Theoretical idea regarding compression ratios and boost

[Dairusire]

So as above, this is completely theoretical. Albeit, something I'd like to give a shot now that technology is much better these days in regards to engine building.

So idea is this:

Take a EJ207 or EJ257 and give it a compression ratio of either 9.5 or 10:1

Close the deck of either engine.

assumed of course Forged pistons rods and crank are up to the task.

Now why do that? Lag, I hate it. Secondly, I'd rather high response and better low-mid torque. Third, less boost needed and in theory more fuel efficient.

Thought's or ideas?

Do note, this is conversational, and I'm learning at to the pro's and con's

[loner]

what turbo and how much boost do you want to run?

[Dairusire]

 loner said:

what turbo and how much boost do you want to run?

Let's say for arguments sake, we keep the turbo a reasonable size. GTX3076R or Holset 35/40 both twin scroll. Unsure on boost levels. Like I said, this is just simply for conversational purposes and my own learning.

So lets start with the point of the CR being upped, we'll go with 10:1, 20% increase in compression ratio, soooo factory boost being 15PSi drop that down to say 10-12PSI

[Marky]

Plenty of turbo vehicles with 9.5:1 CR these days, low comp is nice for seeing the boost gauge read high but makes for a pig off boost, or at least not as nice.

10:1 is getting a little silly on pump gas, if you had meth injection or E85 then go mad but fuel quality can be the limiting factor with silly CR's, ditto for turbo sizing.

Most new-tech turbo motors are quite high comp - likes of the mazda 2.3 MZR, audi/vw direct injection turbos, etc etc all run 9.5:1 upwards and they all drive like you have a massive diesel under the bonnet, compared to a peaky older tech engine especially. Round town "normal" use is where you feel the difference, the dyno sheet not so much

In a way same idea as going to a larger capacity, work smarter not harder

[Guest]

Run 9:1 safe on pump or good juice.

Avcs

Twin scroll

Hrc35/40, td06h/mse hybrid or gt3071/6/gt3576

Ej25/ez30

Lag is a stupid term and loosely used. Do the above it will deliver what you want.

[lachlan]

Put a ez30 in it . No lag .

[Kiwi_Fozze]

The 30 does have a lot of torque...

Id imagine an ez30 with a sc hanging off the side would make for one unique car

[Dairusire]

Oh no doubt a EZ30 will have a lot of torque. problem with EZ30 is fitment in most cases.

Idea behind this, is to get fast engine response and spool, with good drive experience. Mind you I got the idea from the Mine's R34 GT-R, just the way it revs and it's response is unbelievable. I just wonder how something could be attained from an EJ or EZ

video of the Mines R34 GT-R

Edited January 9, 2016 by Joker

[Guest]

 Dairusire said:

Oh no doubt a EZ30 will have a lot of torque. problem with EZ30 is fitment in most cases.

Idea behind this, is to get fast engine response and spool, with good drive experience. Mind you I got the idea from the Mine's R34 GT-R, just the way it revs and it's response is unbelievable. I just wonder how something could be attained from an EJ or EZ

video of the Mines R34 GT-R

Watched the video didnt see amazing spool. Spends all its time between 6-8.5k with that power and obviously having all things matched well means it pulls like a school boy thro the upper region.

Look at ballsrburning dyno sheet things got a good balance of low/mid/high on a 2l.

Subaru arent a 2j that will deliver across the whole curve. The design of headers specifically has a huge effect. So you either slant the engine design to low/mid or mid/high.

Regardless what you do its going to be soggy or fall over up top. Unless youre mr money bags.

[Guest]

 Dairusire said:

So as above, this is completely theoretical. Albeit, something I'd like to give a shot now that technology is much better these days in regards to engine building.

So idea is this:

Take a EJ207 or EJ257 and give it a compression ratio of either 9.5 or 10:1

Close the deck of either engine.

assumed of course Forged pistons rods and crank are up to the task.

Now why do that? Lag, I hate it. Secondly, I'd rather high response and better low-mid torque. Third, less boost needed and in theory more fuel efficient.

Thought's or ideas?

Do note, this is conversational, and I'm learning at to the pro's and con's

I'm doing exactly this atm. I'm running a 207 block with the forged internals. I'll be running 8.7-9 CR. I've got a holset hrc35rs off Steve Murch although it is only single scroll. Tomei pro cams. And 1000cc injectors. I'm predicting over 300+kW atw and steves predicting 20 odd psi of boost between 3500-3700 and holding it till Redline. That's wat I'm upto and it will be done in the next month or so.

[hunter951]

 VADZTER said:

I'm doing exactly this atm. I'm running a 207 block with the forged internals. I'll be running 8.7-9 CR. I've got a holset hrc35rs off Steve Murch although it is only single scroll. Tomei pro cams. And 1000cc injectors. I'm predicting over 300+kW atw and steves predicting 20 odd psi of boost between 3500-3700 and holding it till Redline. That's wat I'm upto and it will be done in the next month or so.

imagine that sort of response with twin scroll!!!??? even so, Sounds like an absolutely awesome build, would love to see some videos of it getting pushed around a track

[knockoutgiant]

This is also pretty much what I'm trying to achieve with my build at the moment.

EJ257 stock block, rods and crank (Would love to go CDB but don't really need to for the numbers I'm looking at) CP forged pistons. Somewhere around 8.7:1/9.0:1 compression ratio with Dual AVCS EJ20 heads and a GTX3076R twin scroll (Hopefully but can't seem to find one that's released yet?!) I'm hoping to get mine done by the end of the month.

Aren't the EJ20Y/X's 9.5:1 compression factory anyway?

[lachlan]

Anyone seen a quick spool valve on a ej ?

Twin scroll on a 4 cylinder is a bit wank anyway

[Guest]

 lachlan said:

Anyone seen a quick spool valve on a ej ?

Twin scroll on a 4 cylinder is a bit wank anyway

Yes look in oldest dyno thread rac used one on an ej25/v3 sti heads. Used electronic solenoid and an actuator to control it. Worked well but t/s is better.

Not wank if it works well.

My ej25 is running stock 8.2:1 and love the off boost nature of it.

[Andy_Mac]

The new Borg Warner EFR twinscroll ones uses a similar method to a quick spool valve. Should give impressive spool along with solid top end.

[Guest]

Funny thing they sell those turbos for 2-3x a holset and get similar results with just a dirty twin scroll on the latter.

[Andy_Mac]

Yea they are stupidly expensive, but most murica ones are.

Is that the new ones that get similar results or the current gen efr's?

[Guest]

Efr ones like umadbo runs.

[Guest]

 lachlan said:

Anyone seen a quick spool valve on a ej ?

Twin scroll on a 4 cylinder is a bit wank anyway

Why are twin scrolls wank on 4 cylinders? If anything they improve the performance and response of the car. Wonder why Subaru went to twin scroll?? And how are they any different to twin scrolls on 6 cylinder cars theoretically. The principle is the same just less exhaust gasses due to less cylinders. In saying that a lot of the response of the car depends on the cam and valve train setup, manifold design, manifold runner size etc. You don't lose boost up top either. ( on the holsets anyway from my experince) all you get is on boost faster.

[Guest]

You could literally buy 3 holsets for the price of one efr turbo loool definitely not 3 times better that's for sure. Plus they added the stupid sensor that measures the rpm of the turbine which is completely useless unless your in rally and have people who actually know what do with that information

[hunter951]

 lachlan said:

Anyone seen a quick spool valve on a ej ?

Twin scroll on a 4 cylinder is a bit wank anyway

lol twin scroll on a v8 would be wank... twin scroll on a 4cyl ftw. they kill down low and up top + equal length sounds like heaven.

[Guest]

 hunter951 said:

lol twin scroll on a v8 would be wank... twin scroll on a 4cyl ftw. they kill down low and up top + equal length sounds like heaven.

I agree and if you got nice cams... Omg I literally can't wait to see how this setup is going to go. Trap times down the quarter will be good too

[Zenki]

 hunter951 said:

lol twin scroll on a v8 would be wank... twin scroll on a 4cyl ftw. they kill down low and up top + equal length sounds like heaven.

BMW would like a word with you. Flat torque curve from 1500-5000RPM.

[Dairusire]

So, I guess the general consensus here is the following.

Up the compression to around 9.0-9.5:1

Use Twin-Scroll because #ballerstatusenabled

Use AVCS heads to enable even earlier spool and even greater baller status

Forge the motor

Factory cams? Unsure on that one, I assume if one was to replace the cams, typically you're going to loose low down response due to aftermarket etc.

EDIT: Oh and seems like using a 2.5L motor is preferred to boot.

[Marky]

My additional 2c (so, my 4c?) is don't worry about what boost pressure you want to run

People get fixated on "I want to run 20psi", or whatever number they have picked

End of the day with a bigger motor, which breathes better, you might not -need- 20psi to make the number you wanted anyway. It's purely an example of how much restriction there is to the turbo pushing air in remember, so if you have a more efficient motor to start with, it's less restriction, so at the same airflow you show less manifold pressure (sort of)

Hence why you can make such easy power on a turbo honda motor (for example) compared to having to push 2 bar into a beat up 8.0:1 EJ20 to make the same on the same turbo. Ditto for how on some cars a camshaft change can net huge gains, again it's making the base more efficient, which then snowballs once you add boost. More capacity is the same, combine both for max win