Bcak pressure and beating a dead horse!

[BCompy]

I know this topic has been run around the block more than our cars but just one more spin, if it's ok. I finally got my mufflers from Arizona exhaust and one of the header guru's here in Ny has stated my little 302 is going to suffer from a lack of back pressure. I have the 36 inch mufflers with an inside dia. of 3 inch straight thru. The motor is a stock 225hp 302 with giggle juice , dual plane manifold , underdrive pullys and 355 gears,with overweight driver on the scales , 2450 lbs.
Any advice is appreciated I havn't gone thru the expense of putting them on yet. Once ceramic coated the deal is done. Am I making a rookie mistake. I know louder doesn't mean faster.

[CobraEd]

The backpressure myth is Horsesh**T!!!!!!! A good performance system actually scavenges the exhast and pulls (vacume) the exhast out of a cylinder!!! The myth comes in because the average Joe blow on the street doesn't know that he will have to richen up the mixture to work with the new scavenging.

Drive on down to Washington and I'll show you what a lack of backpresure can do!!!

Ed

[CobraEd]

Now that I have vented my frustration at this neverending Old Wives Tale, I can talk about it in a more helpful manner. Yes if you just install the mufflers, you MIGHT experience some breakup under load. I did. This is normal. Just jet up richer about 3-4 sizes on the primaries and secondaries and the car will run like its on a catapult. This is engine building 101!! If you have questions or concerns, give me a call. Email me and I'll give you my number.

Also try calling someone like Hooker Headers and discuss it with them. They will tell you the same thing.

[BCompy]

Alright Ed Thank you I'm with you, I forwarded a copy of your reply to my buddy who brought up the whole mess , and who I threatened to shoot (the messenger, and he threatened to shoot back) I'm going forward , dam the torpedoes, and nay sayers. What exactly is a nay sayer?
Jimmy You reading this I've got somebody on my side. I can't really shoot you your the only guy I know that can change jets
LOUD IS GOOD!

[JAM1775]

Good News ! Let's do the jets bud !

[Tony Ripepi]

Hi Guys ,

Just an old A&P mechnic here that sells software for a living....

Go To: www.sandersonheaders.com and link over to the technical stuff. The discussion there put the old wives tale to bed with a very good set of back up information by Tony Garisto, Owner of Sanderson Headers. The discussion and charts are the old argument of Small tube vs. Large Tube headers, and a lot more.

I firmly believe modern automotive technology is the right answer and the only way to get it is go to the experts.

Best Regards,

Tony R.

[Double Venom]

"B",

Remember, I'm the guilty party as charged, for starting the sidepipe mod craze.

Tell you what, you Dyno the car now. Change the sidepipes, do NOTHING more and get back to the Dyno.

For every HP you loose, I pay for $5.00 !
For every HP you gain, your mechanic owes me $5.00

Tell your mechanic to cut the old side pipes apart and look inside. That should be all he needs to know that you are making a huge improvement.

Then once the work is done, have your mechanic re-set timing and carb. Then..back to the dyno once more.

You will be a very happy cobraphile!

DV

PS... you heard it here first: The Dyno WILL be here for the DVSF II

[JAM1775]

Sorry guys...I kind of started this re-hash of an old topic with my own purchase of new pipes for my FFR. My 351w produces 460HP and I just installed a 100 shot of nitrous for 3rd/4th gear down the lane. My old FFR sidepipes were wide open just like the baffles you folks are using on your Classic Roadsters. I loved them ! My primaries were 1 3/4" but very sloppy welds and hand made bends. These pipes were manufactured when FFR first began making 351W 4x4 headers. I recently upgraded to custom made 1 7/8" primaries. MY new side pipes contain 9 discs that are fashioned to produce a spinning velocity effect. The manufacturer of these new pipes is a NASCAR chassis sonic test certifier who also custom designs headers. He assures me the discs direct air flow in circular motion for smoother exit to the atmosphere. I responded by describing the new baffles your guys are using on your CR Cobras and my satisfaction with my old FFR open baffle design sidepipes. He then advised me the open baffled sidepipes would crush TQ on a 350HP SB Cobra. I ran very fat (74F/84R) jets on my carbed 351W and I believe my open sidepipes required that fat jetting to make power....and they did. He advised the 9 discs will make more power by producing heat and velocity in the sidepipe. So as B Compy upgrades his CR sidepipes I relayed the expert comments but still cling to my very positive experiences with my open baffled old FFR pipes. Heck, I may enjoy my equal length mandrel bent new primaries and drop the same muffler section in the side pipe that you folks are using . I fear the discs will cause flow restrictions whether they swirl the air around or not ! I am confused and I rattled B Compy in the process ! I agree...running the least back presssure, straight out and jet fat for power. Apologies.

[Double Venom]

Darn it Jam!

Now you are going to confuse him! YES, what you say has volumes of technical reality to it. Could you be talking about....
"back pressure?" Yup, well sort of anyway. Heat is important, smooooth excavating is also good, BUT dumping 151 cubic inches, which equeals volumes of exhaust into a 1 1/2 +/- inch tube that dumps into a wall, forcing it the other way into another 1 1/2 +/- tube, before exiting is a total "Torque" killer.

Better than stock..that's all.

DV

PS...wonder if I can find some spiral inserts that will fit??

[CobraEd]

UHhhh Ed, . . . . I think that after his whole technical barage, Jam 1775 was agreeing with us

Where are all you guys who already made this conversion. Where is the guy from NC who called me at home all dejected because his 400 inch smallblock Chevy who could not even break the tires loose from a dead stop by flooring it in his automatic Cobra, and after the new sidepipe instalation, he couldnt get any traction all the way thru first AND SECOND??? Where is GaryUNC??? Where are all you guys. BCOMPY needs some encouragement!!


Ed

[JAM1775]

DV....No doubt the best bang for the buck on the Classic Roadsters is to make that sidepipe upgrade !
Compy showed me his stock pipes and of course the new wide open glasspack upgrades. The stock units have got to be choking power from any motor above 4000 rpm. I cannot imagine the benefits gained from YOUR monster motor after the upgrade !
The problem I am suffering from is "too little knowledge can be dangerous". As long as Compy can richen up to offset the tremendously minimized back pressure that is great. Our goal is to see our buddies get the most power when they mash down their foot. It seems Compy will be smiling wide !! As stated above I loved my original straight through glasspack muffler design. I guess the new pipes I purchased are designed to
enhance scavenging. While the 9 discs may visually appear to me as restrictive...perhaps my technical experience ends right there. Either way my hope is that we both benefit from our new exhaust upgrades. Just tryin to squeeze out a few more HP's !

[CobraEd]

Jam,

When I upgraded from those 1 1/2" reverse flow mifflers to the 3"id glasspacks the torque increase was not above 4,000rpm. It was across the board at all rpms. And the amount of the torque increase was phenominal. I would love to see the look on Bcompys face after he starts that thing for the first time and hears the sound. And then again when he mashes the gas in first gear for the first time.

Bcompy, what heads and cam are you running?

Ed

[Double Venom]

OOooops,
Boy did I come across wrong! Sorry. Ed I was totally agreeing with Jam! I just didn't want "B" to get discouraged.

If I owned my own dyno I can promise that we would do all kinds of testing on the exhaust systems. That's why I mentioned having the spiral disc set up to test in the system.

I am not only sure, but I am positive there are better systems than what we are using.

Bcompy...just do it, then show us your
DV

[BCompy]

This thing is bone stock, iron heads and whatever cam came thru Ford svo. The only changes I made were a poilshed high rise manifold ,underdrive pullys and a, ram air set up courtesy of Jam1775.
Thanks for everyones input I am now really looking forward to this upgrade. I know we have done this to death but you guys probably saved my motor with the mention of the rejetting. Besides the lean condition the pipes will cause , I am running laughing gas too , which is all more the reason to run larger jets. A lean condition at the carb and a little blast could have been nasty.
I let you know what I pick up. I do plan on a Dyno run this summer. It's Jam's favorite pastime too, next to hunting a certain twin turbocharged vet. He can run and run fast but he can't hide.

[Randy Resetar]

BC...Not to worry. I had lucian do my exhaust a month ago. My car has a 351 cleveland about 385 horse. The sound is a little deeper than the other mufflers that were on the car. I also received about 3 to 4 more inches of vacuum. The car runs so much better and about 20 more horses.

[Don]

I do not have the technical background, ........but. When I first viewed DV's comments on replacing the CR mufflers, it was a real quick decision to obtain the Arizona Exhaust mufflers and proceed with the replacement.

The sound, engine music NASCAR style, is what the American V-8 is all about, with a Don Scott 351W. Can't prove it, but it sure did seem as a step in the right direction.

The ultimate compliment is when the younger generation asks, what can I do to make my car perform/sound the same way. Still hard to comprehend that the mufflers cost , at that time, only $25/ea. Yes, I would do it again.

[Jack21]

I'm about to que up on this one. Went a tad on the conservative side with 2 1/2" x 30" glasspacks from Page Muffler. I have to cut the collecters, and they're ready to slide on. I too was appalled when, like you I cut the CR pipe open and found that dinky tube inside.

Been reluctant to do much with carb & ignition tuning until new exhaust is on. Will let you know how it works, and sounds.

[CobraEd]

Randy, is your car a Classic Roadsters?

Jack, Yeah, not only is it only 1.5" in diameter, it is reverse flow. It is like Mike Tyson having to fight while breathing thru a cigar!!

Ed

[jdean]

After reading about the small pipe inside these, I looked into mine with a small mirror and a flashlight to see around the curved extension.

To my horror there it was, the small internal pipe!

I immediately ordered the replacement glasspacks from Lucien in Arizona.

If not for these posts, I don't know if I would have ever figured out why my engine might have seemed "held back" when the day comes that my CR build is completed.

[BCompy]

This is just a minor update. Cut the old pipes yesterday, unbelievable interior design. What lunatic came up with putting four pipes unloading into a collector and then hitting a wall. No wonder the dam car won't rev. Put the new ones on, spot welded for fit , they are perfect, will finish friday.Grind off excess and off to coater.
I think I may set off some car alarms with this setup. Hell I am losing my hearing anyway

Seriously does anyone know who makes these pipes and why?