General Category > Quadrajet Carb Talk and Tips

17082224/SMAB /Fuel Economy

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Turbo26T:
 17082224 1672 FJP  Got it free and its  really clean & complete . Its an '82 SMAB ,no CC, single front pulloff. Should be OK for my near -stock 350 Chevy build.
 My questions are :
Being SMAB ,I assume its a truck carb
 Can it be tuned for decent mileage ?
 What was the original engine size that it came on ?
Thanks
Stan

Cliff Ruggles:
Those carbs have APT and "M" series tapered primary metering rods, so a nice carb all the way around. 

What are you trying to  use it on?

Turbo26T:
Cliff: To be built 350 Chev , #2800 Model A Project ,2004R
 So Far I have:
 Early 2pc seal block
 Vortec 906 heads
 Edelbrock Performer Q/J intake
 Cam - TBD ( would appreciate suggestions)
 C/R -  at least 9.5/1
 Low speed mild street ,good manners , smooth idle ,good vacuum. Mainly interested in dialing in economy later
I'm 82 ,drive like an old man. 2000-2500 RPM tops ( occaasional blast to 3000/3500..Wow !) . I'm a data-driven tinkerer ,so looking forward to tuning this carb. Will be ordering everything I need from you eventually..
 Thanks for the reply & info
 Stan


 

Cliff Ruggles:
Vortec heads have excellent flow potential plus super efficient combustion chambers, but lack exhaust crossovers so hopefully you live I a warm climate or don't plan on using it in cold Winter months.  Heat is your friend with these things and why all wet-flow systems use a heated intake manifold. 

LOTS of places to screw up a good SBC build so I'll cover a few things I see nearly EVERYONE do to them that yield negative results.

NEVER use a high volume/high pressure oil pump.  It robs power and wears the distributor gear out much faster.  I've also seen oil pump drive shaft failures in cold weather with thick oil in the sump.

Do NOT use a "double roller" timing set, at least 95 percent are JUNK and even the better ones get loose and start flopping around as there is no tensioning system for them.  I use and prefer the stock link-belt Morse chain set-up.  The early 3/4" wide versions are still available and USA made.  I just grabbed a mint condition TRW set with 3/4" wide steel gears off Ebay for a build that's coming up here......$28 shipped.

Establish tight quench.  Shoot for .035", never over .040" for any reason.  WAY too many folks don't check deck height and ALWAYS put thick "rebuilder" head gaskets on these engines.  Many aftermarket "builder" pistons can be WAY down in the holes at TDC, some to and past .030".  Combine that with a big thick composite head gasket and you've just built yourself a "turd" no matter what else you do to it.  You need to check deck height, deck square and combine head gasket thickness to get into the range above, but it is not optional for one of these builds if you really want the best out of it.

Use a stock cam in it or something very close to stock with longer seat timing and gentle opening/closing ramps.  Yes, the CS-274 cam (basically a duplicate of the 350/300hp cam is the best truck cam out there.  Most folks jump right to the "RV" cam, 204/214/112 LSA but they have lowered the compression and put so much squish area in the engine they just build a big "turd" instead of a powerful smooth running efficient set up.  The stock cam LOVES 9.5 compression, I've even ran them higher than that on pump gas with tight quench w/o issues.  Smooth idle, tons of vacuum, good fuel economy and butt-loads of power right where a truck engine needs it.  If going roller there are several roller profiles very close to that cam, just avoid the ones that are ground on tight LSA's.  GM offers one in particular on a 109LSA, it's not that great so I'd avoid that deal.  I wouldn't go tighter than 112LSA and around 194/204 @ .050" or even a single pattern cam is fine with those heads.

Continued.....

Cliff Ruggles:
Do NOT use roller rocker arms, especially Comp roller tip rockers.  Roller rockers are heavy, and have way too many places to wear out.  Every single variety we've tried here have cracked, worn out the roller tips where the pins goes thru or burned up the bearings.  Even had a few pins walk-out of the ends, and bearings walk out of the bodies.  Stock stamped steel are light, strong and make sure to use SOLID rocker balls in them, not grooved.  Comps roller tip rockers have a poor fit between the rocker balls and bodies plus grooved balls and the oil runs down the studs instead of out on the rocker tips to get atomized for spring cooling and valve guide lubrication.  I've pulled down more short lived engines that used those parts than I can count with rockers turned blue or even black from the heat, springs tired and valves guides worn slam out WAY before they should have been.  I'll bet 99 percent of the folks reading this thread have never even heard of or thought about this.....

Use stock GM retainers and springs and standard pressure.  You only need 80lbs on the seat not 150-180, and 200lbs over the nose is PLENTY of pressure.  Using heavy retainers and strong springs from a cam "kit" is the best way I know to knock the lobes off the cam and the entire time you are wearing everything down faster and putting more drag on the timing set plus robbing more power from the assembly.

I wonder how many folks have actually tested some of the springs these companies send in their cam "kits"?  I've logged quite a few with over 300 and some in the 350-380lb open pressure range.  That's STOOPID spring pressure just to run some over-rated fast ramp lobe profile to keep things in check.  Cripe that's like having 16 fat guys standing on your pushrods.  Talk about a recipe for disaster......duh?

Maybe that's why all the Forums are FULL of folks with threads running on the cams lobes failing in their new engine "builds"?  Probably didn't help that the company they bought the parts from sent them cheap offshore lifters made from whatever rusty old car bumpers that country melted down that day to cast them from.

ALWAYS insist and use genuine USA made lifters on your flat cam and follow the spring pressure advise above and you can go on to worry about something other than cam lobe/lifter issues.

Anyhow, there are some things to ponder on for your new build.  The carb is the easy part, just call me at the shop when you are ready and I'll help you set it up so it's "plug & play" right off the bench........tks....

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