MrDude_1

iTrader: (4)

ok, ive been thinking about this and looking up what i can for the last 2 days..

someone is going to have to explain to me how the exhaust valve effects the intake runner length.

i understand the runner length tuning for RPM, and the intake valve timing, the pulses and echo pulses from the valve slamming around... but how does the exhaust valve timing have any effect on it??

i could buy into the theory that the valve OVERLAP has an effect.. but the overlap isnt dependant upon LSA.. sure the LSA effects the overlap for any given set of lobes, but its not what actually sets the final overlap, its just a factor in that equation, and therefore isnt the variable to be looking at...


maybe im overlooking something simple. can anyone writeup a quick explanation for me?

SStrokerAce

iTrader: (2)

Of course! I still don't understand why people think EFI changes the cam choice?

Bret

SStrokerAce

iTrader: (2)

Nope it's overlap.... the fact that it creates a lower pressure in the port at intake valve opening is the key.

Bret

DJ's Z

iTrader: (10)

So does this whole theory (LSx vs Single plane) hold true when using an intake elbow and 90mm TB?

I can see using the accufab set up on top of the intake not being quite as effective as using an intake elbow with a 90 TB giving more plenum area and more velocity...I could be full of sh** though...

MrDude_1

iTrader: (4)

lower pressure in the port or lower pressure in the chamber??
my thought would be that you want the pressure in the port to be as high as possible inrelation to the pressure in the chamber/cyl so that the air wants to rush in harder.

following that train of thought in my head, i could somewhat imagine that fast moving gas (moving = high pressure) going out the exhaust valve could make the intake port have a lower pressure in relation.. and if both valves are open at the same time, that could have an effect...

am i thinking correctly? how do you use this to your advantage?

SStrokerAce

iTrader: (2)

Lower pressure in the cylinder relative to the pressure in the intake port. Overlap is all about using the exhaust to cause this.... The larger the pressure difference between the intake port and the cylinder the better the filling. This is one of the things that helps you get over 100% VE.

Bret

Rick@Synergy

iTrader: (5)

From what I have heard from others that tried this, they lost even mre power than the TB on top of the Vic Jr.

Rick

MrDude_1

iTrader: (4)

do you know of anyone that used a plenum instead of an elbow? a nice size box over the manifold itself, with the throttlebody feeding the box??

SShark

iTrader: (1)

Rick at Synergy will putting that set-up on my 408 in probably a week or so. So you can maybe check mine out.

Pro Stock John

iTrader: (34)

"You need more intake" is something to think about here.

Certainly if you look at a 346ci with a mid sized street cam like that, I would posit that you are not out of intake.

Now in the case of a a friend with a 4xxci SR engine that went over 148mph on motor, he runs a hogan sheetmetal that is practically a tunnel ram. And he's out of intake.

A 346ci with say a hydraulic 252/260 with 225 AFR's would need more than a LS6 intake, because it would be choked. Might see more value with the single plane stuff with the SR stuff revving 7200-8500 NA and with hydraulic 252/260//108 type stuff. I'm generalizing bigtime here but my point is that a big cam big head setup will need an intake that will work in higher rpms.

And you should not have to add major timing to the LS1, the heads are much better than SBC's which typically need a a lot more timing.

MrDude_1

iTrader: (4)

now, now... i know you're still "generalizing bigtime", but that statement depends greatly on WHAT SBC heads you're running...

SShark

iTrader: (1)

Hell i'm a little concerned about my choice of intakes now. But ole well we will see what happens, and maybe we can swap a Fast on there for comparison sake.

DJ's Z

iTrader: (10)

Not something I wanted to hear. Wondering if this was on a small (346) CI motor running a N/A set up...? If that even matters.

So your under the impression the 90 degree intake elbow with TB for a bigger (408) CI with good aftermarket heads/bigger camshaft and FI would loose more power than the TB's sitting directly on the top of the Vic Jr.?

That sucks!! Guess I'll find out and post results...I knew I should have waited until some testing was done on these.

What would be the reasoning behind the elbows not working as well??

SShark

iTrader: (1)

I'm in the same boat as you!

Ed Wright

iTrader: (1)

Air does not like to turn.

DJ's Z

iTrader: (10)

Even though the transition seems to be pretty smooth without any sharp angles...? I've seen many FI cars with plumbing "to" the TB at a much worse angle of entry than these intake elbows...does it matter if the restriction is before or after the TB that effects the rush of incoming air and its efficency?

Hopefully it wont be as bad as some suggest. We'll see shortly. Which one does everyone think will be less of an issue with air "restriction"?

Because of clearance issues most of the F-body guys that are running this set up are using the sheet metal intake elbow...

93LS1RX7

iTrader: (8)

Forced Induction doesnt get affected as badly by the bends. The airflow restrictions can be made up but turning the wick up a little.

stang90gt50

iTrader: (6)

On this test that this topic started on, is the motor a 346" ? what cubic inch was this test done on?? (I think its been asked like 4 times already)

Rick@Synergy

iTrader: (5)

yes, it was a 346, a 230-234 cam. IT was a basic test to see if there was any difference for those seeking a different style manifold.

Rick

SStrokerAce

iTrader: (2)

I've done some tests on the out of the box intake elbows like the Wilson 110° and it only hurt flow thru the intake and head by 3cfm. With some porting and a 1" spacer that is basically gone.

Bret