nathantheman

so i was coming home from work yesterday, and i pulled into a parking lot for some ****. when i went to drive back out this hyundai was right in the way, so i thought i could go around it. i backed up and heard this CRUNCH! I was like **** i hit a car! then i went to move forward and i heard this deep rotary rumbling from deep inside my hood..... haha i knocked my exhaust off on a snowbank! all i have now is the hollowed out precat. its actually not as loud as i would have thought, but fack man! i have a question though, my tII obviously boosts higher now but besides that, i think it is really alot slower, like less torque and worse on gas. is this possible or am i just imagining? i thought with a turbo no exhaust is the best for power, but i think my car is pretty poky now in the low end. maybe i lost tourque and gained hp? who knows ?

YearsOfDecay

Thats the way its works man....

By freeing up the exhaust, you shoot the low end torque to **** and gain High RPM horsepower. Thats why the exhaust guru's get paid what they do... you have to design the pipes so that you only free up the exhaust enough so that you still have useable power.

as you free up the exhaust... you gain high RPM horsepower, however, the RPM point at which you gain that horsepower usually increases as well..

If you free up the exhaust too much, you can actually extend the max horsepower RPM beyone the capable range of the engine.. thereby blowing your take off torque to hell and not even getting the high end horsies in return because your engine simply won't rev that high!!

Even Turbos need some amount of backpressure to run at reasonalbe rpm's

1987RX7guy

iTrader: (3)

easy exhaust mod? which ones aren't easy? unless your doing a custom job it should be easy enough for a 12 year old to do it.

Santiago

nathantheman

haha thanks guys! NOW I GOT THE FIRE BREATHING SOUND! but no power, nice

1987RX7guy

iTrader: (3)

I would just bust out the cash for a dp/mp and a good cat-back like RB or Borla. But watch for that boost. You could run into fuel cut.

NZConvertible

Turbo'd engines get all the backpressure they need (and more) from the turbo itself. They don't need any more after the turbo.

Aaron Cake

iTrader: (1)

If you had much experience working on cars, you know that exhaust work is probably some of the most annoying work you can do. This is mostly because of rust, the position in which you have to work, etc. True, if you don't need to save what you are removing you can pull out the plasma cutter. But if you need to reinstall, you need to be careful and properly deal with all the rust, broken fasteners and such that will result...

1987RX7guy

iTrader: (3)

If your replacing one peice or the whole thing it all comes down to nuts and bolts. A simple shop manual and hand tools with the addittion of penetrant spray will make short work of any rust.

Santiago

SureShot

First - look under your car & see where your hot gases are venting. (remember Challenger?)

BDoty311

Exhaust on our cars are rather simple, but many other cars exhaust systems are hard to work on. Some cars you have to remove the rear suspension to install a system, others have bolts that are really hard to get to. And rust never helps. Plus everything is under your car, which can get annoying fast when on your back.

Templeswain

with the addittion of penetrant spray will make short work of any rust.


yeah.

My easiest exhaust mod wasn't too long ago. Nathan's got his way of doing things I got mine. Though I think mine was easier. I went to drop my presilencer, and whamo broke of one of the bolts connected to the y-pipe even after spraying it to death with w-d40.

Now I have this cool chatter from underneeth my car. And this awesome exhaust smell comming through the shifter that kinda makes my eyes burn.

1987RX7guy

iTrader: (3)

I don't use WD 40 anymore. I tried out PB blaster and that stuff really does the trick. And time is worth the wait. Just leave it for some time it will losen it up.

nathantheman

haha had to drive my peice to work today(45 min each way) and my eyes are still burning. hey NZ you say the turbo prvides all the backpressure? so why is my car so much slower now? and worse on gas? i think you know what your talking about, just explain to me please. oh and when i go to the exhaust shop tomorrow i was thinking about getting them to build me a 3 inch downpipe instead of my hollowed precat, and then put my exhaust back on. will this flow better that my current hollowed precat to 2.5 inch straight pipe to bosai catback? will it sound different? i like the low end torque and if i can keep it lower than ten lbs boost that would be sweet! thanks

White_FC

NZConvertible is right, turbo engines need the least poosible resistance to flow after the turbine blades...

Your car might be slower now because maybe your hitting fuel cut? Maybe your cat isn't actually gutted out but is infact clogged up (have a look sometimes the inner mesh will come out and clog them *after* you've gutted them).
Or it could really be something else entirely...

Is it really noticibly slower than before? or is it just you butt dyno telling you that it _might_ feel slower?

BDoty311

Maybe it is because its louder, making you think it should have more power.

I know when Ive driven around with open header my car seemed slower, but that might be the fact I have a chainsaw going off in my ear.

nathantheman

haha i'm not a total noob. i have a feul cut defencer, and i cleaned the cat out myself, and theirs nothing inside and it will go past ten psi on my autometer but i never let it. no its slower like i almost stall it at the lights now, i guess it really just has alot less torque. but when you open it up it facking rips. the top end is fast. but that might be because of the extra boost. its way worse on gas now, just driving today i noticed huge. but now that it's loud don't you think the butt dyno would feel faster, cause its so loud?

BDoty311

But you think your cars loud, so its speed should match its volume. But your car is alot louder, but not any faster.

nathantheman

well it'll be better tomorrow, but does any one think that going to the downpipe instead of hollow cat is a good plan? remember this is my daily driver and i like the torque and gas milage. will it be louder, say i go three inch, than the hollow cat? cause when it was all together its sounds as quiet as stock. and it would be nice to have some growl

White_FC

Your stalling at the lights problem and apparent lose of low end torque has got absolutly nothing to do with your post-turbo exhaust system... nothing at all..

Maybe you blew your motor from over boosting.. You should do a compression test.

Failing that you have some other problem which, and i'll say it again, has nothing to do with your post-turbo exhaust.

But yes I think you should get a new exhaust pipe made up from the dump of the turbo to the main cat, 2.5 would be the most sensible if your going to keep the stock cat..

There not much point opening up a 2.5in turbo to a 3in pipe then back down to 2.5 at the cat is there?

brokenwankle

from what i know of turbos this is true...its the wastegate that causes the turbo to spool...as long as your actuater can is strong enough to hold exhaust gasses back

Digi7ech

iTrader: (1)

Be careful with the boost. Over 10 is the semi acknowledged area where the stock injectors max out and you get ready to detonate.

I'm taking a total guess here about the gas mileage but maybe the O2 sensor is seeingreally fucked up readings because of the leak.

I know my 88 NA was super slow when I developed a leak right before the cat. I mainly contribute that to not enough psi to actuate the 5/6th though.

White_FC

Contrarry to popular belief the o2 sensor wont throw your fuel consumption right out the window.
Sure it changes it, but hardly noticibly. What difference in it are you seeing now nathantheman?


.....bad fuel economy, stalling at the lights, loss of low end torque... Do a compression check.

You probably boosted more than 10psi if you really only have a dump pipe on there and nothing else.. So maybe its only boosting 10 now, but it might have spiked to alot more than that..

NZConvertible

I think the others have pretty much covered this. It'll be interesting to see what happens once the new exhaust is on.
Hell yeah, miles better.

ddub

thats for sure... like on my 01 Ford Escape, it came with single exhaust but i had a custom dual set up made, it took them a full day to do at a shop just for a simple cat back because the whole thing had to be custom made and routed around my suspension and ****, the guy doing it did a very clean job but seriously i wouldnt want to be the one who would've had to make it




looks so much simpler from the back than under the car

mason-rx-7

If you are going to do an exhaust mod be sure to buy a good system that will not lower your backpressure too much but still keep exhaust flowing smoothly. Stupid guys with Civics buy ricer exhausts and lose alot of torque. If you have your fuel system changed to match the new exhaust you shouldn't lose much torque. Plus anytime you do something to your exhaust just cut out your cats. It freed up nearly 20 hp on my car by just cutting out the cats and putting a straight pipe where they used to be.