Got O/R Prochamber Installed..

fast97gt said:

then tell me this, laser red, if you have a clogged cat to much backpressure will chew the exhaust lobes off the cam, so ford designs the comp. to detune the engine to cut down exhaust pressure by cutting fuel pressure to the engine, like deisels do when the exhaust temps get to high...

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I'm not sure who told you that too much back pressure can hurt the lobe of a camshaft, but that's totally untrue. Exhaust back pressure has nothing to do with the spring load of an exhaust valve and therefore has no correlation to an exhaust lobe failure.

The PCM/EEC does not make any spark or fuel alterations of any kind no matter how badly the catalyst efficiency is observed. The motor and PCM could care less how well the cats are performing, the codes or CEl just comes on as a courtesy to the driver.

iight wise guy if you have cork (a clogged cat) and no exhaust pressure can get by it whats gonna happen, ill tell ya the pressure stays in the pipe and manifold between the cat and the head. now the valve is harder to open due to the extreme pressure of exhaust and the first thing wear out is the exhaust lobe(s) of the cam on the side of were the cat is, if there is dual exhaust on the vehicle. ive seen it too many times to have someone tell me that it doesnt happen, thats why they put the o2s after the cats to moniter efficient flow of the exhaust so no internal damage to engine occurs...

I drove with the CEL on for months. Performance was was actually better on the top end than before (I guess due to the Prochamber freeing up some horses). The rear O2s are for emissions only. They only tell the ecu that the cats are functioning. The front O2s affect A/F ratio and performance.

What if you have little back pressure? What does that cause? Say from an dumped exhaust with no mufflers?

mossberg i know the rear o2s are for emissions, and there to tell the comp. when theres restriction in the exhaust, (due to a clogged cat.) but you dont have to worry about your ride because you know that your car is fine because the cats arent there any more, im guessing, but, for those who do have them they can be detrimental to an engine if proper care isnt taken when they fail.

and for you merc123 that just means more ponys cause your exhaust is more free flowing than stock enjoy it

merc123 said:

What if you have little back pressure? What does that cause? Say from an dumped exhaust with no mufflers?

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Torque loss?

fast97gt said:

iight wise guy if you have cork (a clogged cat) and no exhaust pressure can get by it whats gonna happen, ill tell ya the pressure stays in the pipe and manifold between the cat and the head. now the valve is harder to open due to the extreme pressure of exhaust and the first thing wear out is the exhaust lobe(s) of the cam on the side of were the cat is, if there is dual exhaust on the vehicle. ive seen it too many times to have someone tell me that it doesnt happen, thats why they put the o2s after the cats to moniter efficient flow of the exhaust so no internal damage to engine occurs...

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The piston is still moving down when the exhaust valve begins to open. On relatively stock or mild cams, the EVO or exhaust valve opening point takes place around 40°-55° BBDC. At this point the peak cylinder pressure has long subsided. Tests have shown there is around 10-15 PSI left in the cylinder at EVO on a relatively stock motor.

The exhaust valve closes at around 15°-20° ATDC completely overlap, and at which time the intake valve is wide open meaning not only is no pressure in the cylinder but there is negative pressure in the cylinder.

By the time the exhaust pressure wave reaches the end of the header/exhaust manifold, there is less than 3 PSI present at the collector. The motor can only exert as much exhaust backpressure as it is mechanically capable of doing, regardless of an exhaust restriction or not. Please explain how an exhaust lobe gets hosed with a exhaust valve spring that is rated at 130-140lbs open?

Take an air compressor that can output a maximum of 150 PSI. If you were to measure the PSI at the end of the hose it would be roughly 150 PSI. Now if you were to completely block the hose and measure the pressure, it will still read 150 PSI. The blockage in the hose does not somehow magically give the compressor the increased mechanical advantage to generate more pressure. The exact same applies to an internal combustion engine.

There aren’t even any hard or soft programmed provisions within the PCM/EEC to alter the fuel or spark based upon input from the rear O2 sensors.

97stang_guy said:

Well I finally got it installed. We did the radioshack MILs. Well on the way home my CEL came on. Guess they didn't work.....

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are you sure you did it right? i've had mine on for about 8 months and they're still working. yea, pretty crappy craftmanship but it gets the job done

laser red thank about what your sayin, i get your point about the air compressor, but it seems i cant seem to pound it in your head, think about it the pressure in the a/c has to build up some how, oh wait theres PISTON IN A CYLINDER WITH AN INTAKE AND A exhaust or exit valve just like the I/C ENGINE. so what that tells me and what your telling us is that a stock or mildly modded engine only pushes out 10 to 15 psi, but with a CLOGGED cat THE PRESSURE BUILDS UP, but unlike the air compresser the i/c engine doesnt have shutoff switch when the pressure reachs a predetermined setting like umm 150PSI. now the new advanced i/c engines have a simple warning system THE REAR o2 SENSORS to measure exhaust flow. so if you have a clogged cat the presure builds and builds and builds then the pressure makes the valve harder to open and lobes are the ultimate peice to fail I KNOW IVE SEEN IT HPPEN A DOZEN OR SO TIMES...

fast97gt said:

laser red thank about what your sayin, i get your point about the air compressor, but it seems i cant seem to pound it in your head, think about it the pressure in the a/c has to build up some how, oh wait theres PISTON IN A CYLINDER WITH AN INTAKE AND A exhaust or exit valve just like the I/C ENGINE. so what that tells me and what your telling us is that a stock or mildly modded engine only pushes out 10 to 15 psi, but with a CLOGGED cat THE PRESSURE BUILDS UP, but unlike the air compresser the i/c engine doesnt have shutoff switch when the pressure reachs a predetermined setting like umm 150PSI. now the new advanced i/c engines have a simple warning system THE REAR o2 SENSORS to measure exhaust flow. so if you have a clogged cat the presure builds and builds and builds then the pressure makes the valve harder to open and lobes are the ultimate peice to fail I KNOW IVE SEEN IT HPPEN A DOZEN OR SO TIMES...

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Read this one more time:

"The piston is still moving down when the exhaust valve begins to open. On relatively stock or mild cams, the EVO or exhaust valve opening point takes place around 40°-55° BBDC. At this point the peak cylinder pressure has long subsided. Tests have shown there is around 10-15 PSI left in the cylinder at EVO on a relatively stock motor.

The exhaust valve closes at around 15°-20° ATDC completely overlap, and at which time the intake valve is wide open meaning not only is no pressure in the cylinder but there is negative pressure in the cylinder.

By the time the exhaust pressure wave reaches the end of the header/exhaust manifold, there is less than 3 PSI present at the collector. The motor can only exert as much exhaust backpressure as it is mechanically capable of doing, regardless of an exhaust restriction or not.

Please explain how an exhaust lobe gets hosed with a exhaust valve spring that is rated at 130-140lbs open?"

There is absolutely no such thing as too much exhaust back pressure causing even a single pound more resistance than normal on the exhaust valve spring, not a single pound. Like I said, when the exhaust valve opens BBDC, the peak cylinder pressure is long gone and the piston is moving down away from the exhaust valve, not towards it. The only thing the starts the exit of the exhaust gas is it's own end gas still combusting and expanding. There is absolutely ZERO pressure on the face of the exhaust valve when it opens. Due to the mechanical nature of the valvetrain it is physically impossible to mess up an exhaust lobe from poor catalytic flow.

Lazer I agree with you.. The point is even with 500 psi in the exhaust the valve opens tward the piston when the cylinder only has 15 psi inside. Any cam wear will be from the valve spring itself.

I can understand that if you look at it in one step and thought the valve had 500psi pushing against it while the cam was trying to open it then yeah...not good. But the engine runs in many phases so that it will never try and open the exhaust valve right after tdc when the cylinder is at max pressure.

If you can show me 1 picture of cam wear from excess exhaust pressure then I will sell my car and give you the money.

from my experince the rear o2's do have an impact on fuel trim. i have a supercarged 04 mach 1 and the rear 02 went bad and the idle went to crap at times and it blew gas out the rear pipes when it turned up the fuel on wot. i clear the codes and it runs fine for a bit

i aint argueing no more like a couple two year olds but until you see it i guess you wont believe, cause ive seen it happen and i do believe...

dads got a custom 78 chevy pick up rebuilt the engine, (with brand new block and everything didnt short cut nothing) and left the exhaust the same(ypipe off the manifolds into the cat) with the stock cat and it melted and clogged we just ignored the problem for like two months and guess what? had to pull the motor down to put a new cam and lifters in it cause the #1, #3, and #6 exhaust lobes were ground to a circle. thought it might be the springs so i had an engine builder buddy of mine check it against the old cam specs and they were fine, so we replaced the cat, and thats been six years ago, and by the way ive been a engine builder for 11yrs. and dads been piddling around for 25yrs. so i think we new what were doing

fast97gt said:

i aint argueing no more like a couple two year olds but until you see it i guess you wont believe, cause ive seen it happen and i do believe...

dads got a custom 78 chevy pick up rebuilt the engine, (with brand new block and everything didnt short cut nothing) and left the exhaust the same(ypipe off the manifolds into the cat) with the stock cat and it melted and clogged we just ignored the problem for like two months and guess what? had to pull the motor down to put a new cam and lifters in it cause the #1, #3, and #6 exhaust lobes were ground to a circle. thought it might be the springs so i had an engine builder buddy of mine check it against the old cam specs and they were fine, so we replaced the cat, and thats been six years ago, and by the way ive been a engine builder for 11yrs. and dads been piddling around for 25yrs. so i think we new what were doing

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I'd like to see a picture of a cam lobe "ground" to a circle.

On a pushrod motor, cam lobe damage only comes from 2 things; a bad valve guide or a lifter bore that was improperly prepped and the lifter is hanging in the lifter bore. What did the lifter bores mic at before you dropped in the lifters? Lifter bore tolerances are very critical. Were these hydraulic or sold lifters?

I know this is old (found by searching), but I wanted to add something to it.

There is absolutely NO way back pressure can affect pressure applied to the exhaust cam lobe. It is not physically possible. Why? Here's an explanation:

Say you built up 150 PSI in the exhaust. Where is that pressure applied? To the BACK side of the valve head where the stem is, not the part in the cylinder. In all actuality, it relieves pressure from the cam by applying force to the back of the valve to help open it. If you force enough pressure into the exhaust port, it will slightly open the valve, relieving pressure, thus causing the valve to close again due to the loss in pressure (much like a BOV).

Think about this, too. If you have no back pressure at all, when the exhaust valve is opening and the the piston begins to make it's way back up, the velocity will be higher because there's no apposing force. You have x amount of PSI inside the cylinder and 0 outside the cylinder, needing y amount of force to move the gasses out of the cylinder at z velocity. Now, if you have back pressure that measures 50% less than cylinder pressure, your velocity will decrease and the force needed will be greater. However, the pressure witnessed by the valve is greater when they're NO back pressure, as it's relative to pressure differences. The valve sees 100% of the pressure difference. If your cylinder pressure and exhaust back pressure are equal, there is ZERO difference, thus the valve moves as if you're turning it over by hand (no fire, no real cylinder pressure, no back pressure, just like opening in closing at atmosphere). Think of a one-way check valve. If the pressures are the same on either side, the valve basically flops around until pressure changes on either side, at which point the valve either opens or closes.

Now, a vehicle will have trouble running with a clogged cat because; A) it's harder for the motor to push out the exhaust gasses, and B) residual pressure in the cylinder may cause a slight 'push' into the intake when the intake valve opens. These two combined cause a motor to lose efficiency.

Now move along...lol!

Where did you guys go, I need you.

I have a pair of Jeep Wranglers, 05 and 98. The 98 recently blew up its CAT after a fairly long trip. Replaced it and fixed a small crack on the exhaust manifold. It ran like an unbalanced washing machine. Replaced the obvious 6 sensors plus plugs and wires, still nothing. Took it to the dealer who swapped out the computer, distributor, and a few more sensors, nothing. They didn't like the look of the flywheel so they replaced it, nothing. The pulled the valve cover and saw a broken spring, replaced, and nothing. Pulled the head off saw some ugly stuff, machine shoped it, nothing. I am going to pucik it up tomorrow and planned to continue down the path of the broken spring by pulling the cam, then I read this and don't know who is right. I hope you will restart the discussion/fight for me?

Compression check? What motor (i4, i6, v6, v8, etc)?

I could see higher EGT burning a valve, but if a machine shop rebuilt the head, that would take care of that.

Do a compression test (engine warmed up, no plugs in any cylinder, done at WOT), and post your findings.

Had my CEL on for over 8 months.. I doubt its in limp mode and come on.. a stock vert 96-98 GT cant get any slower really than is .. lol.

My car is faster with my catted h than with my o/r H and o/r prochamber. I dunno but my car like cats better for some reason and maybe that the back pressure the cats make.

I am just a dumbass shade-tree mechanic and a 50 year-old phd-trained scientist. But how the hell do you argue with a been there-done-that trained mechanic. I am pulling the cam.