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Discussion Starter · #1 ·
hey guys i have a friend that keeps telling me straight piping your car burns your valves and causes other mechanical issues. me myself do not believe this. what do you guys think???
 

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Its not good for an NA engine to run with no back-pressure, this is true. But if you keep the stock size exhaust piping it will create enough restriction to not cause any issues while still giving you a good velocity to evacuate the exhaust gasses. If you went with a 3" straight pipe on a stock motor you would actually be taking away from your performance and also losing all back pressure. Instead of a steady flow out the pipe you will create turbulence in the exhaust because the engine cannot emit enough exhaust gas to fill the pipe to create a high enough velocity to evacuate properly.

I may be mistaken, but I believe the higher compression or horsepower the motor has, the less need there is need for back pressure. If your goal is just to make noise, straight pipe it but keep the 2" pipe.
 

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True
Some cars more than others however.
It messes with the EGR system (by lowering back-pressure specifically, I believe). And the EGR system lowers combustion chamber temperatures drastically (to reduce NOx).
 

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Discussion Starter · #4 ·
haha cool thanks. I also have another question. i have an 84 supra that i just put a brand new thermostat in. but yet when i drive it will still over heat. it is topped off with fluids and there is no leaks as far as i can tell?
 

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mk2-1jz just beat me to the back-pressure part, haha.
But while the scavaging plays a role in removing heat from the engine (via the exhaust gasses), I don't believe it would have as big of a negative effect as the EGR.

Yes, it is true the the JDM 6m runs no EGR, but for all we know they could enrich the fuel mixture to carry away combustion temp with atomization that way, you know what I mean?
In the US, the EGR was designed to reduce combustion chamber temps because of the high NOx emissions (created from high pressure & high temp [2500 degrees+]).
So less back-pressure may not recycle as much inert gas through the combustion chamber.
Just my :twocents:

Now on modern tech cars, the EGR system has been replaced with variable valve timing. This allows the exhaust valve to close early; essentially trapping in a small amount of inert gas (exhaust gas)
 

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haha cool thanks. I also have another question. i have an 84 supra that i just put a brand new thermostat in. but yet when i drive it will still over heat. it is topped off with fluids and there is no leaks as far as i can tell?
Have you purged all of the air out of the system?
It may be a trapped air pocket that the coolant temp sensor is reading (much higher temp then water). So you may not even have a problem at all.
 

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Have you purged all of the air out of the system?
It may be a trapped air pocket that the coolant temp sensor is reading (much higher temp then water). So you may not even have a problem at all.

I agree as it is relatively common to need to "burp" the cooling system after draining it (or maybe partially draining in your case). Do you have cabin heat? If not the system probably has air.

The nose end needs to be raised (jack stands, hill, or ramps) and the car run with the radiator cap off, and the cabin heat turned on. Add coolant as necessary if it ever drops below near the top of the radiator fill tube. Also, make sure you have the coolant expansion tank filled to the proper level - I usually pull it out to check or add fluid - just slides upward. This might be a bit messy as air bubbles leave the system.
 

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Discussion Starter · #9 ·
yes i have cabin heat, i have also burped the system. today it started to warm up as i was on my way home after a new thermostat and burped the system. im now thinking i have a leak somewhere just have to find it. ill get back and let you know what happens. thanks alot for everyones input. i have learned alot from you guys on the forums.
 

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I had a heater hose leak when it was at operating temp, but not when it was cool. So be sure to check for leaks under all conditions. Good luck
 

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Back to the original post: I think that's from the days when the vehicles ran carburetors. Changing exhausts (i.e. adding a header) without rejetting the carbs could lead to problems for some set ups. They ran too lean, got great gas mileage, and could see issues with valves.
 

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+1 on Plugged radiator/Air flow issue. Look for physical obstructions in front of radiator..
 
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