Cam question

[spencergt66]

Well you just asked a whole mouth full. The camshaft is one of the most important parts of the engine it will make the engine make power in higher rpms or lower rpms depending on how its configured. On a conventional engine N/A usually the more lift and duration you have the better the engine preforms @ higher rpm but with a diesel engine, turbo charged that is, Usually the rpms are lower and the torque is made lower there for the time that the valves are held open during operation or travel of the piston is less cause the engine is being force fed air,turbo charging, instead of relying on vacuum.

Now this is where you need to pay attention to where your valves open and close. On a turbo charged engine before the end of the exhaust stroke both the intake and the exhaust valves should be open for a given amount of time, valve over lap, creating what they refer to as scavenging. This is when the charge air from the turbo is pushing out any remaining exhaust gases before starting the intake stroke usualy the intake valve stays open more than the entire downward travel of the piston (180 degrees of crank shaft rotation) say the intake opens @ 10 degrees BTDC exhaust stroke and stays open until 35 degrees after BDC intake stroke or 35 degrees into the compression stroke.
Right here is where what engine types differ.

Most conventional engines are still letting charge air into the cylinder during the upward stroke or compression stroke, like our engines IDI's, this cause more heat and cylinder pressure at TDCC Where as other engine types close the inlet valve before the intake stroke has ended thus letting the charge air expand in the cylinder. And when a volume of air that is already compressed, from the turbo, and is let re-expand quickly during the downward piston travel it becomes cooler decreasing the amount of cylinder pressure and heat in the combustion chamber. When this system is used it is necessary to have a larger quantity of charge air to make up for the air expansion in the cylinder Therein lies the problem and possibly some solution to the IH IDI turbo engines.

Because the 7.3 IDI inlet valve closes @ 42.8 degrees ABDC , from what i was told, the inlet air is crammed in there to the point where its probably being pushed back out of the cylinder due to the length of upward piston travel.

More then likely if the inlet valve was closed before the bottom of the intake stroke then you could have more charge air less emissions and a better balanced engine


Hope that helps

 

[ameristar1]

Well you just asked a whole mouth full. The camshaft is one of the most important parts of the engine it will make the engine make power in higher rpms or lower rpms depending on how its configured. On a conventional engine N/A usually the more lift and duration you have the better the engine preforms @ higher rpm but with a diesel engine, turbo charged that is, Usually the rpms are lower and the torque is made lower there for the time that the valves are held open during operation or travel of the piston is less cause the engine is being force fed air,turbo charging, instead of relying on vacuum.

Now this is where you need to pay attention to where your valves open and close. On a turbo charged engine before the end of the exhaust stroke both the intake and the exhaust valves should be open for a given amount of time, valve over lap, creating what they refer to as scavenging. This is when the charge air from the turbo is pushing out any remaining exhaust gases before starting the intake stroke usualy the intake valve stays open more than the entire downward travel of the piston (180 degrees of crank shaft rotation) say the intake opens @ 10 degrees BTDC exhaust stroke and stays open until 35 degrees after BDC intake stroke or 35 degrees into the compression stroke.
Right here is where what engine types differ.

Most conventional engines are still letting charge air into the cylinder during the upward stroke or compression stroke, like our engines IDI's, this cause more heat and cylinder pressure at TDCC Where as other engine types close the inlet valve before the intake stroke has ended thus letting the charge air expand in the cylinder. And when a volume of air that is already compressed, from the turbo, and is let re-expand quickly during the downward piston travel it becomes cooler decreasing the amount of cylinder pressure and heat in the combustion chamber. When this system is used it is necessary to have a larger quantity of charge air to make up for the air expansion in the cylinder Therein lies the problem and possibly some solution to the IH IDI turbo engines.

Because the 7.3 IDI inlet valve closes @ 42.8 degrees ABDC , from what i was told, the inlet air is crammed in there to the point where its probably being pushed back out of the cylinder due to the length of upward piston travel.

More then likely if the inlet valve was closed before the bottom of the intake stroke then you could have more charge air less emissions and a better balanced engine


Hope that helps

You said it better than I ever could. Excellent.

 

[ameristar1]

You think an adjustable cam sprocket might be enough to alter the timing of the stock cam to get the intake closing point to where it needs to be?

 

[typ4]

My cam grinder split patterns the cam and increases the intake lift to 261 lobe lift/392 valve
exhaust remains stock with 253 lobe 380 valve.

rocker ratio is 1.5 they calc it at .050 tappet lift.
the intake centerline is opened up to fill the cylinder longer.

 

[spencergt66]

Probably not, then your changing all your cam timing basically you want to shorten the length of time the inlet valve is open may require cutting a cam from scratch not sure what you can get away with as far as grinding a cam

 

[ameristar1]

Thanx Russ, I had a feeling it was a tiny, tiny cam from the factory. The old girl needs to breathe and spin. Goodness, how did it even run?

 

[typ4]

They developed it in the na days for the loggers, those trucks sold by the thousands in OR and WA. It really works good in my engine with the turbo. I can outpull my buddy and I have 355 gears and haul about 13k with the camper on and the buggy trailer.

 

[ameristar1]

Probably not, then your changing all your cam timing basically you want to shorten the length of time the inlet valve is open may require cutting a cam from scratch not sure what you can get away with as far as grinding a cam

I think there's room to grow, especially based on the numbers Russ just gave for the stock cam and rocker ratio. There looks like a ton of power left on the table, and it won't require gigantic boost to make it happen.

 

[ameristar1]

They developed it in the na days for the loggers, those trucks sold by the thousands in OR and WA. It really works good in my engine with the turbo. I can outpull my buddy and I have 355 gears and haul about 13k with the camper on and the buggy trailer.

I don't know if I asked you, but do you have cylinder flow data for the IDI or do you know anyone that might have it.

 

[spencergt66]

That is true things to think about

 

[crashnzuk]

Did the factory turbo IDI have the same cam? Does anyone have cam specs for the 1st series of Powerstroke, and would those specs be a decent start for a turbo specific IDI cam?
Travis..

 

[david85]

Well crap! maybe a custom cam is in the works for me after all, Russ. Didn't realise the stock cam was a smogger retard like the ford big blocks. And here I was thinking these engines were untouched by emission devices. Turns out the enemy was from within all along.

Had no idea that the scavenging effect often described in the detroit 2 strokes borrows over to these 4 stroke engines.

Great breakdown of the theory there, spencer!!!!

 

[typ4]

Did the factory turbo IDI have the same cam? Does anyone have cam specs for the 1st series of Powerstroke, and would those specs be a decent start for a turbo specific IDI cam?
Travis..

yes, no and no ,different pistons and valve arrangement

 

[seawalkersee]

Justin, the timing of the cam and the specs are what makes the engine work. The heads controll the power of the engine. As much air as you can get through the heads, that is where the power comes from. Now, the cam is the heart of the engine. It opens and closes in reference to where the piston is in the cyl. (BTDC) and opens a certain height (lift) and stays open for a certain amount (duration). That is for the intake. The exhaust uses timing of the valve for a partial scavenge effect. You can effectively move more air into the cyl. if there is overlap between the exhaust and intake. This allows the exhaust to be evacuating the cyl. until there is negative pressure and the intake will open. It pulls air from the intake in. Now, the more overlap you have, the engine will want higher revs to run within the power band. There is a TON more to it than that...but that should get you close.

Ameristar, do you sell cams too?

SWS

 

[seawalkersee]

I have to start looking for a second page before I reply...

SWS