I've had the new Powerflo system on for almost 2 weeks and have well over 500 miles on it. I like the sound and the looks, but I've found a significant problem.

Pros:
Looks great
Sounds great (especially at full throttle in an underpass)
Fits nicely

Cons:
Does have some drone at cruise, but not too bad
Significant torque loss
Significant mileage loss

I've noticed in "normal" driving that the torque is certainly down from the Flowmasters that were on it before - and that was already going down ans they rusted away inside, so this is much worse. This morning I did a hill climb (Hwy 92 from 101 up to Ralston) that I could previously do in 6th gear - I had to drop down to 4th just to maintain speed uphill without using half throttle. Also, last week I had a chance to run it up through the gears from a stoplight (late at night on a deserted stretch of road) and going up through 1st, 2nd, and 3rd was not nearly as impressive as before. Grabbing 2nd with the TC turned off was nothing special where with the Flowmasters it would be serious tire spin.

Mileage has dropped radically. I ran my same mileage test route this morning. Previously I got consistent 36 mpg (+/- .5 mpg). Today I got 29.9. That jives with the recent refill rate as I've gone through 4 tanks already in less than 2 weeks and am already at half a tank again for my typical driving. I'll fill up tomorrow morning. I'm usually at 2 tanks a week without extra driving.

I can see where the torque loss could easily cause the mileage loss. I keep having to drop down several gears to get up to speed or need to use much more throttle to maintain speed than I did before.

I asked about bigger injectors here http://forums.corvetteforum.com/c5-t...r-my-99-a.html because I really feel like the car is lean. I'm going to go ahead and try them just to see what happens. I think I'm also going to take it back to TPS for another dyno session to see what the real numbers are.

Before you ask, no, it didn't pick up anything on the top end to counter the low-end loss. It just appears to be a loss at lower speeds and either a push or a loss in mid-range and upper RPM as well.

No difference in running regular or premium. It's just not making the same power that it did before.

Comments/questions/ideas?

 

OK, I'll play..... I'm of the opinion that a catback change would not result in any significant differences in the performance, or mileage that you think you're experiencing. On another note; if you were getting over 36 mpg before, you must have the patience of Job, and the feather-like touch of the infamous "Ballonfoot Bodine".

 

Not so much patience, just letting it do it's thing:

skip to about 1:20 for the 65 mph cruise test


A little while back I did a test driving to my job in Santa Clara - no cruise just careful throttle use - 36.6 for the average.

 

You have some other problem that just occurred near the same time as the catback swap. No way could your problems be caused by just a swap. SLP would be out of business in a heartbeat. Have you pulled codes?

 

How do your dic mileage numbers compare to miles driven divided by gallons consumed per tank?

 

Yep. Put your old cat back on.....and see if order is restored to your "green" C5.

 

yes to the comments and idea..... my comment and idea is.... I'll swap you my modded Ti's for your PowerFlo system.

 

I just go by the DIC since I have been so busy I can't keep track of mileage and gas purchases.

 

No codes, no CEL, nothing unusual other than what I've described in the first post.

 

4 tanks of fuel to go a little more than 500 miles?

A change from driving up a hill in 6th to needing to use 4th to climb the same hill at the same speed?

A 6mpg change in your fuel mileage?

There is no way this big a change is caused by the catback unless something is seriously wrong with it. Not a chance.

Something is wrong but it's not caused by a slight change in the flow capabilities of a catback.

Don't believe the "a more open exhaust hurts the low end torque" BS on the internet. That DOES NOT apply to the catback. If you can be bothered to search you will easily find 3 or 4 different catback dyno compare graphs or tables and they all show a slight increase in power through the whole rpm range. It's possible with a full exhaust to hurt the low end torque but a few of the header companies can provide you with dyno curves which show that even 1-7/8" headers don't hurt the low end power.

Peter

 

Peter,
I don't recall the actual mileage when I installed the system I could easily have 1,000 miles on it already. I know the mileage was below 77K, I'll check it tomorrow morning to see what it is now.

I know something is seriously wrong - it just happens to coincide with the cat-back swap. It could be something else. I'm going to give it a good check-out tomorrow before I leave for work.

 

That makes more sense, 1000+ miles would be around 4 tanks of fuel.

Yes, something has certainly changed but I still doubt it's the catback itself. You likely need to do some data logging to make sure everything the ECM is seeing looking OK and take it from there.

Peter

 

Well I hope you figure out where your power went but the car sounds great. I wish my LG's/TI's sounded that good. Makes me think about going to shorties. (flame suit on)

 

Thanks, I'm really pleased with the sound. I was great driving it in the city - idiots about to cross against red lights heard it and looked instead of stepping out into the street in front of me.

 

After checking everything out carefully this morning I found the cause of the problem. Yesterday I burned off more than 1/2 a tank of gas for the 85~90 mile round trip to work, with a small detour into SF. Everything was completely normal under the hood, and no codes at all. Since I was now down to reserve gas, I went to Arco and tanked up. Within a couple of miles, everything was back to normal! Recently I'd been buying gas at random places due to being way too busy - I guess I know better now.

CLIFFS: It was BAD GAS!!!!!

Yep, back to 35+ mpg on my standard mile test route, throttle response back to normal, torque feels like it's back to normal. I'm still going to take it to TPS for another dyno session next week just so I have a direct comparison between this and the previous setup.

Matt, thanks for meeting me last night to get me the injectors! I may still try them just to see what happens, or they might just sit in the "projects nor later down the road" box at home.

 

Your instant mileage reading is completely meaningless. You shouldn't say you get "36.6 mpg" when in reality, it's much less. Catbacks are for sound only. You get as big a power boost with a "turbonator" .

 

Sure no problem, glad to hear it's back running like it sounds.

 

For those of you still watching this thread, I finally had a chance yesterday to make a short video of the Powerflo system. Sorry about the rattling and squeeking noises from the camera mount, I'll have to find a better one.