How Much Do S4 Cats Affect Power?
10-02-2003, 03:33 AM
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How Much Do S4 Cats Affect Power?
At what horsepower level does it start to make a difference? I think I read that the S4 cats were relatively high-flow & rated for 400 hp? Anyone have any dyno results on S4 cats vs. bypass on higher output engines? Any anecdotal info? If that is the case, then I should probably upgrade... I really like how quiet it is now, though, so I may be against a tough choice.
10-02-2003, 03:53 AM
#2
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Old&New,
Just depends on how much boost you plan to run. I'm not sure of the HP "rating" of the cat, but the bottom line is this - on a dyno, swapping a NON-clogged S-4 style dual-cat with a "test pipe" will net you 5-8 HP. Maybe. The most I've ever seen was 10HP, and those cats had a LOT of miles on 'em.
If you have a high-output motor, you need higher performance cats. These are readily available off the shelf for all sorts of apps, just find 2 units capable of handling a built 2.5 L 4 banger. You'll pay less for a pair than for a factory replacement, and they will flow pretty much anything you can throw at them, with very minimal restriction.
They only become a real obstruction at higher r's, and if you need it that for a track car, it may matter. If you really want to free up the exhaust, eliminate the rear muffler - or at least replace it with a drilled baffle hole straight through design - no silly delta flow, or punched holes, or such like, just a high quality straight through design.
You will definately gain some dB, but more HP than elimation of the cats and retaining the stock rear muffler will provide. Then there's the whole environment angle which I won't bother to preach on.
Greg
Just depends on how much boost you plan to run. I'm not sure of the HP "rating" of the cat, but the bottom line is this - on a dyno, swapping a NON-clogged S-4 style dual-cat with a "test pipe" will net you 5-8 HP. Maybe. The most I've ever seen was 10HP, and those cats had a LOT of miles on 'em.
If you have a high-output motor, you need higher performance cats. These are readily available off the shelf for all sorts of apps, just find 2 units capable of handling a built 2.5 L 4 banger. You'll pay less for a pair than for a factory replacement, and they will flow pretty much anything you can throw at them, with very minimal restriction.
They only become a real obstruction at higher r's, and if you need it that for a track car, it may matter. If you really want to free up the exhaust, eliminate the rear muffler - or at least replace it with a drilled baffle hole straight through design - no silly delta flow, or punched holes, or such like, just a high quality straight through design.
You will definately gain some dB, but more HP than elimation of the cats and retaining the stock rear muffler will provide. Then there's the whole environment angle which I won't bother to preach on.
Greg
10-02-2003, 09:50 AM
#3
Three Wheelin'
By Old & New
Anyone have any dyno results on S4 cats vs. bypass on higher output engines?
Anyone have any dyno results on S4 cats vs. bypass on higher output engines?
My original 492 rwhp dyno was with factory exhaust manifolds, cats, air pump, small GT resonators, and an RMB.
My new exhaust system will consist of factory exhaust manifolds, Ott x-pipe, 2.5” mandrel bent pipes, DynoMax mufflers where the resonators reside, and another DynoMax dual 2.5” inlet/outlet where the factory muffler resides.
When I dyno the new combo, the results should prove interesting and answer many outstanding questions regarding the factory setup and it's cats.
Since predictions are so much fun, let’s do one now and ‘see’ how much the new exhaust might be worth.
First and foremost, we always start out with the engine’s normally aspirated (NA) power, which in my case is an S4 with 316 crank hp.
According to the knowledgeable Jim Bailey, he reports that a fellow 928 International employee installed a somewhat similar exhaust onto his GT and netted approximately 30 rwhp; not bad considering no headers were used!
However, my car is an S4 with a much milder cam, so I won’t net the same gains I am sure. With that said, I’ll guess that maybe I’ll get an additional 20 rwhp NA with my new exhaust.
So let’s figure the approximate crank hp gain using 15% drive-train loss:
20 rwhp x 1.15% = 23 crank hp
New NA Crank HP = 316 hp + 23 hp = 339 crank hp.
Now that we have the ‘new’ NA crank hp, what is it’s 11 psi horsepower numbers?
Using the ‘standard’ 85% inter/after cooler efficiency, the spreadsheet reports:
535.44 rwhp.
Well, we’ll see for sure when I dyno it and post the results. You guys can hang me (..rightfully so) if I’m off! But I'm hopeful that we'll have some interesting things to discuss regarding the results and what they imply.
10-02-2003, 02:40 PM
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Originally posted by Old & New
How Much Do S4 Cats Affect Power? At what horsepower level does it start to make a difference?
How Much Do S4 Cats Affect Power? At what horsepower level does it start to make a difference?
Originally posted by Lagavulin
Using the ‘standard’ 85% inter/after cooler efficiency, the spreadsheet reports:
535.44 rwhp.
Well, we’ll see for sure when I dyno it and post the results. You guys can hang me (..rightfully so) if I’m off! But I'm hopeful that we'll have some interesting things to discuss regarding the results and what they imply.
Using the ‘standard’ 85% inter/after cooler efficiency, the spreadsheet reports:
535.44 rwhp.
Well, we’ll see for sure when I dyno it and post the results. You guys can hang me (..rightfully so) if I’m off! But I'm hopeful that we'll have some interesting things to discuss regarding the results and what they imply.
10-02-2003, 02:48 PM
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I think it is awesome to do the math first, make predictions, then post results.
If you are right, it backs up a lot of the other math you guys have been doing...
If you are right, it backs up a lot of the other math you guys have been doing...
10-02-2003, 03:21 PM
#7
Where is your guy getting the mandrel bent tubing Lag?
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10-02-2003, 03:33 PM
#8
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Brendan .... Allied exhaust systems 1-800-800-4746 supplies all kinds of tubing , mandrel bends , stainless etc... they have a distributor in San Diego ..sell to muffler shops .
10-02-2003, 03:43 PM
#9
Thanks Jim. I had an exhaust made for my 81, and I was hoping it woudl fit my 89, but the 89 seems to have a bunch more room for the dual mufflers next to the trans.
10-02-2003, 06:31 PM
#11
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Make sure you use the righ math though!
20hp with a 15% loss you divide by .85, not multiply by 1:15.
20hp would then be equal to 23.5hp.
400hp is more like 470Hp flywheel. but remember, this figure is probably near the 5000 to 6000rpm range. its not fixed at some eff number (ie 15% ) its probably more like a range of 8% to 15% depending on the speed. some of its drive train related, some of its rolling friction related!
mk
math police
20hp with a 15% loss you divide by .85, not multiply by 1:15.
20hp would then be equal to 23.5hp.
400hp is more like 470Hp flywheel. but remember, this figure is probably near the 5000 to 6000rpm range. its not fixed at some eff number (ie 15% ) its probably more like a range of 8% to 15% depending on the speed. some of its drive train related, some of its rolling friction related!
mk
math police
Originally posted by Lagavulin
Tomorrow I'm having a custom made mandrel bent exhaust system installed, and will dyno it soon thereafter.
My original 492 rwhp dyno was with factory exhaust manifolds, cats, air pump, small GT resonators, and an RMB.
My new exhaust system will consist of factory exhaust manifolds, Ott x-pipe, 2.5” mandrel bent pipes, DynoMax mufflers where the resonators reside, and another DynoMax dual 2.5” inlet/outlet where the factory muffler resides.
When I dyno the new combo, the results should prove interesting and answer many outstanding questions regarding the factory setup and it's cats.
Since predictions are so much fun, let’s do one now and ‘see’ how much the new exhaust might be worth.
First and foremost, we always start out with the engine’s normally aspirated (NA) power, which in my case is an S4 with 316 crank hp.
According to the knowledgeable Jim Bailey, he reports that a fellow 928 International employee installed a somewhat similar exhaust onto his GT and netted approximately 30 rwhp; not bad considering no headers were used!
However, my car is an S4 with a much milder cam, so I won’t net the same gains I am sure. With that said, I’ll guess that maybe I’ll get an additional 20 rwhp NA with my new exhaust.
So let’s figure the approximate crank hp gain using 15% drive-train loss:
20 rwhp x 1.15% = 23 crank hp
New NA Crank HP = 316 hp + 23 hp = 339 crank hp.
Now that we have the ‘new’ NA crank hp, what is it’s 11 psi horsepower numbers?
Using the ‘standard’ 85% inter/after cooler efficiency, the spreadsheet reports:
535.44 rwhp.
Well, we’ll see for sure when I dyno it and post the results. You guys can hang me (..rightfully so) if I’m off! But I'm hopeful that we'll have some interesting things to discuss regarding the results and what they imply.
Tomorrow I'm having a custom made mandrel bent exhaust system installed, and will dyno it soon thereafter.
My original 492 rwhp dyno was with factory exhaust manifolds, cats, air pump, small GT resonators, and an RMB.
My new exhaust system will consist of factory exhaust manifolds, Ott x-pipe, 2.5” mandrel bent pipes, DynoMax mufflers where the resonators reside, and another DynoMax dual 2.5” inlet/outlet where the factory muffler resides.
When I dyno the new combo, the results should prove interesting and answer many outstanding questions regarding the factory setup and it's cats.
Since predictions are so much fun, let’s do one now and ‘see’ how much the new exhaust might be worth.
First and foremost, we always start out with the engine’s normally aspirated (NA) power, which in my case is an S4 with 316 crank hp.
According to the knowledgeable Jim Bailey, he reports that a fellow 928 International employee installed a somewhat similar exhaust onto his GT and netted approximately 30 rwhp; not bad considering no headers were used!
However, my car is an S4 with a much milder cam, so I won’t net the same gains I am sure. With that said, I’ll guess that maybe I’ll get an additional 20 rwhp NA with my new exhaust.
So let’s figure the approximate crank hp gain using 15% drive-train loss:
20 rwhp x 1.15% = 23 crank hp
New NA Crank HP = 316 hp + 23 hp = 339 crank hp.
Now that we have the ‘new’ NA crank hp, what is it’s 11 psi horsepower numbers?
Using the ‘standard’ 85% inter/after cooler efficiency, the spreadsheet reports:
535.44 rwhp.
Well, we’ll see for sure when I dyno it and post the results. You guys can hang me (..rightfully so) if I’m off! But I'm hopeful that we'll have some interesting things to discuss regarding the results and what they imply.
10-03-2003, 03:12 AM
#14
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I'll agree w/ Z. I had a cat by-pass made using a stock set that had been melted. My SOTP meter read quite a difference over stock cats. I am using stock cats now as the fine in CA for no cats is steep. Something like $2400.
Z,
I don't think Lagavulin's newest hp gain from enhanced exhaust will require much extra fuel if any. The free flowing exaust will probably let psi drop a bit. This will decrease blower drive power, decreasing charge temps, and decreasing fuel pressure.
I have read reports of installing freeer flowing exhausts yeilding lower psi yet increades HP.
Andy K
Z,
I don't think Lagavulin's newest hp gain from enhanced exhaust will require much extra fuel if any. The free flowing exaust will probably let psi drop a bit. This will decrease blower drive power, decreasing charge temps, and decreasing fuel pressure.
I have read reports of installing freeer flowing exhausts yeilding lower psi yet increades HP.
Andy K
10-03-2003, 03:46 AM
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More freely flowing exhausts also tend to lean out the mixture. Easier exhaust flow allows for better cylinder scavenging, meaning more fresh air charge can get into the cylinder. You're going to need some additional fuel to maintain the proper air/fuel ratio if you've got that increase in fresh air going into the cylinders.