1 3/4 vs 1 5/8 primaries - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 21 Old 09-10-2009, 03:01 AM Thread Starter
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1 3/4 vs 1 5/8 primaries

How much of a difference would it make to step up to 1 3/4 primaries over 1 5/8. Combo is in my sig looking at a precision 76gts for now!

The car is mostly street driven but does see the track 2-3 time a month if not more!

Thanks in advance!


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post #2 of 21 Old 09-11-2009, 03:08 AM
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If you're talking benefit for your set up I would say little to none. There are quite a few turbo cars that make 1000 hp or more with 1 5/8 primaries, 2000 hp turbo cars with 1 7/8 primaries. The smaller primaries would probably help your turbo spool due to increased velocity at your power level. I would concentrate more on having a free flowing downpipe/exhaust. Cheers.


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post #3 of 21 Old 09-14-2009, 01:46 PM
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Smaller is better for street use.. Also depends on how large the engine is..

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post #4 of 21 Old 09-14-2009, 01:54 PM Thread Starter
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post #5 of 21 Old 09-14-2009, 02:40 PM
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I was making 1382rwhp @ 31 psi, 427 cubes twin PT78's with 1-5/8 flipped.
With the new car I made some new 1-3/4 headers and made a couple other small changes had it up to 28 psi and made 1352rwhp.

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post #6 of 21 Old 09-14-2009, 04:46 PM
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I was making 1382rwhp @ 31 psi, 427 cubes twin PT78's with 1-5/8 flipped.
With the new car I made some new 1-3/4 headers and made a couple other small changes had it up to 28 psi and made 1352rwhp.
That is some good information. I always thought 1 5/8's would choke a car making that kind of power. Similar setup in the new car with bigger primaries?

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post #7 of 21 Old 09-14-2009, 05:09 PM
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That is some good information. I always thought 1 5/8's would choke a car making that kind of power. Similar setup in the new car with bigger primaries?
Pretty much. I relocated the turbos no difference I'm sure. Put on a larger A/A IC and went from a 80mm to a 90mm throttle body. Also went from dual 4" steel exhaust to dual 3.5" aluminum exhaust.






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post #8 of 21 Old 09-14-2009, 07:37 PM
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XJHEAD you've got issues.. 1300+ rwhp

i'm at nearly half that in a street car... and it's retarded!

got any vids of your car?

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post #9 of 21 Old 09-14-2009, 09:56 PM
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XJHEAD you've got issues.. 1300+ rwhp

i'm at nearly half that in a street car... and it's retarded!

got any vids of your car?

paul k
Just go to youtube and search xjhead. Here is one that someone else took.
http://www.youtube.com/watch?v=elo4tksn9rc



..

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post #10 of 21 Old 09-14-2009, 10:34 PM
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That is some good information. I always thought 1 5/8's would choke a car making that kind of power. Similar setup in the new car with bigger primaries?
What I was told long ago by TTI is the smaller actually helps build velocity and improves spool up.


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post #11 of 21 Old 09-15-2009, 04:37 PM
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XJHEAD you've got issues.. 1300+ rwhp

i'm at nearly half that in a street car... and it's retarded!

And a serious pair in his pants for sure!

Dart 347, High Ports, FAST XFI, TH400, Precision 78GTS,E85, 836hp 714tq.
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post #12 of 21 Old 09-15-2009, 07:03 PM
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1 5/8's are plenty up to about 15psi on that motor
then 1 3/4's might help. Below 18psi wouldnt worry about it.




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the smaller actually helps build velocity and improves spool up.
Ding Ding. Velocity is just as important as flow. Bigger is not always better
on turbo applications

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post #13 of 21 Old 09-15-2009, 07:41 PM
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1 5/8 was actually recommended by a few reputable custom turbo kits for the last motor in my old car. The TWR heads on that car needed a 1 3/4 tube just to cover the exhaust ports fully. So for the longest time that is what I was trying to find until I got "schooled" on my flawed thinking.

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post #14 of 21 Old 09-15-2009, 07:47 PM
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And a serious pair in his pants for sure!
sounds like the two of you are close

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post #15 of 21 Old 09-15-2009, 07:54 PM Thread Starter
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snipe so I take it you used 1 5/8 then? Thats where im at right now Ive read everything saying 1 5/8 would be prefect but the exhaust ports are partially covered with 1 5/8

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post #16 of 21 Old 09-15-2009, 07:59 PM
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You can always open up the flanges some and taper to the tube if you worried about sealing issues due to the size difference.

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post #17 of 21 Old 09-15-2009, 10:50 PM
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A covered exhaust port is not good for any application. I even had to open up my flanges and spread the 1-3/4" tube to cover my TFS-R heads.

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post #18 of 21 Old 09-16-2009, 11:14 AM
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I have seen a few reputable turbo guys say that 1 5/8" primaries are good for about 150hp per cylinder. On a V8 that is 1200hp. So extra velocity would be a bonus. Unless you plan to make more than that???

And like the other guys said you never want the primary to be smaller than the post. So if opening up the first inch or so is doable have at it.

Good luck!

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post #19 of 21 Old 09-17-2009, 07:13 PM Thread Starter
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not to sound like a tard but how could I open up the ports on 1 5/8 headers without f'ing them up?

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post #20 of 21 Old 09-17-2009, 07:21 PM
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On some there is enough material in the flange to grind it out so that you have an opening that covers the exhaust port but it tapers down to the 1 5/8 tube on the other side of the flange.

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post #21 of 21 Old 09-17-2009, 08:05 PM Thread Starter
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Gotcha thanks. I didn't even think of that.

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