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Several years ago I bought a 350 Olds Engine and 700R trans combo slightly used. It has the following:
*Flat top pistons, actual comp unknown, but runs on 89 OK.
*Double valve springs and roller rockers
*Cast exhaust Manifolds
*#5 Heads
* Holley 600 4 barrel
*Performer dual plane intake
My car is a 1971 Cutlass Convertible with stock Torque converter and a 12 bolt 3.42 posi rear end. The problem is the cam is too much, not even enough vacuum for the power brakes. I have an electric vacuum booster but I dont trust it. I would like a cam with good mid range and produce adequate vacuum at idle for my brakes. I would like to leave the rest of my set up alone (stock converter, rear end, etc). Thanks in advance for any suggestions.
You need to find out what your actual compression is and your current cams specs are. Why did you leave the stock 1600 stall with such a lumpy cam? You will need 91 or 93 octane with a smaller cam.
Have you thought about adding a vacuum collector system? When you first start up you have to give the system a minute or two to build up a little vacuum in the collector, but the one added to my 1967 400ci with an aggressive cam works great.
I initially had an issue with the new cam and too low of vacuum for the power brakes to work well, but I got the vacuum up with some ignition tuning.
My car has a GM HEI distributor that I initially set up to mimic the points distributor with 10º initial advance and 24º mechanical advance, and with the 217/221 cam that resulted in 14" bouncy idle vacuum. Recurving the distributor to give higher initial advance of 18º and 18º mechanical advance, then connecting the vacuum advance to a full manifold source resulted in a bit over 16" vacuum that was very steady. The idle also smoothed out and is no longer so lumpy sounding.
So I guess my point is try some tuning, with more initial advance and less mechanical advance, to see if you get enough vacuum to work the brakes before going to the effort of changing the camshaft.
I bought a package deal already removed from the car. I asked about the cam and he said it wasn't too much. Weeellll,,,,,maybe his opinion of what too much is and mine are not the same. It was in his wifes 72 coupe and he went for an LS swap. Anyway, Premium gas no issue .
I had a Vacuum Canister initially but wasnt reliable. I bought the vacuum pump and it was noisy but worked OK. lately, its faded out and not worked on occasion, which is scary. Ive parked the car until I can resolve this. Never thought about combining the two (canister and Pump).
I'm running a Howards CL510011-12 cam/lifters kit (with their matched valve springs kit) in my '72 ragtop Cutlass 350, also with flat top pistons, MSD electronic ignition and E-brock 2711 intake with performance modded Qjet
With 3.08 posi gear and a 2300-2500 stall TH350, it pulls strong in low and mid ranges (even with the A/C going) but idles at a nearly stock level. I run 92 - 93 octane and have no detonation issues. Decent vacuum just around 18psi so decent braking vacuum using a stock Delco booster power front disk setup.
I tried an electric vacuum pump for a very short while just for some hopefully added braking capacity, quiet enough to barely be heard, but ultimately pulled it out after it blew a fuse, luckily occurring when I was already all but stopped at an intersection.
Last edited by 70sgeek; November 22nd, 2020 at 07:55 PM.
What rpm does the cam idle at? I would think you want something in the 220 duration range and seriously consider a 2000+ stall converter. Both with make it faster off the line and nicer to drive. I am guessing you have at least 9.6 to 1, might be more like 10 to 1. My 350 with a 214/214 cam idled near stock on my 9 to 1 350 with plenty of vacuum.
I currently run a solid lifter can 245/250 that pulls 10 inches of vacuum with the timing set properly and carb adjusted right. With the idle where I want it it's about 7 . Due to my timing curve I have to run 14 initial with a steep ramp . It likes 20 initial. Have you tried adding more initial timing. Where is it at.
I plugged the vacuum advance and got out the old timing light. At idle, in park its 14 degrees or better. Its actually off the degrees Tab. Seems like a lot, but It always starts easily?
Now what's the idle timing at with the vac advance. Sometimes cars will favor no vac advance. The vacuum advance is for fuel economy and with after market cams it can cause issues in my experience. Does it drop when you put it in gear ?.
I disconnected the vacuum line to the distributor, so that's all mechanical advance. I dont have anyone to keep a foot on the brake , so no way to check in gear at present. No one to hold the brake pedal.
An old mechanic's trick is to use a block of wood and push the seat forward to lock the pedal down. But first test with your self in the car to make sure it won't roll away. And use a wheel chock as extra safety.
November 22nd, 2020, 03:54 PM
