Exhaust Temps

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gimpy
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Exhaust Temps

Post by gimpy »

I have a noob question about exhaust temps with a turboed engine,but a little back ground first.
I'm running a F2T mazda with the stock VJ11 turbo,with a home built exh. manifold(setup is in a 90 B2200 Mazda pickup) with MS2 for fuel & spark control.The exh. mani was built with 1/2 cold rolled plate for flanges,schd.40 steel pipe.I know that this turbo is SMALL making the exhaust manifold run extremely hot(I would guess from color about 1100 deg. F) I recently added an EGT gauge with the probe in the orginal O2 senser port(back of the turbo in the orginal casting)

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With all of that the first test drive the new gauge showed me a high temp of 1050 F(no boosting ,just normal driving) and settling to about 850 after letting the engine idle for 3 or 4 min. Are these somthing like reasonable numbers?And at what temps should I become alarmed?This project is my first shot at turboed anything so I've no experince with them at all,but have been working on cars and engines for ever.
Any in put would be great :mrgreen: Thanks in advance Gimpy
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jharvey
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Re: Exhaust Temps

Post by jharvey »

How hot it to hot you ask, well, when your paint catches fire and burns the rest of the vehicle to the ground, or when you spit molten metal out the tail are certainly temperatures that are to high. Other than that, I believe the higher the temp, the faster the bearing wear and oil viscocity breaks down. So it's really just a decreased life cycle. I've seen other forums noting that above 1400F is reasonably common, and 1200f to 1300f is very common.

I'm of course not an expert with it, but sounds like your fine to me. I'm sure you expected the increase power will shorten the life any how. If you can keep it cooler, it's certainly better.

I understand that detonation, AFR, ect are more common to cause failures than the temperature.

Welcome aboard and good luck with it.
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BenFenner
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Re: Exhaust Temps

Post by BenFenner »

While EGTs are a great way of tuning the timing of an engine, I'll get to your specific question.

788°C (1450°F) is usually the upper limit. Anywhere from 788-843°C (1450-1550°F) your exhaust valves are likely to melt. That is the real danger of high EGTs.

Sodium filled exhaust valves might get you to 843°C (1550°F) before melting, typical exhaust valves you'll be in trouble around the lower limit of 788°C (1450°F).

That being said, you aren't getting proper readings at all with the probe after the turbo. It needs to be immediately after one of the exhaust head ports.
Last edited by BenFenner on Mon Mar 09, 2009 3:29 pm, edited 1 time in total.
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Fred
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Re: Exhaust Temps

Post by Fred »

Good spotting Ben. I'd just like to point out that the VJ11 is so small that ... ummm... its pretty damn small. The OEM installations run glowing red hot after normalish driving. I've driven one and seen this first hand, pretty funny.

Get rid of that turbo ASAP regardless of EGT. Get something moderately sized and you will like the setup a lot more than you do now. Everyone that upgrades those on the f2t likes it and none ever regret it.

Other than that, you lost me with the *F readings and I have no idea anyway :-)

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jharvey
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Re: Exhaust Temps

Post by jharvey »

Me not so good with this, but if your run hot on the ext, doesn't that increase the intake temp? If the intake temp increase doesn't that increase the chances of detonation?

Heres a thought on how to help keep it cool. You take some sharp turns right out of the block, this will cause the hot gasses to hit the side walls and dissipate the heat through the side of the exhaust pipe side wall. If you can keep smooth bends, I'd imagine that would help keep it cool.

If your running a hight AFR, you may be dumping more fuel in the ext than is required to keep your turbo spinning. Because you turbo is so small, you may want to think about running it a bit more on the lean side. Seems like 11 is about right for you, perhaps less.

Looks like you have a "nice" long run on the intake, perhaps an inter-cooler there as well. If so great, that will help keep the intake temp down. If not, you may want to add one.

I know my suby has a water cooled turbo, so I'd image 1400F would be to hot for mine.

1400F is 760C

http://www.google.com/search?hl=en&q=14 ... h&aq=f&oq=
gimpy
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Re: Exhaust Temps

Post by gimpy »

Thanks fellas,your input helps :mrgreen: Puts me a little more at ease!
MR. Harvey,yes I do have an intercooler(tiny by Freds monster)is a Saab unit I believe from a 2.4 liter settup, and the VJ11 is water cooled also.My intake temps run about 10 to 30 deg. higher than outside air temps(depending on how long I boost)and I show no signs of detonatin.
Sorry about the Deg. F thing Fred,I don't do C.I'm looking for a bigger turbo now,and have been since you recomended to me & Dealwithit.
Ben, thank you ,Those are the numbers I was looking for.When it gets a bigger turbo I'll move the sender closer to the exh. valves,that port was handy and cheap & quick way to get a reading of some sort .
Thanks again Gimpy
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Fred
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Re: Exhaust Temps

Post by Fred »

With respect sensor location, think of it as an aerosol. IE as the gas moves through the turbine it expands and cools. Thus the reading you have is not really representative of what is going on inside your manifold at all.

Fred.
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BenFenner
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Re: Exhaust Temps

Post by BenFenner »

Fred wrote:you lost me with the *F readings
I usually do everything in °C unless the poster shows a preference. And even then I do both. I was being lazy. I'll edit my post.
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Fred
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Re: Exhaust Temps

Post by Fred »

Well, I meant gimpy, but good on you anyway. I don't mind most imperial units, but that one is too cryptic for me. (IE I can't quickly do the conversion in my head/get a feel for it simply by seeing the number and unit)

Fred.
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