Vf52 experiences vs 46

[dja]

Manifold pressure leads into the cylinders mate.
Just simplify it, air sucked into turbo>compressed and exits it>into pipe work/FMIC>into manifold>then into the cylinder, where it all goes bang.
When it gets spark and expands thats where things can get lifted, cylinder pressure goes through the roof.

HTH Mate

[bigBADbenny]

Indeed, 20psi vs 500 (stock)to 1000psi (race/built).

I wonder where the advice "stock heads lift at around sustained 21psi boost" originates and if its even a useful metric as regards stock HG integrity.

[owen]

"stock heads lift at around sustained 21psi boost"

Let's see how long I can prove this advice wrong for..9 months of hard driving so far @ 23.8psi

[bigBADbenny]

It's true. You're proof it's in the tune and supporting mods.
Anyway it's meant as a guideline eg that 20 might be somewhat safer for HG's than say 25.

Just trying to dig up the source of the info I quoted.

[dja]

Theres alot to it, no 2 factory engines are the same.
services intervals, abuse etc.

You also get stress failures in bolts and gaskets.

When i retune ill stick it to 10/18/20 via Si Drive and see how i go.

[KiDo_Tuning]

Thanks for the clarification.
I'll have to hit the books.
Q: what is the relationship between cylinder pressures and manifold pressures?

The ignition timing, AVCS and fuel maps all reference engine load in g/rev which is the amount of air passing the inlet port per engine revolution. 4cyl 4 stroke motor has 2 cyls open per revolution so g/rev is double g/cylinder. This is why adding fuel and retarding timing as engine load increases keeps cylinder pressures low and stop heads from lifting etc. My wife's FXT sees 4.2g/rev on 18psi and DR20T was seeing over 5.4g/rev and to put that into perspective, I know an E85 tuned car from Brisbane lifted heads at 3.8g/rev.

A tune I retuned recently only had engine load tuned despite bigger turbo and more boost, capped at the stock 2.56g/rev engine load. I assume because tuner though g/rev meant 2.56 bar absolute or 23psi... Stock VF52 WRX is tuned through to 3.2g/rev as it sees more engine airflow past intake port than a VF46/TD04 etc

This is why I refer to g/rev so much. There is a 600whp EVO on 16psi but it sees 7g/rev because there is lots of air in the cylinder, not in the manifold.

Big boost is more likely to pop an intercooler hose than lift heads. Big engine load plus lots of timing = lifted heads

I will email you an example

[bigBADbenny]

Nice one.
So for the purposes of our pre-tune guide to tuning, it would be more accurate to suggest that the maximum boost limit for the stock long motor (block, heads, head gaskets etc) would be close to the middle of the actual or imagined compressor map of the turbo being used, that is, wherever the turbo is at its peak efficiency, if fully supported with a safe tune and the appropriate hardware?

That the question is less about inlet manifold pressures and more about optimizing the tune and hardware to operate with peak efficiency and some headroom for reliability under variable operating conditions?

[kiahatsiu]

Yay tapatalk. Ric, feel free to delete my empty posts when you see them.

[kiahatsiu]

That car in bris dropped a sleeve. Just quietly.

[KiDo_Tuning]

That car in bris dropped a sleeve. Just quietly.

Not that car, this was early this year and I saw the motor. Head bolts stretched past yield but block was reused

[Newbie GT]

Consider the age of your car.
Yes it would apply - support is a good thing.
DIY read the AVO install guides on PDF.

Support it first for safety and reliability.
I'm supporting the stock stuff first then ill consider the bigger upgrades.
There's plenty to gain and yes ultimately the vf52 is a stock turbo with a slightly different design providing a little more top end.
During a 3rd gear pull, Bruce eventually pulled away from me as we reached the 5000rpm range.
We were somewhat surprised. Similar supporting mods, my lib is heavier being a wagon...
In normal driving its all about bottom end, thus I'm not really in the market for this upgrade unless mine fails.

Benny from what I know the vf52 is better bottom end slightly than vf46 and pulls better up top

[kiahatsiu]

Yeah Matt, about two thirds of all ej257s in South East QLD lifted heads this year. Haha.

[KiDo_Tuning]

Consider the age of your car.
Yes it would apply - support is a good thing.
DIY read the AVO install guides on PDF.

Support it first for safety and reliability.
I'm supporting the stock stuff first then ill consider the bigger upgrades.
There's plenty to gain and yes ultimately the vf52 is a stock turbo with a slightly different design providing a little more top end.
During a 3rd gear pull, Bruce eventually pulled away from me as we reached the 5000rpm range.
We were somewhat surprised. Similar supporting mods, my lib is heavier being a wagon...
In normal driving its all about bottom end, thus I'm not really in the market for this upgrade unless mine fails.

Benny from what I know the vf52 is better bottom end slightly than vf46 and pulls better up top

Let me know when you can get a VF52 making 19psi at 2700rpm.

[Newbie GT]

Matt what r you trying to say ? The vf52 losses bottom end and won't spool
as quick ?

[PoidaGT]

There's a mob in the US that advertises upgrading the VF52 with a larger billet compressor wheel.
http://6starspeed.com/vfbicowhandt.html