backpressure measuring?

[summit]

Anyone done any measuring of backpressure on their turbos? I'm running an PTE88 four bolt on a stage II headed 274 and was wanting to compare. Don't have much choice as far as exhaust housings, but was wondering if going to a 4 inch downpipe from the 3.5 could affect it any. My preliminary readings seem to be higher than Harry told me to expect, but we haven't got to play with it much yet. Had a little trouble getting the check valve to seal to get a true peak reading, but it looked like 30 PSI of backpressure on a 20 PSI boost run. Little hard to remember to look at the gauge at 115+ 1/8 mile trap speeds. Just trying to track down my next hurdle to making more HP.

Greg Kring
Arlington, Texas
150 MPH and street driven

P.S.: Excessive spring pressure pointed me towards checking back pressure. I am having to run upwards of 700 PSI over the nose to keep from floating the valves at 7K rpm. Yes the motor still has titanium valves and retainers, so I don't know where else to go to ease the spring pressure. Stage II roller cams with even fire lobes and an odd fire nose with roller cam bearings aren't exactly stocking items and I would hate to tear one up with the crazy spring pressure and street miles.

 

[Joe Lubrant]

Hi Greg,

Probably not much help, but 4yrs ago, we measured the back pressure on a GN-1 Headed engine with PT88 3-bolt with a 3.5" & 4" DP and both were in the 45-46# range at 30#. My old PT88-3bolt in TSE trim with a 3" DP was way above that.

Not sure what you were told to expect?

 

[EightSecV6]

Are you sure you are floating the valves? Try opening the lash up a little or add a rev kit.

 

[summit]

Comp speced the cam at .018 lash, how much higher could I safely go? I have a rev kit, but not looking forward to new lifters, pushrods, and tearing the motor down to install it. may get to that point. I tried running dual springs with 650 open pressure but the car would not even go down the track it was banging so bad. Adding the third spring back in to get to 700 open was smooth running. Still shows a drop of a pound or two boost on the datalogger as rpm climbed, don't think I am out of turbo yet.

Thanks Joe, Harry had us shooting for a little closer to a 1 to 1 ratio on the backpressure. Guess we misunderstood him.

Back to the drawing board

Greg

 

[EightSecV6]

.022 I and .024 E HOT, this will definately help....

 

[HighPSI]

Greg,
I tested the back pressure of the latest PT-88. I found the b/p equalled the boost at around 17-18 psi. After that, the b/p increase quite a bit. At 28 psi, I was over 40 pounds of b/p.

 

[Lee Thompson]

?

How are you measuring back pressure? Tap into the exhaust header some where using a pressure gage?

 

[summit]

I have the O2 bung in the header capped off with a plug since the sensor is now in the downpipe. I just drilled and tapped the plug for 1/8 pipe and installed a fitting. Coiled off some brake line a few turns to disapate the heat and ran it over to the firewall. turned it into nylon vacuum line and using a cheap oil pressure gauge with a check valve to read peak pressure.

Greg Kring