The Truth - 993 GT2 Straight Pipes
09-24-2021, 04:05 PM
#16
OOhh! A technical debate. Me likey! Rennlist wont know what hit them Bill!
That being said, acoustic resonances won't have any measurable effect in a pipe length that is effectively a little over 12 inches. Plus resonant frequency will alter according to gas flow rate so even if it was a miniscule amount of help scavenging the gas flow at certain rates of gas flow, it will impede flow at others. It's been well proven for eons that for turbocharged vehicles, any form of backpressure is detrimental to overall power output. A GT2 will make more power with the GT2 style exhaust removed compared to them being attached all things being equal. Tapering the exhaust down from 3 inches to 2 inches WILL reduce power compared to running a straight 3 inch pipe all the way.
From my vague memory, the real reason GT2 Evo pipes taper is because of FIA homologation regulations. Regs dictate that exhausts can be modified and catalytic converters and mufflers are able to be removed. The only stipulation is that exhaust pipe size remain the original diameter and that the exhaust must exit at the standard location. The GT2 Evo style pipes are designed with this in mind. They route exhaust gas to the standard tailpipe locations in the most efficient (shortest) way possible to reduce exhaust weight and then taper down to the stock exhaust pipe diameter.
That being said, acoustic resonances won't have any measurable effect in a pipe length that is effectively a little over 12 inches. Plus resonant frequency will alter according to gas flow rate so even if it was a miniscule amount of help scavenging the gas flow at certain rates of gas flow, it will impede flow at others. It's been well proven for eons that for turbocharged vehicles, any form of backpressure is detrimental to overall power output. A GT2 will make more power with the GT2 style exhaust removed compared to them being attached all things being equal. Tapering the exhaust down from 3 inches to 2 inches WILL reduce power compared to running a straight 3 inch pipe all the way.
From my vague memory, the real reason GT2 Evo pipes taper is because of FIA homologation regulations. Regs dictate that exhausts can be modified and catalytic converters and mufflers are able to be removed. The only stipulation is that exhaust pipe size remain the original diameter and that the exhaust must exit at the standard location. The GT2 Evo style pipes are designed with this in mind. They route exhaust gas to the standard tailpipe locations in the most efficient (shortest) way possible to reduce exhaust weight and then taper down to the stock exhaust pipe diameter.
just note that the Burns exhaust specialists disagree w/ most of what you have just written
09-24-2021, 09:45 PM
#17
Rennlist Member
That makes me sad. I like a good healthy debate and it's a good learning tool for me. I am surprised that Burns disagrees that exhaust backpressure is detrimental to power output in a turbo application.
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S.White (09-29-2021)
08-02-2022, 01:33 AM
#20
Nordschleife Master
From my vague memory, the real reason GT2 Evo pipes taper is because of FIA homologation regulations. Regs dictate that exhausts can be modified and catalytic converters and mufflers are able to be removed. The only stipulation is that exhaust pipe size remain the original diameter and that the exhaust must exit at the standard location. The GT2 Evo style pipes are designed with this in mind. They route exhaust gas to the standard tailpipe locations in the most efficient (shortest) way possible to reduce exhaust weight and then taper down to the stock exhaust pipe diameter.
Here's a related question, though. Suppose that you install straight pipes without taper, just a short section of 3" or 76mm pipe, in a stock 993 turbo with stock K16 turbochargers. Does the ECU lose control of boost because the wastegate circuit gets saturated? Or does the wastegate circuit in a stock 993 turbo flow enough that the wastegate can control boost even with only atmospheric turbine outlet back pressure?
08-05-2022, 04:25 AM
#22
Nordschleife Master
I’m asking these questions as Johnny-come-quarter-century lately! There seems to be a lot of knowledge here on this board so I figured I’ll ask before making any bonehead moves.
Here’s another question. If you compare say WLS2/S/GT with their respective stock catted exhausts and with these race pipes, how does the boost curve and dyno graph change? Basically, the question I’m trying to ask is how much of a restriction the stock catted exhaust is on these cars?
Here’s another question. If you compare say WLS2/S/GT with their respective stock catted exhausts and with these race pipes, how does the boost curve and dyno graph change? Basically, the question I’m trying to ask is how much of a restriction the stock catted exhaust is on these cars?