buick jet & rod sizes?

Just looking at the basics of what's going on, a 10 to 1 compression 350cid engine with the size cam mentioned should be making more vacuum at idle than what you are seeing.

There are a lot of factors that effect idle quality and vacuum, ignition timing and idle fuel delivery from the carb being most important.

The 110LSA isn't helping the situation, but a cam that small, even on a 110LSA, I'd expect to see at least 12-13" vacuum at 750rpm's with 10 degrees of initial timing in it.

Having less than 10" at idle tells me something isn't quite right someplace.

Any ideal what the cranking compression is?.......Cliff

 

Tomorrow I will do the vacuum check, but I will have ask; what is 110 LSA?

The only gasket that was old was the intake manifold metal gasket, maybe that is leaking, I will try to confirm that tommorrow. I did try to be very careful during engine assembly, but anything is possible..

 

I just finished working on a 1968 Buick GS with a 350 and that cam. Pretty interesting findings, if you don't mind a long read.

I built the correct numbers matching carb for it, and the owner supplied the basic information for the engine and drivetrain. Stock rebuild on the engine a few years ago, and they intalled the T/A Performance 212 camshaft. 2 speed trans and 3.23 gearing.

Since the owner was local, he asked me to install the carb for him. I upgraded the carb for modern fuel, and added an external APT screw so I could raise the metering rods to fine tune part throttle A/F.

I opened up the idle tubes to .036", and idle downchannel restrictions at .052". The carb wasn't set up for idle bypass air, and I didn't figure it would need it.

Prior to the install, the owner said the engine ran OK, but pinged a tad at WOT, with some "gurgling" as it pulled up thru low gear (2 Speed Auto). He biggest complaint was idle quality, basically, it idled like crap.

The distributor had been sent out and "custom tuned", so I just installed the carb and fired it up. It ran great on the fast idle, but pretty "rough" at curb idle, with a LOT of "lope". The mixture screws would kill off the engine, but when backed all the way out wouldn't give it enough idle fuel.

I also noticed that the distributor was set at 8 degrees initial timing, and add a TON of timing via the mechanical and vacuum advance curves. The vacuum unit was adjustable for spring tension, but not for amount of advance. It had what looked like a piece of aquarium hose on the bent part of the arm to reduce the travel some.

Anyhow, I worked with the carb for a while, then told the owner we needed to pull the distributor and recurve it.

He happened to have another one in the trunk as a spare, so I did that one instead. I reduced the mechanical advance to 11 degrees (22 at the crank).

This allowed me to raise the base timing to 12 degrees, providing 34 total. I MIG welded up the vacuum unit to add another 15 degrees timing via ported vacuum.

The distributor was installed, and base timing set at 12 degrees. This smoothed out the idle some, but it just wasn't enough. Even with the idle mixture screws just about falling out of the carb, I could place my hand over the choke housing and it would smooth out ever to slightly.

I pulled the carb and drilled the idle downchannel restrictions to .058". Once back in place, I had plenty of idle fuel, and ended up setting them at 3.5 turns out from seated.

Between adding idle fuel, and initial timing, the heavy "lope" was not gone, and the engine idled pretty smooth, with a "deep/heavy" sound. It liked to be idling about 800rpm's, then fell to about 600rpm's in gear, smooth and steady.

To sort of sum things up here, I was quite surprised at how "big" the little 112 cam acted in the relatively high compression 350 engine. Vacuum wasn't really all that low, but it did require some additional ignition timing and idle fuel delivery from the carb to be happy at idle speed. Stock settings just weren't going to cut it......Cliff

 

Typo on my part, the cam in the 350 I tuned yesterday is the 112. Sold to the owner as one size over "stock", good idle, strong low and mid-range power.

It wanted a LOT of idle fuel, and timing. When we started the job, it was idling very "rough", with a LOT of "lope". It just wanted more timing and more idle fuel than the stock settings to be happy.

IMHO, it's a decent choice for the 350 engine with some compression in it. It's not a "home-run" for the 68 Buick I worked on with a stock converter pushing against a 2 speed auto transmission. I really don't know if there would be a "performance" cam that would work good there, as it's a pretty tall order for the little 350 to push the big GS around right to start with, let alone coupling it's power to the ground thru a 2 speed transmission.

Reminds me of a 67 Impala SS I restored a few years back. 3.31 gears and a PG trans behind a 300hp 327 engine. It was a "turd" off the line.

I replaced the PG with a 700-R4 and 2400 stall speed converter, and turned the big "boat" into a missle off the line!.....Cliff

 

That is very intresting. One thing tough my cam is TA 112, The cam mentioned was TA212? But on another note my idling is almost excactly the same: Idles like crap, lopes like it would have a huge cam in it. The mixture screws on mine do the same thing also, atleast I think it isnt getting enough fuel with the screws fully out.

I didnt have time today to do the vacuum check, still it wonders me why the vacuum goes up&down about 2". I have (if I remember correctly) 72-model qjet it does not have APT. I did do some work on it (idle tubes are stock size, ide downchannel is about .052" and I added Idle bypass air to it.

I also have to mention that it is incredibly difficult to find drill bits of correct size here in europe, eg. thats why the the idle downchannel is about .052" = 1.3 millimeters (thats the drill bit I could find) I am now cosidering to drill the idle downchannels to about .059". Do you think this is worth a try?

 

Sounds like that 112 might've been installed on the retarded side, or maybe something else was up. I ran a cam with ten more degrees of duration at 0.050" in my mom's tired, smogged out low compression SBC 350 at four degrees advance...and it idled with only a couple inches less of vacuum at idle, sounded like a stocker. Didn't have to touch the q-jet other than idle mix and speed and throw in a bit more initial advance.

Devon

 

As with many cam installs, it was NOT degree'd. Certainly acted pretty "big" for the little 350 engine, but only at idle speed.

I really don't think there is a good cam upgrade for a stock 350 with a 2 speed trans and stock converter behind it. Any cam that hurts idle quality and shoves power further up in the rpm range, is NOT going to be any better than, if as good as a stock cam, in that particular application...IMHO.

Good news is that we got the engine to idle fine in and out of gear, and the owner is planning a TH350 upgrade with a mild stall converter at some point. This will really let the cam show it's colors......Cliff

 

A little update on this:

I finally decided to swap the old camshaft in the engine, and guess what, IT SOLVED EVERYTHING!

With the old cam (I suspect its the stock cam) the car has 19" of vacuum, steady vacuum, with no fluctuation in vacuum readings.

It got a lot better MPG

Acceleration improved quite a lot. Still not what it used to be, Ill be fitting the carb with the old rod&jet sizes instead of stock.

I have no idea why the TA 112 idled so crappy in there, keeping in mind that I did mod the carb to allow it more fuel & air. I put the cam up for sale, I am not about to go buying different pushrods and/or stall converters just for a few HP.

 

Higher stall converters, taller gearing, and bigger than stock cams have been driving this hobby since I got into it back in the mid-1970's.

It's quite interesting that I was so poor back in those days that I had to use and modify a lot of stock parts, and when I could save up for, or "horse trade" for fancy aftermarket stuff, they went SLOWER than the stock parts I'd been "tweaking" on for years.

As you found out, there are no "free lunches" with a cam swap. Larger cams on tighter LSA shift the power curve, and make more power in a narrower rpm range, and higher in the rpm range.

Without changing a few parts to compliment the new power, we end up dealing with a crappy idle and little, if any improvment in vehicle performance.

The stock cam will idle better, broad power curve, and make as much as or more power in the loaded rpm range with the stock drivetrain parts.

A slight converter change and taller gearing would quickly make the aftermarket cam the better choice for the application. So would raising the compression ratio a half point or so. It also requires, as you found out, a slight distributor re-curve and some additional idle fuel from the carburetor to be happy.

The decision you made was the right one. I just wanted to let the readers know here that the aftermarket cam would have been a great choice as well, with a few required changes to compliment it......Cliff

 

I also learned all this the hard way, I can tell now that I was a victim of advertisting, I listened to too much ads and didnt get enough of proper information.

I think all this though me a lot, the only thing that saddens me about this is the money lost on the new cam. I can live with the time spent on repairing this problem (since its my hobby).

Im also glad that everything else on the motor is completely stock, well I do have TA aluminum intake and electronic iginition, but everything else is stock, and I intend to keep it that way.

Also I learned a TON about quadrajets. During all this I went through two qjets, checking every component in them. Escpecially thanks to you CLIFF, I now understand better what it is in qjets that intrest people so much.

 

Aftermarket parts have a place in this hobby, always have. Just don't sit at a car show or cruise and tell me how your shiney aluminum intake and carb, MSD and a cam swap put your daily driver into the 10's. Been there more times than I can count, and when you see the same guys at the track with their junk barely running into the 14's, they ALWAYS have a hat full of excuses on that particular day why it's so slow.

In recent years I've back to back dyno and track tested just about every aftermarket part I can get my hands on. Even did some cam testing right on the dyno, and LOST 10hp and 22ft lbs torque installing a "modern" cam profile vs a 43 year old factory design. I even picked a profile that was 10 degrees bigger @ .050", with .060" MORE lift.

I still get FLAMED on the Pontiac boards even mentioning the cam swap testing. Usually by shops who use and recomend those parts, followed by them telling me how stupid I was not to change a half a dozen other items so the new cam would make more power.

Same crap with some intake testing I did a few years ago, and discovered that my iron intake made 6 MORE HP than an RPM intake on the dyno, and ran quicker at the track. It also outran the Holley Street Dominator, Torker I, Performer and the new Tomahawk intake. I didn't know I was supposed to install a looser converter, taller gearing, and shift higher in the rpm range to make those intake work?.......What was I thinking there?....ou: ......Cliff