Web Cam stock (142) vs. 73 grind

[hiwaycallin]

I am in the process of configuring an engine rebuild for my 78 camper with stock FI. The longblock will be built by Adrian at Headflow Masters and will include solid lifters and his improved heads with enlarged valves etc. I am trying to decide on camshaft and have narrowed things down to either a Web Cam stock grind (142) or the 73 grind.

I have read a bunch of threads mentioning both of these cams and from what I have read both are excellent but the 73 grind will provide more HP if used with the improved heads and larger valves. Given that I will be using these heads, is there any reason for me NOT to go with the 73 grind?

Also, I am posting a side-by-side of the specs for both cams. Can someone please explain in layman's terms what the actual differences in specs mean? Thanks!

[SGKent]

the 73 will give you a peak rpm of about 5400 RPM vs about 4900 RPM for the 142. The stock bus cam had a peak HP of about 4400 RPM. The stock snorkle and FI will be limited in how much air it can pass vs dual carbs. The 142 is listed as a stock type 4 cam but it is really a 914 grind so it is already an upgrade over the stock bus cam. IMHO there is a slight reduction in vacuum levels with a 142 and it shows up as a little wandering at idle - maybe 50 RPM or so. I think the 73 is too much for a stock FI bus but maybe someone here who has that combo can chime in. FWIW, we pass smog cleanly and have lots of power and top end using the 142 grind. I don't like to push the engine because parts are too hard to come by if I scatter it but when I need extra umph it is there with the 142. Certainly someone with a 73 and dual carbs plus an extractor exhaust would outrun me but with stock FI I can give any bus a run for their money. Be sure to balance all the rotating parts to get rid of vibration. Make sure all your pushrods are straight by rolling them on glass or a flat steel / granite block if you plan on pushing it upwards of 5,000+ RPM very often.

Here is an Isky cam page. Remember that type IV includes much lighter VW and 914 engines. Buses were the odd man out.

_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[Bleyseng]

If you have to pass smog tests then don't go with the Web73 as it will be really hard to do. Cold idle is not that great either due to a rich cold idle condition caused by the grind.
You will make more hp using the Web73 but I don't know how the CHT's temps are since I have not run one in a bus.
Now the 9550 cam from Raby runs cooler due to its grind which is nice.
I have run the 142 cam only in 914's and its a nice stock cam with a good idle due to its strong vacuum at idle.
_________________
70 Ghia Black convert-9/69 build date-stock w/133k 1600 SP-barn find now with a rebuilt tranny and engine
77 Westy 2.0L w/Ljet, Camper Special engine-95hp and with LSD!(sold)
76 Porsche 914 2.1L L20c, 120hp Djet (sold)
87 Syncro Westy Titan Red 2.1L 2 knob 100k miles

[bajafreaks]

I recently installed my Adrian built 2.0 with a web 73 and bigger heads etc. and honestly I'm thinking it may have been too much cam. Im running the stock F.I. but my elevation is at around 4500 so that is definately a concern you need to compute. I had trouble getting it to run right but after having a shop adjust the AFM it does run alot better. It has low vacuum readings around 12 but I think some of that is due to elevation Ive eliminated the risk of vacuum leaks. My head temps are high also which I'm hoping will go down with the breakin. The compresstion ratio is important as well with running a bigger cam...you need air. I havent driven it but about 100 miles with our crappy weather, I'm hoping with more tuning and breaking in it will run better, but right now I honestly dont see a big improvement over the stock 2.0 I had before, my advise would be the 142.

[Jake Raby]

I will post plots of each from my cam Doctor over on my forums in the next few days... Lots of people with these questions this time of year.

Digital plotted overlays show the differences tremendously. Keep in mind that the .020 and .050 numbers are just two points of measurement. When the entire lobe is measured one can see where the differences really are.

My grind has a much better chamber fill at lower valve lift and on the exhaust side it really shines after the blowdown period.
_________________
Jake Raby
Raby Engine Development
www.rabyenginedevelopment.com
"I've never given anyone Hell, I just told them the truth and they thought it was Hell"

[bwiencek]

[Jake Raby]

Its impossible to judge a cam by .020 and .050 numbers only. What about .200 lift? How does the cam correlate with the strongest area of the cylinder head intake and exhaust ports?
_________________
Jake Raby
Raby Engine Development
www.rabyenginedevelopment.com
"I've never given anyone Hell, I just told them the truth and they thought it was Hell"

[BUSBOSS]

Anybody running the Raby grind in a 2.0 with stock FI in California smog test country?
_________________
All the redemption I can offer, girl, is beneath this dirty hood
1976 Westfalia
1970 Karmann Ghia Convertible (sold - but not forgotten)

[SGKent]

[Jake Raby]

[hiwaycallin]

Thanks everyone for the great info. Sounds like of the two, the 142 grind is probably the best option for me.

I'm really going to expose my ignorance here, but can someone please explain, in terms of how the engine works, the effect of the differences in cam specs? For example in the screenshot I posted above, the valve lift and duration numbers are higher for the 73 grind vs. the 142 ... what does this mean exactly?

[Althea78]

I had the same question a year ago, webcam 73 or 142. After a year, I am still very happy with my 73.
78 westy, manual trans, stock FI (stock AFM setting). 7.5:1 compression, solid lifters, everything balanced, heads re-done by Rimco, extractor exhaust. Everything else is stock.
Gas mileage stayed at 20mpg or better.
Head temps are the same as stock up to 60mph. Head temps became lower at higher speeds with the 73. Now with the 73 the head temps change very little going up small grades on the highway. With stock, the temp would rise quite a bit. The stock motor could have been a little tired.
The idle sounds quite a bit more “lopey” than I thought it would (I am a big fan of that). I am often asked “that thing has a big cam in it, right?”
With the 73, you will tend to shift at a higher RPM. Not because you have to, but you can really feel when the cam hits that sweet spot. It reminds me of the power band on a dirt bike.
I do not have to pass smog. I am not at a high elevation.
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'78 Westy

[Amskeptic]

[SGKent]

This is the only way I can think to explain what you are asking other than saying the sky is blue because it is ...

picture a swimming pool with no water in it. At each end is a door that lifts to let water in from a canal and then drains out at the other end through another door.

When you open the gate to let water in there is how long it is open and how far it is open. Water flows in. Then the gate closes. The pool is full. Pretend the water gets dirty and now the exit gate opens and the water flows out. Again how far it opens and how long it opens determines how fast the water can flow out.

Every time the entry gate closes the water behind it in the canal piles up against it and a wave goes back up the canal. Likewise water in the pool is sloshing back and forth as it filled. When it empties as the water goes out at some point the exit gate closes and water piles up against it because it had momentum and the pool wasn't quite empty.

Now your job is to manage those gates to get as much water in and out of the pool as possible. If you only need to fill and drain the pool once a day you can raise them to a comfortable level and then let them stay open for hours until the pool drains, then refill it. But what if that process had to happen hundred of times an hour? Suddenly you are looking at how fast water can flow in the canal, harnessing those standing waves created when the gates open etc. If you can time opening that entry gate when the water is sloshing back towards the gate down the canal it has speed already when it hits the gate so more water goes in. Then if you can time the opening of the exit as the water sloshing in the pool is already sloshing back towards the exit gate then when that gate opens the water already has momentum that carries more out.

Now suppose the oppisite happens, that the water left in the pool is sloshing back at the entry gate as it opens. It will counteract some of the water that wants to enter the pool and slow it down. What you find is that for any frequency of water going in and out of that pool there is a set speed and timing of how you can open and close the gates to get the water in and out. You can also play with the canal size, its length, the gate size, how far you open the gate etc.

A cam does the same but with air flow. It is controlling the gates which are the valves. As the RPM's go up on the engine the column of air entering and the column of air exiting develop a mind of their own. You choose the duration, lift and valve size to get the most air in and out at any speed. You may even need to open that valve earlier than the cylinder begins to ask for air so that the column of air gets a chance to start moving.

An engine builder looks at what he (or his customer) expects from the engine and chooses the cam that best matches those needs. One that is designed to work at 8,000 RPM has to lead the intake and exhaust cycles so much that at idle the engine would not run well. We used to run around 285 degrees split duration when racing but the idle was set up to around 1500 -1600 RPM to keep that column of air moving so the engine wouldn't stall.

You are going to drive that engine in a set RPM range. What is it? If you want peak power from 4500 - 5500 RPM that means you will give up power down low. Likewise if you make it really efficient at 2500 - 3500 RPM, it won't have much power when you get on the freeway. Part of choosing someone like Jake to build your engine or plan your engine is he has the dyno runs and performance combinations that work well together. But he can't give that info away for free because it cost him time (money) to develop that data and knowledge. On top of it, in my pool example it isn't just the gates that make it all happen. There is the pool size, depth, canal length and width etc. Putting in a huge gate that stays open a long time may not work well if the canal is small - in fact the water may enter slower than a smaller gate where the water speed is kept flowing fast. You also have the profile of how that gate opens - quickly or slowly. So someone like Jake will be careful about just tossing a cam at you and saying this will work best for you. He needs lots more info to help you make that best guess decision and that is time and time costs money. I don't build engines for others and don't want to. There is grief in it from my perspective cause of the associated issues as it would morph into a full time job when I already have a full time job. But you can do like I did and hang around the track, wrench for someone, find a professional shop that builds high end engines and has a history of winning. Over time you will read books, watch dyno runs and learn what works and what does not. There are many here who have done that and we are blessed to have so many people here whose love was cars and racing and VW's were something they also enjoyed. It really makes the Samba special because we also get the benefit of knowledge of the Porsche crowd too - and they did everything from LeManns to F1 racing. My background was Fiat, Lancia and Ferrari as well as some Indy cars, NASCAR and NHRA boats and cars.

Smogging a car usually requires a clean burn at idle. That is hard with a longer duration cam. Trying to choose a cam when you are building your first engine is a very hard thing to do. Please keep in mind that a bus has unique needs unlike a light sand rail, type 4 or Porsche.

I don't know if the explanation helped or made the pain worse. Good luck.
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[hiwaycallin]

Thank you Colin and Steve. I totally get it now. Steve, your pool analogy was perfect for explaining the whole lift/durantion thing. And both of your explanations about how differences in cam translate to real world driving experience at low vs. high rpm have made things crystal clear for me. Can't find this sort of info in any manual that I know of!

[Amskeptic]

[Jake Raby]

[SGKent]

[Jake Raby]

The test above was gathered with both engines using the standard Thunderbird exhaust system. This effectively raised the performance of the stock engine by a small amount and created a torque peak a few hundred RPM higher. Had I used a stock muffler on that engine it would have definitely been a more "crippled" performance by the stock engine. The only thing that wasn't stock on that 'stock" engine was the exhaust.

Today I re-plotted the stock cam, my 9550 and a Web 73 and will post the data on my forums tonight. The only problem was the straight 73 grind I had has been on the shelf since 2002 and gone unused... I learned the reason for that was because it wasn't ground properly. That means I can't use it for a compare effectively as it had both split lift and split duration and wasn't "straight pattern" at all. It is stamped #73, but has the same plots as a 107i grind.
_________________
Jake Raby
Raby Engine Development
www.rabyenginedevelopment.com
"I've never given anyone Hell, I just told them the truth and they thought it was Hell"

[manikmike]