Turbo Backpressure seems high, opinions please

[Flyin Brian]

I have been suspecting my turbo backpressure is too high so I measured it today. At 14 psi boost measured at the throttle body I get 35 psi backpressure measured at the tap in the header about 1" below the turbo inlet flange. That gives a turbine backpressure to boost ratio of 2.5:1. Is this considered excessively high?? I have a 3.5" DP going to a 3.5" "Y" pipe for the dump with the dump closed. No cat with 2.5" dual after the dump with dual no baffle magnaflows and dual out. I say the turbo is a T60 but I really don't know exactly what exhaust turbine wheel size is in it. The exhaust turbine housing is a garret .63 A/R. I know this turbo is small for my motor but was just wondering what a good backpressure ratio is for a weekend/strip car?
Brian

 

[lazaris]

Thats on the high side. Your turbo is small for your cubic inch. You could go bigger which will give you a larger exh side, and still spool up good for a street car.

 

[JT'sV6]

I beileve 1.8:1 is idea. I would like to check my bp as well.

 

[bison]

I have been suspecting my turbo backpressure is too high so I measured it today. At 14 psi boost measured at the throttle body I get 35 psi backpressure measured at the tap in the header about 1" below the turbo inlet flange. That gives a turbine backpressure to boost ratio of 2.5:1. Is this considered excessively high?? I have a 3.5" DP going to a 3.5" "Y" pipe for the dump with the dump closed. No cat with 2.5" dual after the dump with dual no baffle magnaflows and dual out. I say the turbo is a T60 but I really don't know exactly what exhaust turbine wheel size is in it. The exhaust turbine housing is a garret .63 A/R. I know this turbo is small for my motor but was just wondering what a good backpressure ratio is for a weekend/strip car?
Brian

I woudlnt worry too much about backpressure if you have a street driven car and want it to spool decently. If you plan on making peak power with a given turbo with a 3 bolt you will have 2.5-3x intake pressure in the exhaust. Since most on here wont spring for a converter that works really well they are better off with the backpressure. Its very surprising you have so many high $ engine parts and dont know exactly what turbo you have. Personally id go with a 6262 and a PTC 9.5" with those parts. It will take you as far as you are willing to crank it. You are running E85 and dont have to worry about detonation. Spend the $ on a turbo/converter and put in a dedicated dual fed fuel system before you try and go fast.

 

[Flyin Brian]

I woudlnt worry too much about backpressure if you have a street driven car and want it to spool decently. If you plan on making peak power with a given turbo with a 3 bolt you will have 2.5-3x intake pressure in the exhaust. Since most on here wont spring for a converter that works really well they are better off with the backpressure. Its very surprising you have so many high $ engine parts and dont know exactly what turbo you have. Personally id go with a 6262 and a PTC 9.5" with those parts. It will take you as far as you are willing to crank it. You are running E85 and dont have to worry about detonation. Spend the $ on a turbo/converter and put in a dedicated dual fed fuel system before you try and go fast.

Thanks. The turbo is the last part of the car that has not been replaced. It worked good with the stockish motor but I broke a main last year and one thing led to another and I ended up building the stroker. I was going to run it long enough to break in the stroker and do some tuning which is where I am now. It is becoming obvious that the turbo is way too small for the new motor. I figured the extra backpressure might be causing some tuning issues as well as it has some knock retard occasionally even at 15 psi and 20 degrees of timing with a rich A/F ratio. A/F ratio is around 10:1 on the gasoline scale at 15 psi boost. I will for sure need more fuel system to keep up on E85 when I start turning the boost up. New turbo is next on the list. Will keep my current thousand dollar torque converter for a while before I buy the PTC 9.5" but that day is coming as well.