Questions about increasing Turbo PSI

[Vilmenay]

When increasing boost, besides detonation, does there come a point where too much boost actually makes less power? Does increasing PSI change when boost pressure actually starts to kick in? And finally is it theoretically possible for a turbo to make a car reach red line faster when shifting, yet not make more power?

[hannibal]

When increasing boost, besides detonation, does there come a point where too much boost actually makes less power?

Yes, but its more a function of the turbo than the engine. If you run a smallish turbo at high boost, it will heat up the air drastically (in addition to pressurizing it). This can happen with any turbo, but occurs at lower pressures with a small turbo.

Also, at some point, its likely the turbo will experience a diminishing return of power from adding boost. Say you gain 50hp going from 10 to 15psi. You may only gain 30hp going from 15 to 20psi. I tihnk these decreasing gains will occur until the turbo runs way past its efficiency range, and begins creating excessive heat as mentioned above.

Quote »Does increasing PSI change when boost pressure actually starts to kick in?[/quote]It shouldnt. Boost should start to build at the same point, but naturally it will take longer to develop 15psi than 5psi. They only way I can see boost threshold changing is if an inefficient manual boost controller is used (bleeder type??). I cant recall how the different types of MBC's work...

Quote »And finally is it theoretically possible for a turbo to make a car reach red line faster when shifting, yet not make more power? [/quote]I doubt it. The motor would have to make more power at some point in the rev range in order to hit redline (and accelerate) faster.

[evildky]

ok we could go on for days about turbo theory, the bottom line is that the stock turbo's are not "efficient" beyone 16-18 psi, what this means is the blades are designed to scoop air up to a certain rpm, and beyond that they simply spin in a pillow of hot air, the main consideration is "VE" (volumetric efficiency), this is finding the sweetspot at which the impeller flows the most amount of air possible (these things spin at well over 100k rpm), this is expressed in VE maps, the total "LBS/MIN" (pounds per minute) ultimately limits the amount of power available from a specific turbo based on it's abulity to move that much air, the stockers flow somewhere around 20 lbs/min ( just a guess based on the hp limits of stock turbos) to confuse you even further all PSI (pounds per square inch) are not created equal, 15 psi of boost form a turbo flowing 20 lbs/min, wil make less power than the same 15 psi form a turbo flowing 25 lbs/min, while the boost level remains the same you are actually flowing 25% more air! now add to this that you need extra fuel with the extra air wether it's gained by adding boost of lbs/min you have to increase the fuel or you will pre-ignite and thats what makes engines go boom! as fow ehen the boost kicks in this is determined by the "knee" of the VE maps, it requires a great deal of math, the size fo the hotside (or turbine) of the turbo as well as the cold side (compressor) and even the materials used to make the wheels and the "bearings" most turbos (all but the ball bearing models) actually use bushings, sorry if I rambles but most people have very little knowledge and are happy to tell everyone how many psi they are running when it has so little to do with anything

all that and a paper sack is worth a paper sack

the good news is all the math has been done and educated retailers are more than willing to help you achieve you needs, some legit some not, be careful whose advice you take when it ends in a sales transaction, JWT, MSA, CZP, Z1 are all experienced and sell good product with presictable results! that being said, there is nothing so rewarding as upgraded turbo's, they flow more air throughout the power band and change the attitude of a car

[Wetmyson]

1. how much boost can you "safely" run on stock internals?

2. how much boost can you run before you need to upgrade injectors?

3. how much boost can you run with 555cc injectors?

thanks

[evildky]

answers:

1. depends on the the turbo

2. depends on the the turbo

3. depends on the turbo

assuming you mean sotkc turbo:

1. more than the stock turbo's can make

2. the injecotrs max out about the same point as the stock turbo's (about 16 psi)

3. more than the stock turbo can make

[Wetmyson]

answers:

1. depends on the the turbo

2. depends on the the turbo

3. depends on the turbo

assuming you mean sotkc turbo:

1. more than the stock turbo's can make

2. the injecotrs max out about the same point as the stock turbo's (about 16 psi)

3. more than the stock turbo can make

thanks man.