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Old 04-21-2009, 03:42 PM   #1 (permalink)
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16V cam regrind idea

We know cams can have a pretty dramatic effect on FE and powerbands. So, we know a regular regrind with decreased duration will likely give us more low rpm power which increases low rpm efficiency which is where most of us spend our time driving.

We also know that high swirl heads decrease the tenancy to ping and knock which allows higher compression ratios. Higher compression ratios increase efficiency as well. David Vizard wrote a nice technical article on a head porting technique that does just this. His technique works pretty well it seems, but is tuned for high rpm racing engines. With a bit of playing around I think we can alter that to our advantage.

So, the idea is basically to combine the two above ideas. Vaguely similar to Honda's Vtec-e, one of the two intake valves would open up first. This gets air flowing in one side and creates a nice swirl effect. Then, the second valve opens up, but the cam lobe has a shorter duration and lift, so it closes first too. This leaves the first valve still open to keep the high swirl effect going strong. The downsides are that we probably don't get as much swirl as the vtec-e head, and we don't get the high power output of both valves fully opening.

Here is a rough idea of what the cam lobes may look like.


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Old 04-21-2009, 06:42 PM   #2 (permalink)
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If you are willing to go to the expense and effort of custom-ground cams, why not run with the big dogs of MPG? Get a set that make your engine an Atkinson engine? That's all the "Atkinson" engine in Priuses and Ford hybrids have done.

The trade-off:
20% more efficient
35% less torque
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Old 04-21-2009, 08:41 PM   #3 (permalink)
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Can you simply regrind a stock cam to atkinsonize your engine?
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Old 04-21-2009, 09:25 PM   #4 (permalink)
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That's what Ford and Toyota did.

Grind the intake valve to stay open into the compression stroke. Viola! The power stroke is longer than the compression stroke and you have achieved Atkinson.
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Old 04-21-2009, 09:33 PM   #5 (permalink)
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The swirl combustion thing, you can find hint of on Larry's site. (TheOldOne.com)

Basically, the same method you're thinking, but with more work applied to actual flow dynamics and combustion shape manipulation. I believe the articles you'd be looking for are "Talking heads" and "Swirl Power". They're Mag articles from years ago (more like decades) that Larry was working with Hot Rod and Circle Track magazines as reporting bodies.

They're interesting reads, at least.


Magazine Articles

When these articles were released more than a decade ago, they generate lot of interest and controversy. Many have heard T.O.O. mentioning "Soft Head" on chat boards, these articles should provide you with enough back ground information to understand what it is. Don't miss the 1999 update below!

September 1999 - The Soft Head 1999

February 1986 Hot Rod - Talking Heads part 1 (317 KB)
February 1986 Hot Rod - Talking Heads part 2 (306 KB)
February 1986 Hot Rod - Talking Heads part 3 (316 KB)
February 1986 Hot Rod - Talking Heads part 4 (308 KB)
February 1986 Hot Rod - Talking Heads part 5 (366 KB)
February 1986 Hot Rod - Talking Heads part 6 (342 KB)
February 1986 Hot Rod - Talking Heads part 7 (230 KB)

January 1986 Circle Track - Commentary by Larry Widmer (323 KB)

August 1985 Circle Track - Swirl Power part 1 (287 KB)
August 1985 Circle Track - Swirl Power part 2 (338 KB)
August 1985 Circle Track - Swirl Power part 3 (351 KB)
August 1985 Circle Track - Swirl Power part 4 (342 KB)
August 1985 Circle Track - Swirl Power part 5 (346 KB)

July 1985 Hot Rod - The Soft Head part 1 (310 KB)
July 1985 Hot Rod - The Soft Head part 2 (313 KB)
July 1985 Hot Rod - The Soft Head part 3 (332 KB)
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Old 04-21-2009, 09:58 PM   #6 (permalink)
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funny... I can buy a factory original VW cam that was ground specifically like that, new, had one shipped to my door for $35 LOL

I wish I still remember who I had contact about cam-regrinding... they would regrind and map just about anything from a stock cam
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Old 04-22-2009, 08:29 AM   #7 (permalink)
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Quote:
Originally Posted by Big Dave View Post
That's what Ford and Toyota did.

Grind the intake valve to stay open into the compression stroke. Viola! The power stroke is longer than the compression stroke and you have achieved Atkinson.
Not nearly being a cam expert, I really have no idea where I'd start. Would a normal cam regrind shop be able to do this? I'm thinking it would be well out of their scope. Performance shops usually know squat about efficiency enhancements.

Also, your method would require welding on additional material I assume. I've heard some bad things about running welded regrinds, but I'm sure they can't be that bad. On the other hand, my idea only includes grinding. Yours obviously would provide larger FE gains, mine would be cheaper although I don't have any idea how much cheaper.


Thanks for the info on the magazine articles Christ. I assume I can get those online somehow? I checked Hot Rod's website, but I couldn't find where I could get old articles.
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Old 04-22-2009, 10:46 AM   #8 (permalink)
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Another thing about just trying to regrind to open one valve before the other is that, depending on the top end design, both valves might be actuated by a single rocker arm, so there's only one intake lobe/cylinder or perhaps two in the case of some variable valve timing systems, but that still leaves the rocker arm issue. Modifying the lifter on one valve for later engagement would end up in rapid wear and a hell of a racket coming from the engine.
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Old 04-22-2009, 01:50 PM   #9 (permalink)
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I think this could be done to honda vtec engines with good results, as they have separate low cam lobes but shared high cam lobes. The only downside would be a bit of a flat spot between the econo-mode and high vtec as the flow died off before the switch point.
I don't agree with changing engines to Atkinson design, warm air intakes, etc. All that does is limit your *availiable* horsepower and make your car slow.
Aero, gearing, fuel/air mixture, and cam profiles that make the most torque at low rpm(and gearing to compliment) for freeway cruising are where the gains are found.

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Old 04-22-2009, 01:59 PM   #10 (permalink)
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The Old One - Energy Dynamics - they're in that link, just scroll down.

I posted the article headers in case you wanted to track down those issues of the magazines... some people think they're collectibles.

The files on that link that you want are downloadables, they're not hosted as pages on the site. You'll have to either download them one by one, or I think there might be a zip at the bottom of the page for them. Look around, while you're on the site. You might find something you like!

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