Nice, streetable, wide 308 2V torque curve

I just put 500 miles on the car. Elevation varied between 3000 and 7500 feet, MSL.

It runs wonderfully. One hell of a lot more zip that it had in the past, and no annoying cam drive bearing whine from a bearing going bad......

The car will actually put you back in your seat under full throttle. Not as much as my 2016 Z06 Corvette, but I don't have to worry about garbage trucks beating me in the 1/8 mile like before in the 308.

Doug

 

Hi Mark,

Do you have tabulated output files for the sims you did for me? It's hard to compare results without putting the data on the same chart. I'm measuring the OE headers more closely and will post my measurements in the Big Bore thread. It will be interesting to see how the factory headers compare to your modern tri-y design. How close are they? This is what I have so far:

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Hi Doug,

Congratulations on getting your car back on the road. Can you post a couple of photos of your engine installation? I'd like to your engine bay without the emissions equipment.

Bill

 

The output looks like this...well actually its the input, the software simulates what a design will do but the user inputs the design to test so this is a design I created for you and "tested" in the software:

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This is a tri-y step header. The pipe closest to the head is 6.00" (but that includes the port itself so call it 4") and is 1.375" ID (so about 1.5" OD), then the next piece is 12.0" long and 1.5ID

Then a merge type collect that matches the 2 pipes entering it and is 8.0" long from where the 2 entering pipes open in the the collector and where the end opens into the next collector, with an ID at the end of 1.75" (basically ignore the inlet ID as that is just the effective calculated dia of the 2 pipe that enter). That makes the Pre-collector pipe length of 18.00"...that is the tuned number, the actual length of the 2 pieces of pipe can vary without changing the tuning a whole lot. I tried to keep the 1.375"ID section fairly short as its the most restrictive but it doesn't change much if you got to say 9"/9" instead of the 6"/12" so I would wouldn't worry much about this or trying to get each cylinder exactly the same...about the same is fine and even changing the 18" number up to say +/-2 cylinder to cylinder to allow bigger radius bends would be fine and better than using a bunch of tight bends trying to perfectly match lengths.

Then the final merge type collector is 5" long entrance to choke, choke ID is 1.75". That choke ID is pretty important......smaller boost midrange but costs top hp, bigger costs midrange while adding topend.....that 1.75 is kind of a balancing point. After the choke you would add an expander to go up to the 2.5" system size you wanted iirc, after the choke nothing is very critical as long as the system is big enough to flow enough air its good and really doesn't impact tuning at all.

 

Here is something to mess with your minds:
The only diff between Tq curve #1, and Tq curve #2, was a H pipe was added right behind the header collectors. Both are thru full exhaust out the back, and rear wheel numbers on a chassis dyno. An extra 175 ft-lbs of tq at 1500 RPM from the H pipe.

Notice the AFR, we couldn't tune enough fuel into the car without teh H pipe in that narrow RPM range, there was some sort of reversion going on. Those are using 4 into 1 commercial headers.
Doug
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That is a big change!

That's the no chokes on the headers effect is full swing. When the exhaust pipe basically matches the collect ID then the entire exhaust system right to the tail pipe if its a glass pack type muffler becomes the collect and that just doesn't work well, an H pipe cause the flow area to double and that causes a wave reflection at the H-pipe and making a much more helpful tuned length. When burns did the design of my system they said an H would help a little if there was anyway to do it ....but with a transverse setup it really wasn't possible for me and probably not for most 308 owners