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I have a 70 cutlass supreme (stock 350) with #8 heads, dual exhaust (manifolds), HEI ignition.
Looking to upgrade the CAM to provide more spunk and just as important to get that old school muscle car thumper idle sound.
Any help on CAM selection would be appreciated (would prefer to have something that would only require the change of the CAM and lifters, if possible).
A basic problem with the Thunder cams and other rehashes of the 1960's performance cams is they are intended to run with high compression or they run rough introduce a pile of operating problems and don't deliver the power you'd expect. Add to that if you go back and look at OEM history the engines that had these cams in addition to their 10 through 11 someting compression ratios they only came with manual transmissions and stump pulling axle ratios. Todays constraints n octane ratings takes different thinking than what worked in the summer of 69.
Some website wrote that. Essentially, the cam is picked for the engine setup; you don't just put a 'romp romp' cam in and expect it to be wonderful.
What is your rear ratio, tire size, and transmission?
For one, #8 heads are not stock for a 1970 350, should be #6. You probably have 8 to 1 compression, unless flat top pistons were used. You could do the generic 204/214 cam, a 2000+ stall and consider a gear swap.
These gentleman speak from experience. I just replaced a cam that was too large for my engine. It sounded great but lacked low end torque and not enough vaccum to properly operate my power brakes. The biggest issue was lack of compression to handle a larger cam. Much knowledge and helpful people on this sight. I hope this helps your decision.
A cam and lifter change is no magic bullet. More grunt would be gained with a rear gear change and different mufflers could provide the sound.
I have posi rear with 3.42 gears and flowmaster mufflers,. It still doesn't seem to have much spunk (can't even spin tires), looking forghe cheapest way to add spunk, could the timing be off?
With 3.42’s that thing should be able to blow the tires right off the wheels if the engine is even near “right.” With the mix of short block and heads I think a compression test would be a good idea to see what kind of pressure is being produced in the cylinders. As mentioned above, if that is indeed a ‘70 short block and happens to be the lower compression 2 bbl version, those #8 heads, along with likely thick replacement gaskets could lower the compression to that of a WW2 Jeep. Based on the description of uninspired performance, that’s my suspicion.
Don’t make any moves on a cam until you get some compression readings and post them up here. Chances are a cam will hurt performance, especially in the lower rpm torque spectrum. Changing the cam is not what I consider a small job and may not be straightforward, possibly leading to a parade of complications - mushroomed lifter removal, pushrod length, worn parts, etc
Other considerations are tune up level, timing, distributor advance weights and curve, carb calibration, even torque converter though not really likely. Plenty of help to be had from people on this forum, keep a dialogue running.
Edit - Late thought, is this 2 bbl or 4 bbl carb? What type? Do you know what the base timing is?
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Last edited by bccan; April 11th, 2022 at 07:03 PM.
The factory torque converter stalls around 1600 rpm, dam useless for a hard launch. Look at upgrading to a 2000+ stall. Does it have an EGR intake? If so it could be a mid 70's direct motor swap. Check your timing, dwell, if still points and adjust the mixture screws. Also do a cranking compression test to determine engine health and whether a cam swap is currently possible. Does it have dual exhaust? That also makes a noticeable difference. As said, with 3.42 gears, 2350 stall and stock 76 Olds 350 with #8 heads and a 204/214 cam, shorty headers with 2.5" exhaust would roast the tires, 140 to 142 psi after the cam swap and ran 9.9 in the 1/8 mile with ignition break up over 4000 rpm. Not fast but equal to mid 15's. 15 flat should have been possible with a new ignition coil in a 3750 pound car. Good luck.
The factory torque converter stalls around 1600 rpm, dam useless for a hard launch. Look at upgrading to a 2000+ stall. Does it have an EGR intake? If so it could be a mid 70's direct motor swap. Check your timing, dwell, if still points and adjust the mixture screws. Also do a cranking compression test to determine engine health and whether a cam swap is currently possible. Does it have dual exhaust? That also makes a noticeable difference. As said, with 3.42 gears, 2350 stall and stock 76 Olds 350 with #8 heads and a 204/214 cam, shorty headers with 2.5" exhaust would roast the tires, 140 to 142 psi after the cam swap and ran 9.9 in the 1/8 mile with ignition break up over 4000 rpm. Not fast but equal to mid 15's. 15 flat should have been possible with a new ignition coil in a 3750 pound car. Good luck.
I have updated the converter (2000-2200 stall) and installed a shift kit for the TH350 over the winter (haven't tested it yet). it does not have an EGR intake, has a HEI distributor and is dual exhaust (Manifolds not headers). I haven't checked to see what the timing is yet, but will do and report back here (will also check the compression and report back as well).
A good tune-up is critical to good performance. 34-36 degrees at 3000rpm. Depending on where your HEI came from, and who installed it, that may be a huge issue with lack of performance
As said, with 3.42 gears, 2350 stall and stock 76 Olds 350 with #8 heads and a 204/214 cam, shorty headers with 2.5" exhaust would roast the tires, 140 to 142 psi after the cam swap and ran 9.9 in the 1/8 mile with ignition break up over 4000 rpm. Not fast but equal to mid 15's. 15 flat should have been possible with a new ignition coil in a 3750 pound car.
Sweet, that's 3 seconds quicker than a bone stock 1976 350 Cutlass.
Dupshall, my 69 Supreme runs almost as quick as Olds 307 and 403. 10.0 in the 1/8 mile. She is aftermarket dual exhaust, but otherwise stock. 2.78 open rear, stock torque converter 1400 stall, factory th350. And will lay rubber from a 15 mph roll, if I punch it.
Your setup is not the problem, unless the mods were botched during installation. Your 350 seems to be the problem to me. Either the engine is tired, or the tune is so out of wack it's mind boggling. But in reality what you are describing is the dogshit performance of most of the mid to late 70s factory cars...
If the latter is the issue the cam swap should make the difference. As Olds 307 and 403s post clearly indicates.
Who knows what was done to that 350. If it has an HEI and a non EGR intake, who knows what was mixed and matched. Is it a factory or an aftermarket aluminum intake? What is the carb off of, any numbers on it? Get an advance timing light and get it set to 34 to 38 total in by 2500 to 3000 rpm. Most factory HEI even with aftermarket lighter springs don't come all in before 3000 rpm. Most that means around 20 base timing but there are a few different advance curves, some are closer to the points distributors for base timing. It should spin pretty good with street tires, especially with your new converter.
Last edited by olds 307 and 403; April 12th, 2022 at 08:26 PM.
Confirmed last night that the engine has #6 heads and not #8 as i previously stated (6 looked like a 8 when I quickly looked at it before). will check the compression and timing over the weekend and repost here.
That’s good that it has the #6 heads. As said above, a good check up is in order. Verify compression and timing.
if your timing is off it will kill its performance.
that thing should fly with the info you have provided. My 69 4bbl had the highway gears and would roast the tire..
also make sure your secondaries are opening and not being caught by the tab from the choke.
let us know what you find.
I wonder is someone put the HEI in with the points base timing? Around 10 degrees retarded will make it sluggish. Maybe the secondaries aren't opening properly as mentioned. It may just be a tired engine, it is 52 years old. It will interesting to see what the issue is.
I would concur with olds_307_and_403 on the 204/214 cam for a low compression, stock converter, car with 3.42 gears. With a little more compression and a slightly higher than stock converter you can move up to a 214/224 at .050 cam.
These gentleman speak from experience. I just replaced a cam that was too large for my engine. It sounded great but lacked low end torque and not enough vacuum to properly operate my power brakes. The biggest issue was lack of compression to handle a larger cam. Much knowledge and helpful people on this sight. I hope this helps your decision.
If in doubt always go with the smaller cam. A too small of a cam for your engine will maybe loose you a little horsepower on the top end, but it should not give you any drivability issues. A cam that is too big can completely kill the engines power output, kill your power brakes, and make the car almost undriveable.
I will give you a story to illustrate the fact. Back in the late 80's I sold my 1972 Demon 340 4 speed to a friend of mine, who ended up selling it to my neighbor. The Demon had a stock 340 with an unknown, but slightly larger than stock cam, and 3.55 gears, everything else was stock and it ran really well. One day an acquaintance of ours, who was a body man by trade, comes around with 1971 Roadrunner in plum crazy that he has just painted, the car was straight as an arrow and beautiful. The car had a swapped in low compression 440, with a 727 auto, stock converter, and 3.23 gears. The Demon by comparison was a rust bucket, you could brake like Fred Flintstone, and the trunk was so rusted out, that the fuel tank hangers were no longer there and the fuel tank was held in place by a piece of rope... Anyways or buddy with the Roadrunner had just gone to a guy that had a 10 second 70 Cuda 440 drag car, and he decided to buy one of the "King Kong Cuda" (that was the cars name) old camshafts and put it in the 440 that he just put in the Roadrunner . That Roadrunner sounded nasty as hell, but it could not peel a tire in a puddle of grease and could not get out of its way, plus the power brakes did not work. It idled at 1200 RPM's and when you put it in gear it wanted to die. I told the guy the issue was the cam, but he was tired of dealing with the car and the engine, and just wanted something fast. He offered my neighbor a straight up trade; the mint 440 roadrunner, for the rust bucket 72 Demon. My neighbor could not get his title out fast enough. As soon as the guy left we bought a Crane HMV 272 cam kit, with lifters, springs, retainer, timing chain, and all the gaskets we needed. We changed the cam and that car changed completely, this was a newly rebuilt engine with the now ancient Edelbrock CH4B intake, a Holley 750 vacuum carb, and a set of headers. That Roadrunner could spin the tires for blocks, when my neighbor got out of that car he had the biggest smile I had ever seen. The car went from being a dud, to being a really fast car in the time it takes to change a cam...
I would concur with olds_307_and_403 on the 204/214 cam for a low compression, stock converter, car with 3.42 gears. With a little more compression and a slightly higher than stock converter you can move up to a 214/224 at .050 cam.
Yeah, if it isn't tired and it is a tune issue, his motor should be high 9 to 1 at minimum with factory pistons and shim head gaskets. He should be able to move to that cam or bigger and still have acceptable cranking compression.
Is she original intake manifold ?
What carburetor ? Lack of performance sounds like an Edelbrock ... HEI came into play when performance was fading. And in my opinion is overrated. Unless your car has extreme performance.
What grade of gas are you using ? Does she ping without a booster. If not maybe the timing is pulled back to protect the engine. To the point that it feels like a 140hp g body ...
Maybe invest in a Dragy to get some sort of gauge on performance. Being that she doesn't peel out. You can get a decent idea on 0-60 etc. Or other ranges like 40-70 mph, if you are more comfortable going that way. Our cars stock can cover the 30 mph increase in about 5.8 seconds. From a constant 40 mph roll.(Our set-up no shift kit with 2.78 rear gear.)
My car performs on par with Automobile Catalogs simulation. The fine print states how to conduct the test.
They are on the low side for a high compression motor. That leaking at the head cylinder, was it at the threads? I assume it would be higher with a proper seal. It still should peel rubber, even with those numbers. Start with adjusting the idle mixture screws with a tach, get the highest idle. I would also ad 2 to 4 degrees of timing. What carb is on this motor?
Last edited by olds 307 and 403; April 15th, 2022 at 05:06 PM.
It has the 4bbl quadrajet, do you think a new set of rings would help with getting the compression higher, not interested or have the funds to do a full rebuild (i.e. having block bored, pistons, rings, etc.)
Last edited by Dupshall; April 15th, 2022 at 06:39 PM.
Maybe. How is the oil pressure? Is it burning oil? A leak down test would be handy to see where it is losing compression. How is the tension on the secondary air door on your Qjet? Usually they are too loose but someone may have adjusted the air door too tight. That would definitely hurt acceleration.
Not sure about oil pressure, but it don't appear to be burning oil. Also don't know much about quadrajet either, may have to do some research on them to make sure it is working properly. Also does the oil test in the cylinder work with respect to determining if compression is being lost though the piston vs the valves?
Last edited by Dupshall; April 15th, 2022 at 07:28 PM.
If I was to take a guess you have an issue with the ignition timing curve. If someone just threw a stock HEI in there, the advance curve could be really slow. you could potentially not be getting full advance till the engine hits 4,500 RPM or even higher. Get an advance curve kit for the HEI, have all your advance come in 2,500-3,500 RPM, and set the total advance to 36-38 degrees. Make sure that your damper has not slipped and the timing marks are accurate, that damper could have slipped and you could go nuts and never get the car running right. Make sure the secondaries on the Quadrajet are opening. With the compression you have and 3.42 gears that car, if tuned even close to correctly should easily peel the tires for a couple hundred feet.
Here is a good article on how to do this: https://www.motortrend.com/how-to/ba...i-distributor/
I once installed a replacement cam using the dot to dot method and the engine had no low RPM power. Later I checked with a degree wheel and found the cam was 8 degrees retarded. So if the engine runs smoothly and everything else checks OK, it could be retarded cam timing.
I think OP said above that he has 34° in by 3000, which is pretty good for starters.
Agreed. Another 2 to 4 degrees might add a little pep but shouldn't be night and day. It very well could be carb related. I would go through everything, change plugs, cap, rotor wires. Maybe even a coil and module, I like the aftermarket performance ones personally. The next thing I would check would be the secondary air door tension, secondary rod movement, make sure the air door cam isn't damaged or missing and what hanger and rods are in there. With his new converter and 3.42 gears, he should be able use light tension on the secondary air door. It definitely makes a difference on tire spin.
Last edited by olds 307 and 403; April 16th, 2022 at 11:29 AM.
April 11th, 2022, 10:02 AM
