Boost pressure for built engine

[Kodename47]

Originally Posted by Sportsguy83

Do you have E85 available in your area?

UK.... we don't do E85

[ChrisD]

Originally Posted by Sportsguy83

You're still kind of missing the point. You can't magically make the boost come in sooner. The turbo needs X amount of exhaust in order to generate boost. If you lower the compression, there is no way around it, the turbo will spool later (i. e. the exhaust "energy" lost by lowering compression will be made up by higher RPMs) and thus move your power band to later RPM's. Yes, you get a big amount of margin in the knock department, but at the expense of building boost at a later RPM because of the lower compression.

Do you have E85 available in your area? If so, I'd stick with 12.5 and keep that turbo spooling as quick as it does now, but with infinite room to grow because of the beefier internals.

If no E85, I'd say lower compression at the most to 11, so get some knock margin, but not too low as to drastically move your spool RPM range too far up.

Ah ok, I guess I was thinking that normally the turbo could give power a lot earlier in the rev range but that it just wasn't tuned to do that because too much torque low down can damage the rods. So I thought if you have stronger rods then you remove that limitation and can let the boost come on sooner. Sounds like perhaps that is not the case.

No I'm not going to have E85, but we do at least have 98 and 99 RON fuel widely available here. I thought 10:1 wasn't that low really - most places I found online that sell the Carrillo pistons only have 9:1 and 10:1 listed as being suitable for a forced induction FA20, so I figured I was going for the higher CR out of the two most common options.

[AVOturboworld]

Originally Posted by ChrisD

Ah ok, I guess I was thinking that normally the turbo could give power a lot earlier in the rev range but that it just wasn't tuned to do that because too much torque low down can damage the rods. So I thought if you have stronger rods then you remove that limitation and can let the boost come on sooner. Sounds like perhaps that is not the case.

Spool is affected (in the main) by amount of exhaust gas versus size of turbo. A big v8 can spin a single large turbo up almost instantly, while a small 2.0-liter motor, such as the ej20 subaru motors, can take a while to spool up even a smaller turbocharger. Subaru can get the FA20 turbo motors to spool up by even 2000 rpm, but they are using a very small twinscroll turbocharger to do so. That spools up quick, but also runs out of steam pretty quick as well.

One of the reasons the FA20 non-turbo spools up turbochargers as quick as it does is because of the high compression. Lowering the compression will increase the time it takes to get to maximum boost on a turbocharger. The main reason to lower the compression is to lower the amount of detonation you will see under boost. But you'll have to raise the amount of boost to match the power output you had at the higher compression, plus it comes in slower (unless you move to a smaller turbo).

No I'm not going to have E85, but we do at least have 98 and 99 RON fuel widely available here. I thought 10:1 wasn't that low really - most places I found online that sell the Carrillo pistons only have 9:1 and 10:1 listed as being suitable for a forced induction FA20, so I figured I was going for the higher CR out of the two most common options.

Those lower compression pistons are designed for the turbo motor, which also has different cams, and is optimized for turbocharging. The cams in FA20 in the BRZ/FR-S were designed around higher rpm naturally aspirated power, while the cams in the FA20DIT would be optimized for low-end torque.

Speaking from a drift perspective, if you were doing it in a competitive sense, you'd be looking at race gas, e85, or other solutions to make the amount of power you'll need anyways. Moving to a lower-compression motor and raising the boost won't change power drastically.

[Reaper]

Low comp fa20s are silly.

[350matt]

sounds like a stronger rod is going to be on your shopping list regardless

I'd say go for 10.5:1 with your turbo and get a 3" exhaust on there so you can pump the spark in and avoid det for as long as possible

[King Tut]

Originally Posted by Reaper

Low comp fa20s are silly.

Agreed.

[ChrisD]

Originally Posted by 350matt

sounds like a stronger rod is going to be on your shopping list regardless

I'd say go for 10.5:1 with your turbo and get a 3" exhaust on there so you can pump the spark in and avoid det for as long as possible

Already got a 3 inch exhaust from the turbo back. Yeah its starting to sound like 10.5:1 or 11:1 is going to be the better option...

[ChrisD]

Originally Posted by King Tut

Agreed.

You're really adding a lot to this thread... saying "good luck, you'll need it" and "agreed, low comp FA20s are silly". Keep the informative posts coming How about making some suggestions or providing some explanation rather than just telling me what I'm doing is not right

[ChrisD]

Originally Posted by AVOturboworld

Those lower compression pistons are designed for the turbo motor, which also has different cams, and is optimized for turbocharging. The cams in FA20 in the BRZ/FR-S were designed around higher rpm naturally aspirated power, while the cams in the FA20DIT would be optimized for low-end torque.

Speaking from a drift perspective, if you were doing it in a competitive sense, you'd be looking at race gas, e85, or other solutions to make the amount of power you'll need anyways. Moving to a lower-compression motor and raising the boost won't change power drastically.

Ah ok, I didn't realise they were aimed at the FA20DIT turbo engine.

So what would you guys recommend to get more power out of your turbo without blowing the engine up - is race fuel (or E85) the only decent solution? I know Fensport use the same turbo setup that I've got in their GT86 track car and make 420 bhp on stock engine internals with just over 1 bar of boost, but they're using race fuel.

How does the stage 4 AVO turbo differ to the stage 3 one that I've got in terms of power delivery? Presumably it would take longer to spool up but would make more power when it does kick in, so wouldn't this be pretty much the same effect as getting the lower CR pistons that you're saying are kind of pointless? Is the stage 4 only really intended to be used to make high power if you're using race fuel?

[Xuningshen]

^^ just ignore the "cool kids" up on their high horses^^ I've learned something new from the people providing info in this thread, so thanks.

[Jaden]

Originally Posted by ChrisD

You're really adding a lot to this thread... saying "good luck, you'll need it" and "agreed, low comp FA20s are silly". Keep the informative posts coming How about making some suggestions or providing some explanation rather than just telling me what I'm doing is not right

low comp fa20's are NOT silly if done right.

Here's some qualifying information. The reasoning behind them saying that low comp fa20's are silly is that they become dyno queens that aren't really all that useful (in most cases) because you lose that low end torque sacrificing for high end power which isn't all that useful.

There are ways around this. One way is compounded boost. You use a supercharger AND a turbo, one feeding into the other. The supercharger gives you the low end torque and the turbo compunded with the supercharger gives you good mid range and insane high end power.

Compounded boost setups are difficult to setup right though.

You have to have the airflow from whichever one is pulling from ambient.

If you're feeding a turbo into a roots blower, you'll need a rather large turbo to get the airflow at lower boost levels, because if your final boost levels are say 25-30 psi, you won't be spinning the turbo for more than about 10-14 psi depending on what you are spinning the supercharger at.

So if you want a final hp figure of say 550, you'll need the compressor map of the turbo in this case to provide about 40 lbs of air a minute at whatever psi would be needed to reach the compounded boost level of 25-30 or whatever final boost level you want to run.

The other benefit of a compounded boost setup is that the SC is putting more fuel and air into the engine sooner so it has more exhaust to spool up the big turbo faster so max boost comes on sooner.

Apart from being slightly more complex to tune, you will also have a bigger issue with boost creep requiring a better boost controller and a bigger exhaust bypass valve will be needed to avoid overboost conditions.

Jaden

[AVOturboworld]

Originally Posted by ChrisD

Ah ok, I didn't realise they were aimed at the FA20DIT turbo engine.

So what would you guys recommend to get more power out of your turbo without blowing the engine up - is race fuel (or E85) the only decent solution? I know Fensport use the same turbo setup that I've got in their GT86 track car and make 420 bhp on stock engine internals with just over 1 bar of boost, but they're using race fuel.

How does the stage 4 AVO turbo differ to the stage 3 one that I've got in terms of power delivery? Presumably it would take longer to spool up but would make more power when it does kick in, so wouldn't this be pretty much the same effect as getting the lower CR pistons that you're saying are kind of pointless? Is the stage 4 only really intended to be used to make high power if you're using race fuel?

Stage 4 is 100% aimed at e85/race gas, meth, or any other exotic fueling setups. e85 lets you get away with murder in terms of making power. Not so much because of the higher boost levels, but because of the huge amount of ignition timing you can add.

The additional spool time on the stage 4 is only 300-500rpm, so given we can get the standard turbocharger reaching peak boost from 3000rpm, another 300-500rpm is still long before some setups that won't reach it till 4500-5000rpm.

[ChrisD]

Originally Posted by AVOturboworld

The additional spool time on the stage 4 is only 300-500rpm, so given we can get the standard turbocharger reaching peak boost from 3000rpm, another 300-500rpm is still long before some setups that won't reach it till 4500-5000rpm.

OK this is what I was talking about originally - I'm pretty sure my turbo is not reaching peak boost until about 5K RPM and I assumed it was mapped this way for safety on the stock engine. So I thought with stronger con rods and lower CR pistons, we would then be ok to make the boost come in quite a bit earlier without breaking anything... but then everyone kept telling me I was "missing the point" and that wouldn't be possible. But are you saying we can make the boost come on a lot earlier if we have a stronger engine? Or is that still only if using E85

[King Tut]

Originally Posted by ChrisD

You're really adding a lot to this thread... saying "good luck, you'll need it" and "agreed, low comp FA20s are silly". Keep the informative posts coming How about making some suggestions or providing some explanation rather than just telling me what I'm doing is not right

Your first response to me has told me all I need to know. I have no desire to provide you with any further information. Enjoy your new found power, however you choose to find it.