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Author Topic: Honda CA77 Dream to do the ton?  (Read 316 times)

Offline Scooter trash

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Honda CA77 Dream to do the ton?
« on: Nov 23, 2017, 16:34:45 »
I have a set of CB77 cams, just need to rotate one notch back to work for 360 firing order. Some porting and polishing, rejetting, and some high dome Italy made pistons. I have to run cold plugs, pull about 5 degrees timing, and make sure the squish band is at least .050". It should make about 27 hp. I noticed the Dream cams have more lift for torque, but nowhere near the overlay of the Super Hawk cams.
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Offline stroker crazy

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Re: Honda CA77 Dream to do the ton?
« Reply #1 on: Nov 23, 2017, 16:45:55 »
Subscribed!

Crazy
“Ride like the Wind” W.H.

Offline teazer

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Re: Honda CA77 Dream to do the ton?
« Reply #2 on: Nov 23, 2017, 20:17:14 »
Don't rev the motor too hard with those pistons.. They tend to break up.   You can machine a ton off the head to raise compression with lower crown pistons.  With High crown pistons add in a few MORE degrees of advance - start at say 42 BTDC.  Seriously.  You would be surprised how much advance they need with lump pistons.  With methanol I have run 52 degrees of advance....

Lighten the valve gear to let it rev and you can probably use a slightly larger carb without flooding it and an ignition upgrade - GL1000 Dyna on the cam is simplest, but there are options. Lots of cam options but keep it simple - it would be a shame to lose its easygoing nature.  And there are two different splines - shallow and deep.  Use the matching cam sprocket/advancer.  Stock cam lift i.e. nose less base= 5.5mm inlet and 4.45 exhaust on a CB77.  I can't find C72 dimensions in my old files.  I used to have piles of cam cores after I brought a lot from Read Titan back in the day when I built and raced CB77s.

Think of the bike as a grown up CB92....

Not a c92 that grew old and fat.. Anything is possible.

Offline Scooter trash

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Re: Honda CA77 Dream to do the ton?
« Reply #3 on: Nov 24, 2017, 13:31:17 »
I've never really been a fan of high dome pistons, getting high revs seems impossible. I've ran these pistons before at high revs, but one cylinder burned a hole in the top indicating pre ignition or too much advance. Even with stock pistons, advanced ignition timing will burn a hole through. If you look at modern performance pistons, they are flat as a pancake. Exhaust and intake gasses, hate mountain tops.
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Offline teazer

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Re: Honda CA77 Dream to do the ton?
« Reply #4 on: Nov 24, 2017, 15:39:38 »
That came from the obsession with Hemi heads which do offer large vales relative to other options and the lowest volume:surface area.  Unfortunately they also are inherently low compression unless the piston has a high dome.  Fine for low compression low rpm motors, but a high dome makes flame propagation a slow and inefficient process. That's why on my CB77 race motors, I machine "a lot" off the heads and use lower dome pistons to get the smallest possible total surface area at the same time as highest compression (we're still talking small numbers).

I use modified CB350 pistons for years because I could machine them to get a decent squish band, lower the barrels and then machine a matching squish band into the head.  Those pistons have thick heavy rings which are an impediment to high revs but on a lower revving motor, they work fine. Unfortunately that is the path with the most amount of work and cost, but hey, can't have cheap, fast and quality can we?

Those motors need a serious amount of spark advance with high domes and that speaks volumes about the inefficiency of that design. Go with lower domes, machine the head and pistons if necessary to get an angled squish band and reasonable compression and run much less advance.

They have a 360 degree crank, so a siamese inlet is not a problem, but the inlet tracst do need to be opened up a little and try a CB750 carb.  Same slide diameter as a CB77 carb but taller oval shape, so the same at low throttle openings and bigger at WOT.

Offline Scooter trash

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Re: Honda CA77 Dream to do the ton?
« Reply #5 on: Nov 24, 2017, 19:20:03 »
Teazer, do you know how much hp you wound up with?
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Offline teazer

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Re: Honda CA77 Dream to do the ton?
« Reply #6 on: Nov 24, 2017, 20:57:50 »
I did not dyno test it after the first build, but I would estimate somewhere around 42-45. That was on a CB77 at 350cc not a stock CA77, but that's a long way up from stock.  By comparison, we tested a CB160 at 11hp and ended up around 21hp from 175cc. Those are dynojet HP, so it's anyone's guess what real hp was.  :-)


Just a thought, but do you really want to do the ton with those brakes and odd leading link front suspension?  Just thought I'd ask..
« Last Edit: Nov 24, 2017, 21:05:16 by teazer »