does increasing the pipe size change the rpms or anything like that, or adding or removing cats or mufflers. I was reading something but couldnt gather a solid answer on how altering an exhaust will effect the engine, good or bad. I am not looking for anything better I am just looking to avoid poor performance as well as loosing gas mileage.

Some people said losing some of the restriction is bad. I dont get it. someone clue me in so I can make a better decision.

Thanks

 

Yes, any change in flow rate will affect the engine. Increased flow will reduce back pressure making the engine breathe better. Which, in most OEM vehicles, isn't a bad thing at all. However increasing too much or scavanging too much exhaust away will actually reduce the power output due to loss of backpressure which helps the engine develope torque. Pull the exhaust gasses away too quickly and there is not enough backpressure to build torque against. On fuel injected/computer controlled engines you may not actually see changes because the computer will compensate. The drawback is that if the increase in flow rate is too high, the result will reduce fuel mileage because the computer will attempt to compensate for the change by increasing fuel/air mixtures and alter spark and injector timing. Its not a really fine line between "just enough" and "too much" exhaust flow but slapping "school bus" sized exhaust behind a small block V8 will actually ROB the engine of power rather than help it produce more. This is the primary reason many of us recommend a complete system or group of exhaust components that have been "tuned" for the engine/vehicle combination you are working with.

Keep in mind too that an engine is like a mathematical equation, what you do to one side, you should do to the other side to keep things balanced. In other words, if you put a really good exhaust system under it and leave the induction system OEM, you could inadvertantly create the kind of adverse exhaust setup already mentioned. So, when adding better exhaust, remember to improve the intake area as well. High volume air filters, cold air intakes etc. are good places to start.

 

awesome info. I have the 351 5.8 93 bronc. Is the drop in K&N a good enough mod in the front? I am not sure if I want to jump to the cold air just yet.

Also besides environment concerns on a personal level what do I have to worry about when taking things out like a cat or something. I live in michigan and we dont have inspections so I can slip bye on that,

Thanks again

 

93bronc84, I have the KN drop in filter and am very happy with it. As far as the cat, You can get a high flow cat for better performance and still be enviormentally friendly.

 

I personally don't ever endorse the idea of removing or tampering with a catalytic converter. I know many have and do. Thats their prerogative.

The most commonly mentioned aftermarket exhaust setup around here is, I dare say, the Bassani system which utilizes a 3" IN and OUT cat. Its a high peformance, high flow unit and the Y-pipe and "cat back" setup is tuned for the Bronco and F-series trucks. Of course there are other products out there but Bassani seems to have done something that most aftermarket exhaust manufacturers have overlooked when engineering replacement exhaust systems that are superior to the OEM equipment... the Y-pipe. Other than the Ford OEM unit or a custom-built version, this is your only option. And it certainly allows much better breathing than the stock unit with 2.25" arms and a 2.5" tail that widens out to 3" at the cat. This diameter in the Y-pipe tubing helps keep the flow from scavanging too much too soon from the headers.

I run the K&N drop-in filter in the stock airbox with the cross-tubes to the throttle body insulated for cooler intake air temps. The exhaust is Bassani's complete "Street Thunder" package from shortie headers to the 4" exhaust tip. The eventual plan is to increase TB size to BBK's twin 56mm unit and couple that with Edebrock's Performer series intake for EFI truck 302's. I am planning on stopping just short of new heads etc. just to see what I can gain without it. I will most likely want more! Just mentioned these last few items as a reference. Obviously, the options are numerous.