Custom Cams For 3 Litre

[Scooby]

G'day

Just wondering if anyone has used custom grind cams in their 3 litre. I know there are people out there getting big power from using RB26 cams, but I've often wondered if, with the longer stroke of the 3 litre, we should be looking at cams that are more specifically designed for that engine. For example, should the cam duration reflect the longer stroke duration of the engine.

That said I think the OS Giken kit uses RB26 cams so perhaps my suspicions are unfounded.

Cheers

[bubba]

A few people are using customs grinds from Camtech and Tighe

[dorifticon]

Wouldn't turbo selection, compression ratio and intake/turbo manifold choice play more of a role than comparatively minor changes to lift and duration? I mean sure you can probably get away with bigger cams on a 3.0 than on a 2.6 and still have it streetable but they make plenty lumpy cams for the 2.6.

[Scooby]

A few people are using customs grinds from Camtech and Tighe

Didn't know that, any ideas around specs? I was able to find an old thread done by Cubes about 3 years ago but that was it. Spoke to Tighe and they said just use RB26 cams, Camtech guy was adamant that a custom grind is the way to go for a 25/26 30 and he has a 25/30. Of course he does sell cams, but then he wasn't simply recommending something like Poncam specs so he's probably pretty sure of what he's doing. Otherwise the results would go backwards pretty quickly. So I'm persuaded he's got good reasons for recommending a dedicated grind.

Wouldn't turbo selection, compression ratio and intake/turbo manifold choice play more of a role than comparatively minor changes to lift and duration? I mean sure you can probably get away with bigger cams on a 3.0 than on a 2.6 and still have it streetable but they make plenty lumpy cams for the 2.6.

Sure but those factors you mentioned are more of a known quantity in terms of their effect, cam timing is more of a black art and hence why there's probably not much discussion on the forums. That and the fact that there are lots of proven RB26 cams out there. In the case of a 26/30 most of us are putting cams onto an engine they weren't meant for so I'm keen to have a cam expert work out some specs for a dedicated twin cam RB30 based on the characteristics of that engine rather than something with 400cc less and shorter stroke. Most bigger RB26 cams have increased duration and stroke. Purely speculative but maybe the 30 needs something with greater lift but to the stock duration as they have a longer stroke (meaning the valve needs to be open for longer)but generally don't rev as high in most cases. Just speculating but that's the line along which I'm thinking.

Edited March 15, 2011 by Scooby

[bubba]

Most people are very cagey about their custom cam specs.

I had my turbo builder spec up some cams for my engine, if I can find the piece of paper I wrote the specs down on I'll pass them on. They were very specific to the engine capacity, turbo selection, use of the car and where I wanted the power though.

[dorifticon]

When I was researching the available cams for my build, it seemed like the starting point for designing a cam is how much lift is required, then what is the steepest ramp angle you can get away with for that lift. I think in street cars, and even track driven cars, people want to try and maximise lift but minimise duration for some semblance of driveability and useable low-rpm. As a result I think there's not a great deal of variation in the types of duration available for any given lift.

[Scooby]

Most people are very cagey about their custom cam specs.

I had my turbo builder spec up some cams for my engine, if I can find the piece of paper I wrote the specs down on I'll pass them on. They were very specific to the engine capacity, turbo selection, use of the car and where I wanted the power though.

It's understandable that people aren't keen to share that data but it'd be interesting to know the general direction people are going for the 30 when using a custom cam. Camtech mentioned the same thing re wanting to know specs, which is a logical place to start. Do you have an indication of whether in your case it was worth going custom compared to off the shelf stuff? I guess you'd have to go 'back to back' to figure that out. What specifically made you decide to go custom? Same reasons as I'm suggesting?

When I was researching the available cams for my build, it seemed like the starting point for designing a cam is how much lift is required, then what is the steepest ramp angle you can get away with for that lift. I think in street cars, and even track driven cars, people want to try and maximise lift but minimise duration for some semblance of driveability and useable low-rpm. As a result I think there's not a great deal of variation in the types of duration available for any given lift.

That's true those considerations all play a part. Small changes can make a difference, hence I want to see if I can optimise the grind for the 3 litre and my usage. Camtech said they could get the same power at 5psi less in their 25/30 with a custom cam. Not sure what happens if they up the boost 5 psi after that but assuming there's nothing given away elsewhere I'd go custom to run with 5psi less as to me that represents an increase in efficiency for no extra cost.

Edited March 16, 2011 by Scooby

[bubba]

It was my turbo builder that was pushing the custom cam specs. When advised what the standard cam specs were and my power goals (I had asked for the most responsive 500rwhp possible through a T3 flange) he spec'd up some cams to suit the engine and turbo setup.

IIRC it was a little more duration and a lot more lift but since I've moved offices I can't find the post-it note it was written on

[Scooby]

It was my turbo builder that was pushing the custom cam specs. When advised what the standard cam specs were and my power goals (I had asked for the most responsive 500rwhp possible through a T3 flange) he spec'd up some cams to suit the engine and turbo setup.

IIRC it was a little more duration and a lot more lift but since I've moved offices I can't find the post-it note it was written on

Bugger, but I was thinking along the same lines anyway. Happy with the outcome? Did using custom cams come about as a general good idea or as a result of there being no dedicated 26/30 cams available?

Edited March 17, 2011 by Scooby

[bubba]

Plans changed and all the goodies are going in my wagon now so no comment.

The use of custom cams came about when I queried re-using my 25DE cams or going to some 20DET cams (as they had a little more lift and a little less overlap), turbo builder said neither of them would be that great for the response/power goals. It was also because he was going to build me a custom Holset turbo instead of an off-the-shelf generic turbo.

[T04GTR]

i think they do. because the majority of the dyno charts ive seen make as much power at 5k as they do at redline. seeming like the head cant flow hte extra air for high rpm. instead of the nice diagonal line with ever increasing power with revs.

hell we have a very tough rb30 at work with kelford 280/10.5's and -10s and it is only making 330rwkw on 20 pounds.... seems abit low to me. cam timing would apear to have an efect.

[rob82]

I had a RB30/26 with twin -5's and standard gtr cams. Was making about 280rwkw at 12Psi of boost with the power starting to drop at around 5800rpm. I spent hours of both dyno time and street driving to find the best cam timing for a braod power band. It was highly sensitive to cam timing changes and I could move the peak power rpm point from around 5400rpm to 6000rpm(no higher). Now we all know that -5's at 12psi is harly working those turbos so my thinking was that it would continue making power to the rev limit which was set at 6800rpm but this was not the case. You would think with the runner length of the rb26 manifold combined with lots of head room in turbocharger flow it would be possible to continue making power - it did not. I put it down to a combination of the rb30 rod/stroke ratio and the factory 26cams being too small.

If I were to do it again I would use the rb25 neo head to gain intake phasing and the longer runner length which would bring it onto boost sooner and make more midrage. I would go for something around the 10mm lift @ 260deg ad dur.

[tm_r33]

I use kellford cams in my 25/30 track car. They are not of huge duration, only 275 from memory but big lift. Over 10 mm

[bubba]

I had a RB30/26 with twin -5's and standard gtr cams. Was making about 280rwkw at 12Psi of boost with the power starting to drop at around 5800rpm. I spent hours of both dyno time and street driving to find the best cam timing for a braod power band. It was highly sensitive to cam timing changes and I could move the peak power rpm point from around 5400rpm to 6000rpm(no higher). Now we all know that -5's at 12psi is harly working those turbos so my thinking was that it would continue making power to the rev limit which was set at 6800rpm but this was not the case. You would think with the runner length of the rb26 manifold combined with lots of head room in turbocharger flow it would be possible to continue making power - it did not. I put it down to a combination of the rb30 rod/stroke ratio and the factory 26cams being too small.

If I were to do it again I would use the rb25 neo head to gain intake phasing and the longer runner length which would bring it onto boost sooner and make more midrage. I would go for something around the 10mm lift @ 260deg ad dur.

Could the exhaust housings on those turbos have been too small to flow anymore?

[Scooby]

-5s are good for 400rwkw, I'd have thought the exhaust housings wouldn't be a problem?

[bubba]

-5s are good for 400rwkw, I'd have thought the exhaust housings wouldn't be a problem?

Ok, I've never played with twins so no idea what they're good for but the 3L pushes a fair bit more exhaust gasses, especially up high.

I had a baby turbo on my 3L and while it made the same power as the 2L, it did it a lot sooner and choked the exhaust housing up (even though there was still more flow left on the compressor side).

[T04GTR]

i wonder what the vl guys have been doing for all these years..

[Scooby]

Yeah I wondered that too, the RB30 oem cams were never going to cut it so I reckon they've always had to go down the custom path.

[rob82]

i wonder what the vl guys have been doing for all these years..

Seen lots of single cam VL's not make power over 6000rpm even with mild cam but heaps of turbo headroom.

I also still beleive that the rb26 manifold is a waste of time on an Rb30 unless your looking at making most of your power above 5000rpm.

And there is no way I was choking up the exhuast side with twin -5's.

[Dale FZ1]

Seen lots of single cam VL's not make power over 6000rpm even with mild cam but heaps of turbo headroom.

It seems that fairly stock-type (head porting + cams + manifolds) 30DET builds can go this way too. Pretty streetable and a step forward from the short stroke bottom end, but not a particularly wide useable rpm range where it makes best torque.

The better builds of those using a 25DET head seem to go with decent fabricated exhaust manifolds and open out those exhaust port restrictions. Mine is a mild build with OEM cast manifold but holds peak torque from 3400-7000 with Tighe cams 8.9mm lift and 265 duration. Might not be best for everyone's needs but it suits mine.