Could clogged cats cause this?

Reply Subscribe

Thread Tools

Search this Thread

Dec 7, 2001 | 03:53 PM

CHRISPY

Thread Starter

TECH Senior Member

Joined: Nov 2001

Posts: 10,341

Likes: 1

Could clogged cats cause this?

My car has been feeling a little flat up top lately.
Here are my mods:
ARE 360 with S1 blower ported heads and 221/221 114LSA 558 lift cam
Yank 4L70 tranny
12 bolt with spool 4.11s
dual 3inch carsound cats in MAC Ypipe with a 3inch extension and bullet muffler under the axle.

Dynoed today and my horsepower curve with the converter locked is almost straight across from 5000rpm and up. (spiked at 365RWHP and 404RWTQ)
I lost 2mph when I put the cats on the car (118mph to 116mph) (Best ET 11.70116.5mph with a half throttle 1.67 sixty in first with cats on the car)
I am wondering if they could be clogged up or would I have another issue. The cam should be peaking around 6400rpm.
Any ideas?
Thanks,
Chris
ps- My converter was flashing to 4800rpm on the dyno!! <img src="images/icons/shocked.gif" border="0">

[ December 07, 2001: Message edited by: Chris ARE 360 ]</p>

Dec 7, 2001 | 04:01 PM

RPM WS6

LS1Tech Administrator

iTrader: (3)

Joined: Nov 2001

Posts: 34,661

Likes: 2,592

From: Schiller Park, ILL Member: #317

Re: Could clogged cats cause this?

2 mph drop is like loosing ~20HP. That's a lot to lose for just adding cats. Usually for a good set of cats you only lose ~8 to 10HP...

Dec 7, 2001 | 04:02 PM

Dgarza

Teching In

Joined: Nov 2001

Posts: 19

Likes: 0

From: Houston TX

Re: Could clogged cats cause this?

<img src="graemlins/gr_cheers.gif" border="0" alt="[cheers]" /> usually when you put cats on a car, you decrease your performance a little. I think the two mph you are losing is pretty normal and actually pretty minimal considering one run was without cats and one was with. You will lose some sort of horsepower even with the Hi flo cats

hope this helps some danny

Dec 7, 2001 | 04:06 PM

CHRISPY

Thread Starter

TECH Senior Member

Joined: Nov 2001

Posts: 10,341

Likes: 1

Re: Could clogged cats cause this?

I am not so much worried about losing 2mph with cats as I am about the dyno graph being flat across from 5000-6500rpm when the cam should peak at 6400. This indicates a intake/exhaust restriction or a fuel/spark problem IMO. I am going to put on the offroad Ypipe and change the fuel filter and see if that helps.
Should run a lot better when it is all straightened out <img src="images/icons/grin.gif" border="0">
Chris

Dec 7, 2001 | 04:11 PM

RPM WS6

LS1Tech Administrator

iTrader: (3)

Joined: Nov 2001

Posts: 34,661

Likes: 2,592

From: Schiller Park, ILL Member: #317

Re: Could clogged cats cause this?

Unless the cat(s) is/are bad, you shouldn’t go flat from 5000 to 6500. That sounds like a bigger problem than just adding cats. Most guys only lose about 8-10 HP at peak, and maybe half that under peak.

Have you a-taped on the dyno? Maybe you’re getting real lean above 5 grand?

Dec 7, 2001 | 04:12 PM

CHRISPY

Thread Starter

TECH Senior Member

Joined: Nov 2001

Posts: 10,341

Likes: 1

Re: Could clogged cats cause this?

Nope no lean condition at all.
Things are solid fuel and timing wise.
I am going to switch to the offroad and dyno again next week if there is no snow. That will tell me if the cats are the problem.
Cheers,
Chris

Dec 7, 2001 | 04:17 PM

RPM WS6

LS1Tech Administrator

iTrader: (3)

Joined: Nov 2001

Posts: 34,661

Likes: 2,592

From: Schiller Park, ILL Member: #317

Re: Could clogged cats cause this?

Were the cats new, or used?

If used, maybe someone messed them up with heavy back-fire, race gas, poorly running engine, monster cam, etc.

If new, <img src="images/icons/confused.gif" border="0">