First thread how about aerodynamics on our trucks?

[Cms83]

Good day everybody. My name is Chris. I have a daily driver 70 c20 with 3 on the tree. I drive a hour to work to Bristol pa everyday. I am at about 20-30$ a day in gas. That’s not going past 55 mph. I wonder how much lowering and adding a front spoiler would improve my aerodynamics. In 69 when they went to the steep hood. That gave another 5mph according to the Chevy engineer that was on c10 talk podcast. So could other improvements be made? I plan to change rear ratio to. I can go 15 mph in 3rd gear. So she’s a screamer
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[Warrens69GMC]

For the crew to help with mileage-

WE need-
engine size
carb - brand
transmission
rear gear ratio
tire size (OD)
if you are carrying and weight

[jocko]

Originally Posted by Cms83

Good day everybody. My name is Chris. I have a daily driver 70 c20 with 3 on the tree. ... I wonder how much lowering and adding a front spoiler would improve my aerodynamics[/i][/size]

It may improve aerodynamics but it will not improve gas mileage. You're still pushing an upright brick through the air. Tough situation at $20-30/day. At a minimum, you need an o/d trans. It is likely you ALSO need a higher rear gear. Or - a less expensive approach might be to get a smaller or at least newer dd for work that already sips gas. If you can stomach a small car, there's your answer - if you're like me, you can't, unfortunately. My dd is an 01 Silverado 5.3 w/OD trans from the factory. Still not great on fuel econ, approx 13-15 mpg - but also less expensive than a trans+rear gear swap on your 70 and you'd still be driving a truck - and have time to work on you 70 if you wish without worrying about getting it up and going for work the next day. Don't know your circumstances - however, the spoiler is a waste of money if the reason is for fuel economy. And I'd avoid that podcaster - the hood change between 68-69 may have added 5mph if it were pushed out the back of a C-130 at 10k', but that's about it.

[Jonny Hotnuts]

I have vested a significant amount of effort in learning the evil ways of aeros (landspeed racing on the Bonneville Salt Flats).


You have 2 issues with these trucks. Fa (frontal area) and Cd (coefficient of drag).
These combined give you your CdA (drag x Fa).

The C10 has a LARGE Fa. You can gain a decent improvement on Fa and Cd by lowering (note the Cd is improved due to lowering by limiting the amount of dirty air under the vehicle). You can get a noted improvement on MPG by lowering.....but it wont be life altering.


This is because......


Most of the aero drag is generated in the aft sections (behind cab, behind tailgate). The stark drop off behind the cab generates a large low pressure area and this MURDERS the Cd.


If you wanted to make the truck more efficient you will need to find a way to decrease the low pressure area behind the cab. You 'could' chop the top (this will also lower the Fa as well) or put a slight rake in the roof (lower in the back of the cab). You could also install some sort of NASA ducts in the side of the bed to take air from the sides of the truck and 'fill' the low pressure area of the bed OR cut some venting in the bed floor so the higher pressure under the vehicle would help equalize the lower pressure in the bed.


All this being said.....

its a truck, its a brick. It can be made better but the cost of aero improvements is very high.


good luck.

~JH

[Cms83]

it’s Dana 318,rear ratio is 4:53 ish. Engine 1978 305. Rochester 2brl
I do plan to change the rear ratio. Just not sure if the aerodynamics would be worth it. Seems not so much. However I do have to cut the roof off and put in the one from my spare cab. Perhaps I could chop the top at that point. I’d already be there. Would just need to do doors and glass right? I have been driving a economical truck for 8 years. Need less to say I love driving again. You guys are great though so fast to help. I’ve been referencing this site for a long time. Even at that it’s a huge help. So for delayed response I am trying to get the engine out of my wife’s 09 traverse. Crank is locked up and can’t fit the block out with the trans converter. What a nightmare this is why I got a 70 Chevy
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[Cms83]

235/85/16 for tires
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[HO455]

I'm afraid I have to respectfully disagree. Any improvement in aerodynamics will require less horsepower to move the vehicle, which in turn means less fuel used. Which is why Prius's and Insights look the way they do. Yes it is a brick but lowering, air dams, removing mirrors, skinny wheels and tires, flush fitting wheel covers, and tonneau covers are all things that will help to remove drag. See photo. Think Bonneville!
My S10 went from 18-19 mpg highway to 21-22 after I lowered it. Well worth the $450 dollars I spent to lower it 100,000 miles ago.
Getting a O/D transmission will help as well as making sure it has a working lockup convertor. Getting a wide band air/fuel guage getting your distributor curved will allow you to get the most out of your engine combo.
But all of these things cost money. Whether you drive enough to pay for them over the long haul is something we all have to decide ourselves. This thread may help the OP.

http://67-72chevytrucks.com/vboard/s....php?p=8374984

[Jonny Hotnuts]

Originally Posted by HO455

I'm afraid I have to respectfully disagree. Any improvement in aerodynamics will require less horsepower to move the vehicle, which in turn means less fuel used. Which is why Prius's and Insights look the way they do. Yes it is a brick but lowering, air dams, removing mirrors, skinny wheels and tires, flush fitting wheel covers, and tonneau covers are all things that will help to remove drag. See photo. Think Bonneville!
My S10 went from 18-19 mpg highway to 21-22 after I lowered it. Well worth the $450 dollars I spent to lower it 100,000 miles ago.
Getting a O/D transmission will help as well as making sure it has a working lockup convertor. Getting a wide band air/fuel guage getting your distributor curved will allow you to get the most out of your engine combo.
But all of these things cost money. Whether you drive enough to pay for them over the long haul is something we all have to decide ourselves. This thread may help the OP.

http://67-72chevytrucks.com/vboard/s....php?p=8374984

I raced along that truck (Webb team from Texas and the trucks name is 'Chock full o Nuts').

(we also partnered with the Schnell automotove truck from Portland so we wouldnt have to take duplicate equipment from PDX to Wendover.)

The AA on the side represents the engine side. AA is unlimited after 500ci...and they have a monster motor.

Even with all of the 'aero mods' they did they still only were able to post just sightly north of 200mph (ok, that is still fast...) but no where NEAR as fast as other vehicles with significantly less horsepower (*and this is with the low air density of Bonneville!). This is because with all the aero mods you STILL cant make much improvement on the low pressure areas behind the cab and tailgate and this is where the lions share of the bad aeros happen on trucks. Removing mirrors and other little things on a truck is like pulling a dixie cup of water out of the ocean.

~JH

[Cms83]

So would some sort of bulkhead or headache rack that would fill that gap help?
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[71gmcC15]

Originally Posted by Jonny Hotnuts

I have vested a significant amount of effort in learning the evil ways of aeros (landspeed racing on the Bonneville Salt Flats).


You have 2 issues with these trucks. Fa (frontal area) and Cd (coefficient of drag).
These combined give you your CdA (drag x Fa).

The C10 has a LARGE Fa. You can gain a decent improvement on Fa and Cd by lowering (note the Cd is improved due to lowering by limiting the amount of dirty air under the vehicle). You can get a noted improvement on MPG by lowering.....but it wont be life altering.


This is because......


Most of the aero drag is generated in the aft sections (behind cab, behind tailgate). The stark drop off behind the cab generates a large low pressure area and this MURDERS the Cd.


If you wanted to make the truck more efficient you will need to find a way to decrease the low pressure area behind the cab. You 'could' chop the top (this will also lower the Fa as well) or put a slight rake in the roof (lower in the back of the cab). You could also install some sort of NASA ducts in the side of the bed to take air from the sides of the truck and 'fill' the low pressure area of the bed OR cut some venting in the bed floor so the higher pressure under the vehicle would help equalize the lower pressure in the bed.


All this being said.....

its a truck, its a brick. It can be made better but the cost of aero improvements is very high.


good luck.

~JH

You could put a topper on it that would eliminate the low pressure in the bed. The air would go strait over

[HO455]

Originally Posted by Jonny Hotnuts

I raced along that truck (Webb team from Texas and the trucks name is 'Chock full o Nuts').

(we also partnered with the Schnell automotove truck from Portland so we wouldnt have to take duplicate equipment from PDX to Wendover.)

The AA on the side represents the engine side. AA is unlimited after 500ci...and they have a monster motor.

Even with all of the 'aero mods' they did they still only were able to post just sightly north of 200mph (ok, that is still fast...) but no where NEAR as fast as other vehicles with significantly less horsepower (*and this is with the low air density of Bonneville!). This is because with all the aero mods you STILL cant make much improvement on the low pressure areas behind the cab and tailgate and this is where the lions share of the bad aeros happen on trucks. Removing mirrors and other little things on a truck is like pulling a dixie cup of water out of the ocean.

~JH

The point I am trying to make is that those little aero modifications are worth the work. Your friends and everyone else who races for speed records do them because the little things add up. They are not going to change the basic physics of a truck body. But for under $1000 you could do the modifications I listed and they would pay for themselves in 25000 miles or less.
And in a minor hijacking.
I noticed that Schnell Automotive has closed up shop. Did they move or close?

[Jonny Hotnuts]

Originally Posted by HO455

I noticed that Schnell Automotive has closed up shop. Did they move or close?

I spoke in length with Tim about this last year. They packed it in and retired. Bill was getting 'forgetful' and they both were tired.....mostly because time and time again they would take in a young person, train them in the art of building a race engine and then they would leave, open their own shop and start soliciting business from long time clients of Schnells. Tim and Bills kids all had white collar jobs; the granddaughter had no interest although she could often be found in the back cleaning up a head or block.

Sad really.

I looked through all my landspeed pics and the only ones I could find with Bill and Tim were when we were in their shop doing a 3 angle job on my head.
-That engine 1.3l made over 550 WHP!!! (I had to crashed that car +200mph a couple of years ago). Good times.

~JH

[truckster]

Originally Posted by 71gmcC15

You could put a topper on it that would eliminate the low pressure in the bed. The air would go strait over

If that would make a significant difference the Blazers would get better fuel mileage than the trucks. They don't. It's a brick.

You don't state what your current fuel mileage is. If you're really running a 4.53 rear, changing that will make the most difference. That and a good tune up should get you in the neighborhood of 13-15 MPG. After that you'll be throwing dollars after dimes, because there's only so much you can do to make a brick aerodynamic.

[Warrens69GMC]

I think he means something like this. Additionally, you could have a sacrificial tailgate that you could have holes cut into and ducted up to the side windows in the topper to alleviate the pull on the back of the truck

[Overdriven]

When Toyota was developing the Xrunner version of the Tacoma they did some experiments and the engineers shared some info after the trucks release. To “clean up” the air coming off of and behind the cab they used some “disrupters” on the back of the cab similar to what Mitsubishi put on the Evo 9 MR above the rear window. These do increase drag slightly but also slow the air coming over the top of the cab allowing it to fill the area behind the cab creating less of a low pressure area. It also allows more air to flow over a tonneau cover to a bed mounted rear wing which was their main goal.

The other area they looked at and saw major improvement was with a rear diffuser. Again, this was more for stability and reducing lift not decreasing drag and improving mpg. But I can only assume it was effective at these things by reducing the low pressure area behind the tailgate. The rear diffuser was most effective with a front belly pan that extended to at least the end of the transmission, they never tested a full belly pan. There are more pics of the mule out there, some with small lengths of string attached to the tonneau cover, apparently they couldn’t get Toyota to invest in wind tunnel time so they went low tech for some tests.

One nice thing about aero is you can make and test some mods for cheap. If you have some cardboard, scraps of plywood and some duct tape you can try out a belly pan, front spoiler, blocking off some of the grill and more pretty easily. If it works then you can transfer the design over to metal.

Edit: Another truck to look at for inspiration, in the 1990’s GMC went land speed racing with a V6 powered S15. If I’m not mistaken they didn’t run a tonneau cover and instead make some boxes in the bed to change how the air moved in the bed. Might be worth looking into.

[Overdriven]

Last post was in the spirit of the thread discussing aero, but I have to agree with others that you won’t see much if any mpg gains from aero without addressing your gear ratio. If you don’t have much stop and go and are mostly on the highway then changing only the rear gear would be the most cost effective route. If your commute is mixed or you want to maximize overall mpg then an overdrive trans and rear gear change will yield the best results.

I second getting a wideband O2, becoming a carb tuning guru and finding the best timing curve for the distributor as well. Another trick would be to hookup a throttle activated switch to a light on the dash to indicate when the secondaries on the carb open. If you’re into the secondaries you’re using more fuel. Carb choice can help too, especially if you have a double pumper on there now. I’d consider a q-jet with it’s smaller primaries.

Edit: just noticed you said the carb is a 2bl. Switching to a dual plane with a small 4bl can be more fuel efficient if you stay out of the secondaries.

[Cms83]

Gotcha I’ve been playing with the timing. That’s why I was asking if any mods would be worth it. Other then gear ratio.but it seems like that would be the best bang for the buck. I really want to keep the original trans. I found a 350 from a 1970 c20. That’s what my truck is. Definitely not interested with down sizing from a 3/4 ton. It’s funny you mention the blazer. That is on my radar for my next truck and use it as a daily driver. It’s hard to find them at a descent price. I do have a 700r4 trans. Just I need to rebuild it. But I’d rather keep the 3 speed. I’ve been debating lowering it. I’ve herd people cut the coil spring. But it don’t seems right. The coils seem to have a certain shape for the mounting to the frame and trailing arms. I was thinking the best way would be have custom springs made. My truck have the upgraded HD springs. I don’t want to go with 1/2 ton springs. Not that I am hating on them. Just would have bought a 1/2 ton if I wanted a 1/2 ton. I appreciate the time you guys took to help me out.
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[Cms83]

Also I like the dual plane 4bl idea. What size would you recommend? I’ve worked on heavy equipment for 18 years. So I am no automotive guru. But I know enough to get myself in trouble 😁.
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[Cms83]

I am down for any tips about adjusting the carb. I have been told the adjustments are only for ideal. Is that the case?
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[CG]

There have been a lot of threads on trying to squeeze better gas mileage out of our bricks in all sorts of ways. From all Ive read the time and money required to get a couple extra miles per gallon is seldom well spent.

I'm not a Bonneville racer but I do go down to Speed Week quite a lot. Its high on my list of favorite things to do despite the long drive. I already have it on the vacation calendar for this August. I'm pretty sure making the racers more aerodynamic has everything to do with speed and zero to do with gas mileage. But I didn't stay at a Holiday Inn last night soooo?

This one is a brick and very fun to watch run.


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[Cms83]

That is cool. I dig the look of all 4 tires being racing slicks. If that’s what they are I am in east coast so no salt flats here. Check this truck out. This is the picture that started my aerodynamics question

[Cms83]

As for mpg. To be honest I’ve never figured it out. I should I’ll get back to you on that. Also if anyone has equipment questions I might be able to help. Worked on many different equipment ,cranes,man lifts, telehandlers,ships(the hydraulic parts) that’s my speciality, dams,army corps dredge ships and all kinds of equipment. If I don’t know I will not pretend to know. I am a firm believer in if you don’t know what you don’t know you will never learn and learn more.

[Steeveedee]

Originally Posted by Cms83

Also I like the dual plane 4bl idea. What size would you recommend? I’ve worked on heavy equipment for 18 years. So I am no automotive guru. But I know enough to get myself in trouble ��.
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I had an Edelbrock Performer on a 305 SBC which gave great performance and didn't hurt mileage. I bought it in y2k, so maybe something better is around now.

Originally Posted by Cms83

I am down for any tips about adjusting the carb. I have been told the adjustments are only for ideal. Is that the case?
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I don't think that you're going to gain anything by tweaking that carburetor. Maybe I'm wrong, though. A dual plane manifold with a small-primary bore carburetor like the q-jet and much taller rear gears will help. It's going to take all of that. You will need tall enough gearing to keep the RPMs down to a point where you won't be bringing in the secondaries. That's what will kill your mileage.

3OTT should be OK for mileage. If you aren't hauling heavy stuff, you can go all the way down to a 3.07 ratio axle. That's about 35% less revs on the engine. That makes for a ton less engine wear, too. I'd say that that would be the #1 consideration- matching hauling against mileage, for the rear gear ratio.

[Cms83]

I do plan to haul stuff with the truck. I got 2 1/2 acres here south jersey. So plenty of need for hauling. Just can’t haul much until I fix the bed. It’s pretty rough. Do you think that 3.07 would allow for decent hauling? With out it being a dog? Let’s face it 305s are good engines. But not much power out of them. I think my truck originally had a 307. I believe they used the heads, carb and intake from the original engine. I don’t recall the heads cfm. I think it is around 62 64 66 maybe. I am sure I got high compression because of the heads. If I am wrong about that don’t be afraid to school me. I say that about the 307 because that’s what the carb was from. So I’ve been told

[Cms83]

Care to post pictures of the inside of your cst longhorn? I would like to upgrade the interior of my truck. I would like to go with the Highlander bench seat upholstery. Yes I know they didn’t do that in 70 but me likes it. I understand if you don’t want to post pics. So please don’t feel obligated