Archived exhost pressure.

[cbraket]

My first time on the 911 forum. I have a 97 2500 with a pacbrake with the 1/4" hole in the butterfly valve rather than the pressure regulater. I plugged the hole and the exhaust pressure holds better and it slows the truck down much better. How high is it safe to let the pressure go up to in the manifold? Will it cause the exhaust valves to float and kiss the pistons? I hear that's bad.

 

[ScottLewis]

Yep, quite bad. If the exhaust springs in your '97 haven't been changed to 60# ones, anything over 30# PSI puts you at risk. Plugging the hole will give you better braking but probably will cost you major money in engine damage.

 

[Sticks]

Floating the exhaust valves... . bad juju.

Get the upgrade done if not already. Easy enough to DIY.

 

[cbraket]

ehaust pressure

Yep, quite bad. If the exhaust springs in your '97 haven't been changed to 60# ones, anything over 30# PSI puts you at risk. Plugging the hole will give you better braking but probably will cost you major money in engine damage.

I do have the 60lb springs installed. The pressure has gone slightly above 60 but I don't know how much is ok.

 

[Sticks]

60 is OK. 61 and your exhaust valves start floating. 70 would be bad.

I would drill a 1/16 hole and enlarge as needed, or engineer a relief/blow-off valve for 57#.

This is why I like my US-Gear D-celerator brake. Built in wastegate. Now if I could just seal off the damn exhaust leaks at the clamps.

 

[cbraket]

exhaust pressure

60 is OK. 61 and your exhaust valves start floating. 70 would be bad.



I would drill a 1/16 hole and enlarge as needed, or engineer a relief/blow-off valve for 57#.



This is why I like my US-Gear D-celerator brake. Built in wastegate. Now if I could just seal off the damn exhaust leaks at the clamps.

Thanks guys.

We've just towed our camper from Ontario to Missouri and haven't blown it up yet. Just don't turn it on over 1800rpm for know. Will try manufacturing a relief valve when I get home.

cbraket.

 

[AH64ID]

On 3rd gen's the springs are 60# springs, and 65 psi of backpressure is what a couple of brake mfgrs state at the max.

Rpms will really increase that pressure without a relief hole.

 

[jdooner]

There should be an adjustment on the brake arm to control how far the butterfly closes. If you still have the directions that came with the brake it should tell you there. IIRC it's a bolt and a lock nut. Good luck!