Subjug4tor

iTrader: (1)

Replace both pre-cat sensors, you don't want to mix new and old here. You can get a universal 4-wire bosch sensor pretty cheap if you don't mind cutting and soldering wires, or get some OEM sensors from lexus/toyota.

guku0701

and is there any way i can just take them off and clean them?im not planning to spend much these days as money is kind of tight at this moment.

g4ebguy90

This is how it works.

. Of course there is backpressure think about it. Your creating a block for the air to overcome. Baffles in the cats and mufflers etc.

The thing that people concern themselves with is Cyl, scavenging. Which on are cars, they V8's I don't see a very good exhaust design to take advantage of this. So I don't think Toyota designed it with cyl scavenging in mind.

The issue is, when you decrease this backpressure by putting headers on and etc. You increase the velocity and temperature of the air leaving the combustion chamber. Think of it as blowing on a ember and make it red hot. Your technically doing the same thing here to your already hot valves.

The exhaust valves will be fine, the issue will be the intake valves as there not made to stand the heat.

Should they burn on 1 or more hot cyl's probaly the middle ones. You will notice a every now and then misfire, and a low loss of compression. Depending on how burnt the valves are. Or how good they still seal.

Subjug4tor

iTrader: (1)

Of course backpressure exists, the misconception is that its a good thing. The 'hot ember' analogy only works in a scenario where there is still fuel to burn, in an engine the combustion is done in a second, and the faster you get air in the more the intake valves are cooled. I dont really know why you think exhaust mods can burn an intake valve, but it just doesn't make sense. This isn't 1970, I don't know why people still believe this.

g4ebguy90

You need backpressure on stock cars usually to avoid that. The air does cool the valves, but again, there is alot of variables. Carbon build up, that creates hot spots. The air velocity does not cool the combustion chamber that much. Were talking a couple more degrees if you remove some backpressure. There is FUEL left to burn, why do you think we have cats.... To eat up them hydrocarbons.

I know they burn intake valves as I have done alot of experience messing with Hyundai Accents. with a 1.5L I made them things breath N/A as much as you could. Without going turbo.

Burn'd the intake valves on cyls 2&3 couple months after I do my average mods. NO backpressure at all besides the inital header turndown. 4-2-1 header, NO cat no resonator, 2 1/4 pipe all the way back to a canister. Compression was always lower on the two also, after 2 years of driving with the mods, the cyl 3 had a compression of 90 vs the rest which were around 140, cyl 2 was around 120. Cyl 1 and 4 were fine as they are cooler cyls. This has happened to all 4 that I have owned.

I am into the WHOLE get the most velocity out of your engine. But the reality is, most people on here do not go NA on the inline 6, and most do not do a FULL NA setup on the v8's as its real expensive. 2 headers Full true dual exhaust etc.

When your into 4 cyls like me for 6 years you do everything you can to make them breath but there are consequences on stock cars, When you really make them breath.

Subjug4tor

iTrader: (1)

So you're saying that keeping hot exhaust gas in the cylinder for longer makes the valves cooler? Sorry, I don't buy that. If valves, or any other internals get burned to the point of failure, its because your combustion temperatures are too high, end of story. There is just no way that getting exhaust and unburned gas out of the chamber faster is causing more heat damage. I take it you never compared real EGT data before and after the mods on the accents so until that datalog shows up this is just heresay. Im not trying to be a jerk, I just dont want people learning incorrect information here, we have enough of that as is. Either way, we're pretty off topic now.

millertime

on a track or on a dyno, im sure that my setup with no back pressure, and this is me guessing.. would make more power say at 4000rpm than the setup with back pressure. the sc400 is not a turbo car and shouldnt need to rev to high hell to make power. with a 1800 stall converter, the vehicle being a v8 should start producing "torque" at around 2000 rpm. with open exhaust at partial throttle the vehicle bogs. with the cats it now makes "torque" at 2700 rpm.
By torque im saying the point at which the car noticably throws you in the seat compaired to before.

Subjug4tor

iTrader: (1)

I'll concede that exhaust restrictions can give you more power on the low end. It's really a trade off, weather you want more total power, or you want to get your power sooner. This is why variable valve timing (VVT-i, V-tec) was created. To allow for the best cylinder scavenging and air intake profiles at all RPM's, with one intake and exhaust system. Non vvt-i engine though, have to choose one generally when it comes to exhaust systems- Higher horsepower higher in the powerband or low end torque.

One excellent combo that has been discovered is a free-flowing exhaust system coupled with a higher RPM stall in the torque converter. This gives more power overall, and lets the engine access more of it off the line.

g4ebguy90

What I am saying is, that with backpressure less air comes into the combustion chamber during valve overlap. Without backpressure, more air comes into the combustion chamber, this WOULD increase temperature.

Were not off topic this we are completely on track, and I don't need to dyno my hyundai as I knowed what was happening. I don't got to tear apart a motor or dyno to know it has burnt intake valves.

There would also be no point in using EGT as I do not care about how rich I am running, and because it is not boosted there really would not be any useful data. I did run open loop the whole time though, so I did have excessive amount of fuel in the engine.

I think you are using heresay information. As you have no real world experience running a all NA setup and having the exact issue were talking about.

PRetty much, Velocity, friction, heat. Thats it. You increase one you increase the other.

I mean really all you have is a intake and no mufflers you still have 2 log manifolds and 2 cats to push air through. My hyundai had no such. Even with that it's VE was around 75-80% but the datalogger I used was only giving me between 75-80% data.

INTIMAZY

iTrader: (5)

Burnt valves are a different topic not really related to "backpressure" directly.
I've seen valves burn up for countless reasons including clogged cats (high backpressure), valve seat issues, and running lean. The amount of valve overlap is really not a significant factor on any stock cammed car. If it was, you would have MAJOR issues with 1UZs handling boost (which, clearly is not the case). With big NA cams this can be a problem but I don't even think any off the shelf cams for the 1UZ are wild enough to be of concern.

Scavenging is almost entirely complete by the time that the primaries leave the merge collector anyway. Having 1" of pipe after that point or having 10' will not really matter for powerband as long as exhaust velocity is maintained. That topic, however, applies more to properly designed headers and matched cams, not really an NA motor with relatively sh#tty stock manifolds that don't take advantage of scavenging anyway. I agree with ya on that g4ebguy90

There are countless motors running equivalent to open headers with no exhaust valve issues (much less an intake valve) in every type of powersport from quads, motorcycles, sand rails, and even tons of old street rods that don't burn up valves. I'm more inclined to believe that a cooling issue, valve seat problem or simple lean condition caused a burnt valve on any motor in general. Not to bash on certain brands, up until recently the korean brands have had miserable build quality especially when it comes to machining and tolerances. I respect the amount of time and work you put into the little 4 banger but I'm still suspicious there was something else going on.

g4ebguy90

Well as you know bro, Lift as in BIG NA cams, is not the same as duration which determines the overlap. So on a stock car, with low lift and long duration I think that the incoming air would be a issue on a low backpressure setup.

As far as the hyundais engine burning up valves, again it was intake not exhaust. Them motors were really not meant for high rpm NO backpressure driving. It would be a change and running pig rich would deff heat some stuff.

The design is, a 4-1 Log manifold Which does this instantly from the head right into a CAT just like the 1uz. It is a horrible ineffcient design. Then it went to the resonator and muffler. I deleted all the bottlenecks on my setup completely.

In therory I was running no backpressure at all, or as little as possible besides initial header.

Idk I am tired will have to think about it more. Maybe some engines have this problem and some don't.

Badsupra10

Straight pipe it....fun

g4ebguy90

I think were all getting idea of what to say, then about the end of the first paragragh we don't even know what were yelling about anymore lol.

Subjug4tor

iTrader: (1)

There's really no point arguing about it on the internet anymore, so meh. The facts are that more exhaust restrictions = higher combustion chamber temps, and high velocity/low pressure in combination is all that matters for making power across the whole band. Hopefully this advice helps someone here who chooses to listen.

INTIMAZY

iTrader: (5)

Amen.