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Would really like to learn what other have to say about the idea a 30 degree valve job will require a different cam advance than a 45 degree valve job?
That would imply the defacto cam advance ground into the typical cam may not be in the ballpark depending on the heads valve job.
25 hp gain changing from +4 advance to -1 advance in Vizard's 383 SBC?
Last edited by 99 Black Bird T/A; 11-01-2022 at 08:44 AM.
Wade, this is summarizing what I mean when I say that I like my valves to sit ON the seat and not IN the seat…without me actually saying too much. I’ve mentioned this on Tech a few times in cylinder head discussions. In a nutshell, as David said, the 30 degree seat setup will “act” like it’s coming off the seat much quicker than a 45 or 55 degree setup, even though camshaft hasn’t changed. It’s a simple matter of angles. This takes advantage of low lift properties immensely, which allows you to alter the “built in advance” or centerline to help you make more torque. Torque makes hp.
Everything David says here about cylinder head & Camshaft combinations is spot on. If the cam designer doesn’t know what the heads are doing, then the combination isn’t optimized. I thought of Tony a dozen times while watching this video, because it’s exactly his business model. He fully understands how and WHY his heads are the way they are, and therefore he can design a custom camshaft better than anyone for his heads. Seat angles are huge in the world of max-effort, and Tony has the added benefit of setting all this up to work together, which means the consumer is getting the very best package available for the intended use. I’ve read a few of David’s articles through the years, but this is the first video of his I’ve watched.
To answer your question as to why a different advance is “required” as to the setup seat angle?…it’s definitely not a requirement per-say, but in the world of max-effort builds, your leaving power on the table without the fine tuning required here to get this right. In a 400 hp street build, you’ll notice less of an increase in power, vs a 800hp race build. It’s an area of the build that gets overlooked 9 times out of 10, but when it’s right…it’s RIGHT.
I could see 25hp change in changing the cam centerline 5 degrees, he did lose low-end torque and gained top end which is the textbook result you should expect from a bit of cam retard. As for the valve job angle being a contributor, it could be, but so could a few other things like valvetrain stiffness as he did wring the wee out that engine to 7500+ rpm.
From what I know, the reason advancing the cam on performance engines (especially performance street engines) being par for the course is that it works, and not just in LS engines. I've seen old Engine Masters engines with the most beautiful valve jobs you could imagine advancing the cam a lot more than four degrees before seeing any power losses in the curve. It even works with stock cams that have to pass emissions and idle quality tests. If you have a racing engine with a big solid roller that spins to 7500 then consider installing the cam straight up.
I watch David Vizard's videos all the time. He has SO much knowledge to share! And not afraid to step on the occasional toe while doing so....
I regard Tony Mamo in a similar way. Does he do videos on porting? I haven't seen that he does.
Scott, that an amazing post & explanation, much appreciated 👏 👍
if the first angle is say 30 does it matter if the valve job is a standard 3 angle or more complex 4, 5 angle etc? In other words to the other valve angles play a role in this or is it mostly based on the initial angle?
Makes a great argument to buying the H&C package from one knowledgeable person that did the heads and spec's the cam like Tony or Darin Morgan etc.
Valve seat angle has an impact on low-lift flow numbers which has an impact on how overlap and valve events effect the combination. Generally speaking if you keep the duration and overlap the same, the 30* seat will respond more radically then a 50* seat. The 30* seat will flow more with less lift because it makes for more valve area at low lifts. A 50* seat is the opposite, it will block flow until higher lift. That being said a 50* seat will let the port build more energy by blocking some of the port flow from equalizing into the chamber until the piston really starts to move downward on the intake stroke. A 50* seat will allow wilder cam timing and tighter LSA to run more tamely at lower rpm to a point. Then when the rpm climbs and the intake and exhaust pulses become stronger it really helps ram the mixture into the cylinders in the mid-upper rpm range.
I'm putting a 242/256 110+4 cam in a motor paired with trickflow ls3s. Their 3 angle valve job measurements are 37°, 45°, 64°. A fast mid length intake, does this mean I should retard the cam a bit to gain more top end power? Cam specs seat and .050.
This information couldn't possibly apply in every circumstance. What about us high elevation guys? If I retard the cam 5 degrees, that will bleed off way more cylinder pressure and at 5000+ feet this could be a huge detriment, regardless of the fact that I have 37 degree valve seats.
This information couldn't possibly apply in every circumstance. What about us high elevation guys? If I retard the cam 5 degrees, that will bleed off way more cylinder pressure and at 5000+ feet this could be a huge detriment, regardless of the fact that I have 37 degree valve seats.
I agree with you to a large extent. However I will say this is where dynamic compression ratio should come into play. As altitude increases, cylinder pressure decreases. Higher altitude will need an earlier IVC to keep the same cranking compression.
This information couldn't possibly apply in every circumstance. What about us high elevation guys? If I retard the cam 5 degrees, that will bleed off way more cylinder pressure and at 5000+ feet this could be a huge detriment, regardless of the fact that I have 37 degree valve seats.
High elevation does tend to mess up a lot of stuff when it comes to internal combustion engines. Forced induction guys are screwed, and even the strongest NA cars feel the lack of air. I sold a C5Z to a guy from Denver once. He flew out here and drove it back. He was disgusted that the car would absolutely haul booty here, yet when he got to Denver he said it felt 75 hp slower.
High elevation does tend to mess up a lot of stuff when it comes to internal combustion engines. Forced induction guys are screwed, and even the strongest NA cars feel the lack of air. I sold a C5Z to a guy from Denver once. He flew out here and drove it back. He was disgusted that the car would absolutely haul booty here, yet when he got to Denver he said it felt 75 hp slower.
The difference is that boosted guys can turn up the boost to partially compensate for the elevation and air density difference...can't do that NA unless you open the bottle.
The difference is that boosted guys can turn up the boost to partially compensate for the elevation and air density difference...can't do that NA unless you open the bottle.
I once got to take my car over Lizard Head Pass in Colorado on a nice warm day, 10,200 feet, it probably had a density altitude of 14,000 equivalent. The gas pedal felt like it was broken. The EFI accounted for it and kept running but damn.
Wade, this is summarizing what I mean when I say that I like my valves to sit ON the seat and not IN the seat…without me actually saying too much. I’ve mentioned this on Tech a few times in cylinder head discussions. In a nutshell, as David said, the 30 degree seat setup will “act” like it’s coming off the seat much quicker than a 45 or 55 degree setup, even though camshaft hasn’t changed. It’s a simple matter of angles. This takes advantage of low lift properties immensely, which allows you to alter the “built in advance” or centerline to help you make more torque. Torque makes hp.
Everything David says here about cylinder head & Camshaft combinations is spot on. If the cam designer doesn’t know what the heads are doing, then the combination isn’t optimized. I thought of Tony a dozen times while watching this video, because it’s exactly his business model. He fully understands how and WHY his heads are the way they are, and therefore he can design a custom camshaft better than anyone for his heads. Seat angles are huge in the world of max-effort, and Tony has the added benefit of setting all this up to work together, which means the consumer is getting the very best package available for the intended use. I’ve read a few of David’s articles through the years, but this is the first video of his I’ve watched.
To answer your question as to why a different advance is “required” as to the setup seat angle?…it’s definitely not a requirement per-say, but in the world of max-effort builds, your leaving power on the table without the fine tuning required here to get this right. In a 400 hp street build, you’ll notice less of an increase in power, vs a 800hp race build. It’s an area of the build that gets overlooked 9 times out of 10, but when it’s right…it’s RIGHT.
^^^^^^This^^^^ Absolutely on the $$. Everything I've ever studied on engine design theory states you don't want the valves recessed into, or even parallel to, the valve seat. I don't profess to know everything, because nobody does. But when it comes to engine cylinder heads/cams relationship, if anyone comes closer than David Vizard, I've not met him. Some of the things he postulated, and then proved, are over my head, until I really listened and dissected what he's saying. I feel bad for him, as David has suffered a stroke recently. But, I'm happy for him because he appears to be well on his way back to 100%. His thought process is still as good as ever. Reminds me somewhat of Fetterman. I recently started watching some of Vizards videos online. IDK if anyone will ever be more of a gearhead than David Vizard. Using his "128" formula for my LS7, with stock valve sizes, my LCA=105.92!!!🤯 I have more research to do, as I'm not certain of what the valve angles are that AHP machined. Maybe Kohle can chime in on this one. But Vizard gives a warning at the beginning that most LSA's need to be tighter than what most people are familiar with. Good stuff.........
Speaking of David Vizard''s 128 rule, doe it apply equally to all 2 valve V8's or is it platform specific?
According to 128 rule my 383 LS stroker would want a 108 lsa cam. (107.6 rounded up for 11.4 compression etc).
Honestly, I cringe at the ideal of the smell and loss of driveablity from adding ~ 6 to 12 degrees of overlap to the typical LS cam and going from a 111 to 114 to 108 LSA.
How much hp are we talking with that extra 6 to 12 degrees of overlap?
Last edited by 99 Black Bird T/A; 11-08-2022 at 04:13 PM.
Speaking of David Vizard''s 128 rule, doesn’t it apply equally to all 2 valve V8's or is it platform specific?
According to 128 rule my 383 LS stroker would want a 108 lsa cam. (107.6 rounded up for 11.4 compression etc).
Honestly, I cringe at the ideal of the smell and loss of driveablity from adding ~ 6 to 12 degrees of overlap to the typical LS cam and going from a 111 to 114 to 108 LSA.
How much hp are we talking with that extra 6 to 12 degrees of overlap?
Its not so much hp, its midrange torque. Tightening the LSA typically advances the intake closing point. Combine that with the improved scavenging and it is not unusual to get 20-30 ft/lbs more midrange torque.
Its not so much hp, its midrange torque. Tightening the LSA typically advances the intake closing point. Combine that with the improved scavenging and it is not unusual to get 20-30 ft/lbs more midrange torque.
Its not so much hp, its midrange torque. Tightening the LSA typically advances the intake closing point. Combine that with the improved scavenging and it is not unusual to get 20-30 ft/lbs more midrange torque.
11-01-2022, 08:14 AM
Cam Company Cam Cards Usually Wrong? Relationship of valve job angles to cam advance? 
🤯 I have more research to do, as I'm not certain of what the valve angles are that AHP machined. Maybe Kohle can chime in on this one. But Vizard gives a warning at the beginning that most LSA's need to be tighter than what most people are familiar with. Good stuff.........
Wow! That must be insane!