[gumby79]

In the60's, 70's, and 80's gas v engines had a diverter valve it 95% blocked the passenger ehxsost manafulld. Rerouting the hot gas through a passage under the carburetor and out the drivers side . On a 61' GMC 305ci V6 the valve had a bimetal spring to open it ,hence not full blockage. My 79 Chevy K-20 with a 350ci V8 was normally closed vacuum actuated via a thermal valve in the coolent . I had the vac line brake causing the spring to close the valve . At 70mph the passenger manafulld was glowing in direct sunlight, well over 700°f. Let it cool then wired it open as my Edelbrock Rpm Airgap Intake did not have the passage.
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As to diesel there are 3 ways to slow with the motor .
1) Engine Braking. Just let off the throttle.
Same as a gas but less effective.
2) Ehxsost Brake. The flap in the ehxsost. On my Cummins this up grade requires up-graded ehxsost valve springs 60# vs stock 30# to hold the valves closed on the intake stroke. Exced 60psi on the brake and it will still over ride the spring.
.. Cummins,Duramax, Ford use option 2 by way of the VGT Turbo closing the vains enuph to act like this type.
3) Jake Brake . A device that prevents the ehxsost valves from opening, normally multi stage in pairs 180° out .
... 6.7 Cummins has a kit avaliable. Its the only small US diesel I'm currently aware of with this Big truck technology.