Recipe for rebuild for more mid range

[m in sc]

another way around it is to oring the heads,  this moves the whole casting down which will basically require you to recut anyway.  (using the short reach plug heads, us models 70-75). however,  VP makes a nice billet head if you're willing to spend a bit. I'll be going that way on my t500 as the stock heads are just fucking garbage.

https://vintageperformanceproducts.com/shop/ols/products/yamaha-rd350-billet-heads

[Jung]

Those billet heads are really nice. I'm going to find a pair of late model Euro 250 1A0 heads next time - they have an extra fin and are for long plugs, so you have a lot more to play with. In a, probably rash, move - I decided to bite the bullet and ordered the cheapest, taiwan made, 4mm banshee crank I could find yesterday. Will let you know how I get on with squeezing it in...

[RDDave]

another way around it is to oring the heads,  this moves the whole casting down which will basically require you to recut anyway.  (using the short reach plug heads, us models 70-75). however,  VP makes a nice billet head if you're willing to spend a bit. I'll be going that way on my t500 as the stock heads are just fucking garbage.

https://vintageperformanceproducts.com/shop/ols/products/yamaha-rd350-billet-heads

Their dyno sheet shows about a 10% improvement in horsepower AND torque at 8,500 or so. From just a combustion chamber change. Seems a bit optimistic to me. Does it to anyone else?

And I would prefer to stay with the OE look. But that is not set in stone. Can that combustion chamber be accomplished with the OE head? And at what cost?  I always run 93 octane anyway as a safety factor. O-ring is usually a good thing and I used to index plugs on our wedge engines so spacing the plug up is no big deal.

[m in sc]

no, it makes a notable difference of done well. you can get a lot done with stock heads... finding someone to profile them though, thats another story.  i have had had a few sets (modded stock ones) that either i did or were done , its not that bad. if you are competent on a lathe, its not -that- hard. just reangling the squish and correcting the height and chamber volumes is pretty easy

[RDDave]

So, who here is competent with this procedure on OE heads and wants to do it? I have spare 350 heads now. But if enough better, I would find a pair of 250 heads.

[RDDave]

I just looked into the Zeeltronic and Vape.    I was shocked. One is on sale and the other is on back order. But together they are about $845. I have bought a lot of ignitions for my cars over the years but have never paid anywhere near that much for one. Or even two. Just WOW!

[Twill864]

So, who here is competent with this procedure on OE heads and wants to do it? I have spare 350 heads now. But if enough better, I would find a pair of 250 heads.

I will be experimenting with them over the next year. Just bought my license for engmod and need to get it all set up for the RD now.

[RDDave]

"license for engmod" ?

What is that?

[Jung]

engmod is a very sophisticated engine modelling software - you can model everything from intake through to exhaust as a system.

I'd think about the whole package before you get cutting. 350 barrels need the lip skimmed from the top, for o-ringed OEM heads, or RD400 gaskets and you kinda need to do that before you can set the squish gap. Also, total head cc is going to be dependent on the rest of the tune (porting and pipes.) A stock 350 has a head volume of about 22cc and runs fine on pump gas. Add good porting and pipes and it probably won't, as the dynamic compression goes up from the effects of the tuned pipe. Mine had detonation @ 22cc / 0.95mm squish gap. Still at 23cc / 0.95 and eventually cleared up at 23.5cc and 0.85mm. An experienced tuner will have done all the experimenting already.

I like the HPI ignition which is relatively cheap but seems to work well. Doesn't have a lot of output for lights but works fine with LED bulbs.

[m in sc]

yup the vape is pricy but worth it. i run 4 currently... they are that good. ;)

is it nec? no. absolutely not. the hpis is great, as is just a dyna-s.

But its also the charging system.

so by comparison... figure a full msd billet distributor, a 6al, super nasty coil and a 150amp alternator equivalent with a tunable curve box. (car). thats what you get.   OR... similar to this.. https://www.jegs.com/i/MSD-Ignition/121/7531K/10002/-1

[RDDave]

I don't mean any disrespect but that system is for a complete ignition system and will do just about everything that you might EVER need an ignition system to handle. I count 3 main components, 3 wiring harnesses, O2 sensor and harness, 8mm wires, etc. Very, very few hot rodders would ever need that one. You notice that it has NO reviews. And that is for a system for SBC which is probably the most common application on the planet.

Hardly the same as a simple programmable CDI. Not really an apples to apples comparison.

Since I am not a hard core racer, bang for the buck, or ponies per dollar comes into play. The head mods interest me greatly, but I simply cannot justify that much money for just an ignition.

But I don't want this conversation to get derailed. I am learning so very much and I appreciate the willingness to share so much hard earned knowledge.

Thank you.

One thing that does surprise me though is that I cannot find any dyno tests on mods to our bikes from anyone other than a vendor. Am I looking in the wrong places?

[m in sc]

you aren't wrong... but, well i cited 2 scenarios. the 1st being comparable. the 2nd being off the rails. (as far as car stuff), so i agree, it's not comparable per say. For what you get  benefit wise from a cdi for these bikes... its worth it. adding a dyna, for example, then trying to chase down charging issues is a common occurrence. the vape cures all that. the zeel is an add on from a different supplier and not 100 nec. on my t500 and 70 r5, they run a straight timing curve. 2 rds run them w boxes, and my tzr has a programmable cdi. 

  vape is 500 bucks with charging system included. an hpi is around 300 but has a mush weaker charging, but bang for buck, its the best hands down as its a complete system. A dyna for an rd is over 300 to run on stock coils and stock charging.  its the easiest to install though.

dyno runs are usually not very easy to find. one change doesn't usually do a whole lot, and its easy to get big numbers, but at the cost of rideability.

[RDDave]

 

[Jung]

Have a peek on Mick Abbey's Facebook page. He's a UK tuner that does a lot of vintage stuff and almost always posts dynos of his results. He's an absolute gentleman and has given me a lot of really useful tips. This is for a 350, and was what I was aiming for with mine...

https://www.facebook.com/photo/?fbid=2703540803238979&set=pcb.2703540876572305

[RDDave]

I see the trade-off.

30% loss of power below 4,000 is a lot. But man, that thing rocks 5k on. I would like to ride one just to see what the area under 5k was like for street driving. Losing a full third may make it a pain. Like a big lumpy camshaft, what is fun for one is intolerable to another. I wonder what the happy medium is? Less bottom end loss vs how much more power in band?

I sure would like to ride one on the street to see what it's manners are and to see more dyno sheets. But......

Thank you for that, it is very informative.