Which grill cools better

[1-PU70]

I have a 70 with the center bar grill and was wondering if a 71-72 grill would cool better. It has a BB with AC and the FL heat is just to much. I have been a mechanic all my life and worked on these trucks when they where new. Yes Im an old man. But Im trying to think outside the box. If anyone has some real experience with changing grills I would appreciate it.
Thanks Gary

['68OrangeSunshine]

It would be an interesting aerodynamic study -- to see which of the three Grille styles flows more CFM from frontal airflow.
I would conjecture 1st Phase [67/68]* and 2nd Phase [69/70] would induce more drag than 3rd Phase [71/72]. Except that piece is plastic, so it's less robust to heavier physical forces. *67 and 68 slso have a sheet metal plane from the bottom of the Radiator Bulkhead to the front. Deleted on Model Year 1969 and later.
In the end all three Phases are stopped by the Radiator Bulkhead and Radiator, just behind the Grille. So you have a barrier that causes a buffeting airflow rebound.
If resources were no barrier to research, wind tunnel tests might show some data. Realistically, the speeds should not exceed 100 MPH. More likely around 70, which is the road speed I have experienced to get best freeway handling. Faster, and the road vibrations make the fabric want to tear apart. That's on an un-rebuilt truck. A Frame-Up Rebuilt may be a lot tighter.
But the New Breed trucks have always had the reputation of having similar aerodynamics to a red brick.

[Ayrok]

https://undercoverinnovations.com/pr...s-show-panels/

I have these on my truck. Seems to help keep air from going up and over the radiator. Not a grill I know but it might help with your heat issue.

[Steeveedee]

You'd have to measure the thickness of the grid strips on a '71-'72 grill and compare to the earlier grill's blockage area. If someone gives me the thickness, I can calculate the area. I'm out of town so won't be able to measure my '70 grill until Sunday at the earliest. I suspect that the difference is small. I had a '71 grill in my truck and got rid of it (it was a butcher job) and I didn't notice any difference in cooling when I went back to a stock grill. My FiL may have in fact put that grill in with the running-hot problem this truck has had in all the time he owned it. I cured it a few years ago.

[Stocker]

Can't advise as to grill differences. Forgive me but I must ask about your cooling system details. Radiator type & condition, shroud, fan fitment in shroud, sealed system with recovery tank, HD clutch fan in good working order, 7-blade factory-type fan?

[Orefactory4x4 swb]

I’ll keep it simple.
Yeah, 72 grills are cooler

[Richard]

Kind of curious to me that a former mechanic would go this direction with cooling problems? Thousands of 67-70 trucks built with who knows how many still on the road. Even my 94 Chevy truck has a similar grill opening with the bar in center. If you like the 71-72 grill and want it, go for it. My favorite as well. IMO there will be no cooling difference.

[1970cstblazer]

Always preferred the 1969-1970 style grille over the 1971-1972. Doubt there is a huge difference in air flow between the two.

[MJN]

even the bowtie in the middle of the '71-72 grille could be hindering cooling

https://gmauthority.com/blog/gm/gene...rolet-flowtie/

It would be interesting to run a model and do some CFD (computational fluid dynamics) and see the air flow but with how these trucks are fit together you would probably find more air leaks or air going around/under the radiator than through it

Besides the BB and A/C what is the rest of your setup like? Big radiator, fan and shroud?

[Keith Seymore]

Originally Posted by Richard

Thousands of 67-70 trucks built with who knows how many still on the road. Even my 94 Chevy truck has a similar grill opening with the bar in center. If you like the 71-72 grill and want it, go for it. My favorite as well. IMO there will be no cooling difference.

This is the most salient point.

All of these front ends were validated to provide adequate cooling at GVW in Death Valley, even up to Medium Duty use.

If the OP is experiencing cooling problems its because of the hardware (radiator, fans, etc), not the front end air flow.

K

[Keith Seymore]

The other thing is this: the airflow is not intuitive.

We decided one time we were going to use some parking lamp openings for an air inlet. Looked like a nice spot for some "ram" effect.

We ran the tests and the made no difference. We couldn't figure it out until we ran them using smoke: the air was going in the outboard edge of the inlet and coming right back out the inboard edge of the inlet. It wasn't even entering the ductwork.

You are not going to know anything until you smoke it.

K

[Keith Seymore]

Found this while looking for something else:

Originally Posted by Keith Seymore

It's gonna be somewhat tough to prove out in the real world.

I should preface this by saying I was the engineering manager on the Chevy Volt program (both domestic and export; and related variants: Opel Ampera, Vauxhall Ampera). CdA for the Volt was .284 which at the time was the lowest GM had ever done for a midsize sedan. We spent a ton of time in the wind tunnels (we have two: the aero tunnel that the NASCAR boys borrow, and a Climatic tunnel for hot/cold operation).

The problems with doing a truck program on the outside as I see it are:

a) Airflow over a vehicle is not intuitive. You don't really know what's going to happen 'til you smoke it. Example: We introduced a duct at the front of the vehicle one time, looking for a ram air effect. It wasn't working like we expected so we brought it into the tunnel for evaluation. With the smoke, you could see the air was actually hitting the inside corner of the inlet, scooting across the opening and shooting out the outboard side of the inlet and around the vehicle. No air was actually going into the duct and in the hose. We would never had known (or even guessed this) without the smoke and video. The whole "tailgate up vs down" and bedcover debates that just won't die (in spite of objective data) are a symptom of this.

b) You need to be able to focus on one small area. On the road testing incorporates the overall vehicle, which is fine for a final "capping run" evaluation, but for development work you need to isolate one area and gage the effects that can be attributable to those specific changes. Sure - the NASCAR and Bonneville guys to some testing on site with duct tape and cardboard - but if they're smart it's after spending hours and hours iterating and developing inside a tunnel like ours.

c) Things change while you are looking somewhere else. So - the bad news is while you are focus on one area of the vehicle the other end can be changing without you knowing it. Hopefully you find out and can nuetralize the effects but if not it can generate a lot of confusion.

We had been working for years on prototype and preproduction vehicles so we were quite anxious to do a "sense check" on the first saleable vehicles off the line. We put them in the tunnel and the results were .289 - not good because it was higher than expected but also because the media reports the values rounded to two decimal places = .29. We very much wanted the .28 value reported, so we had to be below .285 to achieve this.

After much angst and diagnosis it turns out the cars were building 5mm too high. This change in trim height was affecting our test scores, the advertising numbers and our fuel economy certification. Dropping the cars down 5mm brought everything back into line. Note that's 1 count of aero drag for every 1 mm of trim height, in this case (your results may vary).

With my duct example above, we could've changed something at the rear of the vehicle, changed the flow under or around the truck and suddenly our front duct could've started working. You never know.

d) Small changes have big results and big changes can have small results, like the example above. My boss used to joke that he would give his finger for .001 CdA (one "count" of drag). Little scallops and skegs and flanges that look like styling features can actually be aero enablers. Things like mirrors and door handles and grille openings are fairly significant aero disenablers.

[70STOVEBOLT]

Originally Posted by Keith Seymore

The other thing is this: the airflow is not intuitive.

We decided one time we were going to use some parking lamp openings for an air inlet. Looked like a nice spot for some "ram" effect.

We ran the tests and the made no difference. We couldn't figure it out until we ran them using smoke: the air was going in the outboard edge of the inlet and coming right back out the inboard edge of the inlet. It wasn't even entering the ductwork.

You are not going to know anything until you smoke it.

K

I always smoke first...

[weq92f]

Originally Posted by Keith Seymore

...<snip>...

You are not going to know anything until you smoke it.

K

.

[72c20customcamper]

Originally Posted by 70STOVEBOLT

I always smoke first...

Thought it was customary to smoke afterwards?!

[howzzzit]

Take your grill out and see if there's a big difference. Might not be your problem.

[Keith Seymore]

Originally Posted by howzzzit

Take your grill out and see if there's a big difference. Might not be your problem.

Gah!

There's your answer -

The simplest one that works.

K

[70STOVEBOLT]

Originally Posted by 72c20customcamper

Thought it was customary to smoke afterwards?!

Tomaaato. Tomattto. Woop

['68OrangeSunshine]

Originally Posted by 72c20customcamper

Thought it was customary to smoke afterwards?!

Largely depends on what is smoked. \\
Some before,
or Some after...

[1970-CST]

Try the 2747 HD fan clutch. Almost all fan clutches are designed for emissions era 210-220*F lockup. The 2747 locks up at 180-190.

Does your vacuum advance can match the vacuum characteristics of your engine? This is the most common cause for overheating issues.

[68isgreat]

The 68 grilles are the worst. Most of the 68 trucks blow up because the grilles are so horrible. Please send all those ugly 68's to me and I'll make sure to dispose of them properly.

[dmjlambert]

Originally Posted by 68isgreat

The 68 grilles are the worst. Most of the 68 trucks blow up because the grilles are so horrible. Please send all those ugly 68's to me and I'll make sure to dispose of them properly.

That is great advice. I can take the 69-70 grills off your hands and dispose of them properly. You need to go with 71-72 grill, it helps the real classics become more rare.
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