Jeep Strokers

My son and I have built a 4.7 l stroker with the below specs. this is our second engine after burning up #6 piston. This time around we clamped a thermocouple to each exhaust runner about 4 inches from the head. We were looking for deviations which might indicate a piston is in trouble. in down the road conditions (65 mph) we have the following temps #1 = 850F, #2 = 910 F, #3 = 910 F, #4 = 910 F, #5 = 960 F and #6 = 910 F. I have a few question;

1. what temperatures should we expect?

2. #5 runs about 50 F higher, is this a problem?

3. #1 runs about 100 F lower than #5. We think this is due to cold air from the fan, what do you think?

4. Running at 60 mph and shifting out of overdrive with rpm rising from 2000 to 2500 increases #5 temp over 1000 F, are we ok?

58 cc 7120 head (cc'd)
944 21 cc KB pistons
Zero decked
Comp Cams 68-232-4
27 # Bosch injectors

Known data from OBD II analysis
idle timing 16 deg advance
down the road 38 deg advance
O2 0.1 to 0.8

You should be ok with 1000*.

Lee @ Hesco said that I could see 1500* during cruise. http://www.hesco.us/forum/forum_posts.a ... -egt-probe

It is interesting that #5 is hotter than both 4 and 6. #1 is also up against the water pump so it may run cooler. For a test I would swap injector #5 with another one and see if the temp moves with the injector. I would swap with #4 or #3. There are also many other reasons it could be a bit hotter. Intake and exhaust design can contribute to it.

SilverXJ wrote:#1 is also up against the water pump so it may run cooler.

Yeah I think that's indeed the most likely reason why #1 cylinder runs slightly cooler.

SilverXJ wrote:For a test I would swap injector #5 with another one and see if the temp moves with the injector. I would swap with #4 or #3.

You'd expect #6 cylinder to run hottest being furthest away from the water pump, but the cylinder temps. seem pretty uniform so this would indicate that there's very good coolant flow inside the block.
I agree it's possible that the #5 cylinder is running slightly leaner than the others so swapping injectors would be a good exercise.

The water pump pumps hot water out of the engine so i would imagine thats where the hottest water would be.

No, the water pump pumps water into the engine block. The pumps sucks water from the radiator, via the lower radiator hose. Then the water flows through the cylinder block, up through the head and out the thermostat. It is it then dumped into the radiator through the upper radiator hose.

If the water pump were sucking it through the block it would be taking up water through the upper radiator hose, which would not work if there was air in the system.

Thank you for conformation on the temps. We've lost one piston and not really interested in loosing another.

Here are some pics of the setup. Injectors 5 and 1 were swopped with no impact. We also switch 5 and 6 injector wires again with no change. This eliminates injector, wiring and electronics as potential culprits. There are slight differences in thermo couple locations so we will adjust to test for a change. We will also install one of the spare TCs and check for a faulty TC.

Ohhh.. the probes don't actually go in the exhaust stream? Not sure how accurate that setup is since it is measuring the pipe, not the gas. It would be interesting to see how that compares to an in pipe EGT probe.

I don't think there is a significant difference between gas temperature and outside wall temp. The pipe does not offer much thermal resistance or in other words the inside of the wall and outside have similar temperatures due to the high conductivity of steel. Also, the gases are quite turbulent such that there would be minimal temperature gradient across the stream. We've also mounted them close to the port outlet such that there is little time for the pipe to radiate and cool the gases appreciably.

It´s a huge differens outside a pipe depending on many things.
I have work in a company that´s produce exhaust manifolds and in a bend and close to it´s much higher temperature because more gas flow inside the wall.
If i look at the picture some probe are placed on a straight and a bit away from the bend but cylinder 5 is placed just at the end on a bend soo it should be hotter.
Some ware i have pictures from our Engine test center that show the diffens in color taken by a ir camera, i should look after these pictures and upload it because it´s show clearly the differens in a manifold.

SilverXJ wrote:No, the water pump pumps water into the engine block. The pumps sucks water from the radiator, via the lower radiator hose. Then the water flows through the cylinder block, up through the head and out the thermostat. It is it then dumped into the radiator through the upper radiator hose.

If the water pump were sucking it through the block it would be taking up water through the upper radiator hose, which would not work if there was air in the system.

Yup. You're right. I don't know what i was thinking when i wrote that.

Turbostroker, thank you, the pics would be extremely helpful particularly if they are a thermal imager.