Nahh,

I think i just read it wrong. i thought you said something about, boost isn't created up high, because the exhaust isn't assisted out of the motor, like the intake side is, being as it is forced.
on that subject, tri-y headers are suppost to create a suction. this might work better than the standard 4-1 type header. something i had heard.

on the original topic, the correct valve events will give the lsa needed. i think it seems the wider the seperation the more power, is because we're just decreasing overlap.

put the correct events for the engine combo, and the wider lobe seperation wont help.

boost begins so early w/ the radix, i think its hard to tell the effects of a wider lobe seperation. gains will be seen up top, this is certain. so i think this is attributed to everyones belief that wider=better in forced induction.

 

I agree with Flyer's thoughts on the blower cam.

sportside - I know what you are thinking. You are trying to apply the concepts of valve events and proper cam specs for your specific combo from those camshaft discussion threads. Those were focused mainly on N/A systems. Spend just a bit thinking about the difference in a Radix motor and a N/A motor:

The NA motor depends on getting the intake charge open at just the right time to take advantage of scavaging, yet closing it soon enough so that it builds good pressure. That motor depends on the quality of the heads, the intake port runner length and size, the valve shape and diameter, etc... The cylinders get filled with vacuum created by the downward movement of the piston. The valves have to open and close at the right moments to maximize power and take advantage of the engine specifics.

The Radix motor doesn't depend on intake runner length, it has an intercooler crammed in there instead. The intake valves have pressure behind them, so the cylinders aren't filled from vacuum. The intake duration isn't as important since the cylinders get filled much easier with the boost. Exhaust on the other hand need more duration. Much more air and fuel are getting used here, so the exhaust need more duration to get it all out. When the valves open and close is important. But allowing the cylinder to get maximum pressure and getting all that exhaust out takes different events for boosted motors.

The correct valve events for a blower motor will have less overlap than a NA motor. The wider LSA is a result of a smaller intake duration and not needing overlap to aid cylinder filling.

What do you think?

 

That's not to say that the blown motor wouldn't benefit from good, nice free flowing heads and a nice exhaust.

In the grand scheme of things ... it's basically the same principle as why you would want a GOOD free flowing exhaust on a blown motor. On a 'stock exhaust' truck, you can compensate in a way for the lack of free flowing exhaust with a big split duration cam.

Does that make any sense at all?

 

man i knew you could put all this in perspective. i need to learn more about cams. thanks bigtex/

 

I'd like to take one of the camshafts alot of us use, and then change the ve's to match a blower motor.

I wrote this on another forum, see if you agree tex.

Ok, take the Comp 216/220 w/ 114 lsa 110 ICL 118ECL

ve's @ .05

-2* after top
38* after bottom
48* before bottom
-8* before top

I need to go. I'll get back to it this afternoon.

Thanks for your post B.T.

 

sportside, post a link to that thread you quoted. I'm not sure I agree with that, but want to read it in the right context.

flyer - I was trying to focus on why a blower cam needs to be different than an NA cam. No doubt the exhaust system is important. In essence, a blower motor and NA motor can apply the same principles to make power - fresh air in, burnt gasses out. Each need the proper setup to run perfectly. The same individual components and theories apply but the order of importance is a lot different.

I'll get back to this later too.

 

That's what I've been trying to get into the correct wording...

I didn't know about the smaller intake duration though. Does the intake duration still dictate how high the powerband will be in a F/I application like it would N/A?

 

Richard,

This is where that response can be found. Its only a couple of posts, so if time permits, read the whole thread if you would like. There are some good views and information.

Post

I really have no interest in a blower, other than knowledge.

Here's also another response I recieved on efficiency and flow numbers:
Relates to one of my first questions...

Marc,

The intake duration takes part in judging the amount of air entering the motor. If you can't fill the cylinder completely at a higher rpm, you wont create power. Therefor, giving you the drop, seen on dyno graphs. That's also why holding the valves open longer for higher rpm work, hurts bottom end. Kills velocity.

--
Marc,

I might be reading your question wrong.
Duration has a direct effect in overlap. Seen in the equation for degrees of overlap:
Intake Duration + Exhaust Duration / 2 - (2 * LSA)

So holding back the intake duration, shortening the power band. Going wider with the lsa, holding power longer up top to fit your power band. and also keeping overlap to a minimum.
I think this is how many are approaching their FI setups. But alot use way to much duration on both sides. IMO
I think thats one way to look at it.