which cam is best for the predator

[TheDullCarbide]

Lol! You think Dave needs a moron like you to stand up for him? Get off the man's dick you little suck-up. I'm sure Dave's been called worse over his many, many years...lol! I have plenty of respect for him and others on this forum, but you deserve none. You're just a know nothing hater trolling the site.
Thanks for the legit responses from Ole, Danford and TheDullCarbide. Once again, I got lost in Ole's technical jargon, but now have a little better understanding of LSA. I agree the Mamba JR is one hell of a cam and that the stock compression is too low for any real fun. But if doing a billet connecting rod anyway, I would get the .020 longer rod and ditch the thick fiber head gasket,(Hemi) for a nice little bump in compression. But to a guy just building and tinkering with their motors for the first time, a $30ish-$50ish cam may sound more doable than a $70-$100 cam, which is why I was sticking in that $50ish price range. I also believe the Mamba Jr might be a bit too much of a leap from stock for a novice/amateur, especially the $100 .310 lift custom grind where you will probably have to clearance the block. Some guys prefer baby steps and or just might not need that much cam. My Mamba JR motor is a beast! Almost violent in the bottom end...

Thanks Dan, glad I could give useful information. There's a first for everything...

About the long rod and thin gasket, I've had everybody almost yelling at me to keep at least a 0.030" piston to head clearance. I'm going to heed their warning but I have no experience to tell you what to do...just sayin'.

Wonder if anybody's played with a squish-band setup. It'd probably make sense to do it on a Hemi.:shrug:

 

[Daniel Coop]

About the long rod and thin gasket, I've had everybody almost yelling at me to keep at least a 0.030" piston to head clearance. I'm going to heed their warning but I have no experience to tell you what to do...just sayin'.

Really? Who and why? I thought the long rod and thin gasket was for beginners... I always try to run as close to zero deck as possible and run milled heads with shorter pushrods on all my motors with no issues. I don't personally own a single motor with a stock length rod.

 

[TheDullCarbide]

About the long rod and thin gasket, I've had everybody almost yelling at me to keep at least a 0.030" piston to head clearance. I'm going to heed their warning but I have no experience to tell you what to do...just sayin'.

Really? Who and why? I thought the long rod and thin gasket was for beginners... I always try to run as close to zero deck as possible and run milled heads with shorter pushrods on all my motors with no issues. I don't personally own a single motor with a stock length rod.

I'll look back in my threads. I want to run close to zero deck but a +0.020" rod gets me to 0.015"-0.010" below but that's enough for me. The long rod plus a 0.027" MLS gasket keeps me well in the so called "safe zone" and I can always tear a layer off the gasket.

It makes sense to keep some clearance as the rod, piston, crank, etc. all stretches at high rpm. 0.030" sounded a little overkill to me but I'm used to GY6s and my 2-stroke snowmobile. Both of those engines have needle crank bearings and the snowmobile also has a needle wrist bearing. The snowmobile also is designed to have zero piston to head clearance (in the squish band) close to redline. So are the engines different? Hell yeah! But do you really need 0.030"? IDK yet but I ain't pushing it on my first build.

 

[ole4]

What does zero deck and milled heads have to do with piston to head? You can run zero deck then you need a .030 gasket at least. If you don't your piston will hit the head where the squish is supposed to be. It is all controlled by the head gasket thickness and how much in the hole you are.

 

[TheDullCarbide]

I found one post from CarPlayLB:

We all missed the larger point here. You claim to be a beginning builder, yet you are absolute in getting the .020 rod. Will you be milling the piston to achieve the .030" head to piston clearance? Or will you run the .040" head gasket? have you measured how far the piston is in the hole now?



I'm aware that milling a head doesn't result in a closer piston to head clearance. I assume these engines have no squish when they are stock or even with a long rod and flat-top piston. The inside of the head doesn't match the piston crown at all like a 2-stroke.

I started a new thread to continue the conversation.

 

[Daniel Coop]

Squish is the amount of room the piston has to squish before hitting the next hard item.
Then there is quench..... That is the room available before hitting.
Engines like tight quench and high compression to make power.
I always run zero or .005 below with a .009 gasket and haven't hit the head yet.
I dont buy into the .030 theory.
Im sure it is engine building 101 or something but they sure seem to like zero and a nice thin gasket.

 

[David wulf]

Squish is the amount of room the piston has to squish before hitting the next hard item.
Then there is quench..... That is the room available before hitting.
Engines like tight quench and high compression to make power.
I always run zero or .005 below with a .009 gasket and haven't hit the head yet.
I dont buy into the .030 theory.
Im sure it is engine building 101 or something but they sure seem to like zero and a nice thin gasket.

What RPM's are you turning ? With around .014 clearance I wouldn't go much past 6000 maybe . All my motors run up past 9 k and have lift from 308 to 370 and I fun atleast 25 thou piston to head .
Speaking of clearance what piston to valve do you run in your motors ? I worry more of that than I do the piston to head .

 

[ole4]

Squish and Quench are the same.

Squish band or Quench is the area between the flat of the piston and the flat of the cylinder head at TDC. It is generally accepted that .032”(.8mm) is the minimum safe piston to cyl head clearance. It is also generally accepted that when the piston to cyl head clearance exceeds .060”(1.5mm) the squish effect is severely diminished. Some side effects of too high of a quench area consist of increased heat, and increased risk of detonation.

 

[San Diego]

Here's some great cam info from a few years back by Russell at NR Racing:


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 opening 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.

NR RACING THE LEADER IN HONDA GX & CLONE PERFORMANCE

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

The key to making power with a Honda head is mild porting, smoothing out the short side radius, blending the bowl, and shortening the valve guides by .100". Together these will yield about 60% better flow than stock. Trying to remove any material (i.e. making the port larger) tends to hurt performance and there is really not enough aluminum to do so. In fact raising the floor of the port improves flow quite a bit. Honda ports (esp. the exhaust) are intentionally oversized to promote cooling. The ports should also be left rough since this creates a boundary layer that improves flow. Best is too sand blast the ports after porting/smoothing. This type of surface will flow much better than a polished surface, plus it helps fuel atomization. The exhaust is not so critical since carbon buildup creates a rough surface on its own.

A good three-angle valve job will allow up to 15% improvement in flow on a GX160/200 head. Unless running huge Mikunis or Tilly’s and turning 7000+ rpm, the stock valve sizes work very well and are capable of making up to 16+ hp. Stainless valves do flow a bit better than stock stuff. For high RPM operation (with big carbs & cams) the 27.5 mm intake valve will help and will allow 20 hp. We have tested 28.5 & larger valves but have not seen any improvement. In fact, we have seen power decreases on the dyno using these. The exhaust valve size should be left alone as it is too big to begin with. A few years ago we installed a smaller seat along a 120 intake valve in a GX160 exhaust port. The motor showed improvement, esp. on the low end.

It is important to know that actual flow through the head is also a function of valve lift. Needless to say, the more lift, the more flow. (Note: higher lifts can decrease velocity, which in turn decreases torque). For the most part, GX200s show improvement as lift is increased. However, on the flow bench a GX160 race head (big valve, ported, milled) does not show any additional flow after about .350 lift. Dyno testing combos above .350 lift (i.e. .400 lift) has shown only minimal high RPM improvement usually at great losses at the low end. Also, the Honda valve train does not do well with a lot of lift. There are a lot of geometry issues that one must address. In fact 1.3 rockers should be avoided as they really play havoc on the geometry. We have seen many failures from using 1.3 rockers with big cams. You can get them to work, but custom valves, spring pocket, and other head work is needed. Stock with stock or 1.2 ratios if possible.

The best combinations for max power tend to be big duration cams (~260 at .050) at .330 to .350 lift. Cam with .280 to .290 lift using 1.2 rockers or .308 cams with 1.1 rockers tend to work the best. However for most applications (i.e. all around performance), a .270 to .280 lift 220 to 230 duration cam combined with 1.1 or 1.2 rockers will be the best set-up. Cam timing is also critical…..

Some head info too:


18cc vs 14cc Heads...The chamber (on both styles) are bowl shaped. As you mill the head it removes part of the chamber and actually unshrouds the valves. A 18cc head milled .080" has much better flow potential than an unmilled head. I say potential because edge treatment can effect the flow. (i.e. round off the edges). We have a digital SuperFlow flow bench and have flowed 100's of heads in all kinds of different configurations with every type of porting one can imagine. We have backed up a lot of this with dyno testing (which does not always agree with the flow bench). In the end, unless major work is done to the chamber, the 18cc heads will always outflow the 14cc.

The only advantage to a 14cc head is that compression can be increased to around 10.3 to 1 by just bolting on ahead. You need to mill a 18cc head .050" to achieve that. However, a .050" 18cc head can make more power than an un-milled 14 cc head....Thanks Russ.......

Some additional comments after asked questions about the above statements:


I would like to add a few comments to what was previously written.

1) While we still recommend 1.2s, the rocker arm geometry issues with 1.3 rockers have been addressed with changes to valve & push rod length, improvements in springs, and better rocker arm designs. Care and correct part selection is still needed to prevent binding and misalignment, plus the higher ratios will put increased stress on the valve train. As a side note, 1.3s do not work well with 18lb springs because of potential coil bind

2) We do see some improvement using 1.3 rockers on large duration (260) cams with 106 or greater ICLs. However, the increased stress on the valve train does not always justify the increase in power. On .274 lift cams it is usually not an issue, but on high lift cams it becomes an issue.

3) On small duration cams and cams having lots of advance (102 ICL), the 1.3s usually do not make any improvement.

4) My comments regarding the 350 lift maximum are simply that unless major modifications have been made to the intake tract system (ports, carb, valve size, etc.), the is not a lot of power to be gained beyond .350 lift. And as it creates a nightmare of valve train geometry problems and tends to cause failures, why do it? We sell a .356 and a .410 lift cam for those who do not believe me, but our testing has shown a 274 cam with 1.3 rockers will make as much or more power than any other cam we have tested (not a sales pitch, just observations)

5) In addition to the valve train geometry issues, high lift cams require increased spring pressure which can cause cam breakage. The cam is a weak link in the engine due to the way it is held at each end without any support. Honda did not design this engine for stiff valve springs. Use of high rate springs or valve float (from weak springs) will cause the cam to snap in half. The only way to eliminate the problem is with a billet cam, but that eliminates the ability to start using a recoil. The problem has been somewhat reduced in the last few years as we switched from using Honda cores to using clone cores. The Hondas are harder and more brittle and therefore more likely to break. The clone cores are softer and will flex. Unfortunately, the flexing can cause other problems and they still break (just not as much). Even on the billet cams, we have seen the bosses snap. Most of the time, the failed engine had either dual springs, or were running 8000 rpm with 26lb springs (and floating the valves). We rarely see a problem with single springs in the 35 to 40lb range and max rpms in the 7500 range.

6) Lastly, there is no perfect cam. Because a cam determines when, how long, and how much power is applied, every application will be different. What works on one track, will not work on another. What works for one driver, will not work for another, etc. Not to mention, races are not won on dynos (especially short tracks which tend to be won getting off the corners).

Also a quick comment regarding 14cc heads. They should not be used, period! They don’t flow well and nor do they promote good flame travel. Years ago, before we had long rods and flat-tops, they were an easy & cheap way to get compression up. However, now with the selection of correct parts and a little milling, it is easy to get above 13.1 using the stock head. The stock head is far superior in flow and chamber design to the 14cc head.

Even better is the 18cc Honda head. The great thing about the 18cc head is the price has come way down on these. Our 18cc heads are actually cheaper than the 14cc clone heads, use bigger valves, and flow a whole lot better. Okay, this is a sales pitch

Another issue we constantly see with 14cc heads, is the final compression ratio. At least once a week someone orders a 14cc head milled .050, usually with a flat-top and .020 longer rods. I guess there are a lot of diesel conversions in karting. We also get a lot of tech questions regarding motors that will not run right, have blown head gaskets, destroyed cranks, and split blocks. Ninety percent of the time it turns out to be excessively high compression ratios, and yes, there is usually a 14cc head involved.

 

[David wulf]

Squish and Quench are the same.

Squish band or Quench is the area between the flat of the piston and the flat of the cylinder head at TDC. It is generally accepted that .032”(.8mm) is the minimum safe piston to cyl head clearance. It is also generally accepted that when the piston to cyl head clearance exceeds .060”(1.5mm) the squish effect is severely diminished. Some side effects of too high of a quench area consist of increased heat, and increased risk of detonation.

Thanks I just learned what squish and quench was .

 

[ole4]

There are a few mistakes there narrow lsa builds more compression as intake Valve closes sooner. Now you can compensate with changing ICL but wide 114 for ex builds less dynamic compression than tight 104 lsa In addition he says overlap is needed to bleed off compression but overlap is at TDC on exhaust stroke. The intake closing later bleeds off compression

From the NR data above. The info I posted about lsa wide and narrow is correct. I think he may have just mixed up tight and wider..

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.

 

[Daniel Coop]

What RPM's are you turning ? With around .014 clearance I wouldn't go much past 6000 maybe . All my motors run up past 9 k and have lift from 308 to 370 and I fun atleast 25 thou piston to head .
Speaking of clearance what piston to valve do you run in your motors ? I worry more of that than I do the piston to head .

My Mamba JR motor is running 1.3 ratio rockers for a total of 357ish lift. It is a Hemi block with .020 over rod and was about .006 below deck when I bolted on the .070 milled and ported 27/25mm stainless valve clone head with the thin gasket. My latest build was similar except only .002 below deck & with 308 lift cam. I have a BSP short block from NR with the optional flat top piston and is .015 below deck and I just ordered a .010 longer rod to get closer to zero deck. I've run similar setups with smaller cams too.
I've yet to mount a tach on any bike so I can only speculate what RPM I'm running based on the cams max target RPM, but I'm full throttle 95% of the time.
I am an amateur and cheat a little...Dan at Childish Concepts Racing does all my head and any needed machine work. I build the bottom ends with minimal equipment and only feeler guages, straight edges, Plasti-gauge and a basic digital micrometer as my only measuring tools, so I don't know what my valve to piston clearance is but I have only made contact with an occasional spark plug electrode closing the gap and cutting off spark. I haven't studied much in engine theory, outside of hours of conversation with Dan. He's taught me a lot and we've built a good personal and working relationship. I just got back a box of 4 heads I had sent him.

 

[ole4]

Daniel if you have a dial caliper you can use thin Rosen core solder thru spark plug hole and place it in the squish area turn over engine so piston compresses solder and measure the flattened solder and you can measure actual squish. Also if you increase piston skirt clearance there is more piston rock which can decrease your piston to head clearance.

 

[TheDullCarbide]

Here's some great cam info from a few years back by Russell at NR Racing:


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 opening 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.

NR RACING THE LEADER IN HONDA GX & CLONE PERFORMANCE

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

The key to making power with a Honda head is mild porting, smoothing out the short side radius, blending the bowl, and shortening the valve guides by .100". Together these will yield about 60% better flow than stock. Trying to remove any material (i.e. making the port larger) tends to hurt performance and there is really not enough aluminum to do so. In fact raising the floor of the port improves flow quite a bit. Honda ports (esp. the exhaust) are intentionally oversized to promote cooling. The ports should also be left rough since this creates a boundary layer that improves flow. Best is too sand blast the ports after porting/smoothing. This type of surface will flow much better than a polished surface, plus it helps fuel atomization. The exhaust is not so critical since carbon buildup creates a rough surface on its own.

A good three-angle valve job will allow up to 15% improvement in flow on a GX160/200 head. Unless running huge Mikunis or Tilly’s and turning 7000+ rpm, the stock valve sizes work very well and are capable of making up to 16+ hp. Stainless valves do flow a bit better than stock stuff. For high RPM operation (with big carbs & cams) the 27.5 mm intake valve will help and will allow 20 hp. We have tested 28.5 & larger valves but have not seen any improvement. In fact, we have seen power decreases on the dyno using these. The exhaust valve size should be left alone as it is too big to begin with. A few years ago we installed a smaller seat along a 120 intake valve in a GX160 exhaust port. The motor showed improvement, esp. on the low end.

It is important to know that actual flow through the head is also a function of valve lift. Needless to say, the more lift, the more flow. (Note: higher lifts can decrease velocity, which in turn decreases torque). For the most part, GX200s show improvement as lift is increased. However, on the flow bench a GX160 race head (big valve, ported, milled) does not show any additional flow after about .350 lift. Dyno testing combos above .350 lift (i.e. .400 lift) has shown only minimal high RPM improvement usually at great losses at the low end. Also, the Honda valve train does not do well with a lot of lift. There are a lot of geometry issues that one must address. In fact 1.3 rockers should be avoided as they really play havoc on the geometry. We have seen many failures from using 1.3 rockers with big cams. You can get them to work, but custom valves, spring pocket, and other head work is needed. Stock with stock or 1.2 ratios if possible.

The best combinations for max power tend to be big duration cams (~260 at .050) at .330 to .350 lift. Cam with .280 to .290 lift using 1.2 rockers or .308 cams with 1.1 rockers tend to work the best. However for most applications (i.e. all around performance), a .270 to .280 lift 220 to 230 duration cam combined with 1.1 or 1.2 rockers will be the best set-up. Cam timing is also critical…..

Some head info too:


18cc vs 14cc Heads...The chamber (on both styles) are bowl shaped. As you mill the head it removes part of the chamber and actually unshrouds the valves. A 18cc head milled .080" has much better flow potential than an unmilled head. I say potential because edge treatment can effect the flow. (i.e. round off the edges). We have a digital SuperFlow flow bench and have flowed 100's of heads in all kinds of different configurations with every type of porting one can imagine. We have backed up a lot of this with dyno testing (which does not always agree with the flow bench). In the end, unless major work is done to the chamber, the 18cc heads will always outflow the 14cc.

The only advantage to a 14cc head is that compression can be increased to around 10.3 to 1 by just bolting on ahead. You need to mill a 18cc head .050" to achieve that. However, a .050" 18cc head can make more power than an un-milled 14 cc head....Thanks Russ.......

Some additional comments after asked questions about the above statements:


I would like to add a few comments to what was previously written.

1) While we still recommend 1.2s, the rocker arm geometry issues with 1.3 rockers have been addressed with changes to valve & push rod length, improvements in springs, and better rocker arm designs. Care and correct part selection is still needed to prevent binding and misalignment, plus the higher ratios will put increased stress on the valve train. As a side note, 1.3s do not work well with 18lb springs because of potential coil bind

2) We do see some improvement using 1.3 rockers on large duration (260) cams with 106 or greater ICLs. However, the increased stress on the valve train does not always justify the increase in power. On .274 lift cams it is usually not an issue, but on high lift cams it becomes an issue.

3) On small duration cams and cams having lots of advance (102 ICL), the 1.3s usually do not make any improvement.

4) My comments regarding the 350 lift maximum are simply that unless major modifications have been made to the intake tract system (ports, carb, valve size, etc.), the is not a lot of power to be gained beyond .350 lift. And as it creates a nightmare of valve train geometry problems and tends to cause failures, why do it? We sell a .356 and a .410 lift cam for those who do not believe me, but our testing has shown a 274 cam with 1.3 rockers will make as much or more power than any other cam we have tested (not a sales pitch, just observations)

5) In addition to the valve train geometry issues, high lift cams require increased spring pressure which can cause cam breakage. The cam is a weak link in the engine due to the way it is held at each end without any support. Honda did not design this engine for stiff valve springs. Use of high rate springs or valve float (from weak springs) will cause the cam to snap in half. The only way to eliminate the problem is with a billet cam, but that eliminates the ability to start using a recoil. The problem has been somewhat reduced in the last few years as we switched from using Honda cores to using clone cores. The Hondas are harder and more brittle and therefore more likely to break. The clone cores are softer and will flex. Unfortunately, the flexing can cause other problems and they still break (just not as much). Even on the billet cams, we have seen the bosses snap. Most of the time, the failed engine had either dual springs, or were running 8000 rpm with 26lb springs (and floating the valves). We rarely see a problem with single springs in the 35 to 40lb range and max rpms in the 7500 range.

6) Lastly, there is no perfect cam. Because a cam determines when, how long, and how much power is applied, every application will be different. What works on one track, will not work on another. What works for one driver, will not work for another, etc. Not to mention, races are not won on dynos (especially short tracks which tend to be won getting off the corners).

Also a quick comment regarding 14cc heads. They should not be used, period! They don’t flow well and nor do they promote good flame travel. Years ago, before we had long rods and flat-tops, they were an easy & cheap way to get compression up. However, now with the selection of correct parts and a little milling, it is easy to get above 13.1 using the stock head. The stock head is far superior in flow and chamber design to the 14cc head.

Even better is the 18cc Honda head. The great thing about the 18cc head is the price has come way down on these. Our 18cc heads are actually cheaper than the 14cc clone heads, use bigger valves, and flow a whole lot better. Okay, this is a sales pitch

Another issue we constantly see with 14cc heads, is the final compression ratio. At least once a week someone orders a 14cc head milled .050, usually with a flat-top and .020 longer rods. I guess there are a lot of diesel conversions in karting. We also get a lot of tech questions regarding motors that will not run right, have blown head gaskets, destroyed cranks, and split blocks. Ninety percent of the time it turns out to be excessively high compression ratios, and yes, there is usually a 14cc head involved.

Oh my God that is some awesome stuff right there!:thumbsup: That article answers 1/2 of the questions in this subforum. I need to make this into a poster for my wall! Somebody please sticky!

 

[San Diego]

Yeah, I thought it had a lot of nuggets of wisdom, in helping to understand why one cam performs differently from another. Makes selecting an appropriate cam for your needs a lot easier.

 

[San Diego]

I won't even pretend to act like I understand cam technology enough to tell you how a cam with less lift and duration seems to pull the same as one with more of both, but it does. It seems to be a smoother more consistent powerband across the entire RPM range. They are quite similar in performance somehow and have the same max target RPM and both recommend the use of larger carbs. I couldn't honestly tell you that one was better than the other.

Russell at NR's info sort of answers why the CL-220 would have a wider powerband, since it has a 105 ICL on the intake & 111 on the exhaust, while the CM has a 108 ICL on both. It is set up to have a wider range, regardless of the lift & duration differences.

 

[stargazer7467]

Ive used the Black Mamba Jr low end torque cam and also the Black Mamba Sr with great results, 275 lift cams. I just installed a dyno cams 308 cam this evening and have yet to see how it rides...

 

[Daniel Coop]

I recently swapped out a CS grind cam for the 308 in one of my 212's myself. That's a nice cam... It too, has the same twin 108 ICL's as the CM grind cam but a little more duration, and a lot more lift. Although I don't have personal experience with the Mamba SR, the 308 should have a little more top end. I'm digging the 308 so far. It's got a pretty wide power band and is easy on the valve train. Im now upgrading to a GX390 carb, because my bored stock carb is now reaching it's limits. I'm considering swapping out my JR for a SR, in another 212 because it runs out of steam a little sooner than I'd prefer, but I'm torn because I love the brute torque of the JR. I've cheated with billet 1.3 ratio rockers from the beginning, so I don't know what the cam was intended to feel like, but with those rockers, the SR could be even more potent than the 308, with around .357 lift and about the same duration.

 

[TheDullCarbide]

I recently swapped out a CS grind cam for the 308 in one of my 212's myself. That's a nice cam... It too, has the same twin 108 ICL's as the CM grind cam but a little more duration, and a lot more lift. Although I don't have personal experience with the Mamba SR, the 308 should have a little more top end. I'm digging the 308 so far. It's got a pretty wide power band and is easy on the valve train. Im now upgrading to a GX390 carb, because my bored stock carb is now reaching it's limits. I'm considering swapping out my JR for a SR, in another 212 because it runs out of steam a little sooner than I'd prefer, but I'm torn because I love the brute torque of the JR. I've cheated with billet 1.3 ratio rockers from the beginning, so I don't know what the cam was intended to feel like, but with those rockers, the SR could be even more potent than the 308, with around .357 lift and about the same duration.

Shame you can't get the original Black Mamba...

 

[Daniel Coop]

Shame you can't get the original Black Mamba...

Sure I can... I know a guy who knows a guy.