Magnaflow XL mufflers - yay or nay?

[findog78]

I went from a 2.25 straight dual system and installed a new 2.5 with X pipe and a set of XL mufflers exiting in front of tires. Sounds good at an idle but I swear I lost power like Im missing a gear now? Not sure wtf? Could it be from going from 2.25 to 2.5 diameter or is it the muffler? Anybody else using these mufflers experience the same?

[Scottcoda]

I am about to install the magnaflows with the x pipe on a 2.25 system.. The reason I chose the 2.25 was because on Clifford performance's website they strongly recommend not going larger than 2.25 as a loss of power will happen.This is referring to a set up on a inline 6, not sure what u have.

[CC69Rat]

Loss of back pressure will cause power loss. IMO it's the 2.5" change, not the muffler. .. but it could be the free flow design of the Magnaflow that contributed to it too. Regardless of what muffler you chose if it has a free flow design (Flow Master, Borla, Magnaflow, Spin Tech) it would have done the same thing. Just my .02

[djgebert]

A lot depends on your engine. CC69Rat is correct, it may be a backpressure issue. 2.5" exhaust was not designed for non-performance engines, they need some back pressure to run at their best do to lower compression and cam profiles. Do you know what engine and compression you have? You may need to go to a more restrictive muffler if you have a fairly low compression engine. If you are running 10:0-1 or higher compression, there shouldn't be a power loss issue, it should have actually improved performance.

[Elefuntman]

I don't think going from 2.25 to 2.5 is hurting you, I think the exiting in front of the tires is "tricking" you, now you are hearing the exhaust from one side, not a fully balanced tone. Try a full tailpipe, it may "sound" smoother, balanced and maybe even faster! I did some actual drag strip testing on a car some years ago and went from a Dynomax Hemi muffler to a Flowmaster to the Magna flow, the magna flow produced the lowest ET's and the nicest sound.

[findog78]

The old exhaust had cheap glass packs with the seams blown out from backfiring so Im thinking its not because muffler is too "free flowing". Its not tricking me either. When I pin it it feels like Im starting of in 2nd gear. Even my kids notice it! Im leaning toward the back pressure scenario with the change to 2.5 diameter? The motor is a mild 350. 9.5CR, cast 1.94 heads, Lunati street cam, performer RPM. Nothing outrageous but not a stocker. I really did a lot of work cutting, splicing, and welding a jog in the collectors so the exhaust would hug the bottom and not hang down as much like the old one. Its really tight and the X pipe fits perfect and its all welded. Im wondering to save the work I did if I could use a reducer after the 2.5 X pipe to a 2.25 mufflers and go out 2.25 tail pipes? Im just reluctant to get the smaller XL magnaflow again and end up with the same thing?

[dajn]

Rap them pipes. Its funny when you see people with there y pipe. They don't know what a good sound is.

[Norcal72]

Did you remove the exhaust manifolds? If you did, did you check the gasket for port matching? Maybe partial blocked ports? Just throwing out ideas, not being a SA.

That 350 should love the 2.5" dual pipes. Should of definately gained some horse power. Hows the power after 2500 rpms? Should of at least gained some top end power.

I wouldn't put a choke in the exhaust by going from 2.5" to 2.25".

[68Stepbed]

The free flowing design of mufflers like Magnaflow, Borla, & Corsa tend to give up some low speed torque for higher end horsepower gains. I noticed a similar(not as much as you describe) loss in torque when I switched from Flowmaster to Magnaflows on my truck. It seemed as if I'd lost some of the low speed pep, but in the upper rpm ranges it really soared.

It sounds as if you have very little restriction in the exhaust system which reduced the backpressure. Before blaming the exhaust, look into re-tuning the engine some. You probably tuned the engine to run it's best with the exhaust system it had. Start with bumping the timing, read your plugs to see how the carb is mixing A/F, readjust the idle mixture screws, etc.

An engine is essentially just an air pump. It sucks in air, and pumps it back out. When you change the levels on which this happens(better flowing exhaust) it can change the amount of air it needs to intake to exhale according to what it's capable of.

[jwatson355]

Originally Posted by 68Stepbed

The free flowing design of mufflers like Magnaflow, Borla, & Corsa tend to give up some low speed torque for higher end horsepower gains. I noticed a similar(not as much as you describe) loss in torque when I switched from Flowmaster to Magnaflows on my truck. It seemed as if I'd lost some of the low speed pep, but in the upper rpm ranges it really soared.

It sounds as if you have very little restriction in the exhaust system which reduced the backpressure. Before blaming the exhaust, look into re-tuning the engine some. You probably tuned the engine to run it's best with the exhaust system it had. Start with bumping the timing, read your plugs to see how the carb is mixing A/F, readjust the idle mixture screws, etc.

An engine is essentially just an air pump. It sucks in air, and pumps it back out. When you change the levels on which this happens(better flowing exhaust) it can change the amount of air it needs to intake to exhale according to what it's capable of.

amen! If you haven't heard them check out hooker max flow.
https://www.youtube.com/watch?v=11vh...RDndUyQbLTJVeA

[CC69Rat]

Now that I know more about the engine, yes I agree it can handle the 2.5" exhaust and Magnaflows. My previous post, I had assumed a stock 350 with 2.5" exhaust, X Pipe, and MF, .. I wouldn't do 2.5" stock personally. I'd do 2.25" but with a few mods such as what this engine has it's not going to be an issue running 2.5" IMO.

I agree with Matt too, a little tuning might be necessary now that she can breathe a little easier. It may have more power than it ever did before.

http://www.howrah.org/exhaust-system.html

Do you have a local performance machine shop? I'd drop it by there and let them put it on their machine and dial it in just right.

Backpressure is a weird animal. Too much and it will impact performance. Too little and it will impact performance. Once you hit that sweet spot you'll know it.

[findog78]

Thanks for all the input. I agree the first step should be a tune. I rebuilt the carb and it actually runs like crap now anyway. I do remember a little loss of torque like 68stepbed describes when I took the pipes that exit out the rear of the tire off and just went straight out mufflers on the old exhaust. Id really prefer the low end to the top end but was set on having them exit in front of tires this time. I also think this is a classic case of bigger is not always better.

[68Stepbed]

I may be opening a can of worms here, but, what kind of carb do you have on it?

[CBrown680]

I had a set of Magnaflows installed on my 67' short stepside. I have a SB 350, Hooker headers, and 2 1/2" pipes with no crossover that exit in front of the rear tires. IMHO it made my truck run better. Maybe it's just that the weight of the old system with glass packs out the back is gone?

[findog78]

Carter competition series...before Edlebrock bought them out I believe…now the 1406? 625 CFM with vacuum secondary’s. Tried to adjust a/f screws but didnt seam to change idle?

[68Stepbed]

I can't help you much on tuning the Carter. I never could those to run right. I know you need to start getting into the jets and metering rods, but just don't know where to start. I know there's very little adjustment in the idle mixture screws on those style carbs.

I suggest adjusting the timing first. Where do you have your initial timing set? Try bumping initial timing to 12 degrees and see what that does.

Also, what is your rear gearing? What trans?

[Fitz]

Originally Posted by findog78

Thanks for all the input. I agree the first step should be a tune. I rebuilt the carb and it actually runs like crap now anyway. I do remember a little loss of torque like 68stepbed describes when I took the pipes that exit out the rear of the tire off and just went straight out mufflers on the old exhaust. Id really prefer the low end to the top end but was set on having them exit in front of tires this time. I also think this is a classic case of bigger is not always better.

Engines are just air pumps. Anything that changes the flow through the engine affects the entire system. By going to a 2.5 in exhaust you have changed the flow characteristics and that means the carb is no longer set up correctly. The drop in backpressure has increased the air flow on the intake side and that means mixture is no longer correct. Adjusting the idle screws changes the mixture at idle but does nothing for any other throttle position. If you can get an air/fuel ratio meter that will save you from having to 'read' your plugs but I'm betting that carb needs a jet change because of the increased flow.
Here is a link to a PDF (http://www.crankshaftcoalition.com/w...rafbtuning.pdf) that will help you set your carb up correctly. I can't tell you how because I won't use anything but a Holley. it's a Ford Chevy thing not an issue with performance. The AFB is a good carb, but I can't get them to run correctly.

Set Initial timing, if you have an HEI then start on that carb but if you are running points, adjust the dwell and recheck timing BEFORE digging into the carb. Once that is done check advance at 4000 rpm to see where the max is. Somewhere around 36 degrees total is a good starting point. Gap and install new plugs and put 10-15 miles on the truck. Remove the plugs and take a close look. Sooty black means you are rich. Tan means you are on the lean side. 14:1 is about the right air to fuel ratio if you have a meter. If you are running rich drop a jet size. Lean go to a larger jet. Here in Tucson I am at 3200 ft above sea level but in winter, density altitude drops that to sea level and I have to change to a richer jet. In mid summer, density altitude is 7000 ft so I change to a smaller jet to lean out the mixture. Good Luck!

[findog78]

That carb used to run sweet. Motor also had a point dist with Mallory electronic conversion. Choke was never hooked up and cold or hot motor started before I could let go of key and it shut right down. I got an HEI dist awhile back and it never ran as well. Then I let my step father do his "by ear" carb adjustment and I could never get it dialed in even with timing light. Now it cranks too long to start …diesels...dies at stop sign and hard start when its warm. That’s when I rebuilt the carb. Even with these issues the old exhaust seamed to have more low end than these XL mufflers with the 3 chambers. The other magnaflow muffler ($40 more ea) is straight through like my old ones? Seems I have too many variables to narrow it down without spendy trial and errors.
I have 4:11 gears with a Super T-10.

[findog78]

Thanks for the info fitz. She's in the paint shop right now but I will definately start with a tune and maybe take it to someone with the tools to do it right before I start changing exhaust.

[69GMCLonghorn]

Sell that carb to a FORD owner and buy a Holley. Tune/jet it properly, get your timing set right for the engine and carb setup and you will have the best amount of power you can get with that setup. It all has to work in harmony or it will all go down the crapper.

[Fitz]

Originally Posted by 69GMCLonghorn

Sell that carb to a FORD owner and buy a Holley. Tune/jet it properly, get your timing set right for the engine and carb setup and you will have the best amount of power you can get with that setup. It all has to work in harmony or it will all go down the crapper.

Like I said, AFB vs Holley is a Ford vs Chevy thing BUT, the Holley will always be my choice!

[findog78]

WHich holley?

[Fitz]

Originally Posted by findog78

WHich holley?

Holley 4150. Mechanical secondaries and an electric choke. They run from 600 to 850 CFM so you should be able to find one to match your engine

[NoNeck]

I really did a lot of work cutting, splicing, and welding a jog in the collectors...

Another train of thought on your loss of low end power. In your info above you said you welded a "jog" in the connectors. I don't know what a jog is, but did you RESTRICT the exhaust when you modified it for the X-pipe? The more twists, turns and obstructions in the exhaust would cause a loss of low end torque. A picture of your system might help.

Just my 2 cents...

POP