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Post by ferox100 on Sept 24, 2019 11:58:52 GMT 1
Ok,
I'm looking to upgrade to 421cc, what kit do I get, what bhp have you got, what mpg and are they reliable. Hoping for some enlightening motivation.
Cheers
John B
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Post by dusty350 on Sept 24, 2019 12:28:46 GMT 1
I think Mutts on this forum does a ride in, ride out service for a 421 conversion. Send him a pm and I'm sure he will tell you what you need to know😉
Dusty🙂
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Post by ferox100 on Sept 24, 2019 13:50:30 GMT 1
Anyone on the forum own a 421 who can give me some feedback?
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Post by dusty350 on Sept 24, 2019 15:37:51 GMT 1
jonw for sure, and there are others. He has a website with his build listed in depth. A great resource for what you want to know  Dusty  |
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Post by bazzer5115 on Sept 24, 2019 16:35:49 GMT 1
Built 421 cheetah cub.
Didn’t like it all.
The power delivery was too vicious to make a good road bike.
My bikes are all built to ride(not just to the local chippie and the local bike night)but some serious scratching around the roads of north Devon.
Without the power valves you are either frustrated with a huge useless flat spot or panicking because of the sudden vicious ppwerband.(And I used to race in club championship,and if any knows me from practical sportsbikes track days at Caldwell park I can still ride a bike even though I’m getting on a bit now!)
Reliability I doubt is any good if you like me and ride 5,000/6,000 miles a year.
They may be good on the Dyno or in a straight line but without power valves for proper road use and a well sorted and tuned 350 ypvs is a better bike and faster from A to B.(I’ve been there and done that)
100bhp in a lc or ypvs frame with a vicious power band may sound like a lot fun,but in reality I found disappointing!!(and bloody expensive)
I know I will probably get some stick from members on here,but you asked the question and I gave my honest opinion!!!!!
Of course you can de-tune them with smaller carbs and mid-range pipes,but you still got no power valves!!
You will get a softer power delivery with an Athena kit apparently,but not tried one so can’t comment.
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Post by muttsnuts on Sept 24, 2019 20:20:44 GMT 1
it all comes down to what you want, I think I replied to another post a while back on options etc
As Bazzar says, you can have big bhp screamers which can be a handful for sure, but you can also have mid range monsters, Bazzer has only experienced a cheetah cub 421 and no doubt had big carbs and exhausts made to suit big bhp, my Aprilia RS421 was in practical sportsbike last month, they test rode it and was hugely surprised how well mannered it was and easy to ride at low speeds, but how the power delivery was controlled and just pulled without being stupid.
You can go Athena, Assassin, Cheetah Cub, Serval and a few others to boot in all manner of configurations, 385, 392, 421, 443, 465, 472, 496 etc, etc
So the first question to ask yourself is what do you want from the bike/engine, every customer who has asked me to build them a bike/engine, this is the very first question I ask them, once we know that, you can be better advised.
If you go to somebody who supplies the parts and doesn't ask you that question, then I'd be questioning how much they actually know about these engines and what is best, its not just the engine you need to think about, its the exhausts, carbs, electronics, clutches, primary gears, gearboxes, cooling etc, the list goes on
Reliability wise, again, comes back to the "what do want question", my Aprilia RS has done 1500 miles with no issues and a lot of dyno time/testing, I have customer bikes that have done over 1000 miles as well, with one customer who has done over 4500 mikes (its now due some pistons etc) - so that should give you some idea, MPG, if your worried about that, then your going down the wrong route anyway, but expect an average of 25mpg with mixed riding and maybe as low as 20mpg with enthusiastic riding
With regards PV options, there are some available for the big bore stuff, but they don't have a good reputation as such, so I've tended to avoid them for now
HTH
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Post by 2banger on Sept 24, 2019 20:49:41 GMT 1
Built 421 cheetah cub. Didn’t like it all. The power delivery was too vicious to make a good road bike. My bikes are all built to ride(not just to the local chippie and the local bike night)but some serious scratching around the roads of north Devon. Without the power valves you are either frustrated with a huge useless flat spot or panicking because of the sudden vicious ppwerband.(And I used to race in club championship,and if any knows me from practical sportsbikes track days at Caldwell park I can still ride a bike even though I’m getting on a bit now!) Reliability I doubt is any good if you like me and ride 5,000/6,000 miles a year. They may be good on the Dyno or in a straight line but without power valves for proper road use and a well sorted and tuned 350 ypvs is a better bike and faster from A to B.(I’ve been there and done that) 100bhp in a lc or ypvs frame with a vicious power band may sound like a lot fun,but in reality I found disappointing!!(and bloody expensive) I know I will probably get some stick from members on here,but you asked the question and I gave my honest opinion!!!!! Of course you can de-tune them with smaller carbs and mid-range pipes,but you still got no power valves!! You will get a softer power delivery with an Athena kit apparently,but not tried one so can’t comment. Couldn't agree more on cheetah not suitable for road use. Guzzle fuel, eats piston/ring kits and hot rod cranks My Aprilia rs250 fitted with white knuckle racing 465cc conversion 10 mil stroker ported 68mm on original Yamaha cylinders runs 39vhsh carbs on airbox pulls like train from tickover , no flat spots or hesitation, even does rolling acceleration in top out 40 50 speed restricted areas. Road Using front 19t rear 37t sprockets Good on fuel over 100 miles before reserve. Don't need powervalves with 10 mil stroker crank if ignition timing is adjusted , correct pipes and carbs dialled in . |
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Post by Deleted on Sept 25, 2019 0:02:19 GMT 1
I rode a 398 once. Didn't like it at all .
Reminded me of my 98 r1 if you twist it a bit hard.
Thing I like about my stock lc is if i grab a hand full
of throttle , it sometimes come up a bit in first and second.
No surprises , controllable fun. I'm not very brave.
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Post by JonW on Sept 25, 2019 0:34:13 GMT 1
What Dave said is bang on, you must know what you want from your bike to know what you want from a big bore, dont just think 'id like 100bhp' etc. This is what I said about the thought process a few years back, I think its still useful: www.2smoked.com/Yamaha_RD_%26_RZ_upgrades_-_RZ350_RD350_Big_Bore_Primer.htmlPlenty of bikes have Athena kits in them and have done quite a few miles, I dont think anyone expects any tuned engine to last as long as an OEM and would be looking to do more maintenance etc. Ie think 2 stroke MX or Enduro bike, ie pistons after a time as Dave says a customer needs etc So while not great for those wanting 10,000 miles a year the Athena bikes do work on the road and cane be made to perform and ride well. If youre in the UK Dave (Mutts) is the man to talk to. |
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Post by JonW on Sept 25, 2019 0:36:37 GMT 1
I rode a 398 once. Didn't like it at all . Reminded me of my 98 r1 if you twist it a bit hard. Thing I like about my stock lc is if i grab a hand full of throttle , it sometimes come up a bit in first and second. No surprises , controllable fun. I'm not very brave. Lol, I loved that about my R1! What a rush! I do like the way the original LC goes as well tho, but there are times when I just want a bit more aggression and acceleration. |
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Post by Deleted on Sept 25, 2019 6:11:59 GMT 1
"I loved that about my R1! What a rush!"
Tell ya what Jon, it frightened the crap out of me the first time grabbed to much throttle.
I'd had the bike a couple of weeks and thought wow.Then I put in new plugs and air filter
and the thing nearly looped over on top of me. Didn't even start it for a couple of months.ha
sorry to hijack ya thread ferox.
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Post by donkeychomp on Sept 25, 2019 22:47:07 GMT 1
Cheers for that link Jon. A very informative and funny read!
Alex
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Post by JonW on Sept 25, 2019 23:50:04 GMT 1
Cheers for that link Jon. A very informative and funny read! Alex Surprised you hadnt seen it Alex, its on the site about all my projects. |
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Post by earthman on Sept 26, 2019 7:53:41 GMT 1
Ok, I'm looking to upgrade to 421cc, what kit do I get, what bhp have you got, what mpg and are they reliable. Hoping for some enlightening motivation. Cheers John B That's the bit that concerns me the most about any of these conversion kits/power mods,....my guess is that you would be rebuilding the engine sooner than later. Personally I think that Yamaha knew what they were doing, keeping the engine standard is the best bet in the long term. |
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Post by JonW on Sept 26, 2019 8:06:08 GMT 1
Really its kind of predictable tho that if you tune an engine that the reliability suffers and that it would need more frequent tear downs. Even when tuner ported bike back in the day it meant the above, why should now be that different now. Remember that youre asking more of the gearbox and clutch and final drive parts as well by adding more power, this would mean more frequent maintenance on those parts as well. None of this makes doing this a bad thing, just like having Stan or someone else tune your bike, it just means you need to be aware of it. If you want solid reliability you need to stick with what Yam intended, but if you want a wild ride then you can tune or go big bore. Its not for everyone. |
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Post by headcoats on Sept 26, 2019 13:07:08 GMT 1
My build is an Athena 392 and I have no idea yet how it will ride and I may too not like it as Bazzer mentioned with a horrible flat spot etc
It has Zeeltronic fitted but that will be fighting the Lomas pipes !
Having the standard crank though , it would just be a straight swop to re fit the YPVS top end
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Post by Tobyjugs on Sept 26, 2019 14:00:27 GMT 1
My build is an Athena 392 and I have no idea yet how it will ride and I may too not like it as Bazzer mentioned with a horrible flat spot etc It has Zeeltronic fitted but that will be fighting the Lomas pipes ! Having the standard crank though , it would just be a straight swop to re fit the YPVS top end You won't have any problems I have 68 mm pistons on a standard stroke engine with no power valves and it's very rideable. |
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Post by Tobyjugs on Sept 26, 2019 14:12:08 GMT 1
The one thing I have thought about a lot, is with the long stroke big bore engines.
Are they losing that 2 stroke characteristics and becoming more like a 4 stroke with linear power in a small fragile engine?
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Post by 2banger on Sept 26, 2019 17:37:55 GMT 1
The one thing I have thought about a lot, is with the long stroke big bore engines. Are they losing that 2 stroke characteristics and becoming more like a 4 stroke with linear power in a small fragile engine? Some may say that's progress |
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Post by Tobyjugs on Sept 26, 2019 17:48:29 GMT 1
The one thing I have thought about a lot, is with the long stroke big bore engines. Are they losing that 2 stroke characteristics and becoming more like a 4 stroke with linear power in a small fragile engine? Some may say that's progress Is it like that then?. It' the sort of thing I always talk about with the tuner I use. He loves tiny pistoned high revving engines. |
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Post by ferox100 on Sept 26, 2019 22:33:44 GMT 1
Ok thanks all, a lot to mull over here, there are good sides and bad sides to these conversions. Can't be much difference from a tuned 385 v a 421 conversion in bhp or am I just assuming? The 385 route sounds like it has more driveability. Anyone compared the two, Dyno graphs to show. Appreciate any more info if possible.
Cheers
John B
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Post by arrow on Sept 27, 2019 7:02:58 GMT 1
Ferox, you can run the oil pump on an engine up to 392cc, but you are on the top limit of the oiling spec. You can also run the 421cc engine with the oil pump, but the pump will need to be uprated. The pump can also be brought 'back in line' for the 392cc engine if desired.
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Post by midlifecrisisrd on Sept 28, 2019 10:47:04 GMT 1
Ok thanks all, a lot to mull over here, there are good sides and bad sides to these conversions. Can't be much difference from a tuned 385 v a 421 conversion in bhp or am I just assuming? The 385 route sounds like it has more driveability. Anyone compared the two, Dyno graphs to show. Appreciate any more info if possible. Cheers John B Here's an old dyno graph of my 385 from Nick's dyno which reads on the shy side It still needs some work on the inlets and the ignition map is just a finger in the air guess 80hp is achievable but 75ish reliable Steve  |
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Post by donkeychomp on Sept 28, 2019 22:17:46 GMT 1
71 ponies is mighty impressive!
Alex
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Post by arrow on Sept 28, 2019 22:21:50 GMT 1
71 ponies is mighty impressive! Alex And that's at the back wheel, correct? |
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Post by ferox100 on Sept 29, 2019 0:06:10 GMT 1
Am leaning towards a 385 now, especially with the powervalves still in use and 75-80 bhp! That sounds like the best road bike set up with good spread of power. Steve, can a standard head be used on these? And I take it oring head set up would be best to save opening up head gaskets ID's?
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Post by midlifecrisisrd on Sept 29, 2019 10:17:39 GMT 1
71 ponies is mighty impressive! Alex And that's at the back wheel, correct? Yes at rear wheel As said it's a bit shy on that dyno. Mick says it reads up to 8% lower than others I do have one done a year earlier and before I fitted the v4 reeds and it was 73 I've been saying for years it needs a proper ignition set up on a dyno. I'll get it done one day 🙄 Steve |
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Post by midlifecrisisrd on Sept 29, 2019 10:25:56 GMT 1
Am leaning towards a 385 now, especially with the powervalves still in use and 75-80 bhp! That sounds like the best road bike set up with good spread of power. Steve, can a standard head be used on these? And I take it oring head set up would be best to save opening up head gaskets ID's? It's a recut standard head on mine with single inner o rings, long rod crank and wiseco 795 pistons on +1mm I did see Wiseco made a batch of ultra stroker pistons with a 6mm pin offset that allowed a standard head and gasket to be used but not sure how that affects the port map I'm hoping if it's dry at the weekend I can get it out the workshop and fired up. May even run it to the mot place if all ok but think the rear brake may have seized up 🙁 If you were closer you could have had a go lol Steve |
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Post by Tobyjugs on Sept 29, 2019 11:42:45 GMT 1
And that's at the back wheel, correct? Yes at rear wheel As said it's a bit shy on that dyno. Mick says it reads up to 8% lower than others I do have one done a year earlier and before I fitted the v4 reeds and it was 73 I've been saying for years it needs a proper ignition set up on a dyno. I'll get it done one day 🙄 Steve That is a nice dyno graph no stutter to be seen.  |
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Post by midlifecrisisrd on Sept 29, 2019 11:48:09 GMT 1
Yes at rear wheel As said it's a bit shy on that dyno. Mick says it reads up to 8% lower than others I do have one done a year earlier and before I fitted the v4 reeds and it was 73 I've been saying for years it needs a proper ignition set up on a dyno. I'll get it done one day 🙄 Steve That is a nice dyno graph no stutter to be seen. Yes it will pull WOT from 3k Before the v4 reeds it wasn't as much of a flat spot but there seemed to be a slight lull before the power rush Here's the earlier dyno graph Steve  |
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