Denny
Canned Monster
Eth is good! Well, not as bad. 
212 Hemi restoration.
- Thread starter Rat
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bob58o
SuckSqueezeBangBlow
Dynamic compression ratio is a more accurate way to understand the pressure in the combustion chamber vs Static Compression Ratio. Camshaft specs along with SCR give DCR. The earlier the intake valve closes, the more dynamic compression. I can imagine more overlap reducing dynamic compression ratio if port design is not optimized for perfect scavenging.
I like the way NR advertises cams. Cams built for TQ (early intake closing) will have a higher DCR and will require a “lower” SCR or higher octane. Cams built to scream (late intake closing) will have a lower Dynamic CR and thus require a “higher” STC.
DCR calculators are a bit more tricky because you need to know cam timing events and it’s not always clear if they want 0.050” or seat timing.
For example the cam with a 102 ICL requires a certain SCR or LESS. The cam with 106 ICL requires a certain SCR or more. A SCR of 10.5:1 to 11:1 works for both cams in this example and both are listed as “torque” cams.
I don’t know the true specs on stock style cams, but the CL1 has ICL of 108.5, so I’m assuming pump gas is fine even with 11.5:1 STC.
I like the way NR advertises cams. Cams built for TQ (early intake closing) will have a higher DCR and will require a “lower” SCR or higher octane. Cams built to scream (late intake closing) will have a lower Dynamic CR and thus require a “higher” STC.
DCR calculators are a bit more tricky because you need to know cam timing events and it’s not always clear if they want 0.050” or seat timing.
For example the cam with a 102 ICL requires a certain SCR or LESS. The cam with 106 ICL requires a certain SCR or more. A SCR of 10.5:1 to 11:1 works for both cams in this example and both are listed as “torque” cams.
I don’t know the true specs on stock style cams, but the CL1 has ICL of 108.5, so I’m assuming pump gas is fine even with 11.5:1 STC.
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BrownStainRacing
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DCR should be the #1 most important calculation for any engine build.
Here's a SCR calculator with DCR in advance mode.
www.omnicalculator.com
Heres a cam degree calculator.
It'll show you how 2 cams with very similar specs will act totally different in the same engine.
IVC is the most important out of the 4 valve events, but retarding or advancing a cam will change ALL 4 events.
NRRacing makes some very strong cams, they have ALOT of advance built in. That's no big secret, auto cam makers have been doing it for yrs and yrs. It's a crutch, used when the builder picked too big of a cam.
There is absolutely nothing wrong with either of those 220* NRRacing cams. They are both great for moving weight, fast. We call the 0211 cam the "Fat Boyz cam". It works exactly the way it was designed for.
I'd rather use a smaller single pattern cam, with less LSA and no advance or retard built in the cam.
Isky is the only cam grinder to put the clone style cams on a 104* LSA.
Compare the isky custom .260"/ 220*/ 104 lsa cam with the NRRacing 220* and you can see how the 4 valve events are being changed.
Here's a SCR calculator with DCR in advance mode.
Compression Ratio Calculator (Static and Dynamic)
The compression ratio calculator finds both the static and the dynamic compression ratio of your combustion engine.
www.omnicalculator.com
Heres a cam degree calculator.
It'll show you how 2 cams with very similar specs will act totally different in the same engine.
Wallace Racing - Cam Degree Calculator
www.wallaceracing.com
IVC is the most important out of the 4 valve events, but retarding or advancing a cam will change ALL 4 events.
NRRacing makes some very strong cams, they have ALOT of advance built in. That's no big secret, auto cam makers have been doing it for yrs and yrs. It's a crutch, used when the builder picked too big of a cam.
There is absolutely nothing wrong with either of those 220* NRRacing cams. They are both great for moving weight, fast. We call the 0211 cam the "Fat Boyz cam". It works exactly the way it was designed for.
I'd rather use a smaller single pattern cam, with less LSA and no advance or retard built in the cam.
Isky is the only cam grinder to put the clone style cams on a 104* LSA.
Compare the isky custom .260"/ 220*/ 104 lsa cam with the NRRacing 220* and you can see how the 4 valve events are being changed.
Wallace Racing - Cam Degree Calculator
www.wallaceracing.com
Rat
Well-known member
That's actually the SCR I used, totally missed the advanced settings... I have my cam specs from Dover as well despite it being a RevPro cam.DCR should be the #1 most important calculation for any engine build.
Here's a SCR calculator with DCR in advance mode.
Compression Ratio Calculator (Static and Dynamic)
The compression ratio calculator finds both the static and the dynamic compression ratio of your combustion engine.
Heres a cam degree calculator.
It'll show you how 2 cams with very similar specs will act totally different in the same engine.
Wallace Racing - Cam Degree Calculator
www.wallaceracing.com
IVC is the most important out of the 4 valve events, but retarding or advancing a cam will change ALL 4 events.
NRRacing makes some very strong cams, they have ALOT of advance built in. That's no big secret, auto cam makers have been doing it for yrs and yrs. It's a crutch, used when the builder picked too big of a cam.
There is absolutely nothing wrong with either of those 220* NRRacing cams. They are both great for moving weight, fast. We call the 0211 cam the "Fat Boyz cam". It works exactly the way it was designed for.
I'd rather use a smaller single pattern cam, with less LSA and no advance or retard built in the cam.
Isky is the only cam grinder to put the clone style cams on a 104* LSA.
Compare the isky custom .260"/ 220*/ 104 lsa cam with the NRRacing 220* and you can see how the 4 valve events are being changed.
Wallace Racing - Cam Degree Calculator
www.wallaceracing.com
bob58o
SuckSqueezeBangBlow
The thing I don’t understand about the way small engine cams advertises their custom cams is the LSA.
It says 104 LSA for max torque.
108 best all around
110 for top end.
This would make sense to me if it were ICL, but it says LSA.
I’ve thought that less LSA would increase overlap. I thought more overlap would be better for top end, not torque.
in my mind, more overlap would bleed off compression at low rpm. The overlap would be useful at higher RPM when scavenging helps.
I’ve tried to understand this. I’ve had many agree with me and thought it was a typo on the Isky site. It doesn’t give you a choice for ICL with their custom cams, and Centerline and duration would give you intake closing.
It says 104 LSA for max torque.
108 best all around
110 for top end.
This would make sense to me if it were ICL, but it says LSA.
I’ve thought that less LSA would increase overlap. I thought more overlap would be better for top end, not torque.
in my mind, more overlap would bleed off compression at low rpm. The overlap would be useful at higher RPM when scavenging helps.
I’ve tried to understand this. I’ve had many agree with me and thought it was a typo on the Isky site. It doesn’t give you a choice for ICL with their custom cams, and Centerline and duration would give you intake closing.
Rat
Well-known member
With the 76° intake closing I get 8.6 dynamic assuming the head is 18cc like I believe it to be, since all I did was swap the dished piston for a flattop it follows with the factory spec of 8.5:1 that the head IS IN FACT 18cc.
If I can get a 14cc head to toss on it, that looks to jump the CR all the way up to 10.8:1
Cam Specs
Intake
Open 30 Close 76
Lift 234
CL 112
Duration @ 050 > 220
Exhaust
Open 67 close 42
Lift 240
CL 105
Duration @ 050 > 223
If I can get a 14cc head to toss on it, that looks to jump the CR all the way up to 10.8:1
Cam Specs
Intake
Open 30 Close 76
Lift 234
CL 112
Duration @ 050 > 220
Exhaust
Open 67 close 42
Lift 240
CL 105
Duration @ 050 > 223
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BrownStainRacing
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Isky cams are single pattern cams.
Straight up, is a cam with 104* lsa, will be 104* icl and 104* ecl.
108* lsa, is 108* icl and 108* ecl.
110* lsa is 110 icl, 110 ecl.
It's easier if you look at automotive cams, they will give you more specs.
Advertised duration (could be at .004" tappet lift or .006", depends on how the manufacturer is measuring it).
Subtract the duration .050" # from the advertised #, the cam with the smaller # will be a more aggressive, faster ramp camshaft.
ECCarbs has got the best cam cards for these clone style cams. They are very aggressive, fast ramped cams. They are not playing games when it comes to springs and head work.
I DONT recommend ANY Tennessee Thunderstick for a new builder.
For some reason, who knows why, some so called wanna be clone cam makers wanna keep things secret,
, I quess they try to hide the REAL truth about how and when power is made.My best guess is, so they can sell as many bs, useless, under powered, overpriced, pos cams they can until.......people wise up and start buying cams made for men.
Ed Iskederian
Harvey Crane
Sig Erson
Know more about cams then I will ever understand.
Davis Vizard knows a thing or 2 about how those lil bump sticks work too.
Look em up. You can only learn..... as much as you are willing to learn
Overlap is not a bad thing, but too much will kill power brakes.
I don't know too many karts or mini bike running power brakes.
, but who knows.I dont wanna get into the vacuum deal, as some body mentioned earlier, but they might be jus a tad bit MORE involved then jus "lack of pressure".
It might jus be about what's going on inside the combustion chamber causing that lack of pressure, when it should cause that lack of pressure, where that pressure should be pushed.... at a certain time.
Maybe and jus a wild guess..... valve timing???
BrownStainRacing
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The only 208's I have pulled the head off of was 20-22cc small valve heads, but they were old used worn out engines. Idk if they had the factory head on em or not.
My small genie is a 208, but I be damned if I'm pulling that head off for you to have a look see,
.I've never had the chance to take a NEW 208 apart. They on log splitters, water pumps and genies around here.
What numbers are you inputting in the CR calculator???
11.6 is high for jus adding a long rod and ft piston.
Don't believe that stock 8.5:1 crap. Only stock engines I seen that was 8.5+ was the 224 pred and ducar.
The 196 and 212 is only 7.7-8.3, that depends on the head and gasket.
Rat
Well-known member
LCT Husqvarna 208 Winter SpecThe only 208's I have pulled the head off of was 20-22cc small valve heads, but they were old used worn out engines. Idk if they had the factory head on em or not.
My small genie is a 208, but I be damned if I'm pulling that head off for you to have a look see,
I've never had the chance to take a NEW 208 apart. They on log splitters, water pumps and genies around here.
What numbers are you inputting in the CR calculator???
11.6 is high for jus adding a long rod and ft piston.
Don't believe that stock 8.5:1 crap. Only stock engines I seen that was 8.5+ was the 224 pred and ducar.
The 196 and 212 is only 7.7-8.3, that depends on the head and gasket.
27/25 valves w/5.5 stems
I dont run a head gasket at all currently because with clean, smooth, even surfaces, it don't need one if it's torqued properly.
It has proven to be an odd engine (in good ways) at every turn.
ReRead 10.6:1 is what the DCR would come up to with a 14cc head (not 11.6) not sure where you got 11.6 from.
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BrownStainRacing
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Here you say 11.5, sorry my bad on the 11.6.
bob58o
SuckSqueezeBangBlow
Ah Thank you.Isky cams are single pattern cams.
Straight up, is a cam with 104* lsa, will be 104* icl and 104* ecl.
108* lsa, is 108* icl and 108* ecl.
110* lsa is 110 icl, 110 ecl.
It's easier if you look at automotive cams, they will give you more specs.
Advertised duration (could be at .004" tappet lift or .006", depends on how the manufacturer is measuring it).
Subtract the duration .050" # from the advertised #, the cam with the smaller # will be a more aggressive, faster ramp camshaft.
ECCarbs has got the best cam cards for these clone style cams. They are very aggressive, fast ramped cams. They are not playing games when it comes to springs and head work.
I DONT recommend ANY Tennessee Thunderstick for a new builder.
For some reason, who knows why, some so called wanna be clone cam makers wanna keep things secret,
My best guess is, so they can sell as many bs, useless, under powered, overpriced, pos cams they can until.......people wise up and start buying cams made for men.
Ed Iskederian
Harvey Crane
Sig Erson
Know more about cams then I will ever understand.
Davis Vizard knows a thing or 2 about how those lil bump sticks work too.
Look em up. You can only learn..... as much as you are willing to learn
Overlap is not a bad thing, but too much will kill power brakes.
I don't know too many karts or mini bike running power brakes.
I dont wanna get into the vacuum deal, as some body mentioned earlier, but they might be jus a tad bit MORE involved then jus "lack of pressure".
It might jus be about what's going on inside the combustion chamber causing that lack of pressure, when it should cause that lack of pressure, where that pressure should be pushed.... at a certain time.
Maybe and jus a wild guess..... valve timing???
bob58o
SuckSqueezeBangBlow
Since this turned into a camshaft discussion… lol…
I stole this post from Bob’s 4 cycle, where it was stolen from somewhere else and supposedly gives a somewhat simple explanation of Russel’s (from NR) approach to cams.
For purposes of making “secrets” public…
There are four important numbers on a cam. ICL (intake center line), LS (lobe separation), duration, and lift.
Don’t worry too much about lift. The Honda head (i.e. port design) does not respond much once the lift at the valve exceeds about .350. A .275 lift cam with 1.3 rockers will achieve this. We have spent a lot of time on the flow bench, and unless the head is radically changed you will not see much gain past .350 lift.
Duration is another story. This is how long the valve is kept open. Hondas love lots of duration. We have run as much as 300 at .050, but 260 seems to be a good compromise better power and tractability. As duration goes up, so does the rpm at which max power is made. At the same time idle quality goes down along with low-end torque. An engine with a lot of duration will scream and make lots of power but can be a dog off the corners and/or trying to get started, not to mention idles at 3000 rpm.
Typically 210 to 220 makes for high torque motors that start and stop a lot, use low rpm stall/clutches, and see a wide range in operating rpm. These motors will peak somewhere between 4500 and 5500, and will pull to 6500.
250 to 260 are for the 7000+ motors that don’t see RPM much below 5000.
Needless to say, 230 to 240 cams fall in the middle.
One interesting thing about duration, the smaller the carb, the more duration can help a motor. With small carbs, usually the cam/ports will flow more than the carb can deliver. The only way to improve power is the hold the valve open longer. In other words, where going from a 240 to a 260 cam on a motor running a 28 mm Mikuni will only show a 10% improvement in peak HP, doing the same on a motor with a stock carb can show a 20% improvement.
Almost as critical as duration, is the ICL. This is the intake [center line] and will range from 98 to 116 degrees. It is also referred to retard or advance in the cam. This determines the where the peak torque will occur. Most cams fall in the 102 to 110 range. FYI: Honda 160s are around 105 and GX200s around 110 from the factory (retarded for emissions).
A cam with a 102 will have power range/peak around 1000 to 2000 rpm lower than a cam with 110 ICL. It will also have considerable more low-end torque and will pull a lot harder off the corners. For very, very small tracks this can translate into significantly lower lap times despite having lower HP. For Boats, winch boarding, rock climbing ATVs, these cams can make huge differences. Depending on the application, it is possible to stall a motor that has a high ICL, whereas advancing the cam produces great results.
At the other extreme, a cam with 114 ICL might peak in the 9000-rpm range. On a large track (1/2 mile) where the rpms never get below 7500, it would be unbeatable. However, you would need a clutch that engages at 5000+ just to get moving. Not always fun for a street toy.
The other important number is the LS (lob separation), which determines the amount of overlap. These will range from 100 to 115, but most cams will be in the 106 to 110 range. As a general rule the lower the number, the more HP, but the with a smaller power band. However, the wider (less overlap) the LS, the more dynamic compression a motor can build. For high compression engines, overlap is needed to bleed off compression at lower RPMs preventing detonation. Anything over 11 to 1 should be using a 106 to 107 LS. For lower compressions, it depends on how wide a power band is desired. If you want a power band of only a few 1000 rpm (typical for oval tracks), then go with a narrow LS, however if your rpm ranges from 2000 to 7000 (road courses), then you may want a wide LS.
The duration, ICL, and LS all work together and changing any or all of these numbers can have a significant impact on how a motor performs.
One final note, what works on the dyno does not always work on the track and vice versa. What works great in a Mini Bike may not be the best for a Kart, a dirt track cam is not going to be the same as a paved cam, etc, etc.
www.nr-racing.com
The part number of our cams tells the ICL and LS. The first number is the lift, the second set is the CL, and the last set is the LS. For example
280 0207 .280 lift 102 ICL 107 LS
252 0607 .252 lift 106 ICL 107 LS
252 0207 .252 lift 102 ICL 107 LS
252 0211 .252 lift 102 ICL 111 LS
274 0607 .274 lift 106 ICL 107 LS
I stole this post from Bob’s 4 cycle, where it was stolen from somewhere else and supposedly gives a somewhat simple explanation of Russel’s (from NR) approach to cams.
For purposes of making “secrets” public…
There are four important numbers on a cam. ICL (intake center line), LS (lobe separation), duration, and lift.
Don’t worry too much about lift. The Honda head (i.e. port design) does not respond much once the lift at the valve exceeds about .350. A .275 lift cam with 1.3 rockers will achieve this. We have spent a lot of time on the flow bench, and unless the head is radically changed you will not see much gain past .350 lift.
Duration is another story. This is how long the valve is kept open. Hondas love lots of duration. We have run as much as 300 at .050, but 260 seems to be a good compromise better power and tractability. As duration goes up, so does the rpm at which max power is made. At the same time idle quality goes down along with low-end torque. An engine with a lot of duration will scream and make lots of power but can be a dog off the corners and/or trying to get started, not to mention idles at 3000 rpm.
Typically 210 to 220 makes for high torque motors that start and stop a lot, use low rpm stall/clutches, and see a wide range in operating rpm. These motors will peak somewhere between 4500 and 5500, and will pull to 6500.
250 to 260 are for the 7000+ motors that don’t see RPM much below 5000.
Needless to say, 230 to 240 cams fall in the middle.
One interesting thing about duration, the smaller the carb, the more duration can help a motor. With small carbs, usually the cam/ports will flow more than the carb can deliver. The only way to improve power is the hold the valve open longer. In other words, where going from a 240 to a 260 cam on a motor running a 28 mm Mikuni will only show a 10% improvement in peak HP, doing the same on a motor with a stock carb can show a 20% improvement.
Almost as critical as duration, is the ICL. This is the intake [center line] and will range from 98 to 116 degrees. It is also referred to retard or advance in the cam. This determines the where the peak torque will occur. Most cams fall in the 102 to 110 range. FYI: Honda 160s are around 105 and GX200s around 110 from the factory (retarded for emissions).
A cam with a 102 will have power range/peak around 1000 to 2000 rpm lower than a cam with 110 ICL. It will also have considerable more low-end torque and will pull a lot harder off the corners. For very, very small tracks this can translate into significantly lower lap times despite having lower HP. For Boats, winch boarding, rock climbing ATVs, these cams can make huge differences. Depending on the application, it is possible to stall a motor that has a high ICL, whereas advancing the cam produces great results.
At the other extreme, a cam with 114 ICL might peak in the 9000-rpm range. On a large track (1/2 mile) where the rpms never get below 7500, it would be unbeatable. However, you would need a clutch that engages at 5000+ just to get moving. Not always fun for a street toy.
The other important number is the LS (lob separation), which determines the amount of overlap. These will range from 100 to 115, but most cams will be in the 106 to 110 range. As a general rule the lower the number, the more HP, but the with a smaller power band. However, the wider (less overlap) the LS, the more dynamic compression a motor can build. For high compression engines, overlap is needed to bleed off compression at lower RPMs preventing detonation. Anything over 11 to 1 should be using a 106 to 107 LS. For lower compressions, it depends on how wide a power band is desired. If you want a power band of only a few 1000 rpm (typical for oval tracks), then go with a narrow LS, however if your rpm ranges from 2000 to 7000 (road courses), then you may want a wide LS.
The duration, ICL, and LS all work together and changing any or all of these numbers can have a significant impact on how a motor performs.
One final note, what works on the dyno does not always work on the track and vice versa. What works great in a Mini Bike may not be the best for a Kart, a dirt track cam is not going to be the same as a paved cam, etc, etc.
www.nr-racing.com
The part number of our cams tells the ICL and LS. The first number is the lift, the second set is the CL, and the last set is the LS. For example
280 0207 .280 lift 102 ICL 107 LS
252 0607 .252 lift 106 ICL 107 LS
252 0207 .252 lift 102 ICL 107 LS
252 0211 .252 lift 102 ICL 111 LS
274 0607 .274 lift 106 ICL 107 LS
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BrownStainRacing
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bob58o
SuckSqueezeBangBlow
I changed “intake opening” to intake [centerline] in one spot when he was talking about ICL.
It seemed like an obvious simple mistake that tends to happen when the thought car outpaces the typing car.
Almost as critical as duration, is the ICL. This is the intake [center line] and will range from 98 to 116 degrees.
What the line on 4cycle is…
“Almost as critical as duration, is the ICL. This is the intake opening and will range from 98 to 116 degrees. “
This seems related to be the “bandaid” you mentioned for people who pick too large of cams and also the “NR advance” as well.
“Depending on the application, it is possible to stall a motor that has a high ICL, whereas advancing the cam produces great results.”
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Rat
Well-known member
Static comp, my bad too
BrownStainRacing
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I understand.
Those numbers become a jumbled mess....if you look at em too long.
Rat
Well-known member
Yep
I understand.
Those numbers become a jumbled mess....if you look at em too long.
Based on that recent post it seems I'd be smart and happier with the results not sticking a 14cc head on my 208 though.
As for the Hemi, I'm thinking I want to copycat my 208, drop an 18cc wedge on it but keep the stock cam in it