Stroker Upgrade

Captain Phoenix said:

I was hoping that while he was doing dyno testing if bolt on mods he would have tested it after a week of driving to see.

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It doesn't matter. The 4.0L PCM doesn't learn and undo actual power mods. Full stop.

His changes were incremental. Sure some were stacked and done in a day. Most were a week apart. Some didn't actually produce any power. If it did what you think it does, then it would have reverted to 136hp by the end of the series. It clearly did not.

I think we are consolidating two positive impacts of the cowl intake, and that is confusing the discussion. I can only speak to my experience with the Hemi, but I believe the same idea applies to the 4.0.

Cowl Induction (or any true cold air intake) does two things, both related, but each means something different to the PCM. First, the air is cooler. Second, the cooler air is more dense (meaning it contains more oxygen molecules by volume). On the surface it seems like the same thing, but temperature and density mean different things to the PCM. Density drives mixture, temperature drives timing - in simple terms, anyway.

When I first built the Hemi, it needed to have it tuned before I could drive it at all. To get it tuned quickly, I slapped an air filter right on the intake - like this:



I thought it would be fine for the tune - especially with the hood open. But it was not. This mill makes heat better than it does just about anything else, and the IAT's were exceeding 250. Seeing those IAT's, the PCM immediately pulled timing to avoid detonation (the hemi also has knock sensors which the 4.0 does not, but I think the end result it still the same. It pulls timing.).

As I recall, in this configuration it made a little less than 350 hp at the wheels. Less than I was expecting. The heat impact was such that the tuner could not get a good tune. He was able to make it drivable, but the hot air charge was certainly limiting power.

To address this, I added the cowl intake (as shown below) and went back to the same tuner and his dyno.



In this configuration the IAT's went from the 250 temps down to not too much above ambient. My tuner was then able to get a good tune. With just the addition of the cowl intake and much cooler air, it added 40 or 50 ponies at the wheels. All because the PCM was not pulling timing to protect the engine.

So technically the cowl intake by itself does not make more horsepower, but it does keep the PCM from seeing under-hood heated IAT temps, pulling timing, and limiting its power.

The increased density of the cooler intake air charge does make a bit more power, but not much at all by itself in the 4.0 as has been discussed. But in my case at least, the overall impact of the cowl intake was significant.

NashvilleTJ said:

I thought it would be fine for the tune - especially with the hood open. But it was not. This mill makes heat better than it does just about anything else, and the IAT's were exceeding 250. Seeing those IAT's, the PCM immediately pulled timing to avoid detonation (the hemi also has knock sensors which the 4.0 does not, but I think the end result it still the same. It pulls timing.).

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NashvilleTJ said:

So technically the cowl intake by itself does not make more horsepower, but it does keep the PCM from seeing under-hood heated IAT temps, pulling timing, and limiting its power.

The increased density of the cooler intake air charge does make a bit more power, but not much at all by itself in the 4.0 as has been discussed. But in my case at least, the overall impact of the cowl intake was significant.

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In the TJ PCM the primary drivers of spark and fuel are MAP sensor and RPM. Intake air temp (IAT) and Engine Coolant Temp (ECT) can both advance (cold) or retard (hot) the main spark table and the ECT pulls back harder -6° at 248F which would be a bad situation, but the IAT will pull -3° above 148F and in my 04 the stock advance at WOT can be as low as 2°. 148F is a common temp on the 4.0L intake on hot days, especially those with the IAT in the intake manifold. Fuel is pulled or added in small amounts indirectly through a temp factor adjustment, but 99% of the time it is managed by the closed loop upstream O2 sensor feedback, MAP and RPM.

On the 4.0L alot of this IAT heat comes from the intake sitting right on top of the exhaust and it's hard to mitigate. When you hit WOT the IAT temps drop fast with a reasonably placed underhood CAI or cowl CAI and even the stock airbox. Jezza's traditional underhood CAI and Windstar cowl tests reached the same gains from prior state on the dyno. For whatever reason the stock TJ 4.0L airbox has restrictriction that limits airflow resulting in lower peak MAP readings than expected.

The only learning function on the jeep has to do with rebuilding the part throttle closed loop STFT and LTFT tables following one of 3 triggers. A PCM reflash, disconnecting the battery for than 10 minutes or clearing emissions fault codes. That doesn't mean it won't use closed loop logic, it just isn't as good at predicting your next move for 10 minutes or so.

There is a whole bunch more on why I think strokers often don't match the builders numbers when they're placed under the hood without tuning. Spark and fuel are it in a nutshell.

Rickyd said:

I went with russ's parts. Though I went 10.2:1 cr,bigger cam and edelbrock head. Sometimes I wish I'd gone with lower compression since 91 octane isn't always available in rural areas. Octane booster and crossed fingers aren't my favorite situation.

Btw,the windstar intake i run didn't magically stop giving my motor extra hp.

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What cam did you go with and how much are your pistons dished. What did your dynamic compression end up being. Im in the process of building one now with Russ parts and debating on if I wanna dish my pistons more or go with different cam.

Apparition said:

@Woodrow

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Golen 4.6 stroker I've had now for 10yrs.