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evanfrucht Samba Member
Joined: July 24, 2016 Posts: 2180 Location: Laurel Canyon, CA
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Posted: Wed Oct 20, 2021 12:23 pm Post subject: Big valves/Hot Cam vs. Smaller valves/Hotter Cam |
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Ok guys, so bear with me... I have one of those "theoretical" questions I'm just kinda curious as I see the subject danced around lot.
This is mainly directed towards those who have seen or have access to a fair amount of dyno results and/or enough experience to really be able to point to some sort of solid relevant comparison.
I know there is a lot of other factors at play so let me try to hone in on this and make what I'm wondering as specific as I can.
Theoretical situations with popular cam shaft grinds:
A. #1: W110 (w/ 42x37) #2 W120 (w/ 40x35)
B. #1 FK7 (w/ 42x37) #2 has an FK8 (w/ 40x35)
C. #1 86A (w/ 42x37) #2 86B (w/ 40x35)
*** all engines are otherwise identical 2276's. "A" will use stock rockers and "B"&"C" will use 1.4 ratio rockers. Let's say #1's have 9 CR and #2's have 9.5 CR (or maybe that's not the best way to make it "fair?" Please enlighten me if you feel so)
Question is, how would the #1's and #2's generally respond differently? Such as what would make the most HP, power band differences, general behavior, etc. _________________ 1967 Bug ( the daily rod )
1964 Fury Wagon ( the pavement shredder ) |
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bugguy1967 Samba Member
Joined: January 16, 2008 Posts: 4338 Location: Los Angeles, CA 90016
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Posted: Wed Oct 20, 2021 12:39 pm Post subject: Re: Big valves/Hot Cam vs. Smaller valves/Hotter Cam |
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Assuming they have a proper port range % to valve size and good velocity? So let's say both are ~88%? A - 1: -6000 rpm powerband peak, but with a less than optimal bottom end. 2: probably also a 6000 peak, but the cam would want to keep making power if it had more flow.
B - 1: could probably peak beyond 6000 with decent bottom end. 2: The FK8 will want more head.
C - 1: Done it. Peaked at 6500 with strong bottom end. 2: too much cam for the head. It'll have a stronger bottom end than if it had a bigger head. Would run out of steam at 5,500-6K, desite wanting to rev to 7K+. _________________ "A petrol engine can start readily, run smoothly and give every appearance of being in good order, without necessarily being in good tune." - Colin Campbell, "The Sportscar Engine" |
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Danwvw Samba Member
Joined: July 31, 2012 Posts: 8892 Location: Oregon Coast
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Posted: Wed Oct 20, 2021 12:43 pm Post subject: Re: Big valves/Hot Cam vs. Smaller valves/Hotter Cam |
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I would probably choose the 86A with injection or dual 2 barrel induction with the big valves in a beetle and with smaller valves for a bus.
The other cams with a single carburetor. _________________ 1960 Beetle And 1679cc DP W-100 & Dual Zeniths! |
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Alstrup Samba Member
Joined: July 12, 2007 Posts: 7182 Location: Videbaek Denmark
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Posted: Wed Oct 20, 2021 1:55 pm Post subject: Re: Big valves/Hot Cam vs. Smaller valves/Hotter Cam |
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bugguy1967 wrote: |
Assuming they have a proper port range % to valve size and good velocity? So let's say both are ~88%? A - 1: -6000 rpm powerband peak, but with a less than optimal bottom end. 2: probably also a 6000 peak, but the cam would want to keep making power if it had more flow.
B - 1: could probably peak beyond 6000 with decent bottom end. 2: The FK8 will want more head.
C - 1: Done it. Peaked at 6500 with strong bottom end. 2: too much cam for the head. It'll have a stronger bottom end than if it had a bigger head. Would run out of steam at 5,500-6K, desite wanting to rev to 7K+. |
Interesting. I have never ever been even remotely close to have paek power so high with either the 86a or b. With 42/37 valves and good off the shelf cnc heads and the b cam peak is typically around 6000 rpm. The A cam is just lazy. Peaks around 54-5500 and not really worth writing home about.
A W110 with such heads in such combo will peak around 53-5400. Very "driveable, but lazy.
The FK7 I don´t know good enough to say much about other than it pulls more like a Web 163 than a W110 cam.
I think the FK7 could work well in a 1776 or 1914, - or a 2275 bus engine. _________________ https://www.thesamba.com/vw/forum/viewtopic.php?t=435993 |
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Brian_e Samba Member
Joined: July 28, 2009 Posts: 3228 Location: Rapid City, SD
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Posted: Wed Oct 20, 2021 4:26 pm Post subject: Re: Big valves/Hot Cam vs. Smaller valves/Hotter Cam |
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Do the math and see what each valve size will allow the engine to rev to. Pick the smallest valve what will allow the engine to rev to that rpm. Then pick a cam that will make the power in the range you will be using most.
I have done a few FK8/86B/2288 2276cc engines. The 40x35 engine was much more pleasant to drive in daily use. The 42x37 engine was sluggish down low, but had more top end. The 40x35 engine had a wider power band. Both engines were run in the same car.
The problem with the smaller heads and hotter cam is the heads start to run out of steam just about the time the cam starts making good power. Unless the heads are REALLY well designed and built, its a mismatch. If the heads are top notch, all the ratios are dead nuts, and the cam is good....small valves can make some big power. JPM does this very well, but his engines are also VERY high revving.
Big valves and a small cam won't make enough airspeed down low, and will always seem lazy till the cam is about to run out of steam.
Of all the situations listed, I would take the big cam and 40x35's every time, but the 40x35's better be done correctly, and they will make big power across the board, and be much nicer to drive.
Brian _________________ www.type-emotorsports.com |
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modok Samba Member
Joined: October 30, 2009 Posts: 26743 Location: Colorado Springs
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Posted: Wed Oct 20, 2021 5:23 pm Post subject: Re: Big valves/Hot Cam vs. Smaller valves/Hotter Cam |
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Hard to answer because the way I "think about it" is totally opposite. SO, instead
I'll try to predict the results rather than discuss.... how I think about it.
A. #1: W110 (w/ 42x37) #2 W120 (w/ 40x35)
#1 would work as a SMALL cc, lets say 1915, or 1600!, 1600 de-stroker, but it still NEEDS lots of compression to work. 9.5 MIN, Probably 10-1
#2 is ok, lets make it a 2007 or 2165cc, 9-1 compression mild street engine
or 2275 offroad engine
B. #1 FK7 (w/ 42x37) #2 has an FK8 (w/ 40x35)
#1, bigcc, TURBO!
#2 ok for mid-large cc, only really need 1.3 rockers
C. #1 86A (w/ 42x37) #2 86B (w/ 40x35)
Same as above but the ideal valve lash will be zero to + .005"
instead of zero to negative .005" for engle cams |
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Dan Ruddock Samba Member
Joined: October 25, 2012 Posts: 3574 Location: Sarasota, in my adopted state of Florida
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Posted: Wed Oct 20, 2021 7:19 pm Post subject: Re: Big valves/Hot Cam vs. Smaller valves/Hotter Cam |
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modok wrote: |
Hard to answer because the way I "think about it" is totally opposite. SO, instead
I'll try to predict the results rather than discuss.... how I think about it.
A. #1: W110 (w/ 42x37) #2 W120 (w/ 40x35)
#1 would work as a SMALL cc, lets say 1915, or 1600!, 1600 de-stroker, but it still NEEDS lots of compression to work. 9.5 MIN, Probably 10-1
#2 is ok, lets make it a 2007 or 2165cc, 9-1 compression mild street engine
or 2275 offroad engine
B. #1 FK7 (w/ 42x37) #2 has an FK8 (w/ 40x35)
#1, bigcc, TURBO!
#2 ok for mid-large cc, only really need 1.3 rockers
C. #1 86A (w/ 42x37) #2 86B (w/ 40x35)
Same as above but the ideal valve lash will be zero to + .005"
instead of zero to negative .005" for engle cams |
Interesting, is your 86a lash idea assuming steel or aluminum pr’s. |
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modok Samba Member
Joined: October 30, 2009 Posts: 26743 Location: Colorado Springs
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Posted: Wed Oct 20, 2021 7:36 pm Post subject: Re: Big valves/Hot Cam vs. Smaller valves/Hotter Cam |
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Does not even have to do with those cams just the old WEB vs engle thing.
I don't mean to pick one one grind VS another.
But USUALLY web has a longer lash ramp and smoother acceleration, and usually engle doesen't, so, I do suspect some would benefit from negative lash.
If it were not for that, some of the grinds would be the same.
Last edited by modok on Wed Oct 20, 2021 7:42 pm; edited 1 time in total |
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[email protected] Samba Member
Joined: May 17, 2003 Posts: 4863 Location: Harmony, PA
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Posted: Wed Oct 20, 2021 7:37 pm Post subject: Re: Big valves/Hot Cam vs. Smaller valves/Hotter Cam |
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Brian_e wrote: |
I have done a few FK8/86B/2288 2276cc engines. The 40x35 engine was much more pleasant to drive in daily use. The 42x37 engine was sluggish down low, but had more top end. The 40x35 engine had a wider power band. Both engines were run in the same car.......
......Of all the situations listed, I would take the big cam and 40x35's every time, but the 40x35's better be done correctly, and they will make big power across the board, and be much nicer to drive.
Brian |
CB’s listings of specs on turnkey engines are growing by leaps, and bounds using Ponchito heads. Whether Pat is exploiting their open casting for optimum cooling, or has simply created a 40x35.5 Head with excellent ports off the shelf, there are many surprising combos using them. |
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modok Samba Member
Joined: October 30, 2009 Posts: 26743 Location: Colorado Springs
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Posted: Wed Oct 20, 2021 8:23 pm Post subject: Re: Big valves/Hot Cam vs. Smaller valves/Hotter Cam |
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My reading comprehension is very low today, I'm misreading everything.
But oh well check this out.
A lot of people want to try HIGHER ratio rockers, but....
It just doesn't really work. If you have worked out the best spring with just enough pressure for the job so it's no heavier than it needs to be(literally), and set them up .060-.080 from bind for best surge control, and worked out where the rockers have to be to keep all angles under control..... then you can't just slap on higher ratio... But you almost always can try LESS.
so, if you want to know how it would run with less valve lift, you can find out pretty quick. If everything is set to work with a higher ratio then it will be OK with a lesser ratio.
But what about DURATION?.....you can alter the lash....! set it loose to simulate less seat duration, and maybe set it a little tight to simulate more... but not much, of course.
So just far as TESTING, it seems better to "overcam it" and then try lower ratio rockers or loosening the lash to find out what less would feel like, if you want to know |
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[email protected] Samba Member
Joined: May 17, 2003 Posts: 4863 Location: Harmony, PA
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Posted: Thu Oct 21, 2021 6:17 am Post subject: Re: Big valves/Hot Cam vs. Smaller valves/Hotter Cam |
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modok wrote: |
My reading comprehension is very low today, I'm misreading everything.
But oh well check this out.
A lot of people want to try HIGHER ratio rockers, but....
It just doesn't really work. If you have worked out the best spring with just enough pressure for the job so it's no heavier than it needs to be(literally), and set them up .060-.080 from bind for best surge control, and worked out where the rockers have to be to keep all angles under control..... then you can't just slap on higher ratio... But you almost always can try LESS.
so, if you want to know how it would run with less valve lift, you can find out pretty quick. If everything is set to work with a higher ratio then it will be OK with a lesser ratio.
But what about DURATION?.....you can alter the lash....! set it loose to simulate less seat duration, and maybe set it a little tight to simulate more... but not much, of course.
So just far as TESTING, it seems better to "overcam it" and then try lower ratio rockers or loosening the lash to find out what less would feel like, if you want to know |
This also seems to be a trend Pat is doing at CB with the Panchito heads. The 2242, 2246, 2292, and 2300 seem to be commonly used cams. They range from .389-.430 lift at the cam with 298-321 degrees of duration. The commonly used 1.25 rockers create from .486-.537 at the valve. |
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jimmyhoffa Samba Member
Joined: February 16, 2014 Posts: 1047 Location: St. Louis
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Posted: Thu Oct 21, 2021 7:57 am Post subject: Re: Big valves/Hot Cam vs. Smaller valves/Hotter Cam |
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Good note gkeeton. I have also noticed that good-flowing 40x35 heads tend to target just at or barely over .500" lift at the valve on average, from builders who know what they're doing. It's worth mentioning that the one engine I did tear down that did not appear to follow the "rules" was from a big-name offroad builder with multiple Baja wins, and I spent a lot of time trying to figure out what the goal was there. I finally had a conversation with the person who drove the car in Baja when that engine was in it, and he stated that it was "...the slowest thing he had ever driven in that class, it made no torque, and we immediately abandoned that engine geometry. It was a recipe for multiple wasted hours in silt beds. It made power in about a 1000RPM window, and it was really hard to keep it there. We torched the clutch in a tight section and we were done."
For Modok's reasons regarding the ease of "backing off" of lift to investigate behavior, I have chosen an FK42 on my next 40x35 head build, which will lift ~.525" at the valve initially-perhaps near the high side of what makes sense, albeit with less duration for reasons that fit my purpose. This gives me the flexibility of, say, installing 1.25 slipper foot rockers on the exhaust side and leaving 1.4 on the intake.
It's worth planning a build to anticipate experimentation like that IMHO, especially in situations like ours/mine where we don't have the data like Pat Downs or Fat or Major or others who have a better idea of what to expect from a given combo, considering they have built thousands of engines which have stood the test of competitive motorsport of one form or another. _________________ 1974 Chenowth 2RL #1244 Street Legal
My other car isn't ridiculous. |
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Brian_e Samba Member
Joined: July 28, 2009 Posts: 3228 Location: Rapid City, SD
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Posted: Thu Oct 21, 2021 9:41 am Post subject: Re: Big valves/Hot Cam vs. Smaller valves/Hotter Cam |
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[email protected] wrote: |
CB’s listings of specs on turnkey engines are growing by leaps, and bounds using Ponchito heads. Whether Pat is exploiting their open casting for optimum cooling, or has simply created a 40x35.5 Head with excellent ports off the shelf, there are many surprising combos using them. |
This is because the VW world is finally catching up to the V8, just 20 years later. The V8 world has been using small efficient ports for years now. The VW world is just shooting for big CFM numbers with blown out big ports. Big CFM numbers sell parts to unknowing customers. Look at CB's, and others advertised flow numbers listed at .600" lift. Very few normal VW people are able to figure out how to run .600" lift on a VW head and make it last more than a week. They just want to see the biggest number they can find without understanding what is really going on.
Darin Morgan is one of the best cylinder head developers in the US or maybe the world. Many times he has said the three most important things when choosing a cylinder head are airspeed, airspeed, and airspeed. How many times have you ever seen airspeed mentioned in ANY ad for a VW cylinder head? The Panchito ad is the only one I have ever seen, an there are no real numbers given, just a mention.
Once you have a properly sized head, with perfect airspeed, everything becomes easier. The intake charge is able to move easily and has a bunch of momentum in the column of air. This faster speed is able to pack the cylinder more full of air before the intake valve closes. This is called ram filling, and if done correctly, it can be above atmospheric pressure. This is also why a very efficient, smaller valve head than what most are used to can be used successfully. The efficient heads can also stand more cam duration because the fast airspeed down low makes up for the loss of low end power usually associated with high cam duration. More power across the board.
Old style VW heads with huge hogged out ports were the opposite of this. They had very low airspeed, but big impressive CFM numbers at high lifts. Super sluggish down low, because the column of air was barely moving. They needed to be wrapped way up before the cylinder was able to start filling.
Airspeed, airspeed, airspeed......
Brian _________________ www.type-emotorsports.com |
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Ohio Tom Samba Member
Joined: February 09, 2006 Posts: 1657 Location: Marshallville Ohio
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Posted: Thu Oct 21, 2021 10:30 am Post subject: Re: Big valves/Hot Cam vs. Smaller valves/Hotter Cam |
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Oh boy....
The 86B and it's brethren (290-300 deg duration) can make power to 7,000rpm with the right heads and springs.
Most folks never see the high side of an FK-8, or 86B, or W-125 cam because they just don't have enough spring pressure and only notice that the power falls off at 6,500rpm.
Jacob and I saw the same thing years ago with the 86B cam. Changed the springs in his heads to LS Chevy springs, and his 70' beetle suddenly went from 13.20's, to 12.80's in the 1/4mi.
I am a firm believer in "smaller cam/ better flowing head" combinations for best overall performance.
It's really about the total area under the power curve. Smaller cams with better flowing heads give the widest powerband. Thus stretching the "pull" thru the whole gear, and bridging bigger gaps between gears.
Plus, I believe that folks in the VW world tend to over-cam motors often. Ending up with a more narrow powerband they they could have. |
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Alstrup Samba Member
Joined: July 12, 2007 Posts: 7182 Location: Videbaek Denmark
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Posted: Thu Oct 21, 2021 10:38 am Post subject: Re: Big valves/Hot Cam vs. Smaller valves/Hotter Cam |
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Ohio Tom wrote: |
I am a firm believer in "smaller cam/ better flowing head" combinations for best overall performance.
It's really about the total area under the power curve. Smaller cams with better flowing heads give the widest powerband. Thus stretching the "pull" thru the whole gear, and bridging bigger gaps between gears.
Plus, I believe that folks in the VW world tend to over-cam motors often. Ending up with a more narrow powerband they they could have. |
X2 _________________ https://www.thesamba.com/vw/forum/viewtopic.php?t=435993 |
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Brian_e Samba Member
Joined: July 28, 2009 Posts: 3228 Location: Rapid City, SD
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Posted: Thu Oct 21, 2021 10:50 am Post subject: Re: Big valves/Hot Cam vs. Smaller valves/Hotter Cam |
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X3
When I am running different combos through the analyzer programs, I will always go for the combo with the highest average torque, over peak HP numbers. Lots of low end, and a wide powerband will be WAY nicer to drive than an extra 5hp for bragging rights.
Brian _________________ www.type-emotorsports.com |
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Ohio Tom Samba Member
Joined: February 09, 2006 Posts: 1657 Location: Marshallville Ohio
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Posted: Thu Oct 21, 2021 2:57 pm Post subject: Re: Big valves/Hot Cam vs. Smaller valves/Hotter Cam |
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Panchito head flow numbers are published.
Both with and without CNC chambers.
CNC chamber heads flow better at lower lifts.
Right now CB Performance is out of the Panchito castings.
Maybe 4 weeks they say.
Stuck on a boat I guess.. |
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NJ John Samba Member
Joined: September 21, 2007 Posts: 2173 Location: HdG, MD & NJ
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Posted: Thu Oct 21, 2021 3:49 pm Post subject: Re: Big valves/Hot Cam vs. Smaller valves/Hotter Cam |
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And don’t knock on the FK7 cam for the street. Lots of usable power. _________________ 1973 standard, yellow, lowered, 3” narrowed front, 1600 blo-thru turbo w/single dell 15.4@86, so far
11.41 et buggy. Long gone
Let’s go O’s! Let’s go O’s!
https://www.youtube.com/@AirSpooledGarage |
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bw65vw Samba Member
Joined: August 04, 2020 Posts: 149 Location: Tennessee
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Posted: Thu Oct 21, 2021 6:23 pm Post subject: Re: Big valves/Hot Cam vs. Smaller valves/Hotter Cam |
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I was curious about some of the comments about the "C#1" combo. I am getting together parts now for a 2276 build and have that combo except 86A+3 and Tim's Stage 2 heads
bugguy1967 wrote: |
C - 1: Done it. Peaked at 6500 with strong bottom end. 2: too much cam for the head. It'll have a stronger bottom end than if it had a bigger head. Would run out of steam at 5,500-6K, despite wanting to rev to 7K+. |
Seems like you had a good experience with this one.
Alstrup wrote: |
I have never ever been even remotely close to have paek power so high with either the 86a or b. With 42/37 valves and good off the shelf cnc heads and the b cam peak is typically around 6000 rpm. The A cam is just lazy. Peaks around 54-5500 and not really worth writing home about.
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Curious about the comment of the 86A being "lazy"? Is this due to the lower lift? Would the added duration of an 86A+3 help with this? and lean more towards this idea below?
Ohio Tom wrote: |
Oh boy....
I am a firm believer in "smaller cam/ better flowing head" combinations for best overall performance.
It's really about the total area under the power curve. Smaller cams with better flowing heads give the widest powerband. Thus stretching the "pull" thru the whole gear, and bridging bigger gaps between gears.
Plus, I believe that folks in the VW world tend to over-cam motors often. Ending up with a more narrow powerband they they could have. |
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Ohio Tom Samba Member
Joined: February 09, 2006 Posts: 1657 Location: Marshallville Ohio
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Posted: Fri Oct 22, 2021 9:29 am Post subject: Re: Big valves/Hot Cam vs. Smaller valves/Hotter Cam |
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I think it's a matter of jargon.
The 86A is a milder cam. As such, the power comes on early (2,000rpm) and peak torque around 3,000rpm. Peaking out around 5,500rpm. While nice for pushing a bus around, it makes un-inspiring HP.
that might be considered to be "Lazy" by some accounts.
As we go up in duration (86B, and C), the power band (Torque curve) shifts up. HP numbers rise dramatically. The formula for HP is torque x rpm. So a shift upward in RPM with the same torque equals more HP.
A good rule of thumb is every 10deg of duration, shifts the powerband 1000rpm upward. Both starting and ending points (as long as everything else can support this).
To me, "Lazy" is what happens when your 2276 with FK-89 cam (326 deg duration) at 3,500rpm and stab the throttle and it feels like a 1776 until you hit 5,000. Then a light switch turns on... |
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