1uz header design

[Disturbed1]

for those with some knowledge of naturally aspirated motors or specifically 1uz's.... im thinking of makign up a set of custom headers in replacement of stock soarer ones.

my question is - if I ignore every aspects of header design (length,equal runners etc) and build a 4-1 system, could i very well be takign a step backwards?

is hard to imagine going backwards when looking at a stock header but with room a premium, my plan was to have flanges with tapered ports from 1.5 (same diameter as exhaust ports) to 1.25", then go 4 (1.25") into 1 (2.25") merge collector where its convienient (headers will end up fairly short). The rest of the system will be twin 2.25" all the way to the back of the car.

being used to turboo cars, im sticking with a N/A motor and i dont expect to make any massive power gains etc.

so i guess what im saying - should i just keep factory ones?

[Sciflyer]

I think youd really have to fuck something up badly to go backwards from the stock soarer headers, theyre not great.

Having said that i know SFA about the theory so im sure others will comment

Only thing i would add is that for a twin system i would go 2.5", particularly if its press bent, ive used 3 different twin systems on my soarers and there was a noticable reduction in power with the 2.25 press-bent system i have (although that could just be because its shit...)

If you do want to stick with stock i would track down a set of factory VVTi headers, although theyre cast and considerably bigger than the Soarer ones

[timbosaurus]

I don't know much about it either, but interested to hear others' opinions.

So is the aim to keep cross sectional area the same all the way along? Or gradually decrease as the air cools.

Because 4 x 1.5'' ports converted to a single pipe of the same cross sectional area is a 3'' pipe.

[matty12]

When i went from my dodgey logs to the 4-1's i noticed only a very slight improvement between them. In saying that when the vehicle had the original tune that i was given from my ecu supplier checked to make sure everything was cool he did say he had to pull timing from it to stop it from rattling. So im sure now i could ramp up the timing a bit. Im also running larger diamter pipes that the standard 1 5/8 or what ever it is so scavaging may be down.

The car was supposed to be supercharged at one stage but looks less likely every year. Mine are in no way tuned length due to the space available, if i had to do it again i would do tri-y's just not realy enough room to run four pipes through the back of the engine/firewall, tri-y's would reduce this to two.

If you want to have a look at mine pop into the workshop sometime the VL currently lives here.

[Supra967]

Chris I think the americans are selling block hugging short headers for about $400. Even if you have to chop them up a bit it'd save you a whole load of hassle.

If you make you're own i think the only way you can do worse than stock is make them from RHS At the same time you probably won't get much more out of them either. I wouldn't worry about tapered ports unless you have cheap CNC or are doing it with a die grinder. Just get some 1.5 tube stepped down to 1.25 (only takes about 10mm, bit ugly but serves a purpose.

I found once mine were bolted in there was more room than I thought, but I wasn't going back towards the steering shaft.

[George]

Disturbed1 - if space considerations don't allow you to take advantage of resonance effects, it's a good idea to dump them where possible. For example this is achieved by introducing steps at head ports (so the gas can easily exit the head but it would feel the step when trying to enter it from the exhaust side). I've seen another interesting trick, some kind of restriction pipe. It looks like gradual decrease in diameter and then increase follows, something like 3" to 2,5" then back to 3" again.

Also if you have time for some experiments, you can determine where to put final Y-pipe by painting the two pipes running down from your headers and letting the engine run for a while

[boxh34d]

Also if you have time for some experiments, you can determine where to put final Y-pipe by painting the two pipes running down from your headers and letting the engine run for a while

Can you please elaborate on that one a bit more George?

[Disturbed1]

my reasoning for tubing size is as follows.

although the ports are 1.5" the ID of the first runner of stock manifold appears to be around 1.25". which flares out to approx 1.5 (of which two additional runners 'T' into it and the 4th seems to enter against the flow of the other 3. the stock header then flares out to 2.25 or 2.5" (knew i shoud have wrote these measurements down)

it seems the common trend is for dual 2.5" merging to single 3" behind the gearbox. when u consider the cross sectional area of 1x3", 2x 2.25" is slightly larger (based on OD).

although no show pony - car will be pretty low so i want ground clearance to be not limited by the exhaust - hence some nice smallish 2.25" muffler tucked away and piping under the rear subframe.

was going to go 1 of these


2 of these flowmaster hp2 shorty


http://www.youtube.com/watch?v=EUUteVjNdI0

and finish off with one of these


using 2.25" mandrel bends
and cross fingers it sounds half decent and not too loud

[Hack]

Can you please elaborate on that one a bit more George?

While not George...

I think it may have been an old Street Machine I read years ago, but as best I can remember...

Using an old motorcycle engine tuning trick, a line of spraypaint is run down the pipe from the headers and the exhaust is cut where the paint stops burning off.

I believe that by cutting the pipe here, a worthwhile increase in power was gained. Unfortunately I dont know if they attached a larger pipe on after...

Hack

[George]

been away at dragstrip =) So, like Hack said, you merge the pipes at the point where paint stops burning off. I think this method relates to the velocity of exhaust gases. As the temp cools down, gas travels slower and piping joint becomes less restrictive.

[twentyEight]

Thread revival as I'm up to the same point in my conversion.

How did you go with this?