1.9 SOHC Exhaust Chord Length Calculations?
Posted: August 31st, 2018, 8:35 am
Greetings All!
This is my first Post here and I'll jump right into it.
I'm building a 1.9 SOHC for my 128 Rally. It will be a Fast Road/Canyon car. I'm using a 1.6 punto, sporting block bored to 87.02mm with a ZRP 78.4mm crankshaft and 128.5 mm ZRP rods. Head has 32.5ccm chambers with 40/35 Int/Ex 6mm stem valves, 10,000 R.P.M. springs with Titanium retainers, Cam specs are; Duration: 242 degrees duration (intake / exhaust) @ .050 lift (seat-to-seat) Lift: (.430") maximum lift, Lobe center: 108 degree. The Pistons are 28mm compression height Becker Telle's. I'm on the USA West coast so 91 octane is what we get, unless race fuel is used, which I'd like to avoid. My Compression target is somewhere between 10.6 -11.0 :1. Those Pistons were supposed to be Forged, but they look cast to me. Also, they have a sizable dish in them so I'm not sure they're going to get me to my compression target. Fueling is coming from a Bank of 4 Yoshimura TMR-MJN32mm Carbs on a LaRussa custom Manifold.
Now, with that said, I am trying to design my exhaust Header and have been using information from this forum to calculate the necessary specs and what considerations need to be taken into account. I've found a lot of information on Layout, tube diameters, Radius' and the need to tune for the resulting pressure waves from the transitions between Primaries and Secondaries. For my 'Optimum' 4-2-1, what I am trying to figure out is how do you calculate the necessary tube lengths for these pressure waves? Can this be calculated, or approximated without back and forth trips to the Dyno? (Obviously that would be ideal, but not practical or attainable for everyone.) Also, what is my final Pipe I.D. at the collector and through to the Muffler at the rear of the car? The EX Valve is 35mm, but the port as it exits the head is only 32mm. I would be grateful for the passing on of any experience from the Collective!
This is my first Post here and I'll jump right into it.
I'm building a 1.9 SOHC for my 128 Rally. It will be a Fast Road/Canyon car. I'm using a 1.6 punto, sporting block bored to 87.02mm with a ZRP 78.4mm crankshaft and 128.5 mm ZRP rods. Head has 32.5ccm chambers with 40/35 Int/Ex 6mm stem valves, 10,000 R.P.M. springs with Titanium retainers, Cam specs are; Duration: 242 degrees duration (intake / exhaust) @ .050 lift (seat-to-seat) Lift: (.430") maximum lift, Lobe center: 108 degree. The Pistons are 28mm compression height Becker Telle's. I'm on the USA West coast so 91 octane is what we get, unless race fuel is used, which I'd like to avoid. My Compression target is somewhere between 10.6 -11.0 :1. Those Pistons were supposed to be Forged, but they look cast to me. Also, they have a sizable dish in them so I'm not sure they're going to get me to my compression target. Fueling is coming from a Bank of 4 Yoshimura TMR-MJN32mm Carbs on a LaRussa custom Manifold.
Now, with that said, I am trying to design my exhaust Header and have been using information from this forum to calculate the necessary specs and what considerations need to be taken into account. I've found a lot of information on Layout, tube diameters, Radius' and the need to tune for the resulting pressure waves from the transitions between Primaries and Secondaries. For my 'Optimum' 4-2-1, what I am trying to figure out is how do you calculate the necessary tube lengths for these pressure waves? Can this be calculated, or approximated without back and forth trips to the Dyno? (Obviously that would be ideal, but not practical or attainable for everyone.) Also, what is my final Pipe I.D. at the collector and through to the Muffler at the rear of the car? The EX Valve is 35mm, but the port as it exits the head is only 32mm. I would be grateful for the passing on of any experience from the Collective!