Return-Path: <13brv3@bellsouth.net> Received: from imf17aec.mail.bellsouth.net ([205.152.59.65] verified) by logan.com (CommuniGate Pro SMTP 4.2b7) with ESMTP id 310480 for flyrotary@lancaironline.net; Sat, 10 Jul 2004 11:22:46 -0400 Received: from rd ([65.6.194.9]) by imf17aec.mail.bellsouth.net (InterMail vM.5.01.06.08 201-253-122-130-108-20031117) with ESMTP id <20040710152216.KOQX1742.imf17aec.mail.bellsouth.net@rd> for ; Sat, 10 Jul 2004 11:22:16 -0400 From: "Russell Duffy" <13brv3@bellsouth.net> To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Re: Three candidates for Turbo Failure Date: Sat, 10 Jul 2004 10:22:37 -0500 Message-ID: <003401c46691$bba01c60$6101a8c0@rd> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0035_01C46667.D2CA1460" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.2627 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1409 Importance: Normal In-Reply-To: This is a multi-part message in MIME format. ------=_NextPart_000_0035_01C46667.D2CA1460 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit It's the turbine wheel that failed, not the compressor wheel. On each occasion the weld broke right at the base of the turbine wheel, the wheel came off and blocked the exhaust outlet. My money is on a combination of overspeed, and overtemp. I'm sure the rotary exhaust isn't hot enough to melt the weld, but it might be getting in the neighborhood of that temp, depending on what the stem, and wheel are made of. One of the things that Turbonetics told me was that street turbos never get anywhere near the max exhaust temp, because you just can't sustain that temp long enough to heat soak the metal. That changes when we sell one to John :-) Let's assume we're running the turbo faster, and at higher temps than you ever could in a stock RX-7 on the street. We know that all metals lose strength as they are heated, though some metals have better high temp characteristics than others. That's why we can run thin wall 321 SS exhaust pipes, but wouldn't try that with mild steel, or even 304 SS. Without having any idea what the stem and wheel are made of, I would venture to guess that it's not the best material money can buy. Remember, this is a mass produced item, what was engineered to be as cheap as possible, while barely surviving the warranty period. Under our conditions, the metal isn't as strong as expected, because we're running it at higher temp than designed. We're also spinning the wheel faster which causes more stress on the weld joint. I'd be willing to bet that it's just that simple. The OZ mod won't do anything for the temps, though John can add some fuel to keep the EGT's lower (what was your EGT BTW?). The real benefit will be lightening/slowing the wheel by removing some of the blade area, as well as slowing it with a better porting job on the wimpy wastegate. If they do a super balance job on the rotating mass, that will help too. Will it be enough? I guess John will let us know :-) I do believe it's a huge step in the right direction. Cheers, Rusty (turbo mode off) ------=_NextPart_000_0035_01C46667.D2CA1460 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Message
It's = the turbine=20 wheel that failed, not the compressor wheel. On each occasion the weld = broke=20 right at the base of the turbine wheel, the wheel came off and = blocked the=20 exhaust outlet.
 
My money is on a combination of overspeed, = and=20 overtemp.  I'm sure the rotary exhaust isn't hot enough to melt the = weld,=20 but it might be getting in the neighborhood of that temp, = depending on=20 what the stem, and wheel are made of.  One of the things that=20 Turbonetics told me was that street turbos never get anywhere near the = max=20 exhaust temp, because you just can't sustain that temp long enough to = heat soak=20 the metal.  That changes when we sell one to John :-) =20
 
Let's assume we're running the turbo faster, = and at=20 higher temps than you ever could in a stock RX-7 on the=20 street.  We know that all metals lose strength = as they=20 are heated, though some metals have better high temp characteristics = than=20 others.  That's why we can run thin wall 321 SS exhaust=20 pipes, but wouldn't try that with mild steel, or even 304 = SS. =20  Without having any idea what the stem and wheel are made of, I = would=20 venture to guess that it's not the best material money can buy.  = Remember,=20 this is a mass produced item, what was engineered to be as cheap as = possible,=20 while barely surviving the warranty period. =20
 
Under our conditions, the metal isn't as = strong as=20 expected, because we're running it at higher temp than designed.  = We're=20 also spinning the wheel faster which causes more stress on the weld = joint. =20 I'd be willing to bet that it's just that simple. =20
 
The OZ mod won't do anything for the temps, = though John=20 can add some fuel to keep the EGT's lower (what was your EGT = BTW?).  The=20 real benefit will be lightening/slowing the wheel by removing some of = the blade=20 area, as well as slowing it with a better porting job on the wimpy=20 wastegate.  If they do a super balance job on the rotating mass, = that will=20 help too.  Will it be enough?  I guess John will let us know=20 :-)  I do believe it's a huge step in the right=20 direction.
 
Cheers,
Rusty (turbo mode=20 off) 
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