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RB20_ZED

By RB20_ZED,
in Engines & Forced Induction

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Guilt-Toy Grand Master

Guilt-Toy

Posted
Posted

cruise should be around 15 - 14.5

comming onto boost should be around 14 13.5

low boost can stay around 12.5

boost needs to go anywhere from 12.0 to 11.0 (Depends on tuner)

The richer it is on boost the fatter the tune is - the fatter it is the safer. safer = less power.

Its a trade off =)

Moral to the story is dont run the car on the edge because once the fat lady sings you will know about it :P

an afr of 20 is SUPER lean. around the 9-10 is rich, and 13-14 lean. ideal is 11.8-12.
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Cubes Grand Master

Cubes

Posted
Posted

With regards to running rich and being safe.

There's nothing safer about running a richer and running more ign. timing where the motor sits 1-2degree's under before det sets in then tuning with a slightly leaner mixture 12-12.5:1 with less ign. timing yet still 1-2degree's before det sets in.

The only reason I can see for NOT tuning with a 12.5:1 afr over the slightly richer 12:1 afr is if one is unable to check if every cylinder is actually running the correct afr. Influences such as injector flow, plenum/manifold and exh. manifold design affect cylinder VE.

Many usually guestimate cylinder afr by measuring that individual cylinders egt. You then simply trim the injector correct table slightly until they are all equal.

You are also able to do this by reading spark plugs, while your there ensure you are running the correct heat range plug by once again reading spark plugs.

Once you have the correct trim on every cylinder tune it at the slightly leaner 12.5:1 and run less ign. timing.

A richer mixture achieves a slower burn, this moves the peak cylinder pressure later in the cycle, the peak pressure being later in the cycle also reduces the probability of knock. Much like that of simply running less ign. advance.

A leaner mixture burns faster, the same effect as above can be produced with an optimum power mixture (12.5:1) and less ign. advance.

Ign advance doesn't make power, correct afr and ign. advance does. The aim is to achieve peak combustion pressure off the top of my head.. erm.. I forget.. I remember its some where between 10-20degrees ATDC. :S

Essentially running it richer with more ign. advance doesn't provide safety over running it at the correct optimum power mixture with less ign. advance.

So what do we do... Nothing.. lol

Do what the majority of tuners do.... 12:1 afr and ~2degree's below the det threshold on pump fuel as chances are we are never going to reach minimum advance for best torque.

Some funky fuel... Minimum Advance for Best Torque.

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