Engine build- newbie question

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RD400Fiend
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Joined: Sat Mar 05, 2016 2:34 am

Engine build- newbie question

#1 Post by RD400Fiend » Fri Sep 08, 2017 6:08 pm

Hello,

I am currently building my first RZ. I have had several RD400's. The engine in my RZ is old and tired. Planning on running it until rebuild needed. But might also build an engine for it sooner than later.

I'm wondering what the most reliable pumped up street engine build will be- open to all options. Is stock the best set up or should I go with something more radical? Already have pipes and y-boot filter, few other upgrades as well- mostly chassis.

Hoping that the RZ will be more reliable than my RD's have been. Don't need crazy power but wouldn't mind something more powerful than stock. Reliability is main concern at this point.

Thanks!

hondaror
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Location: Alberta, Canada

Re: Engine build- newbie question

#2 Post by hondaror » Fri Sep 08, 2017 10:24 pm

Keep it stock and use your pipes and new intake. With jetting you'll be really happy with the grunt your mods will provide. Very reliable if you ride it hard.
Rory
2 1984 RZ350s
1985 RZ350
9 1986-1990 RZ350s
2000 ST2
2005 749
2005 749 with 999 engine

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Questo vecchio rz
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Location: Reconquista of California

Re: Engine build- newbie question

#3 Post by Questo vecchio rz » Sat Sep 09, 2017 1:29 pm

What version RZ do you have? Is it a US 85-85 bike or a later model ?
Also your intended riding style are you looking for a RZ to go cruising on interstates or spirited stop light to stoplight and fun through back roads? In addition where you live , elevation factors in as well.

1st thing is as long as everything in functioning as normal your RZ will be far more reliable than a RD.

Sounds like you want to keep things reasonable, on a US bike in addition to your bittom end rebuild,servicing your YPVS system, your pipes & Y boot, I'd add the following:

1.) A Toomey or Dynojet carb rejetting kit.
2.) Have your head machined ( make sure it has not already been done).
3.) I'd recommend a 16 tooth front sprocket.
4.) Good set of aftermarket reeds.
5.) Option to lightly port to later RZ 1UA soecs. These mods will wake up your RZ quite alot and retain most all of the reliability. Note* You also have the option of retaining your stock airbox and NOT rejet just add a drop in UNI foam filter then do the other mods, bike should run just fine.

Pretty basic really, on a US based bike your pipes along with the modifications, you will have a substantially faster RZ, if you have a later model RZ, the porting specs is already done you are ahead already.

This recipe would be a bike you could ride anytime anywhere.
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

RD400Fiend
Posts: 30
Joined: Sat Mar 05, 2016 2:34 am

Re: Engine build- newbie question

#4 Post by RD400Fiend » Sat Sep 09, 2017 6:18 pm

Thanks for replying.

It's an 84 US model.

Mostly riding will be hitting the Twisties, some highway but not touring.

It's already jetted to spec II chambers- I'll prob run a set of motocarrera's or maybe JL if I can get the funds together.

I'm thinking of going with the Vforce 4's.

I don't think the heads have been done. I usually use SCR for head work.

Just finishing up an front and rear end swap and then the pipes are next.

Hooligan
Posts: 1966
Joined: Mon Aug 20, 2012 1:37 am
Location: Calgary, Alberta

Re: Engine build- newbie question

#5 Post by Hooligan » Sat Sep 09, 2017 8:11 pm

On my LC I have been very happy with the performance from an O-ringed head, properly set up squish and a set of CF reeds. Really makes the engine crisp. I am running stock pipes but I suspect a decent set of expansion chambers would also make a huge difference.

In comparison my stock RZ runs the OEM head gasket and very sloppy squish band and it is nowhere near as crisp.
'82 RD350LC in '81 colours, OEM pipes, UNI filters
'85 FZ750

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Questo vecchio rz
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Re: Engine build- newbie question

#6 Post by Questo vecchio rz » Sat Sep 09, 2017 8:40 pm

Sounds like you've done your homework already. Scott Clough@ SCR , Frankly hes as good as it gets on vintage RD /RZ heads, or portwork. You don't have to look much further than him! You also can reach out to Ed Earlenbach ,his port work is very good specifically in RDs & RZs.

And your carbs have been rejetted already as well.
Are they the stock 26mm or Spec 2s 30mm Round slide kit? Either are tried & true and run perfectly fine , I'd recommend any 30mm or less. 26mm-30mm carbs of any brand will work just fine on a street RZ, I prefer the Mikunis...they always run so damned good.

Also did you retain the oil injection, KEEP IT if possible! Just make sure it's in perfect working order, there's a guy here (Arrow)whom rebuilds and/or tweaks them ,that is if you don't do it yourself.

Your choice of pipes is perfectly sound as well, I have had a few brands, currently have JL so stainless GPs, they work just fine, and are easy on the eyes, but since you mentioned Moto Carrera, If I were you ...if you can manage to land a set of Doug's Moto Carrera Millennium GPs..that is a very good pipe design, especially for your application and they look damn sexy too.
If you need info on them, call Doug he will fill you in on the design and their characteristics.
I'd like to score a set too. Doug I think is hit & miss with production runs..

Scott C. & Doug have had a decades long history together of building winning race RDs & RZs together, regardless of any quirks any bring to the table, They each know the RD/RZ /TZ series of bikes like few others, and Scott will provide you with any and all cutting edge port & head design. Scott's crank & machining work is just badass with quick turnaround, he temporarily stopped recently due to a hand/arm/shoulder injury. Get him before he stops doing this work! I need to make that call soon as well, he's only a 1/2 hr. from me.

On a side note* What front end and rear did you go with. ?
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

RD400Fiend
Posts: 30
Joined: Sat Mar 05, 2016 2:34 am

Re: Engine build- newbie question

#7 Post by RD400Fiend » Sun Sep 10, 2017 11:07 am

I'm nearly done with an Aprilia rs250 swap. Using fz600 swingarm. Just need a brake tab welded to the swingarm. Framemaker did the conversion for me- thanks Julian!

I have a set of Doug's pipes but they need to be completed. I actually purchased the RZ from Doug a year or two ago. I have his millineum GP's on my Daytona and absolutely love them.

Unfortunately the previous owner removed the oil pump and reservoir so I'm going premix route. Both my 400's are premix as well so I'm pretty much used to it.

Running stock 26 carbs. Don't know what jets they have- but it seemed to run ok with the spec II's so hoping jetting will be close.

That sucks about Scott. Hope he is ok. He is a great guy in addition to doing excellent work.

Thanks for the feedback. I have always wanted an RZ and can't wait to finish this build.

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