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Old 03-01-2013, 11:25 AM
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Suggestions on improving a Chevy truck 350

I know this is below the typical performance questions discussed here but I figure you guys know the ins and outs of these things. I just bought a 73 Chevy Cheyenne with a fresh GM GoodWrench crate 350 engine. It runs well but has a worn out Q-jet on top. Its 100% all stock under the hood. And it gets typical 1970's crappy fuel mileage. So, I'm looking at putting a carter or edlelbrock universal 600 CFM carb on top but can't decide if purchasing like an Edelbrock Performer dual plane manifold is worth the investment.
I'm also going to replace the old points distrib with a GM HEI. Are the OE HEI's pretty much all the same or should I be looking for a pre fuel injected unit or? Will pull one from a V8 truck at Pick N Pull. Overall goal here is to improve highway fuel economy and low end grunt.
Thanks,
Dave

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Old 03-01-2013, 11:32 AM
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replacement Q-JETS ARE GOOD.LOOK FOR A USED DUAL PLANE,PERFORMER,sorry caps,,install a good exhaust system,2 1/2 inch duals,headers also help,small tube like 1 5/8,stock HEI with external coil or improved inside cap coil...you need to determine if the money spent to save gas will ever pay for itself over time.
hei for sure
good wheel alignment.fully inflate tires to max pressures,never drive over 50 mph if possible.
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Old 03-01-2013, 12:00 PM
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For fuel economy you can't beat the q-jet. Get a rebuild kit for it if it's worn out. Like vinnie said a good exhaust will help a lot. You have to be careful about the distributor since the later ones were computer controlled. A lot of guys run the cheap ebay one and love them. I think they're like $50 brand new. There's a couple other places that sell them a decent prices. The eddy performer is a good all-around manifold and is spread bore to match the q-jet which is nice. Also run the thinnest width tires you can. Less contact means less friction, but don't go too thin obviously. Your gearing changes a lot too, as does your transmission. What tranny does it have? 700r4 is a common upgrade for better mpg's.
Does it have a/c? It will actually help your mileage since driving with the windows down creates drag which hurts fuel mileage by more than what running the a/c would.
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Old 03-01-2013, 12:37 PM
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This is a cheap tow rig I split with my dad. He is the ultimate rig it and run it cheap guy. The exhaust may or may not happen...more $$ then he will see fit to spend. So your saying that 750 CFM "one size fits all" q-jet will provide better mileage than a smaller but very tunable Edelbrock or Carter carb with their tiny primaries?
So back to HEI...I was only aware of the coil in cap style. When did they move over to a computer controlled unit? I would assume at the same time as EFI right?
What is a "cheap ebay HEI"? New Chinese unit? I can find used performers for around $75-100 on craigslist. If I can find used headers I can probably make dad pop for his half.
The truck has OE 8 lug big brakes wheels/tires. Its a 3/4 ton with the tow pkg and 14 bolt axle. AC PB PS.
Dave
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Old 03-01-2013, 04:57 PM
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Quote:
Originally Posted by Elevinpointsixtoone View Post
This is a cheap tow rig I split with my dad. He is the ultimate rig it and run it cheap guy. The exhaust may or may not happen...more $$ then he will see fit to spend. So your saying that 750 CFM "one size fits all" q-jet will provide better mileage than a smaller but very tunable Edelbrock or Carter carb with their tiny primaries?
So back to HEI...I was only aware of the coil in cap style. When did they move over to a computer controlled unit? I would assume at the same time as EFI right?
What is a "cheap ebay HEI"? New Chinese unit? I can find used performers for around $75-100 on craigslist. If I can find used headers I can probably make dad pop for his half.
The truck has OE 8 lug big brakes wheels/tires. Its a 3/4 ton with the tow pkg and 14 bolt axle. AC PB PS.
Dave
Ebay dizzy: SBC BBC Chevy 65K Red Hei Distributor 6501 R | eBay
Q-jet was made for mileage. If it's well tuned no other carb can beat it efficiency wise.
You don't really need headers. Just a nice exhaust with no kinks and a good turbo muffler. Doesn't even have to be duals.
The manifold won't give you much of an mpg boost, if any at all.
I would guess that a 3/4 ton with a 14 bolt has some high number gears in it which is hurting mileage too.
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Old 03-01-2013, 05:09 PM
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I'll climb under her and pull the axle tag...see what gears are back there. Ya I saw those China HEI...scary price...saw one for $36 new. You have to wonder if your gonna be broken down on the side of the road in the middle of nowhere with a rusty farm fresh 35 dodge coupe on your trailer just baking in the sun because your $36 chinese distro pooped out....hence me thinking pick n pull might be wiser....
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Old 03-01-2013, 05:18 PM
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Quote:
Originally Posted by Elevinpointsixtoone View Post
I'll climb under her and pull the axle tag...see what gears are back there. Ya I saw those China HEI...scary price...saw one for $36 new. You have to wonder if your gonna be broken down on the side of the road in the middle of nowhere with a rusty farm fresh 35 dodge coupe on your trailer just baking in the sun because your $36 chinese distro pooped out....hence me thinking pick n pull might be wiser....
Never heard of anyone having a problem with them. A lot of guys on here run them. Even if you buy one and swap out the coil for name brand it's still cheaper than buying a new delco, msd, mallory, whatever else. If you get one from the junk yard you're still going to have to freshen it up.
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Old 03-01-2013, 05:25 PM
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if the engine has ram horns on it, skip headers.. they flow just fine for a stock 350.
get the q-jet rebuilt..
tire choice can make a huge difference in mpg..
what gears are in the rear..?

might want to think about this instead of the hei
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Old 03-01-2013, 05:26 PM
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I can get them for cost...I actually have a hot rod parts biz...I tend to shy away from most of the Chinese stuff in general as the liability is too great (suspension, brakes, steering etc.). I'll have to check with RPC and see what they can offer it to me for.
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Old 03-01-2013, 05:29 PM
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Quote:
Originally Posted by bigdog7373 View Post
Never heard of anyone having a problem with them. A lot of guys on here run them. Even if you buy one and swap out the coil for name brand it's still cheaper than buying a new delco, msd, mallory, whatever else. If you get one from the junk yard you're still going to have to freshen it up.
ya replace coil/rotor/module/ and carbon tip rotor rides on then it'll be fine..
hei's have from day one had problems with rotors when a cheap on is used.. these will be no different.. and towing will load up the ign more than just cruise'n around..
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Old 03-01-2013, 05:44 PM
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China parts are not popular. They are dependable, and most do stand behind their product. That $35 hei is pretty solid.

The Qjet is very good for the road driven vehicle. A qjet on a performer manifold is worth the $40-50 a used intake goes for online. Unless you are racing or winding higher rpms, stay low rise.
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Old 03-02-2013, 05:39 AM
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I have a '75 GMC 3/4 ton 4wd and have tried a few combinations over the years.

My engine is about the same as the Goodwrench 350, except for my Summit 1101 cam. I am running stock exhaust manifolds and full 2" duals, and have a TH350 and full-time 4WD transfer case.
- Edelbrock Performer EPS and 1406 carb ran okay, but once I put in an AFR meter I realized how lean it was. It was good at low speed, but way too lean at cruise, and I could never fix it by swapping jets or rods that came in the Edelbrock tuning kit.
- Edelbrock Performer and circa '86 non-electriconic Quadrajet (converted to electric choke) from a Chevy 1 ton - This combo starts and runs well, and has good low and mid range. It runs about 13.8-14.0 AFR most of the time but is so smooth that I just left it that way and did not try to get it to 14.7. I used an '86 carb because its a more flexible carb than the Qjet used in the early to mid 70's. It has a larger float bowl, adjustable APT, and some other improvements over the earlier carbs.

Most 3/4 ton's of this vintage have 4.10 gears and stock tires are 31". RPM runs fairly high on the highway and you can't really get good mileage. If you look at road tests from the mid 70's, most of these trucks only got 14 mpg max when brand new.

Mine had a factory HEI when I bought it, but it had a lot of play in the shaft and I did not know how old it was. I swapped in a coil-in cap replacement from Pace Performance and that has worked very well.

Its easy to fit headers and 2.5 inch dual exhaust, but you have to consider the tradeoff. These mods increase power, but not gas mileage. You also have to get HD headers with thick flanges if you want them to stay tight when subjected to the road vibration from the truck. I have considering using 2.5 inch Ram's horn manifolds, since you can buy the Dorman replacement right off the shelf, but I don't know how hard it will be to route the exhaust pipe off the straight down outlet. Truck ram's horn manifolds are only 2", but the outlet angles back, more like the outlet of the log manifolds.

If you use larger diameter tires (33's will usually fit with no mods, and you can fit 35's with a short body lift) that will give you a better on road RPM, but the large heavy tires usually have more rolling resistance.

I have also swapped to a 94 amp 12si alternator from the mid-80's, which gives me more reserver power than the stock 63 amp alternator when I am running more lights.

Bruce
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Old 03-02-2013, 05:56 AM
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GM 350 Crate Engine Build II - Chevy High Performance
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Old 03-02-2013, 11:30 AM
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Bruce, thanks. That is very useful info. I have a pair of rams horn manifolds stored somewhere. I'll check the dump diameter and stare at the routing. What is the adjustable "ADT"? I'm not a complete Q-jet novice. I had one on my 83 RV with a 454 and spent a lot time tuning it. I have a very good but early Q-jet book and just about memorized it. My thoughts were since the one on my 350 needs rebuild/replacement and it has the massive secondaries that it may be a mismatch being on the small end for GM's 1 size fits all mentality. Although I read the variable venturi air valve can compensate for the different engine requirements. On the 454 it worked well. I have not looked at the tire size. The wheels are OE and I suspect the ties are of the original equipment size. I ordered door hinge pins yesterday...the damn things sag so bad its difficult to close the doors. The friggen latch bolts are worn flat on one side from years of vibrating down the road resting on the bolt. That, new fuel tank senders and some tie rod ends and this thing should be long haul worthy.
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Old 03-02-2013, 02:59 PM
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There is information on the Adjustable Part Throttle (APT) setting in this thread Quadrajet Carb

Earlier carbs had an APT setting but it was only accessible when the carb was off. Once you messed with the setting it was hard to get it back to factory specs, or to adjust it to compensate for your other mods. The newer carbs have a pressed in plug in the top, and you can remove it and replace it with a threaded plug. Once you do that you can adjust the APT transition by just taking off the air cleaner and plug, and using a homemade tool to adjust the part throttle transition. This can be really convenient when dialing in the carb to compensate for other changes.

I used the Ruggles book for my rebuild, and also bought my rebuild kit from Cliff's Performance. All the info you need is in the Cliff Ruggles book, but it splits the stock rebuild and performance mods into multiple chapters. I wanted to do a good rebuild, but at the same time make some of the performance mods, so I was always flipping between chapters.

In theory almost every Quadrajet can be set up for a wide range of performance requirements. However, some versions are better suited than others for better performance.

Bruce
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