Independant Throttle Bodies (ITB's/IRTB's)

yeah your an M E right Black? I would hope you kept your physics books...

Someone please enlighten me on the notion of 4-2-1 headers being a compromise...Everyone has heard every rumor there is about headers...And I am not getting started on the "back pressure" BS that people throw around...but I am also not saying that 4-2-1's are better...just want to hear both sides of the argument...
 
Nah, I'm not a Mechanical Engineer... My roomie is, though. I'm a lowly UNIX Systems Administrator/Programmer.

As far as the stigma with 4-2-1's, I'm really not sure where that spurs, but I'm sure there's a good reason for it. =) I just don't know what it is. Laminar flow would suggest a more gradual collection of turbulant pulses would prove more beneficial to the velocity inherant in an exhaust system, but then again, you'd be shedding more heat, which means compression of the gasses, and more turbulence from that side of things... I guess I'd have to let others chime in there. =)
 
Yeah I have heard some arguments about 4-1's being better...but never from very credible individuals...which is why I am interested in what Josh and Spec and others on here have to say...some of my high school friends would say that a long time ago...but for reasons I can't even remember...

But its nice to see that someone is familiar with the pulse theory...and correct a number of different factors show more favorability towards a more gradual collection of pulses...especially when the pulses are at moderate frequency and moderate size...which is right at peak volumetric efficiency...which is at max torque, pegged in the middle of the rev range...

So I think I see where this is going...4-2-1's are probably better for midrange, or at least I think that is the argument...and 4-1's are better for high end...Just curious as to what reasons are given to why...small pulse width at an extremely high frequency will not sit any better with being slammed through a single collector...at least on paper it won't...
 
i read ... and re-read the posts ... and still can't understand half the stuff you guys are saying.

i wish i knew more about this.very interesting thread though.
I have a question ... what kind of mods would make my setup run better ? My friend had his intake / exhaust / head ported, which i think i will do too. Anything else we should do ? I know the basic stuff, but when it comes to those little technical details, i'm so lost
 
Metal MP5 said:
i read ... and re-read the posts ... and still can't understand half the stuff you guys are saying.

i wish i knew more about this.very interesting thread though.
I have a question ... what kind of mods would make my setup run better ? My friend had his intake / exhaust / head ported, which i think i will do too. Anything else we should do ? I know the basic stuff, but when it comes to those little technical details, i'm so lost
Click to expand...
Hey Metal, here's a good book to go out and purchase:

"Four stroke perfomance tuning" by A. Graham Bell. I'll be honest and say that I have read 2/3 of it, and a LOT of it is over my head, but it is a good read nontheless. So its not really a starter book like I was hoping for, but its still good info. Eventually I hope to be able to read it and understand 90% of it.

sorry for the thread jack,
scorch70
 
Here's my take on the 4-1 vs 4-2-1 debate. The gains from a Tri-Y(4-2-1) are mostly from reducing pumping losses. They make them to be cheaper(4 tubes for 1/2 the length, then just two tubes to the collector), and space efficient(the tubes can go side by side). Everyone claims they're good for torque and midrange, becuase when you dyno one, those are the only places they give gains, as they're weak in the top end. They just don't flow as much.

With a 4-1 header, you have the reduction in pumping losses, and even more, all 4 primaries run the length of the header, abling them to maintain their velocity longer before having to share any length of tubing. Then there's the 'tuned' factor. The valves opening and closing create pressure events within the exhaust, which travel at the speed of sound(most of you know this, so this is for the ones who don't). Those pressure waves travel down the primary and back up another one and back again, creating a pressure vacuum, helping pull spent gases from the cylinder when the valves open, and the process happens all over again. So obviously the system is only efficient over a narrow powerband, which is related to the length of the primaries. Longer primaries are more efficient at lower RPM and shorter ones are more efficient at higher RPM. The problem with most 4-1 designs, is that they're never long enough. I'm designing my 4-1 with 36" primaries, which is tuned for the 7000RPM region. I don't know of any headers with 36" primaries. So with say an FS-DE 4-1, with a larger displacement and lower RPM range, you'd be looking into the 40-46" primary range to be effective. Even with my design, I'm going to have to push back the flex pipe and cat.

So with a 4-1 header, not only do you get the free-flowing nature of a header, you get a tuned band with is good for another 4 or so hp. Because of that extra hp peak, people also think of a 4-1 at being only good for the top-end, because it's extraordinary up there.
 
Gen1GT said:
With a 4-1 header, you have the reduction in pumping losses, and even more, all 4 primaries run the length of the header, abling them to maintain their velocity longer before having to share any length of tubing. Then there's the 'tuned' factor. The valves opening and closing create pressure events within the exhaust, which travel at the speed of sound(most of you know this, so this is for the ones who don't). Those pressure waves travel down the primary and back up another one and back again, creating a pressure vacuum, helping pull spent gases from the cylinder when the valves open, and the process happens all over again. So obviously the system is only efficient over a narrow powerband, which is related to the length of the primaries. Longer primaries are more efficient at lower RPM and shorter ones are more efficient at higher RPM. The problem with most 4-1 designs, is that they're never long enough. I'm designing my 4-1 with 36" primaries, which is tuned for the 7000RPM region. I don't know of any headers with 36" primaries. So with say an FS-DE 4-1, with a larger displacement and lower RPM range, you'd be looking into the 40-46" primary range to be effective. Even with my design, I'm going to have to push back the flex pipe and cat.
Click to expand...

I thought that the valve pulses could be tuned at any multiple of the full length. What that means is if you have 46" as a design length for 7000 RPM, half of that is 23", and the sound waves would travel up the pipe twice. I've heard that with intake runner design, since you can't have 50" runners that the length is designed to have the wave bounce back like 10 times.
 
I've heard that theory too, but haven't researched it enough to comment. Would that mean that 11.5" primaries would work also? What about 5.75" primaries?
 
If you guys haven't read this, give it a once-over. Some interesting points on header/exhaust therein.
 
What did you pay for these again? Like $300-400. You lucky bastard. Well, you still have lots of custom fabrication to do. Have you decided on which EMS you're using?
 
I paid $70 for these ones, since they were a set that someone never came by to pick up (As of three years ago or so); but they normally would have set me back about $300, and anyone else around $500, anyway. =)

Yep! Lots of custom fab work, and that's what I'm going to start on a little bit today.

The EMS still is up in the air, but I've got it narrowed to four choices, now. The AEM is still the cleanest/easiest option, but pretty pricey. The Haltech is the most complete option, though, again, pricey. The TEC-II looks like it's an option, but it doesn't have a few features that I wanted. And the Perfect Power series of ECU's is now an option, but I'll have to wait 'till I get an e-mail back from them, letting me know a few details about the systems I was looking at. That would be a nice option, but I'm not sure how viable it is, given that it typically retains the stock ECU.
 
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