most boost on cast

[buckwheat]

whats the most boost youve ran on cast pistons with out any prob. and how long did thay last.

[BadAssPerformance]

I've run 27psi on cast '87 T-I pistons...




...wait...




...really? ...




...yes really! ...




...but you gotta ask more questions!!!

Cuz I ran 27psi with a stock T-II (T03) Garrett... if it were 27psi out of a T03/T04 hybrid or Holset or something bigger than a stock Garret... BIG difference in CFM.

Oh... more info.. I run 100 octance Sunoco/Cam 2 race gas... 27psi on 91-93... might have some melty issues?

Oh, more info.... I was running an MP Stage II LM... not some Stage 18, more timing than you thought was possible cal...

OK, I'll stop

But really... its the whole package (mods, settings, etc) that dictates what you can and cannto get way with... "how much boost" is only a part of it.

[Directconnection]

....if it were 27psi out of a T03/T04 hybrid or Holset or something bigger than a stock Garret... BIG difference in CFM.

In the words of the famous "Gus Mahon:" 27 PSI is 27 PSI. HP difference between the turbos has to do with the backpressure in the turbine causing HP losses and compressor temps leading to lesser dense of a charge.

PSI measured at the manifold is just a measurement of the intake tract's efficiency (or inefficiency)

But, I know you know this JT.... we all forget shat over time (especially me!)

[22shelby]

im at 24 on stock 2.5 cast slugs....on 93 pump gas w/ a t3/t4 46 trim....oh wait on a G head and bout to giv'er a few more pounds....

[BadAssPerformance]

In the words of the famous "Gus Mahon:" 27 PSI is 27 PSI. HP difference between the turbos has to do with the backpressure in the turbine causing HP losses and compressor temps leading to lesser dense of a charge.

PSI measured at the manifold is just a measurement of the intake tract's efficiency (or inefficiency)

But, I know you know this JT.... we all forget shat over time (especially me!)

Yes, 27psi is 27 psi, but with a larger turbo there is more CFM produced at 27psi. More CFM means more air in the cylinder which allows for a larger boom. Bigger boom can crush cast pistons...

[Directconnection]

Yes, 27psi is 27 psi, but with a larger turbo there is more CFM produced at 27psi. More CFM means more air in the cylinder which allows for a larger boom. Bigger boom can crush cast pistons...

Same CFM..... just different density, right? If it were more cfm, then there would be more boost. "Cubic Feet per Minute" doesn't tell us how much density said fluid has

Sorry for nitpickin' ya JT!

For the original poster: Gary Donovan may have been the one to run the quickest on stock cast Mahles on his 2.5 reliant somewhere's in the low 11 second range. He also ran his stock t-II full tilt (28psi) on stock 2.2 Mahles to get his Daytona to run 12.6.

[buckwheat]

Just wondering i got a 2.5 40 over cast mahle,s and i am running 20 psi t3/t4 hybrid mild port head stage 5 ecu +40 injectors fmic and i was running 50/50 mix of 91 pump gas and race gas and the ringlands cracked on #1cyl .i just replaced that piston and wanted to see what kinda of abuse thay could take

[turbovanman²]

Just wondering i got a 2.5 40 over cast mahle,s and i am running 20 psi t3/t4 hybrid mild port head stage 5 ecu +40 injectors fmic and i was running 50/50 mix of 91 pump gas and race gas and the ringlands cracked on #1cyl .i just replaced that piston and wanted to see what kinda of abuse thay could take

The issue isn't so much boost, its the tune, at higher boost levels, one snippet of detonation and your done, forged, they can take alot of detonation before failing.


27 psi is 27psi but you also have volume to deal with. 27 psi on a TII is like flowing thru a straw say compared to 27 psi on a GT35R, which is like flowing thru a sewer pipe.

[buckwheat]

i plan on going forged soon. i kick my self in the a_ _ for not going forged.as far as tune goes ive done all i can there realy is no one out in nor cal that tunes 2.2 or 2.5 every now and then chris stops by socal to tune but that's it.

[BadAssPerformance]

Same CFM..... just different density, right? If it were more cfm, then there would be more boost. "Cubic Feet per Minute" doesn't tell us how much density said fluid has

OK, so..... CFM from the turbo's perspective, density from the cylinder volume perspective.

[Directconnection]

OK, so..... CFM from the turbo's perspective, density from the cylinder volume perspective.

I'm just playin' 'round with ya!

[BadAssPerformance]

Ya I kno

About the original question tho... 27psi out of a tiny turbo could be worse than 27psi out of a normal size turbo as well... cuz the air charge is going to be way hotter out of the smaller turbo...

Maybe we should start a thread "how much timing on cast pistons" ?

[turbovanman²]

Maybe we should start a thread "how much timing on cast pistons" ?

Don't need a thread, "not much",

[mopar-tech]

For the original poster: Gary Donovan may have been the one to run the quickest on stock cast Mahles on his 2.5 reliant somewhere's in the low 11 second range. He also ran his stock t-II full tilt (28psi) on stock 2.2 Mahles to get his Daytona to run 12.6.

The 2.5 pistons were good for 11 second passes before the tops of the pistons would start to just peel off from the power level.

No detonation, they just start to stretch and the upper ring would rattle around.

2.2 Mahles have a bit more meat in the ring pack area and piston top, they can go a bit further then the 2.5 piston can.

I use to hit the Daytona with 28-30 psi with a stock TII turbocharger.

[mcsvt]

Ran my 2.5L T-II Daytona at 25psi daily for a few years. 3bar cal, +40's, great tune, no issues.

[Mopar318]

26 psi broke one of my pistons, and all the top rings broke.

These were sealed power pistons. I didnt have detonations, and had a good tune.

[mopar-tech]

26 psi broke one of my pistons, and all the top rings broke.

These were sealed power pistons. I didnt have detonations, and had a good tune.

Sealed Power not as good as the factory Mahles.

[Mopar318]

Sealed Power not as good as the factory Mahles.

Yeah I know, thats why I made sure to say what they were

[T-Bohn]

ok I am haveing a hard time with the psi cfm volume thing....
the enginge is a sealed size 2.2 the pounds measure the boost or pressure inthe cyl.

how does a larger cfm change the volume of air inthe cyl.? as I see it when it's full, pressure goes up and you just squeeze more in and raise the pressure faster.

i can fill my car tire to 50 lbs with a bicycle pump and it takes a long time10 minutes and a very sore back or I could use the largest air compressor inthe world and fill it to 50 lbs. in .13 of a second.

what am I not understanding?

I get lag and heat from smaller and larger turbos but not the voume and pressure part.

links to posts ??

[Vigo]

If you take a given orifice (such as the restriction of the engine) and put a given amount of pressure in front of it (such as 27psi) the SAME volume of air will pass through the orifice over a given time period.

So, two turbos pressurizing the SAME engine to 27 psi are moving the same VOLUME of air through the engine.

However, a 'bigger' turbo with a more efficient compressor section will heat the air less while compressing it to 27 psi, and since the charge air is of a lower temperature it will also be more dense and contain more oxygen per the given volume, meaning you can burn more fuel and make more power at the same boost level, with less risk of detonation.

However, burnign more fuel, even in the right air/fuel ratio, is creating more heat, and there does come a point where you simply put heat into parts like the pistons at a faster rate then they can transfer it away, and then they get soft and deform as Mopar-Tech mentioned.

Also, one thing that the boost level of 27 psi does not tell you is how much reversion you are getting. Smaller turbos such as the stock one create a pretty large restriction on the exhaust side of the motor, and if you are pushing 27 psi on the intake side, you might have 40 or 50 psi between the exhaust valve and the turbine. These high pressures can cause some high-temp end-gas to either stay in the cylinder on the exhaust stroke or leak back into it. This means that you will be running hotter in the cylinder at 27 psi then if you had a 'bigger' turbo with a less restrictive turbine and less reversion.

So, since the smaller stock turbo will pump hotter air into the engine and make it harder to pump the heat out the exhaust side, it is generally pretty delicate to run super high boost numbers without melting something.

On the other hand, while the larger, more efficient and less restrictive turbo may make the same power at 17psi that the stock turbo makes at 27 psi by pumping in the same amount of actual oxygen, turning the big turbo up to 27 psi will ultimately result in burning a lot more fuel and generating a lot more heat in the chamber if the air/fuel ratio is correct. However, with a less restrictive exhaust side, more of that heat will be pumped out of the engine.

Lots of factors! The ability of either setup to survive at 27 psi ultimately comes down to safe tuning, regardless of pistons.

Hope that was accurate/helpful.