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Those big honking primeries would do you any good. Lots of way-too-fast 3800s use 1.5" or 1 5/8.

Throw out the shory style headers, they'll produce hp, but you'll sacrifice low end with them. I have a 1.5 inch primary pacesetter and had the collector reduced .25 inch to help the low end. You want the longest primary and secondary you can have to help low end. I was looking into a looooong tubed drag style application 1 5/8 stepped to a 1 3/4... makes my stock manifold look freaking dinky and puny as can be lol.

98GrandAmLD9 wrote:Throw out the shory style headers, they'll produce hp, but you'll sacrifice low end with them. I have a 1.5 inch primary pacesetter and had the collector reduced .25 inch to help the low end. You want the longest primary and secondary you can have to help low end. I was looking into a looooong tubed drag style application 1 5/8 stepped to a 1 3/4... makes my stock manifold look freaking dinky and puny as can be lol.

is your's supercharged?

Keeping your low end is all about keeping exhaust gasses flowing very quickly... that is why very large tube diameters hurt low end, because you lose the scavenging effect in turbulence created in your flow as the gasses slow down and expand.

Also, even 1_5/8 is pretty big, and should only be considered if you are supercharged. 1_3/4 is the kind of thing you put on a big block... That is just crazy big, you need a bunch of supporting mods on a supercharged engine to support that. 1.5 is more than big enough for a naturally aspirated engine, and I would consider that for my N/A engine if I could find them, but only with some supporting mods.

These engines aren't really THAT big... If we had equal sized combustion chambers, but 8 cylinders instead of 6, we would still only displace 5 liters... And most (smart) guys put 1.5" primary sized headers on their pushrod 5.0 mustangs, even with a couple supporting mods. 1_5/8 is only worth it on them if you have put in a pretty aggressive cam, and have done quite a lot of supporting mods for airflow, or you want pure top end. Of course, 1_5/8" headers seem to sell better, because, bigger is always better...

1 3/4" headers are really not that big for V8's, big block chevy headers are availible in 2 1/4" but 2" is more common. I had a mildly built 289 back in the day and 1 3/4" were all we ran in a NA engine, no one used 1 1/2" unless it was a 4 cylinder engine. I will see if it kills my low end since I bought the Pacesetter's from harofreek and they are 1 3/4" tubes, I believe it can only help. When you say low end, what rpm range are you talking? 2k-3k?

FIND wrote:Keeping your low end is all about keeping exhaust gasses flowing very quickly... that is why very large tube diameters hurt low end, because you lose the scavenging effect in turbulence created in your flow as the gasses slow down and expand.

Also, even 1_5/8 is pretty big, and should only be considered if you are supercharged. 1_3/4 is the kind of thing you put on a big block... That is just crazy big, you need a bunch of supporting mods on a supercharged engine to support that. 1.5 is more than big enough for a naturally aspirated engine, and I would consider that for my N/A engine if I could find them, but only with some supporting mods.

These engines aren't really THAT big... If we had equal sized combustion chambers, but 8 cylinders instead of 6, we would still only displace 5 liters... And most (smart) guys put 1.5" primary sized headers on their pushrod 5.0 mustangs, even with a couple supporting mods. 1_5/8 is only worth it on them if you have put in a pretty aggressive cam, and have done quite a lot of supporting mods for airflow, or you want pure top end. Of course, 1_5/8" headers seem to sell better, because, bigger is always better...

One thing to keep in mind: even stock, these (supercharged) engines flow more air volume than a 350 Chevy engine. Boost does weird things to flow on both sides of the engine.

deano55 wrote:1 3/4" headers are really not that big for V8's, big block chevy headers are availible in 2 1/4" but 2" is more common. I had a mildly built 289 back in the day and 1 3/4" were all we ran in a NA engine, no one used 1 1/2" unless it was a 4 cylinder engine. I will see if it kills my low end since I bought the Pacesetter's from harofreek and they are 1 3/4" tubes, I believe it can only help. When you say low end, what rpm range are you talking? 2k-3k?

I used headers with 1_3/4 primaries on my 454 with a 750 cfm carter feeding it, and flow was never a problem.... Supercharged, these engines can flow a lot of gas, but that's boost. Now you are boosted, so different rules apply when compared to a naturally aspirated engine. Scavenging is not as important, as it is more important to evacuate the gasses from your combustion chamber quickly. I just figured I would add a little N/A talk to the discussion, but, you don't want to overdo it either, even with boost.... Even still, If you are going with 1_3/4 primary headers on even a supercharged 3800, I would be planning on a few supporting mods, just because you want to use that additional volume... Plus, putting lots of gasses in that pipe means you gain additional horsepower from scavenging, which is basically free horsepower... Also, I didn't want to say that 1_3/4 is big for a big block.... I was just saying, that is the flow volume you are thinking about when you consider an 1_3/4 inch primary on a header....

Additionally, I should note, compare the cross sectional area of 6 1_5/8 pipes, 6 1_3/4 inch pipes, and a single 3" pipe, which you are going to have after the collector. Even considering that the 6 primaries mean a much larger area of slow moving gasses next to the edges of the pipe, you still have a heck of a lot more flow potential. Now, the gasses will cool slightly through the primaries, which does reduce the volume... but honestly, I wouldn't really care for 1_3/4 inch primaries feeding a single 3" exhaust pipe... Everything after your collectors becomes a restriction in your exhaust flow. You may have noticed that with larger displacement engines, people tend to ALWAYS run dual exhaust.... because a single 3" pipe just isn't going to do 7 liters of exhaust gasses per revolution any justice.

As far as 1_1/2 inch primary headers....I don't see any reason why those would be relegated to the realm of 4 cylinder engines only... A 2.3 engine has as much displacement per cylinder as your 289 did, and most of those 4 cylinders they are working on were OHV engines that probably flowed a greater volume of exhaust per cc of displacement than a 289 HiPo....

When I am talking about low end, yeah, I mean under 3500. That is why fuel economy suffers when a person puts on oversized exhaust.

But yeah, you are supercharged.... So the rules are a little different. I just like numbers, and I like talking about them is all, so I figured I would inject a little more stuff into here.