curious...

[freak customs]

in order to run anything over 5 lbs of boost or so, i would have to lower the compression. i understand the pistons from a legacy would do this.

assuming they would be for a 2.5litre and same bore size (not sure if there is a 2.2 legacy)...

1.) what year/years would be adaptable?

2.) would it run and drive with the legacy pistons and not turbo installed?

3.) around where would it bring the compression down to?

4.) has anyone tried the above?

[mikecg]

If you do a search you might find the info.

I believe someone said the 2.2L turbo pistons are the correct size. Subaru did make a 2.2L Turbo wagon.

[svxfiles]

Originally posted by mikecg
If you do a search you might find the info.

I believe someone said the 2.2L turbo pistons are the correct size. Subaru did make a 2.2L Turbo wagon.

And sedan.

They had 2.2 Legacys in the USA from 1990-1999.

[SVXtasy]

in order to run anything over 5 lbs of boost or so, I would have to lower the compression.

I do not think this is true. With fuel and timing I believe you can run upwards of 8 lbs. I know of 10:1 Honda’s running 10lbs daily driven.

I understand the pistons from a legacy would do this.

Yes they are from and early 90's 2.2l turbo legacy. They will work because they have the same bore and stroke. And 3.3l/6=.55l vs. 2.2l/4=.55l that would mean they both have the same displacement per cylinder. 2.5l/4=.625l so to have 2.5l piston work the engine displacement what have to be .625*6=3.75.

1.) What year/years would be adaptable?

I think it was 1991-1994 (not exactly sure about this)

2.) would it run and drive with the legacy pistons and not turbo installed?

Yes poorly and it would have a lot less power. It would feel like there was something wrong with the car.

3.) around where would it bring the compression down to?

Robert at Forced air tech said it would bring it down to about 9:1.

4.) Has anyone tried the above?

Yes but for some reason he dose not replay to my e-mails anymore.

[svxsubaru1]

U.S turbo legacy was from 91-94 they had the same engine throught out the ej22t.

[SVXtasy]

thanks it will now be changed (edit that post )

[oab_au]

The compression ratio for blowing, depends on the blower. A turbo can run a lot higher boost on the 10:1 ratio than a positive displacement blower.

The difference is , how much boost there is at low engine rpms. The turbo does not boost at 1500 to 3000 or so. This is the danger rev range for boost, that causes detonation.
A PD type supercharger can provide 90% of its total boost straight off idle. So they need either a lower comp ratio, or a boost controller to limit the boost at these rpms.

The engine is most prone to detonation at low engine speeds, due to the time that the piston takes to move over top dead center. The combustion chamber is held at a fixed volume too long for the burn rate.

Harvey.

[svxistentialist]

Originally posted by SVXtasy

Yes but for some reason he dose not replay to my e-mails anymore.

Care needs to be taken here. 2.2 engine having the same bore and stroke will mean that there is the same swept volume per cylinder, as indicated.

However, it does not necessarily indicate that a change to the Legacy piston will produce the Legacy turbo C/R, unless the shape of the crown of the Legacy piston is different, dished or whatever.

It is highly likely the lower C/R for the Legacy is produced by the shape of the combustion chamber in the head, possibly [probably?] aided by thicker head gasket.

An easier route to go might be to have some metal machined off the SVX pistons to lower swept volume/C Ratio.
[ it will reduce the stroke]

After all, the guys are currently working a boosted system with no engine changes other than controlled ignition and boost.

Joe

[oab_au]

Originally posted by svxistentialist


Care needs to be taken here. 2.2 engine having the same bore and stroke will mean that there is the same swept volume per cylinder, as indicated.

However, it does not necessarily indicate that a change to the Legacy piston will produce the Legacy turbo C/R, unless the shape of the crown of the Legacy piston is different, dished or whatever.

It is highly likely the lower C/R for the Legacy is produced by the shape of the combustion chamber in the head, possibly [probably?] aided by thicker head gasket.

An easier route to go might be to have some metal machined off the SVX pistons to lower swept volume/C Ratio.
[ it will reduce the stroke]

After all, the guys are currently working a boosted system with no engine changes other than controlled ignition and boost.

Joe

Joe we found in the 'bore and stroke' thread that the difference in the 2.2 turbo comp ratio is in the top of the piston, as the compression chamber volume is 40cc for both turbo and std. The SVX has a larger chamber, and a raised section on the piston to produce its 10:1 ratio.

You can't use a thicker head gasket to drop the ratio, as it will be more prone to blowing. It also opends up the squish areas to cause detonation.

Harvey.

Originally posted by oab_au
The compression ratio for blowing, depends on the blower. A turbo can run a lot higher boost on the 10:1 ratio than a positive displacement blower.

The difference is , how much boost there is at low engine rpms. The turbo does not boost at 1500 to 3000 or so. This is the danger rev range for boost, that causes detonation.
A PD type supercharger can provide 90% of its total boost straight off idle. So they need either a lower comp ratio, or a boost controller to limit the boost at these rpms.

The engine is most prone to detonation at low engine speeds, due to the time that the piston takes to move over top dead center. The combustion chamber is held at a fixed volume too long for the burn rate.

Harvey.

Assuming you have an identical lean condition and identical timing advance throughout the rev range at a given throttle position you are correct, however, being that every single case of moderate RPM detonation that I've seen in my days was the result of poor tuning or more commonly just victims of part-throttle timing advance at moderate RPM's because of using an SAFC or similar device to pull output from the MAP/MAF/AFM to the ECU to compensate for larger injectors, typically on a naturally aspriated motor that was turbo/supercharged with aftermarket parts, although gen II 3S-GTE's are also notorious for this problem with an AFC + larger injectors on the stock ECU.
Pulling AFM signal makes the ecu think there is less air incoming than there actually is, and while this makes for appropriate injector duty cycles to compensate for larger injectors, depending on the ECU's timing maps this can cause the timing advance to go dangerously high and fry engines, even with stock 8.5-1 compression as seen in the Gen 2 3S-GTE.

On that note, I'd like to add that Acura RSX Type-S's (Honda Integras) are running 7-10lbs of boost on a stock *HONDA* 11:1 compression motor and making over 300whp reliably and regularly with appropriate tuning i.e. conservative timing advance.


Edit: also, while thicker head gaskets are not ideal ways to reduce compression, again the detonation risks from the boffed up piston quench is only seen when being too agressive with timing advance and a/f ratios. There's nothing wrong with conservative timing maps and a/fs as long as you keep upping the boost. There's at least a dozen 2JZ-GE's (stock NA lexus/MK4 supra motor) that are making well over 600rwhp on a stock GE longblock with the exception of a 3mm MLS headgasket and ARP headbolts/headstuds. With countless more in the 450 rwhp range on stock ECU's w/piggyback management.

[svxistentialist]

Thanks Harvey.

I wasn't actually advocating the use of a thicker head gasket, only suggesting the possibility that the 2.2 turbo might have one as standard.

That is interesting information, and would seem to confirm my postulation that skimming the SVX piston crown would reduce the standard SVX C/R.

No?

Joe

[svxistentialist]

Originally posted by Wreckless


Assuming you have an identical lean condition and identical timing advance throughout the rev range at a given throttle position you are correct, however, being that every single case of moderate RPM detonation that I've seen in my days was the result of poor tuning or more commonly just victims of part-throttle timing advance at moderate RPM's because of using an SAFC or similar device to pull output from the MAP/MAF/AFM to the ECU to compensate for larger injectors, typically on a naturally aspriated motor that was turbo/supercharged with aftermarket parts, although gen II 3S-GTE's are also notorious for this problem with an AFC + larger injectors on the stock ECU.
Pulling AFM signal makes the ecu think there is less air incoming than there actually is, and while this makes for appropriate injector duty cycles to compensate for larger injectors, depending on the ECU's timing maps this can cause the timing advance to go dangerously high and fry engines, even with stock 8.5-1 compression as seen in the Gen 2 3S-GTE.

On that note, I'd like to add that Acura RSX Type-S's (Honda Integras) are running 7-10lbs of boost on a stock *HONDA* 11:1 compression motor and making over 300whp reliably and regularly with appropriate tuning i.e. conservative timing advance.

Generalising madly here, but.....

Does this indicate that 5-7-10 lbs boost on a high compression engine gives equivalent power to 15-20 lbs boost on a lowered C/R engine like the EJ 20, which can run from 8.5 to 9 ish C/R depending on which variant?

And if so, is the major factor in conserving the engine that of retarding timing at the lower RPMs Harvey mentions to keep detonation at bay?

Joe

[oab_au]

Originally posted by svxistentialist
Thanks Harvey.

I wasn't actually advocating the use of a thicker head gasket, only suggesting the possibility that the 2.2 turbo might have one as standard.

That is interesting information, and would seem to confirm my postulation that skimming the SVX piston crown would reduce the standard SVX C/R.

No?

Joe

It was 'not all there' or like that, on you forum that blew a gasket, posted pics of the top of the pistons. I asked him how high the lump on top of the SVX pistons was. He said about 1.5 to 2 mm. Yes you could machine the tops off to drop the ratio.

Harvey.

Power from boost and power from compression are slightly different things and its hard to make a generalization that doesnt leave holes. Roughly speaking, you will make more power with a given fuel by reducing compression and running more boost. The tradeoff is that a high compression engine spools a turbo faster and tends to be more responsive in general. There's a balance to be struck on compression ratio, its easy to go too low.
I've seen that the best compression ratios for boost on pump gas is around 8.5:1 to 9.25:1, and that the most power is made safely by running conservative air fuel ratios and timing advance, and just upping the boost like a madman until you run out of fuel or run out of detonation resistance with a given fuel.

With more compression and lower boost levels, you'll have a far more responsive setup than with lower compression but your peak power will suffer because of the low boost levels you can safely run. However, running high octane such as C-16 or VP-import will allow much higher boost levels safely and will make beau-coup power, but that stuff is expensive *and* addictive, along with the risks to catalysts and o2 sensors that comes from leaded race fuel.
For maximal output, forged high compression engines + boost is king but you need to run exotic fuel like Methanol or high cost race gas like VP-import exclusively.

[oab_au]

Originally posted by Wreckless


Assuming you have an identical lean condition and identical timing advance throughout the rev range at a given throttle position you are correct, however, being that every single case of moderate RPM detonation that I've seen in my days was the result of poor tuning or more commonly just victims of part-throttle timing advance at moderate RPM's because of using an SAFC or similar device to pull output from the MAP/MAF/AFM to the ECU to compensate for larger injectors, typically on a naturally aspriated motor that was turbo/supercharged with aftermarket parts, although gen II 3S-GTE's are also notorious for this problem with an AFC + larger injectors on the stock ECU.
Pulling AFM signal makes the ecu think there is less air incoming than there actually is, and while this makes for appropriate injector duty cycles to compensate for larger injectors, depending on the ECU's timing maps this can cause the timing advance to go dangerously high and fry engines, even with stock 8.5-1 compression as seen in the Gen 2 3S-GTE.

Edit: also, while thicker head gaskets are not ideal ways to reduce compression, again the detonation risks from the boffed up piston quench is only seen when being too agressive with timing advance and a/f ratios. There's nothing wrong with conservative timing maps and a/fs as long as you keep upping the boost. There's at least a dozen 2JZ-GE's (stock NA lexus/MK4 supra motor) that are making well over 600rwhp on a stock GE longblock with the exception of a 3mm MLS headgasket and ARP headbolts/headstuds. With countless more in the 450 rwhp range on stock ECU's w/piggyback management.

I do have trouble reading your posts, not that this on your part. I have trouble understanding some of you yanks.

You quote a lot of numbers that i asume are different engines, that we in Ozz don't have or have by a different name. I agree with a majorty of what you say about using fuel and timing to offset detonation. But these are treating the symptons of an event caused by chamber pressure and volume being maintained for too long.

No amount of fuel is going to fix the problem. Retarding the spark can off set it, but at the cost of cylinder heat. Looking at the cause of detonation, it comes down to the time that the quench area, end gas, can stand the heat and pressure before spontainous combustion takes place.

When the rotational speed is low, the time that this end gas is subjected to heat and pressure is high. Now we can retard the spark, to ignite it at a later time, so that the max pressure is developed around 15degs after top dead center, but the end gas is still subjected to the heat and pressure through the long time that the piston is holding it as it moves over TDC, and detonation will still take place.

I would think that none of the engines that you quote, would see boost at sub-2500 rpms, so they won't have this problem. A supercharged engine certinally will, that is the difference between useing the two types of blowers. Even high compression engines that are run under load at these low rpms will detonate to break the top rings, and this is without boosting.

It is only at these rpms that there is a problem. A turbo will not see it due to the no boost situtation. A supercharged engine will, if the low end boost is not controlled.

Edit; keeping the squish area low is vital to the sucess of any preformance engine, as this is where the detonation starts from.

Harvey.