650 + 28 cc domes = ? psi
- Thread starter tor*p*do
- Start date
very High
like race gas?
Mouthfulloflake
ISJWTA member #2
- Location
- NW Arkansas
what was the original target application of that head?
if that is the case, then why did Yamaha sell this 650 28 cc head???
Boris
The Good Old Days
- Location
- The surf-less coast
That is one sexy looking head.
If you want, you can send it to me and I'll slap it on my 650 and test the compression.
:jester:
If you want, you can send it to me and I'll slap it on my 650 and test the compression.
:jester:
What fuel octane are you supposed to run on that? I don't believe it's pump gas.
Also, I should should clarify myself: My only experience with this is a 6m6 bored out to 82mm :bigeyes: and a shaved stock 701 head.
Blew 220 psi. :biggthumpup:
Like I said, the ports are lower, so you'll compress more along the stroke. HOWEVER: This was more pronounced in my case, because it was bored up so much.
On a stock bore 650 (77), the effects wouldn't be that pronounced.
That said, I don't think your 28cc head is pumpgas safe.
Also, I should should clarify myself: My only experience with this is a 6m6 bored out to 82mm :bigeyes: and a shaved stock 701 head.
Blew 220 psi. :biggthumpup:
Like I said, the ports are lower, so you'll compress more along the stroke. HOWEVER: This was more pronounced in my case, because it was bored up so much.
On a stock bore 650 (77), the effects wouldn't be that pronounced.
That said, I don't think your 28cc head is pumpgas safe.
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The transfers have nothing to do with compression. The exhaust does have an effect on cranking compression but at higher rpm where the pipe comes on and charges the cylinder the only compression that matters is mechanical. Also a 650 can run smaller cc domes because the cylinder is compressing a smaller volume into the head. The only compression that matters is the trapped volume ie: whats the deck height?
I am not talking transfers. If I am not mistaken (I could be) the exhaust port roofs are lower on a 6M6 cyl.
Hence a longer power stroke.
SUPERTUNE
Race Gas Rules
- Location
- Clearwater Fl.
Another question I have, is the Westcoast head an O-Ring head only or does it get used with the stock Yamaha headgasket?
SUPERTUNE
Race Gas Rules
- Location
- Clearwater Fl.
I would give you some advice if I could find my old notebook that has some 650 stuff written in it when I raced Yam SJ 650's.
Have you put this head on yet and tested your cranking compression? I don't think its that high with 28cc's and using a stock headgasket. The headgasket on a 701 displaces about 6.5 cc's with a 82mm headgasket bore, I've forgotten the bore size on a 650 ...78mm I think, that would displace 5.9cc for a stock one that's .052 thick.
Take 28cc's + 5.9= 33.9 total, That doesn't seem to far off for a 650 sized engine.
If you decide you want me to machine them... send them to the shop with some solder taped to the dome after you pre-assembled and checked it, and I'll cc them and cut as needed.
Chuck"SUPERTUNE"Quenzler III
xscream@tampabay.rr.com
TEAM SCREAM RACING
1988 Carroll St.
Clearwater, Fl. 33765
(727)442-7700
Have you put this head on yet and tested your cranking compression? I don't think its that high with 28cc's and using a stock headgasket. The headgasket on a 701 displaces about 6.5 cc's with a 82mm headgasket bore, I've forgotten the bore size on a 650 ...78mm I think, that would displace 5.9cc for a stock one that's .052 thick.
Take 28cc's + 5.9= 33.9 total, That doesn't seem to far off for a 650 sized engine.
If you decide you want me to machine them... send them to the shop with some solder taped to the dome after you pre-assembled and checked it, and I'll cc them and cut as needed.
Chuck"SUPERTUNE"Quenzler III
xscream@tampabay.rr.com
TEAM SCREAM RACING
1988 Carroll St.
Clearwater, Fl. 33765
(727)442-7700
SUPERTUNE
Race Gas Rules
- Location
- Clearwater Fl.
Thanks Matt! All I have in my head nowadays is 85-86-88-90-91mm bores!
So I did the math and 5.9cc's is right, if the headgasket bore is 78mm I.D. x .052 thick.
So I did the math and 5.9cc's is right, if the headgasket bore is 78mm I.D. x .052 thick.
Matt, what you just said makes no sense. What are you talking about? Power stroke referenced to compression? Look at how Supertune figured out the compression, its all mechanical and if the particular compression guage reads what it reads great, but its still mechanical compression. Guages only indicate the sealing condition inside the cylinder.
Here's what I meant:
Compression is calculated as (piston area * stroke after exh closed) / (dome volume)
*This is simplified, as you know. Piston dome, below/above deck height comes into play, but this should illustrate what I mean)
If the exhaust ports are lower on the 650, then they close sooner (than a 61x). All other things being equal (bore, stroke), that 6M6 cylinder will have more volume to compress than the 61X cylinder.
Obviously, on stock cylinders (both 6M6 and 61X), the compressible volume of the 6M6 is smaller due to smaller bore.
However, as stated above: I saw this happen on a 6M6 bored up to 82mm.
Sorry for the confusion...I hope this makes sense now
There are those who calculate compression from the time when the exhaust port closes and those who calculate full cylinder. When the engine comes on the pipe a supercharging effect happens. The duration of the exhaust port moves the highest point of effecientcy in the rpm band, but the compression ratio is still the mechanical function of trapped volume. Compression at starter driven rpm means nothing more than condition of cyl. seal. Compression at that rpm means nothing, but have compression at rpm when the pipe is working and your (psi) reading will go way up, or when the exhaust port matches the pipe. So moving the exhaust port duration around only moves that point. I will type and type and still the same old misinformation will be passed along. I have met and spoken with some of the best two stroke people in the world and they all use the full cylinder method of compression measuring. Building a world leval race engine that runs at rpm for extended duration shows who can build. I,m talking about moto gp guys who have gotten almost 200hp out of 500cc's.