That is an exhaust brake. It works by closing a butterfly valve in the exhaust manifold. It is only as effective as your exhaust valve springs. I think it is around 200 negative horsepower when everything is working properly and at 2000 rpm. The transmission also has to lock the torque converter when it is engaged or it is useless. Will it help? Better than nothing. I have an exhaust brake on my 1 ton manual transmission truck and it helps but it is not anything like a real engine brake or a transmission retarder.
Why can't I get Ivermectin for my horses?