>>>>regarding semi hemi cut heads and compression and dual carbs. He(aircooled.net?) stated that
many racers were running the hemi heads and dual carbs with 6.8 / 6.9:1 compression. They were never able to fine tune the carbs regardless of what<<<
he is referring to street cars, not true race cars.
some of those people do not run enough timing for the semi-hemi cut, or there is something else wrong... and for every one that complains about low c.r., there are plenty who don't have any problems at all, including me... one thing is that carbs can be more difficult to jet when the air speed is lower because of the factory c.r...
>>>>detonation and increase the heat. But he replied that using a 110 cam like NQ is using increases the lift and duration to allow more cooling fuel into the chamber and the cam lobe overlap negated any difficulties encountered with higher cr-assuming all the tin and the flappers were in place and<<<<
what you are referring to is a pet theory of john connelly's, and it's shared by many... it's been argued to death on the clf... i don't see how a cam can modify the fuel/air ratio, so what you are referring to by "cooling fuel" may be a misnomer... more radical cams can only affect the total ingested charge, not the actual ratio, of fuel/air.
as i understand it, what john claims is that a radical cam will "bleed" off compression... actually putting more fuel/air mixture in the chamber can't cool anything, because it has to be burned... the more mixture there is, the more intense the flame will be, i.e., the denser the mixture the more heat it will generate... i don't see any way to get around that.
the only way to get cooling with the intake charge is to alter the fuel/air ratio, which is obviously the function of the carb/f.i...
just an fyi, the actual point at which gasoline burns most efficiently is around 17:1 c.r... that's when you get the most optimal energy(heat) from it.
radical cams work, but at the expense of blowing unburned fuel/air mixture out the exhaust pipe because of overlap... until the rpm's reach the point where flow reversal of the intake charge takes place, and all the fuel/air mixture stays in the combustion chamber... fuel/air mixture going out the tailpipe represents a power loss, therefore there is no loss of compression with a radical cam when it's "on"... assuming it was designed correctly, the cam wants the engine to see the maximum available intake charge.
it would be foolish to spend a fortune porting heads, only to lose unburned intake charge out the tailpipe because it was getting "bled off" by the cam.
at the point of flow reversal, there should be little or no unburned charge going out the exhaust pipe, so the motor will see, at the bare minimum, the same compression it would see with a stock cam.
i believe that is referred to as the mep, or mean effective pressure, of the cylinder... sort of a dynamic compression, if you will, that is very difficult to accurately calculate.
the other thing to remember about john connelly is that he lives at altitude, in utah... he must run higher c.r. than what i run here at the beach, just to make the same h.p. i do... that may have influenced his c.r. recommendations.
dan
oceanstreetvideo.com
cams vs. compression
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JohnConnolly
- Posts: 3336
- Joined: Thu Apr 13, 2000 12:01 am
cams vs. compression
anyone here ever take a course (or two) in Thermodynamics? The concept is SO simple, but unless you have taken it, you can't grasp what's involved, and it applies DIRECTLY to the Otto Engine, which includes the Aircooled flat 4.
I've been meaning to get around to writing an article to clear this topic up, and this post is the one that gets me off my @$$. I'll have it done within 2 weeks, and submit it to VWT for review and publication (it'll be good, so it will be published). Hopefully that will clarify a lot of the concepts; this topic is really mis-understood. Plain and simple, cam duration does affect the dynamic (NOT STATIC) compression that a running engine experiences, and is what really matters to the engine (static is only a starting point).
I've been meaning to get around to writing an article to clear this topic up, and this post is the one that gets me off my @$$. I'll have it done within 2 weeks, and submit it to VWT for review and publication (it'll be good, so it will be published). Hopefully that will clarify a lot of the concepts; this topic is really mis-understood. Plain and simple, cam duration does affect the dynamic (NOT STATIC) compression that a running engine experiences, and is what really matters to the engine (static is only a starting point).
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MASSIVE TYPE IV
- Posts: 20132
- Joined: Fri Jul 07, 2000 12:01 am
cams vs. compression
John is 100% correct...I may not be an engineer, but experience has proven to me that more duration will allow more CR, effectively...without higher temperatures.
The dynamic CR is something that is hard to know, I have a program that is really good for seeing into the depths of the engine, while we are configuring it..
A good rule of thumb is: The more CR, the more duration, but with that comes larger valves, bigger ports and more efficient induction system..
some cams set up in engines with low static CR, lead to crazy dynamic CR..WEB has a 111 grind we use in buggy engines, with most everything else stock, it is a mean and nasty animal, with high lift and almost no duration, anything over 7.5:1 will roast the heads...no matter what....But it makes wild power....The dynamic CR of this engine in my program is a whopping 8.7:1, becasue of the specs of the cam...
The dynamic CR is something that is hard to know, I have a program that is really good for seeing into the depths of the engine, while we are configuring it..
A good rule of thumb is: The more CR, the more duration, but with that comes larger valves, bigger ports and more efficient induction system..
some cams set up in engines with low static CR, lead to crazy dynamic CR..WEB has a 111 grind we use in buggy engines, with most everything else stock, it is a mean and nasty animal, with high lift and almost no duration, anything over 7.5:1 will roast the heads...no matter what....But it makes wild power....The dynamic CR of this engine in my program is a whopping 8.7:1, becasue of the specs of the cam...
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James2
- Posts: 3148
- Joined: Fri Mar 16, 2001 12:01 am
cams vs. compression
Wow, I agree with Dan and John.
First I agree with Dan, when says most people having problems with LOW CR motors are not running enough timing.
Second, I whole heartly agree with John, more cam + more CR =
And really it doesn't need any formulas or explaintions of static vs dydamic CR.
The proof is in the pudding Dan. It works. Run it and try it! I have and many others have also. Odd part is the car didn't over heat or self distruct.
First I agree with Dan, when says most people having problems with LOW CR motors are not running enough timing.
Second, I whole heartly agree with John, more cam + more CR =
And really it doesn't need any formulas or explaintions of static vs dydamic CR.
The proof is in the pudding Dan. It works. Run it and try it! I have and many others have also. Odd part is the car didn't over heat or self distruct.
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dan
cams vs. compression
>>>The proof is in the pudding Dan. It works. Run it and try it! I have and many others have also. Odd part is the car didn't over heat or self distruct.<<<<
so what it sounds like people are saying here is that the high c.r. i ran in past motors didn't work because there wasn't enuf cam... yes, it's true that those 2.1 litre motors had mild cams.
here is another take on the subject:
"Think of two engines that are identical except for their camshafts. The engine with the shorter-duration camshaft will typically have higher dynamic compression at low rpm because the intake valve closes earlier on the compression stroke. The engine with the longer-duration camshaft will have less dynamic compression because its intake valve closes later after the piston has traveled farther up the cylinder. On the other hand, if the long-duration camshaft does a better job of filling the cylinder at high rpm than the short-duration camshaft, more air and fuel will be trapped in the cylinder, and the resulting dynamic compression ratio will be higher."
-David Reher is co-owner of Reher-Morrison Racing Engines.
http://www.nhra.com/dragster/1999/issue ... aking.html
more cam does not always allow you to run higher static compression.
dan
oceanstreetvideo.com
so what it sounds like people are saying here is that the high c.r. i ran in past motors didn't work because there wasn't enuf cam... yes, it's true that those 2.1 litre motors had mild cams.
here is another take on the subject:
"Think of two engines that are identical except for their camshafts. The engine with the shorter-duration camshaft will typically have higher dynamic compression at low rpm because the intake valve closes earlier on the compression stroke. The engine with the longer-duration camshaft will have less dynamic compression because its intake valve closes later after the piston has traveled farther up the cylinder. On the other hand, if the long-duration camshaft does a better job of filling the cylinder at high rpm than the short-duration camshaft, more air and fuel will be trapped in the cylinder, and the resulting dynamic compression ratio will be higher."
-David Reher is co-owner of Reher-Morrison Racing Engines.
http://www.nhra.com/dragster/1999/issue ... aking.html
more cam does not always allow you to run higher static compression.
dan
oceanstreetvideo.com
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MASSIVE TYPE IV
- Posts: 20132
- Joined: Fri Jul 07, 2000 12:01 am
cams vs. compression
Not "ALWAYS", but in most, street applications.
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JohnConnolly
- Posts: 3336
- Joined: Thu Apr 13, 2000 12:01 am
cams vs. compression
Now at least we are getting somewhere.
First off, I want to point out that just because you can find a "source" somewhere, doesn't make it fact. Take EVERY piece of information and disect it (Berg, Yunick, Me, whoever).
"so what it sounds like people are saying here is that the high c.r. i ran in past motors didn't work because there wasn't enuf cam... yes, it's true that those 2.1 litre motors had mild cams."
I have seen a lot of 8:1 engines that overheated BAD because the builder was too conservative on the camshaft.
"Think of two engines that are identical except for their camshafts. The engine with the shorter-duration camshaft will typically have higher dynamic compression at low rpm because the intake valve closes earlier on the compression stroke. The engine with the longer-duration camshaft will have less dynamic compression because its intake valve closes later after the piston has traveled farther up the cylinder. On the other hand, if the long-duration camshaft does a better job of filling the cylinder at high rpm than the short-duration camshaft, more air and fuel will be trapped in the cylinder, and the resulting dynamic compression ratio will be higher."
"more cam does not always allow you to run higher static compression."
yes it does.
"more fuel and air is trapped in the cylinder" ; he's referring to the powerband of the cam. With hot camshafts, this is (for example) in the 4K-7K RPM range. What's happening is even with hot cams, the airflow of the engine is dropping off. The hot cam only prevents it from dropping off "as quickly" as it would if the cam was mild.
Seriously; with high compression and a HOT cam, you get compression bleed at lower RPMs which keeps dynamic CR under control (no overheating), and at higher RPMs, the cam allows good breathing, which means the breathing capabilities of the system (head, carb, etc) don't fall off as much.
"loss of low end due to a huge cam" doesn't happen either, since the high compression gets some of that back. I can only say it works! Try a 320 degree cam with 10:1; it won't overheat, and will haul @$$ and live a long life. Run a stock cam with 8:1 and it'll overheat and destruct prematurely.
Now, the high compression/hot cam will NOT pass emissions! These combos do a lot, but they don't do it all!
First off, I want to point out that just because you can find a "source" somewhere, doesn't make it fact. Take EVERY piece of information and disect it (Berg, Yunick, Me, whoever).
"so what it sounds like people are saying here is that the high c.r. i ran in past motors didn't work because there wasn't enuf cam... yes, it's true that those 2.1 litre motors had mild cams."
I have seen a lot of 8:1 engines that overheated BAD because the builder was too conservative on the camshaft.
"Think of two engines that are identical except for their camshafts. The engine with the shorter-duration camshaft will typically have higher dynamic compression at low rpm because the intake valve closes earlier on the compression stroke. The engine with the longer-duration camshaft will have less dynamic compression because its intake valve closes later after the piston has traveled farther up the cylinder. On the other hand, if the long-duration camshaft does a better job of filling the cylinder at high rpm than the short-duration camshaft, more air and fuel will be trapped in the cylinder, and the resulting dynamic compression ratio will be higher."
"more cam does not always allow you to run higher static compression."
yes it does.
"more fuel and air is trapped in the cylinder" ; he's referring to the powerband of the cam. With hot camshafts, this is (for example) in the 4K-7K RPM range. What's happening is even with hot cams, the airflow of the engine is dropping off. The hot cam only prevents it from dropping off "as quickly" as it would if the cam was mild.
Seriously; with high compression and a HOT cam, you get compression bleed at lower RPMs which keeps dynamic CR under control (no overheating), and at higher RPMs, the cam allows good breathing, which means the breathing capabilities of the system (head, carb, etc) don't fall off as much.
"loss of low end due to a huge cam" doesn't happen either, since the high compression gets some of that back. I can only say it works! Try a 320 degree cam with 10:1; it won't overheat, and will haul @$$ and live a long life. Run a stock cam with 8:1 and it'll overheat and destruct prematurely.
Now, the high compression/hot cam will NOT pass emissions! These combos do a lot, but they don't do it all!
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MASSIVE TYPE IV
- Posts: 20132
- Joined: Fri Jul 07, 2000 12:01 am
cams vs. compression
Once again, I agree with John.
I religously set engines between 7.7 to 8.5:1 and as long as they are cammed accordingly, they won't over heat.
I build a few engines with stock cam specs, for busses...These are very touchy and no more than 7.3:1 can be safely used, atleast with stock carb and heads.
Just 2 weeks ago I built a 2165 for a customer, I ran a 284 degree duration cam, and it runs like a champ at 8.3:1....never has went above 210 on the temp, and head temps sometimes get to 375 under acceleration, up hill..This is with 42 x 37 valves,nice ports and a pair of 45 dells.
I often used to make mistakes, by going with too much cam, and not enough CR...rich running and crappy mileage was a result..
The big cam is better for top end, and the CR being higher forces the piston down harder, for better acceleration. The 2 being higher will correct each other...and make for a great combo..
I religously set engines between 7.7 to 8.5:1 and as long as they are cammed accordingly, they won't over heat.
I build a few engines with stock cam specs, for busses...These are very touchy and no more than 7.3:1 can be safely used, atleast with stock carb and heads.
Just 2 weeks ago I built a 2165 for a customer, I ran a 284 degree duration cam, and it runs like a champ at 8.3:1....never has went above 210 on the temp, and head temps sometimes get to 375 under acceleration, up hill..This is with 42 x 37 valves,nice ports and a pair of 45 dells.
I often used to make mistakes, by going with too much cam, and not enough CR...rich running and crappy mileage was a result..
The big cam is better for top end, and the CR being higher forces the piston down harder, for better acceleration. The 2 being higher will correct each other...and make for a great combo..
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dan
cams vs. compression
>>>"more cam does not always allow you to run higher static compression."
yes it does.<<<
john, what part of "...the resulting dynamic compression ratio will be higher." do you not understand??
"more fuel and air is trapped in the cylinder" is NOT the same as "...the airflow of the engine is dropping off."
not a flame here, but the breakdown in your logic seems obvious... you are unable to grasp the concept that there can be higher dynamic compression in a motor at the higher rpm ranges.
but yet you recognize the power losses in a big cam at the lower rpm ranges... hmmm...
>>>"loss of low end due to a huge cam" doesn't happen either, since the high compression gets some of that back.<<<
i think gary berg proved that 7.5:1 c.r. will work with 48's and an fk-87; granted, it probably wasn't quite as snappy as when he ran it at 12:1 c.r., but he's not here to tell us one way or the other.
in view of all of the above, how people can claim these absolutes regarding high compression and cams is a mystery to me... i think this thread is more of an example of how individuals build and tune motors than anything.
dan
oceanstreetvideo.com
yes it does.<<<
john, what part of "...the resulting dynamic compression ratio will be higher." do you not understand??
"more fuel and air is trapped in the cylinder" is NOT the same as "...the airflow of the engine is dropping off."
not a flame here, but the breakdown in your logic seems obvious... you are unable to grasp the concept that there can be higher dynamic compression in a motor at the higher rpm ranges.
but yet you recognize the power losses in a big cam at the lower rpm ranges... hmmm...
>>>"loss of low end due to a huge cam" doesn't happen either, since the high compression gets some of that back.<<<
i think gary berg proved that 7.5:1 c.r. will work with 48's and an fk-87; granted, it probably wasn't quite as snappy as when he ran it at 12:1 c.r., but he's not here to tell us one way or the other.
in view of all of the above, how people can claim these absolutes regarding high compression and cams is a mystery to me... i think this thread is more of an example of how individuals build and tune motors than anything.
dan
oceanstreetvideo.com
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dan
cams vs. compression
>>>Once again, I agree with John.<<<
who are you, btw? you gotta name??
>>>I often used to make mistakes, by going with too much cam, and not enough CR...rich running and crappy mileage was a result..<<<
this situation has lousy jetting and poor head design vs. the cam written all over it, period... you must take the airspeed into consideration when designing a motor.
it is true that higher c.r. is slightly more efficient, and therefore is easier to tune.
dan
oceanstreetvideo.com
who are you, btw? you gotta name??
>>>I often used to make mistakes, by going with too much cam, and not enough CR...rich running and crappy mileage was a result..<<<
this situation has lousy jetting and poor head design vs. the cam written all over it, period... you must take the airspeed into consideration when designing a motor.
it is true that higher c.r. is slightly more efficient, and therefore is easier to tune.
dan
oceanstreetvideo.com
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JohnConnolly
- Posts: 3336
- Joined: Thu Apr 13, 2000 12:01 am
cams vs. compression
not a flame here, but the breakdown in your logic seems obvious... you are unable to grasp the concept that there can be higher dynamic compression in a motor at the higher rpm ranges.
Not higher compression Dan, higher COMPARED to one with a smaller cam. Aspirated engines, the ones we usually deal with in street trim, achieve about 100% VE. Knowing the static CR lets you have a benchmark to figure out whether it's gonna' work or not WITH A CERTAIN CAM. I have run FK-87s on 7.5:1, and it was a pig COMPARED to how it ran when I bumped it to 9.5:1. I NEVER (EVER) said it won't run on lower compression, I said it's difficult (I NEVER said "impossible", as has been "quoted") to tune. Low compression engines DO NOT RESPOND CLEANLY the way 8:1 or higher engines do. You can tune them, but it's a SOB, and you need an O2 sensor if you want to be done in a reasonable timeline. When the compression is up, you can feel and HEAR when the engine is lean or rich, and it's way easier. You can also do it on low compression, it's just a bitch to do.
"but yet you recognize the power losses in a big cam at the lower rpm ranges... hmmm..."
power losses COMPARED to a smaller cam. But, with the big cam, you make up most (if not all) of the low RPM power loss because you have higher compression. Doesn't that make sense? If you are going to quote me and debate, please keep it IN CONTEXT, and don't just pick out the stuff you want to lance.
>>>"loss of low end due to a huge cam" doesn't happen either, since the high compression gets some of that back.<<<
"i think gary berg proved that 7.5:1 c.r. will work with 48's and an fk-87; granted, it probably wasn't quite as snappy as when he ran it at 12:1 c.r., but he's not here to tell us one way or the other."
it works, but how well? I put my $ to say it would have run better at 10.5:1 and it would have lived a long lifetime. Of course, I also promote the addition of a vacuum advance to get 4mpg better fuel economy, along with cooler running on the highway, but because I don't have a big name/company, I don't get any respect either. However, I DO have a degree in EE, and was a pubic hair from one in ME (before I switched), so I have a pretty decent background in engine theory and operation (what's YOUR education on these subjects?). You aren't talking to a Schmoe that is fluent in Backwoods Hotrodding, we are talking decent stuff, where I worked my @$$ off to learn it (Steve Arndt is on a similar path, ask him how it's going and he's only in his first year; the third one is where they start bustin' balls).
"in view of all of the above, how people can claim these absolutes regarding high compression and cams is a mystery to me... i think this thread is more of an example of how individuals build and tune motors than anything."
I'll bet you I can come up with a decent approximation showing the relationship of cam duration (@ .050") and compression on pump gas, and that would REALLY start some arguments, but I'll bet we could get close.
Tell ya' what, I'll do it and put it up on my site this weekend, how's that.
dan
oceanstreetvideo.com[/B][/QUOTE]
Not higher compression Dan, higher COMPARED to one with a smaller cam. Aspirated engines, the ones we usually deal with in street trim, achieve about 100% VE. Knowing the static CR lets you have a benchmark to figure out whether it's gonna' work or not WITH A CERTAIN CAM. I have run FK-87s on 7.5:1, and it was a pig COMPARED to how it ran when I bumped it to 9.5:1. I NEVER (EVER) said it won't run on lower compression, I said it's difficult (I NEVER said "impossible", as has been "quoted") to tune. Low compression engines DO NOT RESPOND CLEANLY the way 8:1 or higher engines do. You can tune them, but it's a SOB, and you need an O2 sensor if you want to be done in a reasonable timeline. When the compression is up, you can feel and HEAR when the engine is lean or rich, and it's way easier. You can also do it on low compression, it's just a bitch to do.
"but yet you recognize the power losses in a big cam at the lower rpm ranges... hmmm..."
power losses COMPARED to a smaller cam. But, with the big cam, you make up most (if not all) of the low RPM power loss because you have higher compression. Doesn't that make sense? If you are going to quote me and debate, please keep it IN CONTEXT, and don't just pick out the stuff you want to lance.
>>>"loss of low end due to a huge cam" doesn't happen either, since the high compression gets some of that back.<<<
"i think gary berg proved that 7.5:1 c.r. will work with 48's and an fk-87; granted, it probably wasn't quite as snappy as when he ran it at 12:1 c.r., but he's not here to tell us one way or the other."
it works, but how well? I put my $ to say it would have run better at 10.5:1 and it would have lived a long lifetime. Of course, I also promote the addition of a vacuum advance to get 4mpg better fuel economy, along with cooler running on the highway, but because I don't have a big name/company, I don't get any respect either. However, I DO have a degree in EE, and was a pubic hair from one in ME (before I switched), so I have a pretty decent background in engine theory and operation (what's YOUR education on these subjects?). You aren't talking to a Schmoe that is fluent in Backwoods Hotrodding, we are talking decent stuff, where I worked my @$$ off to learn it (Steve Arndt is on a similar path, ask him how it's going and he's only in his first year; the third one is where they start bustin' balls).
"in view of all of the above, how people can claim these absolutes regarding high compression and cams is a mystery to me... i think this thread is more of an example of how individuals build and tune motors than anything."
I'll bet you I can come up with a decent approximation showing the relationship of cam duration (@ .050") and compression on pump gas, and that would REALLY start some arguments, but I'll bet we could get close.
Tell ya' what, I'll do it and put it up on my site this weekend, how's that.
dan
oceanstreetvideo.com[/B][/QUOTE]
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MASSIVE TYPE IV
- Posts: 20132
- Joined: Fri Jul 07, 2000 12:01 am
cams vs. compression
Hey Ya'll "Hillbilly Redneck" from Georgia here.....I run High compression so I can hear the spark knock...I like it to mix with the sounds of Charlie Danials, with a bottle of Jack Danials finest.. Now guess who I's is..
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dan
cams vs. compression
>>>Not higher compression Dan, higher COMPARED to one with a smaller cam.<<<
yesss! more cam may = higher dynamic compression = higher octane requirements.
so if anything, bigger cams could require less compression, if you want the motor to live a long life.
now what is your definition of "good breathing(at higher rpm's)", when comparing cams?
"breathe better" means more air, which will require more dynamic compression to force it in and out of the motor... all other things being equal.
>>>Low compression engines DO NOT RESPOND CLEANLY the way 8:1 or higher engines do.<<<
i can certainly see some truth in that, but it also sounds like a function of air speed thru the intake system to me... if you throw low c.r. at hogged-out ports and a giant cam, the motor could easily be a pig.
funny thing, tho, gary's street motor was run with race heads.
>>>power losses COMPARED to a smaller cam. But, with the big cam, you make up most (if not all) of the low RPM power loss because you have higher compression. Doesn't that make sense?<<<
i never argued that, please don't mis-quote me.
>>>>it works, but how well? I put my $ to say it would have run better at 10.5:1 and it would have lived a long lifetime.<<<
this is where we diverge... it's a known fact that a motor running higher compression than the octane will support is one that will NOT live a long lifetime... the gasoline faq clearly spells that out.
look, i'm not arguing with your background or education, or even the vacuum-advance distributor idea(i think it's great).
i'm just interested in disproving this "theory" that people can always get away with running more compression because of a bigger cam.
i don't care how the motor "feels" by the seat of your pants, if it's detonating and you can't hear it, where is the common sense?
dan
oceanstreetvideo.com
yesss! more cam may = higher dynamic compression = higher octane requirements.
so if anything, bigger cams could require less compression, if you want the motor to live a long life.
now what is your definition of "good breathing(at higher rpm's)", when comparing cams?
"breathe better" means more air, which will require more dynamic compression to force it in and out of the motor... all other things being equal.
>>>Low compression engines DO NOT RESPOND CLEANLY the way 8:1 or higher engines do.<<<
i can certainly see some truth in that, but it also sounds like a function of air speed thru the intake system to me... if you throw low c.r. at hogged-out ports and a giant cam, the motor could easily be a pig.
funny thing, tho, gary's street motor was run with race heads.
>>>power losses COMPARED to a smaller cam. But, with the big cam, you make up most (if not all) of the low RPM power loss because you have higher compression. Doesn't that make sense?<<<
i never argued that, please don't mis-quote me.
>>>>it works, but how well? I put my $ to say it would have run better at 10.5:1 and it would have lived a long lifetime.<<<
this is where we diverge... it's a known fact that a motor running higher compression than the octane will support is one that will NOT live a long lifetime... the gasoline faq clearly spells that out.
look, i'm not arguing with your background or education, or even the vacuum-advance distributor idea(i think it's great).
i'm just interested in disproving this "theory" that people can always get away with running more compression because of a bigger cam.
i don't care how the motor "feels" by the seat of your pants, if it's detonating and you can't hear it, where is the common sense?
dan
oceanstreetvideo.com
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dan
cams vs. compression
>>>Hey Ya'll "Hillbilly Redneck" from Georgia here.....I run High compression so I can hear the spark knock...I like it to mix with the sounds of Charlie Danials, with a bottle of Jack Danials finest.. Now guess who I's is..<<<
lol! i figured as much
btw, on sunday i saw the quickest all-motor street car type 4 i think i've ever seen, out of literally thousands(?) of vw drag racing passes i've been trackside for... it was in a sweet little 914 that was set up for autocrossing... i seem to remember a 15.05(?) 1/4 mile out of what cormack said was a 2.1 liter motor.
>>>>some cams set up in engines with low static CR, lead to crazy dynamic CR..WEB has a 111 grind we use in buggy engines, with most everything else stock, it is a mean and nasty animal, with high lift and almost no duration, anything over 7.5:1 will roast the heads...no matter what....But it makes wild power....The dynamic CR of this engine in my program is a whopping 8.7:1, becasue of the specs of the cam...<<<<
thanks for putting cam design into perspective here... i think that is where john is headed with that "cam duration and compression on pump gas" statement.
the problem is, without measuring the exact amount of airflow thru a port at all rpm ranges, it would seem impossible for even the engine design programs to accurately guesstimate the dynamic compression.
dan
oceanstreetvideo.com
lol! i figured as much
btw, on sunday i saw the quickest all-motor street car type 4 i think i've ever seen, out of literally thousands(?) of vw drag racing passes i've been trackside for... it was in a sweet little 914 that was set up for autocrossing... i seem to remember a 15.05(?) 1/4 mile out of what cormack said was a 2.1 liter motor.
>>>>some cams set up in engines with low static CR, lead to crazy dynamic CR..WEB has a 111 grind we use in buggy engines, with most everything else stock, it is a mean and nasty animal, with high lift and almost no duration, anything over 7.5:1 will roast the heads...no matter what....But it makes wild power....The dynamic CR of this engine in my program is a whopping 8.7:1, becasue of the specs of the cam...<<<<
thanks for putting cam design into perspective here... i think that is where john is headed with that "cam duration and compression on pump gas" statement.
the problem is, without measuring the exact amount of airflow thru a port at all rpm ranges, it would seem impossible for even the engine design programs to accurately guesstimate the dynamic compression.
dan
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