Header Sizing SBC on Nitrous

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lekid
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Header Sizing SBC on Nitrous

Post by lekid » Wed Dec 13, 2017 8:49 am

I have a SBC 400 (4.165x3.750) with 23 deg heads (248cc intake runners 2.100/1.600 valves) that made 700hp on the engine dyno and we spray 350-400hp of nitrous through a plate. So far, we have ran 5.38@128mph with the 400hp jet at 3080lbs.

I currently have 1-7/8" primaries that are 29" long and 3-1/2" collectors.

Are those headers too small for my combo? If yes, what should I be looking into for sizing? 1-7/8 step 2", 2" straight tube or 2" step to 2-1/8"? What size collector: 3-1/2" or 4"? Would the gain be significant or not?

Thanks

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Re: Header Sizing SBC on Nitrous

Post by steve316 » Sat Dec 16, 2017 8:59 am

I would at least step current header to 2" into a 3.750 collector.

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panic
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Re: Header Sizing SBC on Nitrous

Post by panic » Sat Dec 16, 2017 9:40 am

Header primary tracks power output, not displacement.

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Re: Header Sizing SBC on Nitrous

Post by Frankshaft » Sat Dec 16, 2017 9:45 am

panic wrote:
Sat Dec 16, 2017 9:40 am
Header primary tracks power output, not displacement.
What he said. Its not so much cubic inch, its more about total power output and rpm. Hey, Lekid, you from Canada, Blue Camaro?

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Re: Header Sizing SBC on Nitrous

Post by lekid » Sat Dec 16, 2017 10:33 am

Yes, I am. 1980 Blue Camaro from Manitoba, Canada.

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Re: Header Sizing SBC on Nitrous

Post by Frankshaft » Sat Dec 16, 2017 10:48 am

lekid wrote:
Sat Dec 16, 2017 10:33 am
Yes, I am. 1980 Blue Camaro from Manitoba, Canada.
I figured as much. I see you every year at Top end for the Radial revolution race.

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Re: Header Sizing SBC on Nitrous

Post by lekid » Sat Dec 16, 2017 11:21 am

We love that race! Top End is awesome: track, staff and fans are amazing!!!

I don't race in Manitoba anymore (long story). Only race at Brainerd and Top End.

I dropped a valve last August at that race on my first run! Rebuilding and should be back out in this year.

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Re: Header Sizing SBC on Nitrous

Post by Amilcar » Sat Dec 16, 2017 1:27 pm

Are you sure, the exhaust port throat/min.CSA is tuned for the big shot? Maybe it could come in first before, bigger tubes?

I`ve seen some fast cars on nitrous, run umbeliable slow without it. That makes sense.
Just noticed 700 N.A is very good power for an engine tuned for a big shot of nitrous.

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Re: Header Sizing SBC on Nitrous

Post by lekid » Sat Dec 16, 2017 5:46 pm

Both the intake and exhaust throats and ports have been ported for nitrous. It has 2.70 mcsa on the intake and a pretty big exhaust throat with 50deg seats for nitrous.

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Re: Header Sizing SBC on Nitrous

Post by GARY C » Sat Dec 16, 2017 8:15 pm

I was taught that a nitrous engine needs a bigger header but the counter perspective to that is higher cylinder pressure would be similar to higher compression and that favors a smaller header.

I think it would require dyno testing to be conclusive.
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Re: Header Sizing SBC on Nitrous

Post by MadBill » Sat Dec 16, 2017 11:10 pm

The simple analysis would be that exhaust mass increase is proportional to power gain and should be appropriately accommodated in the header specs.
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.

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Re: Header Sizing SBC on Nitrous

Post by Frankshaft » Sun Dec 17, 2017 9:03 am

lekid wrote:
Sat Dec 16, 2017 11:21 am
We love that race! Top End is awesome: track, staff and fans are amazing!!!

I don't race in Manitoba anymore (long story). Only race at Brainerd and Top End.

I dropped a valve last August at that race on my first run! Rebuilding and should be back out in this year.
Yah, I remember that. That sucked. Not to rub it in, but you would have made it to the finals, against us, and you would have won too. Matt's fuel pump died in the burnout box in the finals. Hope all is well with you guys up there, we enjoy that race and seeing all you guys, good group. They are considering a different track for it this year, if Chris puts it on. Its been SO bad the last few years, radial cars need a good prep. We had 15 out for 1.2 seconds, and 80 lbs of weight bolted in, with the limiters and struts full loose to get down. Your car would be a perfect candidate for front fender exit headers. Would be cool. 2 inch by 4. Can't see it hurting it. If it does, that just means your not spraying it hard enough, lol.

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Re: Header Sizing SBC on Nitrous

Post by lekid » Sun Dec 17, 2017 2:51 pm

Hey Frank, I remember you now! we had a great talk!!

Sucks that Matt's pump failed! You ain't rubbing it in, I realized that the next day when I saw that Andy won with 5.5* runs and my car ran 5.46 with a dropped valve!!!

You win some and you lose some! Yeah, traction there in the last few years has been just okay, Chris needs to step it up. My car still hooks real good there, but hooks a lot harder at Brainerd!!

Hope to see you this summer again!!

What do you think of 1-7/8" for around 8" to follow the exhaust port size and than step it up to 2" into 4" collectors?

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