Hakai

I'm impressed by the coherence of this post. I would have thought that seeing school's out as of this morning you would already be off guzzling bags of goon like it's water. That's what you fully sick ghetto thugs do now days isn't it?

So it is in fact true that the 2530KAI will spool faster than the GT-RS, but it's due to less rotating mass, if I understand what you're saying correctly? Sounds like for both purposes (Price and response) the 2530KAI is deffinately my best choice. Infomation has helped alot, thanks all Ben.

I searched for all the keywords I could think of that were relevant, the search function has never liked me at all, I can very rarely turn up anything useful. The links helped, had most of the info I needed to know. Thanks Paul. Ben.

Since toying with the idea of putting a supercharger on the RB20 went down in flames (Read: Cost) I'm currently looking into turbo upgrades, and I was recently talking to Tom from www.bd4s.com.au. I was enquiring as to the price of their HKS GT2530KAI units. He wrote me back telling me that the HKS GT-RS is a better turbo. He claims that it will spool faster than the 2530 and also make more power through the range. I looked at the HKSUsa website and it appears that the GT-RS and the 2530 both have the same exhaust housing and wheel specs, but the GT-RS has a larger compressor side, does this mean, as Tom is saying, it will spool faster and make more power through the range than the 2530? Another thing I am concerned over is the fact that HKSUsa only list the GT-RS as being supplied with a T25 flange, I was under the impression that for a unit to be bolt-on for the RB engines, it required a T3 flange? Any insight would be greatly appreciated, as well as any experienced people have had with either of these units, especially on the RB20. Cheers, Ben.

Don't encourage him! He's a dangerous man.

I don't think!!!! I promise!! *Thinks* *Runs*

This example can't really be related to a turbocharger. The reason for this is because with a turbo you have a compressor pumping air INTO an object that it is then also expelled from. While pumping air into a bike tyre, it isn't being expelled anywhere. As I said in my post above this one, quoting Stocky, the increase in airflow is due to a lessening of restriction on the exhaust side. As SK has said plenty, and has been reiterated here quite a bit. Boost pressure is ONLY a measure of RESISTANCE to AIRFLOW. If resistance changes, then for boost pressure to remain the same, airflow MUST change with it. There is an increase of air going past the afm, there simply has to be. If boost pressure is a measure of resistance to airflow, then boost pressure is, as I said in the post above, a calculation based on both airflow and resistance to airflow. For boost pressure to remain the same when you change the resistance to airflow (Which is what you are doing by decreasing resistance on the exhaust side of the engine), the airflow simply HAS to change. It's a basic mathematic principle. I'm not trying to say you're stupid, don't take me the wrong way, just trying to help you understand I felt like an idiot when Stocky corrected me heh, but in the end I understand a bit better now *EDIT* I just thought of something else. Your example with the bike pumps. You say that when you pumped with 1 cylinder it peaked at about 70psi? And with 2 cylinders it peaked at about 100psi? Those pressure readings are indicitive of the tyres resistance to the airflow that you were generating with the pump. Examine this for a minute. Using 1 cylinder the resistance to the airflow created is 70psi. You'd think that when you're using 2 cylinders, and effectively doubling your ability to generate airflow, that the resistance would increase to 140psi. However; It didn't. The reason I believe this to be, is that while it provided 70psi of resistance to the airflow from 1 cylinder, it could in fact, handle more airflow it just needed that airflow to be provided, which is why, when using 2 cylinders, providing double the airflow, instead of the pressure doubling, you only saw a 30psi increase. Pressure is resistance to airflow, what that tells us is that the majority of the extra airflow generated by the 2nd cylinder did in fact flow freely into the tyre. We can deduce this because that airflow was not resisted enough to turn into an increase on your pressure gauge Using 2 cylinders, you would have in fact pumped the tyre up much faster than using 1. Setting a pressure limit of 40psi (When 1 cylinder peaks at 70spi) is completely negating the advantage of using the second cylinder. See where I'm going with this?

This example you've used illustrates exactly what I was talking about. Yes, each of the cubic inch of areas will have the same pressure and will contain the same volume of air, the key is exactly what you said, there is more of those pieces in the truck tyre. Knowing this, if you add up all the pieces together, you end up with both tyres having the same pressure level, but the truck tyre has more air in it. Same for my example. Sure if you remove one tiny piece of the whole you get each being equal, but when you add everything together to create the final product, they are not in fact equal. Basically, they have the same pounds per square inch of air each, there are just more square inches that require filling in the bigger tyre and hence the bigger tyre has a higher volume of air in total. I will admit that I was unaware of the technical reason for the airflow increasing in an engine when a larger turbo was fitted, I assumed it was because the turbo itself was bigger. The truth as it seems, as Stocky pointed out, is that the flow increases due to a lessening of backpressure on the hotside of the engine. Thereby decreasing the resistance to airflow on the intake side. As the resistance to airflow is decreased, the amount of air required to generate the same pressure level increases. That's about it If you wanted to look at it mathematically, then I'm sure there is a formula for working out pressure based on airflow and backpressure. But mathematically if you have a formula consisting of 3 values and you change one of those values, then it is not possible for one of them to remain the same, unless you also change a second value. In this case, you decrease backpressure, you want boost to stay the same, you must increase the airflow. I suck at explaining, but I hope this helps a bit more.

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.

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?

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. 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. 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?

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

With so many different opinions it's really hard to make a decision. StockyMcStock made some very good points and also provided some very positive information and as he's speaking from experience when he says lynsholm blower of that size would be suited to the RB20 it gives me a bit more hope Stocky, just to clarify, these are the superchargers your're referring to when you say you've dissected them personally before aren't they? If so, what about this one? I know it's a step down from the 1600, but is it more suited to my application? As I've said a few times in this thread, I am looking at supercharging because I want something different, and the off-idle response would be awsome I think. However; I want a compressor that is going to remain efficient until the high side of 6,500rpm on the RB20DET (8.5:1 compression). From your experience, which of these compressors (from the harrop website) would you recommend? Thanks for the replies. Keep em coming, I haven't given up yet *EDIT* P.S: Stocky, maybe you can answer my question in regards to the airflow differences of a lynsholm blower of whatever size you are going to recommend, and a turbo such as the Garrett GT28RS? The reason I ask is because many people will testify that the RB20DET internals will run up to ~20psi through one of these turbos and I would like to have a rough idea of how this compares to a supercharger. How much boost would I be looking at running through this type of supercharger to obtain an equivilant airflow rate? (Ultimately, I don't want to blow my engine, I know the RB20DET is a strong bugger, running ~20psi through a 320hp turbo like the GT28RS on stock internals is impressive, I just want to know what I'm dealing with)

That's really awsome info mate, thanks heaps I didn't know that external compression actually had advantages, what little I could find about it in my short searches was unhelpful, but that info you gave is top notch. Looks like a roots blower wouldn't be too bad of a choice after all. Although, considering I have the RB20DET, it's already got 8.5:1 compression and it can handle like ~20psi from a GCG hi-flowed RB25 turbo (Or so I read on here somewhere) without changing internals, I'd assume it'd be good to cope with 15-16psi from a lynsholm blower? I know that airflow makes power not boost pressure, but I'm not sure on the airflow per psi of boost that type of blower would make, so my guess is just that, a guess, I might be wrong Starting to look like this exercise is not going to be too easy to undertake and might not be for me, but I'll keep looking into it. Keep the ideas coming, if there are any left

That's a really good point SK. How is the 200 Kompressor to drive? I don't think I'll get the chance to hop in one anytime soon My heart is not set on supercharging the RB20, I just want to do something different, if it's at all possible. If it's not a viable option then I will scrap it and go with a built RB20 turbo motor Obviously Mercedes have done it, I would imagine the 200 Kompressor is a nice car to drive with a good powerband, is it as easy as chosing a supercharger that is suited to the engine, or is there alot more to it than this? Cheers.