Exhaust design help

[socalmoto]

We are going to be putting in a v6 4.0L toyota engine into our 01 tacoma and the stock exhaust manifolds will not work as they are. Because of this I would like to build my own headers and exhaust. I figure this will at least upgrade the power over stock, I can make things fit where I want, and its another learning experience. I have decided to just build the header primaries equal length and not get too into the timing of the pulses and all the other stuff that goes into race headers. I took some measurements of the header flange and the space constraints I have and am designing the headers in solidworks for now. Im gonna be using 1.5"x0.65 304ss tubing.

I can get the primary lengths equal within 9inches after the header flange and I can make them up to 18 inches long before the collector. So first question is, what length should I run them at? The engine will be run between 4000-5500rpm. The next question is about the exhaust. Would it hurt the engine too much if I ran a true dual exhaust? Making a crossover pipe would most likely have to go under the transmission and I dont like the idea of having the exhaust in a place where it can get pinched or heat up the auto tranny anymore than it already is. Im not looking for ever last hp, so can I get some best guess opinions and why?

Heres the header design I have layed out. Its widest part is off the head 4.25" with the header flange. Its up away from the engine mount, and clears the engine cage tubes above.

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[Ol' Curmudgeon]

Im gonna be using 1.5"x0.65 304ss tubing.

Why that diameter? You only have a 667cc volume pump to supply each tube.

[Ol' Curmudgeon]

I can get the primary lengths equal within 9inches after the header flange

What?

[Ol' Curmudgeon]

The engine will be run between 4000-5500rpm. The next question is about the exhaust. Would it hurt the engine too much if I ran a true dual exhaust? Making a crossover pipe would most likely have to go under the transmission and I dont like the idea of having the exhaust in a place where it can get pinched or heat up the auto tranny anymore than it already is. Im not looking for ever last hp, so can I get some best guess opinions and why?

What are you going to use it for within that narrow rpm range? Why can't you put crossover behind tranny? I agree under is not a good idea from clearance or tranny life perspectives.

[socalmoto]

What are you going to use it for within that narrow rpm range?

Its for desert racing. I found that with our old s/c 3.4L that when I am actually needing power I tend to stay in that range. I will be in other areas of the rpm range during a race, but when Im in lower rpms Im usually not hard on the gas and so I dont really need huge power down low. I guess down to 3500 would be better though.

Why can't you put crossover behind tranny? I agree under is not a good idea from clearance or tranny life perspectives.

I wasnt sure if a crossover so far from the engine would do much good. Most vehicles I see with a crossover do them closer to the engine. And it would just be easier to run true dual for me. The stock exhaust comes with an a/f and o2 sensor per bank so the computer is already setup for a dual exhaust.

[socalmoto]

What?

Didnt catch that the first time.

The shortest I can make the centerlines of each primary tube is 9 inches long for them to be equal length. I can also run straight tubing back from that and make them 18inch long primaries and still be equal length. I have the space, but Im not sure what the lengths should be about for an rpm range in the 3500-5500 range. Short is better for top end, but again I dont know how short will get me in the range I want.

9 inch long centerline


18in long centerline

[bigtex]

Dual exhaust is just fine, and on the lenth of the primarys, do what will work good and is easy to work on in the truck, the amount of h/p you will gain or give up is very little with your engine set up.

[racer56]

Consider running a step header design. Run like 16" of 1.625 and then 16" of 1.75 into a merge collector.

[DP Racing]

i'd shoot for 26"-28" primaries. DO NOT weld as you go. make sure to only tack the primaries to the flange until they are completely built and welded (i learned the hard way). you will get the scavageing affect with only three primaries in the collector. before you put the collector on make sure to completely weld the area that will be inside the collector and laterally down the primaries 1"-2" where they are the closest, helps eliminate leakage. hope this helps.

[partybarge_pilot]

Hmm, My cheesy exhaust calculator says for peak power at 5500RPM you need a 17.5" primary length.