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OHC! A fun mental exercise.
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Author:  MindforRent [ Fri Nov 30, 2007 8:37 pm ]
Post subject:  OHC! A fun mental exercise.
I have a technical question. If this is the wrong forum, I'll happily ask a mod to move it to the correct one.


I want to keep the answers to this question as simple as possible. This rules out answers that include things like Dual cams, or casting a new head from scratch.


My question is this, has anyone attempted to convert a /6 to an over head cam?


I've used the search function, with two results, I either end up with 130 pages of people wondering which cam to use and how much to take off their head, or with the mutilated corpse of an equine that is the aluminum head debacle.

Doing a Google search reveals that this was briefly discussed about 3 years ago on the .com boards.

Did anything ever come of this?

This leads me to believe that no one has, which seems moderately surprising given the level of ingenuity of this group. On the other hand, we have a head that does work and with porting manages to flow relatively well.

But that's not my concern. Given the sheer number of heads that are about, would it be possible to mill off the rocker stands and go from there. Making something to hold the Cam in place, with a gear on the end?

So here, this would either have to bolt onto the head as it stands now, or would require some time with a basic milling machine, or a hacksaw, drill and a good file.

Is it even conceivable?

To Quote Matt Cramer

"But I digress. You don't need to make a head from scratch for this. You would just need a replacement for the original rocker arm setup. It may even be possible to build a SOHC conversion that bolts to the existing valve cover holes, but it might make more sense to simply mill off the existing bosses for the stock rocker arm shaft and design the new valve train from a clean slate. You'd then just need an external timing belt or chain setup and a tensioner. If I had a milling machine and lathe, the odds are good I'd actually try to build this some day."

This is certainly one way of thinking of it. To create a "bracket" that bolts in the valve cover holes and holds the camshaft in place.

See http://www.aardemasohc.net/index.htm for something along those lines.

Or, could we cut off some of the rocker stand base, and make a "bracket" that will sit in front of each base to hold the camshaft in place? I'd need to see a camshaft in relation to a head to see if that idea holds any water.

I am concerned about hood clearance if one of us succeeded at this, but hell, I'll drive around with out a hood for testing purposes.

I've talked with a few people about this and they agree that while cool, would increase the performance of our engine any more than most other mods that we already do.

I have several questions that have come to mind throughout the day that I can't really figure out on my own simply because I don't have the necessary engineering knowledge about the inner workings of this engine.

1) One of the Biggies: what are the supposed advantages and/or disadvantages, mechanically speaking in something like this?

2) Which design is more feasible, an Aardema design or a set of individual carriers located next to cut down rocker arm studs.?

3)Which block modifications would be necessary, if any, to make this work?

4) Would there be oiling difficulties in the head and/or block?

5)Would this be an occasion where the higher flowing oil pump might be useful?

6)How would the "Button" followers for the valve springs be designed? Anyone know of a picture or a general Wiki-like description?

7)What kind of cam are we talking about here, I've started discussing this with DI and I think I know where our discussion on that will go, but I'm always open to other opinions and ideas.

8)What are all the various components that would be needed this to work?

-Camshaft with a gear or pulley system
-The camshaft "holder" assembly
-buttons for the valve springs
-plugs for the push rod holes?
-something to redirect the flow of oil through the current camshaft hole?

9) In regards to possible clearance issues, it appears from pictures that the major interference points will be the heater hoses and the blower motor. I refer to the following picture courtesy of 65deuce Image

I have no doubt that I've missed something, but I'm tired as only a parent of 2 year old can be, so please be forgiving. I will do my best to answer any and all questions put forth. I welcome all critiques, suggestions, ideas, opinions, and anything else.

I would ask, though, if you are responding to a specific question, that you quote the question, or at least let me/us know the number of said question. That way I don't get too lost.

Let the debate begin.
Author:  SlantSixDan [ Fri Nov 30, 2007 9:03 pm ]
Post subject:  Re: OHC! A fun mental exercise.
Quote:
has anyone attempted to convert a /6 to an over head cam?
Yes: Chrysler Corporation! In 1962 to 1966, Chrysler Engineering developed an OHC version of the 225 under project number A941. It never saw production, probably due to negative cost/benefit ratio, but it is interesting to note that its development was stopped just before Pontiac released their well-regarded OHC Six.
Quote:
This leads me to believe that no one has, which seems moderately surprising given the level of ingenuity of this group
What benefit would you be hoping to gain? I know all the theoretical benefits of OHC vs. pushrod, but offhand I think the practical gains would be very small indeed even if you could just wave a magic wand and OHCify a 225 all at once.
Quote:
1) One of the Biggies: what are the supposed advantages and/or disadvantages, mechanically speaking in something like this?
In converting a slant to OHC? Or are you asking about the advantages of OHC vs. pushrod in general?
Quote:
3)Which block modifications would be necessary, if any, to make this work?
Extensive front-end redesign to drive the cam and maintain accessory drive for the alternator, water pump, etc., and not make the overall engine package too long to fit the engine bay (it's already pretty long)...
Quote:
4) Would there be oiling difficulties in the head and/or block?
I don't see this being a problem. One way or another, probably along the lines of the '81+ hydraulic lifter oiling scheme, enough oil could be brought to the top end.
Quote:
5)Would this be an occasion where the higher flowing oil pump might be useful?
A higher-volume pump might or might not be necessary...that concern would be wayyyyyy down the list. There'd be a lot more to work out before worrying about which oil pump to use.
Quote:
6)How would the "Button" followers for the valve springs be designed? Anyone know of a picture or a general Wiki-like description?
Could probably wind up using something like the cam followers for a Chrysler 2.2 / 2.5 litre 4-cylinder engine:

Image
Quote:
8)What are all the various components that would be needed this to work?
All the stuff you list plus an ultra-high-volume wallet. :shock:
Author:  DusterIdiot [ Fri Nov 30, 2007 9:20 pm ]
Post subject:  Hoses not a problem...
Quote:
In regards to possible clearance issues, it appears from pictures that the major interference points will be the heater hoses
Heater hoses may be a problem in the pre-67 cars, they are not a problem in the 67-76 cars...and in the late versions (like 73-76), the heater hoses no longer clipped to the valve cover, they were routed along the passenger side fender and held there with a black plastic loop ...

-D.Idiot
Author:  slantasaurus [ Fri Nov 30, 2007 9:51 pm ]
Post subject: 
While the basic idea seems to be a good one, the amount of work involved would be way more than the benefits. To really get the full advantage, (at least as I see it) a new head would be the way to go. With a new head things like ports and spark plug placement could be played with to optimise the whole package. Without reworking the ports, they will ultimately limit peak output. You have to get air in and out to make power. I will admit, it is a great topic for bench racing, but probably best left on the bench.
Author:  dakight [ Sat Dec 01, 2007 3:56 am ]
Post subject: 
One thing I don't see mentioned is the fact that the stock camshaft also drives the oil pump and distributor. Alternative mechanisms for these two components would have to be devised.
Author:  68barracuda [ Sat Dec 01, 2007 4:18 am ]
Post subject: 
Yaay -
Some one else also like mental exercises other than the usual jumping to conclusions etc.

In Britain there is a ohc cylinderhead available for the mini a engine as an aftermarket option

while one is fooling around with the head - why not go the full monty and do a dohc setup, with canted valves like the old pollyhead semi hemi.... :D
Author:  slantasaurus [ Sat Dec 01, 2007 5:04 am ]
Post subject: 
Quote:
One thing I don't see mentioned is the fact that the stock camshaft also drives the oil pump and distributor. Alternative mechanisms for these two components would have to be devised.
Dry Sump and crank trigger set ups would be a cake walk compaired to the hurdles you'd be jumping for a OHC conversion.
Author:  Charrlie_S [ Sat Dec 01, 2007 5:15 am ]
Post subject:  Re: OHC! A fun mental exercise.
Quote:
My question is this, has anyone attempted to convert a /6 to an over head cam?

.
Quite a while back someone posted a picture of an OHC converted slant six. If I recall it was a "for sale" in a auto mag from many years ago. I can't locate it it using the search function.

My personal opinion is, just converting to overhead cam, without redesigning the rest of the head, is not cost efective.
Author:  66aCUDA [ Sat Dec 01, 2007 6:12 am ]
Post subject: 
I think what is being said is " dont worry about the money" as this is theory( at least right now) :D I see the question about what are the advantages of OHC's in general being unanswered. I think alot of this is just for learning purposes.
It NEVER hurts us to think(although it may hurt our wallets :twisted: )
Thanks
Frank
Author:  SlantSixDan [ Sat Dec 01, 2007 7:15 am ]
Post subject:  Re: OHC! A fun mental exercise.
Quote:
Quite a while back someone posted a picture of an OHC converted slant six. If I recall it was a "for sale" in a auto mag from many years ago. I can't locate it it using the search function.
That post is here, and the link's in the first post. I could've sworn there was a version of the image large enough to read the ad text, but cannot find it.
Quote:
My personal opinion is, just converting to overhead cam, without redesigning the rest of the head, is not cost efective.
Agreed...there's been some discussion in the past, see here and here.
Author:  dakight [ Sat Dec 01, 2007 9:15 am ]
Post subject: 
Overhead cam eliminates a lot of the reciprocating mass of the valvetrain. In theory, and OHC engine will rev higher but as has been noted, the flow limitations of the induction, head, and exhaust systems will not allow those benefits to be fully realized without some fairly major redesign.
Author:  Charrlie_S [ Sat Dec 01, 2007 9:40 am ]
Post subject: 
Quote:
Overhead cam eliminates a lot of the reciprocating mass of the valvetrain. In theory, and OHC engine will rev higher but as has been noted, the flow limitations of the induction, head, and exhaust systems will not allow those benefits to be fully realized without some fairly major redesign.
The comparitively small bore, long stroke are also limiting factors
Author:  MindforRent [ Sat Dec 01, 2007 10:41 am ]
Post subject:  Ok then.
Wow, this is excellent.

So we've pretty well covered that this would most likely be an expensive project.

I think we've also described that given the current efficiency of our induction, exhaust set ups, and the bore/stroke ratio that the benefits from an ohc cam system would be minimal.

We've also stated that the primary benefit is a higher rev limit.

Btw, here's the link: http://dansby.net/slant/ohc.jpg , my thanks to Joshua for that.

Yes, this is just get us thinking, a learning experience for us all.

Slantasaurus- thank you, I didn't know that the cam drove the oil pump and distributor. EDIS and a dry sump would be a walk in the park compared to this. And EDIS set ups are being used by at least two people here that I can think of off the top of my head.

DI- Thanks for the info on the heater hoses, I hadn't taken a look at my car to see possible interference issues.

Now to Dan- Thank you very much, your insight and knowledge are always a boon to this board.
I'm surprised that Chrysler stopped work on an OHC program, but then again, I'm even more surprised that one of the smaller manufacturers didn't go this route. Maybe they did, I'll have to look.
When I asked what would the pros/cons would be, I was asking a two fold question, the slant ohc, and in general. The former of the which has been answered.
In reference to extensive block modifications, didn't someone here do work on a Serpentine belt set up for the slant, couldn't something like that be modified to work for this?
I like those cam followers, I wonder if that would work for what we're theorizing here. In that, how big are they? I'm guessing they'd be readily available.
You mentioned the oiling system on a '81+ hydraulic set up, how did that differ from the older set ups?

I'm glad this has generated a positive response, that's exactly what I was hoping. I'm not rich enough to even begin a project like this, but working it out on paper/html is a good start, even if someone else takes it and runs with it.

Offhand, I believe someone on one the multitude of Chebby Camaro boards mentioned that the Aardema set up would cost him upwards of $3,000. Just thought I'd mention that. Hmm, i think I paid a quarter of that for my current '71 daily driver. ha!
Author:  MindforRent [ Sat Dec 01, 2007 10:43 am ]
Post subject:  Hrm
Hmm, looking at that picture of the engine for sale, it actually looks like the cam is being driven from the rear some how. Any ideas there?
Author:  dakight [ Sat Dec 01, 2007 10:55 am ]
Post subject: 
A slant has no direct oil galley to the lifters so when hydraulic lifters were installed, the oil to the lifters was piped through the pushrods from the head and rocker arm assembly. It was awkward but it worked.
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