down pipe size and exhaust
02-10-10, 07:44 PM
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down pipe size and exhaust
just curious to see what size downpipes and exhaust everyone is running with their 20b's. also what size turbo along with that?
02-10-10, 08:22 PM
#2
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To give you an idea, my friend has a GT55R and a 5" exhaust on this street driven 20b.
Best regards,
Chris
03-01-10, 03:38 PM
#3
I run a 4202R, 4" to the rear diff, then dual 3" from there.
I disagree about turbo size, I think my turbo is a bit large for street 20B, I wish I had gotten a 4294 or even 4088.
I will note that on my original build I re-used my 3" exhaust from 13b and It was too restrictive, I could only make 2psi of boost with the silencer in, and response wasnt great even with it out. That was on a smaller turbo as well (borg warner s361)
I disagree about turbo size, I think my turbo is a bit large for street 20B, I wish I had gotten a 4294 or even 4088.
I will note that on my original build I re-used my 3" exhaust from 13b and It was too restrictive, I could only make 2psi of boost with the silencer in, and response wasnt great even with it out. That was on a smaller turbo as well (borg warner s361)
03-01-10, 04:21 PM
#4
Rotary Enthusiast
I run a 4202R, 4" to the rear diff, then dual 3" from there.
I disagree about turbo size, I think my turbo is a bit large for street 20B, I wish I had gotten a 4294 or even 4088.
I will note that on my original build I re-used my 3" exhaust from 13b and It was too restrictive, I could only make 2psi of boost with the silencer in, and response wasnt great even with it out. That was on a smaller turbo as well (borg warner s361)
I disagree about turbo size, I think my turbo is a bit large for street 20B, I wish I had gotten a 4294 or even 4088.
I will note that on my original build I re-used my 3" exhaust from 13b and It was too restrictive, I could only make 2psi of boost with the silencer in, and response wasnt great even with it out. That was on a smaller turbo as well (borg warner s361)
Chris
03-01-10, 04:34 PM
#5
fairly large streetport, ported FD inserts.
The 4202 is reasonably responsive, but the thing is that I am nowhere near maxing it out at 600whp, and since I don't plan to increase the power level much if any, I might as well have a smaller turbo that is even more responsive and is close to the top of its efficiency curve at my max power level.
I would argue the same thing for a 13B, the 35r is responsive for high power goals, but there are people who run a 30R or even smaller and still get very respectable peak numbers with a wider curve. Peaky large turbo powerbands make for a street car that is too racy to really be comfortable.
I think the reason the 4202 is considered conservative for 20b is that there arent really many 'conservative' 20b builds. Most people who have a running 20B (which isnt many) are out for major HP levels for either racing or dyno queen goals. The truth is, my car isnt much faster with 600whp than it was with 500. At some point diminishing returns really starts to set in as you get closer to the limit of the chassis.
The whole issue is really sad IMO, because the power curve of the 20b is just SO much nicer. I think that all 1990+ RX7s should have come with a 20B. The 13b is questionable as far as torque curve, and many people avoided the cars for that reason, but the 20B doesnt have this problem. There is really nothing else like it in the world. And, I get better fuel economy than I did with a 13b because I can run a gear (or two) higher than I would have before.
I would love to build a car with a 20B designed for maximum low end, with a small turbo and 400 peak hp spread over as wide of an RPM range as possible. One of these days I may do just that in an Opel GT.
The 4202 is reasonably responsive, but the thing is that I am nowhere near maxing it out at 600whp, and since I don't plan to increase the power level much if any, I might as well have a smaller turbo that is even more responsive and is close to the top of its efficiency curve at my max power level.
I would argue the same thing for a 13B, the 35r is responsive for high power goals, but there are people who run a 30R or even smaller and still get very respectable peak numbers with a wider curve. Peaky large turbo powerbands make for a street car that is too racy to really be comfortable.
I think the reason the 4202 is considered conservative for 20b is that there arent really many 'conservative' 20b builds. Most people who have a running 20B (which isnt many) are out for major HP levels for either racing or dyno queen goals. The truth is, my car isnt much faster with 600whp than it was with 500. At some point diminishing returns really starts to set in as you get closer to the limit of the chassis.
The whole issue is really sad IMO, because the power curve of the 20b is just SO much nicer. I think that all 1990+ RX7s should have come with a 20B. The 13b is questionable as far as torque curve, and many people avoided the cars for that reason, but the 20B doesnt have this problem. There is really nothing else like it in the world. And, I get better fuel economy than I did with a 13b because I can run a gear (or two) higher than I would have before.
I would love to build a car with a 20B designed for maximum low end, with a small turbo and 400 peak hp spread over as wide of an RPM range as possible. One of these days I may do just that in an Opel GT.
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