Best Cut-Out?
03-27-2007, 11:18 AM
#1
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Best Cut-Out? I am wanting to get a cut-out, but am not really sure on what to buy. Which cut-out sounds the best and does anyone have a sound clip? Also, does the size of the cutout have to be the same as my down-pipe or can I get as big as I want? Any reccomendations or advice is greatly appreciated...And one more thing, where is the best place to buy?
03-27-2007, 12:23 PM
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Originally Posted by 95Firehawk
I am wanting to get a cut-out, but am not really sure on what to buy. Which cut-out sounds the best and does anyone have a sound clip? Also, does the size of the cutout have to be the same as my down-pipe or can I get as big as I want? Any reccomendations or advice is greatly appreciated...And one more thing, where is the best place to buy?
But I suggest going stainless. Whatever brand you choose that's up to you, but stainless steel is the way to go. I just purchased a QTP stainless cutout myself.
03-27-2007, 03:54 PM
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I have dual cutouts right off the headers. I wanted to have it dumped prior to the cats.
On the dyno, it showed a peak of 13rwtq and averaged about 9 rwtq more with the cutout open across the entire run without losing any low-end torque.
Without cats, I don't know if it would make much of a difference but you wouldn't lose bottom end. It would probably be too loud under the car to have it open when cruising.
On the dyno, it showed a peak of 13rwtq and averaged about 9 rwtq more with the cutout open across the entire run without losing any low-end torque.
Without cats, I don't know if it would make much of a difference but you wouldn't lose bottom end. It would probably be too loud under the car to have it open when cruising.
03-27-2007, 04:06 PM
#7
Originally Posted by 94 Formula
I have dual cutouts right off the headers. I wanted to have it dumped prior to the cats.
On the dyno, it showed a peak of 13rwtq and averaged about 9 rwtq more with the cutout open across the entire run without losing any low-end torque.
Without cats, I don't know if it would make much of a difference but you wouldn't lose bottom end. It would probably be too loud under the car to have it open when cruising.
On the dyno, it showed a peak of 13rwtq and averaged about 9 rwtq more with the cutout open across the entire run without losing any low-end torque.
Without cats, I don't know if it would make much of a difference but you wouldn't lose bottom end. It would probably be too loud under the car to have it open when cruising.
"Another furphy that has widespread currency is the concept that engines need back-pressure. Simply, there is no properly tuned engine where increasing exhaust back-pressure causes an improvement - in power, torque or fuel economy. One of the reasons that this idea has gained support is because when people change their exhaust they seldom check the air/fuel ratio or re-map the ignition timing to once again give optimal performance. For example, some MAP sensed cars drop substantially in power with a large exhaust fitted because they are then running lean."
"Wollongong (Australia) mechanic Kevin Davis is one who has done very extensive testing of varying back-pressure on a number of performance engines. These range from turbocharged Subaru Liberty [Legacy] RS flat fours to full-house traditional pushrod V8's. In not one case has he found any improvement in any engine performance parameter by increasing exhaust back-pressure! The tests came about because Kevin has developed a patented variable flow exhaust that uses a butterfly within the exhaust pipe. He initially expected to use the system to cause some back-pressure at low loads "to help torque". However, he soon changed his mind when any increase in back-pressure proved to decrease torque (and therefore power at those revs) on a properly tuned engine! What increasing the back-pressure does do is dramatically quieten the exhaust.
One of the engine dyno tests carried out by Kevin was on warm 351 4V Cleveland V8. Following the extractors, he fitted a huge exhaust that gave a measured zero back-pressure. Torque peaked at 423 ft-lb at 4700 rpm, with power a rousing 441hp at 6300 rpm. He then dialled-in 1.5 psi back-pressure. Note that very few exhausts are capable of delivering such a low back-pressure on a road car. Even with this small amount of back-pressure, peak torque dropped by 4 per cent and peak power by 5 per cent. He then changed the butterfly position to give 2.5 psi back-pressure. Torque and power decreased again, both dropping by 7 per cent over having zero back-pressure!"
One of the engine dyno tests carried out by Kevin was on warm 351 4V Cleveland V8. Following the extractors, he fitted a huge exhaust that gave a measured zero back-pressure. Torque peaked at 423 ft-lb at 4700 rpm, with power a rousing 441hp at 6300 rpm. He then dialled-in 1.5 psi back-pressure. Note that very few exhausts are capable of delivering such a low back-pressure on a road car. Even with this small amount of back-pressure, peak torque dropped by 4 per cent and peak power by 5 per cent. He then changed the butterfly position to give 2.5 psi back-pressure. Torque and power decreased again, both dropping by 7 per cent over having zero back-pressure!"
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03-27-2007, 04:13 PM
#8
Originally Posted by 94 Formula
I have dual cutouts right off the headers. I wanted to have it dumped prior to the cats.
On the dyno, it showed a peak of 13rwtq and averaged about 9 rwtq more with the cutout open across the entire run without losing any low-end torque.
Without cats, I don't know if it would make much of a difference but you wouldn't lose bottom end. It would probably be too loud under the car to have it open when cruising.
On the dyno, it showed a peak of 13rwtq and averaged about 9 rwtq more with the cutout open across the entire run without losing any low-end torque.
Without cats, I don't know if it would make much of a difference but you wouldn't lose bottom end. It would probably be too loud under the car to have it open when cruising.
I gained about 9rwtq and 4rwhp with them open VS closed.
But only 3rwtq over what I had without cutouts.
(Translation: Closed cutouts made less power than no cutouts)
03-27-2007, 04:15 PM
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Originally Posted by James Montigny
I've had 3 QTP motors fail in less than a year.
The gains were minimal over the 3" hooker muffler, I just took it off alltogether.
The gains were minimal over the 3" hooker muffler, I just took it off alltogether.
Now if your going to go with a ecutout then DMH is the way to go.Also your not going to notice any real gains from a cutout like I mentioned earlier. Especially if you just goof around on the street. You will loose some back pressure which will cause you to loose some bottom end power (launching).
With a cutout you'll gain a few horsepower but loose some torque, torque is what you feel, what pulls the car.
03-27-2007, 04:17 PM
#10
Originally Posted by Bossz28
Your talking about ecutouts, were talking about "cutouts" the manual cutout doesn't fail. Now if your going to go with a ecutout then DMH is the way to go.
Now if your going to go with a ecutout then DMH is the way to go. now we're on the same page.
03-27-2007, 04:18 PM
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Originally Posted by 95Firehawk
ok, sorry- I'm kind of a n00b. So I went to the QTP website and there is a ton of different cut-outs...which one do I get? Is there any other sites to order from?
For the price buy a stainless manual cutout. 3inch. If you feel compelled to buy a electric motor for it later on you always can. I think the ecutout is useless imo. I never run the cutout open around town only at car shows and at the track, so there's no point blowing 200 bux for something that won't be used.
03-28-2007, 10:00 AM
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Originally Posted by James Montigny
Are those numbers open VS closed or open VS no cutouts at all?
I gained about 9rwtq and 4rwhp with them open VS closed.
But only 3rwtq over what I had without cutouts.
(Translation: Closed cutouts made less power than no cutouts)
I gained about 9rwtq and 4rwhp with them open VS closed.
But only 3rwtq over what I had without cutouts.
(Translation: Closed cutouts made less power than no cutouts)
On a good free-flowing exhaust system a cutout won't do much as I think you've seen.(3rwtq wouldn't be worth putting in a cutout for performance and could be dyno variation)
On mine, I have to run cats so I wanted the cutouts ahead of them which means right after the headers.
Backpressure isn't needed on a properly tuned engine. Exhaust scavenging is which is why you don't want to put a cutout too far up the system.
03-28-2007, 10:22 AM
#14
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Originally Posted by Puck
Agreed. Just jumping in to comment on a common mistake. Its a common misconception that backpressure=tq. Backpressure is fancy word for restriction, its always a bad thing. Quick snippets from another site:
-and-
You will not lose tq anywhere in the rpm range assuming the car is tuned properly.
-and-
You will not lose tq anywhere in the rpm range assuming the car is tuned properly.
I have been saying this for years now and everyone just says no, cars need backpressure. Would sure to kindly inform them of some tests in the area.
03-28-2007, 11:51 AM
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The benefit of a cutout increases as the power output increases. Those who have bolt-on LT1's will see minimal gain over a free flow muffler by going to a cutout.
