Topic: Re: 650 overbore/550 engine hybrid underway...final stages

[paulages]

don't think so, but 550 pipes will work.

[markymark]

i have looked at the 650 pipes(stock) and they are visibly(to the eye) and obviously bigger than the 550 exhasut headers.  Plus I hear the exaust valves on a 650 are at least 3mm bigger than a 550.  I would'nt want to restrict the exhaust flow in fear of losing power. 

[paulages]

i have all three at my shop and will measure them up tonight. i really thought i had compared the 550 and 650 and found them compatible, as i want to keep my 550 headers if possible, but maybe i'm wrong.

[cafe75-550]

I had heard that the 550 and 650 pipes weren't compatible, but I just heard that somewhere on here, I haven't actually tried it myself yet...

[markymark]

I appreciate the help guys.  What is the diffence between header size on 750 versus a 650 also?  Anyone?

[bill440cars]

I had heard that the 550 and 650 pipes weren't compatible, but I just heard that somewhere on here, I haven't actually tried it myself yet...

 I had heard that to but, I think it was the angle of the exhaust ports though. I remember it being said that if you put a 650 head on a 550, you would have to use the 650 exhaust.

                                               Later On, Bill

[markymark]

Paulages  Did you ever do the comparison between the 550 650 and 750 exhasust header sizes?   Did you take any measurments?  Please let me know I have still been waiting to hear.  Hope all is well  Thanks

[cafe75-550]

I took some measurements of my stock 550 pipes and head and a jardine 650 header and 650 head.

I came up with ID of the 550 pipe 27mm, OD 38mm

ID 650 pipe 30mm, OD 42 mm

Further, the 550 head has 27mm exhaust ports, the 650 30mm ports and the spacing of the ports from the 650 to the 550 was 2mm smaller.

The 650 Jardine header wouldn't fit the 550 head because of the spacing, and I suspect that a 550 4-1 header with fixed pipes won't fit the 650.

However, based on the OD, I think the drag pipes on my 550 belong to a 650, which is possible because the pipes are free as far as spacing goes and there's a little extra room around the ports. But only drag style individual pipes would work because of the port spacing issue.

But I wouldn't want to put 550 pipes on the 650 because of the exhaust port sizes....

[paulages]

i did do some measurements, but i couldn't figure out the best way to interpret them, because of the many variables involved. there is an I.D. at the point as far as my caliper would fit into the throat; there is an O.D. at roughly the same point--anywhere past the first few inches; there is an O.D. just behind the flange; there is the O.D. of the flange itself; and there is the I.D. of the flange. measuring the I.D. of the flange is a bit tough to pin down, but i think is important, as it may indicate whether the flange will crush the copper gasket and seal.

the flange sizing and the I.D. past the throat seem the most important to me, and here's what i came up with: (in mm)

                    ID at throat         pipe O.D.       flange O.D.     flange I.D.

550F             25.4                   31.8              37                 28.3

650              28.6                    34.7              40.9              33

750F            28.2                     35                43.5              34.1



obviously, the 650 and 750 seem more compatible in size, but the 550 and 650 share the same spacing. i haven't been able to recheck for certain (both heads are at the machine shop), but when i tried the 550F pipes on the 650 head before, they seemed to line up fine. i'm no exhaust specialist, so i'm not too sure how much of a difference 3.2mm would make on the interior diameter of a pipe otherwise unrestricted. there sure isn't much of a difference between the 650 and 750 sizing, despite the difference in displacement. then again, the 650 was said to be the most advanced of the sohc4 engine family...

[cafe75-550]

3.2 mm doesn't seem like much until you consider how big the pipes are, works out to be 11% of the diameter of the 650 pipes. A little quick math shows that the 650 pipes' cross section is 127% bigger than the 550's, and I don't think I need to dig out my fluid dynamics books to say that a 27% reduction in cross sectional area will be a huge restriction. The 550 had enough trouble breathing as it was, I imagine that a 650 with 550 pipes would act pretty choked...

I went back and did some more fitting as well. I was able to align the 550 pipes to the 650, probably well enough to get it to seal (but the reduction in the flange diameter will make it harder for sure), but I wasn't able to fit my 650 Jardine header to the 550...

[markymark]

Wow guys thanks.   You went to quite a bit to figure all of that out.  That is great.  I guess my biggest question iw weather the 750 headers will fit a 650?  I am for sure going to put a 650 into my 550 and I don't like how the 650 stock exhaust sounds.  I've got some new Jardine (I think) 4 into 2 cans on my 550.  I can tell the cans are prbably for a 750 considering the gap from my stock 550 heders into the exhaust.  I had to make some sleves for the to fit more snug but there is still some exhasut leak where the down pipes slide into the cans.  Hopefully the 750 down pipes will work on the 650 motor I plan to put in.  I guess I will find out.  If you guys get your motors back let me know how the 750 pipes work on the 650 head.   Thanks again for all the measurements.

[Ibsen]

This is how a 650 can sound with a Honda 650 4-2 system.

LINK 1

LINK 2

[markymark]

HEADPHONES were on!!!!!   WOW they both sound amazing to meeeee.    Are both sound clips from the same exhaust?  which one is which?  They sound different.  Love the second one as much as the first. 

[Namba1032]

Wow guys thanks. You went to quite a bit to figure all of that out. That is great. I guess my biggest question iw weather the 750 headers will fit a 650? I am for sure going to put a 650 into my 550 and I don't like how the 650 stock exhaust sounds. I've got some new Jardine (I think) 4 into 2 cans on my 550. I can tell the cans are prbably for a 750 considering the gap from my stock 550 heders into the exhaust. I had to make some sleves for the to fit more snug but there is still some exhasut leak where the down pipes slide into the cans. Hopefully the 750 down pipes will work on the 650 motor I plan to put in. I guess I will find out. If you guys get your motors back let me know how the 750 pipes work on the 650 head. Thanks again for all the measurements.

Nope they dont fit unfortunatly, I tried. They look like they do in pictures, but I'll tell you for sure, they dont. The 650 pipes come out of the head at different angles if I remember corectly, and the 750 come out parallel to eachother. Hope this helps. I put a mac 4-1 system on my bike, sounds pretty good.
Brian

[Ibsen]

HEADPHONES were on!!!!!   WOW they both sound amazing to meeeee.    Are both sound clips from the same exhaust?  which one is which?  They sound different.  Love the second one as much as the first. 

It's the same bike and the same exhaust. But it is recorded with a small digital camera and on one of the clips it was strapped to the handlebars. The exhaust is a stock 4-2 system that was modified by the PO.

[markymark]

Hey ibsen that is the best looking cb650 i have ever seen.  I don't really like the 650's as much as the 550's and 750's, but I sure do like yours.  Very very nice.  I would ride it no doubt. 

So you said that the exhaust was modified, HOW SO?  What did they do to it?  Let me know.

[Ibsen]

I think we have hi-jacked this thread enough already, but you can sse how it was done here:

http://www.sohc4.us/forums/index.php?PHPSESSID=d1680eaf1aa190b5e90115a7e87f6923&topic=11765.0

[kayaker43]

Best thread ever,.. I printed it out in case it ever dissapears. I've got three 550 motors loaded with Yosh parts and a new 650 motor in a crate. I won't be able to start on it till summer, so just lurking for now.

Bummer about the headers,.. I assumed they would interchange too. I'll have to scratch build a set but at least it gives me a chance to adjust the primary lengths.

Speaking of cams, not much info there except that they interchange 550/650. I've heard it said in general terms that a hot cam seems milder as the bore size increases? Soo,.. a Yosh TT cam might work well?

[paulages]

web cam's got some profiles for a 650. they put me in touch with a guy who used to build tons of SOHC racers back in the day, and he really seems like a wealth of knowledge. he has several cam profiles i could have web cam grind that he thinks will work well with this engine, but he wants to know the actual displacement before gives me some numbers.

he suggested something along the lines of a street profile with a .340 lift and a 288 duration, or a race profile with a .345+ lift and 295 duration.

[paulages]

got my head back from Mreick today. can't emphasize enough how excited i am!!!! thanks mike!!     

i'll post endorsement photos soon...

[Pinhead]

How much improvement was done to the 650 head? I was under the impression that the ports were pretty good already, with a true hemispherical combustion chamber. How much was changed??

[paulages]

you'd have to ask mike exactly how much material he removed, but he did say that it started with a much better design that the cb750. didn't touch combustion chamber side, except to regrind the exhaust seats. installed kibblewhite valve springs.

[paulages]

finally, i'm picking up the modified engine parts tomorrow to begin mockup. still have to turn down the 550 stator to fit on the 650 crank, weld in the post for the oil line that feeds the chains in the 650 cases,  and drill and tap for the oil lines to the head, but the major work is done.

so far:
-cases (550) and cylinders (650) bored out to accept 750 liners
-liners shortened and reshaped to fit in the 650 cylinders
-cylinders bored to fit TRW 63mm pistons
-cam tensioner slot in the 550 cases milled to fit the 650 tensioner

this weekend i hope to fit everything together and check my piston/head and piston/valve clearances. it's going slow, but it's getting there...

[Pinhead]

Sounds good!! Can't wait to see this beast run. How much bigger will the 63mm pistons make it?

I went back through the post a little bit and noticed that you didn't like the sound of the stock 650 4-2 exhaust... Try this. It makes the 650's pipes sound a LOT better.

[paulages]

i still won't know until i properly cc the combustion chamber, as there is enough difference between the piston profiles to account for a few cc's + or - per cylinder, but it oughta be around 718cc.

i've made a few mufflers since posting whatever i said before, so i'll probably just fab up some simple glasspack silencers for the 4-2's until i figure out what i really want to do. once i get around to finishing my tubing bender i night try to replicate a 4-1 header like the 550F.