karism

I`am wondering how to set the timing for a bridge,j-bridge,cheesport, peripheral port etc

Seeing that there is no way to set my ignition timing to factory settings.Why ? Because it cant idle at 900rpm.

1.How do i set the timing on a engine that idles at 1500+rpm to the correct specs ?( i turned the engine to tdc,and then set the timing with the engine stasionary.(I dont think its 100% accurate though)

2.Does anyone have the mechanical advance curve ?Maybe i can compinsate for the extra rpm ,by advancing the timing the appropriate amount.

Karis

bill Shurvinton

Normally you set the timing on these at 4000 RPM. Many people go one stage further and remove the vac advance or lock the dizzy.

4000 RPM is chosen because it is the max mech advance point.

REVHED

Mark the pulley using the instructions on Yaw's site and set the timing at 4000rpm. According to the HITMAN and from what I've seen bidge-ports don't usually need any more than 20* leading and about 10 or 11* trailing. Probably worth locking the dizzy as well.

karism

Thanks for the info!
I`ll set the timing at 4000 rpm.

(Lets hope i dont wake the dead with the noise,i have never taken it past 3000 while stasionary)

Karis

EVL-12A

hey i got an rx7 s1 and i was wondering what the timing would be for a 12a 6port right now its on 1500 rpm but i think its a bit much????

rxrotary2_7

in a bridgeport or peripheral 12a (1976-85) w/ an open exhaust at 6000 RPM's L should be 24* and T 5*

in a bridge on a 71-73 motor advance at 6K would be L 35* T 15*
in a bridge of a 74-75 motor you should have L 20*
and T 15*
i believe in the both the last sets of numbers the same would be use for peripheral...
what year 12a are you using? 74 and 75 are different from 71-73 housings as the spark plug locations and combustion chambers changed. this will effect the amount of advance required.

rxrotary2_7

evl-12a assuming you are refering to a motor from 77-83 (i believe that is what you are)
with stock ports using stock intake or a dellorto, holley, or webber you would want L 2*BTC and T to be 19*ATC

if running a street port with an holley, weber or dellorto you may bump it to L 8* BTC and T 12* ATC

you may want to call someone like racing beat before going ahead with the numbers, but i *believe* they are pretty close.

karism

Well,to be honest....

I have no cooking clue!I think its off the `73-75 batch.
All i know is that its Capella housings.

I`ll try to describe them.The Mazda name is big,there is only T and L on the housings not T1 and L1.There is also no emission holes in the exhaust ports,as well as no sleeves.

karism

rxrotary2_7 :
Are you the guy that they had in a fast fours & rotaries ?There was a small article about a station wagon.
I think it was in 1996..?

12abridgeport

Speaking of the sleeves, do they give extra power if taken out or not? I've heard both sides to this question, some say they do give more top end and hardly sacrifice any low end, where as, some say the other way round.

karism

12abridgeport :I kept on having trouble with my old housings.
I took the sleeves out of them,and ported it to the biggest possible size of the housing.The plugs that covered the emission holes kept on burning out.

I can tell you now...it was VERY loud.

The more square a port is,the more noise it will make ,if its more round,it will be more quiet.

What will the intake porting be off it ?

karism

Please refer to the attached pic :

If you take the sleeve out,the area marked in red can be removed(the port can be enlarged)

This will yield extra timing,and flow.
But also overlap,and noise

This is not recommended when running anything less than a bridgeport

12abridgeport

Yeah that looks pretty big. I'm just going to be doing a street port now, but was just wondering. So you say that the actual shape of the port and not just the size makes a noise difference?

Also would you happen to know if there are any limitations on how low i can take the port with the sleeve? I'm saying if there is enough metal there, can i make it open very early and make power kick in earlier?

gonzz

what's timing set on a 13B streetport?

fatboy7

The noise part, with the shape makes sense. If the port is square, it goes from completely closed to practically wide open much quicker than a round port would do. So the initial bite to the exhaust pulse would be weaker with a round port. The rapid opening of the port is what gives the exhaust its brap brap brap, sharp sound.

karism

If you refer to the pic again.Yhere is a substancial amount of porting that can be done with the sleeve still in.

From my experience i have learned that with a streeport,the sleeve can be left,and still make good hp.

Fatboy7 is right about how the noise is generated.

Leave the sleeve in,you will have enough timing.

Jeff20B

iTrader: (13)

rxrotary2_7, what timing setting should I use with '83 rotors in '73 rotor housings? I'd assume it would be the same as '73 rotors.

35º and 15º seems like a lot, even for a bridgeport. Mine is streetported. What timing should I run?

rxrotary2_7

35 IS alot, but it IS for a peripheral or bridge motor...
on 83 rotors being housed the 73 housings i would say L to be 8*BTC and the trailing would brobobly fall at 2* ATC. in 83 housings the trailing would more than likely be 12*after.... again, dont hold me to it, but try calling racing beat mazdatrix or someone else for a second opinion.
karism: that was not me...

wow, i never come in this 1st gen section. there is not enough time to go through all the sections.... i do like it here though.

karism

Mr rxrotary2_7....
1.Come on,tell us..were you featured in Fast fours & Rotaries ?
2.Can you help my identify my housings ?

Karis

Jeff20B

iTrader: (13)

I think for setting static timing (Karis, that's what it's called when you set timing with the engine off) on my '73 engine, I'll just line it up to what looks good and fire it up. Maybe I'll leave Trailing disconnected during break in with the T coil firing the plugs into the air (obviously there would also be plugs in the T holes). This way I can use a timing light and set the Trailing vacuum slider to something like 6-8º from Leading like you said, without worring about a bad split or something. Well, I guess I'm only worried because the dizzy was dismantled for a lube job and when it goes back together, it'll be close, but not perfect untill I use the light.

Anyway, I'll call up RB and explain my situation. What I'd prefer is the timing setting for 4000RPM. Or maybe I can just set it to 0º at idle (if it will idle after it's first fired up)? Thanks for the info.

Yes, I don't have a 7, but the folks here are more well rounded than the other sections. The Other Rotary section is way too quiet.

fatboy7

Too much split won't hurt, cause the spark will just come it too late, so it won't be optimal, power/emissions/fuel economy wise. No split could hurt, but there are even some who run this setup. All I know is that you definately don't want your trailing to fire before your leading plugs.

I wouldn't worry about starting the engine with the spilt wrong. Its easy to fix while the motors running.

karism

I normally set the timing static (thanks Jeff) and then try to start it.I`am worried about the change of plug location on the 70`s engines,seeing that the guy i bought the j-bridge rotorhousings from doesnt know exactly from which year it is.

It did run a bit erratic when i got it started,and i had to keep the revs up (more than 2000 rpm)

I can understand that everything needs to break in,but it didnt really improve when i advanced and retarded the dizzy.

So i was thinking that the timing was so off,that it made it erratic.

It was also very hard to start (took me 2 days to get the thing started,with 2x12v batteries wired in parralel)


Thanks for all the valuable info!

Karis :-)