high flow cat vs. midpipe
10-02-08, 12:01 PM
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high flow cat vs. midpipe
I currently have a high flow cat in my car and that got me wondering the exact pros and cons between a highflow cat and a midpipe. I searched the forums concerning what was better and this was all i could find: (sorry if my searching skills suck)
https://www.rx7club.com/showthread.p...ht=midpipe+cat
I know for a mid pipe I would need a ported wastegate, pfc. bla bla bla and thats no problem because the only thing i would need to fix is my wastegate. I also live in Alberta so emissions are no concern for me. But what im wondering is when it comes down to it what is better: high flow cat, or midpipe, and why? and if you were in my position what would you get?
https://www.rx7club.com/showthread.p...ht=midpipe+cat
I know for a mid pipe I would need a ported wastegate, pfc. bla bla bla and thats no problem because the only thing i would need to fix is my wastegate. I also live in Alberta so emissions are no concern for me. But what im wondering is when it comes down to it what is better: high flow cat, or midpipe, and why? and if you were in my position what would you get?
10-02-08, 12:10 PM
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Hi-flow cats are used when emissions are a factor in the equation, they are a little more restrictive then a mid pipe so they will rob power and create heat.
With any turbo charge rotary the less restrictive the exhaust the better, hence the midpipe is better if you have the supporting mods and loose emission legislatiion.
i have heard some people say that a hi-flow cat will increase torque, but i believe that is only on a pistion engine
With any turbo charge rotary the less restrictive the exhaust the better, hence the midpipe is better if you have the supporting mods and loose emission legislatiion.
i have heard some people say that a hi-flow cat will increase torque, but i believe that is only on a pistion engine
10-02-08, 12:18 PM
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i would think that if a rotary engine requires back pressure, it would be created between the exhaust ports and the turbos, therefore the turbo back exhaust system would be more efficient with no restrictions. Although i dont believe any backpressure is required on a RE.
10-03-08, 11:38 AM
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so does it matter what kind of exhaust i use? for example would an rb dual tip exhaust/hks single tip be better for a midpipe or high flow cat? or do they work independently from each other/
10-03-08, 11:49 AM
#7
The biggest issue with a midpipe is the exhaust fumes. If you use this car to drive to work, I would recommend keeping the hi-flow. It's not very professional to arrive to work smelling like exhaust fumes unless you work in a garage.
I made the switch but added in a metallic substrate cat. I'm almost regretting the choice as my garage gets filled with fumes when I enter/leave in the car. I did have a Bonez hi-flo before and I did run it without the airpump so it's not just not having an airpump hooked up which is causing the fumes.
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10-03-08, 11:59 AM
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Loudness does not matter to me, what matters is what kind of performance i am getting. if i stick to my high flow cat should that sway me to get get a specific exhaust pipe or not., and if i ever do decide to switch to midpipe will my previous choice of exhaust impede the midpipes ability?
also mahjik you bring up another question i have had. do i need to worry about an airpump being attached to my high flow cat or not, mine is currently attached but if i can scrap it i will.
(where i work, no one cares if my car smells like fumes or not.)
also mahjik you bring up another question i have had. do i need to worry about an airpump being attached to my high flow cat or not, mine is currently attached but if i can scrap it i will.
(where i work, no one cares if my car smells like fumes or not.)
10-03-08, 12:16 PM
#10
Loudness does not matter to me, what matters is what kind of performance i am getting. if i stick to my high flow cat should that sway me to get get a specific exhaust pipe or not., and if i ever do decide to switch to midpipe will my previous choice of exhaust impede the midpipes ability?
Find the style of catback that you like and get it. The performance differences for all of them with the same inlet size are pretty minor so it shouldn't be a concern. IMO, it's more important you pick the style you like and go with it.
Also think about any potential passengers. My wife will not ride in my car anymore because of the fume, and she used to love the car. Granted, we don't have the opportunity to do it these days since I have a daughter; but on those few occasions she won't do it. For me it's not a huge deal as the car is really turned into a track only car, but for a street car I don't see the need for a midpipe. If my car wasn't been groomed for being mostly track only, I'd put a Bonez cat back on it.
10-03-08, 12:17 PM
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Thats true, but i usually work out in the country and i dont do much city driving. I dont think it matters much anyways in a city where every one drives modified pickup trucks to look sound and smell like semi trucks (the only difference is that a semipipes point towards the sky, and a pickups point towards my and everyone elses windows.
10-03-08, 12:23 PM
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Any catback that will restrict a hi-flo cat will restrict a midpipe. There is no difference there. Any catback that is loud with a hi-flo cat will be louder with a midpipe. I think you see where I'm going with this: it doesn't matter.
Find the style of catback that you like and get it. The performance differences for all of them with the same inlet size are pretty minor so it shouldn't be a concern. IMO, it's more important you pick the style you like and go with it
Find the style of catback that you like and get it. The performance differences for all of them with the same inlet size are pretty minor so it shouldn't be a concern. IMO, it's more important you pick the style you like and go with it
so i am getting that between all the good exhaust systems basically the only difference is the loudness
10-03-08, 12:27 PM
#13
https://www.rx7club.com/3rd-gen-general-discussion-322/post-pics-your-exhaust-system-buyers-guide-392922/
Find something you like.
10-03-08, 12:46 PM
#14
All you need to know right here
https://www.rx7club.com/showpost.php...8&postcount=17
https://www.rx7club.com/showpost.php...8&postcount=17
Rynberg has said it clearly, but for your understanding here it is, boiled down differently:
First, 'full exhaust' doesn't mean midpipe, but many folks run a straight-thru downpipe and a performance muffler already. These are good, simple mods with few complications. It's the midpipe replacing the main cat that makes it a full exhaust and is the point where you need to be much more educated and observant about the car and it's boost levels.
Midpipes cause two things to happen:
1) Your boost will spike and/or increase in level
2) Your boost will not reach a constant max level - it will 'creep' higher and higher the longer you stay in full boost.
1) is something the stock computer's boost control system simply cannot keep up with. You need to install some sort of boost controller that is more robust - either a manual boost controller or an electronic boost controller. The stock duty-cycling solenoid + restrictor pill setup is simply out of it's useful range.
2) Boost creep pops motors, especially with an aftermarket ECU. (The stock ECU will *usually* cut fuel before going too lean, but ... one day it won't...). The solution is to port the stock wastegate so that it can vent enough exhaust. That's it, but it's not a 5 minute job since the turbos must be pulled and disassembled.
The whole tuning issue depends on the ECU and level of boost you want. Once you get a sufficient boost controller and your wastegate is ported to meet the demands, you have control. But you still need to set your boost to a level that doesn't exceed or push your fuel supply. Stock ECUs = 10psi. Remapped ECUs w/ stock fuel system = 12psi, and so on.
You have 3 options if you're about to install a midpipe.
1) Install the midpipe, and install an adequate boost controller, port the ECU, and upgrade the ECU and/or fuel system as required. Also figure out what you're going to do about emissions (smog tests?), noise levels, and odor.
2) Install the midpipe and install some extra restriction. This reduces the boost control issue and enough restriction will stop boost creep. It may even be enough to remain with the stock boost control system, though I don't recommend it. Restrictor plates or more restrictive components elsewhere (stock intake or stock muffler) are how to add restriction.
3) Don't install a midpipe. Stay with a stock cat or high-flow cat. The high flow cat may require better boost control, but usually it won't creep. High flow cat with a downpipe and muffler can produce nearly as much power as a full exhaust.
So think about it: 1) is a lot of work, which if you're simply after power is better obtained by other mods. Some people think because a midpipe is a little cheaper that it's a good idea - wrong. 2) is adding performance only to restrict it again since you don't have the required supporting mods. Tell me if that isn't silly. 3) is simple, easy, practical, and cheap, and won't pop your motor.
Dave
First, 'full exhaust' doesn't mean midpipe, but many folks run a straight-thru downpipe and a performance muffler already. These are good, simple mods with few complications. It's the midpipe replacing the main cat that makes it a full exhaust and is the point where you need to be much more educated and observant about the car and it's boost levels.
Midpipes cause two things to happen:
1) Your boost will spike and/or increase in level
2) Your boost will not reach a constant max level - it will 'creep' higher and higher the longer you stay in full boost.
1) is something the stock computer's boost control system simply cannot keep up with. You need to install some sort of boost controller that is more robust - either a manual boost controller or an electronic boost controller. The stock duty-cycling solenoid + restrictor pill setup is simply out of it's useful range.
2) Boost creep pops motors, especially with an aftermarket ECU. (The stock ECU will *usually* cut fuel before going too lean, but ... one day it won't...). The solution is to port the stock wastegate so that it can vent enough exhaust. That's it, but it's not a 5 minute job since the turbos must be pulled and disassembled.
The whole tuning issue depends on the ECU and level of boost you want. Once you get a sufficient boost controller and your wastegate is ported to meet the demands, you have control. But you still need to set your boost to a level that doesn't exceed or push your fuel supply. Stock ECUs = 10psi. Remapped ECUs w/ stock fuel system = 12psi, and so on.
You have 3 options if you're about to install a midpipe.
1) Install the midpipe, and install an adequate boost controller, port the ECU, and upgrade the ECU and/or fuel system as required. Also figure out what you're going to do about emissions (smog tests?), noise levels, and odor.
2) Install the midpipe and install some extra restriction. This reduces the boost control issue and enough restriction will stop boost creep. It may even be enough to remain with the stock boost control system, though I don't recommend it. Restrictor plates or more restrictive components elsewhere (stock intake or stock muffler) are how to add restriction.
3) Don't install a midpipe. Stay with a stock cat or high-flow cat. The high flow cat may require better boost control, but usually it won't creep. High flow cat with a downpipe and muffler can produce nearly as much power as a full exhaust.
So think about it: 1) is a lot of work, which if you're simply after power is better obtained by other mods. Some people think because a midpipe is a little cheaper that it's a good idea - wrong. 2) is adding performance only to restrict it again since you don't have the required supporting mods. Tell me if that isn't silly. 3) is simple, easy, practical, and cheap, and won't pop your motor.
Dave
Gotta be careful about the boost creep on an open exhaust. Especially in colder weather. I always creeped to 15+ PSI even with the Greddy Type S boost controller in cold weather when I had a mid pipe.
11-09-08, 09:06 AM
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just wondering if it worth porting the waste gate on the twins or wait and go single later??
just want to clear so thing up ive hear that mid pipes with standard downpipe cause boost creep what i was to just install a down pipe would that coz boost creep or should i just bit the bullet and get the waste gates ported
just want to clear so thing up ive hear that mid pipes with standard downpipe cause boost creep what i was to just install a down pipe would that coz boost creep or should i just bit the bullet and get the waste gates ported
11-09-08, 10:28 AM
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just wondering if it worth porting the waste gate on the twins or wait and go single later??
just want to clear so thing up ive hear that mid pipes with standard downpipe cause boost creep what i was to just install a down pipe would that coz boost creep or should i just bit the bullet and get the waste gates ported
just want to clear so thing up ive hear that mid pipes with standard downpipe cause boost creep what i was to just install a down pipe would that coz boost creep or should i just bit the bullet and get the waste gates ported
11-09-08, 11:59 AM
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2/4 wheel cornering fiend
I know, I know, the wastegate. Good post, Dave.
11-09-08, 12:20 PM
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I'm running an RX-7 Store midpipe and love it, the fumes aren't bad if you have the Power FC tuned lean (15-16+ AFR) at cruise...with that said, a metallic cat does a good job of cleaning up the stink at wide open throttle
I'll probably be selling my barely used SMB metallic cat, send me a PM if interested
I'll probably be selling my barely used SMB metallic cat, send me a PM if interested
11-09-08, 01:19 PM
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it doesn't...in fact, you will see 0.5 to 1 psi less pressure drop with a good metallic cat, like the SMB, compared to a typical high flow, and you'll drop another 1 to 1.5 psi with a resonated midpipe...you need a ported wastegate with either option to be safe, especially if you're running on the hairy edge with a Pettit ECU
