[max 93]

Friend of mine bought a 70 Lemansl. It has a 350 with a two barrel and he would like to put a four barrel on it. Is there much to be gained by doing the swap? Or is the factory cam going to prevent any real gains?

[Dave M]

Would probably need to upgrade the cam at the same time to make it worthwhile


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[Chief of the 60's]

You will pick up a little, but do not expect it to feel like you just installed a magic bullet. Fuel economy will probably go down.

[max 93]

Any recommendations on a cam for this? It probably still has the original 2.56 gears.

[steve25]

If his motor is still in good shape then he should pick up 15 hp just like the factory ratings showed.

Just note that the 4 bbl motors do make use of a different fuel pump with more volume , so as long as he does not switch over to bigger Cam it may be ok.

You will know real quick when the moor does not want to rev above 4500 or so!

[NeighborsComplaint]

Your mileage may in fact improve if you can keep your foot out of it. Small primaries on the Qjet make it efficient.

[Formulas]

Been there done that,
Do it and dont look back its been so long ago i cannot remember the order but i changed out the cam and went to a q,jet, my cam had some real bad lobes it was toast, and i just went mild 204 duration and .411 lift SINGLE pattern Isky

What that process did was vastly increase midrange it was also a 1970 350 with #11 heads

[SRR]

What about the rest of the set up? Dual exhaust? Does it pass a compression test? Engine "tight" little to no blow by? He's going to need the 4-barrel throttle bracket. I've done this exact thing to a 70 Lemans I had because a rocker stud broke. I put a set of 13's on it, Q-jet carb, intake and a dual exhaust. I didn't touch the cam. The difference was nice. I did however have a 3.23 gear ratio.

[unruhjonny]

my understanding, is that there will be no real gains, unless other stuff is swapped to see a real benifit...

As it stands, it's mostly a status thing...

[Tom Vaught]

If you were driving much on 2 lane roads in the farm country, the 4 bbl carb might make passing a bit safer as you could get around the other vehicle a bit quicker.

Most F.E. depends on the driver behavior.

Q-jets do have smaller primaries and could give better F.E is tuned properly to work with your 2.56 gear.

So my opinion is the drivability/MPG/passing ability might improve a noticable amount but the HP/Torque would maybe change slightly.

During normal driving with the engine the 2 carbs should be basically transparent. A good calibration is a good calibration bs it a 2 BBL or a 4V Q-jet.

Tom V.

[OCMDGTO]

I'd tell him save his money and wait until he could change cam, heads, exhaust, and fuel system. I learned this lesson on 350 Chevy years ago, complete waste of money for me.

[android 211]

I've done this a couple times on cars that had 350 2bbl engines when I got them. If all you do is put on a 4 bbl then you won't notice much improvement at all.
If you install duals your mileage will improve but no additional power will be noted past 3000 rpm. But if you put a mild cam in the engine and the duals and the four barrel yes, it will really wake up.
If it has 2.56s then get a duplicate of the 067 factory cam that came in the majority of automatic GTOs. Replace the timing chain and lifters of course. You don't have to pull the heads.

[hurryinhoosier62]

Originally Posted by android 211

I've done this a couple times on cars that had 350 2bbl engines when I got them. If all you do is put on a 4 bbl then you won't notice much improvement at all.
If you install duals your mileage will improve but no additional power will be noted past 3000 rpm. But if you put a mild cam in the engine and the duals and the four barrel yes, it will really wake up.
If it has 2.56s then get a duplicate of the 067 factory cam that came in the majority of automatic GTOs. Replace the timing chain and lifters of course. You don't have to pull the heads.

067 would be an excellent choice for a stock or near stock 350. Likewise, the cam would be hindered until a true dual exhaust is installed as well as the 4 bbl carb and manifold.

[ponyakr]

Originally Posted by max 93

Any recommendations on a cam for this? It probably still has the original 2.56 gears.

"...get a duplicate of the 067 factory cam..."


This sounds like a good idea to me. If the heads have press-in studs, a cam with more lift and/or a steeper ramp, coupled with stronger springs, could pull out a stud.

https://www.ebay.com/itm/Melling-SPC...EAAOSwOVpXZx6n

https://www.ebay.com/itm/Engine-Cams...QAAOSw-vda1dCi

To me, this brings a question to mind. For you guys who have run larger cams/stronger springs with press-in studs, what's the biggest cam/strongest springs you have run, without pulling a press-in stud

How many think an 068 would be safe ?

How about a Summit 2800 ?

https://www.summitracing.com/parts/s...RoCCWIQAvD_BwE

How about a Crower 60240 or 60915 ?

https://www.crower.com/pontiac-287-4...m-270-hdp.html

https://www.crower.com/pontiac-287-4...cam-272-h.html

OR, is ANY cam a crap shoot, with press-in studs ?

[max 93]

The car does already have dual exhaust. I was thinking that swapping in a rear with 3.08 or 3.23 gears may be a better option