Adjusted valves, lost 2 psi of boost and 23 hp???

[RSchwarzli]

Last fall I dynoed my truck. Put down 273 hp @ 2350 rpm and 650 peak tq. Was sitting at 30 PSI on the street. Then over the winter, I added a full 4" exhaust (increased flow), a 4" inline exhaust brake (decreased flow a little), 60 psi intake and exhaust springs, and adjusted my valves. Then I noticed I was sitting at 28 psi street.



Yesterday I put it onto the dyno, and put down 250. 3 hp @ 2200rpm and 640 peak tq. What the heck just happened? Down 23 hp and 10 ft/lbs?



I have heard from people that you loose a few psi when the valves are adjusted, but that makes no sense!



Anyone have an idea of what changed? I would not put it past the fact that many of the trucks do have issues spooling on that dyno, but when I see that it is down 2 psi on the street... . :{



Signed Dear Abby, :-laf

 

[NIsaacs]

Might be winter fuel?



Nick

 

[BHanna]

You may want to double check that you got them adjusted right. It wouldn't be that hard to accidentally set an intake at . 020 instead of the exhaust.

 

[AABEN]

RECHECK your adj would be the first thing I would do. == Good Luck

 

[JLEONARD]

I am thinking that the difference is the variation in the dyno.

Could also be air temp, fuel temp. All those are factors. Can easily account for 10%

 

[RSchwarzli]

Will re-check all of them. Did a check on 3 and 4 as those are the two I did first... - All seemed OK.



Did also hit 30 psi on the street while passing someone Sunday. So the boost still gets up there. Maybe it is just dyno varience.



EDIT: Also thinking, last time I ran 2 stroke oil in the tank. 100/1 ratio. Would that have done it?



EDIT 2: Fuel. Good point. Last year I was running Sunoco premium diesel (Gold Diesel). This year was just regular. I wonder if the fuel would make that much of a difference?

 

[champspa]

why didn't you do it at the same rpm ? would it make a difference ?

 

[RSchwarzli]

Wondered about that too, thats why I put that info in there. I still revved out at the same RPM but.....

 

[ChrisOlson]

Hello

As an Engineer I adjust Valves on Big Multible cylinder 4 stroke diesels. My trick is I use a red paint marker for Premarking Exhaust Valves and a green Paint marker for Premarking Intake Valves. I have My feeler gauge marked the Same color for the EXH or the INT. Feeler Gauge. Also when the Valve has been ADJ I use a Yellow paint marker to mark that it is done.

Good luck hope it helps.

Chris

 

[AH64ID]

If the valves were tight before then you had more restriction, which with the flow being equal means more boost. . So adjusting the valves could lessen the restriction, and if flow is the same it would mean lower boost...

Similar thing happened with my cam... It spools MUCH faster, but peak boost isn't changed until I get above 2300 rpms... Less restriction, more flow means same boost.

The 23 hp could be fuel, dyno, a/c was on. . etc.

 

[RSchwarzli]

Chris - Brilliant. I like it!



AH - Makes sense. Starting to think it was just a variable - weather, fuel, day, etc.

 

[AH64ID]

Also if the numbers are corrected they can vary that much on the same day 4 hours later.

 

[Bob Beauchaine]

Same dyno? If so how about air temp - humidity - time of day for both runs. I've seen all of this play into numbers variations. When I run I like to run early in the morning - cooler denser air = better numbers.



Bob

 

[JLEONARD]

The "rule of thumb" is a 1% loss in hp for each 10 degree F increase in intake air temperature.

The same for fuel temperature.

 

[glhs]

Two questions;

1. After the adjustment, did the truck feel any different?

2. Were the valves out of adjustment by much?





If you can answer no to both of these, I would guess it was just the difference between days.

 

[RSchwarzli]

Same dyno? If so how about air temp - humidity - time of day for both runs. I've seen all of this play into numbers variations. When I run I like to run early in the morning - cooler denser air = better numbers.



Bob

The "rule of thumb" is a 1% loss in hp for each 10 degree F increase in intake air temperature.

The same for fuel temperature.

Thought about that too. Same time of the morning (9:30ish) and temp was about the same. It was raining last time and overcast this time.

Two questions;

1. After the adjustment, did the truck feel any different?

2. Were the valves out of adjustment by much?





If you can answer no to both of these, I would guess it was just the difference between days.

1 - Yes, I added a 4" exhasut, 60psi intake and exhaust springs, and a PRXB all at the same time. :-laf

2 - No, not much.

 

[JHumphries]

What about added valve-train losses due to the higher pressure exhaust springs?
I completely forgot he had added these until the quote. .

 

[JLEONARD]

It was raining last time and overcast this time.

My diesel truck (non IC) would run noticeably stronger on a rainy or misty cool day.

Nice cool air, water injection, made difference for sure.

 

[JaredH]

Valve train losses are generally calculated as "0" due to the fact that no matter the spring rate there is always a spring pushing "up" and "down" on the cam cancelling out the intake and exhaust spring forces... . even though in some "kit's" exhaust springs are a bit higher spring rate. Higher spring rate on exhaust valve than intake since they have to "fight" to open valves under higher cylinder pressures and the intake valves have boost to help open... . Are you running any ZDDP additive in the oil to account for increased spring pressures? "Some" say it helps with scuffing... is the only reason I ask.



I do not know the first thing about exhaust brakes... is there a way to check the "return" spring (if there is a spring) to make sure the valve is fully open?



Ok stupid"er" question time:



Tire size change? Air pressure alot higher than first dyno?

Last air filter cleaning, if cleanable type or paper replacement?

Lube oil type/viscosity change?

Possible your fueling plate slid (loosened)?

Change in boost due to very small boost leak... guage line, boot, seal, etc. . ?

I assume same dyno method including fan placement in front of truck's IC?





~Sorry Bored in Japan

 

[RSchwarzli]

Valve train losses are generally calculated as "0" due to the fact that no matter the spring rate there is always a spring pushing "up" and "down" on the cam cancelling out the intake and exhaust spring forces... . even though in some "kit's" exhaust springs are a bit higher spring rate. Higher spring rate on exhaust valve than intake since they have to "fight" to open valves under higher cylinder pressures and the intake valves have boost to help open... . Are you running any ZDDP additive in the oil to account for increased spring pressures? "Some" say it helps with scuffing... is the only reason I ask.



I do not know the first thing about exhaust brakes... is there a way to check the "return" spring (if there is a spring) to make sure the valve is fully open?



Ok stupid"er" question time:



Tire size change? Air pressure alot higher than first dyno?

Last air filter cleaning, if cleanable type or paper replacement?

Lube oil type/viscosity change?

Possible your fueling plate slid (loosened)?

Change in boost due to very small boost leak... guage line, boot, seal, etc. . ?

I assume same dyno method including fan placement in front of truck's IC?





~Sorry Bored in Japan

No ZDDP additive as I am running CI4 oil. I have some stock from before!



Tire - no

Filter - OK

Oil - No change

Fuel plate - Dont have one

Boost leak - Negative

Fan - Same spot



So from what you are all saying, it is pointing to the dyno more than anything. Guess I will have to try again at somepoint and see if it changes.