which header...1 5/8 or 1 3/4 with AFR 165's...

[Highbredcloud]

Well wich one...I have seen on AFR website that they actually test with the 1 3/4...Also numurous people on FTI's website run the 1 3/4 as well...Currently I have a set of 1 5/8 Bassani headers...I spoke with Ed C and he tells me that I am fine with the 1 5/8...,however, my concern is with the area right at the flinge...For those of you that have seen AFR heads...know that they have pretty big exhaust ports...Well the stock exhaust ports on the AFR 165's is 35mm by 33mm...and the headers right by the flinge are 37mm by 27mm...later on the header opens up to a 39mm...NOW...I have to purchase another set of headers for my other Mustang...and I am curious if I should get the 1 3/4 for the AFR's or keep the 1 5/8? The headers are not installed yet...still waiting for more parts...I really don't want to port the flinge to open it up...since I don't really want to mess anything up...so what are my options here...Would 1 3/4 be too much for a 302? I have a feeling that it would...but the flinge really bothers me with the 1 5/8 actually being 6mm smaller right at the flinge...anyone have any inputs...? maybe I am just overthinking this issuse...

-Greg

 

[90mustangGT]

Well, you don't "need" larger headers. You may gain a horse or two top end, but you'll probally loose a little torque. It's not needed is what I am trying to say. There are other ways to make the power for the money. Are your bassani's longtubes? If not, then I would but the 1 3/4ths LT's on your wish list.

 

[bluevenom867]

The exhaust port will only flow as much as the header will allow.That small "squees" may act like a venturi and help scavenge the exhaust gasses and help them to keep a high velocity.You'll gain some peak power and torque by swithing, but infact the 1 5/8 headers may be more effiecent than the 1 3/4 headers on a 302.Whats the intake to exhaust coeffiecent?If it above 70% than keep the 1 5/8 if it's lower switch to the 1 3/4.

 

[BlooDReigN]

Maybe just take a die grinder to the header and port it a bit. Might not be able to get 6mm out of it, but you can probably get close.

 

[Highbredcloud]

The exhaust port will only flow as much as the header will allow.That small "squees" may act like a venturi and help scavenge the exhaust gasses and help them to keep a high velocity.You'll gain some peak power and torque by swithing, but infact the 1 5/8 headers may be more effiecent than the 1 3/4 headers on a 302.Whats the intake to exhaust coeffiecent?If it above 70% than keep the 1 5/8 if it's lower switch to the 1 3/4.

I was also thinking that the flinge might be smaller to help with the scavenging effect...It only goes about an inch before it opens up to a 39mm...I have no idea with the intake and exhaust coefficient is...how can I find this out? I was also thinking that the 1 3/4 would cause a loss in the low end...but help out the top end...the car will stay a 302...

 

[Highbredcloud]

Well, you don't "need" larger headers. You may gain a horse or two top end, but you'll probally loose a little torque. It's not needed is what I am trying to say. There are other ways to make the power for the money. Are your bassani's longtubes? If not, then I would but the 1 3/4ths LT's on your wish list.

Yes they are long tubes...I don't want to loose TQ down low...and at the same time I don't need the extra HP at 6000RPM...

 

[Highbredcloud]

Maybe just take a die grinder to the header and port it a bit. Might not be able to get 6mm out of it, but you can probably get close.

that is something i don't want to do...since I don't want ot go to far and grind right through the welds where the actual tube meats the flinge...

 

[bluevenom867]

Say the intake and exhaust both flow 250cfm, then its at 100% effiecency.
Now take the AFR 165cc heads, 245cfm @ .500 lift intake and 190cfm @ .500 exhaust.
190 divided by 245 = .775510204, round up you get 78% effeincency between the intake and exhaust flow.

 

[Highbredcloud]

Say the intake and exhaust both flow 250cfm, then its at 100% effiecency.
Now take the AFR 165cc heads, 245cfm @ .500 lift intake and 190cfm @ .500 exhaust.
190 divided by 245 = .775510204, round up you get 78% effeincency between the intake and exhaust flow.

hmm...interesting...So technically I am fine with the 1 5/8...? How would this change the way of calculating if lets say the engine was stroked to a 331 or a 347? with the same heads etc...? it would still flow the same but with a stroker motor is where you need to step up to a bigger header...at least that's what I always considered was the main thing...not sure if the effeciency plays an equal role in all scenarios...

 

[bluevenom867]

Well it's like this.
If a motor were to "suck" only 245cfm @ .500 lift (there would also be fuel to, so the whole charge isn't air) you would still have 245cfm of gas to expel.You heads only flow 190cfm that mean you still got 22% of useless gas in the cylinders.This is why ford cams have higher lifts and duration for the exhaust side.Scavaging is much like a spihone, once the flow starts it helps it self move.
Going bigger in displacment will "suck" more air in and "push" out more exhaust, but you will still have that 22% useless gas still in the cylinder.Exept this time you have a larger amount because 22% of 302 it smaller than 22% of 331 or 347.
See what im getting at?

 

[bluevenom867]

Ok, some math.
Each cylinder in a 5.0 is 37.6992 cubic inchs.A head that flows 245cfm (cfm= cubic feet per minute) will flow 49cis (cubic inch per second).So in less than a second the head will completely fill the clinder.The exhaust would flow 38cis which mean that it would take the exhaust .22 seconds longer than the intake to flow the same amount of air.This motor would operate at more than 100% effeiceny.A 347 has a volume of 43.36904972 per clinder.The intake would still flow enough to fill the clinder, but the exhaust would now need to stay open longer to get the larger volume of air out.So you see biger heads just let you use smaller cams, to make the same power.