Changing lobe seperation from 110 to 112-14?

[69 GTX]

So what effect would moving my lobe seperation from 110 to 112-114 have other than smoothing out the idle? Is there a negative side to doing this? The cam I was looking at had 230-236 @ .050 with .540 lift. I like everything except the idle, was wanting a little more stealth. I was also going to use 1.6 rockers to get more lift out of it. Open to suggestions. I just want it tame enough that anyone can get in it and drive it if need be. No riding the brake and gas, shutting off in gear or low vaccum. Mostly fooling the guy in the other lane! I had asked on the F.A.S.T. forum about how they set their cams up but got no response. Guess they are keeping their tricks secret.
Thanks for any input.

 

[Cranky]

You might check out this page.... http://www.compcams.com/Pages/413/cam-timing-lobe-separation-angle.aspx

Tighten (smaller LSA number)............. Widen (larger LSA number)
Moves Torque to Lower RPM............... Raise Torque to Higher RPM
Increases Maximum Torque............... Reduces Maximum Torque
Narrow Power band.......................... Broadens Power Band
Builds Higher Cylinder Pressure............. Reduce Maximum Cylinder Pressure
Increase Chance of Engine Knock............... Decrease Chance of Engine Knock
Increase Cranking Compression............. Decrease Cranking Compression
Increase Effective Compression.............. Decrease Effective Compression
Idle Vacuum is Reduced............... Idle Vacuum is Increased
Idle Quality Suffers................ Idle Quality Improves
Open Valve-Overlap Increases............. Open Valve-Overlap Decreases
Closed Valve-Overlap Increases.......... Closed Valve-Overlap Decreases
Natural EGR Effect Increases.............. Natural EGR Effect is Reduced
Decreases Piston-to-Valve Clearance.......... Increases Piston-to-Valve Clearance

 

[dvw]

Tight LCA means more midrange torque. Granted the carb calibration is trickier. The bottom line is properly set up the tight LCA on a relative mild duration cam is worth power.
Doug

 

[lewtot184]

there's a reference to FAST racing. does that mean your going to use cast exhaust manifolds? if so do a wide LSA, headers do a tighter LSA.

 

[383man]

Also remember widening the LSA like 110 and going to 114 gives you less overlap as per the same cam and can close the intake valve later for less cyl pressure. You also have to remember the chart Cranky posted is about as per that one cam and not comparing one cam to another. It means moving the LSA on just a certain cam and comparing the same cam to both LSA's. But you could also call a Pro like Dwayne Porter who design's cam's as he speced my flat tappet cam. His # is 802-951-1955 if you would want to talk to a pro who does it everyday for a living. Good luck , Ron

 

[69 GTX]

Thanks for all the great info guys!!!!

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Lew haven't decided yet on manifolds. Was thinking maybe shorty headers, unless I find someone who does extrude porting or something like that on stock manifolds.

 

[lewtot184]

Thanks for all the great info guys!!!!

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Lew haven't decided yet on manifolds. Was thinking maybe shorty headers, unless I find someone who does extrude porting or something like that on stock manifolds.

extrude porting isn't worth the money spent. cast manifold guys are spreading the LSA out. has something to do with letting the intake charge push the exhaust out; a lot voodoo stuff. what intake manifold/carb are you using?

 

[69 GTX]

Haven't nailed that down yet either but was leaning toward a 850 vac sec Quick fuel & a eddy or Indy dual plane

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Building from scratch. trying to pick the cam then build around that.

 

[lewtot184]

i would suggest building around the cylinder heads and type of fuel.

 

[Challenger340]

Rather than DE-NUT'ing your current Cam events by going to a wider lsa..... why not just get a "smaller" Camshaft that "fits" better with what you want to do ?

 

[69 GTX]

Pump gas 91-93, stealth cnc'd heads. So would a smaller cam out perform the next step up with the wider LSA? With lower duration also comes lower lift. So just lets say the 225/230 cam with 525 lift and 110 LSA would out perform a 230/236 540 lift with 112 LSA? All other things being equal. And by performance I mean 1/4 ET.

 

[dvw]

Pump gas 91-93, stealth cnc'd heads. So would a smaller cam out perform the next step up with the wider LSA? With lower duration also comes lower lift. So just lets say the 225/230 cam with 525 lift and 110 LSA would out perform a 230/236 540 lift with 112 LSA? All other things being equal. And by performance I mean 1/4 ET.

It'll have a broader over all torque curve. Heavy street type car with mufflers I bet it's a better choice. I would talk to Dwayne Porter. He knows more than most of us here, more than me for sure.
http://supercarraces.com/Porterracing.html
Doug

 

[69 GTX]

Sounds like what I'm after. I'll give him a call.

 

[lxmodguy]

A properly matched cam to your engine size, exhaust type, and rpm range is the most important thing. Figure out what your intake/exhaust ratio is. Find head flow numbers online for your heads. Post that, your vehicle weight, your cubic inches, your exhaust details and I will spec something out that you can call the comp tech line and order.

 

[robinsonwr]

69GTX,
I chose a camshaft that would support power brakes and possibly A/C later on. I knew my heads flow good at 600 lift. I also knew I wanted to keep a street friendly gear like 3.23's. I had Comp grind a cam that fit my specifications. No, it is not even close to the ultimate performance grind most would have picked. It should still make close to 600hp and 600tq in my 512" stealth headed big block. Camshaft: Hydraulic Roller, Comp Cam custom grind (ADV Duration 281-287,@ .050 230-236, lift 622I & 625E w/1.6 rockers.) GRIND #: CRB3 3194 /3196 HR111.

 

[66Satellite47]

Very interesting thread. Matching cam to the total combination of parts & intended use is tough, especially if the uses differ, street vs strip. I'll see if my antique drag cam will be nearly as street friendly as my Comp XS274 which had no pull above 5000 rpm.

 

[Tempest 455]

May need a converter change to get same ET. Also, you might play with IC installed position to gain back some possible low end TQ.

 

[69 GTX]

Robinsonwr, that would be a tame cam in a 512. I'm looking at using a 440.
66Satellite I would've thought the XS274 would pull hard past 5000.
Tempest 10-4 on the installed centerline.

 

[66Satellite47]

"May need a converter change to get same ET. Also, you might play with IC installed position to gain back some possible low end TQ."


Tempest, not sure if this was meant for me, but not too worried about low end, it had much more than enough. I need more power for the trips to the strip. I should have stuck with my main point for 69 GTX that the whole combination needs to match the intended use. But thanks.

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69 GTX, ya me too!! I changed the cam(& lifters), valve springs & intake manifold. I'll see in a couple months if those make it rev.

 

[moper]

The trick on engines with exhaust manifolding and full pipes & mufflers is not so much the intake valve, but the exhaust valve timing and opening & closing rates. The intake cycle is weak in and of itself, especially when the intake valve is just opening. That's true even with longer stroke engines. The opening point of the exh valve, and the timing of the exhaust blowdown is what's critical here. The motion of the exhaust gases exiting at supersonic speed against the backpressure of the manifold and system at the very beginning of the intake valve event (prior to TDC) is what will allow the cylinder to fill competely with power producing intake mixture. It's not the intake charge inertia at the end of the intake cycle. In fact, especially at low rpm and with a port that's efficient at low lifts, keeping the intake open too long can hurt filling even up into the mid rpm ranges because as the cylinder fills and the pressure within it increases gasses will just as easilly flow back up the port right until the valve closes.