I've got questions about how far the timing should be advanced on a 20B at and above 4000RPM. All I've got to work with right now is what I know about GSL-SE distributors and how they advance to 25º BTDC above 4000RPM. the 12A ones only advance to 20º with a different curve. Granted, both are meant for NA use, and if I turbo or SC a 20B, I'll want less advance as boost goes up, but if I start off with NA (like I plan to), can I copy what was used on the GSL-SE since the rotors are 13B size? I'm sure the answer isn't as simple as that, but am I sorta in the right ballpark? I don't want to over-advance and break a plug or apex seal. Thanks.

 

if your n/a then the gsl-se sounds good to me, the stock cosmo motor has lower compression so it sould be ok, or you could start with the timing a few degrees retarted and advance slowly

mike

 

I can shift between the 12A and 13B dizzys without too much downtime. The only prob is setting up the shafts because they are unique to either 12A or 13B. That and the fact that a 20B dizzy cannot simply be purchased I don't think. The RB version is a kit that you must put together yourself. Oh well, it's one of those learning curve type things that'll get faster each time I do it.

Yeah, I think I'll start with a 13B dizzy and NA, then switch to a 12A dizzy when I go forced induction. Or maybe I'll just start with the 12A dizzy since the 1-5% less power won't be felt if it's coming out of a 20B Forced induction won't require any changes to the 12A dizzy (other than maybe retarding it a bit).

 

well they had 12at distributors too, i wonder if you could buy the boost retard/vacuum advadce things, and put that on later. i'm thinking about a 2 rotor turbo swap.

mike

 

I have access to a 12At dizzy, but I'm sure the owner would want more for it than I'd want to pay. Maybe I could build my own? Gotta get a good look at it some day.

 

one of the workshops in aussie sells a 20B Distributor, its about $1200AUS i believe - would be around $550USD

 

Is that the same as the RB version with the 6 cut reluctor and the clear perspex cap and modified rotor? The price is similar. Do you have any pics?

 

So what is everybody's total advance set to?

 

send me a laptop and i'll tell you =). actually my advace is not going to be much, apparently when you fire the leading and trailing together they dont want as much advance. do a search for timing and rice racing, he lays out a rough map.

mike

 

I didi a serach but didn't see any numbers. It was mostly just arguments over which ECU or EMS is the best to fire a 20B etc. I might need a fuel computer if I go FI (fuel injected), but most likely not a timing computer.

I could delete the split and prevent the total advance from exceding 20º L BTDC. This would make my design a lot less complicated.

Is 20º too far with no split?

 

it did just occur to me that you aren't turbo so that most of this doesn't help.
https://www.rx7club.com/forum/showth...ghlight=timing

mike

 

oh and btw, this is how you can tell i worked for a dealership. after i tried to extract something of value, then i've run you around in circles for 2 days. now i'm supposed to tell you to talk to another guy, or we dont do that here.

mike

 

I'll go with forced induction some day. I'll need less advance if I do that. A lot of you guys are running no split with turbos. I guess what I need to know most of all is what the highest your total advance goes; that will let me know how far my limit can be.

I tested both GSL-SE distributors on my 13B and they only advance to 20º BTDC (not 25º like I thought). This means a 12A dizzy should only advance 15º and I seem to recall that's what they did. In order to get 20º total advance on a 12A dizzy, I had to set my idle timing to 5º BTDC. I could be mistaken, but a 12A dizzy should be perfect on a forced induction engine.

Heh, I've been given the run-around Seriously though, you're the only one who's responded to this thread (other than HWO), so that's worth something. I just need to know what everyone's total advance is set to and maybe a little more about L/T split vs no split.

 

i kinda thought the difference between the 12a and gsl-se dizzy's was the vacuum advances (i know that diff #) and either the advance wieghts or springs (i don't remember). according to what i've read when you have no split it takes less total timing because the flame front moves faster. unfortunately my rotary engine book doesn't talk about timing split, it talks about split in reference to the spark plugs position in the housing.
my 20b is running an out of the box hitman map for a 13bt (3bar map 550inj), i dont have a fuel pump, or exhaust yet so ive got it rev limited to 4500rpm. i know i'll have to mess with the timing i was going to start at about 10degrees, but i have a turbo. if i didn't have a turbo i would set it a little retarded from a stock gsl-se and slowly advance it.

mike

 

My timing map on my 13bt (the motor before the 20b) wad peaks in places (with boost) of 26 degrees.

 

The difference between SE and 12A dizzys is the shaft end piece and springs. I couldn't see or feel a difference in the advance weights. I think to save costs, Mazda used the same weights and only changed the springs and bottom sections of the shafts. The main part of the shafts are identical. I took a couple pics which I'll up to my webpage as soon as the roll is done (I'm at like shot 3 or 4 or something).

So if I run no split, I could get away with 20º total advance instead of 25º? That means I could use my GSL-SE dizzy and the engine would think it's getting 25º when it's actually getting 20º. NA of course.

Hmm, on second thought, I should start out with the 12A dizzy with its 15º (that would make it retarded from stock GSL-SE, like you said), and no split would make the engine think it's actually higher, like maybe 20ºish.

That's cool. I may be getting a 20B (big maybe, but I can always hope) in september, so this info is critical. According to you guys, I could be anywhere from 14º to 26º. Going NA, I could use either dizzy, and when I go FI (forced induction) I'll just use the 12A dizzy.

I've recently been looking into ECUs and their ability to be programed with a laptop. Man, I'd love to do that! Too bad I don't have the cash.

Thankyou for the responses!

 

what are you going to run your 20b with for fuel? its relatively easy to use a haltech, and 3 fc leading coil packs on a 20b. most of them come with the injection on it so you dont have to add much else.

mike

 

I dunno. I guess which ever is cheaper. If a Haltech can be purchased for not too much, I would seriously consider getting one. Does it accept an RPM input? If so, I'm still planning on building my own 20B dizzy. Otherwise I guess it could hook to the stock CAS, right?

If I get a complete 20B minus the ECU (like all the 20Bs I've ever seen), then I'll probably get a Haltech. If it's the bare engine with no manifolds etc, I'll be going NA.

For fuel, I was going to use the intake manifold seen here: http://www.atkinsrotary.com/20b.htm and here: http://www.atkinsrotary.com/chuck.htm and here: http://cpwww.topcities.com/rotary/pg20.htm#20baero and a regular Holley carb (the kind meant for a V8) on an open plenum manifold. It wouldn't have the greatest low end torque, but it would be cheap. Or I could use an RB modded Holley (550CFM) meant for seperate runner manifolds, only I would go two to three on primaries and two to three on secondaries. I'm sure the flow would be less than optimal.

Hmm, now that you mention it, maybe a Haltech would actually be the cheaper route since I was planning on supercharging the 20B someday. At least with a turbo, I could up the boost in stages I suppose. The exhaust would be semi quiet with a turbo (I'd probably lock both open like so many people do) and I wouldn't need much of an exhaust system. I want to be LOUD!! Man, this is like a 180º turn around.

Still thinking...

 

welcome to the 20b world!
the haltech will accept a dizzy signal, or it can output.
personally i think a triple weber or something would
be really cool. the $1200 or so for the haltech seems
like a lot, but it could run the whole engine if you need it to.
or you could use a buick v6 ems that would work too

mike

 

So the Haltech will accept a dizzy signal? Do you know how many pulses it needs per revolution? Any 12A or 13B dizzy will output two pulses per revolution on each pickup. It's because the stock reluctor has four tips on it, and spins 50% slower than the eccentric shaft, so only two tips will pass by a pickup per eccentric shaft revolution. Could I use this signal? If so, I could easily swap between 12A and 13B dizzies.

A Dellorto is really cool on my friend's engine. A triple weber, if similar, would be awesome on a 20B! The Dellorto is on an old 4 port 13B and flows into primary and secondary ports simultaneously. This gives the engine instant throttle response but will bog a bit if floored at too low an RPM. I was trying to think of which carb I could cheaply adapt to a 20B and decided to go with a Holley based on 2x1962cc which would mean I'd need one for a 3924cc engine, or a 4.0liter V8/V6. Huh? An open plenum carb adaptor on Atkin's 20B intake manifold won't flow as well as RB's Holley manifold on a 2 rotor, but it might be cheap. Heh, for that matter, I might be better off building my own intake manifold like Sterling wants to do. That way I could have primaries seperated from secondaries, or have them all flow together in an open plenum, and then flow through all 6 engine ports simultaneously. The primaries on the carb would take care of low end, and vacuum or mechanical secondaries would take care of high end. A 20B has less intake pulsing than a 2 rotor because of the 120º rotor phasing. This ought to work well with an open plenum intake. Right? That's sorta what Mazdatrix originally did with their drag racer before getting an Atkins supercharger (they used a Holley PROjection originally, and are now using fuel injectors under the SC).

What are your opinions on seperate runners vs an open plenum?

For this project, I might be looking at $2000 to $3000 for the engine, $? for the ignition (I'll know when it's done), $500 or less on a carb, $? intake manifold, $42 to $100 exhaust (I want it loud!) $100 driveshaft, $100? custom oil pan, $200 tranny shift kit/filter, $50+ tach, $50+ misc guages. I'm sure I left a few out, but assuming the engine costs $2000 and cutting all corners, I could come in at $2992 (I need a new tach, but the other guages, while rather nondescriptive, are good enough to get the engine running).

I won't seek serious power untill I can afford to do it properly (like maybe in an FC, so I can drive it really fast too). My current projects all need engines anyway, so I figured why not go for the 20B when it's so clearly the right choice?

 

the haltech wants a tach signal. an open plenum is sorta what the 20b has on it now, so i think that would be the way to go. as far as carb sizing, the 20b is a 4 liter v-6, so there ya go. or you could take the racing beat sizing and multiply by 1.5. i wonder if it would be possible to build a "box" on the stock lower intake?

mike

 

Do I multiply Racing Beat's sizing by 1.5 because of the extra rotor? Or because their carbs are set up to run on a seperate runner manifold? A 600CFM Holley is what they recommend for a streetported 13B, so I guess I'd need a 900CFM carb, right? A much smaller carb would work on an open plenum manifold. I bet I could get by with an out-of-the-box Holley from Schuck's. It just needs a custom manifold like the box you mentioned. I think a basic 5.0L V8 carb would work ok, with just a little accelerator pump adjustment. There are more intake pulses on a 20B than a 2 rotor, so an open plenum ought to be ok.

 

actually that sounds right, a 5.0 carb would prolly fit the bill really well.

mike

 

Dude, you rock!

I first wanted to get a basic bare block to add my ignition and a custom manifold to. Now I hope to get a complete 20B like how they come from Japan so it'll come with pretty much everything. I want to see if I can use the stock lower manifold with a carb and anything else that I can adapt to get it running cheaply. I'll definitely be keeping everything else for future use though. When I can afford a Haltech or any other ECU and a great turbo and FMIC, I'll also be able to afford to replace the tranny and diff with stuff that'll take the power. At least having the 20B in there is step in the right direction, even though it'll be gutless by you guys' standards. Heh, approx 225HP in this old car is over twice as much as stock, so I'm not complaining.

 

i like working on projects, its fun when it all comes together, and i dont care how much hp you make. i'm only shooting for 300-330rwhp out of mine. i want the torque, and the sound. plus i get the satisfaction of having done it myself, which is a better high than 1000's of hp.

mike