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Overlap and Valve Events Editorial

 
Old 10-05-2017, 07:32 AM
  #61  
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Anybody makes a PROVEN towing cam for LS motors? If they do I haven't seen one. Otherwise looking in jegs and summit racing you'll see cams specified for towing, 4x4s,hauling etc...
It would be awesome to see a cam provide extra torque from idle to 3000 rpm.
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Old 10-05-2017, 09:34 AM
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Originally Posted by Pulse Red View Post
So I have very recently had installed a Cam Motion 218/226 .595"/.587" 116 +3 (-10 overlap) mentioned in my post above in my 5.7 LS1 that I imported to my country from the USA along with PAC 1218 valve springs. It achieved what I wanted by delivering completely stock like manors with only a bit of lope plus a more quiet valvetrain. Good stuff!

However, compared to the Comp cam it replaced (216/220 .600"/.600" 112 -6.0 overlap) this cam dropped a pretty decent chunk of power, although that wasn't unexpected despite it being larger. Where I was caught out is that this cam feels quite lazy and the change created a hole at lower rpm which is important in a heavy car like mine. Most would say that's due to going from 112 to 116 lsa but as this thread shows that's not right. Its the ICL and advance that matters.

If I were prepared to drop another $4,000 to chase the lost performance and replace this new cam while still retaining its excellent manors, I think I would go back to a 216/220 but have it ground on 114 lsa. So 216/220 .6xx"/.6xx" 114 +4 (-10 overlap). This would have to be a custom cam of course, probably a Comp like the previous cam as they seem to have something very similar already.
The power curve difference between those two camshafts will be in the intake centerline. If you want to move the powerband lower in the 218/226 on 116 camshaft lower in the RPM range, you can simply advance the camshaft with an adjustable timing gear. If you advance it 3 degrees, it will have the same or close to same IVC as your old camshaft and will make the new cam perform similar to what you are used to.
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Old 10-05-2017, 10:09 AM
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Originally Posted by speedtigger View Post
The power curve difference between those two camshafts will be in the intake centerline. If you want to move the powerband lower in the 218/226 on 116 camshaft lower in the RPM range, you can simply advance the camshaft with an adjustable timing gear. If you advance it 3 degrees, it will have the same or close to same IVC as your old camshaft and will make the new cam perform similar to what you are used to.
You beat me to it, Steve. Cheapest easiest fix is to advance it 3-4 degrees with a keyed crank sprocket, and your low end would be back.

In general, torque cams can be tricky. Cause they'r gonna operate at low RPM, so you don't want lots of overlap - and if anything you want high negative overlap, AND you want early IVC and late EVO, so you're sort of boxed into smaller durations.

Probably simpler to just bolt some 1.8 or whatever rockers on the stock cam to pick up some grunt off idle
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Old 10-05-2017, 10:20 AM
  #64  
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Originally Posted by speedtigger View Post
The power curve difference between those two camshafts will be in the intake centerline. If you want to move the powerband lower in the 218/226 on 116 camshaft lower in the RPM range, you can simply advance the camshaft with an adjustable timing gear. If you advance it 3 degrees, it will have the same or close to same IVC as your old camshaft and will make the new cam perform similar to what you are used to.
Thank you for the response, this may be very wrong but I thought if I were to have the shop advance the cam like that it would be likely to induce more low rpm surge? (which this cam has none at all, no matter what you do, its truly like a stock cam in my 6 speed 5.7 which is amazing!) if not that would be just what i need
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Old 10-05-2017, 10:29 AM
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Originally Posted by Pulse Red View Post
Thank you for the response, this may be very wrong but I thought if I were to have the shop advance the cam like that it would be likely to induce more low rpm surge? (which this cam has none at all, no matter what you do, its truly like a stock cam in my 6 speed 5.7 which is amazing!) if not that would be just what i need
I don't expect you will experience any negative drivability effects by advancing the camshaft 2 to 4 degrees.
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Old 10-05-2017, 10:38 AM
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Originally Posted by speedtigger View Post
I don't expect you will experience any negative drivability effects by advancing the camshaft 2 to 4 degrees.
That's good news, I will have a chat with the shop that did the install and mafless tune about getting this done. Do you recommend any particular adjustable timing gear? Thanks.
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Old 10-05-2017, 10:42 AM
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Originally Posted by Pulse Red View Post
That's good news, I will have a chat with the shop that did the install and mafless tune about getting this done. Do you recommend any particular adjustable timing gear? Thanks.
Cloyes make several different adjustable timing sets that can do a good job for you.
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Old 10-05-2017, 10:50 AM
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Originally Posted by speedtigger View Post
Cloyes make several different adjustable timing sets that can do a good job for you.
Thanks for that. I will check it out, I just need to make sure I can get them here in Australia. The only ones I found here so far was comp or rollmaster.
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Old 10-05-2017, 12:44 PM
  #69  
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Hi Trusky, my observation (here) is that the above reports are made from observation "guesses", NOT from an understanding of how an engine operates.

Rule # ONE : The amount of Valve Overlap CHOICE is mostly related to the time the engine is operated at WOT vs being throttled.

YOUR tow truck camshaft : 180/188 .560" .543" 102 C/L.
I use this camshaft on engines that operate in the 2000 RPM RANGE for 25K hours AND Peak HP at 3000 RPM.

NOW imagine, the air that enters the engine is PUSHED by the BARO PRESSURE, the engine NEVER "sucks" air.
The piston is "pushed" up from crankcase pressure by BARO, this is called Pumping Losses.
The weight of the AIR, when dense, (WOT) WILL cause travel "across" open valves into the exhaust manifold in the correct direction.
The engine when THROTTLED will have a REVERSED direction of the air/gasses (exhaust into intake) when the exhaust pressure is GREATER than that of the intake port/cylinder.

BOTTOM LINE : The air flow of the engine should ALWAYS be the same direction, intake into exhaust.

Lance
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Old 10-05-2017, 07:38 PM
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The BTR Stage 1 223 cam has negative overlap. Should have good low end torque, I think.
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Old 10-09-2017, 09:11 PM
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Btw, I'll make this a sticky at some point. Things get a little more traction outside of stickies for whatever reason.
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Old 11-30-2017, 03:31 PM
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Btw, made this a sticky.
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Old 12-03-2017, 01:06 PM
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Jake, I've got a question if you don't mind.

I have a '98 Camaro. Currently equipped with an LS6 intake, ported throttle body, Dynatech 1 3/4 headers into a high-flow cat dynatech Y-pipe that vents through a dynomax exhaust. Car also has a Yank SS3600 converter and 3.42 gears.

Plans for this winter are a heads/cam swap. The heads are a set of 243's with mild work; the rocker arm boss is removed, casting flash gone and the bowls cleaned up. The cam I currently have to install is one of the EPS 222/226 - 113 grinds. I'm not looking for maximum effort, I'm looking for something that'll drive well. Car's a street car.

Am I on the right track?
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Old 12-03-2017, 06:10 PM
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Why remove the rocker arm boss??
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Old 12-03-2017, 09:43 PM
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I was referring to the rocker arm boss in the intake port; the bump in the port wall that consists of the bottom of the rocker arm bolt hole.
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Old 12-03-2017, 09:59 PM
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Ah! Makes perfect sense now! lol
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Old 12-04-2017, 04:36 PM
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OK, maybe I am a good candidate to post in this thread regarding my setup..
My setup is a Twin 88mm ( GT50-88s with a 91mm/99mm turbine wheel) 427" LSX deal 11:1 compression, My cam specs are .715/.715 with a duration of 258/270 @ 0.50" with a 116+5 LSA along with a 111* Intake centerline...which puts me at about 32* of positive overlap. One topic im not seeing anyone on here comment on regarding overlap is their actual Cylinder pressure with "X" overlap. Inform me if im wrong but as far as I know, increased overlap "Bleeds" compression/cylinder pressure. So what im curious to know is, what would happen if you were in a situation like mine? a great deal of overlap (32*) combined with 200-205ish psi of cranking compression with a low intake center line?
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Old 12-05-2017, 09:54 AM
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Originally Posted by The_Bishop View Post
Jake, I've got a question if you don't mind.

I have a '98 Camaro. Currently equipped with an LS6 intake, ported throttle body, Dynatech 1 3/4 headers into a high-flow cat dynatech Y-pipe that vents through a dynomax exhaust. Car also has a Yank SS3600 converter and 3.42 gears.

Plans for this winter are a heads/cam swap. The heads are a set of 243's with mild work; the rocker arm boss is removed, casting flash gone and the bowls cleaned up. The cam I currently have to install is one of the EPS 222/226 - 113 grinds. I'm not looking for maximum effort, I'm looking for something that'll drive well. Car's a street car.

Am I on the right track?
Yeah, that cam will be fine for a street cruiser. And will pair well with the 3.42s and SS3600.
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Old 12-05-2017, 10:00 AM
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Originally Posted by Ron_Stoppable View Post
OK, maybe I am a good candidate to post in this thread regarding my setup..
My setup is a Twin 88mm ( GT50-88s with a 91mm/99mm turbine wheel) 427" LSX deal 11:1 compression, My cam specs are .715/.715 with a duration of 258/270 @ 0.50" with a 116+5 LSA along with a 111* Intake centerline...which puts me at about 32* of positive overlap. One topic im not seeing anyone on here comment on regarding overlap is their actual Cylinder pressure with "X" overlap. Inform me if im wrong but as far as I know, increased overlap "Bleeds" compression/cylinder pressure. So what im curious to know is, what would happen if you were in a situation like mine? a great deal of overlap (32*) combined with 200-205ish psi of cranking compression with a low intake center line?
It doesn't actually bleed compression. But the overlap cycle doesn't allow the compression to build because the valves remain open for a fairly long time in comparison to a lower overlap cam.

With boost, you may see less PSI with that cam until you spin it high... but it'll make a lot of power.

I'd probably go a little milder on the cam and let the turbos work for you...like a 248/262 117+5 with a solid roller setup.
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Old 12-05-2017, 05:36 PM
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I figured it was actually on the other end. When the intake valve is closing really late, at some point, the piston starts to push air back out the intake valve (i.e. reversion), which actually would bleed off pressure. you see this with some of the high HP NA applications - like the 850 HP 441's that spin 8500 rpm and run cams like 275/290 at 050. Edit - cams that large at 13:1 compression and still run pump gas
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