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Exhaust Q

 
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yourconfused
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Joined: 31 Jan 2009
Posts: 46
Location: ATX
1786.52 points


1992 Subaru SVX

PostPosted: Fri Feb 06, 2009 10:47 am    Post subject: Exhaust Q Reply with quote

As if I haven't asked enough questions of you guys already, I have another one for you.

First off I just have to say that I am on quite few other forums and I am just amazed at how nice, honest, respectful and informative you guys are. I am really thankful that Google sent me here.

Here is my exhaust question for this forum question:

So I am at a cross roads on the exhaust. I know that I would like to run 1.625" primaries to a pair of 2.5" collectors then to a 3.5" single exit.
What has entered into the equation is my interest in running a shot of nitrous and the possible need to alter the exhaust design to compensate for increased HP output.
I Was thinking that since there will not be a larger amount of air going through the motor (as if I were to be running forced induction) there shouldn't really be a need for a larger exhaust system. Am I missing something here? I have never used nitrous and haven't read much on the exhaust size demanded of it's use. Any input would be appreciated.
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Big Dave
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Joined: 04 Dec 2005
Posts: 2646
Location: Tampa Florida
119973.02 points



PostPosted: Fri Feb 06, 2009 5:20 pm    Post subject: Reply with quote

You can increase the exhaust port and exhaust valve size to move more volume in less time; or take more time to move it at the old rate by increasing the duration angle on the exhaust cam lobe. This is how most V-8's do it for small to moderate shots.

If you are running a Quick class then get the bigger ports and valves as you will be using multiple stages of NOS and it effectively makes the engine act as though it were physically larger.

Big Dave
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yourconfused
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Joined: 31 Jan 2009
Posts: 46
Location: ATX
1786.52 points


1992 Subaru SVX

PostPosted: Sat Feb 07, 2009 8:52 am    Post subject: Reply with quote

Big Dave wrote:
You can increase the exhaust port and exhaust valve size to move more volume in less time; or take more time to move it at the old rate by increasing the duration angle on the exhaust cam lobe. This is how most V-8's do it for small to moderate shots.

If you are running a Quick class then get the bigger ports and valves as you will be using multiple stages of NOS and it effectively makes the engine act as though it were physically larger.

Big Dave


I am going with one size larger intake and 2 sizes up on the exhaust valves, but am going to try something a little different on the port sizes. I will get to cams a little later, but I am going to have them (all 4 of them) welded up and reground for a much different profile to move allot more air.
I am not sure how much larger I can really go on the exhaust...

Ok what I should really ask is if there is a calculator out theere that takes cam profiles, compression, displacement etc into account to missing variables. I know what I am trying to ask, but not sure how to put it.

I am not sure if I would be going for a Quick class or not. I don't have any idea of what kind of times I will be running. I guess 12's would be nice, but maybe not realistic without spraying a little.
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clay
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Joined: 24 Nov 2002
Posts: 3209
Location: South Carolina
318129.23 points


1972 Chevrolet Nova

PostPosted: Sat Feb 07, 2009 8:28 pm    Post subject: Reply with quote

For anything below a 150 shot, I wouldn't really get hung up with trying to build anything specifically for nitrous. Build a nice exhaust system and let it eat. What you have spec'd should be fine with a good muffler and the e.t. range you are shooting for. From what I have seen a 100 shot will give you around 100 h.p. on about any setup. If you build specifically for nitrous it will start to let more power be made than would be normally be gained - for example a 150 shot will now give you 160 - 170 h.p. You could experiment a little with rocker ratio's. Get a split set of 1.5 - 1.6's and swap them from the intake to the exhaust and see what gives the most benefit (these ratio's assume a SBC, but you get the idea). Clay
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yourconfused
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Joined: 31 Jan 2009
Posts: 46
Location: ATX
1786.52 points


1992 Subaru SVX

PostPosted: Fri Feb 27, 2009 12:49 am    Post subject: Reply with quote

clay wrote:
For anything below a 150 shot, I wouldn't really get hung up with trying to build anything specifically for nitrous. Build a nice exhaust system and let it eat. What you have spec'd should be fine with a good muffler and the e.t. range you are shooting for. From what I have seen a 100 shot will give you around 100 h.p. on about any setup. If you build specifically for nitrous it will start to let more power be made than would be normally be gained - for example a 150 shot will now give you 160 - 170 h.p. You could experiment a little with rocker ratio's. Get a split set of 1.5 - 1.6's and swap them from the intake to the exhaust and see what gives the most benefit (these ratio's assume a SBC, but you get the idea). Clay




i'm not sure what the stock crank will handle I honestly see absolutely no room for improvement on it. I'll get a pic up so you can see what i am talking about. I think sticking to a 150 shot will be good for the time being, but a 250 would be nice.

6 cylinders w/ 7 mains





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