Compression Ratio / Boost

[604rail_king]

I would go between 12-12.5, depending what the engine likes

x2

however you have to make sure you're not hearing pinging/knock even if your target afr is safe.

[atias]

i would even go 11.5 on a wideband to be safe, some cylinders runs hotter then the other and sometimes not all the injectors flows the same.
i would go 12 - 12.5 after all the injectors are checked and the sparkplugs reads the same on all cylinders.

[Coffee Commando]

I assume the reason we maintain that AFR is to help buffer between driving like Mrs. Daisy and Mario Andretti?

Is it absolutely impossible to maintain 14.7 AFR or pretty close with boost?

I would think you would have some leeway with the AFR. Or do people who run 15-30 lbs of boost run even lower than 12 AFR? Like 5-7?

[SilverXJ]

I assume the reason we maintain that AFR is to help buffer between driving like Mrs. Daisy and Mario Andretti?

What? Its to keep you from destroying the engine.

Is it absolutely impossible to maintain 14.7 AFR or pretty close with boost?

Why would you want to even try to do that? You have a bunch of reading before you even plan a supercharger.

[SilverXJ]

I assume the reason we maintain that AFR is to help buffer between driving like Mrs. Daisy and Mario Andretti?

What? Its to keep you from destroying the engine.

Is it absolutely impossible to maintain 14.7 AFR or pretty close with boost?

Why would you want to even try to do that? You don't even want to do that in open loop on a NA engine. You have a bunch of reading before you even plan a supercharger.

[Dezertxj88]

14.7afr is stoich
http://en.wikipedia.org/wiki/Stoichiometry

In closed loop fueling, the computer takes readings from the oxygen sensors which read +/- of 14.65 AFR (Stoich) and makes corrections for it. If your car is idling @ 13.5 AFR, the 02s can see this, and will know to pull out enough fuel to get back to stoich.

In open loop, the fueling is based off the MAF/MAP transfer function and the open loop fuel table. This table has to be calibrated any time you make MAF/MAP changes, and changes that affect the airflow of the MAF/MAP.


The Safc II will take over around 45% throttle at lowest..but can be set for 45+. So anything more than the target throttle position and the AFR is whatever you tuned it to be..On most N/A applications you will want to be 13.5-12.5, pending many variables...My very own personal example; my bolt on jeep 4.0 tuned on 87oct. didn't like anything above 13.1 without pinging. On 91oct which its currently running on, I've got it leaned out to 13.9 at the leanest, and at the richest around 13.4. I'm getting better mileage on 91 although it honestly feels no different between the 2 grades.

The higher the octane the leaner it can possibly be run without issue..lean = more heat though as well, so leaner won't always make more power, you really need to be on a dyno to find the point between lean & rich..to lean you loose power, to rich you loose power..Find the sweet spot and go 1 click richer to keep it safe! Like I said I cannot tell a difference on a 100% bolt on, internally stock 4.0, but I'm getting better mileage, and actually saving money per tank on 91oct

Na-t setups vs purpose built as well...na-t should be run or will need to be run richer to fight of detenation from the higher compression..purpose built forced induction motors won't because the lower compression..thus they are able to run slightly leaner!
With a 9.6:1 src, and 6psi, on a jeep 4.0 or 4.7L in your case...you'd probably be playing it safe. Your basically na-t...N/A motor + turbo. I'd expect on premium grade, it would ping if tuned above 12.2-12.5..Honestly if it were me, I'd get in on a dyno, and if its "safe" around 12.5afr, I'd richen it up so it would go no higher than 12.0afr. Just for safety sake...now it if were staying N/A I'd say run it where it likes, no need to play it too safe, which is exactly what I did.



I've decided the turbo/supercharger setups just aren't for me. I don't want to risk my stroker because I can't afford the correct EMU. Plus it'd only get me into more trouble


Also to toss you the idea...ditch the mechanical fan completely! You don't need it..go electric. Your gonna be spinning your supercharger off the same serp belt, so ditching the mechanical fan will help you got some with parastic (sp?) drag. Plus if you get a OEM ford tarus fan, they pull like 4800cfm...I've had my jeep, a/c blasting in 104* heat so far...the tarus fan has yet to kick on the "high" setting
Stock single core radiator, 180* thermo, tarus fan & OEM electric fan...we will see when it gets to be 115-120* what happens. But it never goes about 190 even sitting in traffic with the a/c blasting

[Coffee Commando]

I have the cooling figured out. I'm going to run a higher flowing Hesco thermostat housing with 180 thermo and the FlowKooler. I've had Electric fans for a while.

Something I just figured out after running the numbers on my 4.7 stroker rebuild from last year...... I'm at 10-10.2 SCR with 8.8-9 DCR. I've been running it on 87 Octane for about a thousand miles. Given the nature of Ethanol in fuel it was probably sitting at 84-85 Octane after sitting in the shop being rebuilt in my spare time for 2 and a half months.

I'm wondering if this is the reason it sounds like a diesel.