New build, driveability and running hot

[O1Z06]

I wanted to share some details of my current Z06 setup and see if experience from anyone here can help critique and/or verify a few points.

416 LS3 9.3:1 static 237/254 115+3 .620 lift (15* overlap).
Trick Flow 235cc heads, -20cc Wiseco pistons
90mm throttle body, Port matched LSXr102 intake
Spinning an F1A to 14psi at 6500 rpm.
DeWitts 2”cut down radiator w/ EOC, Spal fans
Meziere EWP 160* thermostat

The engine is running good but I feel that it is running on the hot side (215F to 190F depending on ambient 90F-75F) at low 1600-2000 rpm cruising load (.30 to .45 g/cyl) 33 to 28 degrees timing. I am going to experiment with timing at cruse and see if this will affect ECT and also watch map. At idle it seems to get very toasty too. Low speed is set to 189F and high at 192F. I am beginning to think that this is going to be a fall winter spring car and definitely not a Texas summer car.

I am idling at 0.30 g/cyl at 900 rpm and 25* advance. Minimum airflow is around 13g/s warm. I think that with the cam, low compression and spinning the blower contribute to the higher airflow at idle. I may need to bump all low rpm cells up 3 degrees just from the low compression and another 6 because of the cam. This will put me at 26 in my idle cells if using a stock tune of 17 degrees.

Regarding timing, I understand that about ¾ degrees of timing = ¼ point in CR. What about combining increased displacement and more overlap at low to mid RPM. What are the affects of each? I am using a modified ZR1 timing map in the low load/rpm and high rpm/low load cells, not WOT as that set to be safe on 93 octane. This is running pretty good but wondering if I need more timing down low as mentioned above?

[Chuck L.]

Voltage at the WP is?

[O1Z06]

WP volts is 13.5 running and 12.5 off. The flow of the water pump seems good as seen in the expansion tank. Maybe I should route my steam vent tubes to the WP out instead of the radiator low pressure side.

I just think that my headers and engine bay are getting really hot and as this is my first high performance build, I'm not sure if the symptoms are normal. I am worried that I am dumping fuel, needs even more timing or I have a vacuum leak. This weekend I am going to check for a vacuum leak. I have my hot idle airflow at 13g/s with a nice hockey stick slope, MAP is 66kPa at 920rpm and 27 degrees advance. With cams that have more overlap than 15* like mine and on smaller engines, I heard can idle at 800 rpm.

Has anyone else been through this?

[joecar]

Running hot may be a symptom of running leaner or with too much timing.

[O1Z06]

Running hot may be a symptom of running leaner or with too much timing.

Thanks Joecar, I agree. I have also heard that excessive fuel and lack of timing will make the EGT very hot, quite noticeable with headers as they glow.

But looking at running lean and too much timing, I idle at 15:1, timing is 27*, idle air is 13 g/s, MAP is 66kPa and dyncylair is 0.30 g/cyl. Does this seem about right for a 6.8L 9.3:1 comp and 15* cam overlap?

[joecar]

That seems to have the right feel to it...


I'm wondering if it might be something simple like a small amount of air trapped in the block (let it bleed out via the steam crossover tubes).

[joecar]

Which water pump style (LS1, LS2+) do you have, and which thermostat style (1-piece, 2-piece)...?

[O1Z06]

It could be air in the top of the heads but I thought with my 4 point vent system (similar to the KUP steam block except I use fittings instead of a block) that the coolant would flow out the top into the low pressure side. The way I understand the flow is that coolant flows out the pump. into the block, up and out the heads into the standard 350 chevrolet thermostat neck. Maybe I should route the steam vent into the radiator in side not the low pressure side it is now. I will crack the vent and turn on the pump.

I am running the Meziere WP319 LS1 water pump and a standard chevy 350 160* high flow thermostat.

[O1Z06]

Just to update this thread, i did have a vac leak. Likely from just the thru bolt holes on the intake rocker, which also sucked a nice oil mist, contributing to some low rpm mid load knock. I'm idling now at 900 rpm at 64.8 kpa avg. I also sealed the fast 102 intake with silicone just in case. I also changed pushrods to some .045" shorter preload, not sure why i was using such a long pushrod during my build.

A tip for checking for vac leak is to plot your desired air curve from cold to warm after a RAFIG at a constant idle rpm. The before and after was soo obvious. Before there were some weird bumps and valleys, now its smooth like a 1/x^2 function.

For the cooling system, i separated the rear and front crossover, so just the front crossover returns back to the radiator. I also removed the thermostat and installed a shutoff valve on the heater bypass.

After these tweaks, the temp seems much more easily controlled by the fans, low fan on at 187 high fan on at 192 temp never goes over 194. For kicks i installed a pyrometer in #6 and idle is 725F and WOT 4th gear maxes at 1412F.

[joecar]

Thanks for posting back.

Good tip on the vac leak checking.

Glad you got the cooling system sorted out.