returning cam timing to stock after slightly milling head - is this necessary?
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returning cam timing to stock after slightly milling head - is this necessary?
i have a 1985 crx si and have had head work done to bump the compression ratio per IT rules. this results in a slightly retarded cam timing.
is it necessary to restore the cam timing via the offset key approach?
and if so, how much power are we are talking about? 1-2 hp or just 0.1 hp?
tia, tom
is it necessary to restore the cam timing via the offset key approach?
and if so, how much power are we are talking about? 1-2 hp or just 0.1 hp?
tia, tom
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From: Browns Summit, NC, USA
Re: returning cam timing to stock after slightly milling head - is this necessary? (tom91ita)
have seen gains of 10-15 hp with just 1degree turn of the cam!
i would try an adjustable cam gear on the dyno then get the offset key made to that offset...
i would try an adjustable cam gear on the dyno then get the offset key made to that offset...
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From: Folsom, CA, USA
Re: returning cam timing to stock after slightly milling head - is this necessary? (tom91ita)
you can't cange cam timming in IT, but don't worry, if youi took .020 off your head, you retarded your cam timming by about .09 degrees. I wouldn't worry about it.
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Re: returning cam timing to stock after slightly milling head - is this necessary? (chad)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by chad »</TD></TR><TR><TD CLASS="quote">have seen gains of 10-15 hp with just 1degree turn of the cam!
i would try an adjustable cam gear on the dyno then get the offset key made to that offset...
</TD></TR></TABLE>
this is correct thinking, but i'm pretty sure that getting the offset key on the cam made to that spec isn't legal. what you're going to want to do is play with the natural slop in the mounting of all the components to adjust your timing ever so slightly. that and look for old old cam gears that have the slots worn out of them so there's more play and room for "adjustment."
i'm pretty sure machining cam gears, or changing the key on the cams is illegal per IT rules, but there are legal ways around that.
i would try an adjustable cam gear on the dyno then get the offset key made to that offset...
</TD></TR></TABLE>
this is correct thinking, but i'm pretty sure that getting the offset key on the cam made to that spec isn't legal. what you're going to want to do is play with the natural slop in the mounting of all the components to adjust your timing ever so slightly. that and look for old old cam gears that have the slots worn out of them so there's more play and room for "adjustment."
i'm pretty sure machining cam gears, or changing the key on the cams is illegal per IT rules, but there are legal ways around that.
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Re: returning cam timing to stock after slightly milling head - is this necessary? (tnord)
Timely topic... JohnG and I have been discussing this at length lately.
Rules state that you can have an offset key made for the CRANK not for the cam. The rules futher state that it can only be used to CORRECT timing not tune it.
So basically you have two options, leave it alone or correct back to zero. If you take the rules literally.
You could use a cam gear to test which of the above makes the best power and if it turns out to be the zero setting you will need to have an offset key made for the crank.
BTW .012" off any part of the elements that determine the "combustion height" ie head, block or head gasket = 1 degree of retard on the cam
Rumor is that SOHC IT motors make slightly better top end power with the cam retarded between 1 & 2 degrees... yet to be proven to me *shrug*.
I will report back findings on my D16Z6 in the next couple weeks as my new motor is right at 1 degree of retard on the cam.
Rules state that you can have an offset key made for the CRANK not for the cam. The rules futher state that it can only be used to CORRECT timing not tune it.
So basically you have two options, leave it alone or correct back to zero. If you take the rules literally.
You could use a cam gear to test which of the above makes the best power and if it turns out to be the zero setting you will need to have an offset key made for the crank.
BTW .012" off any part of the elements that determine the "combustion height" ie head, block or head gasket = 1 degree of retard on the cam
Rumor is that SOHC IT motors make slightly better top end power with the cam retarded between 1 & 2 degrees... yet to be proven to me *shrug*.
I will report back findings on my D16Z6 in the next couple weeks as my new motor is right at 1 degree of retard on the cam.
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From: west, mich, usa
Re: returning cam timing to stock after slightly milling head - is this necessary? (rambler)
the IT rules i am referring to is:
"Where a factory specification for original cylinder head thickness can be proven, a tolerance of .025 inch less than the service limit will be permitted. Under no circumstances may the compression ratio be increased by more than onehalf (.5) point. An offset key may be used to return cam timing to the factory specifications. On engines with dual overhead camshafts, this key shall be installed on the crankshaft only."
my cam pulley is about 4.75" OD. i am assuming that i can take about 0.03" of the head and this will lower the head and the tension pulley then retards the cam.
if i take 360°/(3.14*4.75) * .03, i get ~ 0.7° of cam movement relative to TDC.
is this correct way to figure this? this seems to be closer to the 1° vs. the 0.09°
tom
"Where a factory specification for original cylinder head thickness can be proven, a tolerance of .025 inch less than the service limit will be permitted. Under no circumstances may the compression ratio be increased by more than onehalf (.5) point. An offset key may be used to return cam timing to the factory specifications. On engines with dual overhead camshafts, this key shall be installed on the crankshaft only."
my cam pulley is about 4.75" OD. i am assuming that i can take about 0.03" of the head and this will lower the head and the tension pulley then retards the cam.
if i take 360°/(3.14*4.75) * .03, i get ~ 0.7° of cam movement relative to TDC.
is this correct way to figure this? this seems to be closer to the 1° vs. the 0.09°
tom
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From: www.SavOnTrafficSchool.com, usa
Re: returning cam timing to stock after slightly milling head - is this necessary? (tom91ita)
Retarding the cam timing moves the powerband higher in the rev range. on a B18a
So i think its the same way for the D series engines.
Edo
So i think its the same way for the D series engines.
Edo
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From: Scottsdale, AZ, U.S.A
Re: returning cam timing to stock after slightly milling head - is this necessary? (EdoMoto)
I lost a serious amount of power when I didn't correct my timming. First race back I would get walked down the front strait at PIR like I was in a different class.. next race with correctd timing our cars were about identical!
Not being able to put an adjustable cam gear on has always been strange to me. The gears aren't expensive and cars are already seeing plenty of dyno time, so why not let the timing be adjusted?
ANd if cost is the reason, the"right" tool to figure out the correct timting position practically costs just as much as some dyno time!
Not being able to put an adjustable cam gear on has always been strange to me. The gears aren't expensive and cars are already seeing plenty of dyno time, so why not let the timing be adjusted?
ANd if cost is the reason, the"right" tool to figure out the correct timting position practically costs just as much as some dyno time!
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From: Johntown, NY, USA
Re: returning cam timing to stock after slightly milling head - is this necessary? (DMF)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tom91ita »</TD></TR><TR><TD CLASS="quote">the IT rules i am referring to is:
" An offset key may be used to return cam timing to the factory specifications. On engines with dual overhead camshafts, this key shall be installed on the crankshaft only."
tom</TD></TR></TABLE>
Assuming that this is in fact a correct quote from the IT section of the GCR, and it sounds right to me, you can use an offset key on either pulley. Note the specific mention of DOHC. That is to prevent someone from changing the timing of the cams independently. Since the Si is a SOHC, you are not limited to only the crank pulley. My reading of this also says that you do not have to put it back to stock if it works better. It does sound like Chad's suggestion is your best bet for max power.
" An offset key may be used to return cam timing to the factory specifications. On engines with dual overhead camshafts, this key shall be installed on the crankshaft only."
tom</TD></TR></TABLE>
Assuming that this is in fact a correct quote from the IT section of the GCR, and it sounds right to me, you can use an offset key on either pulley. Note the specific mention of DOHC. That is to prevent someone from changing the timing of the cams independently. Since the Si is a SOHC, you are not limited to only the crank pulley. My reading of this also says that you do not have to put it back to stock if it works better. It does sound like Chad's suggestion is your best bet for max power.
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From: Pacific Northwest, USA
Re: returning cam timing to stock after slightly milling head - is this necessary? (DMF)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DMF »</TD></TR><TR><TD CLASS="quote">Not being able to put an adjustable cam gear on has always been strange to me. The gears aren't expensive and cars are already seeing plenty of dyno time, so why not let the timing be adjusted?</TD></TR></TABLE>
Because compression ratios would get out-of-hand. Testing & verifying compression at the track is difficult. And because it's difficult, you can mill the **** out of your head, deck the **** out of the block, have 10:1 compression and still be able to easily zero cam timing with a adjustable sprocket. That's why it's not allowed.
Honda Challenge rules address this specifically, and say you can only make cam timing adjustments via crank key. I wonder why NASA didn't follow SCCA IT on this one..
12-thousandths total off the head or block = 1 degree cam retard (d-series motors). From what I understand, any more than that on a stock cam and gains start going backwards.
Because compression ratios would get out-of-hand. Testing & verifying compression at the track is difficult. And because it's difficult, you can mill the **** out of your head, deck the **** out of the block, have 10:1 compression and still be able to easily zero cam timing with a adjustable sprocket. That's why it's not allowed.
Honda Challenge rules address this specifically, and say you can only make cam timing adjustments via crank key. I wonder why NASA didn't follow SCCA IT on this one..
12-thousandths total off the head or block = 1 degree cam retard (d-series motors). From what I understand, any more than that on a stock cam and gains start going backwards.
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Re: returning cam timing to stock after slightly milling head - is this necessary? (johng)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by johng »</TD></TR><TR><TD CLASS="quote">
Because compression ratios would get out-of-hand. Testing & verifying compression at the track is difficult. And because it's difficult, you can mill the **** out of your head, deck the **** out of the block, have 10:1 compression and still be able to easily zero cam timing with a adjustable sprocket. That's why it's not allowed.</TD></TR></TABLE>
Rules for both IT and HC state that you cannot gain more than a half point increase in compression ratio.
Because compression ratios would get out-of-hand. Testing & verifying compression at the track is difficult. And because it's difficult, you can mill the **** out of your head, deck the **** out of the block, have 10:1 compression and still be able to easily zero cam timing with a adjustable sprocket. That's why it's not allowed.</TD></TR></TABLE>
Rules for both IT and HC state that you cannot gain more than a half point increase in compression ratio.
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From: Pacific Northwest, USA
Re: returning cam timing to stock after slightly milling head - is this necessary? (.RJ)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by .RJ »</TD></TR><TR><TD CLASS="quote">Rules for both IT and HC state that you cannot gain more than a half point increase in compression ratio.</TD></TR></TABLE>
Right, but not allowing adjustable cam sprockets are one way to help keep that under control.
Right, but not allowing adjustable cam sprockets are one way to help keep that under control.
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Re: returning cam timing to stock after slightly milling head - is this necessary? (johng)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by johng »</TD></TR><TR><TD CLASS="quote">Right, but not allowing adjustable cam sprockets are one way to help keep that under control.
</TD></TR></TABLE>
How so? If someone wanted to they could mill the hell out of the head, and then get creative with an offset key to return cam timing to stock anyways. The rule is the rule - thats like saying making people run a stock exhaust manifold helps keep people putting turbos on their car under control.
</TD></TR></TABLE>
How so? If someone wanted to they could mill the hell out of the head, and then get creative with an offset key to return cam timing to stock anyways. The rule is the rule - thats like saying making people run a stock exhaust manifold helps keep people putting turbos on their car under control.
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From: Scottsdale, AZ, U.S.A
Re: returning cam timing to stock after slightly milling head - is this necessary? (.RJ)
Just seems like a big pita to me!
Have you guys found anywhere that sells offset keys or were you having them custom made? I was having a machine shop make the, but for some reason I thought there should be an easier way.
Also, how "strict" is the rul on just returning it to stock timing. Is Chads way of tuning with a cam gear and then having an offset key made acceptable?
Have you guys found anywhere that sells offset keys or were you having them custom made? I was having a machine shop make the, but for some reason I thought there should be an easier way.
Also, how "strict" is the rul on just returning it to stock timing. Is Chads way of tuning with a cam gear and then having an offset key made acceptable?
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From: Pacific Northwest, USA
Re: returning cam timing to stock after slightly milling head - is this necessary? (.RJ)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by .RJ »</TD></TR><TR><TD CLASS="quote">
How so? </TD></TR></TABLE>
It's easier to cheat with a adjustable gear.
How so? </TD></TR></TABLE>
It's easier to cheat with a adjustable gear.
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Re: returning cam timing to stock after slightly milling head - is this necessary? (johng)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by johng »</TD></TR><TR><TD CLASS="quote">
It's easier to cheat with a adjustable gear.
</TD></TR></TABLE>
Someone who wants to cheat is going to do it no matter what.
Its easier to get caught with an adj gear, if you pull the valve cover off and its been retarded 4 degrees, you know something is not right. You cant tell that with an offset key.
It's easier to cheat with a adjustable gear.
</TD></TR></TABLE>
Someone who wants to cheat is going to do it no matter what.
Its easier to get caught with an adj gear, if you pull the valve cover off and its been retarded 4 degrees, you know something is not right. You cant tell that with an offset key.
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From: Haymarket, VA, USA
Re: returning cam timing to stock after slightly milling head - is this necessary? (.RJ)
for those with SOHC: you can grind one side of the stock key that is part of the cam gear. then get yourself a dial indicator and a degree wheel and get busy indexing your cam. Use some feeler gauges to make spacers on the appropriate side of the cam gear to get it snug. after a few hours of playing with it, cursing, and re-measuring everything a few times, you'll have reached whatever magical setting you are looking for.
snug it up, slam the last couple of Shiner Bocks in the case and call it a day. check your measurements again when sober.
snug it up, slam the last couple of Shiner Bocks in the case and call it a day. check your measurements again when sober.
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From: West Palm Beach, Fl, USA
Re: returning cam timing to stock after slightly milling head - is this necessary? (SJR)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by SJR »</TD></TR><TR><TD CLASS="quote">for those with SOHC: you can grind one side of the stock key that is part of the cam gear. then get yourself a dial indicator and a degree wheel and get busy indexing your cam. Use some feeler gauges to make spacers on the appropriate side of the cam gear to get it snug. after a few hours of playing with it, cursing, and re-measuring everything a few times, you'll have reached whatever magical setting you are looking for.
snug it up, slam the last couple of Shiner Bocks in the case and call it a day. check your measurements again when sober.</TD></TR></TABLE>
You just made my day with that post
LOL
snug it up, slam the last couple of Shiner Bocks in the case and call it a day. check your measurements again when sober.</TD></TR></TABLE>
You just made my day with that post
LOL
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From: Haymarket, VA, USA
Re: returning cam timing to stock after slightly milling head - is this necessary? (Cobra Tim)
I'm glad I could brighten someone's day. and this was a very mild exageration of how i spent a very long evening in a very cold garage last winter to get my car ready... at least the beer stayed cold out of the fridge...
at least the beer stayed cold out of the fridge...
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From: At arms length....
Re: returning cam timing to stock after slightly milling head - is this necessary? (SJR)
Anyone know if there is someone out-there that is making offset keys? Something in like .006" increments would be outstanding!
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From: Boston, MA, USA
Re: returning cam timing to stock after slightly milling head - is this necessary? (rambler)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tom9ita »</TD></TR><TR><TD CLASS="quote">my cam pulley is about 4.75" OD. i am assuming that i can take about 0.03" of the head and this will lower the head and the tension pulley then retards the cam.</TD></TR></TABLE>
I believe from doing the calculations that shaving the head that much would result in gaining more than 0.5 pts of CR. Make sure you don't mill too much!
s
I believe from doing the calculations that shaving the head that much would result in gaining more than 0.5 pts of CR. Make sure you don't mill too much!
s
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From: at the track
Re: returning cam timing to stock after slightly milling head - is this necessary? (.RJ)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by .RJ »</TD></TR><TR><TD CLASS="quote">Isnt the service limit .012" or .015"?
I need to dig up my Helms and check... </TD></TR></TABLE>
helms doesnt list a service limit for cylinder head height. They give you 4 thou of error on the stock casting though. Here's some scans of mine:
I need to dig up my Helms and check... </TD></TR></TABLE>
helms doesnt list a service limit for cylinder head height. They give you 4 thou of error on the stock casting though. Here's some scans of mine:
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Re: returning cam timing to stock after slightly milling head - is this necessary? (stevel)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by stevel »</TD></TR><TR><TD CLASS="quote">I believe from doing the calculations that shaving the head that much would result in gaining more than 0.5 pts of CR. </TD></TR></TABLE>
Recheck your calculations again. For example, on a D16Z6, the stock CR is 9.13:1. Milling 3-thousandths off the head only raises CR to 9.19:1. That's far from the 0.5 CR gain allowance.
$.02
Recheck your calculations again. For example, on a D16Z6, the stock CR is 9.13:1. Milling 3-thousandths off the head only raises CR to 9.19:1. That's far from the 0.5 CR gain allowance.
$.02
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From: Boston, MA, USA
Re: returning cam timing to stock after slightly milling head - is this necessary? (.RJ)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by .RJ »</TD></TR><TR><TD CLASS="quote">Isnt the service limit .012" or .015"?
I need to dig up my Helms and check... </TD></TR></TABLE>
yeah, and?
s
I need to dig up my Helms and check... </TD></TR></TABLE>
yeah, and?
s