4A-G header suggestions needed/header theory ??s

Greetings all,

I am getting down to the final details on a new engine for my AE86 Toyota Corolla GT-S hatchback for 2009 and one of the last stumbling blocks is a header.

The car is going to be used for trackdays, autocross fun (not built for any particular class,) mountain roads, and perhaps a drifting/car control skidpad day here and there. The goal is awesome response, fairly big normally-aspirated gains over stock in the mid and upper ranges, but shy of a full-race state of tune that produces more stress and adrenaline driving to and from the track than the actual event. It won't be a daily driver, just a healthy, but streetable toy.

The engine is a bigport 16-valve 4A-G...basically it is all balanced and blueprinted, slight overbore with 11:1 forged pistons, head ported to Group A rally specs, TRD valve springs, HKS 272 duration 8.3mm lift cams, adjustable cam gears, silvertop ITBs with T3 trumpets, RC Engineering 320cc injectors, FJO standalone engine management/igntion, lightweight water pump pulley, Toda cro-mo lightweight flywheel, yadda yadda...

I want a 4-2-1 header to fit the LHD AE86 chassis, and basically none exist new. There are 50 bazillion nice Japanese headers which all go right where my steering column is. TRD, Tsudo, OBX, and Pacesetter make "street" headers which are generally cheap, cheaply made, and poor fitting. The TRD is probably the best of the bunch, but it is 4-1, and in my experience doesn't do much more than a stock manifold other than save some weight, make access to the starter easier, lose some torque, and make more noise.

I have an old discontinued KBD 4-2-1 header which fits and seems to offer a nice boost/smoothing to powerband over stock.

It offers good bang for the buck, but doesn't have the nicest collector design, and has 38mm primaries (1-1/2") which is a bit small when compared to a lot of the Japanese headers, which tend to be about 38mm for street, 40-42mm for performance/fast street, and 44mm or so for full race. Not that the Japanese know everything, I'm just looking for some sort of yardstick.

Is there some option I am not aware of?

Should I give up on clawing back some torque with a 4-2-1 design and just run one of the nice 4-1 choices available (like Danstoy?)

http://www.danstoy.net/products.html

Should I just run the KBD I have, and see if I can make decent power with a header that might be a bit small?

Any help appreciated, thanks!

Oh yeah...I found these guys in Finland, a seemingly mis-paired 4-2-1 header that is built for rally use, but all the first/secondhand feedback I could find raved about the torque gains WITH a slight gain in power! It is apparently the final design in a long line of different trials, and is designed to offer the best of 4-2-1 and 4-1 in one header, and...fit LHD!

http://www.martelius.com/index.php?module=ekauppa&type=2&product=490045

The problems are:

I don't speak Finnish

I am not aware of a North American distributor

Getting it here is likely expensive

Not a big deal, but I would want to add an o2 bung and get it coated, which all adds up.

Look at the length of those tubes! Now there's you torque improvement.

How about just copying the header you have in a slightly larger size and using a Burns collector?

But first I'd run what you've got and see where or even if you are disappointed. Why make work for yourself if you don't have to.

How much would a custom header cost?

Essentially going to a shop and saying "give me the longest pipes you can fit in the engine bay".

If you want top end gains, you want a 4->1 header.

4->2->1 headers are known for their torque/low-end/mid-range gains, 4->1s for their high end.

carguy123 wrote: Look at the length of those tubes! Now there's you torque improvement. How about just copying the header you have in a slightly larger size and using a Burns collector? But first I'd run what you've got and see where or even if you are disappointed. Why make work for yourself if you don't have to.

i second that thought, make sure your not wasting time and money getting a header that isnt a PROVEN gain over the other... besides, were talking about a decently built street motor, not a hasselgren motor.

carguy123 wrote: But first I'd run what you've got and see where or even if you are disappointed. Why make work for yourself if you don't have to.

I may end up doing that just to get the thing running and start tuning the ECU. I guess the reason I am willing to make work for myself that I might not "need" to is that I have spent the past 10 or 15 years driving Corollas that are semi-random collections of the parts I have or could get easily and cheaply. It seems to me that the difference between engine builds that are so-so and builds that produce remarkable results is just that:

"Well, I these parts, so I might as well install them." versus "What would be the very best way to fully optimize this engine as a system?"

I've done the former...I'm ready to put some time, effort, and some money into the latter. Obviously, I don't want to waste money or effort, but I am not limted to doing a Challenge-type build here either.

The other thing I am thinking is that the KBD works well on a 200,000 mile engine stock other than plug wires, air filter, and exhaust (obviously.) It could still work with a massive compression bump, porting, several steps bigger cams, much bigger injectors, an intake which can flow a big amount more, a 25-year newer engine computer, and 1000-1500 more rpm on the top of the rev range...but I am worried that the header will become the bottleneck at that point. I don't know enough about header design or built 4A-Gs to say for sure. I think I can expect somewhere between a 50%-75% power gain over stock. Does anyone out there in GRM land have thoughts or experience on this front?

ReverendDexter wrote: If you want top end gains, you *want* a 4->1 header. 4->2->1 headers are known for their torque/low-end/mid-range gains, 4->1s for their high end.

I'd love to be corrected if I am wrong, but to the best of my understanding, 4-1=top end and 4-2-1=low/mid is the traditional way of thinking, but is starting to be countered by some new creative designs. The current trend for four cylinder headers seems to be looong 4-2-1 which don't lose much (if any) to traditional 4-1 designs in the top end, but have much better midrange (like Burns Stainless or the Martelius header I pictured above.) There are a lot of older short 4-2-1 designs still in production (like the KBD I have) which were tooled up 15 or 20 years ago so they suffer for top end power or don't have great collectors...or there are also a lot of designs limited by room, so they are short.

Does anyone with a better understanding of header design have any input or further information (or reasons why I am wrong?)

PHeller wrote: How much would a custom header cost? Essentially going to a shop and saying "give me the longest pipes you can fit in the engine bay".

I don't know. Has anyone one here commissioned one? Does anyone in the PacNW have any recommondations of someone good to go to for custom headers?

Well, looks like I am going to try the Burns Stainless X Design and see what they recommend. I doubt I can produce anything that looks that great, but what better excuse to keep practicing my welding?

Asking around has lead to more and more suggestions of a properly designed 4-1, so another thought is to buy the TRD header and cut off the collector, use the flange/primaries/heatshield mounts/bung already there, and extend with a new collector.

I'm sure some of you guys on here have rolled your own headers before...any words of wisdom?

You have gone through Billzilla's site, right? He got into header design a bit. You might try putting an email together with your wants and current setup and tune state and see what he recommends. I would kinda say he probably knows more about 4ag's than anyone else short of a FA team, and he may know a bit more than a lot of those. Remember he has a FA motor in a Starlet, or did a couple years ago. That's hard core. Tell him I sent you.

One thing to keep in mind. Make sure the primaries are not smaller than the exhaust ports.