Anyone tested Cats for performance?
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From: Andrews TX
Anyone tested Cats for performance?
Eckler's lists at least 3 different Cats for C4 L98 with different performance claims for each.
Has anyone run actual performance tests on Cats to determine if there is a significant difference between a $150 Cat and a $300 Cat?
Has anyone run actual performance tests on Cats to determine if there is a significant difference between a $150 Cat and a $300 Cat?
Team Owner
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
There are flow tests published on the web. You can't figure the HP gain based on this, but more flow is more power.
Every test I've seen puts the $50 Carsound and expensive Random tech near the top of the pack. There is some newer bullet cats out now though that may beat both of those.
In short, the price means nothing.
Every test I've seen puts the $50 Carsound and expensive Random tech near the top of the pack. There is some newer bullet cats out now though that may beat both of those.
In short, the price means nothing.
Safety Car
Joined: Sep 2000
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From: Hinckley Ohio
There are flow tests published on the web. You can't figure the HP gain based on this, but more flow is more power.
Every test I've seen puts the $50 Carsound and expensive Random tech near the top of the pack. There is some newer bullet cats out now though that may beat both of those.
In short, the price means nothing.
Every test I've seen puts the $50 Carsound and expensive Random tech near the top of the pack. There is some newer bullet cats out now though that may beat both of those.
In short, the price means nothing.
Team Owner
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From: SE NY
Cruise-In II Veteran
There are flow tests published on the web. You can't figure the HP gain based on this, but more flow is more power.
To avoid HP losses go exhaust back pressure do the math:
-1chp needs 2.2cfm of exhaust flow
For example a 300chp engine needs 660cfm of flow; anything less will begin to take power away from the drive train. If your cat(s) flow ony say 500cfm, you will "free up" some power by installing a system that flows >660cfm.
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From: Andrews TX
A higher flow cat will no more add power than a higher flow intake will; it depends on what your engine "needs".
To avoid HP losses go exhaust back pressure do the math:
-1chp needs 2.2cfm of exhaust flow
For example a 300chp engine needs 660cfm of flow; anything less will begin to take power away from the drive train. If your cat(s) flow ony say 500cfm, you will "free up" some power by installing a system that flows >660cfm.
To avoid HP losses go exhaust back pressure do the math:
-1chp needs 2.2cfm of exhaust flow
For example a 300chp engine needs 660cfm of flow; anything less will begin to take power away from the drive train. If your cat(s) flow ony say 500cfm, you will "free up" some power by installing a system that flows >660cfm.
Team Owner
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Air flow is not black & white. Any cat will flow 660cfm if you put enough pressure into it. And your 660cfm cat will still be restricting flow at 500cfm.
Think of each component as a certain % of the losses in your intake+exhaust system. Let's say the intake base is 15%, TB is 5%, cat is 10%, etc.
So you could put a cat in that "flows" twice as good, but your system only benefitted by about 5%. Your intake accordian tube might be 2% of the total system. So you can see that improving it will still help the whole system, but the gains will be tiny.
Basically anything that is less restrictive will increase airflow by some amount.
(I won't get into tuned lengths or mufflers, that just confuses things.)
Team Owner
Joined: Aug 2000
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From: San Pedro CA
The L98 has the WORST exhaust system... short of the late C3s, of course.
This is what I would do:
Drop the ENTIRE exhaust system.
Install a pair of bullet cats about where the precats are.
Bend in pipe to fit an xpipe and then true duals towards the rear and then mufflers. the 02 can be put on the xpipe.
This will be worth about 40hp and will burn seriously cleaner than the stock exhaust.
This is what I would do:
Drop the ENTIRE exhaust system.
Install a pair of bullet cats about where the precats are.
Bend in pipe to fit an xpipe and then true duals towards the rear and then mufflers. the 02 can be put on the xpipe.
This will be worth about 40hp and will burn seriously cleaner than the stock exhaust.
Team Owner
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From: SE NY
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I couldn't find any actual flow numbers in the forum or on the web. Anyone know where there might be some?
Mfg........P / N......Flow........Price
Pyres......CVM13...450cfm....$71
It is a hi-flow SS bullet style cat w/ 3" in/out.
A pair of these would be good through ~410chp.
Air flow is not black & white.
My numbers come from one of David Vizzard's books on SBCs, ISBN 1-884089-34-8. Exhaust flow, much like intake flow is done at specific pressures for comparison purposes.
He has measured flow through various exhaust components and done dyno work for comparison.
The results show that above 2.2 cfm (under measurement conditions) per HP power loss due to back pressure was negligible.
Below that flow number power dropped off in a non-linear fassion. For example, by the time flow had dropped to 1.75cfm per chp power was down to 95% of the prior figure.
The L98 has the WORST exhaust system...
Though I do not know the flow of the stock cat I seriously doubt that it flows the 530cfm needed, even at the stock rating of 240chp, to keep from sucking up valuable HP.
Last edited by 65Z01; Apr 7, 2007 at 07:29 PM.
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Team Owner
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
The results show that above 2.2 cfm (under measurement conditions) per HP power loss due to back pressure was negligible.
Below that flow number power dropped off in a non-linear fassion. For example, by the time flow had dropped to 1.75cfm per chp power was down to 95% of the prior figure.
Below that flow number power dropped off in a non-linear fassion. For example, by the time flow had dropped to 1.75cfm per chp power was down to 95% of the prior figure.
Also, your cfm and chp are related, so you can't oversimplify it like that. What happened above 2.2cfm/hp? Did power drop off in a linear fashion, or not drop at all? I'll have to check out the book, I enjoy reading Vizards stuff.
Team Owner
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From: SE NY
Cruise-In II Veteran
Vizard is talking 660 cfm for the whole system,...
For example he states that a 2 1/2" pipe flows about 560cfm so a 3" pipe flows about 800cfm. Assuming my Flow Masters flow well too, this means my (w/ mandrel-bent front & rear Ys) system flows at least 800cfm, excluding the headers & cat. So the only way I can come close to achieving that flow is with dual cats.
Indeed the max HP & exhaust flow are related below 2.2cfm/chp. That relation is in fact non-linear, rather like a parabola. That is very flat up around 2.2cfm/chp but once you drop much below that number the rate of loss rises faster & faster.
I agree that, though his books have a lot of data and ideas, there are some tidbits that are gems.
In my case I'm suspecting that, if I went to a "test pipe" in place of the main cat, the stock headers might then be the bottle-neck.
In any case, since I normalize my trap speed for weather, a test pipe and a few passes down the 1/4 mile would tell the story.
Race Director
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St. Jude Donor '07
So, as a guess, what HP gain would you expect from:
TPIS Headers
RandomTech Cat
2.5" SST Cat-Back Exhaust
Borla LT Styles
(All From MAM)
Intake has CAI, K&N, and no porting on a '85.
Worth the $2k in parts & shipping?
Would you ditch the EGR?
TPIS Headers
RandomTech Cat
2.5" SST Cat-Back Exhaust
Borla LT Styles
(All From MAM)
Intake has CAI, K&N, and no porting on a '85.
Worth the $2k in parts & shipping?
Would you ditch the EGR?
Team Owner
Joined: Dec 2000
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From: SE NY
Cruise-In II Veteran
Yes I think experience has shown substantial gains from such mods.
There is no need to ditch the EGR as it is not called for by the ECM except under cruize type conditions and then only after coolant temp has gone above (I believe) ~175deg F. EGR is certainly not called for under WOT conditions.
Is the 25-30chp gain worth the $2k...well only you can answer that one. But my answer for me is "yes".
There is no need to ditch the EGR as it is not called for by the ECM except under cruize type conditions and then only after coolant temp has gone above (I believe) ~175deg F. EGR is certainly not called for under WOT conditions.
Is the 25-30chp gain worth the $2k...well only you can answer that one. But my answer for me is "yes".
Last edited by 65Z01; Apr 7, 2007 at 09:58 PM.
Team Owner
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Think of your exhaust parts like electrical resistors. CFM is current. Voltage is backpressure. Now hook up a bunch of resistors in series and put a voltage across the whole thing. The voltage across any one resistor depends on every other part of the system.
Race Director
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St. Jude Donor '07
Agreed. But my fluid dynamics days told me that a larger pipe with a short span of a smaller section will flow better than a full length of the smaller size. It's a coefficient of friction along the length, etc.
Not sure how directly this applies, other than to say it is easier to address those bottlenecks.
Not sure how directly this applies, other than to say it is easier to address those bottlenecks.
Team Owner
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
It's not very intuitive. Plus you have to consider it's not steady state air flow. You've got pressure pulses bouncing through there that are affected by the pipe size and length. And some mufflers/resonators can actually use this to pull a negative pressure in the the exhaust pipe.
I did some tests on a 3"x2" reducer just for fun. It was more restrictive flowing from the 2 to the 3 than the other way around. Who woulda guessed?
I did some tests on a 3"x2" reducer just for fun. It was more restrictive flowing from the 2 to the 3 than the other way around. Who woulda guessed?
Team Owner
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Nowhere (although some people put a 3x4 step increase right into the TB, bad idea). My point is it's not intuitive. And CFM ratings are solely for comparing one part to another, they say nothing about the whole system or what gains you'll get. Nothing at all.
Bench Racer
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From: Palm Beach Gardens FL
St. Jude '03 thru 14,'25
Alright, I'm getting into this late and perhaps my question isn't germaine to the discussion but I thought some back pressure was good. Or is back presure not considered restriction? I remember in the old days when the muffler finally rotted off one of my beaters, the car seemed to experience a loss of power...
Team Owner
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
No.
Some things will increase torque (and incidentally increase backpressure too), but the backpressure itself never helps.
A tennis ball will also increase backpressure.
A well tuned muffler can actually decrease backpressure over straight pipes at certain RPMs.
Some things will increase torque (and incidentally increase backpressure too), but the backpressure itself never helps.
A tennis ball will also increase backpressure.
A well tuned muffler can actually decrease backpressure over straight pipes at certain RPMs.
Team Owner
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From: Orlando FL
St. Jude Donor '08-'09
Don't even get me started... I have a nice collection of snake oil parts that I bought when I first got my car before I joined the CF and knew any better 
BTW, those aren't Ecklers claims, its from the lying manufacturers that send them that bad info.
BTW, those aren't Ecklers claims, its from the lying manufacturers that send them that bad info.