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2004 8.1 HP down from 340

avalonandl

avalonandl

Full Member
Joined
Aug 4, 2003
Messages
2,066
I have a 2004 2500 with the 4.10 axle. I noticed for 2004 the HP rating dropped from 340 to 320.

Well, I have a contact at GM Powertrain and guess what? here is a response in an email:

Dean, I discussed the 8.1L with RXX XXXXX who is the 8.1L chief engineer, He confirmed that exhaust changes for the latest emission regulations is the culprit for the drop in Hp. He and his folks have no particular knowledge about the flowmaster package. However they agree that a larger exhaust with lower back pressure will improve the performance.

Straight from the horses mouth.

So now it's off to Flowmaster to look at the # 53504 and dual pipes out behind the rt. wheel to pick up some lost ponies.

Where do I find the MAC intake for the 8.1 liter?

Avalon


 
avalon, good choice on the exhaust, that is exactly what I have.
Here is the intake link Mac Performance Here is mine. Very well made, and great price.
 

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Oviedo:

How noisy is it? I do not want something with too much noise.

Do you like the MAC intake?
 
avalonandl said:
Oviedo:

How noisy is it? I do not want something with too much noise.

Do you like the MAC intake?
Click to expand...

From the inside the intake is louder than the exhaust. I love the Mac intake, sounds great, lets alot of air flow. You can actually fit the filter on your head. It is huge. It is a very well made kit, bolted right in very easily. The price was much better than K&N. The 70 series Deltaflow with dual in/dual out is not very noisy. No hum from inside. When they started it up at the muffler shop I thought they put the wrong one on. But is was loud in their garage, and alittle louder than the old. You will quickly get used to it. It is noticable when you stomp on it, but quite for daily driving. Let me know if you need more info.
Dave
 
Oviedo, did you go with the series 50 or 70? With 2 inlets and exhausts also?

The 2004 8.1 factory system uses dual inlets into a single muffler, dual outlets that go into a Y as it goes over the axle. Single 3" pipe out on pass. side.

It looks restrictive and has some drone (resonance) at highway speeds. I have the 4.10 and at 80 mph turns 2800 rpm, so I am putting some volume through there.
Going to the series 70 Big Block # 524704 I hope will increase the efficiency at that rpm.

Avalon
 
Well i have a 2003 ,,,2500....4:10 rear....I put on a K&N FIPK GEN II, and then had a local shop puy on a Flowmaster 50 Delta Flow muffler , that just replaced the existing muffler...The K&N system did increase the "under the hood" noise , it was noticeable in the cab also....The Flowmaster 50 ,,produces a lot of resonance in the cab.....I like it...I also drive a Harley,with straights,,,so thats my preference...I think that if you want to gain true increases, you have to except the fall backs...I have heard that Maganaflow,is agood quite system....Also my muffler guy , said that I would be dissappointed by the Flowmaster 70 Big Block...My Truck sounds more like a stock Dodge...VERY GRRRRRRRRRRRRRRRROWWLLLLLLYY!!!


GOOD LUCK :eek:
 
I am trading in my 02 AV that has the 340 hp but also the 3:73 rear end. I told dealer I wanted the 4:10's but he is saying I would be better off with the 3:73's....How big a difference is there? Milege suffer much?
 
Dix,
I don't think you can really go wrong with eith axle ratio unless you are going to pull a really big load. The 4.10 axle is rated for 12,000 lbs and the 3.73 is rated for 10,500 I think.

I get 11.5-12.0 mpg all around mileage. If you drive like a granny you get better mileage. The 3.73 will cruise on the highway w/ lower rev's. I turn 2800 at 80 mph, yikes!

The issue of the reduced HP is easily taken care of w/ exhaust system and intake.

avalon
 
Their systems do not list the 8.1, only the 6.0 and the old 454!

Look under the exhaust system thread and for a guy named muffman, he knows what he is talking about.

avalon
 
No arguements as to a new exhaust making a difference, however in my opinion you need to take any HP figures put out by the car/truck makers with a grain of salt.
For example the late model Av's are reported to have slightly higher HP in the 5.3 version, yet I went through a bank of dyno tests that the dyno shop had in hostory and the stock 2002 5.3's do a little better at the rear wheels. I think the numbers depend on a whole lot of conditions and how testing was done.

Again, just an opinion.
 
I thought the reduction in HP was to not exceed the specs of the MN8 tranny. And there wasn't room enough for the Allison. HP in the HD p/u's stayed at 340 with the Allison. Now I see that the Caddillac EXT comes with 340 HP and the Allison, so it must fit after all?
I don't understand what good extra power mods are if they're going to burn the tranny.
 
sparky said:
No arguements as to a new exhaust making a difference, however in my opinion you need to take any HP figures put out by the car/truck makers with a grain of salt.
For example the late model Av's are reported to have slightly higher HP in the 5.3 version, yet I went through a bank of dyno tests that the dyno shop had in hostory and the stock 2002 5.3's do a little better at the rear wheels. I think the numbers depend on a whole lot of conditions and how testing was done.

Again, just an opinion.
Click to expand...

I would also agree with this.
 
Texas86:

Cadillac does not have the Allison Tranny, it does not fit.

The 6.0 high output engine in the EXT is lower torque than the 8.1.

avalon
 
Thanks! I just took for granted the 345 hp was the 8.1. And I see on the EXT web page 10:1 compression, which means premium gas? And only 7400 lb tow rating. Glad I got my AV2500.
 
Tex

The caddy uses premium or regular.

The 7400 lb capacity is due to:
tranny- 4L60 on the 6.0 (torque is the real rating here)
rear axle capacity- it is not the bigger one like the 2500 AVY
And ratio- a 3.73

Avalon
 
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