The header / Exhast manifolds Debate

[68ford]

one thing i know, header flanges are max3/8 thick solid steel, they dont expand much, maybe .005 ? now exhaust manifolds are thick from where the bolt head touchs to the head, the grow and contract, creating an oprtunity to break bolts, i dont know if this happens alot or ever, but i dont think it would ever do it with headers as long as they are not over tightened.
in the big deisel industry, i see this everyday, never heard of headers breaking bolts.
as far as heat from headers go, i dont know about that, ive heard tons of"my manifolds were glowing red" stories, dont think it gets a whole lot hotter than that.
i think we all agree that headers flow better,thus no left over burnt fumes still in the cylinder for more lowend compresion, this would tell me that heat is escaping faster than manifolds.
if the comprssion ratios werent so low and the port velocities were higher, the cylinders would be filled with fresh mixture and would make more low end torque.id like to see results on a 9.5 to1 but everything else stock 351 with headers and with manifolds, i think the lowend torque would be either the same or better with headers.

 

[68ford]

Here's a question... I'm not sure where I heard this, but can headers bring down cylinder temps any as opposed to manifolds? Reason I ask is that if they do, it might help lessen likelyhood of pinging due to internal cylinder temps.

2 ways to look at it, it could lower temps by making the engine run more eficiently, or it could make it run hotter because its burning more mixture and creating more heat by performing more work.

or possibly manifolds maybe run cooler by leaving some allready burnt,inert(noncombustible)gas in the cylinder which lowers temps,this is the same theory as egr valves, put non burnable gases back into the cylinder to lower the nox gases by lowering the cylinder temps, to bad this means more hydrocarbons which means hello catalytic converter. ;D
i like the doug thorley theory, use one cylinder to scavenge another to get pure charge of mixture into the cylinder. this sounds the best, ive never seen proof that it really works like that though.

 

[asabadin]

Here's a question... I'm not sure where I heard this, but can headers bring down cylinder temps any as opposed to manifolds? Reason I ask is that if they do, it might help lessen likelyhood of pinging due to internal cylinder temps.

anything that decreases exhaust restriction lowers egt(exhaust gas temp) I know this because of my 6.5 turbo diesel!!! a long way from a bronco

 

[feitctaj]

one thing i know, header flanges are max3/8 thick solid steel, they dont expand much, maybe .005 ? now exhaust manifolds are thick from where the bolt head touchs to the head, the grow and contract, creating an oprtunity to break bolts, i dont know if this happens alot or ever, but i dont think it would ever do it with headers as long as they are not over tightened.
in the big deisel industry, i see this everyday, never heard of headers breaking bolts.
as far as heat from headers go, i dont know about that, ive heard tons of"my manifolds were glowing red" stories, dont think it gets a whole lot hotter than that.
i think we all agree that headers flow better,thus no left over burnt fumes still in the cylinder for more lowend compresion, this would tell me that heat is escaping faster than manifolds.
if the comprssion ratios werent so low and the port velocities were higher, the cylinders would be filled with fresh mixture and would make more low end torque.id like to see results on a 9.5 to1 but everything else stock 351 with headers and with manifolds, i think the lowend torque would be either the same or better with headers.

you bring up a great point , why don't hey use headers in the class 7 and 8 trucks?
I mean they spend millions to get more power and better fuel mileage , why do they not run headers, why do they run cast iron?

 

[mustangmarty]

anything that decreases exhaust restriction lowers egt(exhaust gas temp) I know this because of my 6.5 turbo diesel!!! a long way from a bronco

Then keeping the exhaust manifolds will actually help keep the internal cylinder temps "cooler" thus helping to supress pinging?

 

[feitctaj]

anything that decreases exhaust restriction lowers egt(exhaust gas temp) I know this because of my 6.5 turbo diesel!!! a long way from a bronco

Show us DAta to back this up

 

[68ford]

anything that decreases exhaust restriction lowers egt(exhaust gas temp) I know this because of my 6.5 turbo diesel!!! a long way from a bronco

he was refering to cylinder temps, but in your case i doubt the exhaust temps sare lower,they are just getting out faster and not giving things a chance to get as hot. deisels care alot more about the temp of the air going in, because the exhaust temp is a direct result of that, thats why your international,cats and cummins have intake air temp sensors but dont care about exhaust temp. gale banks might care and maybe bully dog, but those guys dont know. thats why the manufacture doesnt put any kind of exhaust sensing device in the exhaust, but they all have inatake air sensor(IAS).

 

[feitctaj]

he was refering to cylinder temps, but in your case i doubt the exhaust temps sare lower,they are just getting out faster and not giving things a chance to get as hot. deisels care alot more about the temp of the air going in, because the exhaust temp is a direct result of that, thats why your international,cats and cummins have intake air temp sensors but dont care about exhaust temp. gale banks might care and maybe bully dog, but those guys dont know. thats why the manufacture doesnt put any kind of exhaust sensing device in the exhaust, but they all have inatake air sensor(IAS).

I was unaware that International made motors for class 7 and 8

 

[68ford]

sorry they do put turbo speed sensor, but this is just take a reading along with the turbo intake air temp, post turbo intake air temp, intake air presure they take that put it with engine speed and coolant temp,fuel presure which should corespond with engine speed too.........the list of stuuf goes on and on. ;D

 

[feitctaj]

Anyway , we are getting away from the topic

 

[asabadin]

sorry they do put turbo speed sensor, but this is just take a reading along with the turbo intake air temp, post turbo intake air temp, intake air presure they take that put it with engine speed and coolant temp,fuel presure which should corespond with engine speed too.........the list of stuuf goes on and on. ;D

Well than why do egts go up going up a hill under load (while towing)@2500 rpms and cruising down the road at 2500 rpms they are much lower. increasing the size of my downpipe and exhaust lowered the egts by 300 degrees all around. once again if you decrease restriction and increase flow you lower exhaust gas temps and increase engine logevity. At least with diesels

 

[68ford]

international doesnt(i dont think they can ) i was refering to the internation powerchoke baby engine. ;D they do make one larger 8.? liter inline six, closer to a real engine but they werent any good compared to cat or cummins in that size range.
class 7 or 8 ? its cheaper to cast an manifold then make i thin tube header and it needs to support the weight of turbo in just about every application. and on deisel exhaust restrictions are not relevent. the new variable geaometry turbo(non wastegate) the actually restrict the exhaust flow to increase the velocity to the turbine wheel making it spin faster to make more boost. no more turbo lag.

 

[68ford]

Well than why do egts go up going up a hill under load (while towing)@2500 rpms and cruising down the road at 2500 rpms they are much lower. increasing the size of my downpipe and exhaust lowered the egts by 300 degrees all around. once again if you decrease restriction and increase flow you lower exhaust gas temps and increase engine logevity. At least with diesels

your post turbo temps may have gone down but i garuntee you cylinder temps are the same, your boost is the same so the fuel to go with it has to be the same. like i said its a civilian deisel sales pitch to make you buy a gauge. your case is the expansion theory, if you let a gas thats presurized expand, the temp will drop(theory of refrigeration), thats all your seeing if all you changed was stuff after the turbo.

 

[68ford]

Well than why do egts go up going up a hill under load (while towing)@2500 rpms and cruising down the road at 2500 rpms they are much lower. increasing the size of my downpipe and exhaust lowered the egts by 300 degrees all around. once again if you decrease restriction and increase flow you lower exhaust gas temps and increase engine logevity. At least with diesels

have to remember on deisel you can be at minimal air and fuel, or max boost and fuel at the same speed or rpm or both, more boost more fuel more cylinder presure(heat), this determinds exhaust temp, nothing you can do to the exhaust side to change it really.

 

[asabadin]

have to remember on deisel you can be at minimal air and fuel, or max boost and fuel at the same speed or rpm or both, more boost more fuel more cylinder presure(heat), this determinds exhaust temp, nothing you can do to the exhaust side to change it really.

increased boost decreases exhaust gas temps. i mean i could post data on this but it is not the lecture at han
if you want go look here and be proven wrong
http://forum.thedieselpage.com/cgi-bin/ultimatebb.cgi?ubb=forum;f=1;DaysPrune=30

 

[asabadin]

your post turbo temps may have gone down but i garuntee you cylinder temps are the same, your boost is the same so the fuel to go with it has to be the same. like i said its a civilian deisel sales pitch to make you buy a gauge. your case is the expansion theory, if you let a gas thats presurized expand, the temp will drop(theory of refrigeration), thats all your seeing if all you changed was stuff after the turbo.

I this similar in the your theory of telling me to allow my coil bind to be a bumpstop instead of using a bumpstop?
If that is the case, i guess the 2 other mechanical engineers and pro rig builders that posted were wrong and you are right.
http://www.classicbroncos.com/forums/showthread.php?t=62331&page=2&pp=15

 

[asabadin]

So back to the topic. are there any particular exhaust maniflods that are better than the other(any old posts or data on different performance with different manifolds)
(bigger ports,better flow design) if so which ones are best. I bought my rig with headers so i cannot swap them out with the old ones.

 

[68ford]

increased boost decreases exhaust gas temps. i mean i could post data on this but it is not the lecture at han
if you want go look here and be proven wrong
http://forum.thedieselpage.com/cgi-bin/ultimatebb.cgi?ubb=forum;f=1;DaysPrune=30

increased boost(more presure=more heat) means more fuel which means more cylinder compression and more fire, period.
your more than welcome to come with me to cummins tomarrow and you can ask any question you want, ill be there everyday this week.
how can you figure more boost is less exhaust temp, more boost is more restriction because the exhaust is going through the turbo 100% not around it through the gate.
your right i have no idea what im talking about and my suspension sucks, dont listen to me. just keep listening to the small truck deisel talk.

 

[68ford]

Well than why do egts go up going up a hill under load (while towing)@2500 rpms and cruising down the road at 2500 rpms they are much lower. increasing the size of my downpipe and exhaust lowered the egts by 300 degrees all around. once again if you decrease restriction and increase flow you lower exhaust gas temps and increase engine logevity. At least with diesels

i think this contradicts your boost makes egt go down, i think you give it fuel and boost when going up a hill right? ;D

 

[asabadin]

don't be a last word freak
"he who strives for the last word thinks slowest"!