Cam Timing

[Ron Earp]

Jeff and I worked a little on the JH motor yesterday and found it has poor compression on 2 cylinders, so, I'll have to re-ring it at the least. No telling what else.

However, I did notice that the car has position adjustable cam timing gears. There are marks, of course, for various timings but you can change them. Stock US timing was each one at the 100 marks. But, I can advance and retard them slightly.

Now, stock timing is to be used, but, I noticed that in the GCR if the car has adjustable gears they can be used. So, I can set it at one of the other positions? Advanced about 6 degrees would be, from my engine simulations, slightly advantageous and I can almost get that. I would think this completely legal, but I'm the newbie and cautious so I wanted to ask.

Thanks,

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Ron
http://www.gt40s.com
Lotus Turbo Esprit
BMW E36 M3
RF GT40 Replica
Jensen-Healey: IT prep progressing!

[Bill Miller]

Ron,

There's nothing that _requires_ stock timing, per se. If you mill the head on an OHC motor, you're _allowed_ to use an offset key, to return the cam timing to the stock setting, but there's nothing that _requires_ you to do so. So, you can use any cam timing that you can achieve via legal means. And as you said, the ITCS allows adjustable timing gears, if they're stock equipment. So, go for it!

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MARRS #25 ITB Rabbit GTI (sold) | MARRS #25 HProd Rabbit
SCCA 279608

[apr67]

Hmm.. Bill I don't disagree with this being SOP, but.

Rules nerd alert.

Where does it say you can change the timing? Even if you allowed adjustable timing gears, the only thing they are allowed to do is return timing to stock.

If it doesn't say you can...

[Bill Miller]

Originally posted by apr67:
Hmm.. Bill I don't disagree with this being SOP, but.

Rules nerd alert.

Where does it say you can change the timing? Even if you allowed adjustable timing gears, the only thing they are allowed to do is return timing to stock.

If it doesn't say you can...

Hmmm.... Interesting perspective. On further review of the ITCS, I'd have to say that you're right. My bad, and I apologize for giving Ron bad information.

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MARRS #25 ITB Rabbit GTI (sold) | MARRS #25 HProd Rabbit
SCCA 279608

[Ron Earp]

Not sure what to do then. If I mill the head, which will happen if I have to tear this POS down, then, according to my calulcations, the positions I can put this thing back in will not yield a stock timing. They are not infinitely adjustable, just fit into slots on the back of the gear. The closest, after milling I think, would be about 3 degrees advanced or somewhat the same retarded. The belt is toothed, the gear is toothed too to the cam. But, I need to think on it some, seems I should be able to make it work right.

And, it begs another question. I have one set of good cams. I need another set for a motor I got off Ebay to build as a spare, but it has no cams. JH is out of business and the only cams available, if you call Lotus the company that made the engines, are different than what was offered in 1974. So, what does one do here? I've heard of a similar situation with VW Rabbits that run a different grind cam than what was made back in the day, since what was made back then is no loger available.

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Ron
http://www.gt40s.com
Lotus Turbo Esprit
BMW E36 M3
RF GT40 Replica
Jensen-Healey: IT prep progressing!

[This message has been edited by rlearp (edited September 19, 2004).]

[This message has been edited by rlearp (edited September 19, 2004).]

[JeffYoung]

Guys, not to disagree...well, I'm going to disagree....if the stock car has adjustable cam timing, and timing is free, why can't he change the cam timing? Aren't 240zs set up this way? I know at least a few Zs that I consider to be very legal and I know they adjust the cam timing.

In other words, if a car came with something, anything, that is adjustable "stock," isn't adjusting it within the stock range of adjustment, stock?

Whoa...that is a mind bender, sort of, but I think it is correct.

[Greg Amy]

I lean towards Jeff's position. Let me restate it, with IIDSYCTYC in mind.

First, the stock cam timing gear is adjustable. Thus, it is legal to have an adjustable gear on that car as specifically allowed in the rules.

Second, however, comes the question of "how much adjustment is legal?" Absent any allowance in the regulations, the only approved adjustment is as specified in the workshop manual (or appropriate documents) and within the allowable range. For example, is the WS says, "0 degrees +/- 10 degrees" then you can put it anywhere within that range using any allowable W/S techniques.

After all, cam timing must be stock, correct? And that range as specified in the W/S manual is stock, yes? Thus, adjustment within that range is perfectly legal.

Even better, if allowed engine modifications do not allow you to bring the car within those specs using teh adjustable gear, I suggest that you can even add an offset key AS WELL as use the adjustable cam gear...

[Ron Earp]

To complicate things even further - there are many cam timings that were "stock", that is, mentioned in the manual depending on year, month, and country of sale. This was deep in the emissions time, so, it was probably cost effective for JH/Lotus to do this. 100, 110, 115 are just a few of which were available in a single 9 month time period, all of which are available with my cam gears.

And, to muddy it even further, the first batch of JHs with Lotus motors off the line had no adjustable gears at all since this was 1973 and they had not run afoul of their emissions exemption at that point.

R

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Ron
http://www.gt40s.com
Lotus Turbo Esprit
BMW E36 M3
RF GT40 Replica
Jensen-Healey: IT prep progressing!

[This message has been edited by rlearp (edited September 19, 2004).]

[Geo]

I agree with Greg. I think he has it front to back, top to bottom.

The only other thing I'd say is perhaps a letter to Topeka is in order. If the factory adjustable cam gears allow timing outside that called out in the FSM, I could see a case still being made that you can use the adjustable gears to full effect. But I would definitely get a rulling from Topeka before taking this advantage.


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George Roffe
Houston, TX
84 944 ITS car under construction
92 ITS Sentra SE-R occasionally borrowed
http://www.nissport.com

[dickita15]

Originally posted by rlearp:
To complicate things even further - there are many cam timings that were "stock", that is, mentioned in the manual depending on year, month, and country of sale. This was deep in the emissions time, so, it was probably cost effective for JH/Lotus to do this. 100, 110, 115 are just a few of which were available in a single 9 month time period, all of which are available with my cam gears.

just make sure the specs you are using from the manual are for a year on the cars spec line in the gcr
dick

[Bill Miller]

Jeff,

Where in the ITCS does it say cam timing is free? I know it says ignition timing is free, but the only references to cam timing I've seen talk about it being stock, or returned to stock.

I agree w/ Greg, that if there's a set range in the FSM, you are allowed to adjust w/in that range. And, if you can't do that after you mill the head, you are allowed to use an offset key, but not required to use one. And there's a sticky point, if you can't use the adjustable gears to get the cam timing back to stock, and you don't use an offset key, is it legal?

George,

I'd love to hear the logic behind why you should be allowed to adjust to a cam timing outside of what's called for in the FSM. The ITCS says that if you replace plastic/phenolic timing gears w/ metal ones, cam timing has to be stock. If you use an offset key because you milled the head, you have to return the timing to stock. Is your arguement that, by virtue of having the adjustment, you're allowed to use it?

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MARRS #25 ITB Rabbit GTI (sold) | MARRS #25 HProd Rabbit
SCCA 279608

[Geo]

Originally posted by Bill Miller:
George,

I'd love to hear the logic behind why you should be allowed to adjust to a cam timing outside of what's called for in the FSM. The ITCS says that if you replace plastic/phenolic timing gears w/ metal ones, cam timing has to be stock. If you use an offset key because you milled the head, you have to return the timing to stock. Is your arguement that, by virtue of having the adjustment, you're allowed to use it?

OK, first of all, keep in mind I think it should be run past Topeka before setting outside anything called out by the FSM.

Notice that all references to stock timing are all preceeded by an if statement. If A, then you can do B to return to stock timing. Find me a place in the ITCS that flatly states cam timing must be stock.

I could see a case being made that if the adjustment is there in the stock engine, you can use it even if it falls outside the FSM spec. I'm not saying I believe this is the case, only that I can see a case being made. Therefore, rather than just assume, I'd personally write the letter. That was my point Bill.

Regarding your question of non-stock cam timing being allowed if you mill the head and don't use and offset key...

The rule says an offset key may be used, not must be used to return timing to factory spec. By my reading of that, it's perfectly fine to go without the offset key even if the timing is out of factory spec.

edited for formatting
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George Roffe
Houston, TX
84 944 ITS car under construction
92 ITS Sentra SE-R occasionally borrowed
http://www.nissport.com

[This message has been edited by Geo (edited September 20, 2004).]

[JeffYoung]

Hmmm...if the cam gears have a range of adjustment, isn't that "range" stock so that any setting within it is permissible?

[joeg]

This discussion is somewhat silly. Obviously, if you have OEM adjustability built into an OEM component, use the adjustability.

Some of these "no can do if not specifically allowed arguments" get ridiculous because we are not talking about "modifying" a component; just using built in adjustability.

Where, for (silly) example, does it say tire pressures are "free"; or if your car has OEM adjustable spring perches, you can't corner-weight because to do so would be a non-stock adjustment.

Cheers.

[Banzai240]

Originally posted by JeffYoung:
Hmmm...if the cam gears have a range of adjustment, isn't that "range" stock so that any setting within it is permissible?

It's my opinion, based on what I read in the rules, that if my car has something on it that is adjustable (camber, timing, rear-view-mirror...), I'm adjusting it within it's range to optimize my setup...

I don't find anything in the rules that requires that the timing, cam or otherwise, be set to "FSM" specs... It says that a offset key "may" be used to return to cam timing to factory spec... it doesn't say you have to, which means the rules don't care if it's factory spec or not, just that the stock cam-gears are used...

We've had philisophical discussion concerning a similar topic, valve adjustments, and how the ITCS addresses what is acceptable... Again, I see nothing in there that keeps one from using the full range of factory adjustments, but others see this differently...

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Darin E. Jordan
SCCA #273080, OR/NW Regions
Renton, WA
ITS '97 240SX


[This message has been edited by Banzai240 (edited September 20, 2004).]

[apr67]

So lets say a cam gear has extra sets of holes it in. I can use them anywhere I want? Afterall that would be built in factory adjustment, right?

So since the Miata cam gears are identical on the intake and exhaust, but use different holes, I could reverse them and get a little better racing profile for IT?

Hmmm..

Me thinks not.

Alan

[JeffYoung]

Alan, correct, you can't switch the gears but that's really a straw man on the issue of can you make cam timing adjustments if the stock cam timing gears allowed.

We aren't talking about switching an exhaust and an intake gear, we are using built in adjustability.

[Ron Earp]

Although more of a stretch, people don't disable VANOS and VTEC, correct?

Obviously, VANOS and VTEC are what Lotus would have liked to have had 33 years ago when they designed the motor, but, that technology didn't exist at the street car level. But, adjustable timing gears did and provided a small amount of added performance benefit for the cars, although I think the real reason was to meet emissions allowing owners to easily go back to a more agressive timing.



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Ron
http://www.gt40s.com
Lotus Turbo Esprit
BMW E36 M3
RF GT40 Replica
Jensen-Healey: IT prep progressing!

[Greg Amy]

<font face=\"Verdana, Arial\" size=\"2\">Although more of a stretch, people don't disable VANOS and VTEC, correct?</font>

It would be legal if - and only if - it is controlled by the allowed alternate ECU. If it's a mechanical mod, not legal.

[Ron Earp]

Which of course, opens up a whole different topic of advantages with ECUs that the computer controlled cars get that their non-computer controlled competitors do not.

I can understand running a stock ECU with a different program loaded, but an entirely different standalone ECU from a different company without using the stock system at all? Odd rules policy.

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Ron
http://www.gt40s.com
Lotus Turbo Esprit
BMW E36 M3
RF GT40 Replica
Jensen-Healey: IT prep progressing!