Same intake and exhaust duration, same DCR, same lift, different LSA
Just a thought, but with those cam specs, you are a stone's throw away from Spinmonster cam specs(230/234 114) Just from my experience, most 22x cams either do not make any more power than a smaller 215-219 cam and/or have less driveability like what you are trying to avoid. For most of what I build, either customer wants stock driveability or wants big power, not much in between. Spin has been on here lately, you should DM him. His cam works, it's proven and has tons of reference points. The 224-227 have a lot of reference points too, but very few have stood out and outshined something else slighty smaller/bigger. Just some thoughts on what I have seen. For reference, I am taking my own advice and going from a 215 cam to a 230-238 cam. Not even looking at the 22x somethings at all.
I did a search and Holdener did an LSA comparison with a 108, 112, and 120 LSA cams with the same lift and duration. He never mentions whether any of the cams had any ground in advance. Of course, with no advance ground in, the 120LSA cam was dead down low and made an insignificant increase at the very top end.
I think I understand that intake duration and lift determine power potential with the intake valve closing event determining where in the rpm band the power will be made. I have absolutely no idea how ground in advance effects the exhaust side. Anyone care to try and explain this to a farm boy. Try not to use too many big words.
I did consider Spin's cam but wanted to see what could be done with even less overlap. Plus, I absolutely hate any kind of bad manners. I'd rather have a few less hp than having a bucking and lurching car telling me which gear I need to be in.
And all good stuff above. Very enjoyable and enlightening read.
Back in ~2002 a local shop had a little 216/220 ~.53x/.52x cam that would make 400 to 405 whp in a M6, 5.7 Stage 2 ported heads, cam, LS6 intake 1 3/4 LT header car. The shop owner said was it was his favorite cam.
However, stock exhaust system typically killed ~40 whp off of the package. Most customers interested in that H&C seemed to want to keep stock exhaust including cats.
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I did a search and Holdener did an LSA comparison with a 108, 112, and 120 LSA cams with the same lift and duration. He never mentions whether any of the cams had any ground in advance. Of course, with no advance ground in, the 120LSA cam was dead down low and made an insignificant increase at the very top end.
Advancing does the same, retarding moves it up.
Added exhaust duration adds to top end due to scavenging but hurts low end due to overlap.
Raising static compression adds to the entire power band and improves driveability making a cam act as it does in a bigger displacement without a penalty in power band shifting by about 3% in power gains. On 500hp you would be at about 515hp with a full point in compression. Low end Tq improves a bit more by about 4%.
Cam designers that narrow the LSA and add advance are doing it to improve dynamic compression without removing heads. If you bump static compression, there is no need to advance a cam on a narrow LSA.
On an LS3, a 227-230 intake duration on a 114+1 peaks at about 6300rpm where the intake manifold is forcing the peak due to runner length. If you use a FAST intake there are modular runner swaps that allow you to change this. A 230 on a 115+3 is also about 6300rpm. A 230 on a 112 with 3 degrees advance would need more exhaust duration to extend the power band back up to 6300. Cams that peak the power band coincident with the intake manifold result in the best peak HP reading on a dyno. Cams that don't peak coincident with the intake manifold have a lower number that appears as a flat line in the high rpm on a dyno.
Once durations are chosen, the LSA and advance are picked for you in a given power band goal.
https://www.compcams.com/cam-timing-...paration-angle
Last edited by Spinmonster; Oct 11, 2022 at 08:53 AM.
Launching!
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From: Dayton, OH
Thank you @Spinmonster
I am approching the time to pick a cam so I have been reading up on cams. This is very helpful.
I am approching the time to pick a cam so I have been reading up on cams. This is very helpful.
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I went to better heads, more compression, and a much milder cam (1.5 degrees overlap instead of 11), and the car made 10 more whp, but more importantly, drives **so** much smoother and gets 31 mpg highway.
Tony Mamo did the heads and spec’d the cam … he knows his ****. 👍
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To this day I do not understand why people want to calculate overlap at 0.050 and say they have zero or negative overlap. Overlap is more accurately calculated at 0.004 or 0.006. My 271/284 @ 0.006 on a 108 LSA and 106 ICL or commonly expressed 108 +2 camshaft in my 11:1 383 has perfect manners. It has 61.5 degrees of overlap. Using the 0.050" method, with its 218/228 @ 0.050 it has 7 degrees of overlap. I still have cats but it is nowhere near burn your nose or eyes rich at idle even before the cats light off. You can make a cam with substantial overlap still idle cleanly if you have the start of injection timing right in the tuning. By waiting until the exhaust valve is nearly closed to start injecting fuel, raw fuel cannot make it into the exhaust during the overlap period. I have seen some bucking with some cams at low rpm. That being said I typically see that most on cams that have an early IVC and are operating at higher load at lower rpm. With a 0.006 IVC of 61.5 my 383 will pull a light load smoothly down to 1,200 rpm and take full load smoothly by ~1,600. It pulls 7,400 lbs up a 6-8% grade in overdrive at 75 mph and 2,250 rpm smooth as silk operating at a stoichiometric air/fuel ratio.
Last edited by Fast355; Oct 18, 2022 at 02:32 PM.
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I forgot to mention earlier that another highly overlooked area when it comes to overlap and what works in an engine is the valve seat angle. A 30° valve seat will flow more air immediately when the valve lifts off the seat then a 45-50° seat will. A steeper valve seat angle will tolerate more overlap than a shallower angle will because it decreases the flow during the overlap period.
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I forgot to mention earlier that another highly overlooked area when it comes to overlap and what works in an engine is the valve seat angle. A 30° valve seat will flow more air immediately when the valve lifts off the seat then a 45-50° seat will. A steeper valve seat angle will tolerate more overlap than a shallower angle will because it decreases the flow during the overlap period.
Would you consider this a fundamental item, or maybe just a second or third order effect?
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That is very interesting. What would you say the magnitude of this effect is? What is the ‘X’ in “45 degrees will tolerate X degrees more overlap”? Does the steeper valve angle also cost flow near IVC, thereby necessitating a later IVC to achieve the same upper rpm power?
Would you consider this a fundamental item, or maybe just a second or third order effect?
Would you consider this a fundamental item, or maybe just a second or third order effect?
Rethinking The Valve Job (motortrend.com)