RZ392R project

Got a customizing or restoration project? Discuss it here

Moderator: rztom

Post Reply
Message
Author
User avatar
Phantom
Posts: 22
Joined: Wed Nov 04, 2020 7:18 pm

RZ392R project

#1 Post by Phantom » Wed May 25, 2022 9:14 pm

Fill me in with some helpful ideas and suggestions as I ended up opening a lot of headache for my project bike as I am entirely new when it comes to Yamaha RZ engines itself.

So I am currently doing a conversion for a big bore set up for my project bike, the engine will be put on a Cagiva mito rolling chassis once done. I am currently testing the waters with the Athena 392 kit, many people are telling me to just ditch the 392 idea and just go for a 421 kit straight instead but due to budget constraint on my side I am more leaning on sticking to my original plan of getting the 392 kit instead since I have some of the parts needed for it, only few other parts left to complete the kit conversion to push forward.

I am also wondering what would be the BHP will I even get with 392?
any ideas or suggestions to beef up the HP that will be helpful as I am hoping if it can make or give me a 70hp if possible.

so far I have purchased the following parts:
Hot Rods Crankshaft
V Force Reed Blocks
MBD Engine Seals
Zeeltronic PCDI-10T
Hand Held Zeeltronic Programmer

I also have manage to get two 35mm Mikuni carburetors, the chamber exhaust will be done locally by someone whom have been making chambers for 30+ years and they'll also handle the dyno tuning and other conversion needed.

User avatar
Questo vecchio rz
Posts: 1116
Joined: Sun Aug 16, 2015 5:55 pm
Location: Reconquista of California

Re: RZ392R project

#2 Post by Questo vecchio rz » Fri May 27, 2022 3:46 am

I have a Banshee engine Note**( No YPVS) with the following :

1.) I forget, but approx 385 cc with
2nd overbore Weisco pistons.
2.) Typical Hot Rods + 4 mm crank
3.) Chariot Billet 1pc head.( Best head made) for stock & CPI cylinders IMO
4.) 21 cc domes
5.) Mild Dune/MX port
6.) Complete VForce 4 Reed assembly, Note* Tuner Gained a solid 2 h.p. and very nice mid-range grunt w these reeds.
7.) PWK 33mm Air Striker carbs.
7. TOOMEY T-5 pipes , better than T-6 s for ported cylinders.
8.) Professionally Dyno tuned.

I run ONLY 100AL aviation fuel w Synthetic Klotz Super techniplate, Its a 80 %synthetic 20% Castor Bean oil blend. IMO It's the champagne of 2 stroke oil..

I'm at 69 h.p. with a relatively very mild port. I told the builder I want to ride the bike anywhere from Sea level to 4500' and not worry about seizure

NOTE* With more aggressive (drag) port work, and 18 or 19 mm domes, full oversize pistons at 421. Builder said I'd be at approx 80 h.p.
but I'd lose my MX /trail riding advantage..it's FAR too fast for me as a desert racer as is.
As long as I'm not drag racing..my bike weighs about 50+ lbs more than a stock banshee due to the desert gear,.
In a drag race, I'm only 6 bike lengths behind another Banshee w 400 cc , 35 mm carbed C P.I. Cheatah cylinder w power valves
So I'm quite happy w what I had built

So your build w a better designed Athena cylinders should EASILY get you right where you want to be.

FYI..be aware 33-35 mm carbs will cost you dearly in MPG , Easily 1/3 the mpg of stock or 30 mm carbs.
Fuel mileage is absolutely deplorable.

I burn 6 gallons of fuel in just over 1hr if I'm at my racing speed.

I'm telling you right here right now, you can get 70 h.p. with properly jetted "stock carbs", and save yourself $500.00 in carbs & manifolds. And gain massive MPG.
If I had to do it again I would either run stock or 28 mm carbs.
When I had my bike tuned they proved it to me and put 70 horsepower down with a set if their tuned stock 26 mm carbs on their in house ported 4 mil Banshee .

Saw it w my own two eyes, by one of the best off road 2 stroke tuners in the buissness.

It's one of the reasons Banshees ultimately never fared too well in the long desert races, the gas mileage is horrible w larger carbs. My friends 35mm carbs drink noticeably be even more fuel than mine!!...That's nuts.

Other than the shitty MPG of my 33 mm PWKs, I don't have any complaints, nice crisp throttle response, even though I prefer Mikuni's...I'm just fine w these.

Anyways I think you'll "easily" hit your goal of 70 horsepower without having to resort to a 421.

I am not too familiar with the Athena cylinders; but I kept mine at 1 overbore instead of going for a 421 on the last.
if I ever rebuild it I may NIKASIL the cylinders and go 421.. but why fix it if it ain't broke at this point...lol

This Banshee build kind of was a dry run for my RZ engine.

I have been all over the map with silly ideas, back and forth w theories good n bad.
But with the YPVS system, 4 mil crank and aggressive port work, and good pipes, I'm confident I can have about 70 + which in reality is almost 25-30 more h.p. than a bone stock RZ. And be reasonably reliable too :-)

Race tuned RZs were making 6o -70 horsepower in the '80s, so I'm pretty sure my build sheet for the RZ will put me in the mid-upper 70s with all the modern parts & porting that's become available in the last 30 years, and that's w a stock ignition.

There's a lot of room in these little motors for a lot of fun!

Good luck, and post up when yer all done!
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

User avatar
Phantom
Posts: 22
Joined: Wed Nov 04, 2020 7:18 pm

Re: RZ392R project

#3 Post by Phantom » Fri May 27, 2022 9:39 pm

Questo vecchio rz wrote: Fri May 27, 2022 3:46 am I have a Banshee engine Note**( No YPVS) with the following :

1.) I forget, but approx 385 cc with
2nd overbore Weisco pistons.
2.) Typical Hot Rods + 4 mm crank
3.) Chariot Billet 1pc head.( Best head made) for stock & CPI cylinders IMO
4.) 21 cc domes
5.) Mild Dune/MX port
6.) Complete VForce 4 Reed assembly, Note* Tuner Gained a solid 2 h.p. and very nice mid-range grunt w these reeds.
7.) PWK 33mm Air Striker carbs.
7. TOOMEY T-5 pipes , better than T-6 s for ported cylinders.
8.) Professionally Dyno tuned.

I run ONLY 100AL aviation fuel w Synthetic Klotz Super techniplate, Its a 80 %synthetic 20% Castor Bean oil blend. IMO It's the champagne of 2 stroke oil..

I'm at 69 h.p. with a relatively very mild port. I told the builder I want to ride the bike anywhere from Sea level to 4500' and not worry about seizure

NOTE* With more aggressive (drag) port work, and 18 or 19 mm domes, full oversize pistons at 421. Builder said I'd be at approx 80 h.p.
but I'd lose my MX /trail riding advantage. It's FAR too fast for me as a desert racer as is.
As long as I'm not drag racing..my bike weighs about 50+ lbs more than a stock banshee due to the desert gear,.
In a drag race, I'm only 6 bike lengths behind another Banshee w 400 cc , 35 mm carbed C P.I. Cheatah cylinder w power valves
So I'm quite happy w what I had built

So your build w a better designed Athena cylinders should EASILY get you right where you want to be.

FYI..be aware 33-35 mm carbs will cost you dearly in MPG , Easily 1/3 the mpg of stock or 30 mm carbs.
Fuel mileage is absolutely deplorable.

I burn 6 gallons of fuel in just over 1hr if I'm at my racing speed.

I'm telling you right here right now, you can get 70 h.p. with properly jetted "stock carbs", and save yourself $500.00 in carbs & manifolds. And gain massive MPG.
If I had to do it again I would either run stock or 28 mm carbs.
When I had my bike tuned they proved it to me and put 70 horsepower down with a set if their tuned stock 26 mm carbs on their in house ported 4 mil Banshee .

Saw it w my own two eyes, by one of the best off road 2 stroke tuners in the buissness.

It's one of the reasons Banshees ultimately never fared too well in the long desert races, the gas mileage is horrible w larger carbs. My friends 35mm carbs drink noticeably be even more fuel than mine!!...That's nuts.

Other than the shitty MPG of my 33 mm PWKs, I don't have any complaints, nice crisp throttle response, even though I prefer Mikuni's...I'm just fine w these.

Anyways I think you'll "easily" hit your goal of 70 horsepower without having to resort to a 421.

I am not too familiar with the Athena cylinders; but I kept mine at 1 overbore instead of going for a 421 on the last.
if I ever rebuild it I may NIKASIL the cylinders and go 421.. but why fix it if it ain't broke at this point...lol

This Banshee build kind of was a dry run for my RZ engine.

I have been all over the map with silly ideas, back and forth w theories good n bad.
But with the YPVS system, 4 mil crank and aggressive port work, and good pipes, I'm confident I can have about 70 + which in reality is almost 25-30 more h.p. than a bone stock RZ. And be reasonably reliable too :-)

Race tuned RZs were making 6o -70 horsepower in the '80s, so I'm pretty sure my build sheet for the RZ will put me in the mid-upper 70s with all the modern parts & porting that's become available in the last 30 years, and that's w a stock ignition.

There's a lot of room in these little motors for a lot of fun!

Good luck, and post up when yer all done!
Hi Questo vecchio rz!

Thank you for responding on my questions and giving your personal insights and first hand experiences.

To give you a much clearer picture I have bought an RZ250RR YPVS and wanting to make a huge gain leap over the typical 250cc since I have used and abused my later bikes which is a NSR250 MC21 SE, RGV 250 VJ22 that is well tuned and both popping me a 68hp and so I wanted to move on to other brand luckily enough I stumble upon the RZ250 engine for a cheap price thinking that this engine will be my new gate way to experience and to try new things out. I was doing some research for parts since I wanted to do some rebuilds on it since the former owner just trashes the bike and left it to rot in the side for the nature to claim it and so when I stumble upon this forum and the other RD/RZ forums, I did not even expect to know that the upgrade capabilities of the Yamaha RD/RZ/Banshee engines are a lot and astonishing. Upon digging more research and asking numerous people for their insights and help I got hooked up on the hybrid build and so stumble upon the 392cc from Athena and then others suggested to just go for the 421 instead but the price of the parts needed to make the 421 to gain substantial amount of HP for beneficial use is out of me league for the meantime being, but will definitely get that kit when I can in the next rebuild or in another rz250rr engine in my stock room.

The bike will be used more on the road and I rarely do races/circuit. Currently once the engine is done I will be putting it on my Cagiva Mito rolling chasis, since I got mostly new front wheels and other stuff to fancy it.

User avatar
kenny
Posts: 584
Joined: Sat Jun 13, 2009 5:57 am
Location: Worcestershire UK

Re: RZ392R project

#4 Post by kenny » Sat May 28, 2022 12:30 pm

Over here I have seen a 392 hit 78RWHP with 28mm carbs and my pipes so 70is really easy with the Athena kits

User avatar
Phantom
Posts: 22
Joined: Wed Nov 04, 2020 7:18 pm

Re: RZ392R project

#5 Post by Phantom » Sun May 29, 2022 10:16 pm

kenny wrote: Sat May 28, 2022 12:30 pm Over here I have seen a 392 hit 78RWHP with 28mm carbs and my pipes so 70is really easy with the Athena kits
Hi kenny thank you for responding on my question/inquiry

Interesting to read and see that a 392 can get a 70ish as many folks have stated that a mere 60ish is all I can get from it, kinda wondering what are the engine mod done to that 392 you are pertaining with as I may try to replicate it out with slight modifications done to my own specifications

cheers! :smt038 :smt038

Post Reply