Chevy 350 Project.

[elhigh]

I don't see why you couldn't do a little bit of aero modding straightaway. The underside of the bed is just ghastly, a gantry of ironwork. You could close that in with some cheap sheet stock of some kind in an afternoon. Move the spare to the bed, close in that mess.

As to engine mods, I got nothin'. No experience with the SBC.

With the pyrometer and an O2 sensor aboard, could you rig a dashmount adjuster to the high speed mix? Lean it out when cruising and power loads are low? Just a thought.

JC Whitney used to carry fender skirts for American pickups, they may still have some that fit your model. If you're looking for something that looks factory instead of Kindergarten Arts -n- Crafts, maybe take a peek at that.

[slowmover]

I'd continue with friction reduction: tires, alignment, brakes, etc. The O2 is a better bet than a pyrometer, especially wideband. The Qjet deserves Doug Roe's book as one needs to understand how to adjust the part-throttle F/A ratio.

The HEI is a decent piece but I'd rather have an MSD Alll-In-One Ignition (with the #6 box) as you will want to change the entire advance curve not just the initial advance. The HEI is not as receptive to this work as the MSD. (And chase down all the vehicle grounds now [bonds] as electrical reliability on an ancient vehicle can drive you nuts. Get a copy of the FSM).

Grille block, engine blanket are good to try. GM used the emissions controls of the day to maintain constant 100-115F air at the carb intake. A Robertshaw/Mr. Gasket "Balanced Sleeve" HD 195F thermostat, HD clutch fan (with full shrouding) and HD water pump also make the list.

Oldsmobile tried for highway FE with the Turnpike Cruiser. Wish I'd found those articles 35-40 years ago. That CCC air cleaner system would be worth replicating for the Qjet. Highly.

You should state the use of the truck. Most gains, IMO, will be in planning the use thereof (combined trips, route planning, engine time versus miles, etc). A truck used for service throughout the workday is different than one driven here, then there. A guy commuting down from Nederland to Broomfield and back daily is a great deal different use than up to Eldora and some other sites on back roads and then back on down as a skilled worker. Mountains or the flats?

The low lift of the cam is okay to a point. Modern SBC cams -- roller -- feature short duration with very high lift (more area under the curve). Weigh the truck (empty, but driver + fuel; and loaded as in daily use), measure tire rolling height, double check gearing, record vacuum gauge readings and post questions about the "ideal camshaft" for your truck/intended usage on a vehicle-specific board. You'll also want elapsed times from an engine hour meter to see your overall average speed tank-to-tank.

Establish good record-keeping to find overall operating cost per mile.

Read up on how to performance degree a camshaft if not already familiar. Some teeny adjustments at that stage are beneficial, (not just "straight up" or 2-degrees advanced, etc). And ask about best OEM cylinder heads so as to make any runs to Denver-area boneyards beneficial. Later heads are miles ahead of any 1970's pieces.

The right cam and heads will do a lot to maximize FE. Least fuel for most work being key. But one must work from verified numbers to achieve this. Anything written by Marlan Davis and David Vizard about FE is vital (mostly performance stuff but I spent 30-years reading hot rod mags to glean the tidbits of FE and heavy vehicle performance). An SBC can be put together many ways, and combinations of cranks, heads, cams, etc, can be mixed endlessly to find the best torque curve for your intended use.

Warm-up from cold is the biggest impediment. Even here in Texas my old cars took about 30-miles of sustained driving before they were feeling loosened up (coolant, oil, greases, tires, etc). Anything to shorten that would be high on my list as anything shorter in miles is compromised (for an empty truck; heavily laden would be faster) in the quest for best operating FE.

How much time the truck actually spends above 50-mph will dictate the benefit of aero beyond a minor air dam, etc. Only records will show this.

.

[texanidiot25]

Originally Posted by NHRABill

changing the jets from stock may be a mistake. too small and the back bores may need to open sooner. Just play with the a/f screw if you think you can lean it make sure you keep a close eye on the temp gauge and look at your plugs listen for detonation and pinging.

2 things based on my experience with the Q-Jets:
-The secondaries main throttle blades are mechanical, opening around 70% throttle. It's only vacuum in the sense that the upper blades open with vacuum, but air is ultimately throttled by the main blades at the carb base.

-The tuning needles are idle air mixture screws, they won't effect the upper rpm range. Anything else and you'll have to play with jets and needles. You can adjust fuel curves with different needles.

[northboundtrain]

Thanks again for the input. I'm going to rebuild the Q-jet stock and just get the truck running, but ultimately, it would be nice to be able to adjust the air/fuel at cruising speed, based on the O2 and pyrometer readings. I've even thought of rigging a linkage to the dash so it can be done on the fly. What would be good candidates for a different carb that can be screw adjusted?

[NHRABill]

Originally Posted by northboundtrain

Thanks again for the input. I'm going to rebuild the Q-jet stock and just get the truck running, but ultimately, it would be nice to be able to adjust the air/fuel at cruising speed, based on the O2 and pyrometer readings. I've even thought of rigging a linkage to the dash so it can be done on the fly. What would be good candidates for a different carb that can be screw adjusted?

You could always toss on a 2bbl by swapping the manifold or getting a 2bbl carb adapter ... obvious as it is that what you are doing is opposite of what is popular and it should be very cheap. I sold a nice 2bbl carb manifold setup I had on my 68 camaro 327 for $75


good luck, looking forward to see what #'s you pull I will swap my truck to carb if the TBI ever gave me an issue.

[texanidiot25]

Originally Posted by NHRABill

You could always toss on a 2bbl by swapping the manifold or getting a 2bbl carb adapter ... obvious as it is that what you are doing is opposite of what is popular and it should be very cheap. I sold a nice 2bbl carb manifold setup I had on my 68 camaro 327 for $75

good luck, looking forward to see what #'s you pull I will swap my truck to carb if the TBI ever gave me an issue.

There's an easy way to kill the secondaries. There's a lock out for when the carb is in it's fast-idle/choke mode that locks the secondaries shut to prevent full power while the engine is warming up. It's a little arm that grabs a pin on the throttle shaft. My CST10 is 150 miles away, and it's been ages since I've poked at it, but you should just be able to lock that little arm in place with wire or something with out effecting any of the other linkages, or cold start/choke functions.

Q-Jets are actually more fuel efficient than a standard GM 2bbl, if you keep your foot out of the Q-Jet's secondaries. The primaries in the Q-Jet are smaller than the barrels of the 2bbls.

I think you're starting to ask too much out of a carb setup, unless you want to live the life of a Webber carb car and simply love to tweak it for every changing condition. I'd start looking towards EFI conversions. I'd wager even a simple junkyard TBI setup would be far better than a carb for what you're looking for.

[northboundtrain]

An update here:
I fired up the motor yesterday, did the cam break-in procedure, and then drove it around town a few miles. So far so good. A few snafus to attend to like the speedometer and odometer don't work (won't get much mpg feedback without that). They were working before, so I don't know what happened. I need to crawl under and see of something came loose. Also need to insulate the ignition wires from the headers, and do a few other little things, like hook up my vacuum and O2-air/fuel gauges.
Anyhow, I'll post again when I have my first FE numbers to report. Until then, thanks for the help.

[texanidiot25]

If you need spark plug boot heat shields, look up the part number for the Cadillac Fleetwood LT1 from the 90s. They have little metal clip on shields, and they're dirt cheap. I have one boot on my CST10 that with the shield is less than a CM from the header, and for 3 years it hasn't been an issue.

[northboundtrain]

Resurrecting this thread for an update:
Just got back from a 500+ mile road trip. The truck is performing okay, not perfectly by any stretch, but adequately for now. I didn't get a chance to fix the speedo/odo before the trip, so I don't have any good FE numbers (it's fixed now). The best estimate I could make was on the first leg of the trip. I mapquested the distance to the first town we were stopping in, so I filled up before leaving and then filled up there. 12+ mpg, which isn't great, but considering the new engine had only approximately 100 miles on it before the trip, it was still breaking in and so I think that's in line with what's to be expected.
The truck also seems to have good power. At the end of the trip, I finally opened it up (i.e., floored it) on I-70 going up Vail Pass. I was at roughly about 9,000 feet elevation and I'd estimate the grade to be 4-5%. In fourth gear, the truck accelerated up to about 3,300 rpm which corresponds to approximately 75 mph. Not to bad.
The main issue I'm having is that the Q-jet isn't tuned properly, which from my book on Q-jets is a foregone conclusion with the mods I've done, given that the carb rebuild was just all to factory settings. I'm getting exhaust backfire when I let off the throttle at rpms above 2,000, and my lean-rich gauge that runs off an O2 sensor is all over the place at different load-rpm combinations. It seems the consensus is that the Q-jet is about the best street carb out there, when tuned properly, but is also one of the most difficult to tune. I've read through the book once and would probably have to read through it several more times with the carb taken apart and sitting in front of me to really understand how to even begin even fooling with it.
So my plan is to get an Edelbrock Performer 1406 (factory tuned for economy) with an adapter plate for the spread-bore manifold and run it while I delve into the Q-Jet. The Performer/Carter AFB is apparently one of the simplest four-barrel designs and easiest to tune--and it's about the least expensive option out there. I might also get an adjustable distributor vacuum advance canister so I can play with that too.
I guess my one question at this point is whether there's a better carb for me to get in the interim. I like the idea of something different from the Q-jet (as opposed to just finding another Q-jet to try and tune), so I can compare the two and get a better understanding of how various carburetors work. My other option would be a Holley, perhaps, though I haven't looked into the different options there.
Anyhow, thanks for any input/suggestions.

[hondaguy72]

Here's one that would be very easy to work on and could be used indefinitely as a FE carb.
Motorcraft 2150:

Motorcraft 2150 Carburetor

Almost nothing to go wrong on the carb and very easy to tune. I'd put an electric or manual choke on it instead of the heat tube choke, otherwise it looks ready to go. You may even be able to buy one of these new from your local parts store. My 1968 galaxie came with this carb, so I'm pretty familiar with it. You would need the four to two barrel adapter as well.