the scavenging effect benefits engines running cams with a lot of overlap moreso than others. i seriously doubt you'd see much of a gain comparing an x pipe td system with a good y pipe on the stock cam. however, after you install a t-rex, i guarantee you'd see more hp in the upper rpms with the x pipe setup.

 

Take a look at the firing order of any V8 engine. You will find that there are two cylinders on each bank that fire one right after the other. When these two exhaust pulses come together in the header collector it forms a high pressure pulse. As a result the exhaust passage (pipe) becomes "crowded", kind of like two people trying to go through a door way at the same time.
When the high pressure wave gets to the X-pipe, it has access to TWO pipes rather than just being stuck in the one.
Once the high pressure wave is broken up into the two pipes it no longer poses as a restiction, which can increase the flow of your exhaust system. This also reduces the enegy in the pressure wave which also reduces the sound you hear at the tail pipe.
An H-pipe or cross-over serves the same purpose but does not do the job as well.
Ken

 

Only if the Y pipe couldn't flow sufficently. For a stock/ bolt on LS1 a 3" Y flows plenty enough for minimal flow loss. So merging the two pipes is not an issue, in fact due to the smaller area/volume of a single 3" Y pipe exhuast flow velocity is better than it would be running 2.5 duals. So you stand more chance of seeing better under the curve performance with the Y pipe and just as good high end.

Allowing the exhuast gas to release into the atmosphere as quick as possible is not a required attribrute.

The primary lengths need to be correct to allow scavenging from the headers for 'x' rpm range. Short primaries higher rpms (why shorties on LS1's yield little power), longer primaries work at lower rpms, hence LT's produce lots of power on LS1's.

There is then tuning of the exhuast pressure wave. Dumping straight from the header can be counter productive as the pressure won't have straightened out fully.

As long as the exhaust tubing flows sufficently I can't see any reason why a full system will have any real affect on flow or HP. Race cars tend to run open headers because:

a) they have no space for running the exhuast anyhow
b) have no need to have tubing to fit mufflers
c) have no real idea why they run open headers, don't really understand exhaust flow and only run them becuase other people where, hence we end up with this circle where it all ends up on word and mouth and no physics

There are occasions where dumping straigth from the primary's work well. Take a look at any WW2 fighter plane. I guess most notably would be the Sprtfire with it's 27 litre Supercharger Rolls Royce Merlin V12. Each primary faces back and is fairly short, but there are no collectors. It was well known that more power could be made via scavenging but exhaust propolsion (think a bit like a how a jet moves an aircraft) was more valuable at high speed for aviation purposes. The relativley short primaries kept the exhaust gas velocity high.

Click the link in my sig and read post 6 and 13 onwards. David Vizard explains how to design what he claims as a "Zero Loss" exhuast system. It runs to the back of the car, uses 2 mufflers and a resonation chamber. It's a interesting and worth while read.

Provided the Y pipe was of suitable diameter and the merge collector was as of good design as that of the X pipe I would disagree with this claim.

LG make arguably the best LT headers for Corvettes (plus other performance goodies). Yet on their race cars they convert the X pipe to a Y pipe. If this was counter productive to bhp/performance they simply wouldn't do it.

Also in the past I have spoken to one of Magnaflows engineers and they confirmed that they suspected a properly setup Y pipe would perform as well/equally to an X pipe setup.

This is correct but not on ALL V8's. Only most traditional V8's as found in America. Ferrari, TVR and Lotus V8's are single plain V8's which have an even firing order. This is mostly what gives a Ferrari V8 such a distinctive whail of a sound, as opposed to the more tradional rumble we are used too.

single plain V8's are essentially two Straight 4 engines with a common crankshaft, where as a traditional V8 is more or two V4 engines using a common crank.

I kinda agree with that, but not 100%. Yes 2 cylinders fire on the same bank cosecutively (sp?), but that is why an engine such as the LS1 requires 3" collectors as a minimum. A single plain V8 of the same displacement would be able to run much smaller collectors.

And again I think its all about flow where the Y pipe is in use. Two 3" collector pipes running into a Y merge collector and into a 3.5" I pipe will flow more than sufficently for most LS1 setups.

Also the Y merge is generally located far enough away from the header collector for the pressure wave to have straighten out, so having a 3" I pipe after the Y isn't nearly as bad as many believe.

It must be for this reason (IMO ) that so many people have been able to produce fantastic rwhp figures with Y pipes. Even the ones running boost. And also why people don't see a gain going to duals over a good Y pipe setup (I have even seen cases when people have lost HP going 3" Y pipe to 2.5" duals).

Nearly every case that someone claims duals made more power than a Y pipe it turns out to be some other reason. Such as using better suited mufflers on the duals where they where a restriction on the Y setup. Or changing headers over and/or having a tune at the same time.

I personally like duals and if (when ) I go FI I will run 3" duals, but I would be aiming for 650+rwhp.

However I have yet to see any proof which can be scrutinised that proves bolt on (even cammed LS1's) make more power with duals over a good Y pipe. There's always holes in their arguments.


However I could be totally off my rocker and just making this up , so if anyone has any proof/theories to the contrey - post em up!

 

That is the longest single post I have ever seen!!! Do they keep records for that kind of stuff? Cuz I think you'd win.

 

BTW, about these crowding exhaust pulses, I thought this was the reason the LS1 engines have a different firing order than a SBC, i.e 7-4 split.

 

oh my, search his posts. you'll find ones MUCH longer than that

you know when ls1tech bogs sometimes and the bandwith just seems to stop? that's when 300 posts

 

This **** match is about to get the closure code stamped on it.

 

i don't see why people are arguing so much about this. it's simple physics. greater exhaust velocity = more horsepower. flow rate is just a compononent of achieving exhaust velocity. if you put 9" exhaust on your car, your car will lose power since the exhaust velocity is not high enough. too much flow is just as bad as not enough flow unless you make absolutely massive horsepower to support it. you all can argue as much as you want, but arguing with facts will never make you right.

flow is just a step on a ladder.

 

Maby we should run 1.5" exhaust then? We'd have tremendous VELOCITIES. I beleive there is more going on with flow rates than you know about, and pretending like you do is the worst thing there is.

I find myself puzzled with some of the things that are theoretical compared to the things that have been proven in the real world. I know that volumetric flow rate is determined by the cross sectional area and the velocity. I know that a reduction in cross section area (smaller pipe) will cause no drop in flow rate due to the simple increase in velocity that insues (theoretical). I know rule about 2.2cfm per hp needed for un-restricted flow. I also have heard about exhaust pipe flowing 115cfm per square inch, but don't know how they came by that considering the formula for flow mentioned earlier. When I get to fluid dynamics, maby I'll have more to report. Untill then, I'll refrain from making "factual" comments about things of which I have no idea.

3" ORY pipes will have DOUBLE the gas velocity in the I pipe as a set of 3" duals with an x-pipe. Even if the y-pipe was dumped, do you think it would make more power than 3" duals"? No.

 

Click.