use spur gears, easier to follow:

    In case one, both "A" and "C" are driven the same direction at the same RPM. "B" follows in the same direction at the same RPM, as the spur gears do not rotate within their bearings.

    In case Two, "A" is driven at twice the RPM of "C", the spur gears rotate within their bearings in the opposite direction, the teeth following the teeth on the hubs of "A" and "C". "B" rotates in the direction of "A" and "C", but at an RPM half between them (1,500 RPM). The beauty of this setup is that all the motion is in one plain, (no 90 degree loss)

    Th drive sprocket would bolt on "B". Where is the flaw?Click image for larger version. 

Name:	Spur Diff 1000 1000.JPG 
Views:	8 
Size:	29.7 KB 
ID:	9151Click image for larger version. 

Name:	Spur Diff 1000 2000.JPG 
Views:	5 
Size:	30.3 KB 
ID:	9152
    Last edited by KIRBY; 10-09-2019 at 02:00 PM.

  19. #19
    CB750 Guru amc49's Avatar
    Join Date
    Sep 2015
    Location
    Fort Worth TX.
    Posts
    2,598
    The flaw is that you cannot power both sides positively at the same time at different speeds at all. All planetaries have a ratio depending on the tooth count, that ratio to work splits the rotation in the small gears to BOTH sides equally, then you have a gear reduction or overdrive depending on where power applies. That is the planet gear ratio. You are with your idea creating different ratios with every gear that cannot work as the two opposite opposing planets MUST turn equally, you cannot turn one side 10 turn and the other 2 turns as in your example. You are laying a different ratio on top of that, making being in two gears at once.

    The setup works in a car because both tires are unpowered and they give exactly opposite of each other when car turns a corner. One tire turns say 13% and the other 87% to add to 100%, you cannot change that ratio as it is physically there to interfere with any other you may want to lay over it. The 100% means that one planet MUST turn the exact same amount as the other, it cannot do partial amounts which you are asking it to do. Both your engines are going in same gear it's OK, but change one to be in another gear at 15% more rpm and you are saying the planet on one side must turn at a 1.00 ratio and the other side 1.15, that cannot happen. Your 'slip' forward or back depends on the one turn to one turn side to side staying there to make the planetary physically work. The one turn to one turn thing is what negates ratio changing based on the planets being there, the ratio then depends on the input and output gears only in a ratio calculation, the planet gear counts are dropped as they are assumed to be 1:1. When you lay your idea on top of that you are saying the planet gearing must change when it physically cannot, the gears are locked together in a one on one basis.

    The planet gears DO move in very small amounts, you can get even a hundredth of a turn there but if it is not the same travel as your other engine wants to slow it down or speed it up to then you have two different gear ratios fighting each other.

    I know it's difficult to grasp that, I had trouble myself and I build ATX using planetaries (including another sun gear to complicate things even worse) all day long. I had to take ten minutes trying to figure out why it wouldn't work myself. You have to build one and then rotate it to tell what I'm talking about, turn it to get the one to one thing and easy but then turn one side while NOT turning the other as much to simulate a slightly different gear input and it instantly locks up, it cannot be done. The ratio from side to side of a planetary is ALWAYS 1:1 in both directions, it has to be to even physically work.

  20. #20
    CB750 Enthusiast KIRBY's Avatar
    Join Date
    Oct 2019
    Location
    Abilene, Texas
    Posts
    46
    I don't see that. Maybe I'll have to build a model, and power the two sides with hand drills to test it out. You did notice that the spur gears were mounted in bearings, and can rotate freely (when not meshed with the side gears)

Page 1 of 3 123 LastLast

Similar Threads

  1. Does anyone stock 750 DOHC cylinder studs?
    By W_n_R_n in forum Engine / Exhaust
    Replies: 2
    Last Post: 06-10-2019, 11:47 AM
  2. No low End Power other effects of a vacuum leak?
    By tdubsy in forum Carburetors / Fuel
    Replies: 1
    Last Post: 05-19-2018, 02:57 PM
  3. No top end power
    By Chuck Hahn in forum Engine / Exhaust
    Replies: 11
    Last Post: 02-06-2018, 01:45 AM
  4. Nighthawk 750 Fuel Starved at top end
    By SteelerDan in forum Carburetors / Fuel
    Replies: 8
    Last Post: 12-20-2017, 07:23 AM
  5. 2002 kawasaki 750 ninja front end on a 76 cb750
    By shaunbe in forum Frame / Suspension
    Replies: 4
    Last Post: 06-11-2017, 10:02 PM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •