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Re-grinding cams
https://slantsix.org/forum/viewtopic.php?t=54449		 Page 2 of 2
Author:  1930 [ Thu Jan 30, 2014 4:16 pm ]
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Quote:
The way a slant six cylinder head flows (rather well on the exhaust compared to the intake) you actually want longer duration on the intake lobe. If you're sticking with stock size valves you want a 107-108° lobe separation. So if we swap the intake and exhaust lobes and get the compression up to a true 9:1 it should run quite well. The increased performance comes from opening the valves farther and having them open longer, but if you don't increase the compression ratio and close the intake valve later you will experience a loss of low speed torque. Board member DadTruck did a lot of work sciencing out the camshaft for his truck so you might look for his posts on the subject.
I have been checking out his posts and will continue to do so, looking specifically for that cam info you are mentioning within his posts.

Yes I will stick with stock valve size and from what I have gathered so far may not do anything to the head, sounds like the bonus to trying to improve the head flow may not be enough to justify the effort unless I am misunderstanding the replies I have been given.

Thanks

I cant help but to wonder why the head flows better on exhaust?
Author:  1930 [ Thu Jan 30, 2014 4:18 pm ]
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... I cant quite put my finger on how they re-grind the cams to make them larger without adding to the tip of the cam cause obviously if this was done then the cam would never fit in the bore, anyone know how its done and can offer an explanation. Curious ...
The cam grinder will regrind the cam with a smaller "base circle".
Doing that will allow for a "bigger" lobe.
The downside is that this can impact the hydaulic lifter's plunger's position or "pre-load". (plunger moves up in the lifter)
You can off-set this by grinding some material off the head and / or block deck surface.
DD

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Anything else I need to consider such as pushrod length, piston clearance ect with the scenario cam I mentioned above?
Author:  DusterIdiot [ Thu Jan 30, 2014 4:46 pm ]
Post subject:  Inhale, exhale...
Quote:
I cant help but to wonder why the head flows better on exhaust?
"It is easy to empty the cylinder than to fill it..."

Think about how the engine works...the engine will use the piston to "shove" all the spent gasses out the exhaust port to the tail pipe and out to the regular atmosphere...the intake has to rely on pressure differential between the vacuum made by the piston traveling down the bore (and hopefully the intake valve is opening to make it most efficient at that time), and also some help can be had at the "overlap" event on the cam when both valves are open so the exhaust gasses leaving can help "suck" some of the incoming air/fuel mix into the cylinder (headers with their "collector" helps with this event as well...and the V-8 guys run more duration on that side to make the most use of that event...).

If that goes over your head a bit, think of it on a personal level is it easier to make more pressure when you inhale or exhale (I'd bet a fair amount of inner tubes and birthday balloons would vote for the exhale...LOL). That being said, the easiest way to overcome that would be to use a turbo to "force feed" the cylinder...(so would SCUBA gear on a human...)


If you are going to pull the head to improve compression a bit, you might as well get into the ports and clean them up a bit at the very least...I did this on my first slant six build and did it on my beater valiant cast crank engine and it may not seem like much, but at least it takes some of the bottle neck out of the ports so you get the most out of your valve combination (that beater valiant build used a low end comp cam xtreme stick and with the compression bumped up and stock valves with a little porting it showed lots of improvement over a stock engine).

-D.Idiot
Author:  Doc [ Thu Jan 30, 2014 6:01 pm ]
Post subject: 
Quote:
... I cant help but to wonder why the head flows better on exhaust?
This is just another situation where a SL6 is different then a lot of other engines.

Funny thing, I use Dual Pattern (DP) vs Reverse D.P. (RDP) as a little "test" to see if a cam grinder / designer really knows what they are talking about.

If the grinder quickly suggests a DP cam he is "pretty good" because most "best" cams do have different lobes on the intake vs exhaust.
I also know that if the cam grinder suggests "more on the exhaust side", he is not knowledgable about the details around the Mopar SL6 (usually just V 8 thinking)

The top notch cam designers I meet simple say: "get me all the numbers and then we can talk about some cam designs".

So how does anyone know that a RDP cam works "better" in a Mopar SL6? Take a look at some of the early factory cams... they are RDP designs. And ask the really fast SL6 engine builders what they use... most will not tell you :lol: :wink: or say it's an "RDP cam".
DD

Image
Author:  1930 [ Thu Jan 30, 2014 11:14 pm ]
Post subject:  Re: Inhale, exhale...
Quote:
Quote:



If you are going to pull the head to improve compression a bit, you might as well get into the ports and clean them up a bit at the very least...I did this on my first slant six build and did it on my beater valiant cast crank engine and it may not seem like much, but at least it takes some of the bottle neck out of the ports so you get the most out of your valve combination (that beater valiant build used a low end comp cam xtreme stick and with the compression bumped up and stock valves with a little porting it showed lots of improvement over a stock engine).

-D.Idiot
Do you know of anything that I can view with step by step or at the very least pictures of what where to clean within the head. I would not dream of just hacking into it which is what any novice would be doing unless he knew some more specifics.

I know of no-one locally that would have a good idea of what should be done to optimize performance on this engine either. I know alot of guys eager to take my money but again obviously this would not be ideal for me.

Gotta be someone in the past that has done this sort of work and has taken some pictures before/after along the way just to give me a basic idea.
Author:  1930 [ Thu Jan 30, 2014 11:19 pm ]
Post subject: 
Quote:
Quote:
... I cant help but to wonder why the head flows better on exhaust?
This is just another situation where a SL6 is different then a lot of other engines.

Funny thing, I use Dual Pattern (DP) vs Reverse D.P. (RDP) as a little "test" to see if a cam grinder / designer really knows what they are talking about.

If the grinder quickly suggests a DP cam he is "pretty good" because most "best" cams do have different lobes on the intake vs exhaust.
I also know that if the cam grinder suggests "more on the exhaust side", he is not knowledgable about the details around the Mopar SL6 (usually just V 8 thinking)

The top notch cam designers I meet simple say: "get me all the numbers and then we can talk about some cam designs".

So how does anyone know that a RDP cam works "better" in a Mopar SL6? Take a look at some of the early factory cams... they are RDP designs. And ask the really fast SL6 engine builders what they use... most will not tell you :lol: :wink: or say it's an "RDP cam".
DD

Image
Thanks I know that much of what you are telling me is simple and basic to you but majority of it goes over my head. I plan to work on getting some of these terms figured out this weekend doing some more on-line search queries.

I am also hoping that my playing with degreeing the cam that is in the truck now will help me to better understand some of it as well.

I tell you this because I do not want you to think that I am not being rude or un-appreciative of your response by giving you back some more in depth /appropriate response.
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