25/30 R33 Gtst

[Buddah]

Hey guys, I have a R33 GTST was running a 25 making 400hp but droped a vavle so ripped it out.

I now have

RB25 Det Head Reco & Aftermarket Vavle Springs

Rb30 Block

Spool Rods

Cp Pistons

Gt45 Turbo

800cc Injectors

Custom Plenum

90mm Throttle Body

Mircotech Ltx12

50mm Wastegate

Top Mount Manifold

5 speed with Jim Berry Clutch

4" Exhaust

The motor is not yet assembled friend who is building has been busy.

My question is what cams do you think I should run? I want to go the best I can without having to go all out on the head if that makes sense?

The car is street driven but will be seeing the 1/4 time to time.

First pic is the old setup

Second pic is the engine bay getting a tidy up.

Edited July 2, 2009 by Buddah

[DanielH]

I can't help you on the cams mate but keen to know myself, the 25 head i have now has Tomei cams 256 in/ 264 ex with i beleive 8.5mm Lift, it came off a 3L 33 GTST which i beleive made low-mid 400 RWKW's before having fuel issues..

I plan on throwing some spool rods and CP 25/30 pistons in mine so i'm keen to see how they turn out for you.

[Buddah]

Sounds good mate, Hopfully some I can help help me with the cam choice.

[Sydneykid]

When I am chosing camshafts the first thing I do is figure out what rpm range I am going to need the camshafts to work in. One of things that determines the rpm range is the size of turbo. Next I check to see that the rest of the package aligns with the turbo. This is where I run into problems with your selection.

Gt45 Turbo

800cc Injectors

That's a 1000 bhp turbo with injectors that are only good for around 800 bhp on petrol and 650 bhp on E85. So either your turbo selection is too big, meaning that you will have a ship load more lag then is necessary for the power output. Or your injector selection is too small.

Either way I can't make a camshaft suggestion with such a missmatch in components.

Cheers

Gary

[Swiper the Fox]

When I am chosing camshafts the first thing I do is figure out what rpm range I am going to need the camshafts to work in. One of things that determines the rpm range is the size of turbo. Next I check to see that the rest of the package aligns with the turbo. This is where I run into problems with your selection.

That's a 1000 bhp turbo with injectors that are only good for around 800 bhp on petrol and 650 bhp on E85. So either your turbo selection is too big, meaning that you will have a ship load more lag then is necessary for the power output. Or your injector selection is too small.

Either way I can't make a camshaft suggestion with such a missmatch in components.

Cheers

Gary

The above post is spot on (nice one SK)

too many times a mismatch of components will leave a modifier scratching their heads to why it doesn't perform. The above 'rule of thumb' is best worked out before the hand goes in the pocket grabbing cash for components.

[Buddah]

I see I was do have a T66 that I was using also maybe I am best to stick to this.

If I was to keep the Gt45 I will need 1000c injectors?

So say I run the

T66 what cams would be best suited?

[Buddah]

I do have a T66 that I was using also maybe I am best to stick to this.

If I was to keep the Gt45 I will need 1000c injectors?

So say I run the

T66 what cams would be best suited?

[Sydneykid]

I do have a T66 that I was using also maybe I am best to stick to this.

If I was to keep the Gt45 I will need 1000c injectors?

So say I run the

T66 what cams would be best suited?

The T66 is a better match for the injector size, especially if you want to run it on E85. The cam selection is then much easier, with one complication, I didn't see larger exhaust valves on you list of mods and RB's have a missmatch between inlet and exhaust valve sizes ie; the exhaust valves are too small. Even a small (and cheap) upgrade by 0.5 mm makes a noticeable difference. If you stick with the standard valve sizes then I recommend using a slightly longer duration exhaust camshaft. Sure it's a band aid, but it's effective and a no cost option. All of the cams I would be looking at will require head relief, solid lifters and changes to suitable valves and valve springs anyway, so I would do the exhaust valve size upgrade at the same time for zero extra cost.

The T66 is going to give you good boost at 4,000 rpm and will taper off a little at 7,000 rpm running Pump 98. Running E85 will extend that by 500 rpm due to the oxygen content. So what you are looking for is an inlet camshaft duration that works from 4,000 rpm to 7,500 rpm. I always go for the highest lift I can find at the target duration, keeping in mind the useable rpm range. Personally I have a soft spot for Jun cams, they have worked for me everytime, so the choice is between the 264 & 9.7 mm and 272 & 10.5 mm, personally I would go for the 272's & 10.5mm. There is higher lift available in 272 degrees but for road use it will be very doughy under 4,000 rpm with more than 10.5 mm of lift. If you prefer HKS then their equivalent is 272 & 10.2 mm.

That would give you some headroom if you decide to use the GT45 with some bigger injectors, but realisically you are already going to have serious traction problems with the T66 at around 650 bhp on E85, you could stretch that to around 700 bhp with some more fuel pressure. In comparison the GT45 would be unuseable on the street. You may also want to think about driveline durability, the T66 is pushing it and the extra torque from the GT45 will break most things in the drive train.

Cheers

Gary

[Buddah]

Very good read thank you so much, I think I will look into the head work. I am planning to be running pump98. The head is only been reco with after market springs.