Exhaust brake for truck conversion?

[JaysinSpaceman]

Hey guys,

I have to say that I am a bit concerned about asking this question after a search of the site and finding a lot of negative responses in regards to putting an exhaust brake on a stock car with a TDI, but I suppose maybe asking here in the swap/conversion area might be a better place for it. I will be swapping a TDI into a toyota pickup and I live in a very hilly area and could see an exhaust brake being beneficial. I am NOT talking about a Jacobs Brake. Simply a butterfly in the exhaust system that causes back pressure and slows the engine and therefor the vehicle. (Anyone with info on how exhaust brakes work on diesels feel free to correct me if I've got it wrong.) There seems to be a common problem on older Toyota pickups with warping front brake rotors even with a gasser that will supply some engine braking force and I figure that adding a diesel that doesn't, by it's very nature, supply any engine braking (save for a bit of internal friction/pumping losses) this problem might be increased. What would it take to install and exhaust brake on a TDI in a toyota? I know it would take a vacuum operated butterfly valve in the exhaust and you would have to limit back pressure to keep the engine's exhaust valves from blowing back open. Some way to switch the brake on and off, like a electric switch on the throttle so the brake engages when your foot is off the accelerator peddle or a switch on the brake peddle so that you just barely depress the brake peddle to actuate the exhaust brake. Is there something that I am missing here?

Calculating the back pressure that could be allowed should be easy enough, just need to find out the exhaust valve spring seat pressure and the area of the exhaust valve and you could calculate out how much PSI back pressure it would take to blow open the exhaust valve with stock valve springs. Then some sort of blow off valve or orifice in the butterfly to control back pressure keeping it below this limit.

It is just an Idea floating around in my head at this point, so try not to jump my S#!t to bad for it. I would think that those of us using these diesels in conversions might benefit from a technology that larger diesel pickups utilize to save their brakes etc...

Picture of exhaust brake.

Thanx,
Jaysin

 

[ctnatureboy]

Well.... You're brave for posting this. Someone will be sure to flame you for this.

I used to work in the the R&D lab for Jacobs Vehicle Systems and would LOVE an exhaust brake on my TDI (no matter what anyone else says) but unfortunately, have no valuable input on this subject. Subscribed none the less!

 

[JaysinSpaceman]

I figure that while the stock vehicle that TDIs come installed in might not need them conversion vehicles just might.

Let them flame if they want, I've got thick skin and am good at ignoring people.

Thanx,
Jaysin

 

[JaysinSpaceman]

Can someone give me the exhaust valve spring seat pressure or installed height pressure? I found some springs on the internet listed at 39 kg seat pressure but I don't know if that is stock.

Thanx again.
Jaysin

 

[Pat Dolan]

Jay: There are two strategies for limiting exhaust backpressure when using an exhaust brake - as you mentioned, a fixed orifice and a blow off valve. The problem with the fixed orifice is that you have to calibrate it for absolute max RPM, and as revs drop, so does exhaust braking. Best example is 7.3 Ford PSD that has a warm up valve that is easily actuated electronically (HINT - find an old one from someone on a Ford truck website and use the controller that ties into the electronic foot feed - I will look around and see if I still have one). The vendors will tell people they have 100 or whatever braking horsepower, but that is all 100% horse poop. You can BARELY feel the increase in engine braking at max RPM and empty, and it falls to near nothing as the revs drop (second order relationship, not linear) and is useless when towing. The second way to do it (example, US Gear makes both http://www.usgear.cc/dcelerator.htm) is with constant pressure (blow off valve). I have one of these on my F450 that tows at 36,000 lbs gross, and it is fairly effective (no, not an engine brake level, but way better than orifice exhaust brake).

The electronics to do the USG brake are available as spare parts, but there are a few things to watch. They use a HUGE power boost (i.e. max voltage) to run the solenoid that opens the valve, and drop to lower power to hold it open. The electronics box also cycles the brake valve every time you start up - both things being related to the propensity of the valve to stick in the exhaust deposits.

If I might be so bold, though, I would consider finding a used wastegate from some ricer turbo installation gone boom and a cable operated home made butterfly valve for actuation.

If I was spending money for someone else, I would just build an electronic eddy current brake from an old disc and some custom wound electromagnets. If I was to spend a LOT of someone else money, I would build a regen braking motor-generator to give a kick back on the uphill.

I failed to mention the third strategy - using the vanes of the VNT to close off exhaust flow. Dont know if the little Garret will shut down that much - worth thinking about and asking the turbo guys around here. Control would just me a matter of over riding the N75 valve signal to slam them shut (IIRC what the D-Max does now). If it had just a tiny bit of leakage and you had a loud inlet filter, you might hear it spool up from leakage just as a Class 8 does when the Jake is rattling.

Oh, I forgot. You must be crazy to do any of this stuff. What kind of a fool (such as myself) would waste their time and money on this crap.

 

[JaysinSpaceman]

Pat,
Good stuff there thanx.

I have been doing some research on this in the past few months and have seen the differences between fixed orifice and blow off styles. I was thinking of your Idea for the cheap wastegate/cable operated butterfly, however I was going to make it auto/semi-auto with a air cylinder, compressor, electric air valve to operate the butterfly. From a bit of research today (day off) it looks like I could have a max back pressure of about 45 psi with a stock TDI engine(exhaust valve spring seat pressure of 57 lbs stock and an intake valve area of 1.2sq.in.=47.5 psi to float ex. valve).

So a few more calcs...

Now tell me if I am right here. 45psi working against a piston with 7.7 sq.in. (stock TDI 3.13" bore) gives 346.5 lbs of force multiplied by a crankshaft arm length of .313 feet (stock TDI 3.76" stroke) gives us 108.5 ft.lbs. of force. So since we have a 4 cylinder 4 stroke engine (one cylinder on exhaust stroke at all times) we should see a pretty constant braking force of 108.5 ft.lbs. of torque. I would think that much torque would slow you down pretty fast (as fast as 108.5 ft.lbs. torque will accelerate you).

Sounds like an easy way to help out the braking effort of my little pickup to me. If I was really tricky I could get a waste gate that was adjustable from in the cab and be able to change the amount of braking force the engine gives me on the fly. Adjustable engine braking depending upon how much load I was hauling.

But I am cRazY!!
Jaysin

 

[Pat Dolan]

Jaysin:

To start with, cut your number in half because the lever arm is only 0.5 of the stroke. Then, you have to consider that the 45 psi max is NOT available for the entire stroke. What you lose on the compression stroke, you gain back on the dead power stroke, but the resultant discharge into the exhaust system must wait until the entire volume of the exhaust manifold pressurizes, less what leaks into other cylinders (i.e. add that volume), so pressure will take quite a while to build. Then, the geometry is only ideal for the full throw of the crank for a brief portion - as you must now correct that lever arm by the shape of the distorted sine wave.

So, you would have 50 lb-ft momentarily while the crank is at 90 degrees, reducing to zero at 180 and 360. The net result will be less than 20 lb-ft of torque - which is better than what you have now.

 

[JaysinSpaceman]

I knew my math sounded too good to be true. HAHA!!

The more I thought about that math after I posted it the more it sounded way too high mostly because there is only a short time that the crank and rod are at 90 degrees, but I forgot about the lever arm being only half the stroke. Still, like you said it's more then I got now.

Thanx,
Jaysin