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Old 07-08-2018, 02:19 PM   #1
hinsonracing
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Default Head shave timing retarding a myth?

I can no longer find the articles, bit had read somewhere once upon a time that for every .010" shaved on our engines that it retards the cam timing 2* degrees. I am wondering if it was based upon math or realistic data. I am thinking it was only on math and is false and here's why:

First off please note I race Saturns on dirt tracks so this is not street oriented....

After learning this "information" on my latest engine build I have my head shaved .030" and the block was decked .030" to bring aftermarket oversized pistons back to zero deck "actually around .006" protruded. Knowing per the forum community this should DRASTICALLY retard my cam timing, I decided to degree my engine. I fabbed up two solid lifter buckets and set them at .003" lash (smallest feeler gauge in toolbox). When degreeing my engine measuring I got the following at the .050" spec ( .047" to compensate for the lash).

Intake
Opens -11* ATDC
Closes 25* ABDC
Centerline of 108.50*
Spec is 107.25*
So only 1.25* Retarded

Also on a side note when advancing engine timing it was found per factory tooth an average of 18* (+/-) was changed not 9.45* as previously read in prior materials

If that is the case, then all of Saturn "timing knowledge" is incorrect? I am looking for more evidence of the forum math here asap as now I am scratching my head and want to finish this motor up this week.

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Old 07-08-2018, 02:41 PM   #2
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Default Re: Head shave timing retarding a myth?

I asphalt race my 2000 sc2. I shaved my head.040 and have had no issues. I used 13.1 wiseco pistons. My drivetrain is out of a 98. 2000 crank,rods,pistons.
I don't think the outer piston top can protrude at all cause it will contact the head casting, if I remember correctly. Haven't really rechecked for retardation or needed to.
I ready that also somewhere in the forum

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Old 07-08-2018, 03:17 PM   #3
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Default Re: Head shave timing retarding a myth?

I had this engine running before and didnt have the piston to head clearance problem. The thickness of the head gasket makes up for it. I originally didnt assemble this engine when it first ran. My sponsor insisted he build it for me on his dime so I let him, needless to say the timing was off a tooth at the crank and a piston ring seized on no. 1 due to excessive ring gap.... so I know the protrusion will be fine as it ran before for 10 races. I am just trying to figure out if by some other logic or method my calculations are wrong because so many Saturn enthusiasts insists it drastically alters timing.

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Old 07-08-2018, 04:56 PM   #4
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Default Re: Head shave timing retarding a myth?

My buddy tried the adjustable pully on his sohc Enduro car and the ecm kept trying to compensate for the adjusted timing. Did he install it correctly? Idk

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Old 07-08-2018, 05:39 PM   #5
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Default Re: Head shave timing retarding a myth?

Quote:
Originally Posted by hinsonracing View Post
I can no longer find the articles, bit had read somewhere once upon a time that for every .010" shaved on our engines that it retards the cam timing 2* degrees. I am wondering if it was based upon math or realistic data. I am thinking it was only on math and is false and here's why:

First off please note I race Saturns on dirt tracks so this is not street oriented....

After learning this "information" on my latest engine build I have my head shaved .030" and the block was decked .030" to bring aftermarket oversized pistons back to zero deck "actually around .006" protruded. Knowing per the forum community this should DRASTICALLY retard my cam timing, I decided to degree my engine. I fabbed up two solid lifter buckets and set them at .003" lash (smallest feeler gauge in toolbox). When degreeing my engine measuring I got the following at the .050" spec ( .047" to compensate for the lash).

Intake
Opens -11* ATDC
Closes 25* ABDC
Centerline of 108.50*
Spec is 107.25*
So only 1.25* Retarded

Also on a side note when advancing engine timing it was found per factory tooth an average of 18* (+/-) was changed not 9.45* as previously read in prior materials

If that is the case, then all of Saturn "timing knowledge" is incorrect? I am looking for more evidence of the forum math here asap as now I am scratching my head and want to finish this motor up this week.
I've never taken any interest in the S Series numbers, but I haven't seen anything other than guesses to the numbers either.


To find out, you have to know the cam sprocket diameter.

Then multiply that by pi to get the sprocket circumference.

Then divide that number by 360 (degrees) to find out how chain length equates to degrees camshaft rotation.

Then divide that into the amount your decked the head to find out how many degrees you altered timing.


Keep in mind that you need to double the amount shaved, since the belt slack created is double what you shaved off the head (or block).

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Old 07-08-2018, 07:55 PM   #6
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Default Re: Head shave timing retarding a myth?

Quote:
Originally Posted by Signmaster View Post
I've never taken any interest in the S Series numbers, but I haven't seen anything other than guesses to the numbers either.


To find out, you have to know the cam sprocket diameter.

Then multiply that by pi to get the sprocket circumference.

Then divide that number by 360 (degrees) to find out how chain length equates to degrees camshaft rotation.

Then divide that into the amount your decked the head to find out how many degrees you altered timing.


Keep in mind that you need to double the amount shaved, since the belt slack created is double what you shaved off the head (or block).
Well there lies the problem everybody has all been about what it says on paper it should be. I have not seen any proof to anything and I have triple checked my numbers and I get the same thing everytime. I'm looking for hard proof of if what I'm getting is truly accurate or if I did something wrong here.... I'm looking for hard facts not theory.

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Old 07-08-2018, 08:07 PM   #7
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Default Re: Head shave timing retarding a myth?

That is based on real data. The PCM has the ability to compensate for some minor shaving as long as you stay in the 010-015 range. More than that can lead to problems. There are adjustable sprockets that will compensate for this as well but the gain for any head shaving is not worth the cost.

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Old 07-08-2018, 09:15 PM   #8
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Default Re: Head shave timing retarding a myth?

Quote:
Originally Posted by OldNuc View Post
That is based on real data. The PCM has the ability to compensate for some minor shaving as long as you stay in the 010-015 range. More than that can lead to problems. There are adjustable sprockets that will compensate for this as well but the gain for any head shaving is not worth the cost.
What problems? I've been running with 030" no issues. I built one for somebody that had only .060" from just the head, they never had issues. In fact they won 10 races and a championship with it. I never degreed that engine because they were in a hurry to get it. By my measurements from above my engine which has .060" taken from the block and head combined the timing is only 1.25 degree retarded.as far as fuel, plugs and combustion chambers of the engine i just blew with 60+ races show no signs of too lean conditions. The hard data you speak of I cannot locate.... everybody I've read says there is major changes mechanical timing... I cannot find any resources proving the 9.45* per tooth or the 2 degrees of retard per .010" of shave.

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Old 07-10-2018, 12:20 AM   #9
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Default Re: Head shave timing retarding a myth?

It is 9 degrees per tooth on the 98 and older engine. The timing shift is different for the intake and exhaust as you are reducing the distance between teh centerline of the drive and driven sprockets which does change the mechanical timing. That is hard mechanical facts. Street cars and oval race cars are not identical or even comparable cars. If you use a stand alone ECU it is a non issue but if it is a stock PCM there are definite limits to the correction available.

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Old 07-10-2018, 01:09 AM   #10
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Default Re: Head shave timing retarding a myth?

I think you are failing to understand what I am asking...... who or where are you getting the hard mechanical evidence you speak of? Did they prove the theory by degreeing an engine or just math on paper? The way you are explaining it is theory only. I physically degreed my engine and for every tooth I advance/retard comes out to 18 degrees and some change whether I move two or three teeth. I come up with only a 1.25 degree difference from factory centerline specs usig factory timing marks whereas the "hard mechanical evidence" says by the .060" I have removed from the surfaces I should be 12 degrees off. I have triple checked my measurements and math and come up with what I stated above. If you say the 9 degrees etc info still stands then where would I be wrong? I also fail to see the issues you are referring to with the excessive shave as I have seen none. Can you elaborate those issues

I'm using a 96 top and bottom end by the way

Last edited by hinsonracing; 07-10-2018 at 01:17 AM..

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Old 07-10-2018, 07:50 AM   #11
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Default Re: Head shave timing retarding a myth?

Quote:
Originally Posted by Signmaster View Post
I've never taken any interest in the S Series numbers, but I haven't seen anything other than guesses to the numbers either.


To find out, you have to know the cam sprocket diameter.

Then multiply that by pi to get the sprocket circumference.

Then divide that number by 360 (degrees) to find out how chain length equates to degrees camshaft rotation.

Then divide that into the amount your decked the head to find out how many degrees you altered timing.


Keep in mind that you need to double the amount shaved, since the belt slack created is double what you shaved off the head (or block).

First let me fix the red above. Obviously the chain length stays the same. The cams rotate as the tensioner takes up the slack created, thus the timing change.

.... and back to the questions at hand.


Quote:
Originally Posted by hinsonracing View Post
Well there lies the problem everybody has all been about what it says on paper it should be. I have not seen any proof to anything and I have triple checked my numbers and I get the same thing everytime. I'm looking for hard proof of if what I'm getting is truly accurate or if I did something wrong here.... I'm looking for hard facts not theory.
The math above works. As I stated in my first post, I've never spent any time digging up DOHC specs as I own a single cammer myself.

You seem familiar with indexing a cam so I'll assume you have covered all bases in regards to proper indexing. The same applies to all other possible mechanical errors, such as faith in your machine shop, confirmed head gasket thickness, etc. But some of these numbers are readily available.

Quote:
Originally Posted by hinsonracing View Post
What problems? I've been running with 030" no issues. I built one for somebody that had only .060" from just the head, they never had issues. In fact they won 10 races and a championship with it. I never degreed that engine because they were in a hurry to get it. By my measurements from above my engine which has .060" taken from the block and head combined the timing is only 1.25 degree retarded.as far as fuel, plugs and combustion chambers of the engine i just blew with 60+ races show no signs of too lean conditions. The hard data you speak of I cannot locate.... everybody I've read says there is major changes mechanical timing... I cannot find any resources proving the 9.45* per tooth or the 2 degrees of retard per .010" of shave.
Without knowing the cam sprocket sizes, I can't confirm or deny the amount of cam retard per .010 of decking. But if your car runs right with .060 shaved, then you know it as fact and have simply killed internet myth.

As for timing changes per tooth, simple math.

38 teeth on the cam sprocket.
360 (degrees) divided by 38 = 9.47

So if you put your cam on one tooth off but the crank was on point, the cam would either be advanced or retarded by 9.47 degrees. The cam, not the crank.

But since the crank sprocket is 19 teeth, the cams only move at half the RPM of the crank. Thus the crank rotation when you degree the cams is 19 degrees (18.75 based on exacting numbers).

If you put the timing chain set on with the crank off one tooth but both cams were right, both cams would index at 18.75 degrees out of spec.



If you are rock solid sure on your indexing, then just measure the cam pulley diameter and we can apply the math. The number you have seen previously could be complete crap. It's the internet and I see statements on this forum all the time that I know to be incorrect. You have a chance to help sort out fact from fiction, and that info might help others in the same or similar boat.


IIRC the measurement for a chain type pulley is from the center of the valley (between the teeth) to the center of the valley.

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Old 07-10-2018, 10:10 PM   #12
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Default Re: Head shave timing retarding a myth?

So I arrived back home from work and headed straight to the shop, set the degree wheel and dial indicator back and remeasured my open close events for stock timing marks and for one tooth advanced. Here is the following at .050" lift.

Factory marks:

Intake opens -12* ATDC
Intake closes 25.5*

With factory specs being
Intake opens -7.5*
Intake closes 27.5*

Knowing cast cams aren't perfect castings when mass produced the differences I have measured are:
Opening 4.5* retarded
Closing 2.5* retarded
In summary of factory times with an engine with .060" removed from engine and block an average of 3* cam retardation is to be expected not 12*

Advanced 1 tooth at camshafts only:
Intake opens 7* BTDC
Intake closes 8* ABDC

Results with current machine work advancing 1 tooth at the camshaft are :
Opening 14.5* advanced
Closing 19.5* advanced
Average of the two being 16* advanced.

I have not yet measured the factory exhaust cam as at this point I have the opinion the the changes would be similar +/- casting flaws of mass production. I will measure on my own accord and if a large difference is found I will update.

Overall summary:
During measuring this evening I measured each event 4 consecutive times getting the same measurement each time. I made sure the dial indicator started on 0 completed on zero and recycled to ensure no discrepancies. I zeroed the degree wheel before starting and after ending measurements to ensure my wheel did not move/change. Overall I feel comfortable after speaking with some 6thsphere members that I can conclude the 9.45* per cam tooth to be incorrect. I conclude in fact that using a dial indicator that is not super precise from coming from harbor freight (most probable reason for unmirrored results between open/closing) that in fact each cam tooth is approximately 19 to 17.5* to bring an average result of 18.25* of cam timing change per cam tooth.

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Old 07-10-2018, 11:54 PM   #13
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Default Re: Head shave timing retarding a myth?

Okay now it gets weirder...... measuring the factory exhaust cam I get the following:

Exhaust cam set on factory timing marks with the above mentioned machine work:
Opens 21* BBDC
Closes 11* BTDC

Factory spec is
Opens 24.5* BBDC
Closes -12 ATDC

Results:
Opens 3.5* retarded
Closes 23* advanced
????????????

Here's where it gets crazy (I double checked my setup for zeroing out):

Set at one tooth advanced:
Opens 39* BBDC
Closes 31* BTDC

Results:
Opens 15.5* advanced
Closes 43* advanced (WTF inserted here)

Conclusion.... the opening events are consistent with the intake cam with machine work applied. HOWEVER, even after double checking and remeasuring, I am not sure how the closing events are so far off. I measured four times consecutively on factory and advanced teeth and got the same numbers. With no apparent wear, I am under the impression the maybe this cam was possibly a bad casting of what it was intended to be.

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Old 07-11-2018, 05:39 PM   #14
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Default Re: Head shave timing retarding a myth?

Is timing chain tension needed when degreeing?

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Old 07-11-2018, 05:56 PM   #15
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Default Re: Head shave timing retarding a myth?

Quote:
Originally Posted by fdryer View Post
Is timing chain tension needed when degreeing?
Yes because you have to roll it over as it would under normal operation.

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Old 07-12-2018, 05:21 AM   #16
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Default Re: Head shave timing retarding a myth?

After reading all the responses and the initial thread, we can safely conclude that shaving the head does retard camshaft timing, as has been often reiterated on this site to those that wish to mod their S-Series for racing.

I am not getting into the splitting hairs of how many degrees, because I do not have a camshaft degree wheel in my assortment of tools, nor do I care about how may degrees it retards mechanical timing by. I know that shaving a cylinder head may improve compression and I know that is not always a "good" thing. I also understand how camshaft timing drastically affects engine performance more than any other modification, because the camshaft profile and timing determine the rpm power range between peak torque and peak HP, as well as the amount of torque/HP produced.

The Twin Can has a 1,500-6,500rpm camshaft profile from the factory. The peak HP being limited to 6,000rpms is due to the restrictions from the throttle body size. Changing to the Geo Storm 1.6L SOHC TB unit will actually cause peak torque to occur at about 5,000rpms(5,100rpms if you straight pipe the converter), and peak HP to occur around 6,200rpms, and this is on a STOCK PCM and cams, without any shaving, because the ports are short and wide. Shorter, wider intake/exhaust ports and 4-valve-per-cylinder designs favor high-rpm HP while sacrificing low-rpm torque.

This is why these engines, even when stock, will not really roar to life until about 3,700-3,800rpms. The VE is too low at WOT, under that rpm, to properly pressurize the cylinders as air volume and velocity are too low for proper fuel atomization.

Aside from the performance losses associated with shaving the head, you are trying to compensate by raising static compression ratio, which increases combustion temperatures and stress on the cylinder head.

Removing metal make the head weaker, so when the head splits in half like a piece of chopped fire wood, then maybe your condescending attitude will eat a big "Pride Sandwich".

This is why many will state that shaving the head is not worth the cost. The best way to improve performance and efficiency of these engines are modifications that improve intake/exhaust velocity.

Messing with the cams or shaving the head and block are pretty much a waste, unless you are going to do everything, including the PCM.

So, to answer the question of the thread title:

It is not a myth

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Old 07-12-2018, 04:35 PM   #17
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Default Re: Head shave timing retarding a myth?

how many teeth on the cam gear?

that is the gear you are talking about right?

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Old 07-15-2018, 04:33 PM   #18
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Default Re: Head shave timing retarding a myth?

Quote:
Originally Posted by hinsonracing View Post
Overall summary:
During measuring this evening I measured each event 4 consecutive times getting the same measurement each time. I made sure the dial indicator started on 0 completed on zero and recycled to ensure no discrepancies. I zeroed the degree wheel before starting and after ending measurements to ensure my wheel did not move/change. Overall I feel comfortable after speaking with some 6thsphere members that I can conclude the 9.45* per cam tooth to be incorrect. I conclude in fact that using a dial indicator that is not super precise from coming from harbor freight (most probable reason for unmirrored results between open/closing) that in fact each cam tooth is approximately 19 to 17.5* to bring an average result of 18.25* of cam timing change per cam tooth.
Seems fairly close to expected. Just shy of 19 degrees at the crank when moving the cams 1 tooth. No doubt quality of tools and equipment play a role, and it has to be much more precise than it seems it would be. Just the size of the degree wheel and precision of the pointer make a huge difference in consistent readings as well.

Based on the averages you are getting on both the intake and exhaust side, it appears the machining only changed your timing about 3.5 degrees, give or take a little bit for margin of error. I think the consistency there is enough to disprove any of the posts/articles you pointed out at the start of the thread.



As for that exhaust cam, that has be scratching my head. Can you even be certain that it is a stock cam? Looking at the numbers I would almost think they are closer to the opening event being with the marks and sprockets aligned properly, but the closing events are 1 tooth off. Any chance you mixed up the numbers when checking things?

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Old 10-06-2018, 09:41 PM   #19
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Default Re: Head shave timing retarding a myth?

Just my 2 cents... I just renewed my chain set and had the used sprocket & chain to direct measure. Sprocket radius to the chain pin (s) is 58.75 mm. 2(pi)r = 369.14 mm (pitch circle circumfrence length). 369.14 mm/ 360 degree = 1.025 degree per 1 mm of vertical change. However, the chain comes off of the sprocket at approx 45 deg. So, cosine 45 = .707. So, taking a geometry swag, i'd say you get ~ 1.025 x 0.707 = 0.725 degree per mm cut on the head at the cam. 1.45 deg at the crank. Yep using geometry, not empirical. Cheers.

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Old 10-15-2018, 01:55 PM   #20
Thor4SL2
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Default Re: Head shave timing retarding a myth?

[QUOTE=Saturn Night;2277383]Aside from the performance losses associated with shaving the head, you are trying to compensate by raising static compression ratio, which increases combustion temperatures and stress on the cylinder head.

Removing metal make the head weaker, so when the head splits in half like a piece of chopped fire wood, then maybe your condescending attitude will eat a big "Pride Sandwich". QUOTE]

Nonsense, I have been driving my 95 SC-2 w/ head milled 0.04" for over 3 years and about 24,000 miles with NO problems let alone head splitting. How much stress that head can take is debatable, I certainly haven't seen any negative effects.

There will be some advance but very little but noware near 1 tooth (9 deg.) Perhaps 1/4 of a tooth if that much.

I agree that the best way to improve the engines performance is through intake and exhaust modifications. Headers and performance exhaust systems are available and a GEO throttle body helps but the real restriction is the short length of the intake runners and there is nothing that can be done about that, except turbo.

As for cost, if you are doing a valve job or other work requiring removal of the head the head should be skimmed anyway. It is criminal to reinstall a head that might be warped.

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