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#1
10-23-2005, 11:36 AM
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back pressure
Dont engines need some sort of back pressure to run properly? Ive heard that if you run header dumps you can burn a valve. Now ive seen people driving around with their exhaust dumping right out of long tubes with no issues. Id like to get a cutout and ive been told that they usually go as close to the headers as possible. So is the burning a valve thing just a myth that ive heard or what?
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92 z28 camaro 5.7 TPI current - slp intake runners and base-BBK 52mm throttle body-MSD 8.5mm wires, blaster coil, and 6AL Box-edelbrock headers-160 degree stat.-hotchkis strut tower brace waiting in the garage - LQ4, milled heads 317 casting (10.5 to 1), hardened pushrods, ported LS6 oil pump, manley dual spings with titanium retainers, MTI X1 cam, hawks longtube headers 
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#2
10-23-2005, 03:36 PM
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Re: back pressure
i never heard of that, but like i said i never "heard of that", and i plan on running dumps on mines and that has never come up
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#4
10-23-2005, 05:53 PM
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Re: back pressure
cool thanks
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92 z28 camaro 5.7 TPI current - slp intake runners and base-BBK 52mm throttle body-MSD 8.5mm wires, blaster coil, and 6AL Box-edelbrock headers-160 degree stat.-hotchkis strut tower brace waiting in the garage - LQ4, milled heads 317 casting (10.5 to 1), hardened pushrods, ported LS6 oil pump, manley dual spings with titanium retainers, MTI X1 cam, hawks longtube headers
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#5
10-23-2005, 06:56 PM
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Re: back pressure
NO car runs better with backpressure
what the goal is is high exhaust velocity, and pipes being too big or too short can have a negative impact on the e.v. people who refer to this property as backpressure dont have much idea what theyre saying
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97 Camaro - 2.077 60', 14.745 @ 92.20 - still down, one year later. 194k miles-160* thermo-V8 shocks/springs (V6 rear springs)-3" Magnaflow !cat (3" dynomax bullet) back-SLP CAI-stock boxed LCAs-poly tranny mount and torque arm bushing-custom HPTuners tuning-4.10s/eaton/TA girdle-3.5" alum DS-spohn LCA brackets-prostar skinnies 179.75 RWHP, 204.52 RWTQ ON ITS WAY: MORE R.I.P. Andy 87 Benz 190e - DD 01 EX250 - still gotta get my license for this thing
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#6
10-25-2005, 12:45 PM
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Re: back pressure
It's not the backpressure that you need, but the exhaust scavenging effect. Too big a pipe and you lose this causing high exhaust gas temperatures and exhaust that does'nt move out as fast as it should. Bigger is not always better. No engine needs backpressure but with none you actaully lose power due to the lack of exhaust pulsations that help pull the exhaust away from the engine. Hope this helps.
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#7
10-25-2005, 02:17 PM
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I think this is a fitting analogy...
Take a bottle of soda, open it up, and hold it vertically upsidedown, drinking it and guzzling as fast as you can, don't break the seal, and constantly chug it down. Now do the same thing, but just let it pour out onto the floor. It will go CLUG CLUG CLUG and take forever to get it all out. You may not be able to physically drink it faster, but you get the idea i guess... If backpressure were the main priority, then we would be running around without any headers on at all, open valves. Now that WILL burn the valves. Headers collect all of the exhaust pulses and smoothly combine them into one, creating a smooth flow leaving behind them a sort of vacuum which in turn helps to suck the exhaust from the next stroke out of the cylinder head. This is the idea of scavenging as mentioned by scoobytuff.
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-Tony- Sold my Z28 looong ago. Now sporting an '03 TJ. 
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