8.1 Yukon XL dyno results

[8.1L]

I was at the dyno today with my '05 Yukon XL to get the base line stock dyno results. I took 4 pulls, two exactly as it came from the factory, and two with the intake disconnected from the air box in front of the MAS. The truck has only 5200 miles on it, so it is almost a virgin.

 

I am looking at the best run from the first two box stock dyno runs, which were essentially identical. I'd love to post it, but I don't know how to attach a jpg to the message, or paste it here. As I found out, by disconnecting the intake from the air box really made a mess of the intake stream, as it was affected by the fan and other air currents, making the dyno runs jumpy, peaked, and not smooth at all. Removing the airbox was interesting, but made the power curve and results much worse.

 

The bottom line is that the maximum rear wheel HP is 281 and the maximum RW torque is 341. Average RWHP from the graph is 232 and average RW torque is 320.

 

The temperature was very hot, with the dyno showing an air temp in the garage of 103.2, so we're not looking at optimal numbers by any stretch, but this is reality sometimes. Frankly, I was sweating my a** off.

 

By disconnecting the air box, which is the oversized trailering airbox, I was actually worse off than with the airbox. This tells me that the engineers have a clue, and that if you change the factory intake on this model, be careful of what you are doing, where the air comes from, and make sure it is 'clean air'.

 

So, all in all, it was a very interesting day at the dyno. For general reference, the stock figures GM posts are 320 hp/440 torque, so we can easily see the drivetrain and air temperature losses.

 

I'm interested in your comments. I have a Magnaflow exhast going on soon, with headers and a Westers tune being seriously contemplated.

 

Jim

 

[vhato]

That is a loss of around 25%. That is better than expected which is usually around 30%. Outstanding.

[8.1L]

That is a loss of around 25%.  That is better than expected which is usually around 30%.  Outstanding.

 

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Thanks, it was actually a little better than I had expected as well. The heat was certainly an issue, but all the temps (tranny and water) stayed in the ranges.

 

With the hood open and pulling like that at 4800 rpm, it really sounds like the big block, too. Magnaflow goes on soon.

 

Jim

[Butch 02 Denali]

  As I found out, by disconnecting the intake from the air box really made a mess of the intake stream, as it was affected by the fan and other air currents, making the dyno runs jumpy, peaked, and not smooth at all.  Removing the airbox was interesting, but made the power curve and results much worse.

 

By disconnecting the air box, which is the oversized trailering airbox, I was actually worse off than with the airbox.  This tells me that the engineers have a clue, and that if you change the factory intake on this model, be careful of what you are doing, where the air comes from, and make sure it is 'clean air'.

 

 

Jim

 

That hot turbulant underhood air will definatly cause the engine to run erratically and lose power ove the stock air box on hot days. Might want to check out the new Outlaw for the 8.1 Jim. Outlaws are true cold air intakes with many design features that put them way above any other intake IMO.

[8.1L]

I was at the dyno today with my '05 Yukon XL to get the base line stock dyno results.  I took 4 pulls, two exactly as it came from the factory, and two with the intake disconnected from the air box in front of the MAS.  The truck has only 5200 miles on it, so it is almost a virgin. 

 

I am looking at the best run from the first two box stock dyno runs, which were essentially identical.  I'd love to post it, but I don't know how to attach a jpg to the message, or paste it here.  As I found out, by disconnecting the intake from the air box really made a mess of the intake stream, as it was affected by the fan and other air currents, making the dyno runs jumpy, peaked, and not smooth at all.  Removing the airbox was interesting, but made the power curve and results much worse.

 

The bottom line is that the maximum rear wheel HP is 281 and the maximum RW torque is 341.  Average RWHP from the graph is 232 and average RW torque is 320.

 

The temperature was very hot, with the dyno showing an air temp in the garage of 103.2, so we're not looking at optimal numbers by any stretch, but this is reality sometimes.  Frankly, I was sweating my a** off.

 

By disconnecting the air box, which is the oversized trailering airbox, I was actually worse off than with the airbox.  This tells me that the engineers have a clue, and that if you change the factory intake on this model, be careful of what you are doing, where the air comes from, and make sure it is 'clean air'.

 

So, all in all, it was a very interesting day at the dyno.  For general reference, the stock figures GM posts are 320 hp/440 torque, so we can easily see the drivetrain and air temperature losses.

 

I'm interested in your comments.  I have a Magnaflow exhast going on soon, with headers and a Westers tune being seriously contemplated.

 

Jim

 

 

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Well, it was into the shop to get the new Magnaflow installed, and get 2 more dyno pulls. Good news all around. I love the sound of the Magnaflow, and now I have the 'big block' sound I was looking for. It can be relatively quiet if you stay out of it, or it makes noise when you get into it.

 

I was astounded at the dyno results, as was the dyno guy. With only a muffler change, I really gained significantly in hp and torque. Average RWHP stock was 232, and now I'm dynoing at 254. RW Torque was 320 ft. lbs. and now I'm dynoing at 355. Temperature in the dyno building was 93.

 

The only thing I can say is that to keep the sound quiet from the factory, they really must have bottled this thing up. I am extremely pleased with a very simple muffler replacement the gives me sound, HP, and torque.

 

SOTP results are very encouraging, as well

 

This leads me to believe that the 496 c.i. engine has a lot of undeveloped potential if you simply let it breathe. I can tell you I'm a happy camper with results like this, not to mention how much I love the vehicle. I want more power...

[dannyukonxl]

d**n, what magnaflow system are you running, im going to put on some true duals soon and was looking for similar comparisons, also what set up did you use, im thinking about the 5x8x18 cases with dual splits, thats an awesome gain for exhaust

[8.1L]

d**n, what magnaflow system are you running, im going to put on some true duals soon and was looking for similar comparisons, also what set up did you use, im thinking about the 5x8x18 cases with dual splits, thats an awesome gain for exhaust

 

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The way mine is set up underneath, all I can really do is put the muffler on. I used the model 12599 Magnaflow. It isn't a direct replacement, but it's close. I was surprised, too, but those are the numbers. I have dual cats, one on each pipe, staggered, in front of the muffler.

 

Jim

[dannyukonxl]

yea, its a weird set up i was looking under there the other night and right after the 1st upstream cat (driver side), the pipe gets smaller or piinched a little bit when it passes over the torsion bar crossmember