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Discussion Starter · #1 ·
UDHarold or cam experts(Mike Lewis)Too.I am not doubting anyones expertise just asking a question and trying to learn something at the same time.I started with a N/A motor and decided to procharge it.I changed pistons and lowerd comp.I was told the cam I had made would not work on a supercharged motor so I contacted UDHarold and I gave him my goals and asked to make me a cam.I was told that my N/A cam would not work because it was a 108 LSA and the overlap would throw all my boost and fuel out my tail pipes.Well here is where I get confused that 108 LSA has the same overlap as the new 112 LSA blower cam I just got(70* overlap).So seeing they have the same overlap wouldn't I still have the same problem?If LSA is just a figure in overlap and not the tell all wouldn,t 70* overlap act the same in what ever LSA cam 108-116,or would a different LSA's act different even with the same overlap?I'm just asking to learn.I didn't give out cam specs,but if you need them I don't have a problem giving them out.I didn't ask Harold about this,I was just sitting here drinking a beer and had a brain storm while looking at my two cam cards and thought this would make some good conversation.
 

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It seems you got some bad information at some time.. The same cam that works NA(without the blower ) will work VERY WELL with the blower. Where most poeple get real confused is between a RACE engine , andd a STREET. This is where everybody gets it all wrong. The wider lobe centers will be much more street driveable, but the closer centers ( 108 ) will make more horsepower


JOE SHERMAN RACING ENGINES
 

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Discussion Starter · #4 ·
It seems you got some bad information at some time.. The same cam that works NA(without the blower ) will work VERY WELL with the blower. Where most poeple get real confused is between a RACE engine , andd a STREET. This is where everybody gets it all wrong. The wider lobe centers will be much more street driveable, but the closer centers ( 108 ) will make more horsepower


JOE SHERMAN RACING ENGINES
This is a street car 4spd.I was told by many that a 108 lsa wouldn't make as much boost due to the overlap and blowing charge out the exhaust instead of building in the cylinders for boost.
 

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Discussion Starter · #5 ·
I'm neither guy.

But I do want to know both cam spec's.

Please come back and post both up so all of us can learn something right along w/ you.

pdq67
Bullet n/a cam 282/292 252/256 @.050 655/639 108 lsa

UDHarold cam 290 299 259/271 @.050 668/668 112 lsa

I come up with 71* for the first and 70* for the second valve overlap
 

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Discussion Starter · #8 ·
I'm not an expert, but I would think that lowering the compression makes the engine need more overlap.
I'm not sure I agree with that, N/A or supercharged.Why would you want more overlap which would lower your dynamic compression on a low comp N/A motor.Wouldn't it?And on a supercharger your not building boost if your valves are both open.
 

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I'm not sure I agree with that, N/A or supercharged.Why would you want more overlap which would lower your dynamic compression on a low comp N/A motor.Wouldn't it?And on a supercharger your not building boost if your valves are both open.
How does more overlap lower your compression when over lap is Intake Valve Opening (IVO) & Exhaust Valve Closing (EVC) points?

Your cylinder pressure is effected by when the Intake Valve Closes (IVC)

As the piston is coming to TDC the exhaust valve is closing and the intake valve is opening, Thus overlap

Then XX degrees after TDC the exhaust valve closes, this is on the intake stroke.

The piston passes Bottom Dead Center (BDC) then goes on the Compression stroke

So many degrees after Bottom Dead Center the intake valve closes (IVC) and from that point on to TDC on compression stroke is where you actually build cylinder pressure

Then you ignite the compressed mixture just before TDC, this explodes and pushs the piston down thus the Powerstroke. As the piston is being pushed down XX degrees before Before Bottom Dead Center (BBDC) the exhaust valves starts to open to blow the cylinder down, then the piston passes Bottom Dead Center (BDC) then starts going up pushing exhaust gasses out, As it gets near TDC your back where we started

Look at your Exhaust Valve Opening (EVO) points, they are different

This is general is does not take into account cylinder ramming effect
 

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I'm as confused as anyone but this is how I look at the overlap vs LSA question in a blower engine...

A wider LSA will open the exhaust valve earlier than a narrower LSA and will at the same time delay the intake opening compared to the narrower centers.

This works on a blower motor because the earlier exhaust opening is benificial to get the large amounts exhaust gasses out that was produced by the forced induction.
The later intake opening, compared to the closer LSA, means no loss in power in the blower engine because of the PSI in the intake manifold.

The overlap can be the same in both the 108 and 112 LSA cam due to the longer duration in the 112. So they both have 70* overlap on paper but the earlier exhaust opening benefits the blower engine's scavenging.

Do I have this anywhere near correct?
 

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Discussion Starter · #12 ·
The compression ratio listed for any engine combo is always the static compression ratio, which is fixed via component selection and machining practice when the engine is built. As you've surmised, it assumes the cylinder is full of air and fuel at bottom dead center (BDC) and that all the mixture is compressed into the top dead center (TDC) combustion cavity. But an engine really doesn't begin making serious compression until the intake valve closes and seals the air/fuel mix in the cylinder. That's why engines with identical static compression ratios can have significantly different cranking pressures, as seen with a common compression gauge. Although part of this is due to displacement differences (a larger-cubic-inch engine is a bigger pump), the main influence is camshaft design. By changing certain cam parameters, it's possible to bleed off cylinder pressure on the bottom end, decreasing fuel octane sensitivity, even though its static compression ratio remains unchanged. The actual cylinder pressure an engine sees is often referred to as dynamic compression, because (unlike the static built-in compression ratio) it changes dynamically according to camshaft variations. The most important of these variations is the intake closing point, because it extends beyond BDC into the compression stroke. Closing the intake later aids top-end power at the expense of low-end torque. Down low, where the engine is most likely to detonate, the late intake closure bleeds off cylinder pressure, effectively dropping the dynamic compression ratio.
Am I reading this wrong,aren't they talking about more overlap causing lower dynamic comp.cylinder bleed off?But back to my question, giving a set of overlap of 70*on different LSA cams how would they act differently?Would one bleed off more than another being they have the same overlap?
 

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The compression ratio listed for any engine combo is always the static compression ratio, which is fixed via component selection and machining practice when the engine is built. As you've surmised, it assumes the cylinder is full of air and fuel at bottom dead center (BDC) and that all the mixture is compressed into the top dead center (TDC) combustion cavity. But an engine really doesn't begin making serious compression until the intake valve closes and seals the air/fuel mix in the cylinder. That's why engines with identical static compression ratios can have significantly different cranking pressures, as seen with a common compression gauge. Although part of this is due to displacement differences (a larger-cubic-inch engine is a bigger pump), the main influence is camshaft design. By changing certain cam parameters, it's possible to bleed off cylinder pressure on the bottom end, decreasing fuel octane sensitivity, even though its static compression ratio remains unchanged. The actual cylinder pressure an engine sees is often referred to as dynamic compression, because (unlike the static built-in compression ratio) it changes dynamically according to camshaft variations. The most important of these variations is the intake closing point, because it extends beyond BDC into the compression stroke. Closing the intake later aids top-end power at the expense of low-end torque. Down low, where the engine is most likely to detonate, the late intake closure bleeds off cylinder pressure, effectively dropping the dynamic compression ratio.
Am I reading this wrong,aren't they talking about more overlap causing lower dynamic comp.cylinder bleed off?But back to my question, giving a set of overlap of 70*on different LSA cams how would they act differently?Would one bleed off more than another being they have the same overlap?
A guage?

What about my car? It wont hit 100 pounds but blew the tired off though low gear with a 1.765 , 7.49 @94.93mph and 11.645 @118.98mph lifted 50' soon

Cranking compression is "cranking compression" , I will not indicate performance regardless what anyone says
 

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Discussion Starter · #14 ·
A guage?

What about my car? It wont hit 100 pounds but blew the tired off though low gear with a 1.765 , 7.49 @94.93mph and 11.645 @118.98mph lifted 50' soon

Cranking compression is "cranking compression" , I will not indicate performance regardless what anyone says
No not gauge

What is Dynamic Compression Computing your dynamic compression is very critical when designing an engines combination if you want it to perform properly, especially if you are to run pump gas. This is an essential concept in designing an engine for performance use so we will attempt to help you better understand what it is.
We first need to understand what “compression ratio” (CR) is, also known as "static compression ratio". This term represents the ratio of the swept volume of the cylinder (displacement) to the volume above the piston at top dead center (TDC). An example of a hypothetical cylinder having a displacement of 660cc and a 60cc combustion chamber (plus volume over the piston crown to the head) the CR would be 660/60, or 11:1. If we were to mill the head so that the volume above the piston crown was decreased to 50cc, the CR would now be 660/50, or 13.2:1. Now, if we hogged the chamber out to 65cc, the CR would now be 660/65, or 10.15:1.
It is understood that high performance engines typically have higher compression ratios than the average street cars. Higher CR improves fuel efficiency, throttle response & increases horse power. So why not bump up the CR even more, once the compression ratio exceeds a certain point, detonation will occur. Detonation kills power and can destroy the engine. The amount of compression a given engine can handle is determined by many factors. Some of these include combustion chamber design, head material, use of thermal coatings, cam profile, octane of fuel to be used, etc. Higher octane fuel has a higher resistance to detonation therefore it can accommodate higher compression.
A common question among many of my customers is how much compression can I run? Even if you know all about your engine and have decided what fuel you are going to use, the question can not be answered without determining your dynamic compression. How do we determine what the dynamic compression ratio is, by referencing the camshaft specs?
Think about how a four stroke engine works. The power stroke has been completed and the piston is heading up in the bore. The intake valve is closed and the exhaust valve is open. As the piston rises it is helping to push the spent combustion gasses out the exhaust port. The piston reaches TDC and starts back down. The exhaust valve closes and the intake valve opens. Fresh fuel and air are drawn into the cylinder. The piston reaches bottom dead center (BDC) and starts back up. This is the critical point as far as understanding DCR. At BDC. the intake valve is still open, consequently even though the piston is rising up the bore, there is no compression actually occurring because of the intake valve being open. Compression does not occur until the intake valve closes. Once intake vale is closed then the air fuel mixture starts to compress. The ratio of the cylinder volume at IVC over the volume above the piston at TDC represents the dynamic compression ratio. The DCR is what the air fuel mixture actually "sees" and this is what matters, not the static CR. Dynamic compression is dependent upon the intake valve closing. Cam specs have as much effect on DCR as does the mechanical specifications of the motor. Also remember that when under boost or spraying nitrous that your DCR will be dramatically higher then when not under boost or spraying nitrous.
Your dynamic compression will always be lower than static CR. Most performance street and street/track motors have DCR in the range of 8-8.5:1. With typical cams, this translates into static CR in the 9.0-11.0:1 range. When running compression any higher than this there could be detonation problems with pump gas. Engines with "small" cams will need a lower static CR to avoid detonation. Engines with "big" cams having a later IVC point can tolerate a higher static CR. When race fuel is used, much higher dynamic & static compression ratios can be used. This is because of the higher resistance that race fuels have against detonation.
 

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No not gauge

What is Dynamic Compression Computing your dynamic compression is very critical when designing an engines combination if you want it to perform properly, especially if you are to run pump gas. This is an essential concept in designing an engine for performance use so we will attempt to help you better understand what it is.
We first need to understand what “compression ratio” (CR) is, also known as "static compression ratio". This term represents the ratio of the swept volume of the cylinder (displacement) to the volume above the piston at top dead center (TDC). An example of a hypothetical cylinder having a displacement of 660cc and a 60cc combustion chamber (plus volume over the piston crown to the head) the CR would be 660/60, or 11:1. If we were to mill the head so that the volume above the piston crown was decreased to 50cc, the CR would now be 660/50, or 13.2:1. Now, if we hogged the chamber out to 65cc, the CR would now be 660/65, or 10.15:1.
It is understood that high performance engines typically have higher compression ratios than the average street cars. Higher CR improves fuel efficiency, throttle response & increases horse power. So why not bump up the CR even more, once the compression ratio exceeds a certain point, detonation will occur. Detonation kills power and can destroy the engine. The amount of compression a given engine can handle is determined by many factors. Some of these include combustion chamber design, head material, use of thermal coatings, cam profile, octane of fuel to be used, etc. Higher octane fuel has a higher resistance to detonation therefore it can accommodate higher compression.
A common question among many of my customers is how much compression can I run? Even if you know all about your engine and have decided what fuel you are going to use, the question can not be answered without determining your dynamic compression. How do we determine what the dynamic compression ratio is, by referencing the camshaft specs?
Think about how a four stroke engine works. The power stroke has been completed and the piston is heading up in the bore. The intake valve is closed and the exhaust valve is open. As the piston rises it is helping to push the spent combustion gasses out the exhaust port. The piston reaches TDC and starts back down. The exhaust valve closes and the intake valve opens. Fresh fuel and air are drawn into the cylinder. The piston reaches bottom dead center (BDC) and starts back up. This is the critical point as far as understanding DCR. At BDC. the intake valve is still open, consequently even though the piston is rising up the bore, there is no compression actually occurring because of the intake valve being open. Compression does not occur until the intake valve closes. Once intake vale is closed then the air fuel mixture starts to compress. The ratio of the cylinder volume at IVC over the volume above the piston at TDC represents the dynamic compression ratio. The DCR is what the air fuel mixture actually "sees" and this is what matters, not the static CR. Dynamic compression is dependent upon the intake valve closing. Cam specs have as much effect on DCR as does the mechanical specifications of the motor. Also remember that when under boost or spraying nitrous that your DCR will be dramatically higher then when not under boost or spraying nitrous.
Your dynamic compression will always be lower than static CR. Most performance street and street/track motors have DCR in the range of 8-8.5:1. With typical cams, this translates into static CR in the 9.0-11.0:1 range. When running compression any higher than this there could be detonation problems with pump gas. Engines with "small" cams will need a lower static CR to avoid detonation. Engines with "big" cams having a later IVC point can tolerate a higher static CR. When race fuel is used, much higher dynamic & static compression ratios can be used. This is because of the higher resistance that race fuels have against detonation.
You said static, Read your first words in the other post

Guage tells you nothing, NOTHING

BTW, the bottom half of your first post says the samething i said. Be honest i didnt read all of this one
 

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I found this to be a pretty good cal calculator

http://www.projectpontiac.com/ppsite/content/view/16/30/
It doesnt take into account if the head has more cylinder ramming effect, the more cylinder ramming effect the higher cylinder pressure will be

The more you trap in the more power you make, if your engine has a higher ramming effect you will have more cylinder pressure assuming the IVC point is the same , due to the cylinder ramming effect
 

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If you spoke to UD and provided him with your combo an he sent you a cam, I'd say lube that sucker up and let er rip......:yes:
Has anyone heard from Harold lately....I sure hope he is doing alright. I'm sorry I don't have anything constructive to add here.....It reminded me of speaking with the man himself and again I understood about half what he was saying....:D
 

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Discussion Starter · #19 ·
It doesnt take into account if the head has more cylinder ramming effect, the more cylinder ramming effect the higher cylinder pressure will be

The more you trap in the more power you make, if your engine has a higher ramming effect you will have more cylinder pressure assuming the IVC point is the same , due to the cylinder ramming effect
Agree,What do you think about LSA and valve overlap and how they act in relation?Two cams with two different LSA's and having the same overlap.How would they act differently?If overlap is the degree in which both valves are open how would the two different cams act.Wouldn't both of the cams I mentioned have the same amount of overlap,cylinder bleed off,boost bleed off?I'm just wondering how the new cam I got is going to fix my original problem wich was boost bleed off.
 

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Agree,What do you think about LSA and valve overlap and how they act in relation?Two cams with two different LSA's and having the same overlap.How would they act differently?If overlap is the degree in which both valves are open how would the two different cams act.Wouldn't both of the cams I mentioned have the same amount of overlap,cylinder bleed off,boost bleed off?I'm just wondering how the new cam I got is going to fix my original problem wich was boost bleed off.
your changing the entire profile when you do that
 
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