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header tube size question,

General engine tech -- Drag Racing to Circle Track

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chevy art
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header tube size question,

Post by chevy art » Sat Apr 13, 2019 7:47 pm

im running 1 3/4 inch header tubes in my 67 nova. they are the fenderwell exit headers. i have a 383 cube sbc with 14to1 compression. 220 cc intake runners, a 660 lift,274 274 duration cam with a holley 200 25 street strip dominator intake(single plane) and a 950 carb. . i take this engine upto 7800 rpms and come out at 5000 rpms.. i have header extensions aprox 12 inches long at end of headers. am i loosing alot of power by not using 1 7/8 or 2 inch header tubes?. is there any way to improve the current header setup. new headers with the bigger tubes cost aprox $1,000 and this is my last year racing(76 yrs old) and dont feel like investing in new headers. next owner can buy them. thanks art in NY

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Re: header tube size question,

Post by GARY C » Sat Apr 13, 2019 7:59 pm

With your compression and rpm I would not change them unless i had the money and the desire to do a header test.

Everything I have read on the subject suggest higher compression likes smaller headers and longer collector only favor tq below peak.
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Re: header tube size question,

Post by MELWAY » Sat Apr 13, 2019 8:00 pm

I would save your money. I have had many 23 deg chevs make 650-700hp with a 13/4” pipe 3.0” collector
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Re: header tube size question,

Post by ClassAct » Sat Apr 13, 2019 8:17 pm

At that RPM, the tubes are WAY too long. That's another issue with FW headers. 1.875 tubes won't hurt it, but the length is killing it.

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Re: header tube size question,

Post by MadBill » Sat Apr 13, 2019 10:49 pm

ClassAct wrote:
Sat Apr 13, 2019 8:17 pm
At that RPM, the tubes are WAY too long. That's another issue with FW headers. 1.875 tubes won't hurt it, but the length is killing it.
Just to be clear, are you're saying that 12" collectors are too long, or just assuming that fenderwell exit header primaries must be?
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Re: header tube size question,

Post by ClassAct » Sat Apr 13, 2019 10:58 pm

MadBill wrote:
Sat Apr 13, 2019 10:49 pm
ClassAct wrote:
Sat Apr 13, 2019 8:17 pm
At that RPM, the tubes are WAY too long. That's another issue with FW headers. 1.875 tubes won't hurt it, but the length is killing it.
Just to be clear, are you're saying that 12" collectors are too long, or just assuming that fenderwell exit header primaries must be?
In my simple mind, I THOUGHT I typed primary inbetween the and tubes. In my head I typed it, but my fingers let me down.

Unless the chassis is not what I think it is, the primary tubes on every set of fender well headers I've seen is way too long for anything. I'm talking about shelf headers. Certainly, a set of Calvins headers would be the schizznizzle but the OP didn't say he spent Calvin money on them so I ASSumed he had a shelf set of headers.

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Re: header tube size question,

Post by cab0154 » Sun Apr 14, 2019 1:30 am

I dont think a larger header would help, especially with that cam on a 383.
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Re: header tube size question,

Post by chevy art » Sun Apr 14, 2019 1:14 pm

i guess my 1 3/4 headers are ok, but should i remove the 12 inch extensions at the end of my header collectors. i just put them on there a long time ago and dont even know why i put them on. are they hurting or helping me thanks art in NY

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Re: header tube size question,

Post by tenxal » Sun Apr 14, 2019 1:24 pm

chevy art wrote:
Sun Apr 14, 2019 1:14 pm
.....should i remove the 12 inch extensions at the end of my header collectors. i just put them on there a long time ago and dont even know why i put them on. are they hurting or helping me thanks art in NY
You need to try it at the track and see.

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Re: header tube size question,

Post by Keith Morganstein » Sun Apr 14, 2019 1:44 pm

The fenderwell headers for the Chevy II’s don’t all have excessive primary lengths. Some have a long collector that curves and turns at the end.
3523916C-412F-4CCB-970F-465C5665B4E9.jpeg
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Re: header tube size question,

Post by ClassAct » Sun Apr 14, 2019 3:10 pm

Keith Morganstein wrote:
Sun Apr 14, 2019 1:44 pm
The fenderwell headers for the Chevy II’s don’t all have excessive primary lengths. Some have a long collector that curves and turns at the end.

3523916C-412F-4CCB-970F-465C5665B4E9.jpeg
That may be the best set of off the shelf FW headers I've seen. I don't know that I'd add much to collector length but at least the primaries aren't 48 inches long.

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Re: header tube size question,

Post by MadBill » Sun Apr 14, 2019 4:38 pm

My guess is that PipeMax would want maybe 14" collectors. You probably won't find much with any change.
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Re: header tube size question,

Post by Boz-Race Engines » Mon Apr 15, 2019 11:00 am

I would try 14-16in collector extensions, the diameter is fine, testing is the key
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Re: header tube size question,

Post by chevy art » Mon Apr 15, 2019 8:53 pm

thanks guys for the info. going out last sunday of this month at atco in NJ. i will extend the tubes a few more inches after the 1st pass and see what happens. art in NY

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Re: header tube size question,

Post by engineguyBill » Wed Apr 17, 2019 1:25 pm

Your current 1 3/4" primary tubes are large enough for your current application. You might want to experiment with and without the collector extensions, though. If your engine is producing power all the way through your maximum RPM level of 7800, you might realize some performance increase without the extensions.
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