Inline-6 exhaust

[Swede]

What's your take on exhaust manifold design för a inline-6 (BMW) engine.

Background: We have a customer on the rollers(dyno) with a very nice bmw 2.5liter 6cyl engine . 6 individual dual roller throttle bodies, MOTEC fully sequential ecu. We have tried both a full race cam and the current one which is a Schrick 304deg, 106 lobe center. komp ratio 12:1, dynamic comp ratio 8:1

Now to the problem: the whole torque curve is to low, in level with a 2.0l race engine, very flat curve with max torque @ 6500 rpm.

The exhaust manifold is dual 3:1 with cyl 1,2,3 and 4,5,6 connected. Ignition sequence 1 5 3 6 2 4. There are 2 seperated 2" exhaust system from each manifold with absolutly no connection between them.

I would like to connect the 2 manifolds and use one exhaust system but the customer claims that there is nothing to be gained from that, any thoughts........

[OldSStroker]

What's your take on exhaust manifold design för a inline-6 (BMW) engine.

Background: We have a customer on the rollers(dyno) with a very nice bmw 2.5liter 6cyl engine . 6 individual dual roller throttle bodies, MOTEC fully sequential ecu. We have tried both a full race cam and the current one which is a Schrick 304deg, 106 lobe center. komp ratio 12:1, dynamic comp ratio 8:1

Now to the problem: the whole torque curve is to low, in level with a 2.0l race engine, very flat curve with max torque @ 6500 rpm.

The exhaust manifold is dual 3:1 with cyl 1,2,3 and 4,5,6 connected. Ignition sequence 1 5 3 6 2 4. There are 2 seperated 2" exhaust system from each manifold with absolutly no connection between them.

I would like to connect the 2 manifolds and use one exhaust system but the customer claims that there is nothing to be gained from that, any thoughts........

Thoughts:

1) 3 into 2 into 1 CAN be better, but the problem is determining the correct primary and secondary lengths. All of the engine parameters need to be taken into consideration to achieve exhaust tuning which compliments intake tuning. 123 and 456 are the correct primary pairing.

2) Unless you are proficient with a simulaton program like Dynomation (I think it's called) which will help with sizes, consider just adding an H or X crossover close to the collector outlets. Obviously you'll need to do back-to-back dyno runs. "the customer claims that there is nothing to be gained from that..." (exhaust changes). It's his money, so make sure he's on board with any changes you propose. It's always difficult to work with a customer who thinks he knows more than he actually does.

3) More DCR can help the torque curve almost everywhere. You may be able to tune it to live and 8.8 or so DCR on premium.

4) Camshaft selection can help you shape the torque curve to maximize the area under the curve in the rev range the driver uses. They also determine the DCR. Can you get custom cams?

Good luck.

[ADR]

What size are the throttle bodies ?
Dale