Big valves/Hot Cam vs. Smaller valves/Hotter Cam

[Alstrup]

[modok]

BIG TORQUE cams
w110 vs web 218
fk8 VS k10 discussion with ken tabor (still would love to fully understand that)

w125 is KIND OF one, but put 1.25 rockers on it then maybe it isn't.


Does not have to be a weird lobe shape, I think you can get a similar result just getting the cam in the right spot, but not as optimum.

Lifting the valve rapidly from the seat to .050 helps LOW rpm, idle-2500 maybe, but does nothing one way or another for midrange torque.
Will actually make less midrange if the duration at .020 is too short because then it may not have enough overlap to let the exhaust help it breathe.

many people would like, IF it was possible, would have the valve motion be a square wave.
and they would be surprised to find out it's not so good.
The cam can CONTROL the flow to occur when you want it to happen, by lifting the valve right amount, and putting the "flow window" in the right area.
Maybe the key is the right duration at .200 lift, And passes through .200 lift with the valve moving FAST, (closing the door fast) but how do you do that? well, maybe high lift, but the point of this high lift is not to dwell the valve full open for a long time, the point is that extra lift lets the valve get a "running start" accelerate and decelerate more gently up to a high speed passing through .200 valve lift, so lobe might be kinda pointy...... and the opening and closing ramps at .050 lift need to be gradual to play "catch" with that fast moving valve, so the duration at .020 is long, but the duration at .200 might be realatively short, and with what seems like a high lift.

Notice this is VERY different from what a w110 or w120 looks like.....
These cams are more like HIGH rpm cams IMO
The small valve trend is part of the same thing IMO.
Ports cannot control the timing of flow.
On the exhaust side I am a firm believer in 90% throat and the port at least that big too.
Put a big valve on a small exhaust port is making the flow area more like a square wave which is good right? kinda yes, but heck no. Just less control, no advantage. The flow does what it wants which may not be what you want.
Having a large opening in the middle of the exhaust stroke will LET flow occur in the middle of the stroke, which will extend the RPM capabilities without hurting the LOW rpms.

[Alstrup]

Its all in the combo as we have said a 1000 times. That said I have never been even close to pull 100 Nm/1000 cc with a W110. With a 218/119 its almost a walk in the park. The straight 218 bleeds a little too much off so it does not pull quite the same torque.
CB 2239. Awesome cam IMHO. Sort of in the middle of the W100 & 110 but pulls about the same power as the W110 if not a tad more, with a little less rpm. In good set ups about 95 nm/1000 cc.
CB 2241. Good cam. About the same as a W110, but with a little better lower rpm characteristics.
FK41. Good cam with a little more upper end. Roughly same powerband as the W110, but more torque.
Web 163 with stock rockers. good cam. With 1,25/1,3 rockers, awesome! (if the heads can support it)
(A customer of mine built a 1914 with hand ported AA500 heads by me w. 40/35 valves, 9,5 CR 44 Chinese IDF´s 32/36 mm grooved venturies, 1½" Sidewinder and a 123 programmable distributor. It is awesome. It pulls 138 hp @ 5500 and 190 Nm torque, rips from just over idle and is still quiet as a stocker at idle. Beautifull engine.

In addition or ammendment to what Modok wrote I will say, that I use split lifts and split duration cams a lot. Reason is that most type 1 heads actually have too efficient exhaust sides compared to the rpm band they are supposed to work in. That may be ok for aiding in cylinder head cooling, but it is definitely not good for power.
I am trying to fix a set of older Denham heads right now which have a 90% I/E ratio, and that is even after I have gone 2 mm up in intake valve size. I cant sink the exhaust valve as there is already too little distance from the seat to the port floor, so I have now deliberately reduced the efficiency of the chamber and will most likely be using 1,4/1,25 rockers to get the I/E ratio I want, which is around 80 in this case.
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[modok]

I never thought of it before but maybe the ideal lobe shape is different from intake VS exhaust.
I THOUGHT the split cams were just about matching the head flow, but maybe there is MORE to that. 218/119 seems to be such a classic.
Both the 218 and 163 seem to be very popular and both have more of a "torque cam shape"
But is this shape good for the exhaust side?....maybe not.

Maybe quick zero to .050 ramps is GOOD for the exhaust?


if so

The web 110/163 would be kinda backwards!
oh well, I wasn't planning on ordering another one anyway.

I bet you would like a 163/2241

[modok]

how about a comparison with the web 110 and scat c45, they all have about .390 cam lift
I don't have all the numbers but I have a few
only real difference between the web 110 and c45 is SLIGHTLY more pointy lobes and a little wobble in the ramps on the c45

[Paul.H]

I had a look at the Ken Tabor thread back in 2007 and he was going the right way with the comparison and he was on FI . He tried 3 cams in the same engine and dyno tested them. I can't make out the graphs though

[Danwvw]

Web 163:

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1960 Beetle And 1679cc DP W-100 & Dual Zeniths!

[txoval]

Modok,

I do run Scat slipper feet 1.25 rockers, .515” at valves

[modok]

1.3 rockers , good!

[Paul.H]

[Alstrup]

[Alstrup]

[stevemariott]

Thanks Alstrup!

[Alstrup]

Getting back to part of the original question, - W110 & 42/37,5 valves.
My colleague reminded me...
Looooong time ago, something like 10-12 years we actually had a 1914 engine on the rolls with a W110 and Tims stage II heads, 44 IDF´s and if our memories serve a CSO Super comp exhaust. Could have been a BAS street sport though. We both agreed on that it pulled 126 hp and 180ish Nm torque. My colleague rememberred it specificly because he thought the engine pulled well in the entire powerband especially taken into consideration that it was a "big valve" smallish engine.
So there is a part answer for that.
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[RandyV]

So gist is smaller cam/bigger valve > bigger cam/bigger valves???

Had a convo yesterday w/ good vw folk who suggested....

44IDF + FK-41 + 40 x 35.5 is a waste of valves. 35 x 32 better suited.

If agreeing, how much bigger on cam to make 40 x 35.5 viable?

If disagreeing....why?? (Or some valve size between the aforementioned?)

(I know that's a crude pair of options and I know there's far more to a head than just valve size.....but let's assume moderate porting, cc'ing, 8.5:1 comp)

If displacement matters too....I like 78 x 90.5 but if a consideration in it too please spill opinions.

[fuguboy]

I like CB’s panchito K-10 combos on YouTube

[modok]

good 40x35.5 heads on a 78x90.5 the "natural" torque peak be around 4000rpm
Stock size heads will put the torque peak much lower, probably 3300 rpm?

my OWN idea of an ideal "street" engine is a powerband of 3600-5500 rpm, max torque possible from the displacement.... 1.3 foot pounds per cube hopefully.
But there are many things that can be done, with cams, intakes, to shape the powerband a different way, for different purposes.

[Brian_e]

[RandyV]

Well the OP proposition was binary and that being the case (and I totally understand the endless variables) I was looking more for "If you had to err one way or the other, which way would you go?"

Although intentions are good at some point you have to decide....(ex: 35 x 32 vs 40 x 35.5 valves when you've decided you have to have cam "x" for either spring limits, duration limit desired, etc. etc.)

I'm thinking smaller cam/bigger valves is probably better money but that's just my opinion.

One thing I notice (as Alstrup has mentioned before) these "new" cams for the 21st century often appear to have less duration than those of yesteryear.

So for example....even though .500+" lift an FK41 rolls as a rather mild 269 duration so does yesteryear's 40 x 35.5 valve sizing not apply????

[74 Thing]

Its how fast it lifts. Fk cams have fast ramps