[dieselwrangler]

I was wondering if a guy could use a throttled intake on the 4BT? my dad has a exhaust break on his and it sucks!!!, it pretty much dont slow it down! it is a 4" jacobs unit. I plan on just using a ball valve type valve in the intakes system between the turbo and the intake I understand I cant totaly shut the air off it might hurt the engine but it seems to slow the engine down way better then the exhaust brake does especially at lowers rpms and speeds where my Jeep will need it the most for compression breaking< as a side note isnt the new 6.7Liter cummins setup like this?

 

[Dougal]

An exhaust brake will create maybe 30psi of pressure on the engine to slow it down. If you don't think they make a difference then run the same hill twice, one with it on and once with it off (if it's safe).

An intake restriction can only create less than 15psi of pressure difference on the engine as well as allowing the cylinders to simply spring back up once past BDC. It won't do much to slow it down.
You can check this by driving a petrol engined vehicle down the same hill twice in gear with the engine off. Once with the throttle open, the other with the throttle closed.

 

[Lustalbert]

Also, closing off the intake will most likely cause compressor surge on your turbo when you close the ball, as the turbo is spinning at a good clip and flowing a fair amount of air.
Another thing (not 100% sure) I belive the injector pump is still metering a small amout of fuel that will build up in the cylinder while you are going down that hill, and as there is no air coming into the motor, when you open the ball valve this fuel will them burn, and will probably not be good for the motor.
If your rings and valve seals are a little weak, having this vaccum presented against them could draw some engine oil, and could load the cylinder with enough "fuel" to also cause a problem (ping, knock, detonation)
I could be wrong on all of this, but it just does not seem like a good idea.

 

[JimmieD]

It could be explained by what you posted, DW. "...an exhaust brake...." The Jacobs is slightly different from other mfgr's units in the way it slows the engine, as it is a compression brake, not an exhaust brake. Other types use a valve in the exhaust to restrict exhaust flow. That valve has a small orifice in it to allow some exhaust gasses to bypass so you don't scatter stuff. There's a difference in braking performance between various units.

Here's some info from U.S. Gear:
http://www.usgear.cc/dcelerator.htm

Differences FAQ
http://www.usgear.cc/dcel_faq.htm#different

Application differences & sizing
http://www.usgear.cc/dcel_appprice.htm

Exhaust pipe sizing, exhaust brake sizing, bypass orifice sizing and correct application, right brake/size/type to engine & exhaust, has a lot to do with it. Using say a 6BT 4" exhaust brake on a 4BT 3" exhaust system literally won't cut it, off.

 

[rbarnett]

Also, closing off the intake will most likely cause compressor surge on your turbo when you close the ball, as the turbo is spinning at a good clip and flowing a fair amount of air.
Another thing (not 100% sure) I belive the injector pump is still metering a small amout of fuel that will build up in the cylinder while you are going down that hill, and as there is no air coming into the motor, when you open the ball valve this fuel will them burn, and will probably not be good for the motor.
If your rings and valve seals are a little weak, having this vaccum presented against them could draw some engine oil, and could load the cylinder with enough "fuel" to also cause a problem (ping, knock, detonation)
I could be wrong on all of this, but it just does not seem like a good idea.

You're right, when you open the intake restriction, your engine will sound like it has injested water. Makes a terrible knocking sound! Don't do it! I had a 3" rubber intake hose section on my Cat powered Chevy, and under a hard pull it sucked the hose closed. The engine seemed to freewheel, and then the rpm's came down, and subsequently the vaccum decreased and allowed the hose to open, and I thought I blew the engine. Terrible knock, and unbeliveable amount of white smoke. This happened a few times untill I figured it out.
Bob B.