Header design help request, mid-engine LT1 Corvair

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angrycorvair
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Re: Header design help request, mid-engine LT1 Corvair

Post by angrycorvair »

Progress has been slow, plus revised design a few times. About to wrap up primary for #1. Status as of 4/12/2021:
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F-BIRD'88
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Re: Header design help request, mid-engine LT1 Corvair

Post by F-BIRD'88 »

I would get a set of easy fit headers to
A get the car up and running and tuned.

B Compare perf against what you are building.

Something like Hedman #68600 Mid length,
You might save your self a lot of bother and $$$
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Re: Header design help request, mid-engine LT1 Corvair

Post by F-BIRD'88 »

The best headers have a (remote /rear mount) Turbo attached... eg STS turbo systems (Holley) or like.
Even very modest low boost (3-4 psi) will out power any custom design header you can make.
angrycorvair
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Re: Header design help request, mid-engine LT1 Corvair

Post by angrycorvair »

I think not so bad for working with junk. About $48 invested to this point:
1D9A23F7-584E-42BD-ACE9-699792B30AD0.jpeg
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skinny z
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Re: Header design help request, mid-engine LT1 Corvair

Post by skinny z »

Lookng A-OK to me.
Good luck with the rest.
Keep updating.
Is there a turbo in the future?
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angrycorvair
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Re: Header design help request, mid-engine LT1 Corvair

Post by angrycorvair »

skinny z wrote: Thu Apr 15, 2021 11:39 pm Lookng A-OK to me.
Good luck with the rest.
Keep updating.
Is there a turbo in the future?
*distant* future, perhaps, if the rest of the car proves to be a good base.
angrycorvair
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Re: Header design help request, mid-engine LT1 Corvair

Post by angrycorvair »

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angrycorvair
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Re: Header design help request, mid-engine LT1 Corvair

Post by angrycorvair »

Primary tubes are not equal length, but secondary tubes and secondary collectors are money. Drivers side almost complete, all the pieces for passenger side are cut and tacked and ready for assembly.
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skinny z
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Re: Header design help request, mid-engine LT1 Corvair

Post by skinny z »

All bits and pieces salvaged from elsewhere to keep costs down? That's the plan isn't it?
Given the designs of today's off the shelf headers, it seems the emphasis, other than the primary tube diameter, is concentrated on the secondaries. Or so is my understanding anyway.
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Re: Header design help request, mid-engine LT1 Corvair

Post by angrycorvair »

skinny z wrote: Sun May 09, 2021 1:10 pm All bits and pieces salvaged from elsewhere to keep costs down? That's the plan isn't it?
Given the designs of today's off the shelf headers, it seems the emphasis, other than the primary tube diameter, is concentrated on the secondaries. Or so is my understanding anyway.
Yep, mostly salvaged bits. I did buy a couple “J plus 90” bends for the secondary pipes. I’m making my own increasing-diameter collectors by pie-cutting along the length of the larger diameter tube. Time and Argon do not count against the budget. :-)

After all the reading I did, I understood it the same as you: primary pipe diameter is more important than length. Secondary pipe diameter and length, choke diameter, and collector dimensions are also all more important than primary length.

What I’m trying to figure out now is where to place the mufflers (relative to choke and/or collector exit), and how using a full exhaust system affects, or is affected by, the collector design. For example, are the pipes from the collector to the muffler inlet considered additional collector length?
skinny z
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Re: Header design help request, mid-engine LT1 Corvair

Post by skinny z »

My understanding of the technical definition of the secondary/collector is the length of pipe from the ends of the primaries (in the merge) to where it exits into a significant change in volume. That could be the atmosphere, a termination box or similar. It may be that in some cases the muffler could be considered as this transition although I think for the most part, the entire exhaust system becomes part of the secondary in a typical road car. I do know that a muffler designed along the likes of a "glass pack" will serve as a collector extension. Or so it's said anyway. Something I will experiment with one day.
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Re: Header design help request, mid-engine LT1 Corvair

Post by MadBill »

angrycorvair wrote: Sun May 09, 2021 2:00 pm...What I’m trying to figure out now is where to place the mufflers (relative to choke and/or collector exit), and how using a full exhaust system affects, or is affected by, the collector design. For example, are the pipes from the collector to the muffler inlet considered additional collector length?
David Vizard (Google Terminator Boxes) says a glasspack 'tunes' at about 1/2 the core length and an open box -type muffler, eg. SpinTech, Flowmaster, etc. ideally will have the collector extending an inch or two into the interior and will tune to the collector's end.
The gases don't distinguish between collector and pipe, so following maxracesoftware's recommendations:

3rd Harmonic = 43.114 inches long ... greater Low RPM Torque -to- Peak Torque RPM
4th Harmonic = 21.557 inches long ... highly recommended , best Torque and HP Curve combination


You should try to place the mufflers to achieve one of these lengths* and add tailpipes if/as needed. *Half way between is the worst possible length.

As far as diameter, you mention: "I’m making my own increasing-diameter collectors by pie-cutting along the length of the larger diameter tube. Time and Argon do not count against the budget." What will be the end diameter of your meg-style collectors? if it was to be say 3-1/2", I think the only effective way to connect to the downstream system would be via reverse cones** on the ends of the megs. **Google 'Burns Reverse-Cone Megs.' Hopefully this would result in an end diameter of 2-3/4" to 3" and could be plumbed with same diameter straight tubing to a like-sized muffler inlet. (Hopefully maxracesoftware will step in to confirm or dismiss this notion.)

It should be said that a straight 2-3/4" diameter collector right into a like-size muffler would be much easier and the effect indistinguishable by butt dyno....
Felix, qui potuit rerum cognscere causas.

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angrycorvair
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Re: Header design help request, mid-engine LT1 Corvair

Post by angrycorvair »

MadBill wrote: Tue May 25, 2021 12:12 am
3rd Harmonic = 43.114 inches long ... greater Low RPM Torque -to- Peak Torque RPM
4th Harmonic = 21.557 inches long ... highly recommended , best Torque and HP Curve combination


You should try to place the mufflers to achieve one of these lengths* and add tailpipes if/as needed. *Half way between is the worst possible length.

As far as diameter, you mention: "I’m making my own increasing-diameter collectors by pie-cutting along the length of the larger diameter tube. Time and Argon do not count against the budget." What will be the end diameter of your meg-style collectors? if it was to be say 3-1/2", I think the only effective way to connect to the downstream system would be via reverse cones** on the ends of the megs. **Google 'Burns Reverse-Cone Megs.' Hopefully this would result in an end diameter of 2-3/4" to 3" and could be plumbed with same diameter straight tubing to a like-sized muffler inlet. ...
It should be said that a straight 2-3/4" diameter collector right into a like-size muffler would be much easier and the effect indistinguishable by butt dyno....
Wow, life got in the way of me keeping up with this thread -- and of making 9 months worth of progress, LOL. I'll add some pix and comments later. For now I can say that the Z06 pipes are about 2-7/8" OD, and my secondary collector exits are 2-1/8", so i'm planning to taper from 2-1/8" up to 2-7/8" over some reasonable length which may or may not be defined at least in part by the packaging space i have available.
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Re: Header design help request, mid-engine LT1 Corvair

Post by jsgarage »

Your project takes me back to my autocross days. I once built a 6-pipe extractor header system that did not reduce the flat-6 Corvair's rear ground clearance. The operative word is "once". What you're really doing is akin to building your own DeTomaso Pantera as regards to the exhaust. There's no room for much innovation before you're out past the rear body/bumper. You'll also need to leave far more clearance around the pipes than you'd think, as the temperature of Pantera exhaust tips exceeds 400F. There will not be such a thing as 'too much rear body insulation' either, if you really want to street-drive your creation. Good luck.
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