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PostPosted: March 12, 2017, 10:57 am 
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Location: Shawnee, Ks
I am trying to calculate the exhaust diameter on my Se7en. It is dyno'd
at 104HP at 6000 rpm for the 1600cc xflow. The charts I have looked at
say a 1 5/8" or 1 3/4" after the collector. The NOS stock Pinto
competition header that I have is 2 1/2" at the collector. Do I reduce
down or just use 2 1/2" all the way through the muffler and tail pipe?
Tks Russ

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PostPosted: March 12, 2017, 11:55 am 
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Doing reduction after the muffler will help it muffle much better. Can you get a muffler with reduction or elbows with reduction? Tailpipe on my Formula Ford is 2" with 106 HP.

In the end go with doing the reduction where it is easiest for you, but try to wait until the inlet of the muffler so you get a bit of 2" pipe on the way, again don't worry about it if you can't bend the new pipe or something...

Pushrods rock!

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PostPosted: March 12, 2017, 5:04 pm 
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horizenjob wrote:
Pushrods rock!


Wait! I thought pushrods pushed... and rockerarms rocked? :?

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PostPosted: March 12, 2017, 7:04 pm 
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trialsmangasgas wrote:
I am trying to calculate the exhaust diameter on my Se7en. It is dyno'd
at 104HP at 6000 rpm for the 1600cc xflow. The charts I have looked at
say a 1 5/8" or 1 3/4" after the collector. The NOS stock Pinto
competition header that I have is 2 1/2" at the collector. Do I reduce
down or just use 2 1/2" all the way through the muffler and tail pipe?
Tks Russ


Could you share the source of the charts with us? Hopefully, they'd be online somewhere.

Cheers,

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PostPosted: March 12, 2017, 7:38 pm 
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Here are a couple of them
http://www.exhaustvideos.com/faq/how-to ... -diameter/

http://www.mk5cortinaestate.co.uk/calculator5.php

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PostPosted: March 12, 2017, 8:23 pm 
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Check out this old post on the topic of exhaust size. It says that it doesn't really matter how your exhaust is configured so don't sweat the details too much.
Attachment:
Screen Shot 2017-03-12 at 7.20.49 PM.png
Screen Shot 2017-03-12 at 7.20.49 PM.png [ 116.13 KiB | Viewed 142 times ]

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PostPosted: March 12, 2017, 10:12 pm 
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I would pie cut it down to a two inch system, leaves ample flow for when you turbo it....


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PostPosted: March 12, 2017, 10:23 pm 
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No turbo for me. Xflows don't like turbos

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PostPosted: March 13, 2017, 12:30 am 
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These motors have a history going back to something like 900 CC, so at 1600 and then putting a turbo on it - not so good. They have very little space between their water jacket passeges to the head and the cylinder bore, so they cant take the extra pressure of a turbo. On the other hand the small I4 engines that take a turbo weigh a whole chunk more and they are physically huge compared to these, so these engines really are gems for these cars.

A friend of mine built a lot of these for the oval track guys back in the 70's and 80's. I think you can get 130-140 for street use reasonably well. Duratec engines go to around 175 or so for street. These are all engines around 200-225 lbs.

Trialsman I think you drive this car a good bit so a quiet exhaust is probably good for you. It's right next to your head so your going to hear it enough anyway. Having resistance after the muffler really helps it to it's job, so that elbow you have is a good thing. If you can neck it down a bit there too that's also good. Let the muffler and pipe in front of that restriction average out the flow pulses from the engine, there's plenty of volume there to do that averaging. It won't hurt your power.

Think of those high power superbikes that don't make any noise next to you at the stop light. Many of them have a very small exhaust exit, sometime they just make it look bigger than it really is. They have more power than you and what looks like a 1" pipe exit.

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Wait! I thought pushrods pushed... and rockerarms rocked?

:rofl:

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PostPosted: March 13, 2017, 2:22 am 
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trialsmangasgas wrote:

If I had to guess, I'd say the 'mk5cortinaestate' calculator is just doing the 2.2 cfm/hp and 115 cfm/in^3 math, which means you also still need to add the pipe wall thickness...Which takes you right back to 1.75 inch tube. So I'd use that as the starting point.

I'm curious, what is the diameter of the primaries?

Ultimately, I guess it depends what you're looking for. Ease of implementation? Sound level? Performance? I really don't think going over 2.0 inches will be doing you any favors for 'street' performance or sound. You'll also run into the practical limit of what muffler sizes are out there, which often start at a minimum 2.0 inches inlet/outlet.

The easiest solution would probably be to run 2.5 out and cap it after the muffler. This probably wouldn't be the best for performance though. After that, for better performance, would probably be to choke it down to 2.0" after the collector and run that all the way out. Or if you're a glutton for punishment, you might (or might not) even get 'some' benefit out of choking it down to 1.75 after the collector, then expand it out to 2.0 as it continues towards the muffler.

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Last edited by Driven5 on March 14, 2017, 3:05 pm, edited 1 time in total.

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PostPosted: March 13, 2017, 9:11 am 
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Primaries measure 1.48" OD

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PostPosted: March 14, 2017, 3:18 pm 
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Remember that the 1.75 is also 'ideal' flow through a straight section of pipe/tube. So if you can reasonably (and smoothly) adapt the header down to a 2" exhaust you'd probably be pretty set. Cone Engineering makes 'pre-sized' collector transition cones that you could use in reverse to adapt from the 2.5" at the header flange connection down to 2.0" for the remainder of the exhaust, for ~$12 in mild steel or ~$20 in stainless.

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PostPosted: March 14, 2017, 9:11 pm 
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Interesting. Thanks

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