Supercharging An Rb20det?

[mad082]

yeah understand all of that. i understand all the "ifs" and "buts" to it. i sort of mixed myself up a bit with it all. i started adding in power, when i really just wanted to make the point/ask the question that 14psi of air flow is going to be the same amount of air whether its a medium size turbo or a big turbo (same amount of air going past the afm). a bigger turbo will be able to make more power out of it due to efficiency, cooler temps, better exhaust airflow, etc... generally speaking.

[Warpspeed]

Hakai, o/k let's look at the options.

You don't want to go the RB25/RB26 or RB30 route because it has all been done before. Fair enough, although it would be fairely straightforward and give a known good result.

Sydneykid has a point, in that a proven turbo package on your RB20 could be made to give excellent results, but again it has all been done before.

Turning to supercharging, neither of the Toyota superchargers are really large enough to make a conversion worthwhile. The 4AGZE is rated at 150Kw and the IGGZE is rated at 160 factory Kw. Putting one of these blowers on your engine will get you nowhere. Sure it will have more low end torque, but the top end power will be rather dissapointing. Fitting one of these will be a LOT of work, it will certainly be unique, but I am sure you are never going to be entirely happy with the final result after all that work.

A centrifugal supercharger will be easiest to fit, but the engie will be vey peaky, far more peaky than with a turbo. The Skyline is not a light weight car, and the RB20 is not a huge engine. It will feel slow except right at the extreme top end. Centrifugal blowers work best with large capacity engines with very poor top end breathing, I would very strongly recommend you not fit a centrifugal supercharger.

Your best bet is either an Eaton or a screw supercharger. If you are on a very tight budget, get a secondhand Eaton. These are not wonderful, but are very good value. If you want the best, buy an Opcon or a Whipple screw blower. It will be expensive, but the results will be extremely good.

If I was doing what you are doing, I would first fit an RB25DET and gearbox, and get it all going in the car standard, with a Power FC computer. I would then either upgrade the turbo, or fit a screw blower to it as I could afford to do so. Another avenue would be to sell your car and buy an R32 GTR, and start with that. More expensive, but a much better basis to begin from. By the time you have upgraded everything to handle the extra power, an R32 GTR will look like a real bargain.

[mad082]

fitting a late model (s15) sr20 would go ok i reakon. they are about 184kw which is the same as an r33 rb25, but has a bit less torque. but it does have a 6 speed gearbox.

[Hakai]

i've been thinking about the 14psi is not 14psi comment for a while now, and i've come to the conclusion that generally speaking 14psi is 14psi. i have racked my brain over this. sure things like heat from small turbos and that sort of thing come into it, and i'll accept that. but you get to a point where 14psi is 14psi.

this is my reasoning. you look at all the big turbos. they make big power, but at big boost. it is like saying 100kmh is 100kmh. if you do it in 3rd gear it may rev at 4000rpm and produce a bit more heat, but if you do it in 4th you are still going at 100kmh but a bit more efficiently.

the subject car is stock and you change nothing but the turbos. if you have a turbo that is efficient at 18psi running at 14psi and another turbo that is effiecient at 28psi running at 14psi the power is going to be similar. sure the 28psi turbo will have a bit less restriction on the exhaust so the air can escape better, but on the compression side it will flow about the same. the wastegate is controlled by the compressor side of things. the 28psi turbo will have a bigger compressor so it will be able to flow more air. however, because a motor has restricions, like an intercooler, and the motor itself, that limits the airflow. the bigger turbo has a bigger compressor which takes less rotations to pump as much air as the smaller one, but once it flows enough air to create 14psi of pressure the wastegate opens and it stops increasing the air it is flowing. the smaller turbo will be spinning faster to create the same amount of air. the motor can only take in so much air, and once you start flowing above that amount you are raising the boost and the wastegate opens to lower the boost back down to the lower pressure so the turbo slow down.

now not much of that may make sense but i just had a thought of a simplified version.

you have a length of hose with a restrictor in the end of it that limits the flow (the way the engine does. it can only suck in so much air at a fixed rpm) half way along the hose you have a pressure valve that releases any excess pressure (wastegate). this means that the pressure between the regulator and the hose is always 14psi. now turn the hose on so that it just opens the valve. there will be a fixed amount of water coming out of the restricot at the end of the hose. now crank the hose up. there will be more water coming out of the regulator, but no more coming out of the end of the hose than there was.

feel free to debate it or correct me, but use examples, don't just say it doesn't work like that. remember my example is on the one car changing nothing but the turbos.

I'll use the example that best helped me to understand this when I was wondering why as well This is all 100% theory, you could do this in practice, but I have never done it. It is however; an easy to understand explanation.

1)Take two lengths of PVC pipe, one 40mm and the other 50mm. The length is irrelevant but assume they are at least of equal length.

2) Plumb a pressure gauge into each pipe, at the same location in the pipe.

3) Pump water through each pipe until the pressure reaches and sits steadily on 14psi.

4) Observe the amount of water flow coming out of each pipe.

What you will find is that the 50mm PVC pipe will have far more water flowing out of it than the 40mm pipe, even though they are both pressurised to 14psi. The reason for this is simple, as SydneyKid has said a few times, pressure is only a measure of resistance to flow. The 40mm pipe only requires X amount of water flow to be going through it before the pressure inside the pipe reaches 14psi. The 50mm pipe has a larger area to be filled and as such requires more flow before the pressure inside it also reaches 14psi.

A turbo flows on the same principle. A larger turbo has a greater area inside that has to be pressurised before the internal pressure reaches 14psi, as such, more airflow is required to obtain the same pressure reading that you got with a smaller turbo. This is why when a friend of mine got his MR2 turbo rebuilt and hiflowed with T04 internals and bolted it back on, running 2-3psi less boost he saw a drastic increase in power. (not dyno proven, but you don't always need a dyno to tell you you've gained power - let's say he went from having to try to chirp 2nd on a gearchange, to having to try NOT to spin it)

Hope this explanation helped mate

Edited July 12, 2006 by Hakai

[Hakai]

I don’t care how long you spend on your supercharged RB, I bet I can beat it in torque and useable rpm with a turbocharger in less than 1 day. That’s a fact and I am no genius, it’s simply because it’s that easy.

First let me say SK that I do have alot of respect for your advice and I realise that someone with your experience could very easily out-do what I want to put together. However; That aside, I do want to do something different. As Stocky and Warpspeed have both said, I could produce a good power figure with a very drivable street car from supercharging the RB20 and it's something very, very different, which is what I wanted to do

Although, as Warpspeed has pointed out, alot more than I thought, will need to be upgraded and the cost just isn't in my price range I do appreciate your input though SK Cheers.

the lysholm blower will give you crisp boost response right off idle and hold it all the way through the top end. it's the best choice unless you can afford an Opcon Autorotor (basically an upgraded lysholm, but you pay for it)

if i had to guess (which i dont' like doing) your setup might run something like this:

RB20DET

1600 lysholm

excellent intercooler

management

excellent exhaust system

big cams?

i would suggest it would probably take you 12-15psi to get to 200kw atw, although my knowledge of the RB20 is limited. i know when we did calcs on my RB30DE plus a lysholm 2300 we were looking at 14-16psi to make 300rwkw.

either way the final power figure is irrelevant, what matters is how it feels to drive on the road. with instant boost response and a flat torque plateau that just never stops, it will be a very nice thing to drive. it will sound pretty mean too i reckon.

Exactly what I wanted to know. Would be awsome to have snappy response off the line and it hold all the way through the rev range. Your guess as to my possible setup is pretty much what I was thinking as well Except I had thought more towards the 1200A, but if you think the 1600 will be better, I'd trust your judgement.

I also agree that the final power figure isn't that relevant, I too really only care about how it feels to drive. How much torque are we talking about here The sound would be incredible I'd imagine also.

Hakai, o/k let's look at the options.

You don't want to go the RB25/RB26 or RB30 route because it has all been done before. Fair enough, although it would be fairely straightforward and give a known good result.

Sydneykid has a point, in that a proven turbo package on your RB20 could be made to give excellent results, but again it has all been done before.

Turning to supercharging, neither of the Toyota superchargers are really large enough to make a conversion worthwhile. The 4AGZE is rated at 150Kw and the IGGZE is rated at 160 factory Kw. Putting one of these blowers on your engine will get you nowhere. Sure it will have more low end torque, but the top end power will be rather dissapointing. Fitting one of these will be a LOT of work, it will certainly be unique, but I am sure you are never going to be entirely happy with the final result after all that work.

A centrifugal supercharger will be easiest to fit, but the engie will be vey peaky, far more peaky than with a turbo. The Skyline is not a light weight car, and the RB20 is not a huge engine. It will feel slow except right at the extreme top end. Centrifugal blowers work best with large capacity engines with very poor top end breathing, I would very strongly recommend you not fit a centrifugal supercharger.

Your best bet is either an Eaton or a screw supercharger. If you are on a very tight budget, get a secondhand Eaton. These are not wonderful, but are very good value. If you want the best, buy an Opcon or a Whipple screw blower. It will be expensive, but the results will be extremely good.

If I was doing what you are doing, I would first fit an RB25DET and gearbox, and get it all going in the car standard, with a Power FC computer. I would then either upgrade the turbo, or fit a screw blower to it as I could afford to do so. Another avenue would be to sell your car and buy an R32 GTR, and start with that. More expensive, but a much better basis to begin from. By the time you have upgraded everything to handle the extra power, an R32 GTR will look like a real bargain.

Thanks again for the reply Warpseed All this info is starting to come together and scream in my face that it would be awsome, just as I imagined it would be. It's good to hear that it wasn't a completely stupid idea in the first place

You do bring up some really good points though, as I said just up a bit in this post. The costs are something I didn't calculate very well. Cost is the thing that is starting to put me off this whole idea, maybe one day when I have money to throw around

Another thing is that I might still have a buyer for my car, guy who was buying it, his best friends father is a panel beater and can repair it cheap, so I might still sell the old girl, only found out today

Thanks to everyone for the information, I'll be keeping every scrap I've saved and hope that one day I can actually put it into practice. Do what Warpspeed said, start with an R32GTR and build on that... RB26DES anyone?

[StockyMcStock]

you're a bit off with your thinking regarding the reasons the larger turbo makes more power. generally speaking, the reason a larger turbo makes more power, or the same power on less boost, is that the hotside is not as restrictive as it used to be, because it is simply larger.

when you drop your exhaust back pressure, power goes up. pumping losses are reduced so you get more power. the effect is magnified at high RPM and airflow levels as well.

of course, the trade-off is response and boost onset.

cheers

[Hakai]

you're a bit off with your thinking regarding the reasons the larger turbo makes more power. generally speaking, the reason a larger turbo makes more power, or the same power on less boost, is that the hotside is not as restrictive as it used to be, because it is simply larger.

when you drop your exhaust back pressure, power goes up. pumping losses are reduced so you get more power. the effect is magnified at high RPM and airflow levels as well.

of course, the trade-off is response and boost onset.

cheers

I wasn't intending to refer to power, only airflow. I thought my example was correct in explaining why a larger turbo will flow a higher volume of air at the same given boost pressure level than a smaller turbo?

*EDIT*

With the MR2 example, I was under the impression that higher airflow packs more air into the chamber for combustion which = more power? The exhaust being less restrictive makes sense too and I hadn't thought of that, but surely it's a combination of both?

Edited July 12, 2006 by Hakai

[Cubes]

With higher VE comes better cylinder filling. Better cylinder filling means you get more fresh air in and leaving less of the old crap behind.

If you can raise VE then you have a motor that is breathing and pumping air at a greater rate.

To achieve the same airflow with this better breathing motor the boost pressure will be lower.

A motor with a higher VE = a better breathing motor, a better breathing motor = less boost required to achieve a given airflow.

Think of it like taking a deep breath while running then breathing out of your nose vs breathing out of your mouth.

As you know many things affect the engines ability to pump air, head design, cam profile/timing and inlet/exhaust pressure.

An engine is nothing more than an airpump.

[StockyMcStock]

I thought my example was correct in explaining why a larger turbo will flow a higher volume of air at the same given boost pressure level than a smaller turbo?

i'm not sure i fully understand what you're getting at, but here's another way of looking at it that might help.

the bigger turbo can flow more air because it is physically larger in every way, simple really. if the resistance to airflow downstream of the turbo (the piping, intercooler, bends, plenum, and head) remains exactly the same for both turbos, they will flow exactly the same amount of air at the same boost pressure, and the engine will make the same power.

but that's not what happens. when you put a bigger turbo on and change nothing else, your head immediately becomes more efficient and imposes less restriction to the turbo's compressor stage, because the turbine stage is flowing more freely. when your exhaust back pressure goes down, you can cram more inlet charge in more easily each time the cylinder fills, so once again there's less resistance to the compressor stage.

the fact that your compressor stage is physically larger than it was before doesn't mean much, only that it's capacity for outright flow has gone up, and so has its flow delivery characteristics (the compressor map has changed). note that this new, larger compressor stage will probably require less shaft speed to feed the same amount of air as before to the engine (at less pressure), which again lowers your exhaust back pressure as the whole thing doesn't need to be driven as fast. again, power goes up. the end result is a more peaky and nasty engine though.

so i guess what i'm trying to get at is, the power gains you get aren't so much as a result of the compressor stage being physically larger, but as an indirect result of the turbine stage being larger. i hope that clears it up for you.

[Hakai]

i'm not sure i fully understand what you're getting at, but here's another way of looking at it that might help.

the bigger turbo can flow more air because it is physically larger in every way, simple really. if the resistance to airflow downstream of the turbo (the piping, intercooler, bends, plenum, and head) remains exactly the same for both turbos, they will flow exactly the same amount of air at the same boost pressure, and the engine will make the same power.

but that's not what happens. when you put a bigger turbo on and change nothing else, your head immediately becomes more efficient and imposes less restriction to the turbo's compressor stage, because the turbine stage is flowing more freely. when your exhaust back pressure goes down, you can cram more inlet charge in more easily each time the cylinder fills, so once again there's less resistance to the compressor stage.

the fact that your compressor stage is physically larger than it was before doesn't mean much, only that it's capacity for outright flow has gone up, and so has its flow delivery characteristics (the compressor map has changed). note that this new, larger compressor stage will probably require less shaft speed to feed the same amount of air as before to the engine (at less pressure), which again lowers your exhaust back pressure as the whole thing doesn't need to be driven as fast. again, power goes up. the end result is a more peaky and nasty engine though.

so i guess what i'm trying to get at is, the power gains you get aren't so much as a result of the compressor stage being physically larger, but as an indirect result of the turbine stage being larger. i hope that clears it up for you.

Ok from this I'm understanding that when you upgrade to a larger turbo, the exhaust side of the turbo is flowing more freely, which in turn imposes less resistance to the compressor side allow it to flow better?

If I cross that with what SydneyKid said (Boost pressure is only a measure of resistance to airflow), then my brain is telling me that with this new, free flowing characteristic, there is less resistance to the airflow created by the compressor. If there is less resistance to the airflow being forced into the system by the compressor, then the turbo will have to flow a higher amount of air for the boost pressure to reach a given level? Is this correct?

I'm tired I'll think it over some more while I sleep. It'll be good to finally understand this once and for all heh.

Cheers.

[Cubes]

Thats it.

[mad082]

1)Take two lengths of PVC pipe, one 40mm and the other 50mm. The length is irrelevant but assume they are at least of equal length.

2) Plumb a pressure gauge into each pipe, at the same location in the pipe.

3) Pump water through each pipe until the pressure reaches and sits steadily on 14psi.

4) Observe the amount of water flow coming out of each pipe.

What you will find is that the 50mm PVC pipe will have far more water flowing out of it than the 40mm pipe, even though they are both pressurised to 14psi. The reason for this is simple, as SydneyKid has said a few times, pressure is only a measure of resistance to flow. The 40mm pipe only requires X amount of water flow to be going through it before the pressure inside the pipe reaches 14psi. The 50mm pipe has a larger area to be filled and as such requires more flow before the pressure inside it also reaches 14psi.

that doesn't quite work with a turbo though. that example is only valid if you make the whole intake system larger (intercooler piping, valves, throttle body, manifold, etc). to use that example you would have to say

have 2 bits of 40mm pipe. 1 40cm long, 1 30cm long with 10cm of 50mm pipe. then put the pressure gauge at half way and pressurise to 14psi and see what happens. they should both be the same.

[mad082]

you're a bit off with your thinking regarding the reasons the larger turbo makes more power. generally speaking, the reason a larger turbo makes more power, or the same power on less boost, is that the hotside is not as restrictive as it used to be, because it is simply larger.

thanks stocky, thats exactly what i was after.

thats what i thought it was.

and i still think that a late model sr20 conversion would be a good conversion. it is so common to see silvias with rb20s or 25s, but has anyone seen an r32 with a sr20? the motor would out perform an rb20 so you wouldn't be going backwards power wise. you would just want a ball bearing turbo (not sure what sort is on the later model sr20s but i know the early ones came with bush bearing) to spool it up earlier.

Edited July 12, 2006 by mad082

[Warpspeed]

Stocky has nailed it, spot on.

With a turbo, you need to look at total exhaust back pressure as well as boost pressure. If the engine is suffering severe constipation from a very restrictive turbine and exhaust system, it is just not going to flow a lot of air, or make a lot of power.

Too many guys only look at the compressor end of the turbo. It is the exhauust side where all the hidden power is lurking. We all know that a larger free flow exhaust system makes a big difference with any factory turbo car. Fitting a slightly larger a/r turbine housing does too. All without changing anything at all on the compressor side.

Obviously you can get to the stage where the compressor ends up being too small for the job, but when you replace a small factory turbo with a larger aftermarket turbo, it is the reduction of back pressure on the exhaust side that really picks up most of the flow (and power).

The only real problem with this, is that boost threshold and lag get worse. You can keep going after more and more power, with a larger and larger turbo, and the car becomes harder to drive and more peaky. More powerful, yes, but at some stage it just becomes far too impractical for a daily driver. I think we all end up doing this at some stage.

Hakai, if you can get a good price for your car, do it. A GTR has many advantages, including street legality (trouble from cops), and resale value.

[Ryno]

Another thing to consider (in achieving more power from a larger turbo) is the density of the compressed air going into your engine. Density of course is a combination of Temperature and Pressure.

The Pressure (what your boost gauge is showing) shows no indication of what the inlet temperature is.

To give you an example:

1. You're using the standard turbo at 16 psi - this is past its efficiency range, and is struggling to compress the air to that pressure. As a result the temp of the inlet air is very high, and therefore less dense (less power).

2. You've got an aftermarket turbo at 16 psi - same boost px as the standard turbo, however it's in it's peak efficiency range and the temp of the air is lower than the standard turbo - therefore more density, and more power (for the same boost pressure).

[Beer Baron]

when i really just wanted to make the point/ask the question that 14psi of air flow is going to be the same amount of air whether its a medium size turbo or a big turbo (same amount of air going past the afm). a bigger turbo will be able to make more power out of it due to efficiency, cooler temps, better exhaust airflow, etc... generally speaking.

sorry mate that's not correct. boost is just a measure of restriction in the inlet tract/head. 14psi from a large turbo is not the same as 14psi from a small turbo. a large turbo will be producing much more airflow at the same boost so no it wont be the same amount of air moving past the afm.

[paulr33]

spot on, this is because pressure has nothing to do with volume. 30psi in a car tyre is completely different to 30psi in a truck tyre.

a stock turbo at 12psi

a gt3540 at 12psi

clearly the gt3504 will make lots more air, as it flows more air at the same pressure

[mad082]

a large turbo will be producing much more airflow at the same boost

why? because its bigger? if it is bigger it will just be spinning slower to make the same amount of air. if this was true then we would see cars making 400-500hp at 13psi.

that statement is only true if all the piping and any other restriction as been made bigger by the same percentage as the turbo over the smaller turbo. a bit of piping can only have a certain amount of air flow through it at a certain pressure no matter how big the pump is.

[mad082]

30psi in a car tyre is completely different to 30psi in a truck tyre.

yes true. but that is only comparable to saying a car with 3" intercooler piping will flow more than a car with 2" intercooler piping. if you get the 2 tyres and take a 1 cubic inch piece of air out of each tyre, the pressure of that cubic inch of area, and the volume of air, would be the same. the truck tyre just has more of those pieces.

if you get an air compressor rated to run at 500cfm and hook up a regulator to run at 100psi, then get a compressor rated at 2000cfm running all the same hosing and hook it up to a regulator set at 100psi, will the bigger compressor pump air out any faster? no. if you don't believe me got and ask a spray painter. a turbo is just a compressor, and the wastegate is just a air pressure regulator.

[Cubes]

Look at a compressor map....

A turbo is able to flow the same amount of air at low boost levels as it can high boost levels.

A motor that is not breathing as well due to high backpressure reducing VE will require MORE boost for the same airflow.

Everything has already been stated... Uncork the hot side and the motor is able to pump air easier. As a result cylinder filling improves and airflow goes up for a given boost level. More power is made as its airflow that makes power NOT boost.

Throw a small stock compressor on the uncorked hotside and it won't hold boost, add unnecessary heat and run deep in to choke (again refer to a compressor map and look at the efficiency bands)

Its so simple, you need to look at the whole equation, not just the first part (being the compressor).

Don't create analogies and read what has already been said, the answers are all there.