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Mon Nov 03, 2008 4:40 pm

Isn't that what you do with all your IDF intakes?

Mon Nov 03, 2008 5:56 pm

So the reduction in airspeed is regained as it goes into the progressively smaller runner to the port anyway right? At greater airspeeds won't the venturi be blasting it's mixture through the large plenum area? I'll bet something happens to the mixture in both that larger plenum area and in the match throat manifold under both high and low rpm ranges.

Mon Nov 03, 2008 7:12 pm

The plenum is inefficient at low air speeds. It is more efficient at high air speeds. It has less apparent "wall" for the fuel mixture to move against. It depends what you want. Remember Ford's variable venturi carburetor? They were trying to get the best of both worlds.

Tue Nov 04, 2008 1:37 am

Pat D wrote: Bruce wrote: Pat D wrote: Rule of thumb on making H-P. Always run a bigger throat on the manifold than your throttle plate. I'm not going to say how big, it has taken me a long time to figure it out :wink:
OK, I'll bite.
Explain how a big volume under the throttle plate (which causes a massive drop in airspeed) makes more hp?

Then if it is so good to have a big increase in diameter, why don't your manifolds for IDAs have a 60mm hole below them? I'ts called a plenum Bruce :wink: I guess we could just make all our manifolds 70mm on top and call them Super Plenums :D

Why then, do your CE manifolds get smaller from their top flanges?

Tue Nov 04, 2008 7:53 am

I'm going to go out on a limb here and guess that Pat has a lot of first hand experience with a lot of different engine combos on a dyno. More experience in that regard than most anyone here. Probably "combined" even. Probably seen first hand what he is talking about, not just speculating from theory.

Just a guess anyway. Am I even in the ball-park with this one, Pat :lol:

I think based on that, i'd listen very closely to what Pat is saying.

Tue Nov 04, 2008 8:38 am

Eaallred wrote: I'm going to go out on a limb here and guess that Pat has a lot of first hand experience with a lot of different engine combos on a dyno. More experience in that regard than most anyone here. Probably "combined" even. Probably seen first hand what he is talking about, not just speculating from theory.

Just a guess anyway. Am I even in the ball-park with this one, Pat :lol:

I think based on that, i'd listen very closely to what Pat is saying. Thanks for your vote of confidence in me Eric. Like you said, actuall experience not hypothetical speculation. It is really amusing that people will argue with you about something without having any experience with what they are arguing about. Bruce/Mark have you two ever used a velocity probe and checked air speed in a cylinder head or manifold or carburator? What air speed is best for power, torque fuel efficiency? Come on guys, tell me because you must have done some sort of testing to back up your THEORY. I use pitot tubes every where in manifolds to monitor air speed and I know what is too much, not enough and correct for the application. I do this every week, having notes that could write a book on the subject.

Tue Nov 04, 2008 8:45 am

So Pat,

What you are saying is.....

All these tests conclude that a one size fits all 50mm intake bore works best in all applications / carb sizes / engine sizes?

Just Curious? I am not trying to start anything.

Tue Nov 04, 2008 9:26 am

Pat D wrote: Thanks for your vote of confidence in me Eric. Like you said, actuall experience not hypothetical speculation. It is really amusing that people will argue with you about something without having any experience with what they are arguing about. Bruce/Mark have you two ever used a velocity probe and checked air speed in a cylinder head or manifold or carburator? What air speed is best for power, torque fuel efficiency? Come on guys, tell me because you must have done some sort of testing to back up your THEORY. I use pitot tubes every where in manifolds to monitor air speed and I know what is too much, not enough and correct for the application. I do this every week, having notes that could write a book on the subject.

Not trying to be a dick here. Now that you've told us you know all the information that everyone is speculating on, are you going to enlighten us?

Tue Nov 04, 2008 9:35 am

Jengel451 wrote: Pat D wrote: Thanks for your vote of confidence in me Eric. Like you said, actuall experience not hypothetical speculation. It is really amusing that people will argue with you about something without having any experience with what they are arguing about. Bruce/Mark have you two ever used a velocity probe and checked air speed in a cylinder head or manifold or carburator? What air speed is best for power, torque fuel efficiency? Come on guys, tell me because you must have done some sort of testing to back up your THEORY. I use pitot tubes every where in manifolds to monitor air speed and I know what is too much, not enough and correct for the application. I do this every week, having notes that could write a book on the subject.

Not trying to be a dick here. Now that you've told us you know all the information that everyone is speculating on, are you going to enlighten us? Not trying to be a dick either but sorry, No.

Tue Nov 04, 2008 9:35 am

Pat D wrote: Rule of thumb on making H-P. Always run a bigger throat on the manifold than your throttle plate.
For what application? Drag racing, track racing, or street use?

You really haven't said much of anything about how a plenum affects performance over the full RPM range from idle on upward.

Scott Novak

Tue Nov 04, 2008 9:45 am

Type 5 Joe wrote: So Pat,

What you are saying is.....

All these tests conclude that a one size fits all 50mm intake bore works best in all applications / carb sizes / engine sizes?

Just Curious? I am not trying to start anything.

Tue Nov 04, 2008 11:26 am

Pat- If you had a variety of engines starting with a relatively stock 1600
with small dual webers or dellortos and ending with a healthy 2 litre plus
street beast with high compression, 300 degrees or more duration, 48's,
well prepped 42 or more x 37 heads and 1 3/4 in exhaust, is there a point
where a bigger throat on the manifolds becomes a benefit?
As always, anything you can tell us would be beneficial- and as Eric so
tactfully pointed out with your knowledge and experience I'm looking forward to learning something today. Al

A little off topic, your description of the troubles with the dyno challenge
motor was appreciated. Any hint of specs on the one that broke?

Tue Nov 04, 2008 11:45 am

Pat D wrote: Bruce/Mark have you two ever used a velocity probe and checked air speed in a cylinder head or manifold or carburator? What air speed is best for power, torque fuel efficiency? Come on guys, tell me because you must have done some sort of testing to back up your THEORY. I use pitot tubes every where in manifolds to monitor air speed and I know what is too much, not enough and correct for the application. I do this every week, having notes that could write a book on the subject.

I don't doubt your experience/knowledge Pat, but you're not giving any information besides "I know how it works". And that's certainly your right, no one can say different.

But CB's intake product line does not reflect that forward thinking, unless one size fits all, which just can't be. You know that runner length, size, shape, and proportion all matter, a lot. You also know that given the constraints of our engines, the intakes we use have to be a best fit scenario, to a point, for selling them, and something you can play with and change for folks in the know.

I'm contributing my working experience with trying different things, which has been a product of my doing my own homework, but I am not going to get too hung up on intellectual property to try to help a fellow VW guy out. If you think what I have said is inaccurate, maybe you should explain why and help us all. I'm not afraid to be wrong, but I'd like to learn from it.

Tue Nov 04, 2008 1:02 pm

mharney wrote: Pat D wrote: Bruce/Mark have you two ever used a velocity probe and checked air speed in a cylinder head or manifold or carburator? What air speed is best for power, torque fuel efficiency? Come on guys, tell me because you must have done some sort of testing to back up your THEORY. I use pitot tubes every where in manifolds to monitor air speed and I know what is too much, not enough and correct for the application. I do this every week, having notes that could write a book on the subject.

I don't doubt your experience/knowledge Pat, but you're not giving any information besides "I know how it works". And that's certainly your right, no one can say different.

But CB's intake product line does not reflect that forward thinking, unless one size fits all, which just can't be. You know that runner length, size, shape, and proportion all matter, a lot. You also know that given the constraints of our engines, the intakes we use have to be a best fit scenario, to a point, for selling them, and something you can play with and change for folks in the know.

I'm contributing my working experience with trying different things, which has been a product of my doing my own homework, but I am not going to get too hung up on intellectual property to try to help a fellow VW guy out. If you think what I have said is inaccurate, maybe you should explain why and help us all. I'm not afraid to be wrong, but I'd like to learn from it. Mark, Yes one size does not fit all. As to why are manifolds are 48-50mm on top? You can't go smaller but you can always go bigger. It is up to the head porter to decide what throat I.D to use. I have my demensions I use based off of the throttle plate diameter. I have always shared what I have learned with everyone. More and more, I am keeping things to myself. When you go on the classified section and see 10-15 different engine builders, some with cylinder heads nearly exact copy's of what you designed, your attitude changes. I posted that opening up the inlet side of the manifold will help in power. You guys can take it from there because the knowledge I have gained is staying in my head. I do agree on nearly everything you say Mark. I think you are a very intelligent person.
Pat

Thu Nov 06, 2008 12:13 am

Pat D wrote: As to why are manifolds are 48-50mm on top? You can't go smaller but you can always go bigger. It is up to the head porter to decide what throat I.D to use.
That makes no sense at all. If it is up to the porter to decide how big the manifold needs to be at the top, you should make the runner small, so it can be ported bigger.

You've still not given any reason why you think a big toilet bowl under the carb is a good thing.

What is your take on these manifolds then?

Thu Nov 06, 2008 7:08 am

ALB wrote: Pat- If you had a variety of engines starting with a relatively stock 1600
with small dual webers or dellortos and ending with a healthy 2 litre plus
street beast with high compression, 300 degrees or more duration, 48's,
well prepped 42 or more x 37 heads and 1 3/4 in exhaust, is there a point
where a bigger throat on the manifolds becomes a benefit?
As always, anything you can tell us would be beneficial- and as Eric so
tactfully pointed out with your knowledge and experience I'm looking forward to learning something today. Al

A little off topic, your description of the troubles with the dyno challenge
motor was appreciated. Any hint of specs on the one that broke?
Pat- any comment?

Thu Nov 06, 2008 8:03 am

It's funny. People want to critisize, and in the same breath want him to share the info.

I woldn't share anything at this point either.

You guys that 'think' you know more than Pat would do yourselves a lot of good by educating yourselves before getting so cocky. First step would be to look into anti-reversion intake systems.

Thu Nov 06, 2008 9:10 am

Bruce wrote: Pat D wrote: As to why are manifolds are 48-50mm on top? You can't go smaller but you can always go bigger. It is up to the head porter to decide what throat I.D to use.
That makes no sense at all. If it is up to the porter to decide how big the manifold needs to be at the top, you should make the runner small, so it can be ported bigger.

You've still not given any reason why you think a big toilet bowl under the carb is a good thing.

What is your take on these manifolds then?
It never fails, someone will always say, why do you not make it this way or that way. Bruce, I am not going to share any knowledge with you or comment on your manifold pictures. What I have learned over the years is staying in my head. Besides, you allready know what works anyway :roll:

Thu Nov 06, 2008 4:40 pm

Well since we can't be told the info lets think about this. Assuming a larger intake throat under a 4mm smaller radius throttle plate, the first thing that will happen is a slowing of the mixture and also at the same time a lessening of the density of the mixture. This may put more gas into the suspension of the mixture. Then the port tightens up on it's way to the head and the velocity loss is now regained minus a negligible amount to friction on the sides. The mixture redensifies and the result is an improved mixture great for making bigger power. Am I on the right track?

Thu Nov 06, 2008 4:44 pm

Redensifies - is that a word?? :shock: