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Old 11th February 2008, 13:03   #1
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Default AFR - revising the state of tune

The supposedly ideal AFR for combustion- fuel mixture is 14.7 to 1. But we may need to revise this or the existing state of tune while we mod other parameters, especially in case of turbocharging an NA engine.

The above said AFR may provide you with the best combustion result but with other parameters like compression ratio, boost pressure and ignition timing changing - it might be a good idea to create a new map for each one of these parameters where we potentially map out what AFR suits each instantaneous situation.

Considering a situation where we do not alter the factory compression ratio which if considered as 10+, what would be the ideal AFR to run 7-9psi boost considering we have not lowered the compression ratio for this turbo project. Also, how do we factorize iginition timing (retard) in this situation with the end objective being a safe detonation free engine (fuel/ignition/boost)set up.
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Old 12th February 2008, 00:34   #2
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The key is to lower the intake temps as much as possible. This will let you run less retard and less richer.

A ballpark estimate of high 11/low 12 AFR is pretty accurate at max boost (intercooled of course). This is what most people I've spoken to are using, on 93 octane.

Its tough to talk about timing, but people usually start off with 6 to 7 degrees of retard (base timing) and then advance it as they get more confident. Of course, your basic turbo shopping list should include an FPR and a timing controller at the very minimum, regardless of the boost.
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Old 12th February 2008, 18:43   #3
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Erm...first, running 10:1 compression is not a good idea when you're considering 7 PSi of boost. If, for example, cylinder pressures are at 200 PSi+ (about 14 Kgf/cm2) at stock compression, you'll be playing havoc with the internals at 7 PSi.

Second, you can run 15:1 AFR at full boost as well. Provided the ignition runs at least 12 degrees (retard). Ignition is vital here. Since Swift has DDLI, you cannot fiddle with the distributor to run retarded (with the kind of fuel we get here, advanced timing=lesser reliability, & higher chances of knocking). Ignition controller is a MUST.

Ideal loads across rev range should read; about 11.5 AFR, with 8-10 degrees retarded ignition. Hopefully, the IAT & MAP sensor would be suitably jacked (read:lambda <1) to support the values...

Last edited by veyron1 : 12th February 2008 at 18:48.
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Old 12th February 2008, 20:49   #4
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Quote:
Originally Posted by veyron1 View Post
Erm...first, running 10:1 compression is not a good idea when you're considering 7 PSi of boost. If, for example, cylinder pressures are at 200 PSi+ (about 14 Kgf/cm2) at stock compression, you'll be playing havoc with the internals at 7 PSi.
hate to tell you this but you're wrong. stock internals will hold up pretty good at 7 psi and stock compression, provided your fueling and timing is correct. When you start moving into double digits therein lies the unknown.

Quote:
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Second, you can run 15:1 AFR at full boost as well. Provided the ignition runs at least 12 degrees (retard).
Maybe, but the EGT will be so high it will probably burn up everything south of the exhaust valve. Even OEM's dont run 15:1 AFR under boost..look at the datalogs from stock STi's for this....hell, even my normally aspirated BONE-STOCK miata runs 12.5:1 over 4500 rpm at full load.
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Old 28th February 2008, 17:25   #5
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Largest (size) Injector that can be handled by OEM ECU (that will idle well) -
I was wondering if anyone has played around/know what would be the largest flow rate injector that can be handled by the Maruti Zen ECU. What would be effect of lowering/increasing the fuel pressure to compensate for larger injectors. Would lowering it lead to very poor spray pattern ... etc... Thanks - Joe
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Old 28th February 2008, 21:40   #6
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if you let us know more about what you are trying to achieve (as opposed to what you want to do) then more people will be able to help.
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Old 29th February 2008, 21:34   #7
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Quote:
Originally Posted by swiftboost View Post
Largest (size) Injector that can be handled by OEM ECU (that will idle well) -
I was wondering if anyone has played around/know what would be the largest flow rate injector that can be handled by the Maruti Zen ECU. What would be effect of lowering/increasing the fuel pressure to compensate for larger injectors. Would lowering it lead to very poor spray pattern ... etc... Thanks - Joe
RdKarthik is the guy u go to for these questions ...
he's done too much RND on Maruti ECu's ...
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