sa22rally

Hi Guys for 3 nights now ivé been searching the interweb and trying to read hightech english. Im danish and im pretty good at Hightech english and Engine tuning but im getting confused.

First the engine we are talking about is a 13 b 4 port with 12a center iron. 48 mm ida and Dlidfish with 7 Pin HEI.
Im running 100 octane gasoline and no vacume advance.

As fare as i understands the egine needs to ignite at 0Degrees and the trailing at 20 degrees that is with a 0 degree timing gun the first mark on the pulley and L1. and then at 4000 rpms it need to be 26 btdc is that because a rotary dosnt KNOCK at Idle?. does the rotary work like a piston egine where it would be bettere to have the ignition at EXample 15 btdc at 4000 rpm?.. Im reading the people make the gap between trailing and leading 10 degrees instead of 20 is that a god thing with the dlidfish. why is rotary guys scared of knocking when i read the timing is 0 and 20 Atdc i would believe that knocking didnt occure. ..

at last could anyone please tell it to me like im stupid why is trailing firing after LEading when the plug is located before?


I really hope you guys can give me som quick answers i finally booked a time on the dyno on monday nobody here in denmark wanted to touch the engine. and ive just rebuild it so im hoping it will be running great when im understand this timing

Best regards Rasmus Andersen Denmark.

sa22rally

is there any way other than the crank pulley to determin the TDC

DivinDriver

iTrader: (15)

I'm not sure about 13B's built for rally or what changes come along with the dlidfish ignition, but on a stock rotary leading timing is at 0, trailing at 20 ATDC at idle.

The reason rotaries don't like knocking (detonation) is that it can break apex seals.

NCross

iTrader: (18)

I thought 13b timing was more advanced than 12a. Trailing fires after leading. If your running an aftermarket carb tour vac advance could be running on full advance all the time. Thats why there is a solenoid on the Nikki.

Cookboy

iTrader: (10)

This animation may illustrate for you how the trailing ignition works to complete the burn.

midnight mechanic

sa22rally, what are you asking? did you lose loose the timing mark?
I know a quick and dirty way to find the correct position of the distributor.

Mazdatrix says, " the trailing plugs are only for emissions".

peejay

Mazdatrix is wrong, then. None of my bridge/peripheral port engines ran very well at low load if the trailing ignition wasn't working. With the trailing disconnected it would not run at an idle at all. You could feel it on the highway if it was getting a little weak, too. I've pulled off the road to scrape the terminals in the cap with a pocketknife to fix a cruise misfire. (This with direct fire on leading)


The STOCK ignition timing has 20 degrees of advance in it when you measure on the pulley. So if you set the leading timing to 0 degrees at idle, it will have 20 degrees BTDC when the mechanical advance is all-in (over 4000rpm).

If you want 26 degrees of "total" advance then run the engine at 5000rpm and set it to 26 degrees. Idle advance is not critical so it will be where it will be.

sa22rally

Hi guys today i got at little wiser and a little more confused. I put the distributer in at the mark with the mark on the pulley. but the engine ran like crap so i made it about 10-20 Btdc and i ran good. I dont have any vacum on the car i was told not to with weber. is it really because the vacum should have moved the ignition to about 10 btdc if it had been mounted.?

And by the way i keep reading to measure up the pulley to set 26 btdc at 5000 rpm but wouldnt it have been easier to set the timing gun to 26 degrees and just aim at the tdc mark?

Best Regards Rasmus Denmark

NCross

iTrader: (18)

To answer your question of why the trailing fires first, it doesnt. It has 20 degrees of advance. That means BTDC (before top dead center). So it fires after.

j9fd3s

iTrader: (3)

the timing dial on the gun will not work correctly with the rotary. it is much better to mark the pulley, and just rev it up.

sa22rally

just to be totaly clear if the engine was stock with stock carb ignition and everything els vacum and everything hooked up when would the l1 ignite at idle? the mark is 5 atdc but would the vacum advance the timing to 10btdc?

JDF93S thank you i did figure it might be something like that.

so if im understanding correctly becaus i have no vacume i should just measure the timing at 5000 rpms and set it to be 26 btdc and then the idle is what it is

craaaazzy

iTrader: (9)

Ok, this has totally confused me. The way I understand BTDC is it fires before TDC which would be right before the rotor reaches its full compression cycle. So if trailing is set to 20* BTDC and leading is set to 0, the trailing does fire first.

sa22rally

that must have been a mistake by Ncross becaus trailing is firing 20 atdc after full compression and leading is 5 degrest atdc. that is why im guessin that the vacume is advancint the timing to about 10 degrees btdc otherwise it would backfire alot.

At least thats my conclusion after hours of reading and 4 hours in the shop today trying to understand this issue i ended up with the idle tinming about 1" to the right of the l1 mark i thinks thats about 10-15 BTDC and at 4-5000 rpm 20-30 BTDC. im guessin the reason why im confused is that everybody says ditch the vacume but dont mention how to set the timing when there is no vacume

j9fd3s

iTrader: (3)

a totally stock car will fire right on the marks at idle, the stock ecu turns the vacuum advances off at idle.

the stock marks are either TDC (top dead center) and 15 ATDC (After). the mazda manuals say -15 BTDC (before), -15 BTDC and 15 ATDC are the same thing, there are just two ways of saying it.

the later 12A's and all of the 13B's are 5 ATDC and 20ATDC.

as you increase the rpms, the timing will advance, how much depends on the year of the engine.

with a stock car you just set the timing to stock, and it is fine, for a high performance car, we will set the timing at full advance, which is 4000rpm or more.

sa22rally

all right the thing is just that my engine is very rough and sounds bad when on marks and when i set the l1 to about 15 btdc thats about when t1 is at l1 and the gap is 15 degrees the engine sounds and acts fine som some must be wrong about the marks maybe i have to say its an old 4 port 13 b engine but wee have just put the engine together and everything should be fine

KansasCityREPU

iTrader: (9)

Is there any chance your pulley orientation is off?

sa22rally

I really wish it was that would explane alot but i have 3 different pulleys and the only difference is about 5 degrees not nearly the amount of incorrect timing we are talking about but i guess i just have to time it by listening to it, if there is no way to deterime tdc with out terring the engine apart

sa22rally

You´ve gotta explane this to me when mazda says the mark is 5atdc they mean after full compression right? and not as you basicly is saying that atdc is the same as before tdc .?

craaaazzy

iTrader: (9)

Thanks for explaining j9. Sa22, try to find TDC using your flywheel. That's what I'm doing.

j9fd3s

iTrader: (3)

TDC = Top Dead Center. the piston/rotor is at the point in the stroke where the combustion chamber is the smallest. on a piston engine, the piston is up, on a rotary the flat face of the rotor is toward the spark plugs.

BTDC = Before Top Dead Center, the spark plug is fired before the piston/rotor is at top dead center.

ATDC = After Top Dead Center, the spark plug is fired after the piston/rotor reaches TDC.

so mazdas 5ATDC is the same as -5BTDC. 5 after or -5 before.

sa22rally

Hi guys i really dont know if im the only one who had trouble figuring this out. But here i what i ended up doing i will get back to you after the dyno run on wednesdey with horsepower results and final timing.

To be sure it was a 13 b pully i had on i mark the possition of apexseal in L1 turned the engine clockwise and marked the position of the other apex seal in t1. then i turned the engine counterclockwise to the middle between the to. now i know that l1 is 5 degrees after TDC and i was able to mark TDC. When i knew where TDC is i could masure the distance from TDC to Trailing mark wich is 20 ATDC the distance is 20 mm conclusion if i measure like i did 26 mm from tdc clockwise (away from T1 and L1 marks) Then it would be 26 degrees Before Tdc at 5000rpm wich is what everybody recomends as timing on a race engine where smooth idle dosnt matter as much and where the vacume advance is dismounted. i also adjusted the trailing to be 16 BTDC at 5000 Rpm. and i must say that from 1500 RPM the engine revs much better. all this made the idle timing about 15 degrees BTDC for the Leading and 5 Trrailing

Thanks for the inputs and please feel free to comment on my experience.

Best regards Rasmus Andersen