Comp grinds another cam off spec.
01-19-2007, 01:21 AM
#41
Originally Posted by thehammer69
01-19-2007, 01:32 AM
#42
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Originally Posted by Bryan Broaddus
From a practical perspective I have varied cam timming back and forth quite a bit and you do not see very noticable change in the 1/4 mile ET(about .05 seconds). It may feel a little different when you drive it around town but the net result is small.
Had I just based milling my heads off the Cam card, this is the sitution that I would be potentially looking at facing. The Adcole report now tells me the truth and I know what "should" be the safe limit to set my compression.
Anyway, you do make a valid point about the indexing of the crank key. I wonder how often this is off with any significance?
Hammer
01-19-2007, 06:13 AM
#43
I think the real question here is whether the tolerances seen here are typical or acceptable for our application. If Crane or some other company sees the same tolerances as acceptable, then there is no reason to complain. Cams would be ridiculously expensive if the tolerances were kept to unreasonable levels.
01-19-2007, 06:56 AM
#45
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Originally Posted by Grimes
I think the real question here is whether the tolerances seen here are typical or acceptable for our application. If Crane or some other company sees the same tolerances as acceptable, then there is no reason to complain. Cams would be ridiculously expensive if the tolerances were kept to unreasonable levels.
01-19-2007, 09:39 AM
#47
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Originally Posted by thehammer69
You know, my biggest issue about the ICL being 2 degrees more advanced than ordered...How it effects my planning to max my DCR out for 93 Octane. Let's say I get my compression set for a DCR of 8.83:1 which is close to 93 octane's edge. That unexpected 2 degree bump suddenly puts me at about 9:1 and now I potentially find myself to have to retard spark from optimum timing to keep from knocking.
Had I just based milling my heads off the Cam card, this is the sitution that I would be potentially looking at facing. The Adcole report now tells me the truth and I know what "should" be the safe limit to set my compression.
Anyway, you do make a valid point about the indexing of the crank key. I wonder how often this is off with any significance?
Hammer
Had I just based milling my heads off the Cam card, this is the sitution that I would be potentially looking at facing. The Adcole report now tells me the truth and I know what "should" be the safe limit to set my compression.
Anyway, you do make a valid point about the indexing of the crank key. I wonder how often this is off with any significance?
Hammer
What are you going to do when your timing chain stretches a bit? Or when the formula in the fuel you use changes slightly from season to season, or the pistons get a bit of buildup and raise your c.r.? How far are your pistons out of the hole, have you measured that yet before you ordered the cam????
Just a few questions...... from people that understand what your trying to do, but in reality you will never see or feel the difference your worried about.
01-19-2007, 11:09 AM
#49
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FYI the cam help line sucks. they recommended a weeny-lobed tight lsa street NA cam for my turbo motor.
want a help line? call cam motion; they seem to hit it on the nuts 90% of the time
want a help line? call cam motion; they seem to hit it on the nuts 90% of the time
01-19-2007, 12:13 PM
#50
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You should really talk to someone else at Comp not the cam help guys. Call and ask for TIM COLE or GORDEN HOLLAWAY. These guy know cams and can help you get what you are after.
01-19-2007, 12:19 PM
#51
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Originally Posted by Sean Collins
thank you. sometimes i swear i think nobody here has a clue and you step up and say something like this. well siad. I wish i had said that to begin with.
Depending on the valvetrain parts stiffnesses, actual valve movement off and on the seat is ofte quite a few degrees from the nominal or "design" valve events. Everything is a spring, especially pushrods. Again, this deviation varies with rpm. How about 10° less actual seat-seat duration at power peak rpm than design.
Valves bounce when they close, often 2 or three times and as much as .010-.015. This occurs over perhaps 10-15° after the designed IC point. Some of the trapped charge leaks out during bounces which reduces the effective compression ratio from the calculated DCR. How much? In a bad, but often seen case, enough to make the power nosedive say around 6000 when it should peak a few hundred rpm higher.
My point is that + or - 1/2° tolerances on aftermarket cams are so much less than the variations in the operating engine that improving the tolerances to +/- 1/10° or 1/50° wouldn't be noticed by the engine, but would multiply the cams cost by many times. Today's cams are SO much closer to the "design" valve events and lobe profiles than those of even 5-10 years ago that it amazes me, and I'm in the precision grinding business.
The Adcole measuring machine is much more accurate than other (Doctoring) methods used. In some cases by an order of magnitude. I wish that more folks could actually see how stuff is done in the real world, and not just look at numbers without knowing the accuarcy of the measuring equipment.
"Designing" an engine with a DCR calculated to two or three decimal places, and being concerned about the 2nd or 3rd digit makes me shake my head. Hell, most folks can't measure the total clearance volume and swept volume in an actual engine close enough to get an accurate SCR to the 2nd decimal place. eg: .001 longer crank throw in a 350 V8 which gives a .002 longer stroke, changes SCR about .03 if nothing else changes. How many of us accurately measure all 8 cylinder strokes to .001 or less?
My point is try not to get lost in squashinf pissants and miss the 800 lb gorillas.
End of my rant.
01-19-2007, 12:40 PM
#53
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Originally Posted by zipdog
What are you going to do when your timing chain stretches a bit?
Originally Posted by zipdog
Or when the formula in the fuel you use changes slightly from season to season,
Originally Posted by zipdog
or the pistons get a bit of buildup and raise your c.r.?
Hammer Last edited by thehammer69; 01-19-2007 at 03:16 PM.
01-19-2007, 01:00 PM
#55
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Originally Posted by Old SStroker
I rarely post here, but sometimes I stick my nose in in an attempt to keep things somewhat realistic. Not only does timng chain stretch and harmonics move the ICL a few crank degrees during operation, but it varies with rpm.
Depending on the valvetrain parts stiffnesses, actual valve movement off and on the seat is ofte quite a few degrees from the nominal or "design" valve events. Everything is a spring, especially pushrods. Again, this deviation varies with rpm. How about 10° less actual seat-seat duration at power peak rpm than design.
Valves bounce when they close, often 2 or three times and as much as .010-.015. This occurs over perhaps 10-15° after the designed IC point. Some of the trapped charge leaks out during bounces which reduces the effective compression ratio from the calculated DCR. How much? In a bad, but often seen case, enough to make the power nosedive say around 6000 when it should peak a few hundred rpm higher.
My point is that + or - 1/2° tolerances on aftermarket cams are so much less than the variations in the operating engine that improving the tolerances to +/- 1/10° or 1/50° wouldn't be noticed by the engine, but would multiply the cams cost by many times. Today's cams are SO much closer to the "design" valve events and lobe profiles than those of even 5-10 years ago that it amazes me, and I'm in the precision grinding business.
The Adcole measuring machine is much more accurate than other (Doctoring) methods used. In some cases by an order of magnitude. I wish that more folks could actually see how stuff is done in the real world, and not just look at numbers without knowing the accuarcy of the measuring equipment.
"Designing" an engine with a DCR calculated to two or three decimal places, and being concerned about the 2nd or 3rd digit makes me shake my head. Hell, most folks can't measure the total clearance volume and swept volume in an actual engine close enough to get an accurate SCR to the 2nd decimal place. eg: .001 longer crank throw in a 350 V8 which gives a .002 longer stroke, changes SCR about .03 if nothing else changes. How many of us accurately measure all 8 cylinder strokes to .001 or less?
My point is try not to get lost in squashinf pissants and miss the 800 lb gorillas.
End of my rant.
Depending on the valvetrain parts stiffnesses, actual valve movement off and on the seat is ofte quite a few degrees from the nominal or "design" valve events. Everything is a spring, especially pushrods. Again, this deviation varies with rpm. How about 10° less actual seat-seat duration at power peak rpm than design.
Valves bounce when they close, often 2 or three times and as much as .010-.015. This occurs over perhaps 10-15° after the designed IC point. Some of the trapped charge leaks out during bounces which reduces the effective compression ratio from the calculated DCR. How much? In a bad, but often seen case, enough to make the power nosedive say around 6000 when it should peak a few hundred rpm higher.
My point is that + or - 1/2° tolerances on aftermarket cams are so much less than the variations in the operating engine that improving the tolerances to +/- 1/10° or 1/50° wouldn't be noticed by the engine, but would multiply the cams cost by many times. Today's cams are SO much closer to the "design" valve events and lobe profiles than those of even 5-10 years ago that it amazes me, and I'm in the precision grinding business.
The Adcole measuring machine is much more accurate than other (Doctoring) methods used. In some cases by an order of magnitude. I wish that more folks could actually see how stuff is done in the real world, and not just look at numbers without knowing the accuarcy of the measuring equipment.
"Designing" an engine with a DCR calculated to two or three decimal places, and being concerned about the 2nd or 3rd digit makes me shake my head. Hell, most folks can't measure the total clearance volume and swept volume in an actual engine close enough to get an accurate SCR to the 2nd decimal place. eg: .001 longer crank throw in a 350 V8 which gives a .002 longer stroke, changes SCR about .03 if nothing else changes. How many of us accurately measure all 8 cylinder strokes to .001 or less?
My point is try not to get lost in squashinf pissants and miss the 800 lb gorillas.
End of my rant.
I'm not gonna argue nor disagree with anything you just said. In fact, maybe I shouldn't of gave a crap about the extra 2 degrees. But quite frankly, I don't settle for mediocre. I realize perfection can't be achieved but I like to strive for it. I've always prided myself in the various motorsports hobbies I have had over the years that my "attention to detail" has tended to give me an "edge" when up against somebody else with similar or sometimes even sometimes more agressive mods. It's like when my friends told me, "Buy your own tuning software and do it yourself because you're just that **** ****** who tears into his motorcycle's carburators in the middle of the hotel parking lot because you didn't like the way the power came on when getting on the throttle exiting the corners at Deal's Gap." They are right, most would have just accepted it and rode on, I fixed the jetting and better enjoyed the next day's riding. Maybe I have a mental Disorder, or maybe it's just the high standard I hold for myself and the people I do business with. But one things for sure, I ordered an ICL of 112....and that's what I expected.
Hammer
01-19-2007, 01:02 PM
#56
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Originally Posted by edcmat-l1
Classic line. To the point..... Wraps up 3 pages of thread in a one liner.
Hammer
01-19-2007, 02:55 PM
#57
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Originally Posted by thehammer69
But one things for sure, I ordered an ICL of 112....and that's what I expected.
Hammer
Hammer I certainly hope a whole lot of design/simulation, etc. went into choosing the optimum lobes and events for your total engine/rpm/vehicle/driving combination. That's the 800 pound gorilla who isn't all that easy to control, but who prevails in the real world.
Figuring out what we want is fairly easy..the challenge is to figure out what the engine wants. Carried to the (Nextel Cup) extreme, it is what each individual cylinder wants to perform optimally that separates the merely **** engine designer/builder from the terminally **** builder.
Good luck with your build!
