The Diesel Stop banner
1 - 2 of 2 Posts

·
Registered
Joined
·
2 Posts
Discussion Starter · #1 ·
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)
 

·
Registered
Joined
·
2 Posts
Discussion Starter · #2 ·
And I think I can partially answer my own questions... As I do not have the motor restauration manual available right now (it's in the car in the storage facility), I was relying on internet data. After searching for more information on the springs in the engine, it turns out each valve has an inner and outer spring. Inner is rated at 7.6kg AND the outer is rated at 22kg! So working in tandem for 29.6kg (65.3 lbs) keeping the valve shut. Doing the math again I came up with 3.5 bars to open the valve, which is 50,8 psi and that sounds right again. So I think the safe choice would be to calculate the hole on a stable pressure of around 40 psi at 2500rpm (max. torque). This together with an over pressure valve at 50psi for overpressure at a higher rpm. If anybody had different idea's or can point out a fault in my reasoning please let me know. I will need to drill the hole probably on friday!

Kind regards,
Micchael
 
1 - 2 of 2 Posts
Top