Exhaust gas temp?
 

I've read PLENTY of times that the exhaust gas from a rotary is "very hot" or "much hotter than a piston powered car", but I've searched and cannot find how hot "hot" is. Some say fiberglass packed mufflers will last 10 minutes, others say 10 years.

Does anyone really know? Does anyone have an EGT sensor on their car? Thanks...

Well a 4 banger would be in the 1100-1400 F range, your rotary rocket is soaring in the 1600-2000 range. I don't have my RB tech manual handy, but I think I'm pretty close on the numbers....

We run our racecars between 1,550 and 1,750 degrees (farenheit) depending upon how brave we want to get with our mixtures. 1,750 is pretty lean and can cost you a motor when you run advanced timing like we do, but it makes great power.

I think the man from BC is right (2100 degrees), so the real question is at what temp does fiber glass melt? Anyone for a little Googling?

I've got a glasspacked type muffler on my car and have had it for about 5 months... seems to be lasting pretty good.

These are the hard numbers I was looking for - thanks. Thanks to the others that replied as well. Does anyone have any hard numbers for a piston engine? 4, 6, or 8 as I would imagine a/f ratio would have more of an effect than piston count. Thanks.

It's not unusual to see temperatures between 1200 and 1500 in turbocharged cars. I've never really looked into it in N/A cars, but on my WRX, slightly modifed (about 300hp), it'll sit around 1200 or 1300 daily driving, 1400 on top end pulls. I know people with similar setups that will hit 1500, just because of the difference in engine management.

So, judging by the hard numbers provided, there is really very little difference in exhaust gas temps between rotary and piston engines.

Hard #'s provided:

rotary under racing conditions (which I would imagine are slightly hotter than normal driving conditions): 1550-1750

4 cyl turbocharged piston engine under relatively normal driving conditions (which I imagine are cooled a bit by the turbo absorbing some heat): 1200-1500

Where is this vast descrepancy that people seem to want to harp on? I guess maybe it's opinion, but I wouldn't consider a couple hundred degrees "SOOOO much hotter!" as many like to post...

Exhaust Temps
 

In a piston motor, temps are measured 3-6 inches from the exhaust valve generally, while in the rotary, the temp should be measured at 10-18 inches from the exhaust port. We measure at 12 inches, shooting for 1800 degrees in our race cars. Attempts to measure close to the port will lead to probe melt down as the temp can exceed 2000.

Hi there Buttlips and RentSportRacing!

Few questions for you guys, hope you don't mind...

Can I ask what type of EGT sensor and ECU you are using?

Also what internals do the engines have (i.e. apex seals)?

What turbo?

Boost?

Do you monitor the temps across the range or max temps?

Thanks very much in advance.

My motor is a streetported 12 with a Weber 48 IDA carb, therefore, no ECU, turbo or boost pressure. As far as engine internals are concerned, it's set up for racing. It has carbon apex seals, race bearings, hardened stationary gears, etc.

I don't recall the specific brand of EGT sensor it is, I'd have to check. I use the EGT for max temps @WOT in high gears. I have an air/fuel meter with an O2 sensor that I use throughout the RPM range.

Look at sustained crusing temps as well when judging exhaust longgevity.
1250 F to 1350 F sustained is not uncommon on a rotary.
950-1100 F is common on most piston engines.

150-300 F difference is no small amount. Also, remember that glass is a supercooled liquid, so it doesn't have a "melting point", it just gets softer and softer. 300* can be the difference between relatively hard/ geologically slow flowing glass to merely one where it is flowing still slowly, but magnitudes faster than before.

Yet another thing to consider is that the EGT probes are measuring temps in the first 3-18 inches. The fiberglass packing in a muffler is a good ten to twelve feet further down the pipe, many times after a cat. I guess the only way to find out the temp at the muffler would be to have an EGT probe right before it. That would be relatively useless info except for this particular circumstance...

A naturally aspirated car will generally have higher exhaust temps than a turbo car (after the turbo). Tuning and engine design play a big role in what temps you'll see. A piston engine can be anywhere from 1200 to 1400 degrees or so (sometimes less sometimes more). A rotary can be anywhere from 1500 to 1800 degrees (again sometimes less sometimes more). The difference in temperature is generally 200 to 300 degrees hotter or so in a rotary. This is really due in large part to the way the exhaust leaves the engine. The actual internal combustion chamber temperatures aren't very different. The difference is in how the engine dissipates the heat after combustion. On a peripheral port exhaust rotary engine, the ports open relatively quickly and the exhaust leaves with an intense amount of velocity since it is so sudden. This high velocity helps to hold the heat in the exhaust. Sounds a little strange. On a piston type of engine or a side exhaust port rotary the ports (or valves) open more gradually. What this does is to slow down the velocity of escaping gasses which gives them that extra millisecond to cool down a little. Slower moving air also encounters less friction from its surroundings. Less friction is less heat. Rub your hands together slowly and then very quickly. Which way do you get more heat? Similar principal here. Basically the rotary (peripheral port exhaust) is better at maintaining exhaust thermal efficiency over its useful cycle. However an inefficiency does come into play here as well. Due to the slight amount of port overlap some exhaust does get sent back through the engine which not only dilutes the incoming air but also heats it a little. Depending on the cam profile a piston engine may have more or less overlap. Usually less. The new Renesis rotary with its side intake and exhaust ports more closely resembles a piston engine in its timing profiles. There is no port overlap but rather many degrees of dwell. While a small amount of exhaust will always be slightly carried into the next chamber there isn't as much as on the other rotaries which helps to lower intake temperatures by not dilluting it as much. Also on the Renesis like on a piston engine the exhaust ports or valves open more gradually than on the peripheral port based exhausts of the other rotaries. If you move a rotor over the intake and exhaust ports of a torn apart engine sometime take a look at how far the rotor moves before each style port is fully exposed and you'll see it.

As far as glass packs go, the concensus is that they are fine as rear mufflers but not front mufflers. The exhaust system dissipates heat very quickly after it leaves the engine during its journey down the exhaust pipe or pipes. Gasses at 1500 degrees leaving the engine may only be at 200 or so as they exit the rear of the car. Maybe less maybe more. A glasspack won't have much of a strain here unless you have a car that is running so rich that it is constantly blowing flames out the back. On the other hand if you decided to use a glass pack as a pre-silencer by replacing your cat with it, you are in for trouble. The exhaust can still be at 1000 degrees or so here. Fiberglass has a lifespan of seconds maybe minutes but probably most appropriately in blocks driven at this temperature. Stainless steel is the only way to go at this location but preferred everywhere if you can afford it. Most people have fiberglass rear mufflers though and never have any problems. If your rear or only muffler is only 3 feet away from the exhaust then fiberglass will still die. Its all about how much heat there is at the location you are putting it in.

To add some reference numbers in here, I took a trip from CT to Rochester, NY today in a mostly stock WRX. For the whole trip, cruise control, around 80mph, we sat between 1400 and 1500 degrees, 1500 being the highest I saw.