F/I Blowing motors facts

[Xero-Limit]

Originally Posted by lukes Frs

OK so im new to the site looking for info on fi fa20 ? I just bought a new 2016 frs an I read this entire thread so my question is what is safe boost? or is any boost safe on this bottom end? I am only looking to make about 280whp enough to run with new ss ,or 5.0? but I don't wanna hurt a new car. so reply?

Lots of info on this on the forums but the basics are as follows:

7 psi will usually run as long as you'll own the car...about 1% that are safely tuned at that power level will fail for one stupid reason or another. Still exceeding OEM torque by 75%.

12 psi will run a good while, about 10% of those will fail after 30-50k miles.

15 psi (400+ WHP) will fail. Guaranteed, just a question of when. Some go a couple years, others go a few months.

Now nearly universally some knowitall will raise their hand and say they've gone 10 years and 100k miles at 500 whp on the stock motor--it's all in the tune. No, its not. It is more often just all highway miles and likely a very optimistic dyno, or possibly a creative imagination. Steel and aluminum fatigue. At stock power levels they will not fatigue until your bearings are well worn and the car is as the scrap yard. But when getting pounded with double the stress, expect 1/4 the life.

For those worried about the FA20 in the BRZ have some solace--subaru felt it was good enough as is to use in the FA20DIT at near 300 hp with some very minor changes. I disagree with Subaru that that was a good idea (we've taken apart a few) but if you don't beat on it too bad and use good fuel you should have no problems.

[lukes Frs]

im planning to run e 85 to keep pistons a little cooler I only drive the car once maybe twice a week an I usually cruise at 60 on the freeway not a heavy foot at all I just want enough power to run with occasional guy who thinks he is a bad @ss because he drives a new coyote mustang.

[FRS Justin]

Originally Posted by moto-mike

Lots of info on this on the forums but the basics are as follows:

7 psi will usually run as long as you'll own the car...about 1% that are safely tuned at that power level will fail for one stupid reason or another. Still exceeding OEM torque by 75%.

12 psi will run a good while, about 10% of those will fail after 30-50k miles.

15 psi (400+ WHP) will fail. Guaranteed, just a question of when. Some go a couple years, others go a few months.

Now nearly universally some knowitall will raise their hand and say they've gone 10 years and 100k miles at 500 whp on the stock motor--it's all in the tune. No, its not. It is more often just all highway miles and likely a very optimistic dyno, or possibly a creative imagination. Steel and aluminum fatigue. At stock power levels they will not fatigue until your bearings are well worn and the car is as the scrap yard. But when getting pounded with double the stress, expect 1/4 the life.

For those worried about the FA20 in the BRZ have some solace--subaru felt it was good enough as is to use in the FA20DIT at near 300 hp with some very minor changes. I disagree with Subaru that that was a good idea (we've taken apart a few) but if you don't beat on it too bad and use good fuel you should have no problems.

I wouldn't consider heavier rods and almost 2 points less compression, a minor change. I guess it's going to boil down to having to accept lower power levels for longevity.

[ajc209]

Originally Posted by FRS Justin

I wouldn't consider heavier rods and almost 2 points less compression, and no DI a minor change. I guess it's going to boil down to having to accept lower power levels for longevity.

The FA20DIT still uses the direct injection?

[ajc209]

Originally Posted by moto-mike

Lots of info on this on the forums but the basics are as follows:

7 psi will usually run as long as you'll own the car...about 1% that are safely tuned at that power level will fail for one stupid reason or another. Still exceeding OEM torque by 75%.

12 psi will run a good while, about 10% of those will fail after 30-50k miles.

15 psi (400+ WHP) will fail. Guaranteed, just a question of when. Some go a couple years, others go a few months.

Now nearly universally some knowitall will raise their hand and say they've gone 10 years and 100k miles at 500 whp on the stock motor--it's all in the tune. No, its not. It is more often just all highway miles and likely a very optimistic dyno, or possibly a creative imagination. Steel and aluminum fatigue. At stock power levels they will not fatigue until your bearings are well worn and the car is as the scrap yard. But when getting pounded with double the stress, expect 1/4 the life.

For those worried about the FA20 in the BRZ have some solace--subaru felt it was good enough as is to use in the FA20DIT at near 300 hp with some very minor changes. I disagree with Subaru that that was a good idea (we've taken apart a few) but if you don't beat on it too bad and use good fuel you should have no problems.

I asked my friends at Cosworth about predicting rod life once you go over the fatigue limit vs cylinder pressure and the answer was that the sintered rods in the FA20 make it difficult to predict how many cycles they will go before failure, but they will fail.

[FRS Justin]

Originally Posted by ajc209

The FA20DIT still uses the direct injection?

It most certainly does my mistake good catch!!! I don't know why I thought it was not on the DIT, will edit post now...

[Xero-Limit]

Originally Posted by FRS Justin

I wouldn't consider heavier rods and almost 2 points less compression, and no DI a minor change. I guess it's going to boil down to having to accept lower power levels for longevity.

This is what the rods look like:

The WRX has a slightly different small end, which is not where they break anyway. The middle is pretty much identical and where these rods always fail.

The compression difference does not affect the strength of the motor. Only the ratio of boost/vs static compression. 10.5:1 on 16 psi (stock wrx) is not much different from 12.5:1 on 7 psi. On 91 octane the 10:1 will certainly do better since you can run a bit less boost and reduce the effective compression of the motor. Unfortunately the WRX FA20DIT has such shit heads that none of that matters. They blow spark plugs in stock form and Subaru just issued a recall as their factory tune couldn't even figure out how to prevent eventual death until over a year after release. Sounds a bit like 2008 doesn't it?

[ajc209]

Are they made from the same material though?

[FRS Justin]

Originally Posted by moto-mike

This is what the rods look like:

The WRX has a slightly different small end, which is not where they break anyway. The middle is pretty much identical and where these rods always fail.

The compression difference does not affect the strength of the motor. Only the ratio of boost/vs static compression. 10.5:1 on 16 psi (stock wrx) is not much different from 12.5:1 on 7 psi. On 91 octane the 10:1 will certainly do better since you can run a bit less boost and reduce the effective compression of the motor. Unfortunately the WRX FA20DIT has such shit heads that none of that matters. They blow spark plugs in stock form and Subaru just issued a recall as their factory tune couldn't even figure out how to prevent eventual death until over a year after release. Sounds a bit like 2008 doesn't it?

I can't even express how much I agree with this post!! It's like plus 10000
And this is why I consider you one of the top 3 tuners on this platform.

[raven1231]

Yes, it seems that both the FRS and wrx are limited to 350ftlbs of torque to remain relatively reliable. Anything over that and the failure rate goes up exponentially. The sooner this torque appears in the band the harsher it is as well.

[Nickosport]

Originally Posted by moto-mike

This is what the rods look like:

The WRX has a slightly different small end, which is not where they break anyway. The middle is pretty much identical and where these rods always fail.

The compression difference does not affect the strength of the motor. Only the ratio of boost/vs static compression. 10.5:1 on 16 psi (stock wrx) is not much different from 12.5:1 on 7 psi. On 91 octane the 10:1 will certainly do better since you can run a bit less boost and reduce the effective compression of the motor. Unfortunately the WRX FA20DIT has such shit heads that none of that matters. They blow spark plugs in stock form and Subaru just issued a recall as their factory tune couldn't even figure out how to prevent eventual death until over a year after release. Sounds a bit like 2008 doesn't it?

What do you mean when you say "blow spark plugs"? Is the plug failing or is the head failing?

[FRS Justin]

Originally Posted by raven1231

Yes, it seems that both the FRS and wrx are limited to 350ftlbs of torque to remain relatively reliable. Anything over that and the failure rate goes up exponentially. The sooner this torque appears in the band the harsher it is as well.

I talked to Pauter rods yesterday (funny you should mention this), and Mario told me,
"The beginning stages of the pull have the most stress on the rod, if you start in 4th around 2000rpm the motor has enough power to overcome the load but the rod takes a beating on the small end. I have seen small end bushing failure result from this. Try to keep the rpm's above 5000 on a hard pull"
So you are 100% correct in what you stated Mr. Raven +1

[ajc209]

Originally Posted by raven1231

Yes, it seems that both the FRS and wrx are limited to 350ftlbs of torque to remain relatively reliable. Anything over that and the failure rate goes up exponentially. The sooner this torque appears in the band the harsher it is as well.

Relative being; "it will break but maybe not right away" ....


I would say 250lb-ft is a safe max based on the data I have seen.


350lb-ft is 470hp @ 7krpm

[FRS Justin]

Maybe someone should invent plastic rods, they would be cheap, and not destroy the block when they do go... Like a Glock those dam things can take a beating and still work. We could call them GLOCK RODS or GLOCK FA20