This isn’t a misconception. This is a fact. Ripp did piggy back tuning with a 7th injector back in 07 until Diablo started supporting reflashing of the JK ecu.
Yes they were but they were injecting fuel after the centrifugal supercharger and had poor distribution and mixture and less cooling effect. It was controlled by a 'piggyback' but it did not retard the timing during boost.
Keyword is old school. Just because it was done doesn’t mean it’s the best solution. Just like we moved from carburetors to fuel injection so did all of the aftermarket companies you mentioned as well as just about every major reputable performance company in existence today transitioned to full reflashes.
Reprogramming the computer is exponentially better than trying to lie to it. Today’s ECUs can adjust based on input so they will in effect negate what your piggy back does to a certain degree.
Furthermore, adding a supercharger completely changes the airflow characteristics across the board, not just under load conditions further supporting the idea that a reflash is the right way to do it.
Different era's require different solutions. Different applications require different solutions. And yes a Jeep 4.0L and 3.8L engines are 'old school'.
In a simple low out, low rpm, low boost application, the auxiliary injector works well. Would it be better it it was designed and built and tuned at the factory? Absolutely. My '91 GMC Syclone case in point.
Today every major performance company does full flashes, but then again only support the newer vehicles and the abandoned the older('97-'06) or niche/low volume vehicles like Jeep.
There is NO lying to the stock ECU here. It 'steals' some wires and sensor values and is it's own stand alone auxiliary injector controller. It only delays the crank and cam sensor signals to retard timing under boost.
When you are in OPEN loop, the stock ecu does NOT negate what the auxiliary injector is doing.
And adding a SC and changes the airflow characteristics does not support the idea of needing a reflash. So does low restrictive air filters and intakes, bigger throttle bodies and headers also change the airflow characteristics and do not require a reflash as the ecu can adapt to the changes. When the supercharger has a 'ByPass Valve' at the inlet of the SC, there is very little change in airflow characteristics. THe intake air doesn't flow thru the supercharger.
You word your statement like Diablosport failed in relfashing JK ECUs. They have quirks and suck as a company but they certainly didn’t fail. You can successfully tune a JK ECU to handle larger injectors, a different map sensor and forced induction. Just takes a skilled tuner. I have the first relfashed and supercharged JK in the country and have been running strong and without issue for the last 7+ years.
They have their 'Quirks and fail as a company' Yes that is a fail. None of the Big Major SC builders are able to supply a kit with a proper tune. So now you have to employ an outside skilled Tuner to build a tune that the SC company should have supplier. At an additional cost of $500-1000 on top of the $5500-6500 SC kit cost. That's a fail.
That 7th injector is not cooling when you are in a non boost situation like crawling or partial throttle driving where you are still under vacuum but that supercharger is still adding heat to the system. Furthermore, a 7tgh injector doesn’t guarantee even distribution of supplemental fuel across all 6 cyclinders. You can create a lean condition in one cylinder while causing a rich condition in another. Ill take my chances with a water to air intercooler…
Your right, under vacuum the 7th injector is not turned on and is not cooling. The SC has a bypass valve and the air bypasses the SC. The fuel is staying cool and ready to be injectod under boost and cool the charge intake air temps.
Sandwiched under the SC and on top of the engine both heat soak way more and even though there is a bypass valve, the air still passes thru the heated manifold and intercooler core.
Crawling has minimal airflow for a FMIC or the water-air IC heat exchanger. They get hot and heatsoak when crawling.
You are right that there is poor fuel distribution when the 7th injector injects fuel AFTER the SC. When the fuel in injected INTO the SC it gets mixed/homogenized and vaporized and is blended with the air. Everywhere the air goes, fuel is right with it. There is NO fuel distribution issues. It's been tested.
2" thick water-air IC has to try and cool the heated air in only 2" of length. The charged air coming out of the supercharger can reach 250*F. The SC can add +150*F temp to the temperature of the air entering the SC which is already heated 20-40*F above ambient.
Liquid will always cool better than air. Injecting water/meth/fuel will cool the hot charged air more than any air-air or air-water IC.
Tell me which is 'hotter'- Putting your hand in a pan of 200*F water for 5 seconds or putting your hand in the oven at 200*F for 5 seconds. More heat transfer.
And you will be taking your chances with a air-water IC that doesn't work when crawling, gets heat soaked, can have a pump failure, only cools over 2" thick core, etc. On a street driven vehicle, it's a different application and a different story. Or maybe you only street drive your Jeep, IDK.
When one tries to size a supercharger or turbo for an application, they will refer to a compressor map to determine the best fit. Garrett does an excellent write up on this process (https://www.turbobygarrett.com/turbo...compressor_map
) but Eaton provides their maps in cubic meters of flow per hour compared to Garrett’s pounds per minute so I had to resort to this write up to get a good basis (How to Size a Custom Supercharger | eHow
You can use either write up to determine that you will be around 7-8 psi of boost at redline (~5800 rpm) which is ~1.5 pressure ratio.
Next up, assume the stock 200 hp number from the factory is accurate and expecting a 50% increase from a supercharger is fair so our target is 300hp. Based on my dyno graphs, I was making peak torque at around 3550 rpm so that gives us our rpm range and I assumed .9 VE at 3550 and .8 VE at 5800. These are assumptions and are probably a bit high for what the old 3.8 really does but still gives us a good guesstimate of where we need to be.
If you follow along the second write up with the numbers I provided and do some conversion to cubic meters per hour, you should get about 544 and 790 cubic meters per hour at 3550 and 5800 rpm respectively.
We now have enough information to look at the respective compressor maps to get an idea of where we are at. Both maps are posted below.
Starting with M62, with 544 as the x axis and 1.5 as the y axis, we are probably in the 62 adiabatic efficiency circle. The higher that number, the cooler the incoming air. At 790 you are damn near off the graph which means you are essentially outside the blower’s usable range.
Looking at the M90, you are at 60 and 58 adiabatic efficiency respectively. Well within the efficient operating window of that blower and we are spinning the blower quite a bit less (green dotted lines represent supercharger rpm).
So what have we learned here? Yes the M62 is cooler at that lower rpm as you mentioned but only by about 3% and it falls flat on its face as you rev the motor. The M90 has a lot more potential and is better situated to handle the entire rpm range.
Of course you look at compressor maps. But you also have to look at the application engine. the Jeep 4.0 and 3.8 do not rev over 5000rpm. They are also choked of by very poor flowing intake manifolds, low duration and lift cams and poor flowing small valve heads. They really act like an engine is 30% smaller, and they injest air closer to 3L engines. They are very low output engines. 190hp/242cid= .78hp/ci is very low.
5-6psi will give 40% more power and not have the increased heat of 7-8psi.
These engines don't rev, and more boost is not always a good thing, more heat, more problems. Any idea how much additional HP the stock fuel pump can supply? How much more boost can the stock head gasket or head bolts support before failure? How much more boost can the hypereutetic pistons handle?
In case anyone is wondering, 7-8 psi peak is about what I saw on my stock kit and I actually got 55% increase in HP so real world numbers line up fairly well with the math. Also the M62 is designed for 2.5-4.0L engines while the M90 can accomidate 3-5L engines (Fifth Generation Superchargers
) further supporting the fact that the M90 is the better choice for the application.
So you don't need 7-8psi at peak. You want 5-6psi across the whole rpm range. This will add a real +60rwhp and +70rwtq. That is a lot and plenty for the Jeeps when they only start with 135rwhp and 185rwtq.
Yep the M62 is designed for 2.5-4.0L engines and the last time I checked the Jeep 4.0 and 3.8L engines are less than 4.0L and with their poor flowing intake manifold, heads and low lift low duration cam they flow air and only act like a 3.0L engine. Looks like a perfect fit. Lower temps, lighter rotor weight, higher operating efficiency.
IN THIS APPLICATION, stock Jeep 4.0L or 3.8L with low 5-6psi boost and low reving 5000rpm maximum, the M62 is the right fit.