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Underbody braces, turbos and more!

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PostPosted: Thu Sep 22, 2005 8:37 am 
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Changing your exhaust a little may help improve MPG's. I wouldn't worry about porting your head. It flows well enough for your intentions. If you are in it for MPG's an underdrive pulley helps gobs.

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PostPosted: Fri Sep 23, 2005 12:32 am 
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I got mine from member bigbearzuk. Adam at OCC racing.

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PostPosted: Fri Sep 23, 2005 8:51 am 
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Roughly how much does an underdrive pully cost anyway?


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PostPosted: Sat Sep 24, 2005 1:55 am 
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http://www.teamswift.net/3tech

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PostPosted: Sat Sep 24, 2005 11:15 am 
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I know 3Tech's pullies are great for the price.

Dan


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PostPosted: Thu Nov 17, 2005 7:52 pm 
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Does superf1y have a website? Who has an economy(mpg) head kit, head, cam etc.? I want to try to build a MPG Warrior here!
Also, who has used any of these "mpg improvers" and otten good results?

BTW-with the exhaust question-dont you need a certain amount of backpressure or the fuel wont burn fully? I could be wrong.


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PostPosted: Thu Nov 17, 2005 7:59 pm 
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disrespected3cyl wrote:
Does superf1y have a website?

BTW-with the exhaust question-dont you need a certain amount of backpressure or the fuel wont burn fully? I could be wrong.


Look at the bottom, click on my blue firefly.
You are wrong. No amount of backpressure is good for anything.
Its all about the velocity :wink:

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PostPosted: Thu Nov 17, 2005 8:09 pm 
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Sorry, didn't realize you were the owner of that site! DARN NOOBIES!!! :wink:


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PostPosted: Fri Nov 18, 2005 7:29 pm 
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Porting tends to rock the torque curve about the torque peak. Usually it gives you more high end torque and less low end torque.

That's usually bad for MPG.

What you probably want is more low end torque so you can use the next higher gear at any particular road speed. Unfortunately that usually means a loss in the high end torque (also a loss in max HP).

The easiest way to get more low end torque would be to get adjustable cam sprockets and tune the cams to work best at lower RPMs. (retard intake and exhaust with maybe a little less overlap if you have DOHC)

ed


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PostPosted: Fri Nov 18, 2005 9:25 pm 
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it makes sense to me that free-flowing exhaust would net better MPG.

can anyone tell me why do some people (who otherwise know what they're talking about) equate reduced backpressure to burnt exhaust valves?

e.g. http://www.cartalk.com/content/columns/ ... uly/04.htm

what's their logic, and under what circumstances would this be right or wrong?

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PostPosted: Sat Nov 19, 2005 1:19 pm 
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whoops - link above should have been:

http://www.cartalk.com/content/columns/ ... ly/04.html

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PostPosted: Mon Nov 21, 2005 2:47 pm 
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Reduced pack pressure results in more exhaust gas out of the cylinder and more fresh air in, if the amount of fuel supplied remains the same then the air/fuel mixture is leaned out and this can result in higher exahaust gas temperature and burnt valves. With our cars that have feedback systems this doesn't cause a problem. I've never had a problem when adding headers/turbo mufflers to carburated cars either so I don't know how common the burnt valve problem is.


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PostPosted: Mon Nov 21, 2005 5:14 pm 
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I have just heard that it creates more carbon buil-up on the exhaust valve. Not sure about "burning" the valve. Unless they are considering it "burnt" because the carbon may hold the valve open a little-losing compression. . . .?


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PostPosted: Mon Nov 21, 2005 5:30 pm 
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disrespected3cyl wrote:
I have just heard that it creates more carbon buil-up on the exhaust valve. Not sure about "burning" the valve. Unless they are considering it "burnt" because the carbon may hold the valve open a little-losing compression. . . .?


one thing i do know is that if the valve doesn't seat properly, it can't dissipate heat back to the cylinder head. anything that prevents seating would eventually burn the valve (i suppose it warps from excessive heat build up).

i heard on another forum (this is someone else's explanation, not mine) that an open exhaust is a problem because when the engine is shut off, cool air can more easily reach back into the exhaust valves, causing warping and subsequent seating problems.

i think the lean/hot combustion theory makes more sense.

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PostPosted: Tue Nov 22, 2005 11:21 am 
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A burnt valve is what it says, burnt.
I did this to an Austin Mini I had once.
Crashed it and then proceeded to drive it home with no coolant.
Guess what I found when I pulled the head because it was running rough ?
2 exhaust valves were burnt as in the edges of the valve and seats were melted away. The valve wouln't seat because there was a hole and pitting in the valve seating edges. Low or no compression.

If you have a compromised cooling system then the heat generated in the head cannot be shed and this can cause warping of the head or burnt exhaust valves.
The valves in todays modern engines are very tough, some are even filled with sodium for better heat dissipation.
But if you lean out a fuel mixture too much, the burnt gases inside act like a cutting torch.
Try lighting up a cutting torch, as you add fuel and oxy to get a nice bunsen blue that's the optimal fuel ratio, then try adding more oxy to lean out the mix and you have a cutting torch for slicing and dicing.

The exhaust valves are the ones to suffer since the intakes bring in cool fuel and air, but the exhaust opening expels it at superheated speeds past little venturi like openings around the valve into the manifold.
Get the mix too lean , or not enough cooling and you have a cutting torch past the valve edge/seat.

Keeping an eye on coolant temps and fuel ratios can keep burnt valves to a minimum.

My .02 cents.


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PostPosted: Tue Nov 22, 2005 12:14 pm 
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Probably not the best forum to ask, but since we're on the subject.

I have suspect valves in my 3cyl. In the context of no engine teardown experiance, but not afraid of it, how can I check them? Is it just as easy to replace them as to check them? (i.e. should I buy replacements before tearing into it)

thanks,

Jay W
505/287 Dakota


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PostPosted: Tue Nov 22, 2005 12:26 pm 
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woodrufj wrote:
Probably not the best forum to ask, but since we're on the subject.

I have suspect valves in my 3cyl. In the context of no engine teardown experiance, but not afraid of it, how can I check them? Is it just as easy to replace them as to check them? (i.e. should I buy replacements before tearing into it)

thanks,

Jay W
505/287 Dakota


Do a compression check first.

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 Post subject:
PostPosted: Tue Nov 22, 2005 8:25 pm 
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M3 wrote:
Do a compression check first.


Also do a leak down test.
If your valves are suspect, you will be able to actually hear air escaping through the exhaust manifold past the exhaust valve/s or in a rare instance through the intake valve/s.

..


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