Header discussion

[serega12]

Welding up a header shouldn't be too big of a deal for an experienced welder. Designing is a bit tricky though. Diameters, lengths and collector design are all pretty important. I'd be happy to help out. I have a some reference info that will help out. I've designed two headers for other cars I have had. I started making one but never finished it, and the other I never started. Heres a pic of one of them.

Nice, but if I understand your last post correctly, this is for some other car, right? Are you sure the pipes are supposed to be that long before they join together?

[Daox]

Yup, that header was designed for 1.5L Tercel engine.

I'm absolutely sure the tubes should be that long. Long tube headers are always superior to shorty headers. Look on any race car. The longer tubes give you a broader torque band than short tubes. I've read the recommendation for a street car to never go shorter than 32". I think this header is 34" or 36" IIRC. They're also equal length runners which is another good design practice.

[serega12]

Yup, that header was designed for 1.5L Tercel engine.

I'm absolutely sure the tubes should be that long. Long tube headers are always superior to shorty headers. Look on any race car. The longer tubes give you a broader torque band than short tubes. I've read the recommendation for a street car to never go shorter than 32". I think this header is 34" or 36" IIRC. They're also equal length runners which is another good design practice.

Thank you Daox,

Very informative answer. I've heard about equal length design (which is what xiaogary's header for our car looks like...) I haven't measured the actual length, but from what I understand, xiaogary's header which replaces our stock header and cat is not much more than 24", but definitely not 32" or 34"... Is there a way for us to go longer than that? Would it be practical? Are the gains from xiaogary's headers actually the best we can do or can we go with a longer cat-delete header for more gains?

Also, they say that 4-2-1 is a better choice for smaller engines (like aveo and tercel engines)... what's your opinion on that?

Thanks ahead for all the answers.

P.S. I understand that this may not be the most appropriate thread to ask these questions (but it already had a picture of headers in it ) so if you need to, feel free to move this post where it belongs better.

[Daox]

I'm starting this thread to talk about headers and header design. This is in response to a discussion that sprouted up in another post and to keep things clean I moved a few things over.

Edit: I see the merge didn't work all that great. Oh well.

[petrified.rabbit]

a 4-2-1 header is based on the idea that the cylinders have opposing exhaust strokes. I am not sure of the appropriate term, but it does not necessarily restrict the exhaust any, as the pipe would not be doing anything for the other 3 strokes of one piston, so a 4-2-1 design makes it work for every other stroke in relation to the first piston. if i recall correctly, they can actually help improve exhaust velocity when staying in lower rpms versus the 4-1 long tube header depending on other design factors, like engine size, rpm ranges, tuning, etc.

a 4-1 header just gives all the pistons their "own system" so everything is equal for as long a length as possible. Its more conventionally designed, but like they say don't fix what works. This tends to be a more top end system, but they improve performance over stock throughout the power band.

xiogarys shorty 4-1 header is a compromise to keep the cat, the other longer 4-2-1 is a bolt in design that meets at the cat back, both are better than stock, he has the dyno numbers somewhere. you could probably get more out of a longer header but there is not much room under the car (the oil pan is already notched for the exhaust) to run 4 wide wouldnt work, to do 2 and 2 takes away more ground clearance. the avep also has a design where the exhaust goes back up an over the k frame. so to keep the pipes ideal length will just run into clearance issues the rest of the way back..

[Daox]

Rabbit summed it up pretty well.

I think even with the notched oil pan you'd probably be fine running a longer header. You will loose a bit of clearance, but I still doubt it'll be the lowest thing hanging down. Thats been my experience with other cars at least. If it does have some funky bends towards the back of the engine bay that'll be the determining factor in length.

When I was looking for design info I couldn't find anything on 4-2-1 type design. I believe with the extra collectors you get better low end scavenging. At higher rpms, without a great collector design, they'll likely create turbulence and reduce power. Thats really just my best guess though. Beyond that I wouldn't know how to size them properly or what length to make the primaries and secondaries.

IMO Xaiogary's header Is too short. I'm sure its a little better than stock, but not nearly what it could be.

[petrified.rabbit]

my exhaust pipe an flex piece under the engine are already flattened out from driving, not leaks yet, but i can not even think of trying more pipe under there, even oversized.

Xiogary's 4-1 header is 11 hp gain on the dyno with his car.

[Daox]

Wow, the stock manifold must flow pretty bad then. Thats a huge gain on a 100hp engine.

If you're flattening the stock pipe that really sucks. How far are you lowered?

[petrified.rabbit]

measured difference i took when i did it, was right around 2 3/4" in front. i only have 1/2" of fender gap.

[ontarian_frog]

Wow, the stock manifold must flow pretty bad then. Thats a huge gain on a 100hp engine[...]

Well the header in question is the long one and it deletes the cat. The rest of the system is pretty good, except for the stock rear most muffler.