Highest DCR for 92 octane?
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Re: Highest DCR for 92 octane?
Originally Posted by SStrokerAce
The Mahles still need the radiusing,
Bret
Bret
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Re: Highest DCR for 92 octane?
Originally Posted by 67RSSS6SPD
Bret, Can you explane this more!After hearing a lot of good stuff about the Mahle's I had to get a set,And I must say they do look nice,Plus that quote about a possible 20 extra HP sounds good.
Basically you round off all the hard edges left from the tools that cut the valve pockets, or make the dome or dish in the piston.
Bret
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From: GARDNERS,PA
Re: Highest DCR for 92 octane?
Any rule of thumb on how much DCR can be added with every step in octane rating? I get Sunoco 94 here with no problem and could even mix in a lil GT100 if needed. I'm only at about 12.0 SCR/8.9 DCR right now w/ .041" quench and no signs of detonation. That being said, the motor's not really making torque numbers that it should. Still trying to sort that out. 
Steve
Steve
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Re: Highest DCR for 92 octane?
94 ain't bad stuff... your lucky they yanked it away from us up here.
I don't know if there is a general rule as to DCR to Octane.... kinda wish there was. There are lots of other factors that play into it more than just that.
Bret
I don't know if there is a general rule as to DCR to Octane.... kinda wish there was. There are lots of other factors that play into it more than just that.
Bret
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Joined: Nov 1998
Posts: 115
From: WA
Re: Highest DCR for 92 octane?
Ok I'l keep this good thread going... 
So, here's what happends when you choose your cam spects by cam manufactures listed base duration. Me and Ellis finally were stabbing the cam in yesterday...
12.48 SCR = 8.82 DCR with 289 base duration and 114 installed ICL/LSA (very little loss over 110ICL), that's why the 114LSA...I figured why have a cam with 114 icl and 110LSA...Engine Analizer Pro didn't seem to mind this either...what the hay I'll try it.....
Now...after checking cam installed in engine we got exact duration on the exhaust(great), We moved to the intake duration....then a hell broke loose
The .05 was actually 1 degree more in duration...fine....the ICL was pretty close....but the damn supposed 289 cam was actually 294 @.006 .That may not sound like alot but dumped the DCR down, and actual .006 was measures at 83.5 ABDC 
Way off...check, check and recheck everything...same numbers.......8.35 DCR urggggggg So, we sucked up the tuning issues and installed the cam 4 advanced to get atleast 79.5ABDC....Now atleast, I'll have 8.73DCR 
Moral to the story....aaa Maybe I'll think twice about having "CC" grind me a cam... and I'm glad I always degree the cam....Now if I had known this I might have got it on 108 ICL with 110LSA.....bastards.....or atleast 110ICL/LSA....
Jimbob
So, here's what happends when you choose your cam spects by cam manufactures listed base duration. Me and Ellis finally were stabbing the cam in yesterday...
12.48 SCR = 8.82 DCR with 289 base duration and 114 installed ICL/LSA (very little loss over 110ICL), that's why the 114LSA...I figured why have a cam with 114 icl and 110LSA...Engine Analizer Pro didn't seem to mind this either...what the hay I'll try it.....
Now...after checking cam installed in engine we got exact duration on the exhaust(great), We moved to the intake duration....then a hell broke loose
The .05 was actually 1 degree more in duration...fine....the ICL was pretty close....but the damn supposed 289 cam was actually 294 @.006 .That may not sound like alot but dumped the DCR down, and actual .006 was measures at 83.5 ABDC Way off...check, check and recheck everything...same numbers.......8.35 DCR urggggggg So, we sucked up the tuning issues and installed the cam 4 advanced to get atleast 79.5ABDC....Now atleast, I'll have 8.73DCR Moral to the story....aaa Maybe I'll think twice about having "CC" grind me a cam... and I'm glad I always degree the cam....Now if I had known this I might have got it on 108 ICL with 110LSA.....bastards.....or atleast 110ICL/LSA....Jimbob
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Re: Highest DCR for 92 octane?
Jimbob,
Few things...
First thing, cam companies have a few things that they prioritize when they grind a cam. With Comp they make sure they get the lobe profile of the cam right, and the duration specs close. Over the last few years the duration specs tolerance has gotten tighter and tighter which is a good thing, but they still emphisize getting the lobe profile correct. That might NOT sound as important to you, but the problem is you can't measure the problems in the lobe profile of the cam unless you have a Cam Dr and know what the lobe should look like. Little changes here and there can cause bad accelerations, jerks, V^4 etc.... in the valve movement that can be detrimental to valvetrain life and performance. To me i'd rather have the right valvetrain motions than worry about 1 deg @ .050, and when I was tring to push the DCR a little less is always better than a little more, especially since there is such high pressure in the port and IVC that it's doubtful that the motor sees any difference there.
BTW a degree wheel can get you close on cam specs but a Cam Dr is the only way to know... fortuneately all the cams get measured on one at Comp before they go out the door.
Second thing, just because the computer doesn't care if it's 110 or 114 LSA, the motor does.
Bret
Few things...
First thing, cam companies have a few things that they prioritize when they grind a cam. With Comp they make sure they get the lobe profile of the cam right, and the duration specs close. Over the last few years the duration specs tolerance has gotten tighter and tighter which is a good thing, but they still emphisize getting the lobe profile correct. That might NOT sound as important to you, but the problem is you can't measure the problems in the lobe profile of the cam unless you have a Cam Dr and know what the lobe should look like. Little changes here and there can cause bad accelerations, jerks, V^4 etc.... in the valve movement that can be detrimental to valvetrain life and performance. To me i'd rather have the right valvetrain motions than worry about 1 deg @ .050, and when I was tring to push the DCR a little less is always better than a little more, especially since there is such high pressure in the port and IVC that it's doubtful that the motor sees any difference there.
BTW a degree wheel can get you close on cam specs but a Cam Dr is the only way to know... fortuneately all the cams get measured on one at Comp before they go out the door.
Second thing, just because the computer doesn't care if it's 110 or 114 LSA, the motor does.
Bret
Last edited by SStrokerAce; Jul 12, 2005 at 06:40 AM.
Registered User
Joined: Dec 1969
Posts: 1,431
From: Pacific North West
Re: Highest DCR for 92 octane?
Originally Posted by SStrokerAce
Jimbob,
Few things...
First thing, cam companies have a few things that they prioritize when they grind a cam. With Comp they make sure they get the lobe profile of the cam right, and the duration specs close. Over the last few years the duration specs tolerance has gotten tighter and tighter which is a good thing, but they still emphisize getting the lobe profile correct. That might sound as important to you, but the problem is you can't measure the problems in the lobe profile of the cam unless you have a Cam Dr and know what the lobe should look like. Little changes here and there can cause bad accelerations, jerks, V^4 etc.... in the valve movment that can be detrimental to valvetrain life and performance. To me i'd rather have the right valvetrain motions than worry about 1 deg @ .050, and when I was tring to push the DCR a little less is always better than a little more, especially since there is such high pressure in the port and IVC that it's doubtful that the motor sees any difference there.
BTW a degree wheel can get you close on cam specs but a Cam Dr is the only way to know... fortuneately all the cams get measured on one at Comp before they go out the door.
Second thing, just because the computer doesn't care if it's 110 or 114 LSA, the motor does.
Bret
Few things...
First thing, cam companies have a few things that they prioritize when they grind a cam. With Comp they make sure they get the lobe profile of the cam right, and the duration specs close. Over the last few years the duration specs tolerance has gotten tighter and tighter which is a good thing, but they still emphisize getting the lobe profile correct. That might sound as important to you, but the problem is you can't measure the problems in the lobe profile of the cam unless you have a Cam Dr and know what the lobe should look like. Little changes here and there can cause bad accelerations, jerks, V^4 etc.... in the valve movment that can be detrimental to valvetrain life and performance. To me i'd rather have the right valvetrain motions than worry about 1 deg @ .050, and when I was tring to push the DCR a little less is always better than a little more, especially since there is such high pressure in the port and IVC that it's doubtful that the motor sees any difference there.
BTW a degree wheel can get you close on cam specs but a Cam Dr is the only way to know... fortuneately all the cams get measured on one at Comp before they go out the door.
Second thing, just because the computer doesn't care if it's 110 or 114 LSA, the motor does.
Bret
And THAT is why we were calling you saturday Bret
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Joined: Jan 2002
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Re: Highest DCR for 92 octane?
I havent seen a forged piston that came out of the box that didnt need the radius' sanded, there should be no square or sharp edges anywhere in the chamber. This combined with correct quench allows more DCR. Along with MANY other factors.
As far as degreeing a cam, the cam may be spot on when it goes out the door coming to you, cam companies are much better at this. You degree the cam to correct the differences in crank indexing and timing chain tolerances to make sure it is timed in the engine as the cam company intended it to be.
There is no exact science to DCR and pump octane, there are MANY different fuel mixes in the pumps in various parts of the country, local weather also plays a role. What works for me, may not work for you.
The LT1 is capable of carrying more DCR than a "regular" engine with it's reverse flow cooling, which is what GM intended with it's very high(at the time in '92) 10.5 to 1 static compression.
Just my .02
David
As far as degreeing a cam, the cam may be spot on when it goes out the door coming to you, cam companies are much better at this. You degree the cam to correct the differences in crank indexing and timing chain tolerances to make sure it is timed in the engine as the cam company intended it to be.
There is no exact science to DCR and pump octane, there are MANY different fuel mixes in the pumps in various parts of the country, local weather also plays a role. What works for me, may not work for you.
The LT1 is capable of carrying more DCR than a "regular" engine with it's reverse flow cooling, which is what GM intended with it's very high(at the time in '92) 10.5 to 1 static compression.
Just my .02
David
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