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Old 06-13-2019, 12:57 AM
Big_Cuss Big_Cuss is offline
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Join Date: Oct 2018
Location: CA
Posts: 171
Big_Cuss will become famous soon enough
Big_Cuss Big_Cuss is offline
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Join Date: Oct 2018
Location: CA
Posts: 171
Big_Cuss will become famous soon enough
The tune gains are likely very real. If the stock tune is very conservative on target AFRs, it's likely because that keeps it running rich, which allows the cylinders to run cooler than optimal, to reduce knock/ping on really hot summer days, under super heavy load, and/or on low grade fuel (ie 87 in some rural non-top-tier station).

This massive safety margin is why, though, that I debate whether I want to put a tune on my 4Runner.

See, it was an easy call on my 2010 Miata. The gains were real -- I took the stock vehicle from 167 hp at the crank to about 195 at the crank, by improving the intake, exhaust, and headers... and then doing a tune.

That Mazda engine would get best power at a peak AFR around 13.7. However, the stock tune would barely touch 12.0 just for durability's sake. So given that car was my baby, I figured I'd never give it less than 91 octane here in CA, and only top tier gas ever... so I'd be ok to reduce the safety margins... and we started revising the tune around better vvt timing tables and pushing closer to peak 13.X AFR

Interestingly, once I passed about 13.3, under any kind of heavy load (WOT), i'd start to get knock if I was anywhere below the powerband. It's generally called lugging. But the knock here was WAY worse as I pushed leaner and leaner. To the point we had to stop at about 13.3.

In other words, we left some power on the table just to have the practical safety of not having bad knock in a common situation that daily driver would encounter - say, in liike a highway onrap WOT acceleration from 2k rpm. In summary, I figured I'd rather have 195 hp and keep some reliability, over 200-205 hp and possibly blow my engine within a week from terrible knock by trying to get that liiiiittle inch closer to theoretical peak AFR.

So why do I mention all this?

Because there's a reason Toyota, like Mazda, has the 4.0L running so pig-rich stock. It's because they know these trucks are driven hard, often in 115F+ desert heat, on old oil, on bad 87 gas from some shitty podunk station that has lots of water and dirt in the gas tanks, while towing a trailer.... and they thus run enough extra gas into the combustion to prevent knock even with all those factors at once, so that the engine will STILL last 500k+ miles.

And if you get a tune, you'll definitely get more power out of the 4.0L. But if it's say, 300hp instead of 289hp (what the stock 4.0L gets on 91 octane instead of 87)....I'm not sure that's worth losing all the reliability which was the whole point we all got Toyotas in the first place.

And I just flat-out don't trust an aftermarket tuner to do the due diligence to know EXACTLY what threshold of AFR, timing pulling, and safety margin they need for the rare situation I listed above, where it's say a heatwave, you're towing, and using bad gas. I certainly would prefer to go a smidge slower, and be protected by a huge Toyota engineering team's experience in safety margin building, rather than some 5-person tuning company's experience.

PS - if you think I'm overcautious, consider the facts that in the course of tuning my Mazda...
a) my expert tuner accidentally turned off the vvt advance tables altogether one time lol
b) once accidentally set the AFR targets a tad too aggressively, and I only noticed when I logged on a hotter, 92f+ day, and saw a shitton of major, 5+ degree knock simple on part-throttle going up an incline offramp onto the highway. If I hadn't caught that, engine might have blown up and thrown a rod within a week.
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