EGT's What do they tell you - what is normal - and boost questions

[Dan_69GTX]

Let's see if I have this right.



To lower EGT's you decrease the amount of fuel entering the engine.



It's the unburnt fuel that causes higher EGT's.



Is that right?



Why will a 4" exhaust lower EGT's?



What is an average and Max temp you would want for EGT's?



Boost - what is "normal" and what is the max?



Thanks

Dan

 

[BillGotthelf]

Yes its true that with more fuel your egt's will rise-but its all relative. Given the same intake, injection pump settings, injectors, turbo and exhaust system the engine with more fuel delivered to the engine will have higher egt's. All the factors listed above and many others will effect egt. The larger exhaust will reduce back pressure and allow more air through the system therefore cooling the exhaust gas. You never want to see more than 1300 degrees measured in the exhaust manifold for a very long time as aluminum starts to melt at 1325. Not towing anything I see 600-900 degrees depending on acceleration, speed and gear. Crusing at 65 I see a steady 600. Towing I can easily reach 1300 degrees if I'm not careful but my truck is BOMB'ed. Yes a 4" exhaust will usually lower your egt but if your engine is stock you'll be hard pressed to get the egt up to a damageing point.

Boost is the pressure of the air (compressed by the turbo) entering the intake manifold. Boost works along with fuel in the engine to create power. A stock engine has about 18-19 lbs of boost and with the fuel delivered is all that is needed. If you raise boost without increasing the amount of fuel you accomplish nothing. As the amount of fuel injected into the engine is increased you must increase boost pressure to be able to generate more HP. Otherwise all you do is blow smoke-black to be exact-thats why all the companies selling torque plates include a fitting to plumb into the boost line.

 

[Dan_69GTX]

Thanks! I appreciate the explanation.



My truck has been modified, but since I just got it I'm not sure exactly what was done with it - I'll take the post under "dmarple" and see what was done.



I'll have to get some gauges and mount them when I get back from this buisness trip.



Dan

 

[The patriot]

Different year engines (CPL#'s) will have different boost pressures.

Mine is a 98 with a CPL #2175. I have up to 24 psi boost. It's stock. If yours is modified, you can throw this all out the window. That changes everything.

I think there is a chart somewhere on Fritz's web site that will show what boost your (stock) truck will/should be.

HTH

Eric

 

[SLang]

Great explanation Bill, one thing you forgot. If you can cram more boost without more fuel the engine will run cooler. This is one advantage of 4" exhuast on modified engines. The lower back pressure allows the turbo to spin easier. So at a given fuel level (boost is dependent on fuel use not RPM suchas superchargers) the turbo will spin easier and give more boost. Thus cooling your EGT.



Dan_69GTX, factory my truck gave 21 PSI of boost. I cranked the AFC spring and got 24 PSI. The waste gate was useless. I could not see high boost unless in 4th gear with foot to the floor. The boost would max right when the governer started cutting back.

 

[RJ2]

Originally posted by SLang

Great explanation Bill, one thing you forgot. If you can cram more boost without more fuel the engine will run cooler. This is one advantage of 4" exhuast on modified engines. The lower back pressure allows the turbo to spin easier. So at a given fuel level (boost is dependent on fuel use not RPM suchas superchargers) the turbo will spin easier and give more boost. Thus cooling your EGT.



Dan_69GTX, factory my truck gave 21 PSI of boost. I cranked the AFC spring and got 24 PSI. The waste gate was useless. I could not see high boost unless in 4th gear with foot to the floor. The boost would max right when the governer started cutting back.

I have an automatic and get 38 boost in high gear and I know the previous owner set the starwheel way up( for pulling heavy loads). If I turn I turn it back down will I get better low end and less smoke?My milage is down in the 14's also. Thanks RJ

 

[SLang]

The star wheel is there to supplement a well controlled right foot. In a perfect world people would except a little smoke and the driver would only use the smoke when needed to pull. You can take the spring out of the AFC altogether. Then control how much fuel your engine gets with your right foot. The AFC is put on there because most people don't have the knowledge or patience to drive a diesel vehicle. They want to step into it at every light like the goofball's in little imports do at every light. This applies to most "Truck Driver" (actually they are steering wheel holders but... ) that drive diesel every day. Way back when in the early 70's (I think) they came up with a device call a alerion. I know that is spelled wrong but ask any "Truck Driver" he'll pronounce it and maybe even show it to ya. The device does the same as the AFC on our pick-ups. The guy who know whats up usually disabled these devices. On the large pumps it was a connecting rod that needed removed or the preload backed all the way off, like our star wheel. They disabled it so that they could get fuel whenever they needed/wanted it. Any way if you disable the AFC or remove preload by using the star wheel you will get better low end. If you want good low end with little smoke, teach yourself to drive that way. You can determine the conditions a lot better then a preset spring that does the same no matter if you have a 35' GN or empty. As far as fuel milage goes, if you run it without smoking all the time, it whould slightly increase. If you smoke constantly, it will decrease.



Now that I gave the "what I like" opinion. Lets look at the other side. If you disable your AFC your wife will surely smoke out ever intersection (if you even let her drive it). And some people on this forum have had problems with cruise tracking. Their solution was to back off the star wheel and make the truck less aggressive. This may become a problem in some areas.



In short CONTROL YOUR TRUCK TO MAKE IT PERFORM THE WAY YOU WANT.

 

[BillGotthelf]

Patriot he had a 96 and so did I so stock boost will be the same.

SLang-If you put more boost thru the engine without the additional fuel you run the risk of too lean a charge with all the resulting problems running lean brings. The biggest two problems running lean bring is detonation and increasing heat. The additional air flow probably cools the charge as it exits the cylinder but the temp in the cylinder has to be higher.

 

[MY6EATSV8'S]

are you serious Bill, your correct about the lean condition in a gas,alcohal type motor, not in a diesel. The leaner you make it run, the less egt..... by the way another little thing about diesels, they run on detonation.....

the upper boost limit is not determined by a single turbo. Its somewhere around 90 or 100 psi. I try and get people to stay under 40psi with single turbos becouse its somewhat riskey to the turbo above that, not the motor.

 

[SLang]

BillGotthelf



Like MY6EATSV8'S said your thinking of a gasser not diesel.





MY6EATSV8'S



The engine can run at 90-100 PSI. On 17:1 compression thats 1700 PSI before the charge expands. That seams like you would sanp the head bolts. What is the highest boost you have put in a Cummins?

 

[MY6EATSV8'S]

I personally have only seen around 55psi pulling, unfortunately that was terminal to the single turbo I was using at the time. I'm currently working with Bell turbo of stockton ca to come up with user friendly twin trurbo set up. He is the one responsible for most of the twin setups we currently know of, including getting Jeff Prince his initial setup that Dave Mitchel is currently using, he's making 105psi boost in his truck and is the most "over- the - top" phsyco truck I've ever heard of. He's turning 6thousand + rpm.

My target is 90psi with no lag.

 

[SLang]

Dave Mitchel is currently using, he's making 105psi boost in his truck and is the most "over- the - top" phsyco truck I've ever heard of. He's turning 6thousand + rpm.

I take it his turbos are stack (one pushing into the next)? Are they HX-35's?



I guess I'll have to take a trip to his shop one day. That's worth checking out.