+7mm Crank OEM Cylinder Porting

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Smoker
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Re: +7mm Crank OEM Cylinder Porting

#46 Post by Smoker » Sat Dec 22, 2018 6:34 pm

Thanks much for the info.

Took some time and did a better search on the topic.

Didn't find any port maps, but realize this has definitely been discussed before. In 2015, I asked this: "How big can you go with stock cylinders and YPVS power valves?" I'm guessing TDR has the most experience with the +7mm stock cylinder mod.

So, finally, I'm getting around to it.

Then, I get a call this morning from a local friend - with an OEM cylinder +7mm running engine! WTF?? Not sure how I missed that, too.

Very much appreciate you guys trying to help me get the bikes done.

TTperra
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Location: Sweden

Re: +7mm Crank OEM Cylinder Porting

#47 Post by TTperra » Fri Jan 21, 2022 2:51 pm

Did you bulid that +7 stroker?

I was planning a stroker bulild about 8 years ago, bought a +7 crank and cool head, the plan was first to try with Banshee cylinders (and try a little porting) but other projekts came and the RZ has been suffed away..

Now i begin to get interest again for the projekt, and wonder what i was thinking when i bought the crank..
85 RZ350, Project in slow progress, 7mill stroker engine in even slower progress..
Other bikes
Harley Chopper -71 "Swedish style"
Honda CR480 -83
Kawasaki KX250 -82
and some more..

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Questo vecchio rz
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Re: +7mm Crank OEM Cylinder Porting

#48 Post by Questo vecchio rz » Sun Jan 23, 2022 12:25 am

7mm Stroker w YPVS heads...
Seems to be an urban myth perpetuated by several builders I have yet to see one and I have seen a lot and nobody who says they have one has ever come forward with any hint of a actual running engine. if there was even a hint of the one being real I'm sure somebody would have shared it with their fellow enthusiasts at some point over the years.

You can do it with Banshee cylinders that's no problem.

I've been told by builders pushing the piston that far up into the cylinder would longevity , and sizeure issues on a road based machine @ sustained RPMs.

CPI Cheetah & Serval cylinders have been prone to similar issues on many instances over the years.

Also there's been many claims of 75+ h.p. even up to 80+ h.p. stock cylinder RZs...again in almost 40 years now..still never viewed one.

The most I've ever viewed on a stick cylindered YPVS race bike..was 69.5 h.p. was a full race bort on max bored cylinders with a cool head. And If I remember right it won every race it was entered in during the 2 + years it was campaigned.
I've just never viewed any other stock cylinder YPVS RZ claiming figures beyond 70 h.p. winning anything . At least in America.

Realisticlly.. most RZs put down in the 40 h.p. range. So nerz in the 60 range is really an impressive engine especially in person for real on the road.
Banshee (Baja) race bike,+ 2 A Arms,L.E.Ds, Toomey, +4 stroker IMS tank, run flats.
96 GSXR SRAD, Future Yoshimura rep.
85 custom Tri-Z
RZ/YZR bike(project)
86 VFR750 RC24 Merkel replica (project)
Royal Enfield Bullet 500

TTperra
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Location: Sweden

Re: +7mm Crank OEM Cylinder Porting

#49 Post by TTperra » Sun Jan 23, 2022 6:11 am

Well i am a newbie on 2t engine building, when i use different spread sheets/programs i come to this conclution:
I think that transfer duration will be to high and blowdown to small, exhaust and transfer ports being to close to each other.
The single exhaust port dont allow enough area to compensate, or get enough timed area.
On the Banshee cylinders i think i would need to go as wide as 75% of bore, and the rings dont like that.
Risig the exhaust to get enough blowdown/TA to match transfer would be a dragrace setup i guess..

I can be totaly wrong here, and I appreciate if some who knows would tell.

Of course it will run, but will it be any benefit compared to a +4 crank?
The cases will need to be trenched to use +7 but +4 will drop right in.
But more cc is tempting..
85 RZ350, Project in slow progress, 7mill stroker engine in even slower progress..
Other bikes
Harley Chopper -71 "Swedish style"
Honda CR480 -83
Kawasaki KX250 -82
and some more..

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Smoker
Posts: 4778
Joined: Sun Mar 23, 2008 8:08 pm

Re: +7mm Crank OEM Cylinder Porting

#50 Post by Smoker » Mon Jan 24, 2022 2:59 am

I haven't built the +7mm engine. And, for no good reason. Just haven't had the motivation for a while. Still hoping I can get it together and get it done soon.

I definitely know someone close to me with a running +7mm engine. In a nice street bike here in SoCal. Engine built by Roger. Owner is a member here.

Here is the Dyno:

Image

TTperra
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Location: Sweden

Re: +7mm Crank OEM Cylinder Porting

#51 Post by TTperra » Wed Jan 26, 2022 3:09 am

I read about the Wicked +7 stroker when he posted the build here, but i cant find it now, maby its deleted?

But i think that is the only one i have read about.

Rogers dyno graf looks nice thou
85 RZ350, Project in slow progress, 7mill stroker engine in even slower progress..
Other bikes
Harley Chopper -71 "Swedish style"
Honda CR480 -83
Kawasaki KX250 -82
and some more..

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Smoker
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Joined: Sun Mar 23, 2008 8:08 pm

Re: +7mm Crank OEM Cylinder Porting

#52 Post by Smoker » Wed Jan 26, 2022 3:26 am

TTperra wrote: Wed Jan 26, 2022 3:09 am I read about the Wicked +7 stroker when he posted the build here, but i cant find it now, maby its deleted?

But i think that is the only one i have read about.

Rogers dyno graf looks nice thou
If you want to read about Rogers engines, you're looking in the wrong place.

His bigger builds go in drag quads. I think, by far, most of his business is in off-road parts and off-road engines.

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Questo vecchio rz
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Re: +7mm Crank OEM Cylinder Porting

#53 Post by Questo vecchio rz » Wed Jan 26, 2022 2:53 pm

Now this is strange?
I know Rodger the two stroke shows and this website met him half a dozen times or so.
Just last year I stopped by his shop and discussed some RZ builds and I specifically asked about the 7 mm stroker with a YPVS head assembly, and he said he does not use them he uses the Athena heads which have no power valves.? He said the Athena too end head delivers more power, which it does....but one loses the cool YPVS setup, and it's benefits for daily driving

Realistically I don't think the plus 7th going to make much difference than a well-built + 4 technically you usually 3-5 horsepower more from a +7 vs +4....

Would be kinda fun.....either way I'm Over it. At this point I don't care anymore what motor I have in it as long as it's producing about 70.

Shout back if it's a YPVS cylunfder
Banshee (Baja) race bike,+ 2 A Arms,L.E.Ds, Toomey, +4 stroker IMS tank, run flats.
96 GSXR SRAD, Future Yoshimura rep.
85 custom Tri-Z
RZ/YZR bike(project)
86 VFR750 RC24 Merkel replica (project)
Royal Enfield Bullet 500

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Smoker
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Re: +7mm Crank OEM Cylinder Porting

#54 Post by Smoker » Wed Jan 26, 2022 3:21 pm

Questo vecchio rz wrote: Wed Jan 26, 2022 2:53 pm Just last year I stopped by his shop and discussed some RZ builds and I specifically asked about the 7 mm stroker with a YPVS head assembly, and he said he does not use them he uses the Athena heads which have no power valves.? He said the Athena too end head delivers more power, which it does....but one loses the cool YPVS setup, and it's benefits for daily driving

Shout back if it's a YPVS cylunfder
Looks like YPVS cylinders to me! :smt023

Image

I also have pics somewhere of my trenched cases and ported OEM cylinders, ready for the +7mm crank.

Still a nonbeliever? :smt003

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JanBros
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Re: +7mm Crank OEM Cylinder Porting

#55 Post by JanBros » Thu Jan 27, 2022 7:01 am

Questo vecchio rz wrote: Wed Jan 26, 2022 2:53 pm Realistically I don't think the plus 7th going to make much difference than a well-built + 4 technically you usually 3-5 horsepower more from a +7 vs +4....
a square 2-stroke is superior to an over-square. an RD/RZ is seriously over-square, so the closer you bring it to square, the higher the gains, especialy at higher rev's.
it comes down to simple math.
with bigger bore, the available angle-area (effective available port-area dictated by the angle's it enters into the cylinders) of the transfers increaces with a factor "R" which is the radius of the bore (circumferrence is 2*Pi*R. The volume of the cylinder (which in the end, has to be filled through the transfers) increases with a factor "R²" which off course is also the radius of the bore, but squared (volume of the cylinder is 2*R²*Pi*Stroke).
the closer you bring bore and stroke together, the better an engine can breath, and the higher it can rev because at higher rev's there is less time available (that's where the all-important time-area calculations are all about).

so if you overbore a 350 by Xmm, you will gain less power than by stroking a 350 by Ymm (resulting in the same cc's and giving you optimize both engines with the correct timings, angles etc).
if it runs, you can race it !

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Questo vecchio rz
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Re: +7mm Crank OEM Cylinder Porting

#56 Post by Questo vecchio rz » Thu Jan 27, 2022 1:24 pm

Smoker wrote: Wed Jan 26, 2022 3:21 pm
Questo vecchio rz wrote: Wed Jan 26, 2022 2:53 pm Just last year I stopped by his shop and discussed some RZ builds and I specifically asked about the 7 mm stroker with a YPVS head assembly, and he said he does not use them he uses the Athena heads which have no power valves.? He said the Athena too end head delivers more power, which it does....but one loses the cool YPVS setup, and it's benefits for daily driving

Shout back if it's a YPVS cylunfder
Looks like YPVS cylinders to me! :smt023

I also have pics somewhere of my trenched cases and ported OEM cylinders, ready for the +7mm crank.

Still a nonbeliever? :smt003
No 😄 it's not like I'm not non-believer🤪 I keep the faith.
But I previously reached out to Roger @Wicked and Tony @ TDR and the feedback I received was contradictory and dismissive.
I was advised from a retired GP 2stroke tuner that, it would likely be too much into the cylinder and be prone to seizures.
Said tuner ( who will remain unknown). Don't really like the guy but have to respect his opinion.
Then again on the flipside there are thousands of 7 mm engines running around but obviously with Banshee cylinders, and not at sustained road or racing RPMs.
JanBros wrote: Thu Jan 27, 2022 7:01 am
Questo vecchio rz wrote: Wed Jan 26, 2022 2:53 pm Realistically I don't think the plus 7th going to make much difference than a well-built + 4 technically you usually 3-5 horsepower more from a +7 vs +4....
a square 2-stroke is superior to an over-square. an RD/RZ is seriously over-square, so the closer you bring it to square, the higher the gains,
Jan,
I get what you're saying about the efficiency.
I am not saying that a +4 is equal in power to a +7.
Just that a well built +4 will be reasonably close in power output.

This is proven many thousands of times in Banshee builds, The +7 usually deliver approx +4-5 additional h.p. over a +4 all things being equal w porting to match

The ONLY thing I'm interested in is :

With the +7 mm Cranks pushing the pistons deep into the cylinder heads of stock Yamaha cylinder heads and retaining the the full YPVS function.
And assurance that the cylinders can withstand "sustained Hi-RPM" road riding and use without top end meltdowns and seizures.

There was mention of short ring life and piston hot spots the statement was adamant that it would melt down.

That's all I'm concerned about, FYI I'm lost on the math calculations 😄

Thanks for the contiued input guys, your great.
Banshee (Baja) race bike,+ 2 A Arms,L.E.Ds, Toomey, +4 stroker IMS tank, run flats.
96 GSXR SRAD, Future Yoshimura rep.
85 custom Tri-Z
RZ/YZR bike(project)
86 VFR750 RC24 Merkel replica (project)
Royal Enfield Bullet 500

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JanBros
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Re: +7mm Crank OEM Cylinder Porting

#57 Post by JanBros » Thu Jan 27, 2022 6:12 pm

one day I'll be able to tell you (though without YPVS). have everything, but still to busy working on my 50cc moped MX bikes and still learning.

too many projects
if it runs, you can race it !

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