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Performance Cam

Missy Good Wench said:
Keep in mind that there is very little room in this engine as far as dealing with Valve to piston clearance.

The piston comes to within .035" of the head at TDC

Granted the manifolds and such are not Top fuel stuff or even street strip stuff but these engines were designed to make about 200HP and about 400 Lbft of torque and do it at under 3000 RPM

This is not a rocket ship.

A good flowing exhaust system and crossover pipe along with a top notch power chip will get these things to a point at which you are not going to get much more reliable power from them without issues of reliability.

The 6.5 is not a racer and unless one wants to spend Big Dollars and buy a forged crank, aftermarket block (or a new AMG block with the girdle) and then build the thing form the ground up as a MOOSE the excercise is one thats dubious at best.

The results are still limited by the small size of the cooling system and its ability to reject heat.


In a truck/Burb/Blazer/Tahoe 300 HP is about tops and still keep reliability as far as keeping it cool.

Now in a boat with water jacket aftercoolers and all the cold water in the pond to cool the beast, 400 HP is well within the scope of things.

Just my 2 cents worth


Missy
Click to expand...

No need to increase valve lift for the average performance build, is it more about pressure differentials. Without getting into a big long post, there are massive pumping losses on the 6.5 diesel, and they can be overcome.

Stainless steel pipe is more reliable than cast iron, and setups that would replace the stock manifolds and crossovers would not run as much as money as many people have been led to believe.

The engine keeps cooler because you are not adding any extra fuel (among other things) and the manifolds are not hugging the block, keeping it all warm and coszy in the Canadian winters ):h
 
chevyinlinesix said:
I build custom headers :)

And there is someone working on them that is almost done. :thumbsup:
Click to expand...

Interesting, on both counts..

Missy Good Wench said:
Keep in mind that there is very little room in this engine as far as dealing with Valve to piston clearance.

The piston comes to within .035" of the head at TDC

Granted the manifolds and such are not Top fuel stuff or even street strip stuff but these engines were designed to make about 200HP and about 400 Lbft of torque and do it at under 3000 RPM

This is not a rocket ship.

A good flowing exhaust system and crossover pipe along with a top notch power chip will get these things to a point at which you are not going to get much more reliable power from them without issues of reliability.

The 6.5 is not a racer and unless one wants to spend Big Dollars and buy a forged crank, aftermarket block (or a new AMG block with the girdle) and then build the thing form the ground up as a MOOSE the excercise is one thats dubious at best.

The results are still limited by the small size of the cooling system and its ability to reject heat.

So what about the cooling mods? the twin T-stats, w- pump, and rad upgrade are they not capable of supporting the extra power?

In a truck/Burb/Blazer/Tahoe 300 HP is about tops and still keep reliability as far as keeping it cool.

Now in a boat with water jacket aftercoolers and all the cold water in the pond to cool the beast, 400 HP is well within the scope of things.

Just my 2 cents worth


Missy
Click to expand...

See above.
 
dragogt said:
Interesting, on both counts..



See above.
Click to expand...

:ugh: I guess I missed that, having three conversations at the same time :lol: But engine temperature would be more manageable, because no extra fuel is added, and the "extra" power is simply being unlocked, it is already there to begin with, just being wasted :)
 
i dont like the way the manifolds are on the 6.5 and have thought of buiding a 1 off set but there is so little room to work with that it becomes very difficult to fit any thing different in there be interseting to see some pics.
I first found ssd before any other vender and saw the cam and have never heard of any one changing cams in a 6.5. If the intake valves were opened faster it would allow more air to inter the chamber and air plus fuel makes power. sounds like if it was done correct could help to make it breath better. Im not as eduated on this and you guys lost me with all the tec stuff but im tryin to learn it so thanks and keep the info coming please!!!! i get on every day after work hungy for more noledge from the wise 6.5 gear heads here.
 
chevyinlinesix said:
:ugh: I guess I missed that, having three conversations at the same time :lol: But engine temperature would be more manageable, because no extra fuel is added, and the "extra" power is simply being unlocked, it is already there to begin with, just being wasted :)
Click to expand...

No prob, it happens. lol

What about port and polishing the heads and mani's? I'm sure it's been done just curious what the results are, were/ could be..

Unlocking/ building whatever works. lol
 
ON N/A the last 2 points (valve's earlier, and port polish) make large differences due to allowing more air to go in easier. on Turbo Engines, its is a pressurized manifold so the pressure is forced in.

However, Perhaps if you ahve 10 lbs of boost, there probably isn't enough time to get the the full 10psi of air in the cylinder before the valve closes. Perhaps you can get a tad more of the manifold pressuer into the cylinder by modifying the valve timing. That is, if there is room to play with.

Headers would allow the exhaust to exit faster, creating less backpressure? And easier flow of exiting exhaust for sure, possibly compounding the increased valve's ability take more pressurized air.??

I'm way outta my element here, but great reading and brainstorming.
 
you guys got the basic idea as far as i know. yes better flowing manifolds and a different design for the cam will add power. not a whole bunch but i think enough that top end would improve and the turbo would be even more helpful in making power. i just look at the duramax, cummins and , powerstroke guys that got really high horesepower engines and the guys putting cams in are the guys making 600+.

as everyone knows air and fuel equal power in a diesel so the more power of both you pump in the more power you make. a gasser has to worry about 14.7 to 1 ratios and all other breathing garbage so a cam is going to make a big difference. i think it would definetly help but unless your rebulding the motor no need to replace stock one.
 
Matt Bachand said:
ON N/A the last 2 points (valve's earlier, and port polish) make large differences due to allowing more air to go in easier. on Turbo Engines, its is a pressurized manifold so the pressure is forced in.

Understood, but it "should" still make a difference even on a forced induction engine

However, Perhaps if you ahve 10 lbs of boost, there probably isn't enough time to get the the full 10psi of air in the cylinder before the valve closes. Perhaps you can get a tad more of the manifold pressuer into the cylinder by modifying the valve timing. That is, if there is room to play with.

I don't see why it wouldn't work as long as you don't get piston to valve interference.

Headers would allow the exhaust to exit faster, creating less backpressure? And easier flow of exiting exhaust for sure, possibly compounding the increased valve's ability take more pressurized air.??

turbo headers?? I know it works for gasers, so I don't see why it would't work on a diesel... jmho

I'm way outta my element here, but great reading and brainstorming.
Click to expand...

X2, just trying to understand.

Woody35 said:
you guys got the basic idea as far as i know. yes better flowing manifolds and a different design for the cam will add power. not a whole bunch but i think enough that top end would improve and the turbo would be even more helpful in making power. i just look at the duramax, cummins and , powerstroke guys that got really high horesepower engines and the guys putting cams in are the guys making 600+.

as everyone knows air and fuel equal power in a diesel so the more power of both you pump in the more power you make. a gasser has to worry about 14.7 to 1 ratios and all other breathing garbage so a cam is going to make a big difference. i think it would definetly help but unless your rebulding the motor no need to replace stock one.
Click to expand...
.

So whats stoichiometric on a diesel??
 
I am copying and pasting my post from the other site here, as it cleared up a lot of things for people, and I think it describes it very well.

While valve overlap CAN increase power, in a stock engine like the 6.5, with very restrictive exhaust manifolds, increasing overlap is bad. I'll try to explain it as quickly and as simply as I can here. Back pressure is the demise of camshafts with overlap, even more so in turbo'd engines. I know you may be thinking "back pressure has little effect on a turbo diesel" well it has a big effect.

With valve overlap (the point at which both the intake valve and exhaust valve are open at the same time) in our stock engines, the exhaust pressure can become higher than the the intake pressure, so, naturally, having both valves open at the same time will result in the exhaust gasses reversing and re-entering the cylinder (very bad)

Now, why the factory camshaft works so well...

Any valve overlap is bad for an engine if you are looking for more boost while using a restrictive turbine housing (the exhaust side of a turbocharger) What happens with the factory valve timing is; on the exhaust stroke, the exhaust valve closes 10 degrees BTDC (Before Top Dead Center) and stays closed until the piston starts traveling back down the cylinder bore. The intake valve is also still closed at this point, which creates a high vacuum in the cylinder because no air can get in. The intake valve then opens 12 degrees ATDC (After Top Dead Center) and since there is a high vacuum in the cylinder, and a high pressure in the intake, the intake charge rushes into the cylinder.

There is no reversion because the exhaust valve is closing BTDC, and the exhaust doesn't get pushed back into the intake either when the valve opens, because of the high vacuum in the cylinder and the high pressure in the intake.

So... while it's a general saying that the 6.5 engine has no overlap, it actually has negative overlap, -22 degrees of overlap to be exact. Now, while pumping losses with this type of camshaft and turbo/manifold setup are large, it will still use less power than a supercharger.

Now, keep in mind, mandrel bent exhaust crossover, 3" mandrel down pipe, and free flowing exhaust WILL decrease exhaust back pressure, so a camshaft change CAN increase power through less pumping losses, but because of the still restrictive manifolds and turbo, you can only take the camshaft so much further before running into reversion problems.

I'm not going to get into how an entire free flowing exhaust system (turbos, manifolds, and pipes) can take advantage of overlap, unless the original poster wants me to.
 
Stoichiometric air/fuel ratio for diesel is 14.4:1, but they're smoking before getting near that rich a ratio.

The fuel is less volatile than gasoline so it's harder to get it to vaporize & get it spread out & able to interact with all the oxygen in the cylinder.

It's interesting to read about. Seems to be all about getting the diesel droplets to interact with as much of the available oxygen (guess that's sorta obvious) as possible.

Notably different strategy with our IDI pre-cups creating turbulence in the prechamber - vs - modern direct injection 4 valvers creating swirl with the intake ports/valves.
 
Thank You ChevyInlineSix, the most important part I picked out of that is

"while it's a general saying that the 6.5 engine has no overlap, it actually has negative overlap, -22 degrees of overlap to be exact."

Thanks for the specs on that too.

I want to lessen the negative overlap for more air intake then and more exhaust output so there is less left in the cylinder after the stroke, ideally just the space left at TDC with 0 overlap. Ive always thought I dont want overlap, just didnt know it was negative overlap.

I have been trying to explain the same thing about the backpressure since the ATT came out. And now I have an ATT and my turbine drive pressure to boost pressure is very efficient, like 1.2:1 all the time, compared the the GM4 which was like 1.5:1 and as boost grew it climbed to about 1.7:1. It would be more efficient if it closed the exhaust port at TDC.

Thanks Again, sounds very promising actually.
 
buddy said:
Thank You ChevyInlineSix, the most important part I picked out of that is

"while it's a general saying that the 6.5 engine has no overlap, it actually has negative overlap, -22 degrees of overlap to be exact."

Thanks for the specs on that too.

I want to lessen the negative overlap for more air intake then and more exhaust output so there is less left in the cylinder after the stroke, ideally just the space left at TDC with 0 overlap. Ive always thought I dont want overlap, just didnt know it was negative overlap.

I have been trying to explain the same thing about the backpressure since the ATT came out. And now I have an ATT and my turbine drive pressure to boost pressure is very efficient, like 1.2:1 all the time, compared the the GM4 which was like 1.5:1 and as boost grew it climbed to about 1.7:1. It would be more efficient if it closed the exhaust port at TDC.

Thanks Again, sounds very promising actually.
Click to expand...

Are you considering purchasing a cam to try? I am interested in the outcome of this. Do you think the efficiency gained would be enough to warrant the replacement?
 
Depends on the price. I am looking into updating timing chain, and I could do the gears, or a new chain and cam. The new cams are a lot, but looking into options.

Looking at the performance cams it looks like it increases the time between the ports being open. And it states 65 degree overlap, but by the open and close timing I dont see them overlapping. It shortens the durations which seems opposite.
That may provide lower end torque, but less high end power.

I was looking at Delta for their custom grinds. I would want the TDC events as close to TDC as practical with no overlap, but could keep the BDC events where they are stock.
 
buddy said:
Depends on the price. I am looking into updating timing chain, and I could do the gears, or a new chain and cam. The new cams are a lot, but looking into options.

Looking at the performance cams it looks like it increases the time between the ports being open. And it states 65 degree overlap, but by the open and close timing I dont see them overlapping. It shortens the durations which seems opposite.
That may provide lower end torque, but less high end power.

I was looking at Delta for their custom grinds. I would want the TDC events as close to TDC as practical with no overlap, but could keep the BDC events where they are stock.
Click to expand...

Would be excellent buddy to reach into your deep pockets one more time and test out a different cam my friend. I will be watching with great enthusiasm.
 
Dragogt

The precup (located in the head) is the actual combustion chamber.
The injector, glow plug are in this little chamber and this is where it all begins.

As the piston approaches TDC the air in the cylinder is forced into the precup through the little slot that connects to the cylinder.

The angle of the slot in the precup starts the air swirling around inside the cup and then the fuel is injected and combustion begins.

The hot gases build pressure and then exit the pecup into the cylinder.
The little indents in the top of the piston direct the outfloe from the precup into two swirling masses of burning fuel and this causes more mising with available oxygen in the cylinder.

Here is a pix of SOME of the different cups used.

The concept of the precup is to provide a cozy little place for combustion to start and to help the mixing of air and fuel.

The Precup design has been around for a long time. Caterpiller used the precup in diesels back into the late 30's and continued its use way up and even into the 70's

Emmision regs and advancements in design eventually forced the precup design out.
Engines like the Cummins 5.9 have the combustion chamber in the piston top.

The precup has many advantages but also is a slightly dirtier engine (emissions)

The precups in the 6.2/6.5 morphed a lot over the years of production.

The early 6.2's had a very tiny port in them and as time went by the port changed sizes and shapes many times with various little marking being stamped into the cups to identify them.

The late 6.5 TD cups have a diamond stamp on them.
These had the largest size port ever used in a prduction 6.5

As a rule of thumb the smaller ports give higher velocity and better fuel economy than the large ports.

Early 6.2's in K Blazers could be counted on if driven right to deliver 24 MPG Highway with ease.

This was due to in part to the precup design and the fuel delivery settings.

The J series 6.2's of the later 80's had a much larger port in the cup plus a higher fuel setting. They produced more power but at a reduction in MPG's

The 6.5 saw several incarnations of the precup. The N/A version had two common sized ports and the Turbo Charged models saw at least three changes. The most common being the Cups stamped with a "T" and also the one with the "Diamond"

The "T" Port was used in the 92-93 engines and the 94 and later usually had the diamond BUTTTTTTTTT there was always the odd duck.

Now then there is Military stuff, All bets are off here. These critters had a variety of stuff that in many cases was peculiar to the MIL stuff (Just like Injection pumps)

The precups can be swapped back and forth to get just what you want.
The only things is that all the cups have to be the same.

I have pulled engines down that have had two different sets of cups. (heads swapped)
This is a bad thing as it changes the running characteristics of each bank of cylinders.

I have even seen two or three deifferent cups in one head. OMG what were they thinking????????//

The biggy is to be sure the cups are matched (same markings) and they they sit flush to no more than about .003" above the head surface. (Never lower than the surface)

Some aftermarket cups will fit GM heads and some wont.

Some shops surface heads with the cups left in place. This is a bad plan. The cups should be machined afterwards to fit correctly. (Takes a special jig)

The aftermarket heads I have seen come with the precups pressed in and the heads ground afterwards to assure a good finish ?????????/

I have used Clearwater heads and they work fine. (these had the cups and heads finished at the same time)

I used the "T" cups in my DaHooooley build this summer.
Not because of anything special, but because I found them for a right price (free) and they were not cracked all the rat poop like my diamind cups were.

The ports get very hot and they will crack at the mouth. The cracks will propagate outward and if they get over 3/16" long the cup is junk.
If the crack crosses the fire ring on the gasket it will eventually cause the gasket to fail.

Hope this is useful

MGW
 

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