292 4bbl Carb

[Classic1965]

I have a 1965 292 L6 which is all stock as of now. I was told the best way to get better mileage was to change to HEI, bigger headers and bigger carb. I have a 4bbl Quadrajet I pulled off of a Mercruiser 305 marine engine. Will this carb work on my engine? What is the difference between marine and automotive carbs?

[TJ's Chevy]

I don't think there's any difference...but yes...a quadra jet carb will work on your 292...The most common setup I've seen is the holley 390 with the clifford manifold and a set of tom langdon's headers....good hei's would be either stock GM or DUI...both american made. I've got a 600 edelbrock on my 292...runs fine....mileage I'm not sure about cause I don't drive it long enough to really tell...but it makes for a nice cruise and more top end power with the extra fuel and dual exhaust. I've heard of guys getting almost 18 mpg off of 292's with quadra jets....also an od transmission will really help as well.

[geezer#99]

Marine carbs have plugged vac ports on the carb and are jetted richer because they spend most of there time at 3 to 4 thousand rpm. You can make them work if you're adept at pulling out the plugs and installing hose barbs. Likely not worth your time.
X2 on a small carb, langdon's headers and especially an hei. The hei will be your biggest improvement.
There are differences in the intakes too.
Clifford ones can mount your carb either direction. Some clifford's have heat passage built in for heat to your intake plenum.
Offenhauser intakes turn the carb sideways and you need a heat plate adaptor.
You might not see an improvement in mileage but you'll have a sweet looking and sounding motor.

[cg285]

Originally Posted by Classic1965

I have a 1965 292 L6 which is all stock as of now. I was told the best way to get better mileage was to change to HEI, bigger headers and bigger carb. I have a 4bbl Quadrajet I pulled off of a Mercruiser 305 marine engine. Will this carb work on my engine? What is the difference between marine and automotive carbs?

i'll let you know after i finish playing with another eng for one of my trucks. i am going to start off slow and change a few items at a time so i can compare to a baseline vs making multiple changes at once.
what i can assure you is changing to an hei will have absolutely no affect on your mileage or hp. (and here is where a bunch can chime in to tell me i am wrong - but i am not) what you will get, by changing to hei, is loosing the periodic points replacement (although points will last 50k + if matched to the correct condenser) but that will be replaced by changing the module, periodically, while you are stranded dead in the water - UNLESS you use only delco components - especially the module - and follow the directions with the heat paste. and use plugs with a gap of .045 vs .060

[cg285]

on another note: a clifford manifold, 390 holley and langdon split manifolds did nothing to increase the mileage on a 250 i have in a c10. there is a noticeable power difference but not much.

[66Submarine]

Originally Posted by cg285

i'll let you know after i finish playing with another eng for one of my trucks. i am going to start off slow and change a few items at a time so i can compare to a baseline vs making multiple changes at once.
what i can assure you is changing to an hei will have absolutely no affect on your mileage or hp. (and here is where a bunch can chime in to tell me i am wrong - but i am not) what you will get, by changing to hei, is loosing the periodic points replacement (although points will last 50k + if matched to the correct condenser) but that will be replaced by changing the module, periodically, while you are stranded dead in the water - UNLESS you use only delco components - especially the module - and follow the directions with the heat paste. and use plugs with a gap of .045 vs .060

I'll actually agree that when I put the HEI in mine the other day it didn't really seem to do much of anything (kind of what I figured). I gapped the plugs all the way out to 0.060.

A big carb will just (potentially) increase top-end power and if anything I'd probably expect worse mileage.

I stuck a vacuum gauge in my truck (stock '71 250) a while ago and IIRC I had to wind it up to 3,500RPM+ before I really saw any vacuum at WOT. How often do you have it wound up past 3,500RPM with the throttle on the floor?

Small-tube headers will probably add a little power (not sure how much). Might be able to effectively use a slightly larger carb with them. Large-tube headers are not what you want.

Jetting/tuning the carb will probably help, as would reworking the distributor advance curve.

[TJ's Chevy]

Originally Posted by cg285

i'll let you know after i finish playing with another eng for one of my trucks. i am going to start off slow and change a few items at a time so i can compare to a baseline vs making multiple changes at once.
what i can assure you is changing to an hei will have absolutely no affect on your mileage or hp. (and here is where a bunch can chime in to tell me i am wrong - but i am not) what you will get, by changing to hei, is loosing the periodic points replacement (although points will last 50k + if matched to the correct condenser) but that will be replaced by changing the module, periodically, while you are stranded dead in the water - UNLESS you use only delco components - especially the module - and follow the directions with the heat paste. and use plugs with a gap of .045 vs .060

When converting to a bigger carb like I did on my 292...I'm running a 600 edelbrock 4 barrel...an HEI will make a difference..And No I'm not wrong...I've done tests of my own. When I was running points, my plugs were blacker then heck because a stock points coil maybe puts Maybe out 30k volts...where as a DUI or speed master ignition will put out 50k-65k volts. I converted to a 65k volt hei and now my plugs are showing a tad bit on the lean side. So an HEI Will make a difference...but if yer starving the engine of fuel using those original single barrels yer not gonna notice much of a difference. And alot of HEI's call for a gap of .045 anyway....but you Can gap the plug UP to .055 or .060.

[TJ's Chevy]

Originally Posted by 66Submarine

I'll actually agree that when I put the HEI in mine the other day it didn't really seem to do much of anything (kind of what I figured). I gapped the plugs all the way out to 0.060.

A big carb will just (potentially) increase top-end power and if anything I'd probably expect worse mileage.

I stuck a vacuum gauge in my truck (stock '71 250) a while ago and IIRC I had to wind it up to 3,500RPM+ before I really saw any vacuum at WOT. How often do you have it wound up past 3,500RPM with the throttle on the floor?

Small-tube headers will probably add a little power (not sure how much). Might be able to effectively use a slightly larger carb with them. Large-tube headers are not what you want.

Jetting/tuning the carb will probably help, as would reworking the distributor advance curve.

I agree with you, but...put a bigger carb on there and you'll notice a difference over points. That'll little briggs and straton single barrel( LOL!) is like starving a hungry teenager of food. lol

[cg285]

you need to look at the spark line, with a sun scope, on a points vs a hei vs joe blow's super coils. you will not be seeing those 50k + voltages on the hei or what is advertised on the aftermarket brightly colored coils.

[TJ's Chevy]

Originally Posted by cg285

you need to look at the spark line, with a sun scope, on a points vs a hei vs joe blow's super coils. you will not be seeing those 50k + voltages on the hei or what is advertised on the aftermarket brightly colored coils.

Well that May be...But I can guarantee that when I changed to a bigger carb...I felt a difference with the HEI over the stock single barrel. But to each his own.

[cg285]

Originally Posted by TJ's Chevy

Well that May be...But I can guarantee that when I changed to a bigger carb...I felt a difference with the HEI over the stock single barrel. But to each his own.

years back, when accel first came on the market, i had an employee at A-1 Speed Shop, in orlando, swear that he simply changed the oem cap and rotor, on his car, with the accel brand, and he had noticeable more power and could smoke the tires. (sigh)

a coil, capable of 2 million volts, will only put out what is nec to jump the gap, be that 10k or whatever

[AcampoDave]

Mainly, a distributor needs to be in good condition. A 200,000 miler with weights and springs that are either froze up or flopping in the breeze and a shot out vacum advance is garbage. Sounds obvious but I've seen too many of those still in service. Anyone who replaces a garbage distributor with something new should notice a difference. The advance curve is the minder of the motor. If it's a mess, your leaving cheap power on the table...points or electronic.

[cg285]

Originally Posted by AcampoDave

Mainly, a distributor needs to be in good condition. A 200,000 miler with weights and springs that are either froze up or flopping in the breeze and a shot out vacum advance is garbage. Sounds obvious but I've seen too many of those still in service. Anyone who replaces a garbage distributor with something new should notice a difference. The advance curve is the minder of the motor. If it's a mess, your leaving cheap power on the table...points or electronic.

that would be correct. part of a normal "tuneup". back in the 60's/70's pulling the dist and checking all that was part of the job

[66Submarine]

'65 C30 250 inline six + SM420 acceleration test...

There's a clip from today for the carb size debate. That's a 250 with the Monojet (and small factory air cleaner with a filter I'm sure I probably need to change). Watch the vacuum gauge in the middle of the screen; it has to be wound up pretty damn tight to really make any vacuum at WOT (the tach is obviously not working).

Headers will probably help some, but the reality is that you are going to need to be winding it up pretty tight to really see any meaningful gain (IMO).

Another thing is that the siamesed intake manifold and head design is really pretty awful, as I stated earlier. Think a big single-plane intake on a stock 283 would be a good idea? Probably not. A six doesn't have individual runners at all--not even ports! It really works way better than it should, if you think about it. Because of this, I would think that staying conservative with the intake and carb to promote good driveabilty, low-end power, and economy would be preferable to going all-out for a slight HP gain where you don't really even drive 99% of the time (or at all, for some people).

As for the HEI changing the color of the exhaust, the ignition only ignites the mixture that the carb feeds the engine. Too much fuel is also bad for everything.

Just my 2 cents.

[geezer#99]

I hate to tell you this 66, but you won't see any vacuum at wot.

[66Submarine]

Uhh...look at the gauge.

[geezer#99]

I did!
When you're pedal to the metal it drops to near zero. When you shift it flips back to normal or higher due to the sudden closing of the throttle.

[NEWFISHER]

Originally Posted by geezer#99

I hate to tell you this 66, but you won't see any vacuum at wot.

Winner!


I have had several 6's am I an expert...no. Have I learned a lot...yes Do they make more usable and economic power than a V8? Hell no and its roughly 3x the money just to be able to pop the hood and show people it really is a 6 ( I just think that's the fun part for me). What I do know is this. An HEI does make a difference in increased power and cold morning starts. I can not measure this , but it also seems to "feel" better while running. A 2bbl and a 4bbl make a performance and economy difference. These are 2 individual upgrades I have made to these engines separate from other modifications and can only speak for them as in individual bolt on component and adjustment of them independently of each other including timing reset and valve adjustment at the same time.

Does throwing $4500 at a 250 from top to bottom, intake , 4bbl, headers etc make more horsepower and get better fuel mileage than a monojet on a stocker....HELL YES. Do I recommend it? Only if you are in love with the 6 as much as I am and don't want to follow the rest of the sheep ( still have an LS conversion sitting on a crate and I don't really want to switch over).

I can not comment on the Mercruiser carb other than I would believe they run rich as mentioned and that's probably why 3 laps around the lake I am out of fuel in the boat

I would recommend a Clifford "heated" intake, a Holley 390 ( if you can still get one) a set of Tom Langdon's cast headers (remember he was a GM engineer for several years and probably knows a thing or two about the 6) an A/C Delco reman HEI with an A/C Delco module. The A/C Delco or factory GM module is the key. You can get a used HEI, rebuild it but use a GM module. If your budget allows, contact Tom at 12bolt.com , watch his videos and get a set of lup ports from him. They are a couple hour job and are worth it. A swirl design valve for the 6 is also recommended along with an upgraded camshaft that will allow you to use the most of the intake and exhaust. Don't forget the z28 valve springs and the 194 valves.

It's like a stepping stone path to paradise. The path will only get you so far with so many stepping stones. Put down all the stones and you will have the best end result. Will you feel the difference of just a couple stones, sure. Will it be as good as having all the stones laid out in front of you on the path to the perfect 6? No

[66Submarine]

Originally Posted by geezer#99

I did!
When you're pedal to the metal it drops to near zero. When you shift it flips back to normal or higher due to the sudden closing of the throttle.

Not a ton, but it still appeared to pull a peak of slightly less than 4" at WOT just before the shift; If you put it on 1080p and make it full screen you can read the gauge fairly well (you can see it better in the second part).

My point was that although there may a little peak HP to be gained by going to a (slightly) larger carb setup, the gains wouldn't really show up unless you were winding it up pretty tight.

[TJ's Chevy]

Originally Posted by 66Submarine

'65 C30 250 inline six + SM420 acceleration test (0-60...kinda) - YouTube

Another thing is that the siamesed intake manifold and head design is really pretty awful, as I stated earlier. Think a big single-plane intake on a stock 283 would be a good idea? Probably not. A six doesn't have individual runners at all--not even ports! It really works way better than it should, if you think about it. Because of this, I would think that staying conservative with the intake and carb to promote good driveabilty, low-end power, and economy would be preferable to going all-out for a slight HP gain where you don't really even drive 99% of the time (or at all, for some people).
Just my 2 cents.

You probably know this already...but the head design really isn't that bad...they designed the head for brute low end power...top end was outta the question...that's why most of these things fall on their faces after 3000 rpm....think of a 292...with the bolt boss obstructing air flow...those stinking tiny valves...700 gram cast pistons...little bit of compression...and a whopping .381 lift on the cam....and also a tiny single barrel carb...that is one starved engine...Now...with some mods...like small block valves...lump ports...lighter pistons...more compression..better cam...more carb and split exhaust...292's have been known to make 320+ hp and 340+ torque...and that's more then some 350 v8's can brag about...and the mileage..if done right is actually better....Know a guy with a bone stock 292...he installed a quadrajet carb and headers and a 5 speed...he's getting 20 miles to the gallon. So...depends on what ya want...V8's aren't the only way to go. Oh...Did I forget to mention turbos? My buck and a half. lol

[66Submarine]

The head design actually really isn't good anywhere. My only guess is that it was cheaper than the 12 port design and they had already been doing it like that forever. For low-end power (and economy, for that matter) you'd like to have long runners of a relatively small diameter...the siamesed design essentially has no runner. The shape of the ports themselves is also pretty WTF...thus the bolt-in lumps to help that.

Another thing to keep in consideration is that even the 292 is a fairly small engine; the fact that it made all its power at a relatively low speed is kind of the reason it works as well as it does.

Maybe it's just me, but I don't really see going for N/A HP to be that productive with a 292 (or 250, etc.). The head/intake design is poor and it's just very slightly larger than a 283 is. I know the port lumps are supposed to help some, but it's still really pushing rope up a hill (IMO).

If I wanted to try to make any power with one I'd stick a junkyard turbo setup on it (I actually plan to at some point...should be fun).

I like them, but not really as a N/A hot rod engine (or for heavy towing and stuff like that). The small displacement and poor breathing kind of kill it for me.

http://www.hotrod.com/cars/project-v...ckage-install/

That first dyno run is pretty much the engine I'm putting together for my '68 Impala. Just a 350 with Vortec heads and a mild $100 flat-tappet cam...apparently you get 371HP and 409FTLBS through mufflers from that combo.

http://www.hotrod.com/how-to/engine/...-collar-build/

And there's pretty much the 454 that's going into the truck. Just a turd-o-matic oval port 454 with another $100 cam...408HP and 511FTLBS (I may use the existing peanut port heads on mine if the oval port heads I have need work).

As far as fuel economy goes, the much better head and intake design gives the bent engines a pretty big advantage there IMO. Not that I think that a 292 will burn twice the fuel of a 283 or anything, but the SBC has the edge there. I'd also have to imagine that when you start camming them up this will probably become more of a factor.

[TJ's Chevy]

Originally Posted by 66Submarine

The head design actually really isn't good anywhere. My only guess is that it was cheaper than the 12 port design and they had already been doing it like that forever. For low-end power (and economy, for that matter) you'd like to have long runners of a relatively small diameter...the siamesed design essentially has no runner. The shape of the ports themselves is also pretty WTF...thus the bolt-in lumps to help that.

Another thing to keep in consideration is that even the 292 is a fairly small engine; the fact that it made all its power at a relatively low speed is kind of the reason it works as well as it does.

Maybe it's just me, but I don't really see going for N/A HP to be that productive with a 292 (or 250, etc.). The head/intake design is poor and it's just very slightly larger than a 283 is. I know the port lumps are supposed to help some, but it's still really pushing rope up a hill (IMO).

If I wanted to try to make any power with one I'd stick a junkyard turbo setup on it (I actually plan to at some point...should be fun).

I like them, but not really as a N/A hot rod engine (or for heavy towing and stuff like that). The small displacement and poor breathing kind of kill it for me.

http://www.hotrod.com/cars/project-v...ckage-install/

That first dyno run is pretty much the engine I'm putting together for my '68 Impala. Just a 350 with Vortec heads and a mild $100 flat-tappet cam...apparently you get 371HP and 409FTLBS through mufflers from that combo.

http://www.hotrod.com/how-to/engine/...-collar-build/

And there's pretty much the 454 that's going into the truck. Just a turd-o-matic oval port 454 with another $100 cam...408HP and 511FTLBS (I may use the existing peanut port heads on mine if the oval port heads I have need work).

As far as fuel economy goes, the much better head and intake design gives the bent engines a pretty big advantage there IMO. Not that I think that a 292 will burn twice the fuel of a 283 or anything, but the SBC has the edge there. I'd also have to imagine that when you start camming them up this will probably become more of a factor.

The 292 I'm beefing up for power really didn't cost All that much...Especially from a 6 cylinder point of view...My engine is expected to make 310+ hp and 330+ torque...which for 292 cubic inches...is perrty darn fair...How I see it....If a man has the money...why not beef up a 6 banger...Its way more unique...gives a big smile...and is much nicer then the boring and waay to common 350...Remember...the 6 cylinder only has a lift of .371 on the cam...most v8s are running at least .450 I'm sure...but don't quote me...so when running a 6, .500 lift really isn't that bad....but rocker ratio has alot to play as well...1.75 for the 6. Its funny...I read of a naturally aspirated 292 6 cylinder drag engine that put out 650 hp...that's not bad at all...So...all depends on what you want I suppose...I'm a die hard 6 cylinder guy and all because there's plenty of resources for parts and they are far more unique imop. And I just like to encourage people to do something like this if they're considering because there are to many discouragers out there.....its becoming a chevy vs ford thing. LOL!

[66Submarine]

Originally Posted by TJ's Chevy

The 292 I'm beefing up for power really didn't cost All that much...Especially from a 6 cylinder point of view...My engine is expected to make 310+ hp and 330+ torque...which for 292 cubic inches...is perrty darn fair...How I see it....If a man has the money...why not beef up a 6 banger...Its way more unique...gives a big smile...and is much nicer then the boring and waay to common 350...Remember...the 6 cylinder only has a lift of .371 on the cam...most v8s are running at least .450 I'm sure...but don't quote me...so when running a 6, .500 lift really isn't that bad....but rocker ratio has alot to play as well...1.75 for the 6. Its funny...I read of a naturally aspirated 292 6 cylinder drag engine that put out 650 hp...that's not bad at all...So...all depends on what you want I suppose...I'm a die hard 6 cylinder guy and all because there's plenty of resources for parts and they are far more unique imop. And I just like to encourage people to do something like this if they're considering because there are to many discouragers out there.....its becoming a chevy vs ford thing. LOL!

I think it's neat to see them in stuff, but I personally just don't really see them as being a great N/A power platform. Like I said before, I think I'd have to go with forced induction if I was building one as a hot rod piece.

The lift is certainly not the only thing to consider about the cam...what are the other specs?

BTW, what N/A 650HP 292 are you referring to? Cotton Perry's car made 549HP in the article I read (and also seemed to be pretty hard on itself). http://www.12bolt.com/inline_6_articles/cotton_perry

For a comparison, the Hot Rod guys later made 567HP with the same 454 on 91 octane (and 614HP on 114) with a solid flat-tappet cam. http://www.hotrod.com/how-to/engine/...lock-for-4000/

I guess part of it is also the application; your SWB stepside half-ton only weighs something like 3,500LBS and my truck weighs over 1,000LBS more than that at around 4,600LBS. To make matters worse, mine is also going to use a wide ratio truck trans and be asked to pull heavy trailers.

[TJ's Chevy]

Originally Posted by 66Submarine

I think it's neat to see them in stuff, but I personally just don't really see them as being a great N/A power platform. Like I said before, I think I'd have to go with forced induction if I was building one as a hot rod piece.

The lift is certainly not the only thing to consider about the cam...what are the other specs?

BTW, what N/A 650HP 292 are you referring to? Cotton Perry's car made 549HP in the article I read (and also seemed to be pretty hard on itself). http://www.12bolt.com/inline_6_articles/cotton_perry

For a comparison, the Hot Rod guys later made 567HP with the same 454 on 91 octane (and 614HP on 114) with a solid flat-tappet cam. http://www.hotrod.com/how-to/engine/...lock-for-4000/

I guess part of it is also the application; your SWB stepside half-ton only weighs something like 3,500LBS and my truck weighs over 1,000LBS more than that at around 4,600LBS. To make matters worse, mine is also going to use a wide ratio truck trans and be asked to pull heavy trailers.

I agree on the weight as well...In yer 1 ton..a big block would be the smart way to go...or a cummins diesel. ( lol) But on a C10 like mine...a 6 cylinder is plenty capable of making it an 11 or 12 second truck, which is what many small blocks can barely brag about....The cam I'm getting for my 292 is as follows: 268 duration 218 @ .050 .486 lift on a 110 lobe center.....bout .100 lift over stock and a little more duration...I believe the stock cam duration @ .050 was 186 and the advertised was 230 degrees..lift .371 on a 114 or 116 lobe center...But from your stand point...I can understand having a much heavier truck that more cubic inches and more cylinders helps...And that 650 hp 292 I was talking about is in the Inliner's Power manual...Known as the "No frills" 6...No specs on it really...But there's also the Mighty 6 pumping out some 1100 horse power...and it ran 8.44 at 157 in the 1/4 mile....it's beaten its fair share of small blocks for sure. lol But..Its running 30 pounds of boost...But when I get my engine done... I'll show ya that these little 6's can be a blast. 340 torque is plenty of power for a C10...Tom Lowe at 12bolt.com has a naturally aspirated 250 in his 66 chevy station wagon...some 4000 pound car with 2.57.1 rear axle ratio..and a 28 inch tire...he had that thing up to 100 miles and hour..and no..it did have to go across the US to get there. LOL!

[Classic1965]

Ok so I guess I started the debate of the week or something. I don't plan to drive this truck in the snow or winter or in the cold, it is going to be a daily driver in the warm part of the year. I'm more concerned about fuel economy then horsepower and I plan to tow a 20' boat with the truck. Like I said it is a 292 with a 3 speed. I just wanted to know what is the best setup for fuel economy that can still pull a boat without issue. This truck will be driven long distances in the summer as everything up here in my area of Canada is spread apart. So I guess the marine carb idea is a bust, just wondered if it was worth my time because I had a few different carbs from different small block engines. So what do I need for the best fuel economy without losing towing capabilities?