Renix Stroker Motor

[Plug-Y-er]

Question,

Does the Renix ecm learn and adjust automatically if I rebuild with a stroker kit ? 

[ghetdjc320]

To a degree. But it cannot exceed certain limitations such as injector pulse width beyond a certain point nor will it read wideband data or allow you to tune the data stream. What it does have is a knock sensor. If your stroker is very mild with minimal requirements beyond that of a stock engine, you should be be good on a renix system. If you want to seriously ramp up power and tune the map for your engine, you’ll need to go aftermarket ecu. 

[pizzaman09]

My understanding is one can cheat the Renix system into working by changing injector size and fuel pressure to recenter the fuel demands of the engine.  The spark curves shouldn't need to change, plus the knock sensor does a great job taking care of that.  

As stated by ghetdjc320 the Renix system really isn't tuneable except for piggybacking and modifying inputs to the system.  

You can certainly make a stroker work on Renix, but it won't necessarily be optimized.  That said it is probably a great starting point and pretty close unless you do a standalone tune and have it professionally tuned to hone it in the last bit.

The Renix system uses the O2 sensor and knock sensor to retune as it runs, but it can only go so far, at that point you have to start playing with things like injector sizing and fuel pressures.  There is information out there on the topic.  

[Gojira94]

From what I've been able to learn about the Renix ECU, it does have a static 'fuel map' based on stock 4.0 pumping characteristics. This is essentially a table of RPM vs manifold pressure (MAP), with a matching injector pulsewidth. That can't be changed by any known means in the Renix ECU. So if we change the displacement upwards, for a given RPM vs MAP, more fuel is required. The ECU will fire the injectors for the length of time in this table. The O2 feedback will show lean so the short-term fuel trims will add additional pulsewidth (injector open longer) to try to correct it until it gets it right. With stock injectors, the percentage of time the injector spends open ("duty cycle") increases. Generally we don't want to exceed 90% duty cycle, with 80-85% probably ideal. So we look at either bumping fuel pressure a bit (returns diminish more quickly for an injector this way, as it begins to affect the spray pattern) or going to a larger injector (delivers more fuel at same pulsewidth).

 

Sizing a larger injector can be tricky. You'd want one with a good spray pattern at the chosen or stock fuel pressure without being too rich at idle. Ohms resistance determines how long the injector takes to open and begin delivering fuel. Renix expects to deal with injectors at 12 ohms. Higher ohms, say like 16, would take longer to open and begin delivering fuel, so the programmed pulsewidth wouldn't result in a cylinder starting to get fuel until later in the injector open/ close cycle. And then close before the expected amount of fuel is actually delivered. Or worse, still be closing but not closed, and sending a small remainder of fuel toward the intake valve after it's closed during the compression stroke (wasted fuel/ excess fuel for the next intake stroke). This is seen as a 'still lean' condition so even more fuel is commanded, arriving late, compounding the issue (shows lean, smells hella rich, poor fuel economy, compromised power).

 

Guys do Renix strokers without problems, but there's a LOT to think about to get it just right. Switching to the 91-95 7120 head is popular, and so is adding a mild cam, though not necessary. But the 'whole hog' effort delivers the benefits guys are really after.

[Gojira94]

Old 258
3.75 bore x 3.895 stroke, 5.875 rod (258.11 / 4.2L)

87-90 YJ 258 crank snout same as 4.0 crank snout, earlier ones are longer

 

Our 242 4.0L
3.875 bore x 3.414 stroke, 6.150 rod (241.57 / 4.0L)

 

Base 276 stroker (stroked, with shorter 258 rods, no additional bore)
3.875 bore x 3.895 stroke, 5.875 rod (275.61 / 4.5L)

 

281 stroker (base 276 bored .040 over)
3.915 bore x 3.895 stroke, 5.875 rod (281.33 / 4.6L)

 

284 stroker (base 276 bored .060 over)
3.935 bore x 3.895 stroke, 5.875 rod (284.21 / 4.7L)

[Gojira94]

7 minutes ago, pizzaman09 said:

one can cheat the Renix system into working by changing injector size and fuel pressure to recenter the fuel demands of the engine

 

Very well stated.

[Plug-Y-er]

Thanks, I was thinking about the 5.0 kit .4.2 l crank and stock 6.150 rods. Stage 2 cam

[eaglescout526]

I can’t help but feel, if there was someone who was good with editing or making ROMs, that the Renix system could be modified that way for a stroker. That being said, if the ROM from the performance ECU was dumped, it could be burned to a new ROM and put into the board of a standard ECU. Just my technical 2cents. 

[ghetdjc320]

If you are referring to the 5.0 kit from 505 performance, I would strongly suggest reconsidering. 505 is very difficult to deal with and their quality is not very good. On a 5.0 build, I would suggest going aftermarket ecu and getting your maps tuned properly. That being said, it may be worth running a cost/benefit analysis. If you go stroker, be sure to checkout Russ Potenger’s builds at Bishop Buehl. He can get you all the parts you need and is top notch in service and quality. 

[cruiser54]

Just do a poor man's stroker and you will smile from ear to ear while you're driving and sitting on a fat wallet. 

There's plenty of headroom in a Renix system for that. 

[ghetdjc320]

3 hours ago, cruiser54 said:

Just do a poor man's stroker and you will smile from ear to ear while you're driving and sitting on a fat wallet. 

There's plenty of headroom in a Renix system for that. 

Agreed. I’ve built many a stroker at this point. Best bang for buck for me was a 4.2 mini stroker with the old 232 crank and 4.0 rods. Diminishing returns past a certain point. There’s just so much more potential from swap candidates. I do still love the 4.0 but you have to sink a lot of coin into it to get it to perform much beyond stock numbers. A stock well running 4.0 with the right axle gearing is plenty of fun. They are easy engines to build though.