Has anyone ever experimented with programming ignition maps for the RD's?
Seems there 'might be' some decent power going untapped even with the safe stock curves and especially the no curve points system. Especially... how can no curve or stock curve work well for both stock exhausts and aftermarket chambers? Doesnt seem to me they would.
I think you'd need a dyno that can hold an engine at a certain rpm to dial such a thing in though. The reason I'm curious about is because I was watching a guy tune his advance and he he kept the engine at a steady 3000rpm and throttle position and went from 10 degrees up to where the curve started to get flat so he backed off to a point where he got good power and a safe advance. The thing that surprised me was the torque doubled from 10 to whatever number he reached... I think it was 27 degrees. But it doubled.
I want to keep my RD400c build as stock as possible so I dont run into endless jetting loops and loose that low/mid grunt I want to badly for bombing around town and weekend rides but an electronic ignition is certainly something I am planning on... either the HPI or the VAPE.
Im so curious what an hour with a laptop and a dyno and an ignition map could so for one of these engines.
i have, pretty extensively. it will definitely offset a lot of the negative effects of a 'top end' ported motor with racy pipes(to a degree), but there are a LOT of pitfalls. with the vape, you need a zeeltronic added. it gets pricey, i have one, i love it. the hpi has oen built in thats really good, but not programmable unless you upgrade (i didnt). typically on mine its soemwhere around 15 or 17 degrees at idle, up to 23 degrees around 5-6k, then tapering down to about 15 degrees at 11k. ive learned that the (at least 350) motors seem to like 'stock' timing around 7500-7800 rpm. at least how mine are tuned. (19-20 degrees, again, 350)
Ive only really seen it benefit a fairly built motor, stock or stocking bikes doen benefit a whole lot from it, unless you have a normanly peaky motor, example, a 350 triple kawasaki. the down low advance brought back a LOT of bottom end.
the pitfalls are that you don't want it too advanced in the 'cruise' rpm. sure fire way to sunroof a piston. also, cost and complexity. :twocents:
thanks again for sharing your experience with this. Probably saved me from going down this route one day and wasting a load of money.. especially on a street bike I want to last.
I ended up ordering the HPI kit. Was going to hold of on it till spring but its back in stock so I figured what the hell.
John
Good post. Very interesting, thanks M.
There is some benefits with timing curves on our air cooled RD's. More benefits on water cooled engines like the RZ/LC engines.
IMO... the more you modify a RD the less you need it.
On Roadrace engines I build I use the analog PVL magneto's. They offer only a analog retard timing rate (good for high compression race gas engines) This type of curve gives good bottom end pull off the turns, then helps with retarded timing up on the big end not to make too much piston crown heat down the straights and not having to overjet with main jets, which kills the slower drive off the bottom in slower sections of the track. They like lean jetting to pull hard there.
Like Mark said, yes... more advance in the lower to mid RPM's helps a lot. On the same token it's the cruise rpm that can bite you if everything is not perfectly setup on the tune. (porting, compression ratio, combustion design, jetting and even gearing load must be considered)
I think the stock HPI curve will suit most users but not a fits all.
Chuck
as a side note to my comments above.. the way CHUCK ports and tunes a motor, yes, i agree 100% with him. the way MOST do or have, or an old school port job, you tend to lose a lot of bottom end. I hope that makes sense.
for example, my lc benefited a lot due to the porting and pipe choice, was ported by scott c maybe 10-12 years ago. the lightweight has one of chucks top-ends on it, didn't need as much curve. (has an hpi).
Great information :)
This forum and its members are a very valuable resource for sure. I couldnt imagine trying to rebuild one of these old bikes from scratch without it.
I'm going to add another tidbit here too...
When using a advanced timing curve in the lower rpms on these 2 strokes that mostly never used it, they become pretty rowdy with pop and wanting richer jetting up off idle when the timing advanced timing comes on they will feel real rich and they are not rich as the advanced timing makes it feel this way.
So when wanting a very docile bike stay away from heavy lower advanced timing maps.
If liking a Pro Mod style then yes, they run like a radical lopey cam sound and feel.
The RZ's with the Zeel box tend to do it some also, but more mild because the power valves are closed to kill off the high port duration when the advanced timing is all in.
Mikes RD350 is even more like that with his HPI ignition because when he bought the bike it had old school slightly over the top porting done to it, so I did what I could to save them, it's like almost a STG 2 port map.
Chuck