Dynoed Radix = BLEAH!!

GMC_DUDE · July 3, 2004

Well, as you can tell by the title, I did the dyno today and the result was 314 HP vs 240 before, and 320 ft-lb torque vs. 250 before. Not exactly terrible, but not what I expected either. However, the good news is 1) I don't have to worry about breaking the transmission and 2) I know exactly where the problem is as the exhaust sounded like a giant air hose instead of the usual pulsating sound. In fact the exhaust even sounds crummy on the street now, more like a giant 6 instead of a V8. In other words, the Flowmaster 70 muffler, which was barely adequate in n/a mode, is choking the system to death now that much more air is being pushed through. This also explains Magnacharger's selection of a very conservative 3.7" pulley. Anything smaller would have blown up the engine.

So the bottom line is the FM70 has to go. But what to replace it with? I had (still have in the garage) an FM50, which flows better but is awfully loud. I live in town, and although there are no restrictive covenants about vehicle noise, I do want to be well liked by the neighbors. Does anyone have a good recommendation? I almost went with Gibson's, but the exhaust mechanic who was doing the work talked me out of them, saying they had resonance problems in 1500 series trucks (heck so does the FM70). Right now I don't know what to buy, so any suggestions would be welcome.

Durkin, I took some quick and dirty pics of the intercooler reservoir and pump install and posted them here.

http://members.cardomain.com/gmc_dude

This July 4th weekend I will be fixing up some loose ends on the install (fix the coolant leak I discovered taking the pics, fix the coolant pump so it doesn't bang on the PCM, do a better job on the fuel pump bracket), so I will take some better pics when I have everything apart again. But please advise on a muffler choice, I really need some help.

Peace and Coolness,

GMC_DUDE

airdeano · July 3, 2004

use a diesel muffler.

larger cubic inch with more boost than what your capable. so you wont have

to worry about restriction.

airdeano

99Silver6.0 · July 3, 2004

Borla XR-1's flow really really well. Flowmasters do not! Heres a flow test I found on another site a few months ago. Have you done any tuning on your truck at all? After you get some done you will be throwing down alot better numbers.

2 “ Straight Pipe 283 CFM

2 ¼ “ Straight Pipe 365 CFM

2 ½ “ Straight Pipe 521 CFM

2 ¼” Typical Bent tailpipe 268 CFM

2 ½” Typical Bent Tailpipe 417 CFM

2 ¼” Inlet/Outlet_ Glass Pack Tips- No Louvers- Smooth 274 CFM

2 ¼” Inlet/Outlet- Glass Pack Tips-Louvered 133 CFM

2 ¼” Cherry Bomb 239 CFM

2 ½” Cherry Bomb 294 CFM

2 ½” Inlet/Outlet Dynomax Super Turbo 278 CFM

2 ½” Inlet/Outlet Ultraflow Bullet 512 CFM

2 ½” Inlet/Outlet Gibson Superflow 267 CFM

2 ½” Inlet/Outlet Flowmaster ( 2 Chamber) 249 CFM

2 ½” Inlet Outlet Flowmaster ( 3 Chamber) 229 CFM

2 ¼” Inlet/Outlet Thrush CVX 260 CFM

2 ½” Inlet/Outlet Maremount Cherry Bomb 298 CFM

2 ½” Inlet/Outlet Hooker Aero Chamber 324 CFM

2 ½” Inlet/Outlet Hooker Max Flow 521 CFM

2 ½” Inlet/Outlet Borla Turbo 373 CFM

2 1/2" Inlet/Outlet Magnaflow 284 CFM

Standard OEM 2 ¼” Inlet/Outlet 138-152 CFM

Standard OEM 2 ½” Inlet/Outlet 161-197 CFM

Sound levels in db:

1.Borla XS, 80db at idle, 90db at 2,000 rpm, 110db at WOT.

2.Hooker Maxflow, 80db at idle, 90db at 2,000 rpm, 120db at WOT.

3.Magnaflow, 82db at idle, 91 at 2,000 rpm, 114db at WOT.

4.Flowmaster, 82db at idle, 93 at 2,000 rpm, 115db at WOT.

5.Flowtech Warlock, 83db at idle, 92 at 2,000 rpm, 112db at WOT.

6.Dynomax UltraFlo, 83db at idle, 94 at 2,000 rpm, 113db at WOT.

7.Borla XR1, 83db at idle, 96db at 2,000 rpm, 118db at WOT.

8.Bassani Street, 83db at idle, 96db at 2,000 rpm, 120db at WOT.

9.Edelbrock RPM, 84db at idle, 93db at 2,000 rpm, 118db at WOT.

10.Bassani Real Street, 84db at idle, 96db at 2,000 rpm, MAX. (120+db).

11.Flowtech Afterburner, 86db at idle, 94db at 2,000 rpm, 115db at WOT.

12.Flowtech Terminator, 86db at idle, 94db at 2,000 rpm, 119db at WOT.

13.Hooker Aerochamber, 87db at idle, 94db at 2,000 rpm, 114db at WOT.

14.SpinTech, 87db at idle, 97db at 2,000 rpm, 116db at WOT.

15.MAC, 87db at idle, 98db at 2,000 rpm, 119db at WOT.

16.No Muffler, 91db at idle, 103db at 2,000 rpm, MAX. (120+db).

LikeaRock14 · July 3, 2004

I think he wnts quiet, 99

If you're looking for a quiet but still be able to hear it sound, go w/ a 24" Magnaflow. It's straight through and will be pretty quiet. Performance wise it'll be much better than the 70 series. A diesel muffler might work too, I just don't know if a 4" pipe will fit under a 1500

99Silver6.0 · July 3, 2004

I think he wnts quiet, 99

That might be a tough one. Guess his best bet would be a Magnaflow like you said.

frdfandc · July 4, 2004

If you want a nice quiet muffler, but still has a lot of bark on the top end, I would recommend the Dyno-max Ultra-flow. These mufflers are very easy on the ears during idle and part throttle acceleration, but have a really nice tone at WOT.

99Silver6.0 · July 4, 2004

If you want a nice quiet muffler, but still has a lot of bark on the top end, I would recommend the Dyno-max Ultra-flow. These mufflers are very easy on the ears during idle and part throttle acceleration, but have a really nice tone at WOT.

That said, they have sound clips on their website!

Dynomax sounds

Shotgun · July 4, 2004

The problem is not the muffler...It's just that you need 2 of them..You need true duals for a supercharged engine. I mean jeez your defeating the purpose of your headers bottlenecking them into one muffler.

99Silver6.0 · July 4, 2004

The problem is not the muffler...It's just that you need 2 of them..You need true duals for a supercharged engine. I mean jeez your defeating the purpose of your headers bottlenecking them into one muffler.

Jim Nefueldts 10.9 Turbo Z-71 doesnt have true duals.

Shotgun · July 4, 2004

Jim Nefueldts 10.9 Turbo Z-71 doesnt have true duals.

And your point is?

99Silver6.0 · July 4, 2004

Jim Nefueldts 10.9 Turbo Z-71 doesnt have true duals.

And your point is?

None. Cant think of anything e;se tpo post... Too drunk to care now.... GMC_guy needs a new cat-back. YOu fdont have too run tru dools on an F/I setup.. It iznt necessary.

GMC_DUDE · July 4, 2004

If you want a nice quiet muffler, but still has a lot of bark on the top end, I would recommend the Dyno-max Ultra-flow. These mufflers are very easy on the ears during idle and part throttle acceleration, but have a really nice tone at WOT.

That said, they have sound clips on their website!

Dynomax sounds

Thanks for the info folks, I really appreciate it . I really like the sound of the Dynomax units, and their web site suggests that they flow well too. I am a bit leary about glass-packs though, as I've heard that the fiberglass eventually goes to pot, and then they sound like a straight pipe How long do they typically last?

snoman · July 4, 2004

Glass packs do "wear out" with time. It is more of a usage thing (how often and hot hot and hard you use them) than a time thing so it is hard to give a good time line.

99Silver6.0 · July 4, 2004

If you want a nice quiet muffler, but still has a lot of bark on the top end, I would recommend the Dyno-max Ultra-flow. These mufflers are very easy on the ears during idle and part throttle acceleration, but have a really nice tone at WOT.

That said, they have sound clips on their website!

Dynomax sounds

Thanks for the info folks, I really appreciate it . I really like the sound of the Dynomax units, and their web site suggests that they flow well too. I am a bit leary about glass-packs though, as I've heard that the fiberglass eventually goes to pot, and then they sound like a straight pipe How long do they typically last?

Glasspacks are restrictive as hell. They actually have alot of backpressure.

Durkin · July 4, 2004

GMC_ Dude:

Thanks for the photo's of the IC reservoir location!

I do not think it is a muffler problem. Your 4.8L has 91% less displacement than my 5.3L and I got 350 RWHP with about the same equipment and the same muffler setup.

-- 102 MPH; 4,393 RPM; RWHP=335; RWT=401

-- 111 MPH; 4,782 RPM; RWHP=350; RWT=384

So 91% of 350 is 317 RWHP and that is pretty close to your numbers.

You have 4WD and that alone eats up a lot of HP because the transfer case is operating even in 2WD.

I think you should keep the Flowmaster and spend some bucks on a Wester's Tune instead.

The pulley size does keep the blower pressure down so they use the same blower, with increasingly smaller pulleys for the 5.3L and 6.0L engines. The backpressure in the exhaust is not likely your problem; a smaller pulley would likely raise your pressure enough to cause detonation that would end your engines life pretty quickly.

Regards,

Durkin