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Anybody Have Serious Experience With Neo Valvetrains?

BenR

By BenR,
in Engines & Forced Induction

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BenR Rookie

BenR

Posted
Posted

I'm in the middle of a decision point with my project and I'm stuck between two choices.

Firstly, I'm using an RB20DE Neo head, but we'll argue that point later.

It has the same valve train as the rb25 neo heads, which is the same solid lifters with shim over bucket (biscuit type), and I'll be running single coil springs with a seat pressure of 75lbs and 160lbs nose assuming 10mm lift or so.

My first option is the easiest, and that is to run the original biscuit shims and chuck in a set of RB26 aftermarket cams. My main concern is if the shims being spat out and I want to see if anybody has had any experience with the neo engines at high RPM, say 8000-9000rpm. I've never had any problems with biscuits on the european tin I work on (ferrari/jag classic and historics), but tbh they dont get as much of a thraping, even the race cars.

The second option is to convert to shim under bucket (top hat), which was my original plan. Simply because I thought all aftermarket solid lifter cams ran a BCD of 29mm (please remember this is my first foray into RB's) and I've only been looking at RB20/25 aftermarket cams until this point.

I could run the original lifters with 29mm bcd cams if I ran a 1.5mm top hat as a packer shim, but I really dont like the idea of running both top hat and biscuit shims.

To run top hats I would have to run a set of renault clio aftermarket buckets on the exhaust side and a set of supertech KA24DE lifters on the inlet side. I would then need to run approx 1.5mm thick shims on the inlet and 3mm on the exhaust. The inlet wasnt such a problem, but the exhaust shims would only have a 1.5mm skirt depth as the collet sits 2mm below the tip of the valve stem. So a shim with 3mm up top and 1.5mm location below I wasnt so sure about...

This also works out incredibly expensive at over a grand for just valvetrain components, compared to a set of r32 RB26 cams from tomei/kelford etc etc.

So, before I pump for the cheap option, I'd really like to know if any of the big tuners out there have ever run a neo to high outputs/rpm and spat a shim.

I really dont want to spit a shim as I've got a one off engine build with custom head, adaptor plates, custom pistons, custom head gaskets, custom ex manifolds........and a spat shim would destroy that investment and make me cry quite heavily if a rogue valve went exploring around the engine.

But it is over a grand cheaper.

  • 2 years later...
Chids34 Explorer

Chids34

Posted
Posted

Hi mate just wondering if you ever finished this project as I'm looking to convert my neo rb25 head to shim under bucket using gtr buckets, I haven't done any measuring as such yet to see if it is possible but waking up a old thread to see where you eventually got to.

Thanks, J

  • 5 years later...
DiscardTheWeak Enthusiast

DiscardTheWeak

Posted
Posted
On 8/13/2013 at 7:12 PM, BenR said:

I'm in the middle of a decision point with my project and I'm stuck between two choices.

Firstly, I'm using an RB20DE Neo head, but we'll argue that point later.

It has the same valve train as the rb25 neo heads, which is the same solid lifters with shim over bucket (biscuit type), and I'll be running single coil springs with a seat pressure of 75lbs and 160lbs nose assuming 10mm lift or so.

My first option is the easiest, and that is to run the original biscuit shims and chuck in a set of RB26 aftermarket cams. My main concern is if the shims being spat out and I want to see if anybody has had any experience with the neo engines at high RPM, say 8000-9000rpm. I've never had any problems with biscuits on the european tin I work on (ferrari/jag classic and historics), but tbh they dont get as much of a thraping, even the race cars.

The second option is to convert to shim under bucket (top hat), which was my original plan. Simply because I thought all aftermarket solid lifter cams ran a BCD of 29mm (please remember this is my first foray into RB's) and I've only been looking at RB20/25 aftermarket cams until this point.

I could run the original lifters with 29mm bcd cams if I ran a 1.5mm top hat as a packer shim, but I really dont like the idea of running both top hat and biscuit shims.

To run top hats I would have to run a set of renault clio aftermarket buckets on the exhaust side and a set of supertech KA24DE lifters on the inlet side. I would then need to run approx 1.5mm thick shims on the inlet and 3mm on the exhaust. The inlet wasnt such a problem, but the exhaust shims would only have a 1.5mm skirt depth as the collet sits 2mm below the tip of the valve stem. So a shim with 3mm up top and 1.5mm location below I wasnt so sure about...

This also works out incredibly expensive at over a grand for just valvetrain components, compared to a set of r32 RB26 cams from tomei/kelford etc etc.

So, before I pump for the cheap option, I'd really like to know if any of the big tuners out there have ever run a neo to high outputs/rpm and spat a shim.

I really dont want to spit a shim as I've got a one off engine build with custom head, adaptor plates, custom pistons, custom head gaskets, custom ex manifolds........and a spat shim would destroy that investment and make me cry quite heavily if a rogue valve went exploring around the engine.

But it is over a grand cheaper.

Hello Ben, was curious what your findings were with this head project? Mainly curious how using the 20de head worked out. I’ve always been curious how interchangeable these heads were , 25det, 25DE, 20de, 20det, 26, NEO, esc. Obviously the flanges are different and some head stud differences, I believe some coolant passage differences, but as far as castings and flow capability, I’ve been curious how similar they all are 

GTSBoy Grand Master

GTSBoy

Posted
Posted

Neo NA ports are tiny. The 20DE Neo would be a poor choice for a power build. The 25DE Neo is a poor choice for a power build.

The Neo head (turbo more so than the NA) is a good thing, the threat of spat shims notwithstanding. It is hard to quantify how severe that threat is. Not enough datapoints to really tell the story. It seems, though, that most people running sensible sized cams have no problem.

Neo is superior to 26 because of factory VCT, if nothing else. 26 flows more (I think) without any extra work, but that is easily changed in any serious build anyway. Neo combustion chamber is smaller, which is an improvement.

None of this is new knowledge. It has all been posted on here before, over the last 20 years.

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