I checked the Flowmaster catalog and they recommend the 70 series for these trucks. I don't really care much for making the truck louder, but, I do want the best torque and HP results I can get. Has anybody tried the 70 series yet. I was considering the 50 series Delta Flow till I got the catalog. The 50 Delta looked like the way to go, but if I will get more torque out of the 70 that's the route I'll take.

 

I have also been going through the same dilema as you,but here is what I have found out. According to Flowmaster (I have E-mailed them and talked to their tech support guys), if your main goal is performance with very little noise the 70 is the way to go. If
you want performance with "mellow to deep" exterior noise the next quitest would be the 50 series SUV. It is a 50 series muffler with a 5 inch thick case instead of a 4 inch to reduce interior noise. It is also what comes from flowmaster if you buy their complete system. I am planning to use the 50 suv on my Expedition due to be installed 8/25. I'll let you know then what I think.
Timbo

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TRC, over the past few months there have been a couple of post on the 70 series by people who had tried several other mufflers and then the 70 series. They both said the best performance they had was with the 70 series. I have had a 52571 on order for months and it is almost impossible to find. It is the 2 1/2 inch which is a direct replacement on stock system. Hardly anyone keeps 2 1/2 inch in stock because most of the 70 series are put on larger vehicles than the f-150. Most of the shops and distributors have it in the 3" only and don't seem very interested in ordering one muffler. A local shop offered to install 3" with reducers for $200. Get ready to pay $100 to $125 for muffler only. The cheapest place I found flowmasters is Legal Performance out of Ft. Worth, Tx. Tell them you saw their internet add and they knock off 10% on flowmaster and K&N products. Their number is 1-888-336-8001.

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98 Nascar Edition, superchip, K&N with airbox mod.

 

I was told by Flowmaster that their mufflers will give about the same increase in performance when run under about 6,000 RPM. They said below that, just go for the sound you want. There is little, if any, difference in performance.

A local speed shop has the 52571 for $89.95 and has 3 in stock.
http://www.re-racing.com/flowmaster-70-series.htm

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Danny
'98 F-150 Std., RC, SB, 4x2, 4.2L, 5-sp, 3.08, AC, speed control, rear slider
with Syntec engine oil, MTL trans fluid, Edelbrock shocks, 50 Series Flowmaster, K&N with airbox mod, electric radiator fan

 

TRC,I just had a cat-back system put on my truck with 3 chamber 50 series muffler. It was too loud for me, went back to shop and they put a 70 series in and it sounds great.It has a nice low rumble and you can feel the difference in hp gain.

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99 F150XLT Black Sport,Ext cab 4.6,3:55,K&N,Ford seat covers,Vent visors(front only),Draw tight hitch,Superchip,custom cat back with 70 series Flowmaster and stainless tips,soft tonneu cover

 

DBoyz, I saw your message and would be very interested in getting more info from you. The 50 series you had installed-do you know if it was a 4" thick muffler (the standard 50 series) or a 5" thick which Flowmaster refers to as the 50 SUV. Or the muffler part number. I am about to have a system put on my Expedition and I dont want to be sorry with my choice. When you say the 50 was too loud was that inside, outside or both? Are you happy with the sound of the 70 outside the vehicle-specifically is it loud enough that its obvious you have a V-8 under the hood? Any feedback would be much appreciated because I have an appointment 8/25 to have mine done. If you go to the F-150 chat at all I am in there as Timbo. Thanks!!!!!!!!

 

Gaudenti, thanks for the info on re-racing. I ordered the 70 series today.

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98 Nascar Edition, superchip, K&N with airbox mod.

 

obritg, It was a regular 50 series with the 4 inch thick case. I thought it was too loud both inside the truck and outside. The 70 has a better sound than the stock, especially when you get on it. The interior sound is very little with the windows closed.
I don't know how the 50 suv will sound? I was lucky enough to have a muffler shop switch it out at no cost.

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99 F150XLT Black Sport,Ext cab 4.6,3:55,K&N,Ford seat covers,Vent visors(front only),Draw tight hitch,Superchip,custom cat back with 70 series Flowmaster and stainless tips,soft tonneu cover