HKS2535 on RB25DET results...round 1

[Steve]

rev210, I'm interested where the turbo finds another 20hp worth of air to flow. I don't doubt that it happened, but doesn't it mean a standard turbo at 10psi is now pushed higher into its flow range? Just wondering how safe cams on a stock turbo being pushed to its limits really is . I was considering cams on with the RB30DET on a stock turbo, but decided against it till after a turbo upgrade.

Except you don't have the pull the motor down to change cams. We're not running pushrods with cams in the block you know. Cams can be easily changed with the head on

It will happen. Any improvement to flow characteristics (it seems esp on the ehxuast side), will mean more power at lower boost.

If a turbo is pushing 10psi boost, but against a heavy resistance, once you remove the resistance, you get more flow at the same boost.

Boost pressure only comes about because of resistance, so the higher the resistance, the higher the pressure will be with the same volume of flow - and vice versa.

Just like upgrading an exhaust I suppose.

Please feel to flame away if I am off the mark here, but its my understanding.

[Ustasa]

The most disappointing thing I find on the dyno is a car that comes in like a burger with the lot – except for the camshafts!

220rwkw RB20DET’s with 300rwkw turbo’s that only need a decent pair of cams to turn them into the short stroke screamers that they are or 280rwkw RB25DET’s that could hammer out 330+rwkw with just the right set of cams.

Blocks, cranks, pistons and rods are your power support structure that has to hold under the strain. But it’s your head/turbo that delivers the power.

Most of you guys would be amazed what a set of decent after market cams (yes exhaust AND inlet!) can do for your engine in terms of mid range and peak power. With the factory setting up their cams for best emissions and down low response then it makes the upgrade even more noticeable.

[rev210]

Ustasa,

It's something more skyline owners need to take on board. Even when people pull their motors down for a rebuild they almost never consider them.

[Gradenko]

If a turbo is pushing 10psi boost, but against a heavy resistance, once you remove the resistance, you get more flow at the same boost.

Understood. What my question was getting at - will the stock turbo with its higher shaft speed to match the increased flow, not be at greater risk of failure than before? My understanding is that flow rate is propotional to shaft speed, and increase in engine power always corresponds to an increase in shaft speed.

Another way of putting it: reducing intake resistance should mean the turbo has to work harder and increase shaft speed to maintain the same flow resistance (or boost pressure) as before.

Am I way off track?

[Sydneykid]

If a turbo is pushing 10psi boost, but against a heavy resistance, once you remove the resistance, you get more flow at the same boost.

Or the same airflow at lower boost.

reducing intake resistance should mean the turbo has to work harder and increase shaft speed to maintain the same flow resistance (or boost pressure) as before.

Look at it the other way, same air flow = same power but at lower boost. This means less resistance to shaft rotation = lower load on the turbo.

will the stock turbo with its higher shaft speed to match the increased flow, not be at greater risk of failure than before

Not if you net off the lower torque loading on the shaft.

Maybe some examples....

Option 1 = 200 rwkw at 1 bar with standard cams

Option 2 = 220 rwkw at 1 bar with aftermarket cams

Option 3 = 200 rwkw at 0.8 bar with aftermarket cams

Option 4 = 215 rwkw at 0.9 bar with aftermarket cams

Maybe Option 4 is less turbo damaging than Option 1, but there is little doubt that Option 3 is.

Heat is also very relevant here, if we are talking about a standard ceramic turbine equiped turbo. Depending on the efficiency of the turbo and its ability to heat the inlet air and/or the intercooler efficiency, we may well find that Option 4 is still less turbo damaging than Option 1.

Interesting thread this one, hope I added to it a bit

[whatsisname]

Well I'm convinced! My next mod will be cams

[Sydneykid]

Well I'm convinced! My next mod will be cams

Please post the before and after dyno sheets, please.

[benm]

Well I'm convinced! My next mod will be cams

hahaah, I think I need to be banned from these SAU Forums, every thread I read is costing me about $1000 in mods. I'm in debt for the next 4yrs and that doesn't even include my mod list

[whatsisname]

Sk, will do mate. It won't be for a little while though, but as soon as funds are healthy, in go the cams!

I'm hearing you Ben. I could almost buy a GT-R for the cost of my mods/tuning alone (~30k)! That's every little mod I've done though, including non-performance items like stereo etc.

[knore]

Great information,

So what exacly would option 3/4 be?

IE:

What cams are best for RB25DET ?

[b0neR]

Cams will depend upon application, but SK has said before that Tomei PONCAMS (256/260) are timed perfectly out of the box and a noticeable improvement should be seen across the entire rev range.

[Guest Robo's]

So SkylineGTS11, did you fix your problem???

[driftaR32]

ehya dudes

i just got some used hks 264 in/ex cams for my rb20

the only marking are a hks stamp and 264b at the front of each cam

are these step1/step2 ?

any help appreciated

[SeriesIIGTST]

Robo's

Yeah I think so, turns out it was my knock sensor - one wire was loose and sending intermittant signals to the ECU, which would retard my timing and cause a big hole, particularly when the power really came on (ie, at NVCS changeover). I haven't managed to find time to get it back to the dyno yet but i'm working on that. I can't feel the hole any more so we'll see what happens.

Cheers!

[Guest Robo's]

Robo's

Yeah I think so, turns out it was my knock sensor - one wire was loose and sending intermittant signals to the ECU, which would retard my timing and cause a big hole, particularly when the power really came on (ie, at NVCS changeover). I haven't managed to find time to get it back to the dyno yet but i'm working on that. I can't feel the hole any more so we'll see what happens.

Cheers!

You still running the SAFC and not a Power FC?

[SeriesIIGTST]

Yep...but i've also taken off the z32 AFM. Seems to get closing to maxing out but never quite there so i'll see how far I can push it.

I'm not going to sing the praises of my S-AFC just yet, we'll wait for the dyno to see what it does but if it holds up, i'm going to be the biggest fan ever. I realise there's more power to be had from PowerFC but at this point, bang for your buck wise, it's probably not worth it as the turbo would be reaching peak efficiency anyway i'd imagine.

[b0neR]

But even if the peak power gain is not terribly high wouldnt the whole control of a PowerFC and the increase in low/midrange torque and power be appealing? Not to mention it would probably result in a safer tune (less chance of the engine sh*tting itself).