Ported, a14 timing?

[PinoyDat210]

Okay so i have an a14 head on an a14 block. The head has been ported from small oval ports to about the size of the a12gx ports. What should i set the timing to? I ask this because it has been changed from the stock a14 khlb210 model, to about the "gx" version. I took my engine and kind of based all the work off of the "gx" model besides the sidedraughts. I figured because of the better compression and valves that the a14 head has it would be far better than the a12gx when ported. I started it the other day after re-assembly, and i heard a sort of metal ping and a faster idle, I figure the timing and idle speed needs to be set and was hoping for some knowledgable help from you guys who are more experienced! thank you for listening and i appreciate the input.

[josh_t]

did you set the idle and timing to stock? and i have heard rumor that the open chamber heads on our a14's are more prone to detonation. mine is all stock and i keep it at about 5 degrees advanced over stock for a total of 15 degrees BTDC. it idles much smoother and it seems to use a little less gas when you lower the idle and set the mixture to compensate for the advance. all i know is what i've heard. i havent even so much as pulled the head so i wouldnt know much about what it does with higher flow and compression.

[PinoyDat210]

It was set at stock from before, and i havent touched it since. But i know from how crappy it runs right now it the timing needs to be retarded and the idle speed on my carb set. Really more prone to detonation, do you have any reasoning behind this, i would just like to know. I was just trying to set my engine to competition specs, to get a little performance out of the four banger.

[josh_t]

well i have heard that the open chamber design is less efficient and can detonate easier than the closed chamber because the quench area of the closed chamber does just that, quench. it can reduce the chance of two flame fronts forming and meeting which is what detonation is. and i wouldn't retard the timing. it will run rougher, use more gas, and actually reduce power. it can make the motor not burn all the fuel and that directly relates to less power since it didnt effectively use all the fuel and air it was given. it also can in ,extreme cases, burn valves. the fuel in the cylinder can still be burning when the exhaust valve opens and it can still be on fire coming out of the port, making the valve burn. thats a rare case though. the engine will make the most power when it is advanced as far as it can be without detonation. also running lean can cause some extra heat in the cylinder causing detonation. try richening it up a little and see what happens. you can look at the plugs to see whats going on too. it can tell you if you are running too lean or too rich or it looking peppered is a definite sign of detonation.

[PinoyDat210]

I did not port the combustion chamber just flanged the ports, i researched and found out i had the closed heart shaped chamber and that was more efficient and resulted in more power. I can see what u mean though. I will check the plugs and try to enrichen it. thanks man!

[josh_t]

oh ok. i was thinking you had it shaved to get the same compression as a gx. i would start around stock timing and maybe only advance it slightly since its higher compression. what carb are you running? and was the intake port matched to the head?

[datzenmike]

If your motor is stock you could probably set the timing to factory setting, but any changes will upset this. Things that will affect the timing.

 

Compression: generally, the tighter it is squeezed the faster it will burn. So the shorter burn time means that you should light it later by retarding the ignition. Higher compression will concentrate the heat energy closer to auto ignition, (pinging) so higher octane gas or further retard is needed. Head and piston top design, specially those with large quench areas, can actually reduce pinging.

 

 

Spark plugs: generally a colder plug is needed with increased compression.

Air Temperature: Warmer weather or warm air supply from behind the rad, generally requires less timing to prevent pinging.

High Humidity: increased resistance to detonation so slightly more advance can be used

Rich mixture: increased resistance to detonation so slightly more advance can be used

 

 

Any change affects everything else. Start with factory setting. With a quiet exhaust so you can hear the motor ping, try accelerating under load full throttle. Adjust the static timing until pinging is just eliminated. This is your new setting. Try different brands of gas and see if there are any that allow more advance without increased pinging. Think about a fresh air intake with cooler air from in front of the rad. Check plugs for signs of overheating and if so go to a colder set. A bit drastic but a wide band O2 sensor will display your air fuel mixture. Richer mixtures cool the cylinder/piston top/valves and spark plug and reduce the chance of pinging. A larger jet in the secondary will richen the full throttle fuel/air mixture without affecting slower speed mileage. It's trial and error to see what works or not.

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[PinoyDat210]

Yea, i will try this, i have the dch-306 hitachi at the moment, i would upgrade but the manifolds alone burn a deep hole in my wallet. Yea i upgrade my intake system a little larger diameter and a filter outisde the engine bay, with an aluminum shield wrap i got off some dryer ducting. Yes the intake was match to the head and the exhaust slightly shaved for better flow. I will start at stock and work my way from their. Thanks you guys im learning alot here!

[josh_t]

Yea, i will try this, i have the dch-306 hitachi at the moment, i would upgrade but the manifolds alone burn a deep hole in my wallet. Yea i upgrade my intake system a little larger diameter and a filter outisde the engine bay, with an aluminum shield wrap i got off some dryer ducting. Yes the intake was match to the head and the exhaust slightly shaved for better flow. I will start at stock and work my way from their. Thanks you guys im learning alot here!

 

mike's a smart guy. i have read up on all this stuff and i have it floating around up there, so i can do it in practice but i have a hard time explaining things and putting things into words.

 

@mike very well put