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-   -   Anyone know engine bay heat? (https://www.rx7club.com/3rd-generation-specific-1993-2002-16/anyone-know-engine-bay-heat-263491/)

SPOautos 01-22-04 05:06 PM

Anyone know engine bay heat?
 
Anyone know the approxamate engine bay temps after driving pretty hard then shutting down for an hour or so?

Anyone every put a temp in the actual engine bay to see how hot it gets in there???

Thanks,
STEPHEN

spoolin93r1 01-22-04 05:10 PM

no, but my i've relocated my air temp sensor to my elbow and after sitting for 30-60 minutes, it'll climb as much as 20* over ambient

SPOautos 01-22-04 06:27 PM

Yea, I'm pretty familiar with the charge air temps, I was looking more for the engine bay itself, like the ambient air temp inside the engine bay.

I'm working on some thermo calculations for how much the IC would have to be insulated so that it wouldnt heat soak and I need to know a decent idea of engine bay temps. I'm thinking 150-180....anyone else have a better guess or anyone have any way to measure it? My car is down right now so I have no way to measure. Also, I'm kinda wanting to know the temps while the car is traveling and also when the car is sitting for 30 minutes heat soaking.

Thanks,
STEPHEN

Kento 01-22-04 06:33 PM

A lot of people have talked about doing it, but no one AFAIK has actually installed a sensor to accurately record underhood temps. I would be very interested in this info as well.

spoolin93r1 01-22-04 06:49 PM

i'm thinking it also depends on ambient air temps. i could drive mine around for a while and shoot various places with my temp gun. it'd be kinda close

adam c 01-22-04 06:51 PM

I think there are some stats on the fan mod link. As I recall, Robert Kinports (a friend of mine) posted some temp readings:

http://www.scuderiaciriani.com/rx7/fan_mod.html

**Date: Thu, 30 Jul 1998 10:06:04 -0700
From: "Kinports, Robert" (RBK1@pge.com)

As promised, last weekend I used thermal strips to test the underhood temps after shutdown, but with the fans running for 10 minutes on low (Fan Mod). The previous weekend I conducted a similar test, but without running the fans after shutdown. The difference in temps were were amazing! Those who flamed away at this idea when it was discussed on the list a month or so ago can now put your tails between your legs.

For both tests thermal strips spanning 140degf to 310degf were placed in the following locations:

1) On the inside of the ABS shield
2) On the top of the strut tower bar
3) On the stock plastic IC intake pipe
4) On the stock plastic IC outlet pipe

Temps/results were as follows:

WITHOUT FAN MOD
1) 180degf
2) 180degf
3) 190degf (registered 180degf before turning the car off)
4) 180degf


WITH FAN MOD
1) Did not register (less than 140degf)
2) 150degf (registered 140degf before turning the car off)
3) Did not register (less than 140degf)
4) Did not register (less than 140degf)

Both tests (with & without the fan mod) were conducted after driving the car on the freeway for 20-30 miles with some periods of light boost, and an ambient outside temp of around 80degf. The car was idled for 1 min before being turned off & was allowed to sit for at least an hour afterwards. The test with the fan mod was done with the switch turned off after 30 seconds thereby switching the fans to low speed.

The thermal strips were added prior to the 20-30 mile trip, but were checked after shutting the car off (before heat soak) for a baseline. Only IC intake tube registered on both tests (all others were less than 140degf before heat soak).

An interesting note is that the IC intake temp strip increased by 10degf on each test after shutting the car off, even with the fan mod. The explanation I came up with for this is that some residual heat from the turbos rose to the highest point in the system, which is the IC intake pipe.

After reviewing the above data I can't imagine why anyone wouldn't do this mod. It only costs about $50 to complete using a stock fog light switch & takes less than an hour to do. The cost can be cut to $5 using an aftermarket switch. I

It is a slight pain to remember to turn on the switch 2 min before shutting the car off & to wait 30sec after shutting the car off to turn the switch off (fans on low), but it's worth it in the long run!**

Kento 01-22-04 06:52 PM

If you're talking about an infrared temp "gun", it only reads surface temps, which can be far different due to their proximity to extremely hot surfaces and/or exhaust gases. I think Stephen is interested in air temps, not surface temps.

clayne 01-22-04 06:52 PM

130-150F after shutdown.

Monitored with my water-temp probe before I tapped it in (it's a thermistor just like any other probe).

bajaman 01-22-04 07:00 PM

There was an article in Rotary News or some mag where they measured spikes of 600 degree F temps under the hood.
Yeah, it is one hot mother under there!

alberto_mg 01-22-04 09:39 PM

Check Ron K. Miller's "hot air out" mod thread. I think there were some figures in there.

SPOautos 01-22-04 11:02 PM

Awsome guys, thats the info I was looking for. Those numbers are right in the range I though they would be. When doing the calculations I used everything from 150F up to 300F just to make sure I covered it since I wasnt sure. Its nice to see those numbers from Clayne and adam since they are actually on the low side of the numbers I was using

As for that 600F number, they must have been right down at the exhaust manifold or something. The overal ambient air temps in the engine bay dont get that hot. If they did you wouldnt have any paint left on your front clip haha

Thanks a lot guys,
STEPHEN

adam c 01-22-04 11:16 PM


Originally posted by alberto_mg
Check Ron K. Miller's "hot air out" mod thread. I think there were some figures in there.
Don't all of RonKMiller's threads have a lot of hot air?? :D

clayne 01-22-04 11:42 PM

There is no way it is 600F average. That has to be a local temperature close to the exhaust.

My readings were taken with a DEFI temp-probe mounted in the *corner* where the cruise control normally goes.

I think you guys should really tap into Howard Coleman's post off of nopistons - he has hit the nail squarely on the head with the twin manifold being the main issue:

Reposted:

http://www.nopistons.com/forums/inde...3754&st=25&hl=


"it is ironic that the rotary is considered by some to be unreliable. granted there were initial developmental issues with apex seals etc but that was a long time ago and those issues have been long ago successfully addressed. i believe that if properly clearanced and assembled the rotary engine is more reliable than the piston engine. i think most of the root of the rotary unreliablity issue comes directly from the fundamentally flawed fd oem turbo system. it was a great design on paper but it is thermally a disaster on many levels... 72 hoses baking in an oven, 22 pounds of cast iron manifolding heated to as much as 1700 degrees baking the block which is part aluminum. so we have 22 pounds of the most heat retaining material, cast iron, heated to 1500 degrees and transmitting it's heat to one of the most heat conducting materials, aluminum. bake bake bake. in addition, the design of the manifold would make anyone owning a flowbench cry. that's why there probably isn't one oem manifold on an fd today without major heat cracks. chapter 2 of this saga is inevitable. lose an engine from heat, then junk the stock turbo system if you don't want a repeat trip to engine replacemant-land. a step in the right direction but many correct decisions need to be made re fuel supply, boost etc. many opportunities to make the wrong decision. thankfully we have the internet and the incredible resources it conveys...
as i said initially it is ironic that the rotary may be considered as a dicey engine reliability-wise. road racing has been my game. 22 seasons National SCCA racing the last 6 in gt3 running a tube frame mazda rx3. i built around 30 of my piston engines. 4 cylinders, 2 valve head, overhead cam, big weber dcoe sidedrafts... w grafted exhaust ports we made 210 hp from 122 cu in/2 liters. in order to do that we had to run a huge cam (w trick roller followers) and the valve to piston clearance was almost zero... (in order to fill the cylinder). if a valve spring were to fail at 10,000 rpm, or any valve float at all, you just can imagine the carnage that would ensue. pistons rods pieces of valvetrain all over the place.
the rotary has none of that! it just needs fuel, timing and a good port job. in 6 years of racing i had only one rotary engine failure and it was sort of expected as we elected to shorten top gear a click for qualifying making the engine run 10,300 instead of 10,000 at the bottom of the hill at the end of the road atlanta backstright. we lost an apex seal but not the motor. another telling example of rotary durability is the 24 hours of daytona. at the end of the race the piston engine cars that are still running pull in the pits and are unable to idle under 3-4000 rpm as they are completely shot... valve guide are leaking etc etc. the rotaries come in and most mazda drivers make a point of getting out of their cars and letting the motors cool down by idling... and they idle just like they did before the 24 hour race. i really agree w Judge Ito that if properly fixtured and tuned the rotary is more reliable than a piston engine and everyone in SCCA that races against the rotary knows that to be a fact. this thread is about building them right and is valuable especially if it separates the good from the shoddy builders. my point is that if you build it right and put the right support pieces on the rotary should outlast lots of highly modded piston motors.
one other point re making power w the rotary. Crispeed made a huge point recently... he said that turbo'd engine builders don't spend the time they should optimizing airflow and harmonics that NA builders do. most hp gains in NA motors come from using (air)flow benches and dynoing on engine stands so as to ascertain runner length/harmonics. most turbo guys are just looking to turn up the boost, which is o k but missing a huge amount of the total hp picture. the same harmonics, charge air coming to a halt as the intake port closes etc etc apply to the rotary.
howard coleman"

SPOautos 01-22-04 11:53 PM

Yea, thats what I was saying. It it were 600F average you couldnt keep paint in the engine bay or on the hood. They probably stuck it right down at the exh manifold after a nice long hard run.

I think the average in the intercooler area would be less than 140F with the car moving and 180F with the car sitting like the other tests have shown.

STEPHEN

clayne 01-23-04 12:00 AM

You must also consider high and low pressure zones in cooling efficiency, SPO.

RonKMiller 01-23-04 09:59 AM


Originally posted by adam c
Don't all of RonKMiller's threads have a lot of hot air?? :D
I just happen to have a Federal, Commercial license to dispense hot air and make money doing it in my wallet next to my driver's license.

So there!:p:

And if you want to buy some, you can go here:
www.BalloonRideUSA.com

RonKMiller 01-23-04 10:01 AM


Originally posted by alberto_mg
Check Ron K. Miller's "hot air out" mod thread. I think there were some figures in there.
I never got around to it, but the difference in temps is HUGE. ;)


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