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post #1 of 14 Old 01-30-2017, 09:13 PM Thread Starter
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Down pipe size

I am putting together my new combo and have a question. I have a dart 347 that was a Blower car and am switching to a turbo. I have a s480 with a billet wheel and purchased a pony down t6 hotside. My questions are aluminum or steel and five or four inch. How much power has been made with a 4 inch and I will be putting out the front bumper.

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post #2 of 14 Old 01-31-2017, 05:31 AM
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Originally Posted by Greendart347 View Post
I am putting together my new combo and have a question. I have a dart 347 that was a Blower car and am switching to a turbo. I have a s480 with a billet wheel and purchased a pony down t6 hotside. My questions are aluminum or steel and five or four inch. How much power has been made with a 4 inch and I will be putting out the front bumper.
How big is the exhaust housing outlet on the s480?

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post #3 of 14 Old 01-31-2017, 08:54 AM Thread Starter
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The housing is a 96mm 1.32 ar
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post #4 of 14 Old 01-31-2017, 11:41 AM
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The housing is a 96mm 1.32 ar
Sorry I meant the actual diameter where the DP will connect to? My 7675 is 3", I would imagine yours is larger
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post #5 of 14 Old 01-31-2017, 02:21 PM
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As big as you can fit. It will keep back pressure lower and it will make a difference in HP.
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post #6 of 14 Old 01-31-2017, 05:17 PM
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3" with good sweeps got me to 1000 HP or so but start to be a back pressure issue. I got about 3-4 psi on the downpipe.

4" got me to 1200 but the larger 4" downpipe goes back up to 3-4 psi at that power. Most of my BP is at my turbine though (55-60 psi on the hotside) because the turbine is so small. I'm swapping turbos soon and that might move the problem to my downpipe, but for right now it looks like the 4" is OK to about 1200 HP or so in my car before it gets what I consider high.


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post #7 of 14 Old 01-31-2017, 09:57 PM Thread Starter
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Thanks is there any down fall to a huge exhaust?
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post #8 of 14 Old 02-01-2017, 10:30 AM Thread Starter
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Turbo Chargers

I am just going to do a five inch and call it a day thanks for the help.
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post #9 of 14 Old 02-02-2017, 11:12 AM
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Thanks is there any down fall to a huge exhaust?
There is a point of greatly diminishing power increase as the pipe gets larger, but the only negatives are cost, weight, and fit.

At 1000HP plus, almost all of my system's restriction comes from the turbine. The turbine has 50-55 psi across it. The 4" downpipe and exhaust (dual 3") has just a couple psi.

This may change when I put a bigger turbo on it and free up more exhaust flow, but that will really be because the engine will be making more power with less back pressure.


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89 LX. 363, single turbo, Super Vic EFI, TFS high port heads by TEA, solid roller, glide. Holley HP EFI. (exact combo varies)
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post #10 of 14 Old 02-02-2017, 04:18 PM Thread Starter
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Down Pipe

That is a good point I do have a good amount of room in the front as my last setup had a 50mm cog drive and I Moved the radiator really far forward. My next question you mentioned was the weight. How heavy is a five inch steel exhaust going to weigh vs 4. I am just going to drop it down and out the front bumper on the passenger side. Last question it shows you have a holley was it really hard to set up the boost control I have the hp now and am worried I am going to run out of input outputs. On my car I have not used any and kept the gm Iac.

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post #11 of 14 Old 02-03-2017, 08:34 AM
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That is a good point I do have a good amount of room in the front as my last setup had a 50mm cog drive and I Moved the radiator really far forward. My next question you mentioned was the weight. How heavy is a five inch steel exhaust going to weigh vs 4. I am just going to drop it down and out the front bumper on the passenger side. Last question it shows you have a holley was it really hard to set up the boost control I have the hp now and am worried I am going to run out of input outputs. On my car I have not used any and kept the gm Iac.
Weight will be negligible with that short of a downpipe run, whether you go 5" or 4". Personally, I think you'd be fine with necking the 5" output down to 4" for a through the bumper type outlet. We have plenty of cars around here running bottom 8s in the 1/4 mile with an S480 and a 4" downpipe.

I ran a Holley HP on my turbo car for two years and loved it so much, that I just bought the Dominator for my new twin turbo kit. The boost control isn't bad to set up. I actually used a boost controller gauge for my boost control, but I used the Holley Boost Builder function to get my car to launch with boost off my trans brake. Of course, you will need a boost control solenoid to have the Holley control your boost...I bought the Holley solenoid this time to provide a boost ramp for launch on drag radials. I think you'll be fine with the HP for your application. I went with the Dominator because I wanted the dual wide band O2 averaging function that it offers, plus the extra inputs/outputs for future mods.

93 Notch 347 twin 66s TH400...8.54 @ 162 Radials

91 Notch 410W Novi 2000 5 speed...10.99 @ 136
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post #12 of 14 Old 02-04-2017, 07:17 PM Thread Starter
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Yea we will see what happens I'm going to run the Holley boost control and try that. What spring did you have in your gate.
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post #13 of 14 Old 02-11-2017, 12:38 PM
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3" with good sweeps got me to 1000 HP or so but start to be a back pressure issue. I got about 3-4 psi on the downpipe.

4" got me to 1200 but the larger 4" downpipe goes back up to 3-4 psi at that power. Most of my BP is at my turbine though (55-60 psi on the hotside) because the turbine is so small. I'm swapping turbos soon and that might move the problem to my downpipe, but for right now it looks like the 4" is OK to about 1200 HP or so in my car before it gets what I consider high.
More of a BP question here. I'm running a 4" DP on a 76mm .92AR turbo and a 2.5" merge crossover pipe. What kind of BP numbers will I see in each, DP and merge? I'm adding sensors to log in the Dominator ECU but need to know what sensor to start with that is in range and give the best resolution and accuracy. No sense in using a 0-100 sensor if a 2bar will work.

For the op. go as big as you can get. I'm running a 4 out the turbo and all the way to the back of the trans where I split it to dual 3".

Dart 348ci, Ed Curtis cam/valvetrain, Precision 76mm, Holley Dominator EFI, CNP ignition, tons of Holler EFI small parts, 4"dp, 4R70W w/T-brake, new suspension coming soon.

Little 750rwhp at 6,000rpms and only 10lbs of boost before we just got tired of playing with clutches. New 4R70W and we are turning it up. Expecting 1,000rwhp.
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post #14 of 14 Old 02-14-2017, 07:04 PM
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Yea we will see what happens I'm going to run the Holley boost control and try that. What spring did you have in your gate.
I had a 9 lb spring I believe.

93 Notch 347 twin 66s TH400...8.54 @ 162 Radials

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