Precision Billet Turbos

[Lithium]

2 minutes ago, r32-25t said:

You know how you all said the ultimate set up would be the 3.2 with the 6870 and vcam that Jez Tuned. That was reapers car and I’ll let him tell the rest of the story if he wants to

Rightly or wrongly, back when he had talked about that I was definitely pro VCam/6870 for what he said he wanted at the time.

 

[Lithium]

12 minutes ago, r32-25t said:

I also think what happened to his car Might be what happened to mine and part of the reason I removed the vcam

What happened, and how is it related to vcam?

[r32-25t]

Cylinder pressures cracking the deck of the block, head studs are to strong to stretch so the deck gives way instead 

[Lithium]

7 minutes ago, r32-25t said:

Cylinder pressures cracking the deck of the block, head studs are to strong to stretch so the deck gives way instead 

Ahh I see.  And you think that the same cylinder pressures would not crack the block if there was a non-vcam head ?

[Komdotkom]

Surely that's just a matter of cam timing not the V-Cam magically making more cylinder pressure. 

[r32-25t]

The vcam makes more cylinder pressure lower down in the rev range as it’s coming onto boost and that’s what I believe is creating the problem. I’m not willing to experiment and find out on a $13,000 block 

[Lithium]

1 minute ago, r32-25t said:

The vcam makes more cylinder pressure lower down in the rev range as it’s coming onto boost and that’s what I believe is creating the problem. I’m not willing to experiment and find out on a 13,000 block 

I'm bringing up  a couple points not to be a dick, or even defend the fact I've suggested that this kind of combo is good - just like to investigate things which have either turned out well or not... it kinda helps both understand what is working and why to help all of us get better results.  With the info you've presented so far I feel like blaming VCam is a mistake, especially if you have it and you're looking at spending money at moving away from it when its probably not the cause - at least all by itself. 

Peak cylinder pressures happen when the intake and exhaust valves are closed, some time after the spark event happens.  There is absolutely zero influence that valve timing has on this all by itself.   The cylinder pressures are going to be everything to do with the compression ratio, how much air/fuel combo has been forced into the cylinder, when the spark has been lit and how stable the combustion process is after that point.   It is VERY possible with a given static cam head setup to exceed the cylinder pressures achieved using a variable cam head setup.  

Not doubt Vcam (and the turbo setup used) could be making it easier to create a situation where cylinder pressures get to a point the block can't hold it - but blaming vcam for a cracked block is a bit like blaming a Porsche GT3 for being too fast if you don't brake for a corner and throw one off the road.   Things that improve torque naturally have the ability to put more stress on the parts which have to hold the associated forces, its up to the builder to ensure things are best setup to ensure the best chance of sustaining those forces and in this metaphor - the tuner/owner have to decide where to draw a line in terms of how far its pushed so they have less chance of overcooking the combination you have.

By all means remove vcam if it makes you feel better, but it won't necessarily lose you the ability of cracking the block due to excessive cylinder pressures if you were pushing things hard enough to achieve that.   There may be other reasons you are looking at changing as well, but realistically - if the only reason is due to cylinder pressures then perhaps it should be considered to hold back torque where you think it has caused a problem and keep the nice responsive drive that VCam provides while not compromising reliability.    Modern ECUs/control systems make it not particularly hard to target the torque you want, so instead of building the car to be inherently laggier in all situations it is possible to have your cake and eat it too.

[r32-25t]

It’s the same theory as the barra and evo guys who keep the boost low through the bottom and mid range and ramp it in up high to save the rods from bending, just in an rb the rods aren’t the week point it’s the deck or the big ends that let go 

[Lithium]

Just now, r32-25t said:

It’s the same theory as the barra and evo guys who keep the boost low through the bottom and mid range and ramp it in up high to save the rods from bending, just in an rb the rods aren’t the week point it’s the deck or the big ends that let go 

Snap, pretty much what I was getting at with my above post - just a bit confused about why you're blaming vcam instead of blaming the boost target/ignition timing which have far more direct influence on the kind of failure you're talking about

[r32-25t]

2 minutes ago, Lithium said:

I'm bringing up  a couple points not to be a dick, or even defend the fact I've suggested that this kind of combo is good - just like to investigate things which have either turned out well or not... it kinda helps both understand what is working and why to help all of us get better results.  With the info you've presented so far I feel like blaming VCam is a mistake, especially if you have it and you're looking at spending money at moving away from it when its probably not the cause - at least all by itself. 

Peak cylinder pressures happen when the intake and exhaust valves are closed, some time after the spark event happens.  There is absolutely zero influence that valve timing has on this all by itself.   The cylinder pressures are going to be everything to do with the compression ratio, how much air/fuel combo has been forced into the cylinder, when the spark has been lit and how stable the combustion process is after that point.   It is VERY possible with a given static cam head setup to exceed the cylinder pressures achieved using a variable cam head setup.  

Not doubt Vcam (and the turbo setup used) could be making it easier to create a situation where cylinder pressures get to a point the block can't hold it - but blaming vcam for a cracked block is a bit like blaming a Porsche GT3 for being too fast if you don't brake for a corner and throw one off the road.   Things that improve torque naturally have the ability to put more stress on the parts which have to hold the associated forces, its up to the builder to ensure things are best setup to ensure the best chance of sustaining those forces and in this metaphor - the tuner/owner have to decide where to draw a line in terms of how far its pushed so they have less chance of overcooking the combination you have.

By all means remove vcam if it makes you feel better, but it won't necessarily lose you the ability of cracking the block due to excessive cylinder pressures if you were pushing things hard enough to achieve that.   There may be other reasons you are looking at changing as well, but realistically - if the only reason is due to cylinder pressures then perhaps it should be considered to hold back torque where you think it has caused a problem and keep the nice responsive drive that VCam provides while not compromising reliability.    Modern ECUs/control systems make it not particularly hard to target the torque you want, so instead of building the car to be inherently laggier in all situations it is possible to have your cake and eat it too.

By using vcam you are increasing power and torque which is filling the cylinder more and creating more pressure lower in the rev range which seems to where shit happens 

[Lithium]

9 minutes ago, r32-25t said:

By using vcam you are increasing power and torque which is filling the cylinder more and creating more pressure lower in the rev range which seems to where shit happens 

The effect vcam has on power and torque is negligible compared to the boost targeting and ignition timing.  It may make it easier to hit the high torque levels earlier, but you are not obliged to make use of that.   There are MASSIVE amounts of setups running around which would be capable of doing this kind of thing with variable valve timing which are perfectly reliable.  I feel like going to laggier/less streetable setup to avoid cracking blocks when all you have to do is exercise some restraint where it could be a risk is very very strange, though I could be missing something.

[Dose Pipe Sutututu]

Should be going back to 0 degree advance as soon as you're coming onto boost, keeping it on after that is what is causing the issue.

When I tunes SR20s, I do exactly that, use VCT to only get the turbo to come on, and turn it off quick smart.

I've seen plenty of tunes from "workshops" that keep VCT into 6 to 7k RPM, sure you're making much more torque, but can't imagine what cylinder pressures are like.

 

[Dose Pipe Sutututu]

3 hours ago, reaper said:

don't get too carried away with wanting 900-1000whp

but many do it for IG likes

[Lithium]

37 minutes ago, Dose Pipe Sutututu said:

I've seen plenty of tunes from "workshops" that keep VCT into 6 to 7k RPM, sure you're making much more torque, but can't imagine what cylinder pressures are like.

I'm not sure all the rationale or limits you are considering here, but just to pluck a random number out of the blue - what is the difference on the bottom end between making 500nm at 6500rpm with VCT on, or 500nm at 6500rpm with VCT off but running more boost?

Edited May 3, 2021 by Lithium

[Dose Pipe Sutututu]

9 minutes ago, Lithium said:

I'm not sure all the rationale or limits you are considering here, but just to pluck a random number out of the blue - what is the difference on the bottom end between making 500nm at 6500rpm with VCT on, or 500nm at 6500rpm with VCT off but running more boost?

Sorry my response wasn't detailed enough - hence the confusion.

if both were to make 500nm at 6500 with VCT on of VCT off you would assume the motor making 500nm with VCT on would have much greater cylinder pressures.

If VCT were to be turned off for motor making 500nm with VCT on, you'll get a reduced amount of torque also a reduced amount of cylinder pressure.

Motor with VCT off making 500nm, if VCT were to be turned on, you would "assume" that motor would make even more torque, i.e. 500nm+ but now with added cylinder pressure.

[Lithium]

5 minutes ago, Dose Pipe Sutututu said:

if both were to make 500nm at 6500 with VCT on of VCT off you would assume the motor making 500nm with VCT on would have much greater cylinder pressures.

Where does the extra cylinder pressure come from, and why are we seeing no more torque as a result of it?

[khezz]

55 minutes ago, Dose Pipe Sutututu said:

but many do it for IG likes

Hell Yeah!!! That's why I'm spending my kids school funds 🤑

Edited May 3, 2021 by khezz

[Dose Pipe Sutututu]

4 minutes ago, Lithium said:

Where does the extra cylinder pressure come from, and why are we seeing no more torque as a result of it?

Motor 1 could be a S15 motor
Motor 2 could be a S13 motor

both might be the same, but in reality they're not

[Lithium]

4 minutes ago, Dose Pipe Sutututu said:

Motor 1 could be a S15 motor
Motor 2 could be a S13 motor

both might be the same, but in reality they're not

Wut.

I'll try one last time, but I feel like I'm being trolled or something.

OK, so lets assume this.

A "workshop" has tuned an S15 which still has VCT on and with the current tune is making 500nm at 6500rpm at the given boost level.  Timing/fuelling is optimised, but because of silly old "workshop" using VCT it throws its insides out.

The engine is rebuilt to EXACTLY the same specs it was prior to throwing it's insides out.  Lets assume that its identical in every way, pretty much as though Dose Pipe went back in time and pushed "workshop" tuner out of the drivers seat and did the tune instead.

This time the engine is tuned with VCT off at 6500rpm, timing/fuelling is optimised for the conditions, but is running an appropriately different boost level to continue to make 500nm of torque at those rpm.

Are you saying the identical engine which is Dose Pipe tuned is more likely to survive?

 

[Dose Pipe Sutututu]

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.