VikingTrad3r

yes im still getting hot. in fact i hit 247 f and slowed down to cooldown laps.

i was talking with a friend who has a pile of lt5 knowledge and he explained to me that while radiator and less restrictive tstat mods help, they cannot counter what happens at high rpm cavitation.

my next step is the underdrive.

it should work. if i hadnt opened up the tstat, id be concerned about overheating at liw rpm with the underdrive pulley. but my mods should counter that. still searching for an underdrive pulley.

Tom400CFI

May have to "make" one. I'd guess it's not the same bolt pattern, offset etc as a SBC.

Too bad you can't get a better pump impeller, like a Stewart one, but I think under driving it will help a lot.

jrtoffroad

If I need to get one made I could always get a couple fab'd up if need be.

Does anyone happen to have an old water pump I can pull a stock pulley off for dimensions?

jrtoffroad

Wow, how long did it take to get to that temp? You've confirmed both your fans are working properly and have a good seal between the fan shroud and the rad and rad to front duct work? How were your oil temps (also, just for curiosity, what oil are you running)?

Tom400CFI

I don't believe that the fans run above 25 mph.

jrtoffroad

Interesting, never knew that. I've got mine setup based on coolant temp only (not using stock ECM).

Tom400CFI

Ah....not-stock ECM would be different. I believe running the fans "at speed" actually inhibits air flow through the radiator.

BFoster

My motor is currently being rebuilt by Haibeck, and the car is built for the track. He is changing my cooling system back to nearly stock from the old setup, and discussed one of the issues you all are talking about, here:

I want to discuss the LT5 engine cooling on the track. The OE LT5 water pump and accessory belt drive system causes the pump to cavitate at about 6000 engine rpm. When the pump is cavitating the pumping efficiency drops off dramatically.

This is what is seen on the track. When the engine is run over 6000 rpm consistently, the coolant temperature will stabilize because the coolant is not moving past the temperature sensor. The driver will observe the oil temperature rising because the oil is still moving and heating in the overheating engine. Normal oil temperature on the track is about 230 degrees. During cavitation, the temperature will go to 245 degrees in just a minute or so. If the driver reduces the engine speed to less than 6000 rpm the oil temperature will drop quickly back to the normal 230 degree range.

An underdrive accessory belt drive pulley is available for the ATI crankshaft damper on your engine. With the 12% underdrive pulley the water pump cavitates at an engine speed of about 7000 rpm.

ATI no longer makes the pulley. A custom made reproduction underdrive pulley is available for $400. Let me know if you want to order one.

TomH91

Thanks for that info from Marc, Brad.

jrtoffroad

Update from weekend track day:

Cooling system appears to be fixed! With the new upgraded radiator the coolant temp stayed well below mid-gauge (not sure what that temp is exactly) the entire day, even after numerous hard 30min sessions (with 30min cool downs in between). Oil temps were a little cooler too, maybe hitting 245 at the absolute highest. Pretty happy, but it was a much cooler day out with temps in the upper 60's to low 70's rather than 90's like last time I was out there. BUT, I did push much harder and run much longer this time and never had to let off for things to cool.

For the oil consumption I added a catch can to the valve cover breathers. This prevented oil from entering the intake track, but my catch can was basically FULL after 3 30min sessions. Appears most if not all the oil is coming from the driver-side valve cover (or cam cover I guess on these engines). Not sure if I have an oil drain back issue there, or maybe a baffling issue? I've actually never had the valve cover off an LT5, anyone know what the baffling looks like? The factory PCV valves are still in place and at the valve cover breathers there's a nice vaccum at idle and ~3k rpm (no load)...

Overall the car did awesome. This time out I had a set of TOYO Proxes R888R's and they were amazing. With the extra speed I was carrying into corner 10 I was able to hit 130 on the front straight. A fresh set of powerstop track day pads held up great to the abuse, BUT man they do wear fast. I might need to go to a more expensive pad to get more life.

Kingtal0n

I can help with the PCV issue. For performance TRACK vehicles, I strongly recommend you measure crankcase pressure.
CC pressure must be maintained below atmospheric at all times.

Once you establish the CC pressure you can decide what to do from there. If the CC pressure is rising over atmospheric it must be fixed before anything, especially band-aid solutions as catch cans. The internal oil/air separator *IS* a catch can, but it catches oil and returns the oil to the pan. Your best bet is to accentuate the performance of the internal oil/air separator as much as possible. The internal OEM separator runs on kinetic energy of crankcase gas being pulled out by PCV action (Defined by a CC pressure below atmospheric). Thus, you fix the CC pressure issue by applying appropriate vacuum to the CC = provides kinetic energy necessary to organize and improve internal separation of air and oil. Lower CC pressure also prevents formation of large oil droplets and helps return oil to the oil pan and wicks oil from engine parts.

I wrote more here for Supraforums
https://www.supraforums.com/threads/.../post-13998184

jrtoffroad

Thank you for your insight. I'll go ahead and check the crankcase pressure. I happen to have a chassis dyno at my disposal, so pretty easy to test under controlled conditions. Since the PCV system provides no meaningful vacuum under WOT, do you have any recommendations on how to maintain crankcase pressure below atmospheric, short of adding a vacuum pump? In my case I had to eventually move the breathers out of the intake track as I will be installing a remote mount turbo system in the near future. One of the down sides to remote mount turbos in this case will be my inability to reasonably route breathers to the suction side of the turbos.

I have a little bit of testing to do to determine the true issue. Yes, I may have a high rpm / high load blowby issue, but since I only seem to have oil from one valve cover, I can't help but wonder if there's something unusual with that side of the engine in regards to oil return. I'll throw it on the dyno this week and see what I find.

jrtoffroad

If anyone is interested, here's an article about oil consumption from Mark Haibeck:
My experience with oil consumption on the LT5 engine (zr1specialist.com)

The engine in my car is a 368 that was built and installed before I owned it. I assume this engine has iron cylinders. Could be there is some questionable honing that is causing poor ring sealing at high rpm...

VikingTrad3r

Jrt u should start a track thread documentin all your issues and fixes. i will certainly follow it and we can share notes.

I started taking my z to the track regularly a couople summers ago and i really amped it up this year. here is my ZR-1 track thread, id sure appreciate you following along we can compare notes. https://www.corvetteforum.com/forums...post1605656993


with respect to your cooling system, i did the same thing except i cut my tstat. However at sustained high 5800+ rpm, on a +30 c / 86f ambient day, im still dangerously hot. Btw im not sure how new u r to the c4 platform, but if you press the up/down fan buttons at the same time. wait for -00 to appear, and then scroll to 16 using the up or down arrow, and selecting 16 by pressing the button btwn the fan speed buttons, that is the temp your ecu is seeing. so u can grab some accurate data vs the needle.

I also *may* be getting the same ccv breather issues as you. In a hard hard day at the track, my car may consume about 1/4 quart. I chalk it up to pcv and big rpm. ive read that’s perfectly normal and it doesnt consume oil any other time than hard track days.

I am planning to pull my plenum and go after some minor oil seepage in the valley this winter and may check out my pcv at the same time.

regarding the brakes. i started with the powerstop track day pads. excellent pads and i think we get the best our j55’s have to offer when combined with motul 660 or better. its also possible to buy stainless steel caliper pistons to soak more heat up. im not sure if that just means longer to cooldown too.

@1Eyed Willie got me onto dynamic friction “active performance “ pads and i can say they work as good as powerstops and they consume rotors at about half the rate. And slightly less dust. 1Eyed Willie i think made recent pad changes and is now looking for a cooling mod. BTW willie if u read this there is a great picture post in my thread about a brake mod that a grandsport member used with great results.

My LT5 drinks twice as much fuel as my wifes c5 at the track!! Doh!

not many c4 track junkies out there and even fewer ZR-1’s. nice to meet another. 👍👌

Tom400CFI

How do you accomplish that at WOT/no vacuum?

Kingtal0n

here is a video of how I measured/achieved on my 600rwhp daily

Supporting information
Pressure drop is supplied by the AIR Filter. Here is pressure drop vs mileage curve for typical OEM filters, as intended by the factory the pressure drop increases with mileage.




PCV action in natural aspiration applications supplied by throttle valve (just before the throttle body post air cleaner)
Published paper


Here is an example showing the FSM diagram for PCV pressure drop at the throttle valve on random V8 engine (C5 corvette)
all engines use this technique from all manufacturers in the world, every one of them,




Here is a measured crankcase pressure drop between air filter and compressor inlet for example of how to datalog and compare values


This is fluid mechanics book showing us that the pressure drop is a function of


pressure over the specific weight of fluid, or p/y (pressure divided by gamma)
The kinetic energy and elevation are negligible in the majority of PCV WOT pressure drop applications due to the shape and location of PCV orifice

In other words, it isn't much of an venturi influence. The pressure reading at the intake tube compared with engine crankcase is the vacuum signal supplied to the piston rings, which is necessary to reduce and control blow-by gas. To put it another way, high crankcase pressure unseats piston rings and may cause ring flutter which leads to excessive blow by, large oil droplets, oil invasion to ring pack (stuck sticky rings over time, more blowby) and increase oil consumption.
We must keep crankcase pressure low to protect ring seal function, reduce blow by, reduce oil droplet formation , improve oil/air separation of the OEM baffle.

jrtoffroad

Thanks for the info! I'll give the dynamic frictions a shot. I really want to get some ducting to the front brakes. They're doing great, but I'd feel better keep them cooler. Funny you mention the fuel consumption, this last track day I was making sure I didn't have a hole in my tank or something

I need to start a thread on my racing adventures (and mis-adventures). I need to run through yours, I'll probably learn a bunch. I'm about to make some minor suspension changes, be fun to document how that works out.

I'm surprised yours is still getting hot. Have you confirmed both your fans are working properly? There was a comment earlier in this thread about fans maybe turning off at 25mph, is that a real thing? What's the condition of your condenser and oil cooler fins and have you replaced your air dam recently?

It didn't matter how hard I pushed at the track my car would not get hot. RPM didn't seen to be an issue, I was over 5800 a lot. (If I'm honest I like to keep the LT5 as close to 7k as possible at all times)

VikingTrad3r

great pics of a fellow members grandsport diy ducts in my thread.

i love keeping my lt5 high too. im 100% original stock except tires and pads and now radiator. fans do not operate at speed no. i havnt touched my air dam but its also not mangled or loose. i have adjusted to getting into 4th now to compensate but id rather stay in 3rd way up in the powerband.

im about to get some custom valved “moracca” fx3 bilsteins with the stiff corvette challenge cars that i think will seriously improve my stability at speed. i also have a set of drm fx3 coilovers but i want to stay with the transverse leafs for now.

The Dingo

Interesting post Kingtal0n, thanks for sharing that experience with crankcase pressure.

Tom400CFI

I didn't see much content. We all know we want vacuum in the crank case, and I think most of us know the benefits already. How do you get that w/no vacuum?

No 3/8" PVC/crank vent hose is going to pass enough volume to keep up with that generated from blow by...especially at vacuum levels created by a used air filter. So what's going to get you there? And how is pulling crank air into the intake different or better than the factory system, from an oil/vapor stand point? I asked that above...didn't get a real answer. A belt driven vacuum pump will get you there. Who here is going to put a vacuum pump on their street/track day car? Not me. So for something other than a full on, racing only car, I think the catch can IS indeed, a perfectly fine "band aid". Empty it after each session.