HKS2535 on RB25DET results...round 1

[snake]

Hey Series II GTST, what do you think of your clutch? Does it shudder much? Pedal feel? Sorry to divert from the topic at hand.

[rev210]

i dont think so, due to the fact that as mentioned a 2530 on an rb25 wont hold boost up top, i have tried every avenue to fix this on mine, 227rwkw was the max we saw with no cat.  for over 230rwkw id say youd have to go for the next step up, the 2535.

exhaust housing on 2530 too small for 2.5 litres and spins out of efficiency over 5grand. There has been a lot of talk about a 2530 being good for up to 250rwkw, but this is not so.  ideally it is suited to the rb20 where exh gas flow is not so high.

.

Got head work and camshafts?

If you don't that doesn't help.

[benm]

rev210: Would you recommend camshafts or a PowerFC first in this situation ?

[SLY33]

obviously headwork and cams are going to increase power. But from a bolt on point of view, most people going a small upgrade turbo arent going to take the head off, and go into the territory where you spend significantly more dollars for not so significant powergains.

also headwork and cams arent going to change the fact that the exhaust housing is too small, so if you do have a 2530 on an rb25, your wasting your money trying to get extra power from heads and cams when you can just swap it for a 2535 or similar.

[Guest INASNT]

obviously headwork and cams are going to increase power. But from a bolt on point of view, most people going a small upgrade turbo arent going to take the head off, and go into the territory where you spend significantly more dollars for not so significant powergains.

also headwork and cams arent going to change the fact that the exhaust housing is too small, so if you do have a 2530 on an rb25, your wasting your money trying to get extra power from heads and cams when you can just swap it for a 2535 or similar.

If u r gonna go for a low mount setup on the stock exhaust manifold then its still a waste of time and $$ doing head and cam work. It is only worth doing head and cam work if u r going for highmount setup.

[Sydneykid]

If u r gonna go for a low mount setup on the stock exhaust manifold then its still a waste of time and $$ doing head and cam work. It is only worth doing head and cam work if u r going for highmount setup.

OK inasnt I give up, what's high or low mount got to do with it? We run rear/low mount so the weight distribution and the centre of gravity are optimised. Much better than high/front mount. Since it makes no difference as to how much power we make, I am at a loss to understand why we shouldn't run upgraded cams.

Help me out here..

[Guest INASNT]

I am saying if u r gonna stick with the stock cast manifold (gts-t) then it seems a waste of time with cams etc. If u go aftermarket low mount with decent turbo then u will see better gains for ya $.

[rev210]

obviously headwork and cams are going to increase power. But from a bolt on point of view, most people going a small upgrade turbo arent going to take the head off, and go into the territory where you spend significantly more dollars for not so significant powergains.

also headwork and cams arent going to change the fact that the exhaust housing is too small, so if you do have a 2530 on an rb25, your wasting your money trying to get extra power from heads and cams when you can just swap it for a 2535 or similar.

I agree that the head porting/clean up is a little bit expensive if your not rebuilding the engine. Though if you were to rebuild you'd be silly not to.

As for the camshaft upgrade. It's going to cost less than $2k for both camshafts including fitting and a re-tune. Well worth the $$ in terms of its performance returns. I'd do it even on a stock sized turbo. You end up with 15-20hp right through the curve and a peak of almost 30hp extra (thats how it worked on mine with just the exhaust cam changed)

Benm,

I don't think it should be a choice between a PFC and camshafts. The PFC is nice to have over the S-AFC due to the extra fuel mapping and more improtantly ignition recurve. So do both. The S-afc will cope with the camshaft upgrade till you get the PFC.

Having said that I had a S-afc on my old gtst running the HKS 264 /9mm exhaust camshaft and it worked very well. The camshaft was certainly a big improvement over the factory unit even with the lowly S-afc.

The draw back with the 'bolt on boy' approach is it often overlooks this critical area of performance.

[rev210]

I am saying if u r gonna stick with the stock cast manifold (gts-t) then it seems a waste of time with cams etc. If u go aftermarket low mount with decent turbo then u will see better gains for ya $.

Sorry your wrong. You'll see gains even if you have a factory turbo on the cast iron manifold. Try another 15-20hp right through the power band on my old gtst with only the exhaust cam, factory intercooler, s-afc.

[Guest INASNT]

maybe i but personally wouldnt do it unless u had a plan for bigger and better things in the near future

[rev210]

INASNT,

consider the fact that an average of 20hp increase right the the rev range is more average power you will net from a PFC & intercooler upgrade combined. To fit and tune camshafts you are looking at $800 plus the cost of the cams, the cheapest I've seen is $800 for a pair of Tomei. Thats $1600 for a gain you are hard pressed to get on anything else. Plus the car is so much more responsive.

Still seem like low bang for buck?

[Guest INASNT]

hmm, i was told and i agree if i was gonna pull the motor down and change cams, i might as well do new head gasket, forgies, headwork, etc.

[benm]

I need a 6th job, too many mods

[LOW25T]

Any luck fixing ur powerband as yet SeriesIIGTST?

This same turbo is going on my car in the next couple of weeks, and im hoping their might be a cheaper solution than going power fc:)

[Gradenko]

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.

hmm, i was told and i agree if i was gonna pull the motor down and change cams, i might as well do new head gasket, forgies, headwork, etc.

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

[jnr32r]

What are you opinions of RB26 cams into RB20 over say Tomei or HKS cams into RB20?

[Cubes]

Doing head work and cam work with a stock manifold is no doubt going to increase peak power and power over the rev range.

I havn't seen any proof that up to 300rwkw a stocker exhaust manifold restricts power enough to warrant spending another 1k+ on a custom exhaust manifold when you could be spending that 1k on a set of cams or another mod that gains more power per $$.

I guess it comes down to which you would gain more power from...

Spending 1k on a set of cams.

Or

Leaving the stock cams and spending 1k on an exhaust manifold.

I'm going to try the stocker exhaust manifold route then if need be go the custom manifold.

[Guest INASNT]

Doing head work and cam work with a stock manifold is no doubt going to increase peak power and power over the rev range.

 

I havn't seen any proof that up to 300rwkw a stocker exhaust manifold restricts power enough to warrant spending another 1k+ on a custom exhaust manifold when you could be spending that 1k on a set of cams or another mod that gains more power per $$.

 

I guess it comes down to which you would gain more power from...

 

Spending 1k on a set of cams.

 

Or  

 

Leaving the stock cams and spending 1k on an exhaust manifold.

 

I'm going to try the stocker exhaust manifold route then if need be go the custom manifold.

with an RB20/25 to get 300rwkw u gonna need something the size of a GT30 turbo with external gate, and on the stock manifold the turbo would be running very inefficiently!!

[whatsisname]

I'm running an internal gate turbo and stock manifold (cleaned up and port matched). I run ~20psi to make ~290rwkw in non shootout mode. This is with 8:1 compression too.

[rev210]

INASNT,

The main problem with the factory exhaust manifold is that they occasionally are cast so that the ports don't match up. In some cases the ports match up fine in others there is material restricting it (I'm not sure of the fequency of a bad cast but, my old RB25 wasn't bad at all). Besides the fact that getting the exhaust manifold off is about as big a job as changing the camshafts. I know which one I'd rather do.