Back pressure measurement?

Rev · 10-04-2003, 05:28 PM

Has anyone else besides me done this? I welded in some fittings right behind the headers allowing 1/8" steel tubes about 6" long off of the head pipes. I then attatched flexible lines to the interior of the car and attatched a Vacuum guage that also showed positive pessure 0-10 psi.

At idle I got .5 psi and a max of 2.5-3.0 psi at 5500 RPM. The guage actually vacillated alot at that point making a definite reading improbable. I would say 2.75 psi @5500 RPM.

Anyone else ever done this? I think anything under 3.0 psi should be OK. Any comments / opinions welcome.

Rev

tmoss · 10-07-2003, 09:28 PM

Nice work - I've considered doing this myself. you have chosen the right spot in the system. Now, you'll have to switch exhaust componanats to see the affects on power and back pressure.

Rev · 10-08-2003, 09:17 PM

The reason I wanted to measure the back pressure in the first place, is because I noticed that the resonator exhaust tips that I'm using (Pace Setter Monza) actually restrict my 2.5" tailpipes down to 1.75" to allow room for the glass pack material. I figured that must hurt power by increasing back pressure. I have new Hooker non resonator unrestricted tips ordered fron Jeg's that should be here Friday.

First thing I'll do is retest the back pressure. Second thing I'll do is do a G-Tech run to see if there's any difference. Eventually, I'll get back to the track for definitive tests when the weather is cold and dry. I'm hoping for a few more ponies at the wheels. Might dyno it again if it looks like there are any gains.

Rev

tmoss · 10-08-2003, 10:13 PM

Car Craft just did an article on what you did. They said back pressure should be between 2-4 psi.

I'd like to hear your results. The smaller diameter that far back may have less effect than you think - you'll know for sure soon.

10-04-2003, 05:28 PM	#1
Rev Registered Member Join Date: Nov 1998 Location: Houston, Tx. Posts: 3,887	Back pressure measurement? Has anyone else besides me done this? I welded in some fittings right behind the headers allowing 1/8" steel tubes about 6" long off of the head pipes. I then attatched flexible lines to the interior of the car and attatched a Vacuum guage that also showed positive pessure 0-10 psi. At idle I got .5 psi and a max of 2.5-3.0 psi at 5500 RPM. The guage actually vacillated alot at that point making a definite reading improbable. I would say 2.75 psi @5500 RPM. Anyone else ever done this? I think anything under 3.0 psi should be OK. Any comments / opinions welcome. Rev __________________ '66 Coupe, 306, 350-375 HP, C-4, 13.07 e.t., 104.8 mph, 1/4 mi. O.B.C. #2 '66 coupe

10-07-2003, 09:28 PM	#2
tmoss Registered Member Join Date: Mar 2003 Location: Saint Louis, MO Posts: 634	Nice work - I've considered doing this myself. you have chosen the right spot in the system. Now, you'll have to switch exhaust componanats to see the affects on power and back pressure. __________________ Tom (Torque) Moss 88Gt 5spd Vert, FLowmaster Catbacks, stock cam advanced 4° @ 108.5° ICL, NMRA prepped GT40P heads 1.85/1.55 valves and 1.7 rockers, MAC P headers Jet-Hot coated, 97 Exlporer intake (ported lower), TB and injectors. 277RWHP/330RWTQ (SAE). http://www.fastlanecars.com/

10-08-2003, 09:17 PM	#3
Rev Registered Member Join Date: Nov 1998 Location: Houston, Tx. Posts: 3,887	The reason I did it... The reason I wanted to measure the back pressure in the first place, is because I noticed that the resonator exhaust tips that I'm using (Pace Setter Monza) actually restrict my 2.5" tailpipes down to 1.75" to allow room for the glass pack material. I figured that must hurt power by increasing back pressure. I have new Hooker non resonator unrestricted tips ordered fron Jeg's that should be here Friday. First thing I'll do is retest the back pressure. Second thing I'll do is do a G-Tech run to see if there's any difference. Eventually, I'll get back to the track for definitive tests when the weather is cold and dry. I'm hoping for a few more ponies at the wheels. Might dyno it again if it looks like there are any gains. Rev __________________ '66 Coupe, 306, 350-375 HP, C-4, 13.07 e.t., 104.8 mph, 1/4 mi. O.B.C. #2 '66 coupe

10-08-2003, 10:13 PM	#4
tmoss Registered Member Join Date: Mar 2003 Location: Saint Louis, MO Posts: 634	Car Craft just did an article on what you did. They said back pressure should be between 2-4 psi. I'd like to hear your results. The smaller diameter that far back may have less effect than you think - you'll know for sure soon. __________________ Tom (Torque) Moss 88Gt 5spd Vert, FLowmaster Catbacks, stock cam advanced 4° @ 108.5° ICL, NMRA prepped GT40P heads 1.85/1.55 valves and 1.7 rockers, MAC P headers Jet-Hot coated, 97 Exlporer intake (ported lower), TB and injectors. 277RWHP/330RWTQ (SAE). http://www.fastlanecars.com/

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Oil Pressure Very low on new setup!!!	Z28EATR	Windsor Power	17	09-16-2003 04:03 PM
fuel pressure issues	mustang98gt	Modular Madness	3	07-05-2003 10:43 PM
Fuel Pressure 80 PSI???	White5oh	Windsor Power	13	04-12-2002 01:28 PM
Timing and fuel pressure	306 BLUE GT	Windsor Power	2	02-22-2002 12:16 AM
Back pressure good or bad?	RAGE_5.0	Blue Oval Lounge	8	11-23-2001 02:00 PM