Tell me something about this dyno graph

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Oct 25, 2006 | 03:40 PM

black_89_vette

Thread Starter

Melting Slicks

Joined: Nov 2000

Posts: 2,469

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From: Winchester Ontario

Tell me something about this dyno graph

I ended up getting cheap cats. Right, about $40 a piece cuz I thought a hi flow cat is the same as any other hi flow cat , just difference in price due to name brand.

Well, from 4000 RPM up, it only makes 15 more hp and looks like it's running out of breath. My hp curve looks like a damn tq curve. I'm thinking that the cheapo cats I have just don't flow enough.

As RPM rises, the need for more airflow (cfm) rises in order to make more power. Maybe the cats I have only flow enough to make power at 4000 RPM and won't flow anymore?

I'm doing some engine work over the winter and will be buying new cats, probably some off tjwong, as I've heard he has some nice ones.

Is my assumption correct about the cheapo cats not flowing enough and my engine not making power over 4000 because of this?

**FYI**

This basically same engine combo 4 years earlier and precat made 305 rwhp and 398 rwtq on a Mustang dyno, which people say usually reads as much as 10 % less than a dynojet, so it makes me wonder why I'm so low on hp after cats install.

**EDIT**

Sorry, stupid me... it's an 89 with a Super Ram installed on top of a 383 through a ZF6. Hooker #2149 true duals with an H pipe. Cam is 222/226 0.464" (weak I know) running on port n polished 113's ( no flow #'s)

Last edited by black_89_vette; Oct 25, 2006 at 03:57 PM.

Oct 25, 2006 | 04:01 PM

Aardwolf

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Joined: Jun 2004

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From: WI

I can't tell by a dyno graph anything about your cats, but it does look like at 4,000 RPM you are getting a bit to lean. Add some fuel pressure.

Oct 25, 2006 | 04:02 PM

65Z01

Team Owner

Joined: Dec 2000

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From: SE NY

Cruise-In II Veteran

You are making about 340-350 hp at the crank so need about 750-770 cfm from your exhaust system.

With true duals that amounts to 375-385 cfm per side. Even 2 1/2" mandrel-bent pipes will flow 560 cfm each, so that is not the problem.

What do those cats flow and how much for the mufflers??

Oct 25, 2006 | 04:28 PM

black_89_vette

Thread Starter

Melting Slicks

Joined: Nov 2000

Posts: 2,469

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From: Winchester Ontario

I run Flowmaster 2 chamber 40 series mufflers , so there's not much restriction through them.

The cats I bought were called Thunderbolt or something very similar and I am having some issues finding any info on them at all on the net.

A friend told me that cheap cats only flow like 250-300 and the real good ones flow like 450-500 cfm. So, if they only flow like 250-300 cfm, would that be the cause of my lost power?

I don't think the pipes are mandrel bent either. Doesn't that involve a special machine or something? My mechanic made my exhuast system up for me, small town of 5000 people. Nothing special done to my exhaust, just bent to fit, mostly straight back though.

Oct 25, 2006 | 04:46 PM

88BlackZ-51

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From what you told me, you paid around $40 per cat. Rule of thumb is you get what you pay for. I am willing to bet that they really arent high flow cats.

I need to get some cats soon, So we should go in on it, and see if we can get a deal for four high flow magnaflow's.

http://www.car-sound.com/02product/d...niversal=59958

Oct 25, 2006 | 05:04 PM

black_89_vette

Thread Starter

Melting Slicks

Joined: Nov 2000

Posts: 2,469

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From: Winchester Ontario

Found some basic info on the cats.

THunderbolt Part #410300

"Thunderbolt cat's are designed to give high performance in limited spaces. This high flow converter features a ceramic brick with 300 holes per square inch. This 100% EPA legal catalytic converter is designed for engine's up to 5.9L / 6000 lbs."

http://cgi.ebay.com/ebaymotors/ws/eB...0420245&rd=1,1

Oct 25, 2006 | 07:09 PM

tjwong

Le Mans Master

Joined: Jan 2003

Posts: 8,596

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From: Portland Oregon

Quote:

Originally Posted by black_89_vette

That is a ceramic substrate CAT that flows considerably less than a comparable size with a mettalic substrate internal. The main reason is because the Ceramic cores has a 100 cell count per sq/in while the metallic cores have a 200 cell count.