Bang sorted out, now a question on blow...

Varilux

Well-known member
The ignition gremlins seem to have been sorted- for now- so I thought I'd move on to the exhaust. This time, however, I wanted to get advice here before I order anything.

Currently, I have a '68 exhaust manifold with a single 2" exhaust (the only part that is 1.75" is at the manifold outlet).

My goal is to install a dual exhaust that will utilize the GT trumpets / valence (have the valence painted and ready to go). After researching Classic Inlines, reading through the paperback on hopping up Ford 6cyls (think its called "Falcon 6 Performance" or something), and conferring with the shop that will be installing the exhaust, this is the plan (open to critique).

Header = Classic Inlines dual out header in stainless steel (the kit- with the black oxide studs and gasket)
Exhaust = custom fabbed 1.75" dual pipes (with an "x pipe") (shop wants to use 2"- but I understand the 1.75" will not be restrictive and may sound better)
Mufflers = Magnaflows (recommended by the shop)

The shop recommended getting the headers- but letting them fab the exhaust from the headers back, because "it takes more time to adjust a kit than it does to fab up a custom system." I've had a number of people locally recommend the shop's work. The stickiest part of the job (IMO) is going to be alteration of the A/C bracket. I have the compressor on top with the alternator on the bottom, and the compressor will need to move out 2-3".

Going with the Scott Drake trim rings and tips through the valence.

My 200 is +0.040 over with a mild cam, with a rebuilt Autolite 1100 carb, and DUI ignition (that still needs to be recurved). Its mated to a 5 speed manual with a 3.20 in the differential.

Any suggestions before I place the order for the header would be greatly appreciated. I'm going to put a couple hundred of miles on the car the next week or so (just to make sure I'm happy with the way the "bang" is working), then I'll look forward to getting her breathing a bit better.
 
I would run a min of 2 inch Diameter , probably 2 1/4 , you may build a bigger motor someday , forget the " it needs smaller pipes" because after the Header , anything is a restriction to flow , 1.75 would not only be more restrictive , BUT also look lame , the other parts should only help.You will probably need to enrich the Mixture a tad , but the Dist should be gone through first
 
8) go with the 2" pipes, the 1.75" pipes will not flow as well.

second, i suggest going with two "Y" adapters one to go to a single exhaust and use a single muffler, the magnaflow is a good one, and the second "Y" pipe to split back out to duals. it makes for better packaging of the exhaust. classic inlines has the "Y" pipes.
 
Just to make sure I understand, after the dual out header use a "Y" to create a single pipe to a single muffler, then out the single muffler go to a "Y" to create dual lines over the axle and out the back?

Just curious, but if I was going with that configuration, wouldn't it be easier to have a single out header with one line back to the muffler- then a "Y" to create dual lines over the axle?
 
Varilux":1rv3k09g said:
Just to make sure I understand, after the dual out header use a "Y" to create a single pipe to a single muffler, then out the single muffler go to a "Y" to create dual lines over the axle and out the back?

yep, that would be the set up.

Just curious, but if I was going with that configuration, wouldn't it be easier to have a single out header with one line back to the muffler- then a "Y" to create dual lines over the axle?

that depends on the cost of the single outlet header versus the dual outlet header, and which one fits better. it also depends on which one mike has in stock.
 
rbohm":1k1nl8qr said:
8) go with the 2" pipes, the 1.75" pipes will not flow as well.

second, i suggest going with two "Y" adapters one to go to a single exhaust and use a single muffler, the magnaflow is a good one, and the second "Y" pipe to split back out to duals. it makes for better packaging of the exhaust. classic inlines has the "Y" pipes.

With all due respect, how is it that true dual 1.75" pipes would not flow better than a 2" system routed through a single 2" pipe? That's a heck of a bottleneck- why not just run single 2 1/4" if you're going to do that anyway? Packaging is entirely doable for true duals, not much different than the V8 cars...
 
datac":2omuhis3 said:
rbohm":2omuhis3 said:
8) go with the 2" pipes, the 1.75" pipes will not flow as well.

second, i suggest going with two "Y" adapters one to go to a single exhaust and use a single muffler, the magnaflow is a good one, and the second "Y" pipe to split back out to duals. it makes for better packaging of the exhaust. classic inlines has the "Y" pipes.

With all due respect, how is it that true dual 1.75" pipes would not flow better than a 2" system routed through a single 2" pipe? That's a heck of a bottleneck- why not just run single 2 1/4" if you're going to do that anyway? Packaging is entirely doable for true duals, not much different than the V8 cars...

he is keeping a fairly stock engine, so the extra flow from the second pipe isnt needed, besides a straight 2" pipe flows quite well. second going to a single exhaust will improve cylinder scavenging and it will also smooth out the exhaust pulses. third the exhaust note wont be as raspy as true duals on a six.
 
I put a 6 into 1 header on mine and if I had a chance I'd do the dual outs. The 6 pipes from the header dump into this larger chamber and that necks down to a single 2-1/4" outlet. The dual outs look like they would flow a ton better; there is a large pressure drop when gasses expand that much in a 6 intpo 1 configuration. So stick with the dual out.

The only other thing I can pass along is that when I put a "turbo" muffler on, the exhaust had a real bad drone at highway speeds. It sounded good at idle and around town but get it out on the highway and I was deaf for a day. So whatever muffler you get be aware that a resonator might be needed to keep the noise acceptable at all speeds.
 
I believe True Duals will outperform a single system , the ONLY reason to run a single system is for packaging , I disagree with the scavenging comment , 90 % of that happens in the primary's and the collector , after the exhaust exits the collector its ability / energy is much reduced due to the heat loss , stuffing 6 cylinders back into one pipe is a waste of good headers IMHO
 
A few questions (sorry for being such a leech on the knowledge- I try to make up for it by passing things along when I finally get enough info to do the install)...

What is "packaging?"

If I really do not need back pressure (and it seems there is some disagreement on this- e.g., the tech article on the host of this forum suggests it is necessary to preserve low end torque), it seems logical that dual 2" pipes would flow best?

What about the 3-4 port divider? Again, there seem to be plenty of contradictory opinions. Seems like its just a potential future rattle waiting to happen. My biggest concern is I've read that- without the divider- its possible to burn through a header between cyls 3 & 4?

I noticed the suggestion that I might need to run a bit richer with the headers (guessing that's because the volume of air going through the engine will be increasing?). Since I might be running just a bit lean right now (see the end of this post), is there a particular size jet I should order (I see they come from .040 to .078)?

The exhaust will end up going through stock-style '65 GT trumpets mounted through the valence. I believe the pipes are 1.75" at the tips- so that's going to be the greatest point of restriction- right? IIRC, the marking on my current jet is "F69," but I've checked the jet size with an optical device we use to measure rigid contact lenses, and it definitely does not have a .069 opening...

Articles suggest an X-pipe mellows out the sound of a dual exhaust- so should an X-pipe be used or not?

Back to "bang" news, I installed the NGK plugs today and- during a 40 mile drive I had the stumble just one time (but I was able to make it last for a few seconds). I was going up a long slope giving it moderate gas going along at 80mph or so. It felt as if the engine was starved for gas, which would make it a "gulp" problem (sorry, when I was a kid, my grandfather said all you need to know about an engine is "gulp, bang, and blow").

Finally, I've seen references to a stock manifold from the 80s that offers better flow? If I was going to go with the single pipe with a "Y" to dual tailpipes, I might as well try to find a stock manifold if there is one out there that improves flow (plus, I might not have to modify my A/C bracket then).

Thanks as always- this time I'll be ordering after I know for sure what I should be getting!
 
Packaging = Limited space , or only enough room for one, etc , I disagree with many of the " tech " articles on this forum , My engine spoke for its self , and it had a Port divider 8)
 
Sorry, have to chime in here. FSD is part oldschool, part no-nonsense enginuity, part lifelong learning,
modern count/discount thinking. So are others. Take heed.

There is some history missing on early developers. I can't quote but Jack Clifford did a lot of dyno time
developing headers for 6s and part of that was port divider for 144--250
















f
Sorry, have to chime in here. FSD is part old school, part enginuity, part life long learning, part
modern count/discount thinking. So are others. Consider what they say.

There is some history not mentioned on this site ( probably not intentional) I can't quote but the early
developers did work out some things. Jack Clifford spent dyno time developing headers for 6s, and port
divider at 3&4 was part of that.

Most manufactures -Ford, chev , others seemed to want to pair cyls. on intake and exhaust; even on v8.
I think it was for thermal efficiency, broad power output, cost, you name it. K. Sissel or some other great minds said: " Two or more valves working on one port will flow more, but you can't
tune it!" We've come a long way but ignored the obvious. Hence, slant6 and 300 Ford torque??

As far as pipeing goes, there is drag over inside of tubeing.. Just use 2" stuff, save bigger plumbing for
larger engines, greater horsepower.

Keep it inline , have fun, enjoy the scope of it.

Gary
 
You do not need (or want backpressure). What I believe most would agree upon is that you want a system that (1) has no backpressure, (2) retains high exhaust gas velocity, and (3) meets your noise level requirements.
 
I was taught in Fluid Flow that pressure drop is proportional to the square of the velocity e.g. double the velocity, the pressure drop increases 4 times. So wouldn't keeping high velocity in the exhaust make for a greater pressure drop? And seeing how all exhaust systems discharge into atmospheric pressure wouldn't a high velocity system require greater pressure all the way back to the combustion chamber? and that greater pressure is pushing on the piston when the exhaust valve is open? am I overthinking this?
 
mugsy":2oq5q9z3 said:
I was taught in Fluid Flow that pressure drop is proportional to the square of the velocity e.g. double the velocity, the pressure drop increases 4 times. So wouldn't keeping high velocity in the exhaust make for a greater pressure drop? And seeing how all exhaust systems discharge into atmospheric pressure wouldn't a high velocity system require greater pressure all the way back to the combustion chamber? and that greater pressure is pushing on the piston when the exhaust valve is open? am I overthinking this?

you only need high velocity for a short period of time after the exhaust gasses leave the cylinder. usually by the time the gasses reach the muffler, the exhaust has cooled enough that the velocity falls anyway. one other thing is that the exhaust gasses have weight to them, and that weight can be used early to help improve the scavenging effect through the headers.
 
rbohm said:
mugsy said:
I was taught in Fluid Flow that pressure drop is proportional to the square of the velocity e.g. double the velocity, the pressure drop increases 4 times. So wouldn't keeping high velocity in the exhaust make for a greater pressure drop? And seeing how all exhaust systems discharge into atmospheric pressure wouldn't a high velocity system require greater pressure all the way back to the combustion chamber? and that greater pressure is pushing on the piston when the exhaust valve is open? am I overthinking this?

you only need high velocity for a short period of time after the exhaust gasses leave the cylinder. usually by the time the gasses reach the muffler, the exhaust has cooled enough that the velocity falls anyway. one other thing is that the exhaust gasses have weight to them, and that weight can be used early to help improve the scavenging effect through the headers.

Ok, being too much of an engineer here: how long of a pipe is "for a short period of time after the exhaust gasses leave the cylinder"? Sorry, just being picky!
 
Okay, I just ordered the dual out headers (Classic Inlines doesn't sel the port divider, but CJs does so I can order it with the exhaust tips). I went with the polished stainless steel, stainless steel bolts, and the heat tube for my choke. It ships out tomorrow!

I'll go with the shop's recommendation for the 2" dual exhaust from the header back (till the tip- which will be 1.75").

Would everyone agree that an x-pipe is a good idea, or is it unnecessary? Can't say I understand the function of crossing the exhaust flows (other than it might even out the "pulses" of the exhaust since one tube is carrying cyls 1-3 and the other is carrying 4-6).
 
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