Straight thru exhaust?? bad idea?

[egos_86]

Right I can get a straight thru side exit exhaust for only £100 from turbo back and I want it comin out of the front bumper.

everything Ive read suggests that bigger is better and the faster I expell the gas the better. I understand all that but a freind said that I should be carfull as I can blow the seals off my turbo if theres no back pressure

He said a mate with 32,000 miles on a celica gt4 ran it for 15 miles with NO exhaust and he blew his turbo, should there be 'some' back pressure or is it fine to have a straight thru.

He also said that with a ballbearing turbo you should be ok tho, is he talkin ****??? Is the GTX/VJ24 even a ball bearing turbo??

Cheers peeps

[ROB-80E]

Is your car a race/drag car? The thing i'd be more concerned about is if it is legal for where you want your exhaust to exit the car. Here in aus, road legislation states that exhaust gasses are only aloud to exit at the rear of the vehicle.

Food for thought

[dave0r]

the turbo itself creates some back pressure to the engine directly, i ran my Astina with the Evo 6 turbo for 7 km to get the exhaust hooked up, no problems at all
i don't think it'll "blow" because of no exhaust

but as said. all you have to worry about is the noise DB levels as they WILL be high

[egos_86]

Originally Posted by dave0r

the turbo itself creates some back pressure to the engine directly, i ran my Astina with the Evo 6 turbo for 7 km to get the exhaust hooked up, no problems at all
i don't think it'll "blow" because of no exhaust

but as said. all you have to worry about is the noise DB levels as they WILL be high

Nah not a drag car, just a cheaper/lighter option than a full system . Ok, the back pressure I was talking about was post turbo back pressure. I spoke to guys at blueflame and my mate was kinda right. Apparanetly, some turbo cars like VW when you remove the cat and reduce the back pressure they muck up. And he also said that roller ball turbos will be fine.

Is the vf24 a ball bearing turbo???


Anyone?

And side exits I think are fine in the UK as long as they meet emmisions and noise and dont spit flames at pedestrians lol! (driver side only)

[FEM]

hmm, i dont think so? i could be wrong though. Rob will know!
btw, nice sig rob!

[egos_86]

Change of plan now, keepin original exhaust and getting an electric exhaust cutout

http://www.quicktimeperformance.com/QTEC/index.php

Anyone had any experience with these??

[bourbon]

looks pretty cool...thats a pretty good price...alot cheaper than i thought i would be...

would definatly be worth a try...

[DavoAust]

thats cool. you'd install immediately after the cat to avoid resonators/muffler etc downstream i'd assume. not quite sure if i believe the 'Dyno Proven Results!' on the right though. 75hp is a big improvement just from effectively taking the muffler off

[Rupewrecht]

You're going to go deaf. I've run my car with no muffler and yes, the extra power it lays down is great, but the heap of extra noise is uncomfortably loud. At least with the QTEC you can make it normal again.

[bourbon]

yeah...well this would be perfect for drags and track work...but only issue is it would need to be tuned for it to have it so it has a screamer pipe and then tuned for normal...

wouldnt the exhaust flow still go out the rest of the exhaust?

[ROB-80E]

Cheers FEM

EGOS_86 - What turbo are you using?? You've basically mentioned 3 diffrent turbos. GTX, VJ24 and VF24.

None of the turbos are ball bearing. The closest to that is the VF24 which is Roller Bearing off a 97 WRX STi. The GTX turbo is usually a VJ20 which is just sleeve. The only mentions i could he VJ24 is upgrades/hybrid turbos where the compressor wheel is used.

[FEM]

does that cut out exhaust mod thing stop the all the flow to the normal exhaust and direct 100% of it out the cut out? or does it just open the cut out?

[egos_86]

Sorry Im using the vj20 turbo lol, I get a bit confused with all these codes, The QTEC doesnt close up the original exhaust, just the gasses find the easist way out ie: thru the cut out. Im sure some gasses will pass thru ur normal exhaust.

And for the 75bhp gain on the Honda, that probably would have been with the stock N/A exhaust which is prob only 2" or less! So could be possible.

I was thinking of using this direclty on the end of one of the downpipes corksport make for the BP/VF20, Anyone had any experience with that. I cant seem to find any dyno results and I heard that some after market downpipes can actually hinder performance due to the wastegate returning to the downpipe at the wrong point and affecting scavanging what ever that is!?!

http://corksport.com/store/category/...rbo_Parts.html

[DavoAust]

scavenging uses back pressure and vacuums to make the engine more efficient, its more important for NA engines but it affects turbos too. hope you have a good set of ear muffs if you're running it from the dump. it'll be deafening even in the car

[LordWorm]

Originally Posted by DavoAust

scavenging uses back pressure and vacuums to make the engine more efficient, its more important for NA engines but it affects turbos too. hope you have a good set of ear muffs if you're running it from the dump. it'll be deafening even in the car

slight correction... scavenging doesn't use backpressure, and infact, backpressure would be detrimental to scavenging.

Scavenging utilizes negative pressure waves entering the collector to apply suction to all the other pipes - when tuned correctly, this pressure wave can be "timed" to occur at the next cylinder in the firing order's exhaust event to help suck, or "scavenge" the exhaust from the cylinder. It an also be used in conjunction with large overlap cams to help suck in the next air and fuel charge. Both of these actions can assist with improving intake and exhaust charge velocities. An exhaust system should push as much air out as possible, as FAST as possible - which is why smaller exhaust systems make cars pull harder lower in the rev range, the narrower pipe allows the gas to flow through at higher velocities....unfortunately if you are to small, this in itself will lead to restriction at higher engine speeds.

Backpressure i any exhaust system is to be avoided at all costs, although it is not aways possible, or practical to do so. A turbo charger for instance is by its very nature a restricton...and gas entering the exhaust system via the waste gate pipe (obviously not a concern with a screamer pipe) will naturally create turbulence.

[egos_86]

does scavanging have anythin to do with the pulses?

posted at same time as above, that cleared things up

[LordWorm]

Originally Posted by egos_86

does scavanging have anythin to do with the pulses?

posted at same time as above, that cleared things up

scavenging is the collection of the exhaust pulses, leveraging the negative pressure wave that follows behind them.

Think of it this way, when the fuel burns in the cylinder, it consumes the fuel and oxygen present in the cylinder, converting it to exhaust gas (which is made up of lots of stuff, mainly carbon monoxide, unburnt fuel, nox, and any oxygen that wasn't consumed in the burn)....

That gas is then forced out of the exhaust valves by the piston traveling back up towards top dead centre, and escapes through the primary pipe of your manifold. When that gas enters the collector, the vacuum it creates is applied to the other 3 pipes, which creates suction. If this occurs at exactly the moment another exhaust valve opens, it helps to suck the exhaust gas out of the cylinder, and you have scavenging.

This will occur on NA and turbo cars alike, however turbo manifolds generally have very short runners, which means the point at which those pulses will have any useful impact on the breathing of the engine will happen at such a crazy high engine speed, its not even worth worrying about. Thats not to say turbos are disadvantaged, what they lose from not being able to utilize these scavenging waves is more than made up for the fact that air on the intake side is being forced in at well above ambient pressure. Of course, some turbo race cars run tuned length turbo manifolds, to get the last few percent out of their systems at high RPM, but for a street car this usually means terrible low RPM performance and a healthy dose of turbo lag.

According to a variety of papers i've read on the subject (i can provide links if neccessary...), it is more important on a turbo engine to have maximum flow upstream of the turbo, that is at the manifold. This helps dump the tremendous amounts of exhaust gas that a turbo motor on boost creates, and to use that energy to spin the turbine. After the turbo, (essentially) bigger is better, to the point of diminishing return. You should also keep the waste gate pipe from merging into the main exhaust pipe (if you are going to merge them, sounds to me like you want a screamer/atmo dump) as long as possible, so as not to create turbulence immediately after the turbo.

For NA, it is most important to achieve maximum flow AFTER the collector cone - this is because in an NA performance engine, the collector is what is doing the work - at a tuned length the collector is applying the vacuum energy of each exhaust pulse, at a specific engine speed, to assist in sucking exhaust gas out of the cylinders, as well as sucking fresh air in, which minimises pumping loss.

basically, for a turbo motor, flow is king, and for an NA motor, velocity is king.

[bourbon]

since seeing this im thinkin i might get this so that ican use it for drags/track... having this before the cat would mean it would have more flow and as far as i know a drag/track car doesnt need a cat...

my question is...would it need to be tuned everytime i swaped from screamer pipe to normal exhaust?

[LordWorm]

Originally Posted by bourbon

since seeing this im thinkin i might get this so that ican use it for drags/track... having this before the cat would mean it would have more flow and as far as i know a drag/track car doesnt need a cat...

my question is...would it need to be tuned everytime i swaped from screamer pipe to normal exhaust?

a screamer pipe refers exclusively to an atmospheric waste gate dump....without a turbo you don't get a screamer (its called a screamer because of the noise it makes when the waste gate opens.....if you listen to the pro turbo cars next time you are out at willowbank you'll know what I mean)....

what you are refering to is an open exhaust.

I have one for my car, exits just infront of the front wheel, immediately off the manifold, and it does its job very well.

No need for a full retune though, just bump the mix trim up a little bit to add the additional fuel you need to go with the extra flow...(you can also enrich your idle maps a little if you want to get a cool over-run fireball thing happening )

[FEM]

how does your cutout thing go on your exhaust greg? do you have aftermarket extractors or seomthing?