QIK E

Well my headers finally came in, and now i'm a little worried. They headers look great....couple scratches here and there, but nothing major. Here's what I'm worried about and tell me if I'm freaking out over nothing.

The inside diameter of all the pipes after the headers is 2 (6/16) " .....I would have preferred 3" because I have a 3" magnaflow exhaust that i'm going to gave to STEP UP to.....dumb. Will this make that big of a difference?

99SSJarhead

iTrader: (2)

Stepping up won't hurt. It can actually be beneficial in a lot of systems and a lot of people do it (though usually going from a 3" to 4" I pipe back to 3" over the axle). You'll be fine

QIK E

Yea but i'm going to be going from 3"because headers down to a 2(6/16)" y pipe back up to a 3"magnaflow exhaust....I know this will be a bottleneck. I'm eventually shooting for 500hp

QIK E

How big of a bottleneck is this going to be? Im almost thinking of selling these and getting pacesetters instead......if I would have known the I.D. of the y pipe was less than 3" I wouldn't have bought them

99SSJarhead

iTrader: (2)

Oh, misread then. Yeah that'll be a choke point. It won't harm anything but it will choke off some ponies, especially when you start flowing more air through better heads and intake.

TImmy_Jones

iTrader: (4)

I cannot even explain how you JUST wrote the thread I was going to create! (Just got my OBX Headers and Y) My collectors and fake cats are 3" and look awesome....friggin Y pipe is 2.5" to the merge which is then 2.75"...

Quoting someone on here....here are some exhaust numbers:

A 2.75” (stock) single system is good for a 310hp engine with zero loss…
A 3” Single system is good for a 370hp engine with zero loss…
A 3.5” Single system is good for a 503hp engine with zero loss…
A 4” Single system is good for a 657hp engine with zero loss…
A 2.25” dual system is good for a 457hp engine with zero loss…
A 2.5” dual system is good for a 513hp engine with zero loss…
A 3” dual system is good for a 812hp engine with zero loss…

If a 2.25 dual system is good for 457 HP, I should be ok with stock internals. I, am at the same time beyond pissed and wish I just spend $200 less on some BBK headers...this sucks.

I guess I should be fine, my 3" single catback system is obviouly far more restrictive than even two, 2.25" pipes, but damn.

TImmy_Jones

iTrader: (4)

I was also thinking that we may get some help from the Venturi Effect...from the 3" collectors to the 2.5" Y pipe.

There is not a lot gained on a bolt on car, by the size of the pipes on the headers, it is more the scavenging effect and how quickly the car can push the exhaust gas out, you really do want the smallest diameter piping that supports your power.

I am trying to convince myself here, that these headers are not half bad.

99SSJarhead

iTrader: (2)

Proper scavenging in our cars are better served by going 3"-4"-3" not 3"-2"-3". You want an area of decreased pressure to suck the air out, not increased pressure to hamper flow. You end up with back pressure that way which is bad for our cars.

I think you're more or less boned into getting a better Y.

TImmy_Jones

iTrader: (4)

Well, we are going dual 3, dual 2.5, single 3. No restriction until the catback... It seems.

QIK E

Ok thanks for the info! that's not as bad as I thought. I am going for around 500hp eventually so 2.25" won't be terrible.

I guess if I do get to the point where i feel it's robbing too much power, I'll just take off the y pipe and have a flowmaster y300350 welded in with a cutout.....that will be after intake, heads/cam, rear end and trans rebuilt though.....LONG WAY TOO GO

I feel much better now....Stainless for $500 looks awesome

TImmy_Jones

iTrader: (4)

When are you installing? I was going to next weekend.

Darkman

iTrader: (2)

For what it is worth - Based on gas flow formulas, that 2 6/16 inch (2 3/8 inch) pipe will only flow 54% of what a true 3 inch pipe would flow. That is not an insignificant drop in flow rate.

Damian

iTrader: (89)

There is a reason OBX headers are so cheap....

Unertl42

iTrader: (63)

exactly, you get what you pay for.

TImmy_Jones

iTrader: (4)

Dual 2.25" pipes far outflow a 3" pipe....the y is very well built, just seems to be a copy of the bbk setup

Darkman

iTrader: (2)

Actually that is not true. A single 3 inch pipe will flow about 5% more that two 2.25 inch pipes. Flow rates increase exponentially with pipe size such that if you double the pipe size the flow rate increses by a multiple of 6.

got milk??

iTrader: (18)

Where did you come up with that? I know that air and water have similar characteristics when talking about volume and flow, and just going by sheer volume two 2.25 inch strait pipes the same length as a single 3 inch pipe will allow more volume than a single 3 inch pipe. Last time I checked comparing round pipe the more volume you have the more flow you will get as more air is able to pass, keep in mind I am only talking about the characteristics of the pipe without outside forces ie... the engine.

Here is what I came up with taking (1) 2' section of 3 inch round =2.875 liters. Now (2) 2' sections of 2.25 inch round = 1.567 liters per pipe x2 = 3.134 liters

Darkman

iTrader: (2)

My comparisons are based on the exponential relationships from Weymouth flow formula, which is commonly used for designing gas piping systems. The flow relationships cannot be estimated or compared using pipe cross section comparisons.

The complexity of the underlying formulas can be seen here.

http://www.psig.org/papers/2000/0112.pdf

The Weymouth formula can be reduced to the rule of thumb stated earlier, which is that the doubling of pipe diameter will yield a 6-fold increase in flow rate capacity.

TImmy_Jones

iTrader: (4)

Well, my OBX Y pipe is 2.5 inches...dual.

A 2.75” (stock) single system is good for a 310hp engine with zero loss…
A 3” Single system is good for a 370hp engine with zero loss…
A 3.5” Single system is good for a 503hp engine with zero loss…
A 4” Single system is good for a 657hp engine with zero loss…
A 2.25” dual system is good for a 457hp engine with zero loss…
A 2.5” dual system is good for a 513hp engine with zero loss…
A 3” dual system is good for a 812hp engine with zero loss

I think my 3" catback is going to be my restriction, not the Y pipe.

Darkman

iTrader: (2)

Two 2.5 inch pipes will flow 25% more than a single three inch pipe.

Whether the downstream three inch pipe is a restriction depends since the exhaust gas cool and contract, and therefore occupy less space the farther downstream they travel.