540cc Honda 360 Engine

cyclhed

Member
This is a project monster motor that my father is building. Here are the details:
360 case bored to accept CB500 Twin crank 64.8mm stroke, the 360 case was bored to accept the center main bearings, also
clearance for rods and flywheels to swing.
Cylinder block sleeved with KZ1100 sleeves with 72.5mm bore
KZ1100 pistons 72.5mm
3/8" cylinder spacer to get to 0 deck
KZ1000 30T cam sprocket to match crank
Stock head with 2mm oversize titanium intake valves
Intake ports raised 1/2" by welding
Exhaust seats bored 1mm but with stock valves

More to come as it progresses.
 

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legendary_rider

Jump in with both feet.
I thought I was nuts doing the mods on my motor. You make me feel better. Misery loves company though. I'd like to hear of issues that made him want to pull his hair out too. lol. Amazing job though bud.
 

teazer

Well-Known Member
DTT BOTM WINNER
Nice little project there. I would have used 1mm O/S intakes and 1mm o/s exhaust valves and decked more off the head, but that's just me. I would also have left the intake ports and raised the exhaust ports to improve the exhaust flow.

But it ain't my project, so I don't get a vote. Will be interesting to see how it turns out.
 

frogman

'74 CB360, '71 CB450, '75 CB550SS
Just when I thought crazy pj was nutty, then this comes along, DO PLEASE document as much as you can. We will all watch and comment.

Thoughts might be to use 450 pistons if they work and/or check out the aftermarket options for cb500t pistons as they do exist and are better all around then stock. Might cost more but will work better.
 
S

smvirili

Guest
what the fuck is this. :eek:
honestly don't think i can wait to hear it. get your father to work double time.
shiiiieeeeeet
 

Sonreir

Oregon
DTT SUPPORTER
I second the larger exhaust valve/port idea. The intake flow on the 360 head (for a 356cc motor, anyway) is already too big. The exhaust ports are a problem even at that displacement though. If your cam decision isn't yet finalized and you have no plans to enlarge the exhaust ports, you're going to want to see some high lift numbers.
 

Nebr_Rex

Member
Don't want to rain on your parade but,the second pic shows a stock pre '81 KZ1000 piston.
Bore size would be 70mm,factory offered oversizes in .5 steps,I never seen a 2.5 factory oversize.
Aftermarket goes oversized by whole mm,ie. 71,72 etc. .
You can order Wiseco pistons individually,higher dome and deeper valve reliefs.
 

cyclhed

Member
Sonreir said:
I second the larger exhaust valve/port idea. The intake flow on the 360 head (for a 356cc motor, anyway) is already too big. The exhaust ports are a problem even at that displacement though. If your cam decision isn't yet finalized and you have no plans to enlarge the exhaust ports, you're going to want to see some high lift numbers.
Sonreir, Pops says thanks for the information on the heads. I think he is waiting to test the 360 head and said he may try a 3 valve CB500T head. See his message below.

"I'm glad the forum is "Do the Ton", as I read through a lot of the 360
stuff. There seems to be a few sharp guy's on site. Tell Sonreir thanks
for head and flow info, open for more, also that the head is far from
done. With even the possible fitting of a 3 valve CB500T head, which I
prefer and have the mounting figured out but not the chain tension, but
with so much to do first I am starting with 360 head."

Also thank you Teazer for the first mention of the exhaust flow issue! All comments are greatly appreciated.
 

cyclhed

Member
Nebr_Rex said:
Don't want to rain on your parade but,the second pic shows a stock pre '81 KZ1000 piston.
Bore size would be 70mm,factory offered oversizes in .5 steps,I never seen a 2.5 factory oversize.
Aftermarket goes oversized by whole mm,ie. 71,72 etc. .
You can order Wiseco pistons individually,higher dome and deeper valve reliefs.
Hi Rex, Thanks for finding my mistake, I listed the pistons as KZ1000, but Pops corrected me today and they are KZ1100 at 72.5mm diameter. Sorry for the confusion. I will correct my original post also. Please stay tuned and keep an eye on me!
 

cyclhed

Member
Not to muddle this thread up too much, but I thought I'd give you some more info on the engines. At first Pops was going to enlarge the CB350 and here is the start of that conversation and pictures of the 500 twin crankshaft modified for the 350 case. He later decided to use a 360 case because it would accept the bigger bore. Here are his words:

"I finished lightening the 500 crank and put it back together today, now
it's same weight as 350 crank and fits in 350 case. I bought the 500
crank because of specs I read stating that it was the same stroke as
450 but it's not, the extra 50cc comes from a longer stroke(64.8mm). So
now a 350 could grow to 513cc!! I'm still going to use a 360 as it will
take bigger sleeves, should be good for 557cc. 55% increase is a bunch.
Don't know if 360 head will flow enough for this cc. Still looking at a
late model 450t cylinder and three valve head for enough flow, also
bigger bore. Might as well make a BIG bang if it blows."
 

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cyclhed

Member
And this is the 350/513 lower end. Pops said I could have this set-up for my SL, but I would need to bore the case for the cylinders or use this CB case; I may take him up on that this winter. Also his explanation of the pictures is below in quotes. This is why I was confused about the KZ1000 and KZ1100 pistons in my first post which I corrected thanks to Nbr-Rex. Appears a 450 piston is installed and not the KZ1000 at the time which are both 71mm.

"Here's a 513cc CB350 lower end, still need a .225 barrel spacer to get
to 0 deck, too early to tell what that does to the cam chain as I have
to use a 30 tooth cam sprocket also. Thanks to KZ1000, we have one, as
well as sleeves, pistons, pins and rings."
 

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cyclhed

Member
Good to have you along Mr. Longhorn!

BTW: Where are you guys that chimed in about the 360 cylinder head exhaust flow characteristics getting your information from? Has somebody done flow bench or dyno testing to substantiate? Just wondering because that would be the only real way to know. Thanks.
 

Sonreir

Oregon
DTT SUPPORTER
cyclhed said:
BTW: Where are you guys that chimed in about the 360 cylinder head exhaust flow characteristics getting your information from? Has somebody done flow bench or dyno testing to substantiate? Just wondering because that would be the only real way to know. Thanks.
I agree that where empirical data exists, it should always but used. However, the use of flow benches and dynos for every engine modification can break that bank and so it's necessary to look at many problems and approach them with the knowledge gained from other applications.

For instance, it doesn't seem to be an unreasonable stretch of the imagination to make the assumption that today's head design is an improvement over the technology that was available 40 years ago. With that supposition in mind, we can make comparisons between today's technology and that of yesteryear.

We now notice that port ceilings tend to be higher. Valve placements are a bit off center (to promote swirl). And also, exhaust ports tend to be larger (especially in hemi and tubbed heads).

Stock valve sizes for the CB360 are 34mm and 28mm for intake and exhaust, respectively. This gives us a sizing ratio of 82.3%.

Now looking at some more modern engines we can see the following:
Yamaha FJ1100 - 84%
BMW M5 - 86.3%
Cosworth F1 - 87.5%
Ducati 748R - 83.1%
Honda NS50 - 87.5%
Honda VF1100 - 88.1%

After going through a list of two pages of valve sizes, I was only able to find only a few cases of engines that use a smaller ratio than the Honda 350/360 and with the exception of one Harley, all of the others were purpose built race cars (not bikes).

Even with the valve size ratio as it is, you will likely still see gains by reworking the exhaust port. I haven't checked recently, but there may be room to raise the ceilings a little and flatten the floors. The ideal shape would look like a 'D' laid on its flat side. Total exhaust port area should be at least 95% of the area valve, so you're looking for at least 858 square mm. If you do decide to hog out the exhaust ports, don't go crazy. You will want there to be a decent step between the exhaust port and the exhaust pipe as this helps to prevent reversion (especially in the low and mid RPM ranges).
 
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