Cat Gut + MagnaFlo

maxxgraphix · **Joined:** Wed Mar 26, 2008 8:11 am **Posts:** 53

Wife is very happy with the new found power. I gutted the cat and installed a 2.5" Magnaflo.

I made sure to make the 2.5 pipe connections flow well. The sound is nothing more than it was before and the turbo comes on stronger.

Perfect.

I'll report back with new MPG.

fastRob · **Posted:** Sun Jun 08, 2008 12:19 am

I went with a magnaflow 3" and 3 cat back pipe for towing.
No fuel mileage improvement.
More noise, more power, hard tellin'.

MTB_TDI · **Posted:** Sun Jun 08, 2008 12:38 am

I was under the CRD yesterday and looked at gutting the cat. Did you take the downpipe off? How did you do that? It looks like a hose clamp holding it on.

maxxgraphix · **Joined:** Wed Mar 26, 2008 8:11 am **Posts:** 53

I didn't remove it at all. Smashed the comb and vacuumed it out until everything was gone. I just shined a small light into the cat to verify it was clean.
What's funny is that after I removed the muffler, I started it to hear the sound. It really made no difference. After gutting it was loud.

More power should result in less fuel (foot off floor). Towing it's hard to say, since you’re under load and boosting more. Here's some something to think about.
A VW TDI wagon weighs about 3200lbs and has 1.9l with 140hp / 235 torque and can get 45mpg. That's almost the same power as the 2.8CRD of 160 / 280.
The CRD weighs 4360lbs. That's 27% more weight with only 12.5% more HP and 16% more torque. But the engine is 22% larger. The CRD needs to have 320lbs of torque to have the same efficiency as the TDI. Also the ability to put that to the wheel.

We need to increase the power without dumping more fuel and keep foot off floor.
1. Exhaust mods
2. Airbox mods
3. Lift pump
4. ECU Tuning
5. TC Upgrade
6. Tires
7. Aero
8. Gear ratio
9. 6 speed manual and toss that TCU in the can.

A semi truck that weighs 80,000lbs can get 6.5mpg. The FE to weight ratio is incredible and makes everything else on the road look pathetic.

CATCRD · **Posted:** Wed Jun 11, 2008 12:01 am

maxxgraphix wrote:

I didn't remove it at all. Smashed the comb and vacuumed it out until everything was gone. I just shined a small light into the cat to verify it was clean.
What's funny is that after I removed the muffler, I started it to hear the sound. It really made no difference. After gutting it was loud.

More power should result in less fuel (foot off floor). Towing it's hard to say, since you’re under load and boosting more. Here's some something to think about.
A VW TDI wagon weighs about 3200lbs and has 1.9l with 140hp / 235 torque and can get 45mpg. That's almost the same power as the 2.8CRD of 160 / 280.
The CRD weighs 4360lbs. That's 27% more weight with only 12.5% more HP and 16% more torque. But the engine is 22% larger. The CRD needs to have 320lbs of torque to have the same efficiency as the TDI. Also the ability to put that to the wheel.

We need to increase the power without dumping more fuel and keep foot off floor.
1. Exhaust mods
2. Airbox mods
3. Lift pump
4. ECU Tuning
5. TC Upgrade
6. Tires
7. Aero
8. Gear ratio
9. 6 speed manual and toss that TCU in the can.

A semi truck that weighs 80,000lbs can get 6.5mpg. The FE to weight ratio is incredible and makes everything else on the road look pathetic.

The weight is not what's killing mileage at highway speeds - it's the frontal area and wind drag. Do your same calculation with FE to frontal area ratio and I bet the difference is small between the three vehicles you name.

Threeweight · **Joined:** Mon May 14, 2007 5:57 pm **Posts:** 679

CATCRD wrote:

[The weight is not what's killing mileage at highway speeds - it's the frontal area and wind drag. Do your same calculation with FE to frontal area ratio and I bet the difference is small between the three vehicles you name.

My real world experience with a 2006 Jetta TDI bears this out. It is capable of 42-44 mpg highway, add a roof rack with a fairing and it drops to 34-36. That roof rack weighs all of 10 pounds, but the increased wind drag is enormous.

The second factor not considered in the listing above is mechanical friction. A front wheel drive car has inherently less mechanical friction (in the form of a heavy drive shaft, heavy rear axle, heavy tires and rims) to overcome than our CRDs. Though it might not be suitable for off roading (or look as cool), one could increase the MPG dramatically by sticking to a 225/75/16, highway tread tire (or low rolling resistance tread pattern, if such a thing exists in that size).

Might also save a bit by running a thinner synthetic oil in the real differential.

maxxgraphix · **Joined:** Wed Mar 26, 2008 8:11 am **Posts:** 53

Firestone Destination LE 225/75/16 is what I just put on. It has a 50psi max, so overinflated a few and I would call it a LRR.

Yes, that frontal air drag is a killer. But the CRD still needs more torque.

danoid · **Posted:** Mon Jun 16, 2008 12:13 pm

Threeweight wrote:

Though it might not be suitable for off roading (or look as cool), one could increase the MPG dramatically by sticking to a 225/75/16, highway tread tire (or low rolling resistance tread pattern, if such a thing exists in that size).

Michelin XPS Rib - 225/75R16 ($1100 for a set of five from a local shop) http://www.michelinman.com/tires/light-truck/xps-rib/08404/. Pump 'em up to 65 and they stay round sitting still. I can feel the reduced drag during a coast down, at 40 mph the aero stops mattering as much and the truck just sails on...

maxxgraphix · **Joined:** Wed Mar 26, 2008 8:11 am **Posts:** 53

After all the repairs / mods the MPG dropped to 23-24. WTF?!

New tires 225/75/16
Cat Gut + Magna Flow
ORM
new fuel filter + new head
MAP Clean
B20

Thought this would be a good combo, guess not.

Maybe clean the MAP again, better air filter?

Larry R. · **Joined:** Sun Jan 21, 2007 1:35 am **Posts:** 92

I think I'd give the computer a chance to 'learn', give it a couple tanks and check your mileage again.

05crd · **Joined:** Wed Jun 27, 2007 2:54 pm **Posts:** 47

What tires did you choose? If they are significantly heavier it will add a lot of rotational mass. You may also want to check the true dia as that would cause a change in the calculations.

maxxgraphix · **Joined:** Wed Mar 26, 2008 8:11 am **Posts:** 53

Firebomb Destination LE 225/75/16

Should be the same size as stock Goodyears. Weight was 33lbs (FireStone), 27lbs Goodyear.
That's 6lbs per tire. But the PSI is 50 vs 44.

Could it be that 6lbs dropped the FE by 3mpg?

Cat Gut + MagnaFlo

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