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Header primary tube size

sreidmx

sreidmx

Fortify Offroad
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Soo?? how important is this? I see 1 5/8 primary's and 1 3/4 and larger for the sbc. I am wondering what effect it has on the power delivery?
Also the length debate seems to rage on but for mid and upper power wouldnt you want a shorter header? Or is that not the case?
 
So the longer the exhaust the more power you get down low (to a point of course). Its the opposite with upper end power, one of the reasons you see open headers on drag cars.

Now there of course a lot of pissing matches with this topic but theres also a lot of cold hard facts out there.

For every 1/8th inch of primary size increase you generally move the peak numbers up roughly 500rpms or more. Theres a lot of dyno sheets out there displaying that shorty headers are not much of a gain at all so with that said mid to long tubes are really bang for the buck.

Im thinking youll be in the 300-400 hp range? Youll always see 1 5/8's come up for that range.

1 5/8s ftw.
 
yea should be right in there for hp.. I kind of want to run either the Hedman 69320 which looks to fit nicely, or schoenfeld has some fenderwell or standard headers as well.. I have to do some measuring for clearance.. there is also the 180 header that @charity case is running, I have to see that first to even consider it.. That would require major mods.. still dunno yet.
 
sreidmx said:
Soo?? how important is this? I see 1 5/8 primary's and 1 3/4 and larger for the sbc. I am wondering what effect it has on the power delivery?
Also the length debate seems to rage on but for mid and upper power wouldnt you want a shorter header? Or is that not the case?
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The 69230's are the mild or coated steel version of 62230 I believe. Been running my 62230's for about a year now, no issues. Never re-torqued.

Plugs kind of suck to get at in two positions on the heads, I can imagine a 1-3/4 header wouldn't make it easier.

Can't think of any reason to complain about the headers. Make sure you support the exhaust, the ball/sockets will fail if you over-tighten them and if you have to keep re-tightening them they will also fail. Heck of a lot easier to support single 3" exhaust than trying to hang duals solidly.
 
I'd be interested in being a Guinea pig, I just hope I don't have to cut my freshly welded engine cage up..
 
What is your exhaust size port on your heads? You want them fairly close in size, you want the straight through effect not the tumble going from for an example 1.5 port into a 2' collector.
 
sreidmx said:
Id have to measure, they are pretty standard sbc heads, nothing special.
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1-5/8 is going to work if they are anywhere near the SBC exhaust ports, Vortec or earlier. Honestly I suspect for most of us 1.5" would be the proper diameter, but the 1-5/8" is a decent compromise. No idea if a 1.5" would cover the exhaust ports though.

FWIW I went from the looong Hedmans 69890, to the much shorter 62230's, and the butt dyno says there is no noticeable difference in power. It might be noticeable on a dyno, but not just driving it around.
 
I am really glad you mentioned that you moved from the longer header to the shorter ones, I was a little worried about it.
I called Schoenfeld regarding the fenderwell headers, they only come in 1 3/4 and 3 inch collector, he assured me that the primary size would move the power up some but for my needs wouldnt be a bad thing and with the 3 inch collector should still make plently of torque, however they have no pics installed onto a truck nor do they have dimensions.. so aside a single video on facebook with a bbc I have no reference.. so do I take the risk? They do offer it in a kit not welded.. that would make adjusting it really easy.. shipping this would be about 35$.
 
well.. looking at pics of the truck when the motor was in with the shocks, I really dont think Ill get lucky enough for the headers they offer to fit.. so prob those 69230s os what Ill use.
 
sreidmx said:
well.. looking at pics of the truck when the motor was in with the shocks, I really dont think Ill get lucky enough for the headers they offer to fit.. so prob those 69230s os what Ill use.
Click to expand...

Yeah, I'd hate to be the guinea pig for something that may or may not fit. There is something to be said for headers that have been demonstrated to fit your specific vehicle.

I don't think 1-5/8 primary size is so common because the tubing is the cheapest. The larger and smaller sizes are out there, but they are so much less common that there has to be a reason. Based on the math I did, 1-5/8 falls right in the middle of the low end power that 1-1/2" would support, and the upper end power that 1-3/4" would support. Stock truck/engine would probably be best served with 1-1/2" primaries, but anything beyond bone stock starts to flow enough that 1-5/8" is probably the safer choice. 1-5/8" pipe supports 90+HP, so you'd need a really wild motor to need larger. I'd rather go too small than too large, scavenging is going to be better on the lower end. As 1-1/2" gives you VERY limited choices though, I don't think it's worth considering.

My engine does not get above 4400RPM (rev limit) but I routinely hit it. I've never been inclined to feel the headers were the limitation in flow. With no difference between the header lengths (and I forgot, old setup was longer headers to dual 2.5's, vs the the present shorter headers to single 3") in lower or upper end felt power, I don't think you'd be giving up anything to notice going with 1-5/8" or shorter vs. longer. I believe the Hedman's I am calling "short" are still quite a bit longer than true shorty headers.
 
Why no love for an inch and a half primary? Lack of experience I guess.
Somebody said inch and 5/8s is better so that's the end of the story.
 
Considering my goals I think the 1 5/8 would be the minimum, I know on a dirt bike exhaust is used as a tuning tool, and it has a major effect when you change diameter and lengths, but we're talking about serious power from small displacement and overhead valve or two strokes, that might be an apples to oranges comparison. But still I cannot find the hedman in a 1 3/4 primary so I am not going to split hairs, it don't think it's worth it.
 
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