As promised, below is the dynograph. Dyno run #5 (red) is with the cats on and dyno run #7 (blue) is without. This morning was much hotter than when I did the first dyno with the cats on. For what it's worth, both numbers are SAE corrected.

As you can see, it is very dissapointed to find out that I actually lost ~5rwhp/tq across the curve when running catless. I couldn't believe it but numbers don't lie.:D. I guess the car does need some back pressure.

But on the bright side, this gives me a good excuse to put the cats back on.:D

:cheers:
-Tuan

Tuan,did you do 7 dyno pulls in 1 session?

No, the first dyno (#7) was few months back, right after I got my T1 cam and ASP pulley installed. And the second dyno (#5) was this morning after I took off the cats. Beside removing the cats, nothing has changed since then.

:cheers:
-Tuan

"Catless" means 02-sims correct? Did you get a retune to make sure the proper value of 02-sims were used?

Tuan,

How much of a hp gain did you get from your Cam? What did it cost you installed?

Thanks!

Frank

I love that '67.

Question - did you do any kind of tuning after you put the cam in? One explanation is that the cat removal messed up your air/fuel ration and that in turn made you lose power. What did the guys at MTI say about this? You may want to try autotapping the car and re-dailing the air/fuel ratio via MAFT and doing one more dyno...........just hard to believe you would lose power :confused:

Tuan, it was good to meet you and check out your ride. I posted pictures here: http://forums.corvetteforum.com/zero...768777#2768777.

My numbers were down too dude so don't feel bad!

Lates, Justin

Tuan, I told you guys to put those cats back on, now someone in a much higher place than me is telling you the same thing :D

I second the A/F issue. Also, re-learning of the PCM.

What was your new A/F?
How many miles on that setup before the dyno?

:lol: :lol: :lol:

Damn, I just wasted two hundred bucks ($100 to take them off and another $100 to put them back on). Could have spent that $200 on 7 nawesssssssss refills. :D

Let's see....1 refill = 7 runs. 7 runs @ 100hp jets = 700hp. And 700hp X 7 refills = 4900hp. :eek: :lol: :lol: :lol:

:cheers:
-Tuan

Thanks for the pics. They are looking good.

I think our numbers were lower is because today was way much hotter than the last time we dyno. Yeah...yeah....people can always argue about being SAE corrected, but I've seen several dynos from the same car that were +/- 10rwhp/tq.

I don't really care much on the dyno numbers since I can always jet up the juice. :D

-Tuan

I picked up almost exactly 40rwhp/tq from the cam & pulley. And the walk-out cost was ~$1400.

:cheers:
-Tuan

I think you lost power cuz your exhaust tips were crooked;) :lol:

:lol: :lol: :lol:

I didn't notice it until a few people pointed out this morning. Anyways, I will get it taken care of tomorrow. :D

-Tuan

I took the cats off few weeks ago and have put on at least 500 miles on since then so they PCM should have relearned it. And according to the autotap log on that dyno run, the air/fuel ratio was at .84.....that is a little lean, not rich. But then again, the reading is from stock O2's so I'm not sure how accurate it is.

I've autotapped my car several times at the track, after removing the cats & the O2 sims were installed, and the air/fuel readings are from OK to little lean on NA. On the gas, it was reading a little rich (around .939) but that because NX always jet their pills on the rich side to be safe.

:cheers:
-Tuan

I doubt you actually "lost" any power given the different numbers are well within the margin of error for different dyno times and conditions.

Worst case your power stayed the same. All things being equal, (equalizing for differences margins of errors in the dyno run) you do appear to have gained "some" overall power under the curve without the cats.

at least thats my perception. :cheers:

Thanks for pointing that out.

But anyways, it boiled down to messing with the stock cats is not worth the trouble and $$$ because of the little gains, if there is any. Several people have told me that before but I didn't believe them. And $235 later ($100 to take them off, $35 for the dynos, and $100 to put them back on), it turned out that they are right on.

:cheers:
Tuan