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GT40 Enthusiasts Club Forum for the GT40 Enthusiasts Club and Fortyfication

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Old 31st March 2017, 05:21 PM   #21
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Re: P1119

They do a lot of the GT40 engines yes?
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Old 31st March 2017, 05:50 PM   #22
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Re: P1119

No idea Mike to be honest. I last used them in the 1970's! If they're still around I assume so, they were top engine builders back in the day and specialised in American iron.
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Old 31st March 2017, 06:26 PM   #23
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Re: P1119

Yep, Mathwell 289 race engine, sounds great in shop, might just get out on road and see what it feels like in the next couple of days.
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Old 1st April 2017, 03:23 AM   #24
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Re: P1119

Thanks Frank - good to see they're still around, so many are not. Just a thought, those primaries look to be 1" 5/8ths and I assume that is because it is primarily a road car. I would have expected 1"7/8th's with a "race engine," but not an expert on 289's by any means..
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Old 1st April 2017, 07:54 AM   #25
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Re: P1119

Just to satisfy you, the primaries are 1.75" ( inch and three quarter ) , had to go out and unlock the shop to check! Frank
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Old 1st April 2017, 11:05 AM   #26
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Re: P1119

If you measured to satisfy the Professor and not me I'll still say thanks anyway. The collectors look small maybe 2 or 2 1/2". I've done a lot of reading and am going to be doing 1 5/8" primaries on my 302. Everything I have read suggests one should error on the small side and that most go too big. My collectors are 2 1/2". Would like to hear 1119 running.
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Old 1st April 2017, 01:27 PM   #27
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Re: P1119

Quote:
Originally Posted by wealdenengineer View Post
Just to satisfy you, the primaries are 1.75" ( inch and three quarter ) , had to go out and unlock the shop to check! Frank
That's interesting and what I would have expected. I don't know why but they look smaller. By the by, thanks for checking Frank, and try & get a video of your road test..Holy crap Batman, how exciting!
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Old 2nd April 2017, 12:19 AM   #28
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Re: P1119

A lot of people don't know that traditional calculations for optimal collector size go out the window when you are talking about 180-degree headers instead of traditional 4-into-1 headers. In order to capitalize on the efficiencies of the 180-degree design, the collector size needs to be substantially smaller than what would normally be found on a conventional header, all other things being equal. That's why proper 180-degree headers have what looks like puny collectors.

Or so I've been told by some genuine engine experts I know. I'm just parroting what they have told me, but they have done countless hours of dyno research to back it up.

At least one Pantera parts vendor produces 180-degree headers with 3 1/2 inch collectors, and they are hopeless, giving up gobs of bottom end and midrange....
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Old 2nd April 2017, 01:27 AM   #29
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Re: P1119

To expand on Mike's post above the 180 system uses the smaller collector simply because the pulses from each cylinder arrive at the collector at equal 180 intervals, where as conventional V8 side for side systems can have intervals of 90/180/270 in each collector, so there is not an even amount/volume of spent exhaust gas trying to pass thru the collector all the time, in some ways you could say its simpler to design and calculate exhausts for the 180 system, just do not listen/read/ or watch any USA exhaust info! Think Europe & UK!
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