Get a Pyrometer! & comments on mountain trip

[jdmetcalf57]

I just got back from a 6K trip to Idaho. If you have followed any of my post you know that I have a brand new GM engine at their expense. I went ahead and added several gages before I left with this new engine. I added a pyrometer, a fuel pressure, a boost gage a vacuum gage and a back pressure gage. This all presented some interesting info pulling hard in the mountains.

I pulled with about 6K payload total in the truck and pulling my camper. What I found out that is very important is if you try to pull much with the cruise on the pyro temp skyrockets in a hurry. I am sure the computer will alow you to toast an engine at least with my manual trans. I often needed to back off or shift down just to maintain reasonable pyro temps. You could pretty much tell by the boost and back pressure that the pyro would soon climb rapidly.

Usually the back pressure was about 2-3 psi higher than the boost pressure. Under certain hard pulls the boost would jump to 10psi and the back pressure would go up to about 17 psi. The back pressure being higher than the boost robs power and efficiency and I am hoping that the addition of an intercooler will help this situation. I hope to have one installed before next years trip to the mountains. (anyone have any experience with this?)

I'm pretty sure I averaged about 15mpg with this payload. I was pretty happy with this considering the first trip I took out west with this truck netted me about 10.5-11.5 mpg. Even with the hard pulls in the mountains I would get 13.5-14. The worst tank I had was 13.4 and several times I got 16.5 or better. Seems like I always get about 1 mpg or more less when I fill with BP fuel. I have made several modifications.

Also this year witout the auto transmission now having a manual trans overheating was absolutely no problem. With the auto I had to constantly watch the temp gage because it would overheat. I guess this shows how much power is wasted by an auto.

[G. Gearloose]

If you can figgure out how to maintain more boost than backpressure, call me! ;)

[Craig M]

I have not hear of anyone else using a backpressure gauge. Boost, pyro, oil temp, oil pressure yes but not backpressure. Advantages?

[jdmetcalf57]

I installed the back pressure gage to monitor the efficiency of the turbo. The lower the back pressure relative to the boost the more efficient the turbo is running and hopefully the better the fuel economy. I have found that the ratio of back pressure to boost is highly dependent on engine speed and throttle position. The sweet spot for my truck set up with the load I pull is about 67 mph on level ground in OD. At this speed my engine is running about 2050 rpm.

[CleviteKid]

Diesels larger than ours (1800 rpm hi speed diesels and 600 rpm medium speed diesels) with carefully matched turbochargers often have the intake boost pressure higher than the exhaust back pressure pre-turbine. This allows the use of a large valve overlap and a high scavenging effect that helps cool the pistons from the top. This is particularly useful in marine propulsion engines that may operate between 90% and 100% of nameplate power for hours at a time. Imagine your truck climbing a 6% grade, towing a 10,000 pound trailer, at 65 mph, for 500 miles! But then, I am not aware of any mountain passes 30 miles (158,000 feet) above sea level.

Dr. Lee :cool:

[markrinker]

Where did you get the backpressure gauge, and where is the sender plumbed in?

[JohnC]

Originally posted by CleviteKid:
...This is particularly useful in marine propulsion engines that may operate between 90% and 100% of nameplate power for hours at a time...When these are your operating conditions you can choose a turbo that is very efficient under those conditions. The problem we have is that any turbo this efficient would be pretty much useless for normal driving. So, we have a turbo that works well for stop and go driving but is not very efficient under heavy loads.

[jdmetcalf57]

My pressure and vacuum gages are panel mount gages from McMaster Carr. I choose the appropriate ranges and when I mounted them I added a LED in front of them with so they would be lighted. It turned out to look pretty good. I mounted 3 gages recessed in the pocket below the radio which made it easy to put the LED so it shined on the gage.

On the back pressure gage I plumbed it into the cross over tube using about 3' of copper tubing. The tubing is then plumbed into a small steel reservoir which is then plumbed to the gage. In between the copper tubing and the reservoir is a plug with a small hole in it. This smoothes out the pressure pulsations from the cylinders. The hole needs to be as large as possible but yet keep the pulsations from the gage. If the hole is too small it will plug with soot.

In all I spent about $60 to get 4 gages.

[jdmetcalf57]

CleviteKid

Seems like a higher boost pressure than back pressure would provide the scavaging you talk about. The high back pressure would not allow all of the exhaust gases to be removed.

[DA BIG ONE]

I've wondered how there could be any back pressure at all w/full 3" mandrel bent exhaust w/straight through muffler, GM8 and such low rpms.

396 cid diesel @ 2000 rpms= not lots of cfm, add boost say 15 lbs and cfm flow goes up but not by a great deal w/ rpms and VE being biggest limiting factor.

However, in a free flow exhaust system the turbine housing would be the culprit if there is any back pressure, and proper porting of turbine exhaust port would go far to reduce, and even eliminate it.

[DmaxMaverick]

DBO

The back pressure is between the cylinder and turbo, as in the exhaust manifold or crossover. That's where the balance occurs, exhaust gas flow for intake air flow, via the turbo. Less back pressure means less effort required to push the exhaust gasses from they cylinder. If your boost pressure is greater than the back pressure, the boost can help push those gasses out with the valve overlap, and allow for scavenging, and decrease O2 depleated gasses.

[markrinker]

I want one! More fun stuff to monitor...

[RT]

What would be very interesting is to see how the Holset and Schwitzer turbos others have tried perform from a backpressure standpoint. I am relatively sure the Holset is lightyears ahead of the stock turbo. RT

[DA BIG ONE]

Originally posted by RT:
What would be very interesting is to see how the Holset and Schwitzer turbos others have tried perform from a backpressure standpoint. I am relatively sure the Holset is lightyears ahead of the stock turbo. RT Too bad the aftermarket can't see any profit in marketing a real choice for a turbo selection the 6.5 turbo diesel.