[BigRed-L72]

The other thing I didn't mention is that if any of those 147 are assymetrical shaped lobes....that duration @.050"..or .200"...or .400" may not be evenly split beween the opening and closing flanks. And it may be at one of those points..but not at another.

Weird stuff!!

JIM

Weird stuff indeed !!! How`s this for an idea ?...With Harolds cams being asymmetrical, adding an X pipe to help 'over scavange' the exhaust side would, in theory, eliminate the need for more exhaust timing..

 

[Stokerboats]

Think of a lobe as a trip you start here and you want to end up here. Your going to take this trip in corvette. The exhaust lobe is a deuce n ahalf. All you have to do is meet half way of the trip. That is .050". True single patterns and by what I mean the same lobe is used on both intake and exhaust can't be optimal. Why. Anybody here running heads that have the same port design and intake and exhaust?

At the start the duration is going to favor the exhaust. At .050" it is the same. On the big end the duration is going to favor the intake.

I read this today and have been thinking about it all day. Wasn't sure I could accept this analogy. It is true that intake ports and exhaust ports are different and valve diameter is also different. No problem with that and I am a mere novice at this but is not inlet air temp much cooler (slower air) than exhaust temp (faster air) where pressure waves are very different in both cases. Is this not also considered with respect to cam selection. This gets pretty complicated for me but it seems there are many things to consider pertaining to I/E ratio. I don't think we can look at an intake port as being the same as an exhaust port because they do two different things under different conditions

 

[BowtieAaron]

How much does adding an intake/carb/headers hurt or improve the flow compared to just flowing the cyl head?

How would you determine If the intake is actually choking the heads? Will it flow less than the head by itself?

 

[540Hotrod]

You can bolt the intake to the head when flowing it all...as well as carb. Usually intake knock flow off a good bit..but that just depends on the intake and what's been done to it. Could help or be awful close in some cases. Intakes affect things a lot more than people think sometimes. A great set of heads can be killed with an out of the box intake...or the wrong intake.

Just think of what happens in the typical single plane vs dual plane scenario to see what an intake can change on the whole combo. Or a tunnel ram.

The size of the carb usually isn't too much of problem either way..the intake will make a bigger change unless it's way undersized.


JIM

 

[cstraub]

I read this today and have been thinking about it all day. Wasn't sure I could accept this analogy. It is true that intake ports and exhaust ports are different and valve diameter is also different. No problem with that and I am a mere novice at this but is not inlet air temp much cooler (slower air) than exhaust temp (faster air) where pressure waves are very different in both cases. Is this not also considered with respect to cam selection. This gets pretty complicated for me but it seems there are many things to consider pertaining to I/E ratio. I don't think we can look at an intake port as being the same as an exhaust port because they do two different things under different conditions

Dan,
I am not trying to say the intake and exhaust port are the same, I am saying they are totally different and require totally different lobes. Yes you have the intake being low pressure coming in and exhaust being high pressure wanting out. In no way do I think the same cam lobe would be optimal for both intake and exhaust.

 

[cstraub]

How much does adding an intake/carb/headers hurt or improve the flow compared to just flowing the cyl head?

How would you determine If the intake is actually choking the heads? Will it flow less than the head by itself?

For 80% of the applications out there having the head flow numbers is enough. For those class racing or professional racing one needs to flow the entire intake track, carb on intake, intake bolted to heads and then for the exhaust the entire header bolted to the head.

A properly tuned intake and carb should drop the induction side by around 3%. Headers will let you know how good the port is and the valve job. If the header inproves the flow greatly, then the valve job is not all that. If it affects it by 2 to 4% then it is a very good valve job.

 

[Stokerboats]

Dan,
I am not trying to say the intake and exhaust port are the same, I am saying they are totally different and require totally different lobes. Yes you have the intake being low pressure coming in and exhaust being high pressure wanting out. In no way do I think the same cam lobe would be optimal for both intake and exhaust.

Ok, so at what I/E ratio would favor a symmetrical cam?

 

[BowtieAaron]

So if I were to put on a 1-3/4" header instead of a 1-5/8 and pick up power will that say the valve job is bad?

Is I/e ratio hand in hand with the engines VE?

 

[modchevelle]

How do you have a accurate I/E flow test if the HOT exhaust gasses are not present?

 

[BowtieAaron]

If some people design cams to help eith scavenging exhaust gases, then how's an x pipe play in with I/e and can selection?

If you pick up power adding an x pipe does that mean you didn't have the correct cam? Or your heads are worse than expected?

 

[steelcomp]

How do you have a accurate I/E flow test if the HOT exhaust gasses are not present?

Define accurate?

 

[Stokerboats]

Define accurate?

Maybe flowed @ 100 deg int temp and ^1200 deg exhaust temp

 

[steelcomp]

Maybe flowed @ 100 deg int temp and ^1200 deg exhaust temp

Well, we've managed to come to a consensus on where to "test" intake ports, even though engines don't run any where near 28"...why can't we do the same for the ex.?
Is it necessary to duplicat the exact conditions in order to establish relationships and trends? I refer to someone like Chris, who puts a lot of focus on intake/ex ratios, and is very successful. There has to be something to it, wouldn't you say?

 

[MinionII]

So if I were to put on a 1-3/4" header instead of a 1-5/8 and pick up power will that say the valve job is bad?

Is I/e ratio hand in hand with the engines VE?

What I gathered from Chris' statement was that if the addition of headers increased the measured flow substantially, then the valve job was poor. This being in comparison to no tube/header.

 

[cstraub]

Ok, so at what I/E ratio would favor a symmetrical cam?

Dan,
When it calculates out that it needs it. The 75% is a baseline but as I have said CID and rpm range will change this. If combination being cammed falls into the parameters for a single pattern then it is optimal at that time.

Chris

 

[cstraub]

So if I were to put on a 1-3/4" header instead of a 1-5/8 and pick up power will that say the valve job is bad?

Is I/e ratio hand in hand with the engines VE?

Whole different ball of wax. You need to make sure your header primary pipe size is what the combo needs. If the combo needs 1.750" and you put 1.625" on it then the header is killing the combination.

 

[cstraub]

How do you have a accurate I/E flow test if the HOT exhaust gasses are not present?

You don't and some will agrue the point that a flow numbers off a bench are not accurate that you need to flow the head on the block with with piston present in the cylinder with temperature.

The OEM's can do this, I for one don't have a multimillion dollar R&D budget. What I do have is experience and results over the years. The original post here is a prime example. How many here would put a cam with 22 degree split at .050" in there engine? I would say not many. How many would like to pick up 60HP with cam change. I would say most.

 

[cstraub]

If some people design cams to help eith scavenging exhaust gases, then how's an x pipe play in with I/e and can selection?

If you pick up power adding an x pipe does that mean you didn't have the correct cam? Or your heads are worse than expected?

X pipe has to do with proper tuning lengths and scavage area for the exhaust pulses. That is another thread.

 

[BowtieAaron]

How about carb spacers? What role do they play with I/E ratio? Any?

I added a 1" plastic 4 hole spacer (cheap summit one) on top of my 1" open plastic (same cheap one) and picked up 44rwhp and 5mph! This is on top of a Holley 300-36 street dominator intake, (divider cut 1" down and radius edges, was good for 11rwhp and 14rwtq and 2.5mph).

What is that telling me? I need more intake runner volume?

 

[Lilracr]

Aaron,
What you did was to add intake plenum and allow the spread of volume to the upper and lower plenums.

You want the intake and exhaust as free and sized as well as possible before spec'ing cam lobes. It knowing the amount that the combustion chamber see's is sometimes the trick. This is where Chris' experience comes in play.

I would like to have something that would allow me to know intake and exhaust flow and velocity specifics when porting intakes and heads. A good bit of what I do is updating a motor that is already complete and running. Very few actually change the cam to gain even more power.