Prodigy Performance 3.6 Turbo DIY Install

[KaiserBill]

I don't know why you are shouting the obvious at me and think you need to give it to me as a clue. Your "clue" is not inconsistent with anything I have said. Please stop. Your lack of comprehension is hanging out and it's embarrassing.

I'm going to send this new understanding of volumetric efficiency to my buddies over at Caterpillar. They will love it.

P.S. A turbo doesn't have a 1:1 Ratio between exhaust pressure and boost. One impeller is compressing the air flow so it has a different geometry than the one that gases push against! These differences make a big difference in how much boost you get for specific volume of gas accelerating the unit. Also you will notice that the Intake housing is smaller than the exhaust housing[sometimes you need to measure it to see the difference]-- this is because the intake is trying maximize pressure by having a higher rotational speed than the turbine. Where as the exhaust is trying maximize the volume of gas pushing the against the turbine thus increasing the speed of the compressor. It is like having an overdrive where you get more rotations out of the smaller compressor wheel to keep up with the bigger slower rotating turbine.... So really you have more a 4-5 or even 10 to 1 ratio in favor of boost pressure over that of exhaust pressure. This is why the turbo becomes more efficient as the exhaust pressure increases and compress wheel's rpm goes up! You know it is the damn centripetal force formula.

[UselessPickles]

I'm going to send this new understanding of volumetric efficiency to my buddies over at Caterpillar. They will love it.

Just be sure to send it to them properly revised with my own correction of myself that it's all relative to atmosphere rather than the intake manifold. I got it wrong initially, but my error was really irrelevant to the point I was trying to make.

My revised summary of my understanding/explanation of volumetric efficiency:

The ratio of the amount (number of molecules) of fresh intake air that enters into the cylinder compared to the amount (number of molecules) of air present in a cylinder-displacement volume of local ambient atmosphere, expressed as a percentage.

Like you've pointed out a couple times, it's the amount of air (molecules) that matters, which is why I said "volumetric efficiency" is a bit of a misnomer. Volume alone does not describe an amount of air.

P.S. A turbo doesn't have a 1:1 Ratio between exhaust pressure and boost.

I never claimed it did. I only mentioned TiAL's wastegate spring ratings that are based on an assumed 1:1 exhaust:boost pressure ratio. See the fine print in the lower-right of this image:

Spring Pressures are calculated based on a 1:1 back pressure ratio. It is not uncommon to see a +/- 2psi differential.

Now I could be completely misinterpreting this, so please correct me if I'm wrong. They only mention "back pressure", which I assume to be exhaust back pressure. And it's a ratio of "back pressure" to something. Since a wastegate involves a balance between exhaust pressure and boost pressure fighting against the spring pressure, I assumed they are referring to a ratio between exhaust back pressure and boost pressure.

The spring in the Stage 2 turbo kit is rated at 7.25 psi, but it produces about 8.2 psi when used in this particular kit. Therefore, if that ratio TiAL refers to is correctly an exhaust:boost pressure ratio, then my exhaust:boost pressure ratio must be less than 1:1.

I have been unable to find anything that explains what "back pressure ratio" is in terms of a wastegate or turbo system. If anyone can point me to info about this, please do.

I previously claimed that due to this, boost pressure would be higher than exhaust back pressure in the 1800 rpm 0.3 psi situation being discussed. I now admit that I don't understand this exhaust:boost pressure ratio stuff enough to make that assumption. The more I think about it, the more I expect that exhaust:boost pressure ratio would not be constant, but would vary throughout different engine speeds and engine loads. In fact, I'm pretty sure a couple psi of exhaust back pressure is pretty normal even for a NA engine, which is clearly more than the amount of boost in that situation. The turbo would almost certainly create more back pressure than the stock exhaust system... then flow from this idea back to my previous post about how the extra back pressure would lead to lower volumetric efficiency...

[KaiserBill]

Just be sure to send it to them properly revised with my own correction of myself that it's all relative to atmosphere rather than the intake manifold. I got it wrong initially, but my error was really irrelevant to the point I was trying to make.

My revised summary of my understanding/explanation of volumetric efficiency:

The ratio of the amount (number of molecules) of fresh intake air that enters into the cylinder compared to the amount (number of molecules) of air present in a cylinder-displacement volume of local ambient atmosphere, expressed as a percentage.

Like you've pointed out a couple times, it's the amount of air (molecules) that matters, which is why I said "volumetric efficiency" is a bit of a misnomer. Volume alone does not describe an amount of air.




I never claimed it did. I only mentioned TiAL's wastegate spring ratings that are based on an assumed 1:1 exhaust:boost pressure ratio. See the fine print in the lower-right of this image:






Now I could be completely misinterpreting this, so please correct me if I'm wrong. They only mention "back pressure", which I assume to be exhaust back pressure. And it's a ratio of "back pressure" to something. Since a wastegate involves a balance between exhaust pressure and boost pressure fighting against the spring pressure, I assumed they are referring to a ratio between exhaust back pressure and boost pressure.

The spring in the Stage 2 turbo kit is rated at 7.25 psi, but it produces about 8.2 psi when used in this particular kit. Therefore, if that ratio TiAL refers to is correctly an exhaust:boost pressure ratio, then my exhaust:boost pressure ratio must be less than 1:1.

I have been unable to find anything that explains what "back pressure ratio" is in terms of a wastegate or turbo system. If anyone can point me to info about this, please do.

I previously claimed that due to this, boost pressure would be higher than exhaust back pressure in the 1800 rpm 0.3 psi situation being discussed. I now admit that I don't understand this exhaust:boost pressure ratio stuff enough to make that assumption. The more I think about it, the more I expect that exhaust:boost pressure ratio would not be constant, but would vary throughout different engine speeds and engine loads. In fact, I'm pretty sure a couple psi of exhaust back pressure is pretty normal even for a NA engine, which is clearly more than the amount of boost in that situation. The turbo would almost certainly create more back pressure than the stock exhaust system... then flow from this idea back to my previous post about how the extra back pressure would lead to lower volumetric efficiency...

Useless Pickles, as I've said I applaud what you are doing trying to figure out if Ripp's claims are legitimate claims. That is good for everyone. People who can and do test these claims are important. The problem is that most manufactures are really dodgy about the details of their systems on purpose. While they do put little disclaimers on their products like "*** Our Results We Obtained In A Controlled Lab-- Real World Road Experience Does And Will Differ..." That want to blind people with my 86PSI of manifold pressure at 15,000RPM claims. Which is all about marketing-- damn those Madison Avenue Bastards. It is a shame these guys just don't come out and give a full spec sheet of the units capabilities. It would make comparisons so much easier. Then again it would probably daze and confuse a lot of people with way too many numbers.

Back Pressure is a bad term. Let's call it resistance to flow. The impeller creates it in a turbo unit and the exhaust system itself creates it in a Normally Aspirated System. You cannot really get rid of it completely. And yes, you are correct, the Normally Aspirated Engines do indeed have back pressure that is lower than their Turbocharged counter parts. I'm sure that Prodigy has reduced this to a minimum by keeping the lengths of exhaust as short and straight as possible. Increasing the diameter of the exhaust will help a lot too from the turbocharger unit itself. If you are using stock exhaust from the turbo to the catalyic converter and muffler you getting more resistance on the back end of the exhaust then you would if you increase that size. This will make the turbo operate more efficiently at lower pressures. But you might not be able to change those diameters too much. They might have specified a system that uses pretty stock stuff. But I would call up Prodigy and ask what sort of benefit going up a .25 inch or even 1 inch in diameter would do for me. The lower the back pressure is at any rpm the better.

Well, if you are getting 8.2PSI on the manifold but are still using 7.25PSI rated waste gate spring-- then well there is your answer the stage two kit's Aftercooler is giving you 1.17... to 1 ratio of boost ratio. That's good actually. However, freeing up the exhaust system and getting the absolute least restrictive design can improve those numbers. Also letting the turbo operate at higher Boost Pressures can see an improvement on those too.

[From looking at Garrett's website that turbo class the 550HP can put out a lot of Boost depending on the specific size of the unit- they have a couple different ones in that class. But they all create killer power levels at 20-30psi. If you don't like your warranty much-- I would suggest getting a waste that can handle a 30PSI spring or greater. You know one that never actually lets the exhaust gas bypass the turbine... Add Water Methanol Injection and of course custom deep-dish pistons (increase the chamber volume a little and drop the compression ratio from 9.5 to 1 down to 4.5 to 1 or less ) and then stand back and see how much power your 3.6L engine creates! Of course this is only if you really don't like your warranty and your jeep is not your daily driver! It is not impossible to get a 180BHP per L with out much effort doing this. You know 648HP at 6500rpm has a way of intoxicating the owner/operator of the vehicle-- insurance companies are however never that impressed...]


The big problem with the Jeep's hood is that they didn't give you much room to play with in the engine compartment. That's a real bummer actually. Because the ideal setup on a V6 or V8 engine is a twin turbo kit. That will let you maximize the exhaust pressure from each bank of cylinders into its own turbo unit. However, that doesn't seem like it would fit under the hood given the space they have under their. But that would probably let you have a system with better low end performance but you might not be so hot at 6500rpm.

If you want to really want increase your analysis and ask Jeeplab if they can send you their raw data from dyno of the system. If you get the torque numbers you can actually calculate Volume Metric efficiency of the engine for any given boost level. Which means that you can really see if their claims are true or not. Of course I would call anything within 5% of the 40% percent claim too close to call. You will need to get the air-fuel ratio numbers too... you might have to use a range of those to get approximations-- but hey like I said if you get within 5% of that Ripp number then you know it is at least possible to do. And it should be possible to do that sort of performance with the Vortech unit.

Here are some more fun formulas for you:

http://www.turbobygarrett.com/turbob...choosing_turbo