Tin

does the y pipe help better your acceleration (0-60), or is it mostly for power in the high end (around 50-60 and up..)

pinkfloyd

The less back pressure you have the worse your low end torque will be for the most part, but the amount you gain in your higher rpm rang will make up for it. A Y-pip for the most part is suppose to make the exhaust flow smoother and therefore less turbulence and that equals less back pressure. So in the end it’s for more up top power. This is what’s supposed to happen but it’s different for different cars. I deal mostly with turbo non pistons cars so I could be way off, plus I’m drunk.

peace

bonzelite

iTrader: (2)

mmmkay. welp, you're kind of right. kind of not.

the y helps all over. it makes the most difference, yes, at the top.
the whole backpressure thing is a fantasy myth, though, i'm afraid to tell you.
your car would run faster if you removed the exhaust and ran
straight headers.

JohnnyWash1

Does that mean RX7?


As for backpressure and hp, there is sooo much more to the story than the oversimplification that usually manifests in the old "less backpressure less torque" addage.


Jon

Cliff Clavin

iTrader: (11)

I noticed an improvement pretty much all around when I added my y-pipe.

I haven't seen a stock vs. aftermarket VG y-pipe, but on my VE, you can just look at the way the stock one is shaped and tell that it is more restrictive. There is also a back bend that works against the flow on it from the rear manifold.

pinkfloyd

Yes that means rx7; I am in the middle of rebuilding an rx7 that was on fire, fun fun. And yes you are right about how running just headers would give you the most hp, but I'm assuming this is his daily driver so that wont help much. My 1990 maxima's exhaust rusted out and I had no power (torque) at the lower rpms, I had to push kind of hard on the gas to get her to go anywhere from a stop. That is where backpressure comes into play and it’s not a complete myth.

5 ltr. beater

And i'm afraid to ask you if you're serious about what you just said above.
Backpressure myth? There's no myth about it. The whole running straight headers works mostly on carburated vehicles (the old school Big block V8's).
Running straight through pipes on fuel injected vehicles actually makes you loose HP. (I know this because I've already tried it on every car that I've owned)

JohnnyWash1

Let's quit shooting in the wind here. The less restrictive the exhaust, the more hp you get, period. However, you shift your powerband when you increase/decrease backpressure. Less backpressure will lower pumping losses, but if you lower that too much you kill exhaust velocity. Do that, and you lose all low end torque in favor of high-rpm breathing. The car will still make more hp, but it might come at an rpm that is unusable during daily driving or undesirable for stock components.


Jon

MrGone

iTrader: (30)

backpressure






exhaust gas velocity

5 ltr. beater

You're right about the less restrictive the exhaust the more HP you get. HOWEVER..........we're not talking about that! Go back and read bonzelite's post.

bonzelite stated "our car's would run faster if you removed the exhaust and ran
straight headers".

That statement could not be further from the truth. I on the other hand am speaking from experience. A couple of years ago me my friends had access to a dyno and a rack. I have tried to run (for $hit's and giggles) my old 2 camaro's and my other 5spd. maxima with just the exhaust manifold and nothing else. Not only were all 3 cars gutless; but the dyno proved me right. On average, i lost between 35-45 at the wheels on both of my camaro's. The maxima was a little less; if i remember correctly I had only loss 23 at the wheels.

So again, a less restrictive exhaust will net you more HP; but an exaust with NO RESTRICTIONS, is an absolute loss of HP.

Now I hear that carburated vehicles actually benefit from a restricless exhaust; but I would need to look into that one.

JohnnyWash1

Sounds like an interesting study. I'm willing to bet you had too much exhaust flow for your head/cam setup, which resulted in the loss of hp. Bottom line is, we are both right. I was not thinking of what bonzelite said, and now that I have re-read it, I would have to agree with you. Our cars simply perform better with some restriction. However, I do not know what the perfect amount is---one thing is for sure, the stock exhaust is way too restrictive.


Jon

bonzelite

iTrader: (2)

carburated vehicles do benefit from a restrictless exhaust. that is absolutely true. "backpressure" is of no benefit. and the term backpressure, in this case, is used incorrectly anyway. there is really no such thing as that when talking about exhaust pipe restriction.

if you have done the experiment with no exhaust on the maxima, then there is no substitute for that.

i can tell you that the maxima does lose a little bottom end grunt with the y-pipe. but it is brief and below about 2200 rpm. after that, it is all gain. so the maxima does perform better with the y-pipe if you take this into account.

i have two maximas. one bone stock. one modded. and the stock one runs out of breath so soon that it is pathetic compared to the y-pipe car. i would never go back to oem pipes.

the slight bottom-end loss is somewhat offset by a lightened flywheel

JohnnyWash1

How does that work? Heavy flywheels are used to help drivability by "storing" energy in their rotational mass--giving the feeling of more torque. Lightened flywheel cars lose alot of this low end grunt because the flywheel is so light.



Jon

DanNY

iTrader: (14)

how does something store energy? something must give it energy for it to store.

if you changed your pistons to Ti or some new space age very very light metal wouldn't you say that the engine has less mass to move and it would rev faster from idle?

same concept of the lighten flywheel...it's less weight for it to move so it'll rev faster so you feel the car has more torque. at the same time the RPM will drop faster once you're off the gas since there's less mass to store the energy.


the backpressure discussion...too funny.
i'll give u some food for thought...
which motor pumps more air out...V6 or V8?
why do u think people design equal length headers?

bonzelite

iTrader: (2)

you're sort of correct about your physics. the more massive oem fly has more 'potential energy' within it. but it needs to overcome inertia to see this. and this is where the light fly comes in:

you can rev higher, way sooner, with a lightened flywheel, putting your engine into the powerband very soon. with the y-pipe, for example, you want to get out of the lower rpms as soon as possible because some bottom end is gone. the aluminum fly enables this. if you have a lead foot, you'll expend more gas to jackrabbit into speed from rest. but you will experience a peppier acceleration in general -way more than the oem setup. and because 1st gear is rather tall, you can redline it (should stay in it longer), going beyond the 'range of loss,' and be in a sweet spot for 2nd. then sub-redline 2nd and go to the 'bye bye' gear of 3rd. you will whip an oem VG if this technique and setup is used.

the oem setup has natural low-end torque feeling because of what you said. but you lose big time in the oem mid and top, especially top when speaking of the VG, which i assume we are. hence the desire for the y-pipe. breathing.

the driver must adjust to the y-pipe/flywheel mod. if the driver stays driving the same style as oem, the benefits of the mods will not surface. and you will beat a modded 3rd gen VG with y-pipe with oem off the line.

Matt93SE

iTrader: (44)

the ONLY time a heavy flywheel helps is when you're first launching off the line. once the engine and tranny are spinning the same speed, the heavy flywheel is only a hindrance. all it is used for is momentum to keep the engine turning when the tranny side is stopped and the engine is turning. you let out the clutch and it's got more of a 'buffer' before the engine stalls due to the inertia of the flywheel. use a small mass spinning very fast to help a large object moving slowly.
once they're moving in unison, you want as little mass in the way as possible.