Lost 35 ft lbs of torque with high flow cats ???

[Ryder]

Had high flow stainless works cats instaled and a tune done. 433 hp 429 torque was my numbers pre tune . I am now at 433 hp 394 ft lbs or torque lost 35 ftlbs Do high flow cats really restrict torque numbers that much? My tuner said when ever he tried to tune the torque numbers the a/f numbers got wonky. Is there any logic to this? Thanks

[InFiD3ViL]

Is this a stock heads/stock cam car? Bolt ons?

Trying to wrap my head around those numbers without knowing any of your mods.

[Ryder]

Originally Posted by InFiD3ViL

Is this a stock heads/stock cam car? Bolt ons?

Trying to wrap my head around those numbers without knowing any of your mods.

yes it is. cai, vmax, 1 7/8 lt headers to 3 in outlaw cat back was the original mods. Added 3 in stainless works cats and lost the torque. I was expecting a drop just not that much . just seems High. Thank you

[PepeLePew]

Did you go from offroad pipes to HFCs? I would expect a low single digit drop at most given the mods you have.

Do you have the full dyno graph before and after to compare what the curve looks like? You would have to be making the same torque at the RPMs where your peak HP came in as before, which makes me think something is going on in the lower end of the power range where torque usually peaks. I'm wondering if your before had either a spike in the graph giving you a false reading or if there is a dip in the graph after the HFCs were installed. If your graphs have AFRs on them too, I wonder if it was too rich at lower RPMs. Also, do you know what timing the tuner used? If it was too high at lower RPMs maybe there is Knock retard pulling power.

Graphs and Logs would be helpful to see if there is a problem

[shibbs]

Originally Posted by PepeLePew

Did you go from offroad pipes to HFCs? I would expect a low single digit drop at most given the mods you have.

Do you have the full dyno graph before and after to compare what the curve looks like? You would have to be making the same torque at the RPMs where your peak HP came in as before, which makes me think something is going on in the lower end of the power range where torque usually peaks. I'm wondering if your before had either a spike in the graph giving you a false reading or if there is a dip in the graph after the HFCs were installed. If your graphs have AFRs on them too, I wonder if it was too rich at lower RPMs. Also, do you know what timing the tuner used? If it was too high at lower RPMs maybe there is Knock retard pulling power.

Graphs and Logs would be helpful to see if there is a problem

Yeah, something tells me your tune is the reason for the difference.
Tune on different days, even on the same dyno, WILL yield different results.

HFCs should NOT rob 30 ft lbs. If they'd reduce anything, I'd expect a drop in HP to be greater than TQ.

[Ryder]

Originally Posted by PepeLePew

Did you go from offroad pipes to HFCs? I would expect a low single digit drop at most given the mods you have.

Do you have the full dyno graph before and after to compare what the curve looks like? You would have to be making the same torque at the RPMs where your peak HP came in as before, which makes me think something is going on in the lower end of the power range where torque usually peaks. I'm wondering if your before had either a spike in the graph giving you a false reading or if there is a dip in the graph after the HFCs were installed. If your graphs have AFRs on them too, I wonder if it was too rich at lower RPMs. Also, do you know what timing the tuner used? If it was too high at lower RPMs maybe there is Knock retard pulling power.

Graphs and Logs would be helpful to see if there is a problem

yes went from off road pipes with a step down to 2.5 in. Now straight 3 in with hf cats. Both original curve and new curve on both tq and hp were smooth with no dips or spikes.

[InFiD3ViL]

Those are some amazing numbers for a bolt on only car. Kind of goes along with the myth of 1LE's being factory freaks.

Of course, I understand completely that every dyno is different and some are very generous, but it's hard not to notice how high many of the 1LEs dyno.
Does the 1LE have an identical tune to the manual SS's of the same model year? If not, I am wondering if that is where this may be coming from.

[pyroguy]

I'd say either the dyno is off or your tune is off. You 1, shouldn't lose that kind of power adding HFC's, and 2, shouldn't be that far down on a M6 car. A friend of mine here has SW 1 7/8" headers w/ high flow cats, out SW retro chambered catback (3" exhaust from the collectors back) and made 427hp 431tq.

[PepeLePew]

Originally Posted by Ryder

yes went from off road pipes with a step down to 2.5 in. Now straight 3 in with hf cats. Both original curve and new curve on both tq and hp were smooth with no dips or spikes.

Were your AFRs the same across both pulls. If the "After HFCs" pull was richer down low in the power band but the same up top as the "before HFCs" pull, then you'll get the same peak HP with lower peak torque. The same is true for timing. If there is too much timing causing knock in the low end of a pull but just the right amount of timing up top when peak HP hits, your Peak HP will be the same but your peak torque will drop.

I am pretty confident this is a tune issue if the pulls were made on the same dyno with consistent correction factors. The shape of your HP and torque curve should be nearly identical before and after cats. Your peak numbers suggest that you are down in torque and HP in the low end but equal on the top end.

[Ryder]

Originally Posted by PepeLePew

Were your AFRs the same across both pulls. If the "After HFCs" pull was richer down low in the power band but the same up top as the "before HFCs" pull, then you'll get the same peak HP with lower peak torque. The same is true for timing. If there is too much timing causing knock in the low end of a pull but just the right amount of timing up top when peak HP hits, your Peak HP will be the same but your peak torque will drop.

I am pretty confident this is a tune issue if the pulls were made on the same dyno with consistent correction factors. The shape of your HP and torque curve should be nearly identical before and after cats. Your peak numbers suggest that you are down in torque and HP in the low end but equal on the top end.

Pretty close to the same. The shape of both torque curves is identical minus 30 hp.

[Ryder]

Originally Posted by InFiD3ViL

Those are some amazing numbers for a bolt on only car. Kind of goes along with the myth of 1LE's being factory freaks.

Of course, I understand completely that every dyno is different and some are very generous, but it's hard not to notice how high many of the 1LEs dyno.
Does the 1LE have an identical tune to the manual SS's of the same model year? If not, I am wondering if that is where this may be coming from.

Pretty sure the 1les were factory freaks. Most seem to have great numbers. Similar ss with same mods only made 412 on same dyno. Not a 1le. Made more torque tha. Me thoug

[J Rod]

FWIW.... My 1LE made 425/410 with CAI, PTB, 1-7/8 LTs w/ HFCs, and RDP tune.

[frankwjr]

where are the AFR sensors located? Before or after the cats? If after then that is most likely the the prob.


Your tuner put in a "safe" tune so you would not melt something going lean.


good luck!


peace

[Ryder]

Originally Posted by PepeLePew

Did you go from offroad pipes to HFCs? I would expect a low single digit drop at most given the mods you have.

Do you have the full dyno graph before and after to compare what the curve looks like? You would have to be making the same torque at the RPMs where your peak HP came in as before, which makes me think something is going on in the lower end of the power range where torque usually peaks. I'm wondering if your before had either a spike in the graph giving you a false reading or if there is a dip in the graph after the HFCs were installed. If your graphs have AFRs on them too, I wonder if it was too rich at lower RPMs. Also, do you know what timing the tuner used? If it was too high at lower RPMs maybe there is Knock retard pulling power.

Graphs and Logs would be helpful to see if there is a problem

Here is the dyno sheet hope this helps.