yeah

 

about $300 for headers- 100 for hi flow cat- gave me noticable power increase- not much more i can do for my 90 300ci - EECIV computer- nightmare- no maf - cant mess with it.

 

You do need some back pressure, it will help pull the exhaust gas through the system.

 

this is very wrong...google back pressure...

i'd like to know just where he got headers for the 300-6?


today I pulled off my exhaust and my cat and gave it a good drive open exhaust....ran like adding another cylinder or 2....ran GREAT just loud on acceleration...

 

Let me put it this way, if you throw a NOS system on the truck it will make it feel like its got tons more power right? but is it good on the engine? Just because it feels good doesn't mean that its right on the engine side. On some apps it helps the engine to run a muffler, which makes some back pressure, not a whole lot but some.

 

Nitrous and exhaust are two totally different things...

1st the NOS make it feel better because mainly it is a power adder...limited by the exhaust..you stuff it in but can it get out..?

2nd the engine wasnt really designed to handle it and thats where problems arise...you can get away with small amounts until you kill something...

think of back pressure like this...take a small coffee straw and put it in a glass of water...and blow...notice the force needed to blow through the straw...

now take a regular soda straw like the ones from McD's and put it in the water and blow...notice the force needed...it will be much less....

now...if you had to breath only exhaling with the coffee straw and only using your nose as the Intake under light load you may be okay but once you actually move you can get air in but not out efficiently...at a certain point in your cycle you'll no longer be able to take air in because there is no room as the spent air hasnt fully left yet...

now move to the bigger straw...much better removal of the spent breathed air...

this my friend is back pressure and its direct affect...

in mechanics it follows under one of those theory laws...ever action has an equal and opposite reaction...IE: if you restrict the exhaust it will restrict the intake...meaning if it cant get out it cant get in....which limits power...

get all teh exhaust out and you can get a full air charge in and you make the full potential of power...

if you pull the exhaust off and it runs worse that means it is NOT jetted for full AFR (air fuel ratio) it IS jetted for a known back pressure issue...mostly noise cancellation...in EFI it will make up for it'sown here... a carb may not...

 

Your example makes sense but you also have to remember that an engine "pulses" for lack of a better word. IE with your example with a straw, if you blew a constant and steady stream of air, yes it will get it all out with both straws. But take the same two straws and blow it in very small amounts, alternating back and forth. With the air working in pulses, one beathe isn't enough to push it all out, and before the next breathe, backpressure is needed to KEEP that exhaust air in the pipe before the next pulse.....does that make sense? It IS early in the morning and I'm only working on my first coffee cup. :-)

 

From what I hear, you really only need one bend in a pipe to have enough backpressure. It doesn't require very much. My 300 exhaust is cut before the cat and collector and I have a glasspack on each pipe, so its very short and has only a little restriction but it runs pretty well.

 

Yes you are correct BigGrey. Only a small amount is required, MUCH less then factory. I run o/r H to an axelback on my Stang and also a single in duel outlet Flowmaster on the F-150 and whereas I didn't see much difference on the F-150, there was noticable gains on the Stang.

But at least from my knowledge and research, SOME backpressure is required.

 

Yea, I noticed a pretty big difference in mine because my original cat was pretty backed up. But some cars require even more back pressure, what I've noticed is 4 cylinders will need more back pressure than a v6 or v8. I had a 2.3 liter mustang and I was replacing the exhaust and drove it with nothing but the exhaust manifold and a 2 foot section of pipe with no cat or muffler and it was like riding a turtle.