Back Pressure

[427heaven]

My mechanic tells me the Cleveland was designed by Ford to use

back pressure from the exhaust. Installing headers would not

really be a good idea.

mike

Think I would find a new Mechanic:s

Ok on a serious note, an engine is basically an air pump the more in and the faster air is let out with a little mathematics for proper flow numbers the better your engine will perform, agreed a new mechanic might be in the cards for you.:-/
Ditto!

 

[mach1mama]

I have never heard that mentioned. I installed headers and have had no problems. They can be a bit of a b!@##$ to install, but worth it in the long run.

 

[dexleo2]

I have headers on my 351C and they are a big pain in the A$% to put on, but they have been on there for 20000 miles and no problem!!!!!!!

 

[goodnigh]

After reading this thread, that I started, there is no advantage gained from installing headers on a Cleveland.

mike

 

[hyena429]

After reading this thread, that I started, there is no advantage gained from installing headers on a Cleveland.

mike

There is thou..You gain horse power and better gas milage...But its all up too you what you want...Not everyone wants to mess with them.

 

[TommyK]

Some tech material related to this subject.

http://victorylibrary.com/mopar/header-tech-c.htm

 

[guys72Mach1]

After reading this thread, that I started, there is no advantage gained from installing headers on a Cleveland.

mike

More horsepower, better sound.. no advantage?????? :huh:

You originall asked about backpressure. To set the record straight, ALL combustion engine require backpressure, ALL of them, not just Ford's. If there were no backpressure then the exhaust would just turbulantly exit, which would cause a decrease in horsepower at some point. This is why if you go open headers, you gain a little top end, but loose a little low end perfomance.

Through exhaust pipes, too much back pressure it bad and not enough also has a negative effect, just the right amount is necessary. Don't believe me?? Ask Carroll Shelby!

 

[TommyK]

After reading this thread, that I started, there is no advantage gained from installing headers on a Cleveland.

mike

More horsepower, better sound.. no advantage?????? :huh:

You originall asked about backpressure. To set the record straight, ALL combustion engine require backpressure, ALL of them, not just Ford's. If there were no backpressure then the exhaust would just turbulantly exit, which would cause a decrease in horsepower at some point. This is why if you go open headers, you gain a little top end, but loose a little low end perfomance.

Through exhaust pipes, too much back pressure it bad and not enough also has a negative effect, just the right amount is necessary. Don't believe me?? Ask Carroll Shelby!

Not to be contradictory but I respectfully disagree. The loss in power experienced in some situations by some people when trying open headers is not due to a loss of back pressure but rather the loss of exhaust scavenging that a properly designed exhaust system provides. Header tube diameter and length are important in optimizing exhaust performance but from what I have read and from my own limited experience, Collector and exhaust pipe diameter and length as well as muffler selection play an even greater role in optimizing the scavenging effect which promotes cylinder filling and makes power. Everything I have read says back pressure is bad.

 

[Tnfastbk]

After reading this thread, that I started, there is no advantage gained from installing headers on a Cleveland.

mike

More horsepower, better sound.. no advantage?????? :huh:

You originall asked about backpressure. To set the record straight, ALL combustion engine require backpressure, ALL of them, not just Ford's. If there were no backpressure then the exhaust would just turbulantly exit, which would cause a decrease in horsepower at some point. This is why if you go open headers, you gain a little top end, but loose a little low end perfomance.

Through exhaust pipes, too much back pressure it bad and not enough also has a negative effect, just the right amount is necessary. Don't believe me?? Ask Carroll Shelby!

Not to be contradictory but I respectfully disagree. The loss in power experienced in some situations by some people when trying open headers is not due to a loss of back pressure but rather the loss of exhaust scavenging that a properly designed exhaust system provides. Header tube diameter and length are important in optimizing exhaust performance but from what I have read and from my own limited experience, Collector, and exhaust diameter and length as well as muffler selection play an even greater role in optimizing the scavenging effect which promotes cylinder filling and makes power. Everything I have read says back pressure is bad.

Is that not what we have been saying:huh:

 

[goodnigh]

Everything I have read says back pressure is bad.

Is that not what we have been saying:huh:

Then why did Ford design back pressure into the Cleveland?

The Cleveland was a well thought out engine (don't laugh).

I find this thread very fun reading. Glad I brought up the subject.

mike

 

[73vertproject]

Everything I have read says back pressure is bad.

Is that not what we have been saying:huh:

Then why did Ford design back pressure into the Cleveland?

The Cleveland was a well thought out engine (don't laugh).

I find this thread very fun reading. Glad I brought up the subject.

mike

+1 Great thread, Mike!

 

[TommyK]

More horsepower, better sound.. no advantage?????? :huh:

You originall asked about backpressure. To set the record straight, ALL combustion engine require backpressure, ALL of them, not just Ford's. If there were no backpressure then the exhaust would just turbulantly exit, which would cause a decrease in horsepower at some point. This is why if you go open headers, you gain a little top end, but loose a little low end perfomance.

Through exhaust pipes, too much back pressure it bad and not enough also has a negative effect, just the right amount is necessary. Don't believe me?? Ask Carroll Shelby!

Not to be contradictory but I respectfully disagree. The loss in power experienced in some situations by some people when trying open headers is not due to a loss of back pressure but rather the loss of exhaust scavenging that a properly designed exhaust system provides. Header tube diameter and length are important in optimizing exhaust performance but from what I have read and from my own limited experience, Collector, and exhaust diameter and length as well as muffler selection play an even greater role in optimizing the scavenging effect which promotes cylinder filling and makes power. Everything I have read says back pressure is bad.

Is that not what we have been saying:huh:

Not everybody

I was disagreeing with the statement "All combustion engines require backpressure..."

The points I was trying to make were that back pressure does not equal scavenging and all combustion engines require an exhaust system designed for the application.

The fact that the largest tube size does not result in the most flow on any given engine is not a function of back pressure. It is a function of the velocity of the exhaust gas through the exhaust system which when properly sized promotes the negative pressure waves which scavenge the combustion chamber during valve overlap periods.

 

[marks73]

As with all things in a cobustion engine, changing 1 thing affects another. Look at the simple aluminum intake swap and what it does to vacuum/timing/carburation ect. If you could afford it, Changing from cast manifolds to headers and even header diameter while monitoring on a dyno would open your eyes a bit. It's all a part of tuning an engine to get the maximum performance or economy. (depending on what your after)

 

[goodnigh]

As with all things in a cobustion engine, changing 1 thing affects another.

Well there ya go. That is the most succinct answer in this entire

thread. If the Cleveland's designers thought it was a good idea

to put headers on the beast, they would have. That is my real

concern. If I change the basic design of the engine by attaching

something it did not come with.............

mike

 

[Tnfastbk]

As with all things in a cobustion engine, changing 1 thing affects another.

Well there ya go. That is the most succinct answer in this entire

thread. If the Cleveland's designers thought it was a good idea

to put headers on the beast, they would have. That is my real

concern. If I change the basic design of the engine by attaching

something it did not come with.............

mike

WOW is about all I can say at this point. Please refer back to its your car do with it as you please.

 

[hyena429]

As with all things in a cobustion engine, changing 1 thing affects another.

Well there ya go. That is the most succinct answer in this entire

thread. If the Cleveland's designers thought it was a good idea

to put headers on the beast, they would have. That is my real

concern. If I change the basic design of the engine by attaching

something it did not come with.............

mike

WOW is about all I can say at this point. Please refer back to its your car do with it as you please.

The people who designed the cleveland... Designed it for full race.. With only headers...And no mufflers.. It has the biggest equast ports ever in a ford... its all up too you..and what you wanna do..You dont have to have headers....But its a fact..You get more horse power..Torqe..and better gas milage with headers than with out.

SS baselined at 372 RWHP and 372 RWTQ. ... TSP 1 7/8" long tube headers, off-road connection pipes, and cat-back exhaust, the car gained 26 RWHP and 35 RWTQ to net 398 RWHP and 407 RWTQ!...notice the gain over all? That will happen with any motor.. No matter the size...The dyno doesnt lie.
At this point im curious...Are you just tring to defend your mechanic?..Not everyone likes or wants headers...But to say no benifit and thats why ford didnt put headers on our stock cars....is NOT true....."ill put money on it"....Our stock cars have to meet emissions at the time to be rolled out on the street...plus be quite.."mufflers and egr crap"..Even if ford wanted too,they couldnt put headers on the street legaly...wouldnt meet emissions....The cleveland was designed for race first and foremost...street second....and in pure racing they all run headers.....Cleveland was designed during fords total preformace era for racing....Alot have shown you proof of the benfit of headers.....But im not sure you want to see proof ...Which is fine ..Its your car..No one will be upset either way if you pick headers or not..lol....You should of made the thread called..." I dont like headers and this is why " Cause plenty of other reasons to not like them...how they fit or leak..Some have issues.Some dont..Apples oranges...But i will stand up for what i know...And headers will make a diffrent in performance ..Horse power..and more tq.

 

[goodnigh]

At this point im curious...Are you just tring to defend your mechanic?..Not everyone likes or wants headers...But to say no benifit and thats why ford didnt put headers on our stock cars....is NOT true....."ill put money on it"....Our stock cars have to meet emissions at the time to be rolled out on the street...plus be quite.."mufflers and egr crap"..Even if ford wanted too,they couldnt put headers on the street legaly...wouldnt meet emissions....The cleveland was designed for race first and foremost...street second....and in pure racing they all run headers.....Cleveland was designed during fords total preformace era for racing....Alot have shown you proof of the benfit of headers.....But im not sure you want to see proof ...Which is fine ..Its your car..No one will be upset either way if you pick headers or not..lol....You should of made the thread called..." I dont like headers and this is why " Cause plenty of other reasons to not like them...how they fit or leak..Some have issues.Some dont..Apples oranges...But i will stand up for what i know...And headers will make a diffrent in performance ..Horse power..and more tq.

No, I am not defending my mechanic. My mechanic said the

Cleveland was designed to use back pressure. I then surmised it

would not be a good idea to put headers on it. My mechanic would

love to put headers on the car but I don't think it is a good idea. You

may gain 40/50 horsepower but what will the effects be in the long

run on the engine?

mike

 

[hyena429]

No, I am not defending my mechanic. My mechanic said the

Cleveland was designed to use back pressure. I then surmised it

would not be a good idea to put headers on it. My mechanic would

love to put headers on the car but I don't think it is a good idea. You

may gain 40/50 horsepower but what will the effects be in the long

run on the engine?

mike

Ok..Good anser...And ill try my best to anser it...Back prsssure myth started when people tried too upgrade their equast {specialy in motor cycles} And end up destorying a valve...not cause of the need of back pressure..Its because of leaning out the motor and not properly setting the motor up for the more fuel it will need for the bigger equast {adding bigger carb or changing jets}..If you do this too a stock motor and give it waaaaay too much flow than the carb can handle..It will lean the carb out cause the motor now flows more efficent than the carberator does...And leaning out your motor will ruin your valves.

Some say that "an engine needs backpressure to work correctly." Is this true?

No. It would be more correct to say, "a perfectly stock engine that cannot adjust its fuel delivery needs backpressure to work correctly." This idea is a myth. As with all myths, however, there is a hint of fact with this one. Particularly, some people equate backpressure with torque, and others fear that too little backpressure will lead to valve burning.

The first reason why people say "backpressure is good" is because they believe that increased backpressure by itself will increase torque, particularly with a stock exhaust manifold. Granted, some stock manifolds act somewhat like performance headers at low RPM, but these manifolds will exhibit poor performance at higher RPM. This, however does not automatically lead to the conclusion that backpressure produces more torque. The increase in torque is not due to backpressure, but to the effects of changes in fuel/air mixture, which will be described in more detail below.

The other reason why people say "backpressure is good" is because they hear that cars (or motorcycles) that have had performance exhaust work done to them would then go on to burn exhaust valves. Now, it is true that such valve burning has occurred as a result of the exhaust mods, but it isn't due merely to a lack of backpressure.

The internal combustion engine is a complex, dynamic collection of different systems working together to convert the stored power in gasoline into mechanical energy to push a car down the road. Anytime one of these systems are modified, that mod will also indirectly affect the other systems, as well.

Now, valve burning occurs as a result of a very lean-burning engine. In order to achieve a theoretical optimal combustion, an engine needs 14.7 parts of oxygen by mass to 1 part of gasoline (again, by mass). This is referred to as a stochiometric (chemically correct) mixture, and is commonly referred to as a 14.7:1 mix. If an engine burns with less oxygen present (13:1, 12:1, etc...), it is said to run rich. Conversely, if the engine runs with more oxygen present (16:1, 17:1, etc...), it is said to run lean. Today's engines are designed to run at 14.7:1 for normally cruising, with rich mixtures on acceleration or warm-up, and lean mixtures while decelerating.

Getting back to the discussion, the reason that exhaust valves burn is because the engine is burning lean. Normal engines will tolerate lean burning for a little bit, but not for sustained periods of time. The reason why the engine is burning lean to begin with is that the reduction in backpressure is causing more air to be drawn into the combustion chamber than before. Earlier cars (and motorcycles) with carburetion often could not adjust because of the way that backpressure caused air to flow backwards through the carburetor after the air already got loaded down with fuel, and caused the air to receive a second load of fuel. While a bad design, it was nonetheless used in a lot of vehicles. Once these vehicles received performance mods that reduced backpressure, they no longer had that double-loading effect, and then tended to burn valves because of the resulting over-lean condition. This, incidentally, also provides a basis for the "torque increase" seen if backpressure is maintained. As the fuel/air mixture becomes leaner, the resultant combustion will produce progressively less and less of the force needed to produce torque.

 

[goodnigh]

Did not say anything about burning the valves but that was were I was headed. Good answer!

My mechanic did say if I put headers on the car I will need a bigger carburetor.

I want the engine to last for a while as it has maybe 500 miles on it now.

mike

 

[hyena429]

Did not say anything about burning the valves but that was were I was headed. Good answer!

My mechanic did say if I put headers on the car I will need a bigger carburetor.

I want the engine to last for a while as it has maybe 500 miles on it now.

mike

I read many articals on the 351 cleveland...And over and over i read where the stock cast irons are super restrictive on the 351 cleveland's......big gains with headers on them....get that motor breathing...And remmeber...even with headers and a slightly bigger carb...." Counts on your cam lift and duration "....But should still be a bit less horse power than a 351 boss with less compression....So should last quite a long long time with the right treatment

And with all the info i see now days...And headers just in the last 10 years have really stepped up...Better copper gaskets so they dont leak...they fit better and tighter...I use to hate them...Cause i had them on my old chev truck and they leaked..But they was old school..lol...New ones now are better and well worth it too me..But not too everyone..I still got my stock originals in a box...But i can see at one time some one fixed them too...Got a weld on one..lol...but must of been a good fix..i was driving on them for 15 years....All of them are doomed too fail...So if you got matching cast iron originals..Mite be good idea too stick them in a box too..lol

But originals are just fine if you wanna use them..I got my motor torn down right now....Im going 5.25 lift...holley 750...hooker headers...and rest pretty much stock...Should be pushing 425hp..And im still way under what the motor was intended too run...Beauty of the cleveland...Monster gains with little effort..No need for big heads..You got them already...Thats where most people have to spend money on their motor...lol...Not with 4v cleveland guys...But its all up too you...I think your motor built proper will last just as long with headers and the right matching carb...As a pretty much stock 351c.