A question for the cam guys..

[beanhead]

I'm looking at the Comp XE275HL, which carries a lobe separation angle of 110. I know what LSA is, but what effect would grinding this profile on 112 have in a 440, 9.25-1 compression with aluminum heads/intake and 2500 stall? I understand it will affect the overlap period but what does that mean in terms of power output/valve timing/idle characteristics/sound etc? Much appreciate getting edgycated on this subject thanks!

 

[Kern Dog]

A wider LSA means a smoother idle and higher vacuum. It usually also means a lower rpm power peak.

 

[PurpleBeeper]

No info here, but I think I see where your going with that beanhead and it makes a TON of sense!

 

[BSB67]

Narrower LSA:
Less Idle vacuum
Greater low end torque
Greater peak horsepower
Narrower power band
Increased cranking cylinder pressure

Wider LSA
Better idle vacuum
Less low end torque
More-longer horsepower after peak power
Wider power band
decreased cranking cylinder pressure.

 

[beanhead]

Narrower LSA:
Less Idle vacuum
Greater low end torque
Greater peak horsepower
Narrower power band
Increased cranking cylinder pressure

Wider LSA
Better idle vacuum
Less low end torque
More-longer horsepower after peak power
Wider power band
decreased cranking cylinder pressure.

Thanks, and by 'cranking cylinder pressure' you're talking about the dynamic compression, correct?

 

[BSB67]

Thanks, and by 'cranking cylinder pressure' you're talking about the dynamic compression, correct?

Yes. Both the dynamic compression, and cranking cylinder pressure are directly proportional

 

[HEMI-ITIS]

Why is the CR so low with aluminum heads??

 

[beanhead]

Why is the CR so low with aluminum heads??

They were added after the fact..originally built with 452s. CA 91 octane, hot climate...runs 180 all day no pinging though.

 

[HEMI-ITIS]

Are you happy with the performance?

 

[beanhead]

Are you happy with the performance?

Well it ain't no blown hemi! Haha but it was okay, fun enough for the street even though running on spinny-spin Coopers. I thought it could be better...Then I got into it and discovered some issues. Long story short, it was about 8.8 on the compression, with failing rings oiling the chambers pretty bad and a cam retarded by 6 degrees..only about 3000 miles on it..yeah YIKES! Getting it taken care of as we speak before I go into mopar-driving withdrawals. I wish I had the means at the moment to stroke it out or at least build a new rotating assembly, but it is what it is for now. Just doing a little milling on the heads to at least be up over 9 to 1, cleanup, re-ring and re-hone the block as all the bearings are cherry. Cam will be properly installed and degreed (by me this time), should be a tad bit rowdier than it was. It sees lots of miles so it doesn't need to be too pumped up for me. (With all that going on it was still quicker than these 5.7 challengers..and I don't hook for jacksquat!)

 

[HEMI-ITIS]

Cam profiles can help increase cylinder pressures.A cam change might help.Speak to a few can grinders and then speak with Dwayne Porter.!

 

[Challenger340]

This could open a can '0 worms, but you could grind it on 112 lsa, and then given the low CR consider installing it back up around 104* ATDC

 

[BSB67]

This could open a can '0 worms, but you could grind it on 112 lsa, and then given the low CR consider installing it back up around 104* ATDC

The wide verses narrow lsa is a compromise and is somewhat dependant on the goal of the owner. But when a guy is trying to balance power, street manners/low speed torque, and low compression, my gut tells me smaller cam, tighter lsa, and advanced ICL is probably the overall better plan. But I really have no data or personal experience to back that up.

 

[Bee1971]

I run that same Cam in my 383/432 Stroker that I built last year

However 10.5-1 Compression - 195/200 PSI cold cranking compression on all eight

Edelbrock E Street Heads 75cc

Degreed it with help , and installed it zero

12"-14" vacuum at 700/800 Rpms - Very smooth and can set idle pretty much anywhere and running power brakes

Has the typical sewing machine sound at idle running the Comp lifters

Off idle , keeping the car straight anytime in the throttle with 275-60 rear tires is my biggest complaint LOL

 

[451Mopar]

Narrower LSA:
Less Idle vacuum
Greater low end torque
Greater peak horsepower
Narrower power band
Increased cranking cylinder pressure

Wider LSA
Better idle vacuum
Less low end torque
More-longer horsepower after peak power
Wider power band
decreased cranking cylinder pressure.

For cranking pressure and very low RPM torque, the cams installed position (intake closing point) will have a greater effect than the amount of overlap be changing the LSA. The overlap will affect the idle quality, and how the poweband looks. Narrow LSA power band usually starts a bit lower, but peaks quicker, then falls off fairly fast past peak torque. Wider LSA power band is usually flatter, starts off a bit higher, but does not peak as fast or as much, and then power does not drop off as fast past peak torque.

Some useful links:
http://www.compcams.com/Pages/413/cam-timing-lobe-separation-angle.aspx
http://victorylibrary.com/mopar/cam-tech-c.htm

 

[HEMI-ITIS]

http://victorylibrary.com/mopar/cam-tech-c.htm

Jeff Diamond is the arthur of the Victory Library and lives very close to me.One can get lost in that library for days!!!!

 

[beanhead]

This could open a can '0 worms, but you could grind it on 112 lsa, and then given the low CR consider installing it back up around 104* ATDC

THAT is intriguing...

Off idle , keeping the car straight anytime in the throttle with 275-60 rear tires is my biggest complaint LOL
View attachment 718069

Believe it or not I had the same "problem" even in it's sick condition, though I'm sure not as extreme. Same rear tire size and more torque than grip lol..hooked up and running though, it did feel to be somewhat lacking.

 

[Bee1971]

THAT is intriguing...


Believe it or not I had the same "problem" even in it's sick condition, though I'm sure not as extreme. Same rear tire size and more torque than grip lol..hooked up and running though, it did feel to be somewhat lacking.

No compression , Failing rings , and this/your cam installed 6 degrees retarded , I could understand somewhat lacking

 

[BSB67]

For cranking pressure and very low RPM torque, the cams installed position (intake closing point) will have a greater effect than the amount of overlap be changing the LSA. The overlap will affect the idle quality, and how the poweband looks. Narrow LSA power band usually starts a bit lower, but peaks quicker, then falls off fairly fast past peak torque. Wider LSA power band is usually flatter, starts off a bit higher, but does not peak as fast or as much, and then power does not drop off as fast past peak torque.

You make a good clarification. LSA itself has nothing to do with the cranking pressure. It is the ICL. But generally the ICL tracks with LSA. Normal convention would have you install a 114° LSA cam in the 110° to 114° ICL range, and a 108° LSA cam in at 104° to 108° ICL range.......usually. So indirectly, with this convention, the cylinder pressure would go up with the narrower LSA. Certainly there are exceptions on how people might choose to install their cams, which was Bob's point.