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post #1 of 1 (permalink) Old 08-14-05, 06:19 AM Thread Starter
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Join Date: Aug 2004
Location: Toowoomba
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different Exhuasts

Just wanted to know whether people are using exhuasts that are a little different
curently I use 1 5/8 header 4-1 with 30" primarys into 3" collectors then into a twin 2 1/2 with a H pipe. I am not convinced that this is an efeicient system.
First up I looked at X pipes but i still thought that their had to be a better solution. first up I though GT40 style but getting all thoughs pipes crossing over each other in an already low car was asking for trouble. then I thought maybe 8-1. after looking and doing a bit of maths I found it could be done.

So I am just putting the finishing touches on the headers themselves (will put pictures up this week some time) they are still 1 5/8. the drivers side pipes go underneathe the gearbox and meet into a common collector on the LH side. Then I have worked hard to get the LH header to the same length as the RH side to keep 'timing' up. I have tried to work to 42" long pipes (on good advice by people who own and run genuine GT40s and small block cobras).
So far I have come up with a longest of 45" and a shortest of 37" which when i look at most headers isn't that bad (cosidering my old pipes came to longest 34" and a shortest of 17"). I then thought about actual exhuast size. I see many people running twin 2 1/2 like myself and even more runing twin 3". Yet when I look to guys running 400kw+ turbo engines I have seen as small as a single 3" system. So to this end I am running 3" into a hotdog resonator then exiting before the rear wheel on the LH side.

The benifit I see of this system over my current setup.
Length: I currently use the vehicle for hillclimbs and find it has a lot of bottom end power most of which is unusable and not much up top. so going longer will push the power band up the revs a bit.
90deg pulsing: with conventional 4-1s (exept those guys with flat plane cranks) the pulses into the collectors are not even so only a couple of the cylinders of each bank are really getting a good effect of scavenging. with the GT40 set up you give the benifits of a 4cyl or flat plane crank - pulses entering the clolector every 180deg of crank rotation. With my setup I get a pulse every 90deg rotation so the idea is a stronger low pressure singnal for the next pulse to be scavenged with.
3" tail pipe:reduce noise and I have always thought that its best to get the largest flow through the smallest hole.

Other ideas I have thought of but not used.
Stepping up to 1 7/8" about 7 - 12" from the head - trying to stop reversion and further promote top end. I see F1 use this a lot to broaden power bands.
Maybe a 8-4-1 or a 8-4-2-1 aranged into a more even pulse setup. haven't really reseached these so far as I want to see how my current versoin goes. but maybe like more convetional type (4-2-1) they may give better low end torque.

But as I said anyone else running something a little different or have a crazy Idea that you think is different.

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