What are the dynamics of an exhaust brake on the turbo?

[rweis]

I have an ex brake (US Gear D-Celerator). Mine is remote in the pipe mounted just pre muffler (probably 8 feet of 4", pi*r*r*h=2. 79 cu ft). Pipe is all 2" joint fully insert fitted with SS band clamps torqued to 60# except at the turbine output which is V clamped.



You turn on the exhaust brake and effectively block probably 90% of the exhaust (there is a butterfly bypass at 60psi that will bypass about 1 1/2 sq " or 33% of the pi*r*r area). The turbine up at the other end is turning maybe 10,000 rpm (that is a wild ass guess), the turbine + shaft + compressor has a fairly significant momentum going I would think.



So what happens now?



The exhaust flow is abruptly reduced, the pressure wave gets back to the turbine and ???????????????????





The intake manifold pressures are comming down (I assume you have your foot off the go pedal) and what is going on at the compressor end ?????????????????????



You turbine / compressor experts out there - what takes place now?



Bob Weis

 

[Steve Campbell]

"You turbine / compressor experts out there "......NOT

... . any way, my farmer opinion... ... most of the exhaust brakes have some "delay" built into the circuitry. I believe it is about 1 1/2 seconds on the US Gear brake after you let off of the throttle. That delay should eliminate most of the "Momentum" of the turbo.



Again, just my grass farmers opinion.

 

[RustyJC]

Really, not much at all happens. The fact that your right foot has been off the "loud" pedal (if it weren't, the e-brake wouldn't be engaging) has already killed the drive pressure ahead of the exhaust turbine, so there's very little pressure differential across the turbine wheel when the e-brake engages. When the e-brake closes, the exhaust system (including manifold and turbo) just goes to a higher pressure level due to exhaust stroke compression of air in the restricted exhaust system (note that pressure therefore still builds from the engine side), but the pressure is still basically in equilibrium across the turbine wheel.



Note that, due to the high fixed clearance (volume), a remote-mounted brake will be slower to develop retarding force than a turbo-mounted brake.



Rusty

 

[Sticks]

If feels like you are slowly applying the brake. Not a drastic change, very gradual.

 

[HoleshotHolset]

While we're at it....

So - what will happen if you put an exhaust brake on an engine that doesn't have strong enough exhaust valve springs?



AND - define 'strong enough' for the exhaust valve springs... . how strong do they have to be?



Matt

 

[robertyoke]

Re: While we're at it....

Originally posted by HoleshotHolset

So - what will happen if you put an exhaust brake on an engine that doesn't have strong enough exhaust valve springs?



AND - define 'strong enough' for the exhaust valve springs... . how strong do they have to be?



Matt

your exhaust valves float (stay open) ,hit piston & you cry ... allot!

you hear 12valve motors need 60 psi springs, that's the max recommended back pressure for exhaust brakes.

 

[HoleshotHolset]

I've heard of people mentioning valve float..... bummer.



Sounds like it's "for real"... . oh well.



Matt