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The Shop Truck

1971 Chevy C20 with a custom flat bed.
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Well, the first test run was successful. There was much less traffic and we noticed something we hadn't before, when I do a pull, the pressure starts off at about 70psi, but starts to drop as RPMs climb getting down to about 54psi when I let off at about 5000rpm. I went back and looked at some of my drag race datalogs and I see the same behavior, oil pressure drops about 20psi from the start to the end of the run and comes back immediately after you let off the throttle.

We only did 3 2nd gear pulls and I was letting off around 5K this time rather than pushing it to 6K (I'm a bit gun shy at this point). My guess on the drop in oil pressure is the pressure drop across the oil filter. Unfortunately I can't datalog the physical gauge, and neither of us looked at that when we were doing pulls today. That gauge is pre-filter, so if I'm right, that one will stay high while the other one will drop.
For now, we're going to keep the RPMs to below 5500 and finish the break in. My new pan is supposed to be here on Thursday, so I'll figure out the oil cooler, hose routing, remote oil filter, and everything else between then and now. We'll both feel much better with more oil.

The cooling situation is not great, the fans don't ever shut off, but the temps don't really go crazy. Honestly they don't even get to the point where the fans were turning on before. I think I may just buy a high flow, stock temp thermostat and try that with all the fan settings the way they were before, just so I have a good A/B comparison. The higher temps make the radiator work more efficiently, so trying to keep the temps cooler is going to be a struggle when it's over 100 outside.

Thanks for all your input guys., this has been a painful and expensive experience, but hopefully we can move forward now and get this pig ready to go racing.
 
Babaganoosh said:
Fingers crossed it works this time, sucks to hear about budget getting blown out. Mine is shot this year as well. That’s ok, I have plenty to do while I wait on boost.

I just had to look up how to make mozzarella, easier than I thought. Do you guys use a pizza oven or just a steel in the oven? Wasn’t to thrilled about a stone, thinking a steel is the way to go.
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I make mozzarella, ricotta, and cottage cheese. All 3 are very easy to make and are way better and cheaper than what you get in the store.
I have a stone that I use when I make pizza, I need to get a dedicated pizza oven though, we currently make it on our smoker/grill. I'm going to a friends house and he makes his in a cast iron pan in the oven. I just wanted to keep this response separate from the car talk.
 
We took it on a much longer (40+ miles) drive yesterday. We had great oil pressure the whole drive, we did multiple 2nd gear pulls for break-in, and we got stuck in rush hour traffic with an accident.
The cooling situation is still an issue. I ended up having to pull over and let the truck cool for a bit (fans on, engine off). It cools OK on the freeway, but it was probably in the 80's when we were driving, it's going to be much worse when it's 110 out. I know the oil cooler is going to help with this, but I've got to figure out why it's not cooling with the new fans. I'm really hoping it doesn't mean I have to find and mount a new intercooler heat exchanger. That would be a major re-build of the core support.
When it's just idling, the fans can't keep up. You need to be moving for the fans to be enough. I have the fans programmed to shut off at 50mph, but I think if I was driving just over 50 that I may have cooling issues. At 70-80 it gets the temps under 200, but slower than that it was running hotter.
 
r3dd0g said:
We took it on a much longer (40+ miles) drive yesterday. We had great oil pressure the whole drive, we did multiple 2nd gear pulls for break-in, and we got stuck in rush hour traffic with an accident.
The cooling situation is still an issue. I ended up having to pull over and let the truck cool for a bit (fans on, engine off). It cools OK on the freeway, but it was probably in the 80's when we were driving, it's going to be much worse when it's 110 out. I know the oil cooler is going to help with this, but I've got to figure out why it's not cooling with the new fans. I'm really hoping it doesn't mean I have to find and mount a new intercooler heat exchanger. That would be a major re-build of the core support.
When it's just idling, the fans can't keep up. You need to be moving for the fans to be enough. I have the fans programmed to shut off at 50mph, but I think if I was driving just over 50 that I may have cooling issues. At 70-80 it gets the temps under 200, but slower than that it was running hotter.
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I can't remember but don't you have a ron davis radiator in it?
 
Babaganoosh said:
I can't remember but don't you have a ron davis radiator in it?
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Yes, it cooled perfectly before I installed the supercharger and intercooler heat exchanger. The fans would only run if I was stopped and idling, even driving at 35mph would keep the engine cool enough. The only change I made was to swap the old fans (3836cfm combined according to the ad for the radiator) with DeltaPAG fans (6400cfm combined according to their ad). It just seems like the intercooler heat exchanger is blocking the air flow.
 
r3dd0g said:
Yes, it cooled perfectly before I installed the supercharger and intercooler heat exchanger. The fans would only run if I was stopped and idling, even driving at 35mph would keep the engine cool enough. The only change I made was to swap the old fans (3836cfm combined according to the ad for the radiator) with DeltaPAG fans (6400cfm combined according to their ad). It just seems like the intercooler heat exchanger is blocking the air flow.
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That and it is also adding more heat to the stackup.
 
Think I'd put the old fans back on if possible just to see what happens :dunno:

You have them spinning the right direction I'd guess, but do the impellers need flipped or anything, etc.
 
Tnsejed said:
Too large a distance between the intercooler and the radiator could also be a problem. Have to get fan air to need to go through the radiator.
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It's only about 1/4" between the radiator and intercooler. I could slot the holes and make it slightly closer. The shrouds are sealed to the radiator though so the air is definitely going through the radiator.
shady said:
Think I'd put the old fans back on if possible just to see what happens :dunno:

You have them spinning the right direction I'd guess, but do the impellers need flipped or anything, etc.
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They are spinning the right direction and these things move some serious air. I don't think there is any way the other fans could push that much air.

I'm starting to do some testing. I pulled the grill off and drove it around. That pretty much fixed the getting hot while driving issue, but the temps still climb if I stop and idle once the oil is hot. The oil cooler will definitely help with this and may be enough to fix the idle problem, but I'm still looking. I'm considering violating my grill and bumper, dimple dies across where the CHEVROLET is and a big hole where the license plate would go with a duct directing air up into the radiator.

The next test is pulling the condenser and driving.
 
Fastereddie said:
That and it is also adding more heat to the stackup.
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I forgot to comment on this. I checked the intercooler temps and with the supercharger bypassed it's not adding much heat, high side/low side temps we're 105/115. Still cooler than your average summer day in AZ.
 
Wes Harden said:
So these hotter temps are with or w/o the AC running ? Trans cooler in rad ?
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The A/C isn't charged so it's not running, trans cooler is not in the radiator, it's mounted outboard of the frame under the passenger. The 10ish degree difference in intercooler water was on the throttle accelerating, when it's idling I don't think there is a significant difference between the inlet and outlet.
I drove it around again on surface streets without the grill or condenser. It cools even better while moving, but the temps start to climb once you stop, even when the fan's are running.
Next, I'm just going to unbolt the intercooler and swing it out of the way of the radiator and let the truck idle until it gets hot to see if the fans can keep it cool with no other obstructions. The main issue I'm having now is idle temp control, the fan should be cycling on and off, but it never shuts off and temps keep rising.
 
The pump is driven off the harmonic balancer with the blower belt, it's 6% overdrive so the waterproof is already spinning faster than stock.
 
so that has changed since last build, maybe to fast ? grasping at straws. Does sound like an air flow issue
 
If the water was flowing too fast it wouldn't have time for the heat to be removed in the radiator. That is what the thermostat is supposed to do though. Stop the water flow so the heat can be removed then allow it to circulate.
 
Wes Harden said:
so that has changed since last build, maybe to fast ? grasping at straws. Does sound like an air flow issue
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I appreciate your suggestions, keep them coming. I could see it being too fast at 7500RPM and causing problems, but not idling at 850.
This is how the intercooler heat exchanger fits in between the condenser and radiator. It's about 1/2" away from the radiator at the top and about 1/4" away at the bottom. I could see this causing issues with the intercooler's functionality, but not the radiator.
IMG_20260527_124020344.jpg

I unbolted it and the power steering cooler and let them hang out of the way.
IMG_20260527_125951560.jpg

I started it up and let it get up to temp and cycle the fans. They turn on at 205 and back off at 195. The fans shut off after a few minutes, but I had the truck inside the shop which is evap cooled right now about 15 degrees cooler than outside. I backed it out into the driveway, the fan turned on and cooled it down to 201 after 5 minutes or so, but could not get to 195. The oil temps were only at about 215, so if the engine were fully heated up I don't think it could have kept up, even without the condenser and intercooler bocking flow.
Now I'm really confused, we've got the same radiator that worked wonderful before, fans that are sucking almost twice as much air flow through the radiator, no condenser blocking air flow, but it still can't keep up with the heat at idle. I am idling at 850 instead of 750, but I wouldn't think that would create much heat.

Things that are different just to put them all in one list:
-I switched from a LQ4 truck style water pump to an LSA/LS3 style water pump that is being 6% overdriven.
-I switched to a 170°F thermostat that I have drilled 4 3/16" holes in (formerly the factory 187°F thermostat with no holes in the truck pump).
-16" spal brushed fans were upgraded to 16" DeltaPAG brushless fans.
-The supercharger is putting a load on the engine at idle.
-Idle RPM increased to 850 from 750.

It's only 88°F outside right now, this thing used to cycle the fans in the middle of summer (115°F) while I was stopped at a light.
 
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