High flow cats....

[2charmed]

Anyone have any experience with high flow cats? Are they worth
putting on? Any noticable differance?

Thanks,
Steve

 

[treynor]

Absolutely yes. I picked up an average of 9HP and 11 ft/lbs through the powerband when I switched from stock to high-flow cats. See my other posts in performance modifications, or at ViperMods

Roe Racing sells some excellent high-flow cats.

 

[Sean Roe]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by JonB - PartsRack:
The Viper NEEDS some back pressure to make peak HP and TQ, so
if you have no mods, and a 3" cat-back, the stock cat is probably OK...
<HR></BLOCKQUOTE>

Minor clarification:
Normally aspirated gasoline engines need the proper exhaust "velocity" (not backpressure) so that the next cylinder benefits from the scavenge effect. This helps pull more "used" air from the cylinder on its exhaust stroke, allowing the cylinder to then get more "clean" air and fuel on its intake stroke. Exhaust valve opens, flows through the pipe at a high velocity, exhaust valve closes, vacuum forms in the pipe behind the air flow, pulls more air out of next cylinder and so on. That's what makes power. Restriction and backpressure is a different issue.
PS. This may not be the gospel, but is what I've come to learn and understand after many years of working in motorsports.

 

[Robert Dyck]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Sean Roe:
Minor clarification:
Normally aspirated gasoline engines need the proper exhaust "velocity" (not backpressure) so that the next cylinder benefits from the scavenge effect. This helps pull more "used" air from the cylinder on its exhaust stroke, allowing the cylinder to then get more "clean" air and fuel on its intake stroke. Exhaust valve opens, flows through the pipe at a high velocity, exhaust valve closes, vacuum forms in the pipe behind the air flow, pulls more air out of next cylinder and so on. That's what makes power. Restriction and backpressure is a different issue.
PS. This may not be the gospel, but is what I've come to learn and understand after many years of working in motorsports.


<HR></BLOCKQUOTE>

=============================================================
Sean: I'm not so sure that restrictions and back pressures are unrelated issues to flow velocities. Would not back pressure, which is a result of flow restriction, be a measure of static air pressure? I think it would.

Air velocity is related to the static air pressure in the air flow. The higher the velocity, the lower the static pressure within the flow. The reverse is true.

Therefore, in general, I think that exhaust systems having less restriction to flow would have lower static pressures in the exhaust flow, and this would allow for higher velocities.

In general then, we should have improved scavenging with less restrictive exhaust systems.

 

[JonB]

That depends........the best answer: probably !

Gen-1 cars will benefit far more than GenII. But the HP is real.
Esp important if you have other mods up front that make the motor flow better: (headers/TBs, roller-rockers)

The Viper NEEDS some back pressure to make peak HP and TQ, so
if you have no mods, and a 3" cat-back, the stock cat is probably OK...

(PartsRack has some hi-flow bullet cats for 2.5" and 3" applications......they will "flap your pantslegs" 5' behind
the car! Howz THAT for a seat-of-pants flow-test?!?)

 

[Sean Roe]

Robert,

Other than the last sentence in that paragraph, you and I are basically agreeing on the same thing.
I didn't take the time to say it properly, but was trying to get the point across that a catalytic converter that flows less and causes restriction / backpressure in the exhaust, is not what it takes to make peak horsepower and torque. I've never seen a Viper make more horsepower and torque with a stock cat compared to a high flow cat. The stock cats are very restrictive (don't flow well).

Thanks,

 

[SpeedRacer]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Sean Roe:
Robert,

Other than the last sentence in that paragraph, you and I are basically agreeing on the same thing.
I didn't take the time to say it properly, but was trying to get the point across that a catalytic converter that flows less and causes restriction / backpressure in the exhaust, is not what it takes to make peak horsepower and torque. I've never seen a Viper make more horsepower and torque with a stock cat compared to a high flow cat. The stock cats are very restrictive (don't flow well).

Thanks,

<HR></BLOCKQUOTE>
If the stock cats are so restrictive, then why are people only picking up a few hp with hi-flo cats? This seems to be true, even with headers and cat-back systems installed.

 

[Fred(DrivingSchool)Kinder]

A few months ago a test (engine load dyno) using stock cats and no cats showed a 30 hp drop with the stock cats on a modified engine. 635 w/o and 605 with cats. Dan Cragin is going to finalize the engine tuning within the next 2 weeks. He will test the RWHP with and with out the cats. Then each exhaust config. will be checked to verify if they need to be tuned differently to max. performance. This will be an interesting Test/set-up/evaluation. I know Dan has tried a couple high flow cats and they do not provide the same HP gain. Stay tuned for Dan's results.

 

[tzoid]

It's just when you think you know a little about engines, that you read some of these responses and you get snapped back to reality. He's my 2 cents worth.....the hi-flo cats make the sound of the car much better. Deeper, throatier, the way most car types like an engine to sound (i.e. better than the stock cats). Additionally, they are legal in case you live in an area with emissions testing or feel a responsibility to stay within the boundaries the environmental regs. Is the car faster? Dunno, feels strong to me!

 

[Sean Roe]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by JonB-Pace Car Pilot:
2charmed Steve and Speedracer asks the question: WHEN are no-cats a bonus? I have seen several near-stock GenII motors w/ 3" exhausts actually LOSE TQ numbers and small HP numbers when going catless. (The answer is "what ELSE you gonna do?)

However, the mentioned test about Dan C, (cats vs no cats on a 600HP motor) is no "test" and no surprise at all ! Its a DUHHH ! Im only surprised that a 600+HP motor lost ONLY 30HP with a stock cat setup! I would have suspected more loss. This proves to me the OEm cats are fairly high-flowing. (They are)

The REAL TEST is, what HP and TQ would there have been w/ stock cats, vs. genuine hi-flow cats, (ie not some truck pre-cat) and No Cats.
<HR></BLOCKQUOTE>

Jon,
I didn't see in Fred's post where he said that Dan tested the stock cats against truck pre-cats?

Fred,
Have Dan get in touch with me and I'll loan you two 3" genuine high flow cats to test on that engine if you'd like. We use the best engineered ones for the job and I'd love to have some engine dyno numbers comparing them to the stock cats. Generally, Vipers pick up between 9 and 17 rear wheel horsepower with the ones we're using. That's easy horsepower for the money, and it sounds nice too!

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Shop around, there are some others available that flow about the same, but don't have the metallic compression ring that holds the substrate in place. Without it, the exhaust pulses of the V10 can cause the substrate "biscuits" to move and fail prematurely.

 

[Fred(DrivingSchool)Kinder]

Hi Sean, I will contact Dan tomorrow and ask him to give you a call you. I know he is pretty busy at work and home so you may want to give his Viper tech line a call, 310 395 2314. I think he has looked at a couple "high Flow Cats" that were not suitable. I wonder I Jon want to put his "high flow cats" to the test? Perhaps not? as a 600 hp engine is no test for JonB's cats?

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[PhilC]

Hey JonB, you must be doing some thing right for these other vendors to be so agressively sparring with you. I guess your business is doing too well for their liking.

By the way, the cats you shipped me were waiting on the door step for me when I got home. Can't wait to get them on. I'll be happy to post my thoughts on them after I have heard/felt their effects/affects

Phil

 

[Jack B]

94 Gen 1 with Balenagers, dynamax, and Sean's oval cats (3" all the way)

1. 404 rwhp and 471 ft lbs of torque at the rear wheel.

2. The sills at the cats run approx 20 degrees above ambient when moving - that is about 25-35 degrees cooler than stock

3. The sound at cruise is healthy and very livable. The sound at lower speeds is very loud, but, bearable. It might offend some.

4. Throttle response at all rpm's is smoother and more powerful. The item that a lot of people are missing is the fact that an almost stock Gen 1 motor can put out almost 550 ft lbs of torque at the flywheel.

5. An earlier post suggested that the cat be placed forward. Sean's oval cats can't be placed to far forward. The sill flares out to the rear. If you don't want rattles and the cats touching the sill, they have to go to the rear.

 

[DonMc]

so how many folks who have put on hi-flo cats have trouble with engine light?? i have tnt headers, 3" hi-flo cats and 3" catbacks and the engine light stays on...haven't been able to check the code but i suspect due to o2 sensors..not sure if this is the headers or cats or both..man, i hope i pass emmission testing this month!..this is on a 00 gts acr...

 

[Dan Vargus]

No race cars have cats!!!! Street cars have cats! Some back pressure helps tork. Too much back pressure anything over 2 1/2lbs seems to reduce both TQ and HP. Think of the advantage dirt bikers get when they apply the proper amount of restrickters to the exhaust. Tuning the exhaust to YOUR own car will creat different results for other cars. Only good answer, take various systems to a dyno bolt'em on and read the sheets. Imports are finding high gains with the right set-ups Vipers can to.
I vote for more flow......
Dan Vargus/PartsRack

 

[Fred(DrivingSchool)Kinder]

Just spoke with Dan Cragin. If you want Dan to evaluate your product and report the test result of your high flow cats call him and send your product. There will be a charge for the dyno time and installation. The engine being used for this test is slightly modified making 635 HP without cats on an engine dyno.

 

[Robert1994]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Fred(DrivingSchool)Kinder:
Just spoke with Dan Cragin. If you want Dan to evaluate your product and report the test result of your high flow cats call him and send your product. There will be a charge for the dyno time and installation. The engine being used for this test is slightly modified making 635 HP without cats on an engine dyno.

<HR></BLOCKQUOTE>

Touche' !
Please let me know who is "most macho", I need to repair/upgrade
my system very soon. I'd like to see the results on gen 1 cars
with and without cat's (cat's not needed in Hawaii).