Hello,
I am a new member and the proud owner of a 1961 Renault Goelette 4x4 converted to diesel.
As I almost had an accident some years ago on the decent into the Geiranger fjord in Norway (where I overheated my drum brakes) I installed an exhaust brake valve. I never used it since installing it and as I need to take the engine out this weekend I was reading up on exhaust brake functionality. Good that I did as my butterfly valve in the exhaust has no pressure relief holes... It was used on a light truck which probably had a different relief system of which I was unaware. So use in the current configuration would probably result in engine failure..
Long intro, but now the question which is again long!
I need to calculate the diameter of the hole in the valve and probably the rating of an extra safety over pressure valve. To be able to calculate the hole, I need to determin the maximum allowable pressure in the exhaust manifold. I found some general indications of maximum pressures of around 40-60psi (2,8-4 bar). Obviously the pressure cannot exeed the spring force of the exhaust valves. I have a 2.3 liter or 140ci 4 stroke diesel engine in my car. The exhaust valves have a spring rating of 7.6kg or 17,8lbs when closed. Valve diameter is 33.5mm, stem 8.45mm, so surface to exert force on is 825mm^2 or 1,28 square inches. That equates to 0,92kg/cm^2 which converts to 0,9bar which is about 13psi. So at 13psi pressure I would open the exhaust valve which could hit the piston on compression.
First question is ofcorse, is my calculation correct?
Second question , is the value of 13 psi to be multiplied by 2 or 4 exhaust valves?? 2 will be open when the other 2 are closed (and need to stay closed). Even if I multiply by 2 I am still only at 26 psi where I read indications of 40-60 psi backpressure as allowable limits. Who can help?? If I know this I can calculate the hole needed in the butterfly valve to sustain the pressure level at a certain rpm rating given the airintake of the engine.
Kind regards,,
Michael (the Netherlands)
I am a new member and the proud owner of a 1961 Renault Goelette 4x4 converted to diesel.
As I almost had an accident some years ago on the decent into the Geiranger fjord in Norway (where I overheated my drum brakes) I installed an exhaust brake valve. I never used it since installing it and as I need to take the engine out this weekend I was reading up on exhaust brake functionality. Good that I did as my butterfly valve in the exhaust has no pressure relief holes... It was used on a light truck which probably had a different relief system of which I was unaware. So use in the current configuration would probably result in engine failure..
Long intro, but now the question which is again long!
I need to calculate the diameter of the hole in the valve and probably the rating of an extra safety over pressure valve. To be able to calculate the hole, I need to determin the maximum allowable pressure in the exhaust manifold. I found some general indications of maximum pressures of around 40-60psi (2,8-4 bar). Obviously the pressure cannot exeed the spring force of the exhaust valves. I have a 2.3 liter or 140ci 4 stroke diesel engine in my car. The exhaust valves have a spring rating of 7.6kg or 17,8lbs when closed. Valve diameter is 33.5mm, stem 8.45mm, so surface to exert force on is 825mm^2 or 1,28 square inches. That equates to 0,92kg/cm^2 which converts to 0,9bar which is about 13psi. So at 13psi pressure I would open the exhaust valve which could hit the piston on compression.
First question is ofcorse, is my calculation correct?
Second question , is the value of 13 psi to be multiplied by 2 or 4 exhaust valves?? 2 will be open when the other 2 are closed (and need to stay closed). Even if I multiply by 2 I am still only at 26 psi where I read indications of 40-60 psi backpressure as allowable limits. Who can help?? If I know this I can calculate the hole needed in the butterfly valve to sustain the pressure level at a certain rpm rating given the airintake of the engine.
Kind regards,,
Michael (the Netherlands)