Headers and the HEAT QUESTION! - Page 3 - Alfa Romeo Bulletin Board & Forums
Reply
 
LinkBack Thread Tools Display Modes
post #31 of 43 (permalink) Old 06-04-2008, 12:38 PM
Registered User
 
Alleggerita's Avatar
 
Join Date: Sep 2005
Location: BC
Posts: 2,125
Quote:
Originally Posted by Greg Gordon View Post
The risk of internal coating damage is much higher with a turbo because the exhaust manifold upstream of the turbine gets ultra hot. Of course the risk of damage is much greater as well. A flake hitting a small delicate turbine spinning at 2000 revolutions per second can do damage.
Greg, somewhat off topic - but that's one slow turbo . Most turbos spin between 10,000rpm at the low end and above and beyond 100,000rpm at the top-end when the engine is making full power.
Alleggerita is offline  
Sponsored Links
Advertisement
 
post #32 of 43 (permalink) Old 06-04-2008, 01:08 PM
Registered User
 
FMG_V6_btb's Avatar
 
Join Date: Mar 2007
Location: BCN, SPAIN
Posts: 732
Greg wrote 2000 revolutions per SECOND, that is 120,000rpm... not 2000 rpm.

Paco.

- SNO Director, Spain branch, Barcelona
- '90 2.0 Spider -- '93 164 QV -- '93 155 2.0 TS -- '02 156 2.5 V6 -- '?? FMG 3.8 Project
FMG_V6_btb is offline  
post #33 of 43 (permalink) Old 06-04-2008, 01:13 PM
Registered User
 
Join Date: May 2004
Posts: 4,075
Marcus: Thanks for asking, when they are ready, I will announce it here, and on my site.

Paco, Thanks for clearing up that turbine speed thing. My point was, it's moving dang fast!
Greg Gordon is offline  
Sponsored Links
Advertisement
 
post #34 of 43 (permalink) Old 06-04-2008, 01:18 PM
Registered User
 
Join Date: May 2008
Location: Belgium
Posts: 105
and these days they go even faster.... well if they're working properly anyway... seems we're replacing turbos weekly these days...
AR67202 is offline  
post #35 of 43 (permalink) Old 06-04-2008, 02:05 PM
Registered User
 
Alleggerita's Avatar
 
Join Date: Sep 2005
Location: BC
Posts: 2,125
Quote:
Originally Posted by FMG_V6_btb View Post
Greg wrote 2000 revolutions per SECOND, that is 120,000rpm... not 2000 rpm.

Paco.
My bad
Alleggerita is offline  
post #36 of 43 (permalink) Old 06-04-2008, 06:28 PM
Registered User
 
5yearplan's Avatar
 
Join Date: Dec 2006
Location: Michigan
Posts: 625
greg: Can't wait for the book to be finished, I want a copy as well.

"Computer games don't affect kids; I mean if Pac-Man affected us as kids, we'd all be running around in darkened rooms, munching magic pills and listening to repetitive electronic music."
[SIGPIC][/SIGPIC]
You should buy my stuff:
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

Restore and Engine Conversion:
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
5yearplan is offline  
post #37 of 43 (permalink) Old 06-06-2008, 03:14 PM
Registered User
 
lightweight's Avatar
 
Join Date: Aug 2007
Location: northern Utah
Posts: 169
Back to original topic, I was quite fascinated to read through the exchange about exhaust wrapping and coatings. My background includes a master’s chemistry and physics, with a chemist father who was fascinated by metallurgy. I’ve also been fussing with vehicles for 40 years, having a lot of fun some fine machinery, with a quite modest budget approach. If anyone is still following this thread, I might have some useful experiential data, along with some further theoretical questions.
When we moved to higher altitude, at first Laramie, Wyoming at 7,200 feet, nearly 20 years ago, my wife’s beloved RX-7 became pretty lethargic, with its complex pollution plumbing excessively stifling the rotary’s ability to breathe that thinner air. Since the rotary inherently runs clean except at idle or very low throttle openings, and we avoid those special conditions, we installed a set of headers, resulting in about a 20% power increase and 10% better mileage, for a considerable practical and environmental improvement. The replacement problems became icing stalling at temperatures around freezing, since the carburetor pre-heater was part of the original manifold, along with excessive under-hood temperatures in midsummer. I began killing two birds with one stone by noticing the gap between the header pipes was similar to the pre-heater connection to the air cleaner. I found a section of old vacuum cleaner pipe of the same diameter, laid it between the header pipes, wrapped all three with drag racer header fiber tape from Summit Racing, and crudely connected the tube (picture 1) to the air cleaner’s thermostatically controlled intake via metallic flexible hose. A good many years and thousands of miles later, it still works reasonably well, with the headers warming input air coming through the extension tube when needed, while the tape wrap keeps under-hood temperatures perhaps surprisingly lower. Inside the tape, the header pipes are currently in better condition than the rest of the exhaust system, exposed as it is to road salt, etc. Not wrapping each single pipe tightly may well have reduced stress on them.
When I got my ’74 Alfa spider 7 years ago, I was more than annoyed by the hot-foot syndrome arising from the muffler directly underneath the throttle pedal, and, again, high under-hood temperatures. When it came time to replace the exhaust system not too much later, figuring that black body radiation could be notably reduced by the closest coating to white one could get (and having tried white on my Guilia and found it did stay that way for long) I painted it (using a brush, after hours of careful hand sanding) with high-temp aluminum paint from the local auto paint specialist. The positive difference for the feet was dramatic. With that experience, it seemed worth trying the manifold, too (picture 2).
Again, the difference was quite satisfying. With at least 2 years and 6,000 miles, it still looks and acts well, no cracks or other problems, other than I did learn that sanding between coats is requisite to reduce a tendency of the outer coat to flake from inadvertent contact.
Part of the issue for others becomes how the machine is going to be used. Hard racing, long distances, or even regular heavy traffic and its temperature raising delays are going to be quite different in their impact on header stresses than what older vehicles like ours, each of which gets about 3,000 miles a year of use, or others which get modest use have to endure, so results and need for thoroughness of treatment will vary accordingly.
Headers have got to deal with temperature differentials in a lot of dimensions in the best of cases. My solutions cost less than $50, total, to treat two cars. The Mazda work isn’t very pretty, but even that could be improved, like the Alfa’s might be with a more sophisticated form of paint application, but even as is the later looks much better, as well as working better, than the rusty state the headers arrived in just a few years after a quite careful overhaul by the PO.

The question I’ve been scratching my head about is about an internal coating and the practical physics of what happens with a reflective layer that is going to be rapidly covered by fluffy black carbon, at least in older vehicles that cannot be kept in perfect tune or from consuming some oil. The logical part of my mind expects that the now-buried reflective layer might still be helpful, but I’d love to see some experimental results as the carbon layer builds in depth, and whether buildup is reduced, as it could be argued to with higher internal temperatures.

The next step for exhaust scavenging becomes the observation from fluid dynamics that smooth pipes (or streambanks) create much greater reductions in flow rates than do rougher or sinuous ones, from vortex buildup, counter-intuitively if one is coming from traditional streamlining. The details of these arguments are beyond me, but there have been tantalizing hints about possibilities from aircraft and such like engineers.

Terence
[acceleration = force / mass]
74 Spider Veloce

Experienced but gone:
65 Giulia spider
61 Lancia Flaminia PF coupe
67 Volvo P-1800S

Wife's support vehicle
14 Porsche Cayman
lightweight is offline  
post #38 of 43 (permalink) Old 06-06-2008, 04:33 PM
Registered User
 
Alex's Avatar
 
Join Date: Jan 2005
Location: London UK
Posts: 5,958
Great replies Paco, Terence and everyone else, thank you.

Of course, those with RHD cars don't suffer exhaust -> steering box heat transfer, but this just showed up on eBay in Italy and might be useful to someone!
Alex is offline  
post #39 of 43 (permalink) Old 06-09-2008, 03:28 AM Thread Starter
Registered User
Gold Subscriber
 
Join Date: Dec 2005
Location: Alfa World, USA
Posts: 3,152
Quote:
Originally Posted by Alex View Post
Great replies Paco, Terence and everyone else, thank you.

Of course, those with RHD cars don't suffer exhaust -> steering box heat transfer, but this just showed up on eBay in Italy and might be useful to someone!
Here's the link, corrected: ALFA ROMEO GTV TUTTI I TIPI PROTEZIONE CALORE STERZO su eBay.it Alfa Romeo, Ricambi Auto d'Epoca, Auto ricambi e accessori

Randy Lee

"HAVE another cookie!!" - Don Corrado Prizzi

Randy's Italian Lot:
1978 Sport Sedan - "Cecilia", a rustfree Alfetta
1990 Mondial T Cabrio - Engine major service, climate control overhaul, and interior tune up still to go - Short is on it!!
1958 Giullietta Sprint. "G.Sprint" No holds barred. 3.0 Liter 12 Valve V6 and Verde transaxle just to get warmed up!
1976 Alfetta GT. Twin 45 Dellortos. Alfetta maintainence drug while Cecilla gets restored.
1978 Alfetta GT. Ex Keith Martin, and getting a nice set of Euro Bumpers along with the rest of the good parts off the '76.
ON HOLD 196x Lancia Flaminia Sedan - name and the rest TBD.

Ex:
79 Spt Sdn. "Griswold" and never-driven '74 Spider sold to Harry Riley
74 Spider "Isabel" traded for "Cecilia" Thanks Ric!
(Look at Isabel now:
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
!!)
1979 Sport Sedan Alfamatic. Traded to Wilbur for a very sweet bicycle - thanks!
All the parts cars chopped up or sent to Larry...
randyleepublic is offline  
post #40 of 43 (permalink) Old 06-09-2008, 06:17 AM
Registered User
 
MALDI's Avatar
 
Join Date: Aug 2004
Location: Maryland
Posts: 1,120
Question

I have never understood the claim that keeping the heat inside the header is good for exhaust flow and cylinder scavenging. (The other reasons such as keeping the intake charge cooler I understand.)

Specifically:

1) Wouldn't you want the hot, pressurized exhaust gas to cool quickly to create a vacuum in the header?

2) High temperature gases are MORE viscous than low temperature gases, so shouldn't the exhaust be cooled rapidly to increase flow through the header tubes?
MALDI is online now  
post #41 of 43 (permalink) Old 06-09-2008, 07:13 AM
Registered User
 
Join Date: May 2008
Location: Belgium
Posts: 105
when the exhaust gas cools, it gets more dense, ,and consumes less space. this means it'll slow down, and th e vacuum nyou mentioned is created by the speed at which the exhaust gasses travel.

The gasses travel from very high pressure at the beginning of the header to a low pressure at the end, and if the header is perfect to a vacuum. Can't beat the forced flow behind this.
AR67202 is offline  
post #42 of 43 (permalink) Old 06-09-2008, 07:40 AM
Senior Member
Gold Subscriber
 
Subtle's Avatar
 
Join Date: Oct 2006
Location: Vancouver, B C
Posts: 6,135
Interesting thread.

On black particulates on a shiny surface, perhaps the black will increase radiant heat out but the underlying shiny layer will still be reflecting heat the other way.

Bob,
Avatar is the 68 Super, bought new.
Subtle is offline  
post #43 of 43 (permalink) Old 06-09-2008, 06:03 PM Thread Starter
Registered User
Gold Subscriber
 
Join Date: Dec 2005
Location: Alfa World, USA
Posts: 3,152
Quote:
Originally Posted by Subtle View Post
Interesting thread.

On black particulates on a shiny surface, perhaps the black will increase radiant heat out but the underlying shiny layer will still be reflecting heat the other way.
Based only upon thought experiments, that is also what I am thinking. I think the "black stuff" will warm up to operating temp, then be neutral.

Maybe.

Randy Lee

"HAVE another cookie!!" - Don Corrado Prizzi

Randy's Italian Lot:
1978 Sport Sedan - "Cecilia", a rustfree Alfetta
1990 Mondial T Cabrio - Engine major service, climate control overhaul, and interior tune up still to go - Short is on it!!
1958 Giullietta Sprint. "G.Sprint" No holds barred. 3.0 Liter 12 Valve V6 and Verde transaxle just to get warmed up!
1976 Alfetta GT. Twin 45 Dellortos. Alfetta maintainence drug while Cecilla gets restored.
1978 Alfetta GT. Ex Keith Martin, and getting a nice set of Euro Bumpers along with the rest of the good parts off the '76.
ON HOLD 196x Lancia Flaminia Sedan - name and the rest TBD.

Ex:
79 Spt Sdn. "Griswold" and never-driven '74 Spider sold to Harry Riley
74 Spider "Isabel" traded for "Cecilia" Thanks Ric!
(Look at Isabel now:
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
!!)
1979 Sport Sedan Alfamatic. Traded to Wilbur for a very sweet bicycle - thanks!
All the parts cars chopped up or sent to Larry...
randyleepublic is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Alfa Romeo Bulletin Board & Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

 
For the best viewing experience please update your browser to Google Chrome