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Precision Billet Turbos


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Brett is right in what he said about the root cause however I wouldn't blame the vcam you just need to tune around it.

I ended up bowing the cylinder walls between each cylinder, causing the fire rings not to seat properly. This was caused by the high cylinder pressures I was generating with such a responsive setup.

What we have done now (other than going to an rd28 block and a slightly larger turbo) is to torque manage the curve and slowly bring the boost in rather than bring it in in one giant slab.

Whilst it doesn't give you that huge push in the low to mid range it used to it is fairly linear whilst still retaining plenty of mid range.

It has been rock solid now we have done that and I am confident the same could be done with a 6870, 3.2, vcam as well. The only problem with that is it was mostly over by 7 so you aren't seeing the benefits of making it linear and revving the car out to 9k+

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Variable valve timing should be tuned to optimise VE.

The better the VE the more power you can make with less boost. Less boost means less EMAP. Pumping losses are lower.

 if you improve VE and still run more boost and the engine breaks thats on you. The Dyno told you how much torque you were making.

If you try to hit a power target with poor VE, you need more boost. You have more EMAP and higher pumping losses to overcome. The engine is more stressed at the same power output as the losses are higher.

You should be tuning an engine to torque. A turbo engine will make peak torque as it crosses peak efficiency of the compressor. This is towards the midrange airflow/revs of most engines.

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4 hours ago, Dose Pipe Sutututu said:

I would dare say motor with more boost thrown at it with the intake cam not advanced, i.e. VCT off at 6500rpm will survive vs. motor with less boost and VCT on at 6500rpm making the same 500nm at 6500rpm.

DYOR, this is not tuning advice.

Don't get confused here, I wasn't asking for advice - I've been tuning built and stock bottom end turbo cars for over a decade with NVCS or some kind of constantly variable cam timing and have not yet broken one despite being purely adjusting cam timing to suit the real world performance of the car.   I've not heard of anyone sizing or adjusting static cams in regards to bottom end longevity, either. 

 

I'll pay attention next time, but I'm pretty sure there has been a very very close correlation between the torque developed and fuel consumption at any given rpm when changing cam angles...  which suggest there is no major variance in mechanical efficiency when adjusting the cam timing at WOT, which is realistically the only thing which could result in more cylinder pressure being required to achieve the same torque level.... so realistically there will be pretty much the same amount of air and fuel in the cylinder at the time the fire is started whether you use cam timing or boost to try and achieve the torque level, the valves will all be closed at the time so the burn should progress in pretty much the same way, so it really gets a bit hard to explain how there could be any difference in the force the bottom end goes through.   

To me it seems to go back to being sensible about how much torque is delivered when, which you have a combination of cam timing, ignition timing and boost control available to help you manage.... whichever way suits your tastes or situation better.  

3 hours ago, reaper said:

Brett is right in what he said about the root cause however I wouldn't blame the vcam you just need to tune around it.

It has been rock solid now we have done that and I am confident the same could be done with a 6870, 3.2, vcam as well. The only problem with that is it was mostly over by 7 so you aren't seeing the benefits of making it linear and revving the car out to 9k+

That sucks to hear, gutted you had so many issues - otherwise sounds like a potent setup.   The bottom part makes complete sense.   The trick with comparing how it went with the 6870 with and without the boost coming in as hard as it could is it is possibly a false economy type of comparison as how much torque it made down low was not really maintainable, if you'd never had that then it wouldn't necessarily feel like it was lacking.   If the boost curve was brought in a bit more progressively then the shape of the curve would also make it look less like its fallen off a cliff at 7000, and arguably look/feel like a more conventional kind of power curve... albiet MEATY.   It would still have been a complete animal of a road car, would still be very responsive down low etc.... just not quite as psychotic as I'm sure it ended up being.   

I think the discussion was at the time that you wanted >600kw without giving anything away down low to the 2.6/EFR8374 - I'm sure it would have been able to do that without going full send from the start of the rev range, albeit while possibly not having the EFR-esque transient response.

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What I have now is very much like the old 2.6 efr setup albeit with 800kw instead so I am quite happy.

Was just a learning curve for everyone involved and a bit of trial and error.

Very happy with the car now, absolute weapon and still plenty of mid range :)

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9 minutes ago, reaper said:

What I have now is very much like the old 2.6 efr setup albeit with 800kw instead so I am quite happy.

Was just a learning curve for everyone involved and a bit of trial and error.

Very happy with the car now, absolute weapon and still plenty of mid range :)

That's insane, nice work :)  Its on a 7275 now?

The old 2.6 EFR setup is still kinda the benchmark for RB26s for me, never experienced one anything like it.

 

 

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2 minutes ago, Lithium said:

That's insane, nice work :)  Its on a 7275 now?

The old 2.6 EFR setup is still kinda the benchmark for RB26s for me, never experienced one anything like it.

 

 

Yes 7275 now. Funnily enough when it was tuned in the same manner the 6870 was the response was quite similar which suggested the 6870 was a bit small all along.

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11 minutes ago, reaper said:

Yes 7275 now. Funnily enough when it was tuned in the same manner the 6870 was the response was quite similar which suggested the 6870 was a bit small all along.

Wow, that's pretty eye opening.  Definitely when a conversation about it came up at the time it felt like I was saying something crazy suggesting that a 6870 would be fine streetability wise on a 3.2+VCam - wouldn't have considered the 7275 would be a viable parallel to an EFR8374 on a 2.6, and feel like if someone had showed up and claimed that at the time they'd have been looked at like they were an alien.  Times have changed a bit :D

Well done on an epic build anyway, been good seeing it in the Coota videos - absolute beast.  Hard not to build something at that level without going through a few challenges and learning stuff along the way.

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2 hours ago, Lithium said:

Wow, that's pretty eye opening.  Definitely when a conversation about it came up at the time it felt like I was saying something crazy suggesting that a 6870 would be fine streetability wise on a 3.2+VCam - wouldn't have considered the 7275 would be a viable parallel to an EFR8374 on a 2.6, and feel like if someone had showed up and claimed that at the time they'd have been looked at like they were an alien.  Times have changed a bit :D

Well done on an epic build anyway, been good seeing it in the Coota videos - absolute beast.  Hard not to build something at that level without going through a few challenges and learning stuff along the way.

So what you’re both saying is the 6870 on a 2.8 doesn’t sound like the dumbest thing in the world and seeing some results could be interesting?

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2 hours ago, reaper said:

Yes 7275 now. Funnily enough when it was tuned in the same manner the 6870 was the response was quite similar which suggested the 6870 was a bit small all along.

So what you’re both saying is the 6870 on a 2.8 doesn’t sound like the dumbest thing in the world and seeing some results could be interesting?

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29 minutes ago, r32-25t said:

So what you’re both saying is the 6870 on a 2.8 doesn’t sound like the dumbest thing in the world and seeing some results could be interesting?

I've never said it was the dumbest idea, I just made it pretty clear I questioned the spool claims for it and stand by that - given that even @reaper wasn't seeing full boost by the rpm claimed.   I'd be interested in the results, I actually have a feeling I may already know someone who has done a 2.8 with a 6870 too.  

It's going to give away response to the 6466, and I had mentioned that nitrous would allow you your cake and eat it too if you were only occasionally going to aim for more power.   I'd also personally go an XR9569S hahaha, but 2.8 + Vcam + 6870 sounds like a potent setup to me if you were going to do it.

 

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36 minutes ago, Lithium said:

I've never said it was the dumbest idea, I just made it pretty clear I questioned the spool claims for it and stand by that - given that even @reaper wasn't seeing full boost by the rpm claimed.   I'd be interested in the results, I actually have a feeling I may already know someone who has done a 2.8 with a 6870 too.  

It's going to give away response to the 6466, and I had mentioned that nitrous would allow you your cake and eat it too if you were only occasionally going to aim for more power.   I'd also personally go an XR9569S hahaha, but 2.8 + Vcam + 6870 sounds like a potent setup to me if you were going to do it.

 

I’m still going to stick to the 6466 with bigger rear, I’m still curious to see some results though 

a 6466 used to its full potential will scare the hell out of pretty much anyone I know which is the main reason I go roll racing 

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I think a 6870 could be a good match for a 2.8 with vcam and you'd probably be all in under 5. Keen to see someone try it though.

Nothing wrong wit a 6466, its a perfect street turbo imo just doesn't have the legs of the bigger cars.

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22 hours ago, r32-25t said:

I’m still going to stick to the 6466 with bigger rear

Yum, this is my planned next step if I can't get what I want from the baby Garrett :)

Unigroup tuned a 6466 equipped RB25DET non-NEO (home built) with Kelford VCT brap sticks and it comes on about 4k ish and made 465kW at the tyres with 1.8bar of boost. I suspect there's more in it but knowing Yauvz he doesn't like to push motors to their limits (for obvious reasons, warranty!)

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On 5/4/2021 at 10:03 AM, r32-25t said:

So what you’re both saying is the 6870 on a 2.8 doesn’t sound like the dumbest thing in the world and seeing some results could be interesting?

Less 68mm more 72 or 76mm

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  • 4 weeks later...
On 5/3/2021 at 1:33 PM, reaper said:

Brett is right in what he said about the root cause however I wouldn't blame the vcam you just need to tune around it.

I ended up bowing the cylinder walls between each cylinder, causing the fire rings not to seat properly. This was caused by the high cylinder pressures I was generating with such a responsive setup.

What we have done now (other than going to an rd28 block and a slightly larger turbo) is to torque manage the curve and slowly bring the boost in rather than bring it in in one giant slab.

Whilst it doesn't give you that huge push in the low to mid range it used to it is fairly linear whilst still retaining plenty of mid range.

It has been rock solid now we have done that and I am confident the same could be done with a 6870, 3.2, vcam as well. The only problem with that is it was mostly over by 7 so you aren't seeing the benefits of making it linear and revving the car out to 9k+

Did you find big gains going to an RD block? Im thinking about starting to prep one for my car to get that thicker deck. I might need it if we put a little something ontop of the 7685 😂🤦‍♂️

Is yours sleeved or not needed?

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58 minutes ago, klutched said:

Did you find big gains going to an RD block? Im thinking about starting to prep one for my car to get that thicker deck. I might need it if we put a little something ontop of the 7685 😂🤦‍♂️

Is yours sleeved or not needed?

It wasn't about gains for me just the added strength. We didn't push it any harder however with double the deck thickness its worth doing.

Downside is the extra weight and it takes a bunch more machining.

Mine isn't sleeved, isn't needed. Just vanilla nitto 3.2 stroker in it.

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