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camshafts - upgrades and options


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hello! i am looking into upgrading the cams on my rb26 in the future, and wanted to start to understand what goes into this. i did a forum search and nothing obvious came up, so forgive me if this is already discussed somewhere.

currently the engine is stock, save for (pertinent to this discussion):

  • adjustable cam pulleys
  • beefed up timing belt
  • haltec ecu, not yet installed yet
  • oil baffle plates

i am will be converting to a single turbo set up, and that turbo's peak output is reached at somewhere between 5k and 5.5k rpm. this would be for street use.

from what i understand, i should be looking at cams degreed at 272°. does that sound like it makes sense?

there are step 1 and step 2 variants of these cams. i am not sure what the difference is in the to variants, so if anyone can chime in on this it would be great.

i am assuming i would need to upgrade my valve springs as well. other than a tune, what would go into a camshaft upgrade? if i want to go with a v-cam upgrade much later, how does that affect i am doing now?

i understand that it's totally possible that i completely missed something major here, but that's why i am posting this: i am here to learn.

cheers!

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On 12/7/2021 at 8:27 AM, itsforandres said:

hello! i am looking into upgrading the cams on my rb26 in the future, and wanted to start to understand what goes into this. i did a forum search and nothing obvious came up, so forgive me if this is already discussed somewhere.

currently the engine is stock, save for (pertinent to this discussion):

  • adjustable cam pulleys
  • beefed up timing belt
  • haltec ecu, not yet installed yet
  • oil baffle plates

i am will be converting to a single turbo set up, and that turbo's peak output is reached at somewhere between 5k and 5.5k rpm. this would be for street use.

from what i understand, i should be looking at cams degreed at 272°. does that sound like it makes sense?

there are step 1 and step 2 variants of these cams. i am not sure what the difference is in the to variants, so if anyone can chime in on this it would be great.

i am assuming i would need to upgrade my valve springs as well. other than a tune, what would go into a camshaft upgrade? if i want to go with a v-cam upgrade much later, how does that affect i am doing now?

i understand that it's totally possible that i completely missed something major here, but that's why i am posting this: i am here to learn.

cheers!

VCAM requires a special intake cam in order to be able to actuate the cam phaser. So you are limited in your selection there, usually you want to match your intake and exhaust cams to some extent. Turbo engines are not the same as naturally aspirated engines. Once the engine is on boost it matters less if your VE is tailing off when you can just increase the boost solenoid duty cycle to compensate. Most turbos also have significant backpressure which can favor less valve overlap than you'd expect at high RPM compared to an NA engine as the pulse tuning effect of exhaust runner length is competing with the exhaust backpressure causing internal EGR. It's likely that these effects are why the factory exhaust cam is said to be lower duration and lower lift than the intake cam.

I would love for there to be public data comparing the effect of staggering cams in either direction (more duration on intake vs exhaust and vice versa) for the RB26. As far as I can tell nobody has done it.

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On 12/7/2021 at 5:37 PM, GTSBoy said:

Using terms like step 1 and step 2 makes me think that you are looking at shitty old Jap cams, not Kelfords.

Just go to Kelfords RB26 page and pick the cam that sounds like it suits your needs.

they replaced 'step x' with '-x'. brilliant. other than that, is there a reason why you think these are superior in any way to 'shitty jap cams'? it would be helpful if you gave some kind of reasoning behind your recommendation, or at least tried to answer the actual question that was asked.

On 12/7/2021 at 5:58 PM, r32-25t said:

Also unless you clearance the head you are limited on how much lift you can have 

i assume the lift dictates if i will need to modify the cylinder head, correct? at what point does the head need to be modified? if the lift goes above 9mm?

Edited by itsforandres
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On 12/9/2021 at 12:27 AM, itsforandres said:

other than that, is there a reason why you think these are superior in any way to 'shitty jap cams'? it would be helpful if you gave some kind of reasoning behind your recommendation, or at least tried to answer the actual question that was asked.

There's a lot more to how well a cam profile makes air flow into an engine than just the number of degrees and the lift. The lift curve around the seat in particular, the width of the peak of the lobe, the maximum accelerations imposed on the valve on the ramps.....all of these, and some more, are important. The shitty Jap cams do not go anywhere near doing the best on any of these. Kelfords have put some proper thought into all the cams they do for all engines. Cam specialist vs. Jap brand name selling specialists.

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On 09/12/2021 at 9:51 AM, GTSBoy said:

There's a lot more to how well a cam profile makes air flow into an engine than just the number of degrees and the lift. The lift curve around the seat in particular, the width of the peak of the lobe, the maximum accelerations imposed on the valve on the ramps.....all of these, and some more, are important. The shitty Jap cams do not go anywhere near doing the best on any of these. Kelfords have put some proper thought into all the cams they do for all engines. Cam specialist vs. Jap brand name selling specialists.

Reminded me of this

arQ70Gwg_700w_0.thumb.jpg.99fc938eb4effc0fa085aa3d2ee0cbe9.jpg

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On 12/8/2021 at 5:51 PM, GTSBoy said:

There's a lot more to how well a cam profile makes air flow into an engine than just the number of degrees and the lift. The lift curve around the seat in particular, the width of the peak of the lobe, the maximum accelerations imposed on the valve on the ramps.....all of these, and some more, are important. The shitty Jap cams do not go anywhere near doing the best on any of these. Kelfords have put some proper thought into all the cams they do for all engines. Cam specialist vs. Jap brand name selling specialists.

@GTSTBOYthank you! this makes much more sense. from looking at the shop manual for the cylinder head, it seems you can access the valve lifter, valve collet, valve spring retainer, valve spring, valve spring seat, valve oil seal, valve guide, valve seat, and the valve without removing the actual head. am i understanding that correctly?

is it recommended to replace the valve lifters, or just service them?

On 12/8/2021 at 2:25 PM, r32-25t said:

Usually 9.15 is the limit before needing to clearance the head 

@r32-25t thanks! much appreciated.

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does anyone have any dyno results to post of Kelford etc cams vs HKS/Tomei cams on like for like setups, to show the specific gains between the 2? I went with Tomei poncams but interested to see the benefit of others compared to these.

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On 10/12/2021 at 7:38 PM, hardsteppa said:

does anyone have any dyno results to post of Kelford etc cams vs HKS/Tomei cams on like for like setups, to show the specific gains between the 2? I went with Tomei poncams but interested to see the benefit of others compared to these.

I should be able to provide those details soon, however won't be a clean comparison 🤓

Same-ish engine, nearly like for like (new motor, same displacement, same turbo setup, same valve springs, just different intake manifold, different cams)

Not exactly like for like but good enough.

Tomei 260/260 9.15mm vs. Kelfords 264/272 9.60mm

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There are other benefits to going with a dedicated cam manufacturer. It's sad that we're reduced to just Kelfords, now that the Aussie makers are gone. But while we still have them in our backyard, we should support them.

The support you get from people like Kelfords, when deciding what to use and for trying to solve problems is priceless. The extra stuff and effort available in the areas of springs and retainers, etc etc, knowing that they will only provide gear that matches their stuff.....you work out what that is worth to you.

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