Roman's 4GR V6 Carina discussion thread

[mjrstar]

This is probably a dumb question, but how far away from coil bind are the valve springs, and could this vary much when the lifter is pressurized with oil pressure, and have you confirmed spring constant /rate.

I've had a valve failure from a bad spec valve spring (double springs in my case had way more than specified spring pressure) which was totally avoidable if the parts had been to spec.

[Roman]

They bind at 22mm lift, so are miles off thankfully.

The lifters only compress by maybe 5-6mm absolute max from their free length. I havent measured yet but I assume they are partially compressed to some extent when installed.

Someone pointed out that due to the way the lifters work, they need "some" compression before the check ball thing locks them in place when the cam turns. So having the hydraulic lifters gives you slightly less duration and lift than a completely solid setup. 

So might be worth going to a completely solid setup just for sake of that.

 

[sheepers]

that bmw lifter looks very similar to the 5MG unit.

which i rubbish.

just thought id add that in case you wanted to not use them.

[Rookie]

Re Valve bind, I listened to HPA interview Mitch Pullen, and one thing I took away from it was that he was talking about how he sets up his high rpm LS engines to be a gnats cock away from spring bind at full lift, with the theory being that it is much harder for the spring to get uncontrollable harmonics in it when it basically self dampens every cycle, that and something about better heat dissipation, but that part I'm a little doubtful on.

 

Sounds like you need custom cams with 21.9mm of lift...

[Roman]

Haha! 
Well, assuming I stick with the sub 13mm lift cams (as thats all that is available)
If you put a spacer in that squashes up these kelford springs, the new seat pressure would likely be too high.
But the factory springs might end up around the seat pressure of the kelford ones if you squashed them up. If you put a spacer at the bottom, then it's not adding any reciprocating weight either.
I'm mostly wondering if high rpm makes the lifter squash down. As there's no way to really see if it's happening.
If the lifter is squashing down then it means the valve isnt going down instead. So you lose heaps of duration and lift.
I'm not sure if there's really any way to know, short of installing a camera or something. 
So going to a solid lifter might just be best idea either way.

 

[mjrstar]

21 hours ago, Roman said:

They bind at 22mm lift, so are miles off thankfully.
 

Is that valve lift or cam lift? Or does the rocker ratio happen to be 1:1 

[keltik]

55 minutes ago, Roman said:

I'm mostly wondering if high rpm makes the lifter squash down. As there's no way to really see if it's happening.
If the lifter is squashing down then it means the valve isnt going down instead. So you lose heaps of duration and lift.
I'm not sure if there's really any way to know, short of installing a camera or something. 
So going to a solid lifter might just be best idea either way.

Could you dykem/blue up the shaft of a lifter and see how much it compresses after a hearty nang?

Not exactly easy tho but probably cheaper than a high speed keyhole camera

[Roman]

Yeah not a bad idea! 

 

[Truenotch]

4 minutes ago, keltik said:

Could you dykem/blue up the shaft of a lifter and see how much it compresses after a hearty nang?

Haha, I was going to suggest a little oring like a mountain bike shock. 

[Roman]

Oh yeah I'm wrong about that spring height anyway. It's actually ~14mm

As it's 36.3 - 22.35, not 22.35 total

 

[xsspeed]

1.45mm is a big gnats cock just sayin

[mjrstar]

in my mind that rocker layout increases lobe to valve stem motion, but if the cams are specced for valve lift not lobe lift then thats all gravy, if however they are ground for lobe lift you'll get more at the valve.

[Roman]

the lift on the actual cam is only tiny, like 7mm but it has a 1.7 rocker ratio that ends up being 12something mm pushing the valve down.

Kelford spec sheet shows some info from both.

[shrike]

Heads from your orginal motor are still ok?

So you'll swap them on at a later date?

[anglia4]

The engine / Intake / Header combo looks sexy.

[h4nd]

Should sell that 3 into 1 design to Gwynne at SpaceX; then when they lose an engine or 4, Starship won't spin like a top from lopsided thrust

[Roman]

11 hours ago, shrike said:

Heads from your orginal motor are still ok?

So you'll swap them on at a later date?

The driver's side bank is still okay. 

But the passenger side took a hammering for a variety of reasons. 

I dont think I will reuse them though, but they will still earn their keep in other ways. 

Being able to mock things up with a motor outside of the engine bay can be very handy! 

I really need to figure out some sort of airbox, so I'm considering just enclosing the entire lot of stuff in the top in the box. From the heads up. 

[Hurmeez]

I thought I heard somewhere that disabling direct injectors alone can cause them to melt and start leaking combustion pressure? Something about them being designed to be cooled by the fuel flowing through them and not standing up to combustion temps without. Have you ever heard anything like that or am I making it up? 

[Roman]

Yes that can happen but I'm skeptical that temperature is the actual issue.
I think there are two possibilities. 

Temperature related, it all overheats.
But it's all stainless? The injector is completely enclosed in the aluminium head which is a great heat sink.
Aluminium will start melting before stainless does. 
There is a teflon ring on the injector but it's well into the head and isnt exposed to combustion temps or close to it.

Or:

The lack of fuel pressure is the problem 
The fuel pressure stops the combustion pressure from pushing the injector pintle open. 
Apparently direct injection runs somewhere between 100-300 bar, which is why it needs the mechanical pump. 
Then peak combustion pressure is somewhere around 35-70 bar. 
So when you have the fuel pressure, you have 230 bar pressure differential, working in the direction of holding the injector closed.
Without the fuel pressure, you have 70 bar (~1000psi) working in the opposite direction.
Trying to push the injector open and nothing to stop it except for the small spring inside the injector that pushes the pintle to the home position.

The only instance that I've heard of the injectors blowing their guts out, was with a BMW/Supra engine where they were aiming for ~1000hp and were stuffing a zillion pounds of boost in it. 
So my thoughts are that if I just mechanically lock the injector in its closed position & give the pintle return spring an infinite rate (fill injector with high temp epoxy) then it's going to be fine with an NA motor where combustion pressure isnt going to be mega.

I filled the injectors yesterday. Had to pull the filter baskets out, fill with a small syringe, and use the heat gun on the injector body to thin the epoxy to help get the air bubbles out. 
Now this might not work and it may indeed be that high temps make the injectors blow their guts out. But will see how it goes.

[xsspeed]

might as well be grouting the block puerto rico spec now