455 stage 1 vacuum advanced

Houtan

Member
Hi everyone,

I have a question about vacuum advanced on 455 stage 1 engines, In 1974 455 Stage 1 vacuum advanced was 10 degrees, non stage 1 engines was 18 degrees. I overhauled the engine and changed compression ratio higher, also get rid of 1974 emission parts and used street strip camshaft with 112 degree lobe separation, my distributor is original 1974 HEI stage 1 with original vacuum advanced 10 degrees on it. my question is it is better to stick with original 10 degrees vacuum advanced or I must going for higher degrees 18 or maybe 20?

Cheers.
 
You are obviously trying to get a little more performance, so I would stick with the 10 degrees because it will give you a little more room for initial and mechanical advance. If you wanted more timing in the vacuum component after pushing the initial and mechanical get a fully adjustable aftermarket vacuum advace which will allow you to adjust the number of degree maximum and the rate at which it comes in.
 
The vacuum advance canisters fitted to the 455 and 455 Stage1 are almost identical, both prove 14-19* of vacuum advance. The only difference is at what vacuum level that is attained.
1974BuickIgnitionSpecs.jpg
More important is the amount of mechanical advance built into the distributor you are using. Don't just assume that the distributor currently installed in your engine is the one it left the factory with. Unless you are the original owner and bought the car new, you can't know that. The distributor may have been changed by previous owners. If so, the stock numbers listed above no longer apply. Have a look at the thread I wrote over on V8buick years ago.


See if you can locate a part number on your distributor. See if it matches any of the numbers in the above attachment.
 
The vacuum advance canisters fitted to the 455 and 455 Stage1 are almost identical, both prove 14-19* of vacuum advance. The only difference is at what vacuum level that is attained.
View attachment 10270
More important is the amount of mechanical advance built into the distributor you are using. Don't just assume that the distributor currently installed in your engine is the one it left the factory with. Unless you are the original owner and bought the car new, you can't know that. The distributor may have been changed by previous owners. If so, the stock numbers listed above no longer apply. Have a look at the thread I wrote over on V8buick years ago.


See if you can locate a part number on your distributor. See if it matches any of the numbers in the above attachment.

Thanks Larry, I checked parts when I started to overhaul the engine, The distributor`s body number is 1112521 3H 2 and its vacuum advance number is 520 10, I`m third owner of the car and all parts as I checked on engine bay and rear end was matching numbers but I`m not sure about vacuum advanced itself. I don`t have any other numbers on it but it`s old 70`s GM vacuum advanced and it`s playing groove is shorter than other 455`s vacuum advanced for example I have another distributor from Electra 455 and it`s vacuum advanced is 477 18 and its playing groove is almost double. I thought 10 or 18 numbers on them are their playing degrees or it is their playing numbers? also I checked the springs on mechanical advance and they are little harder than other 455 distributor that I have.
 
That's a good distributor, basically an HEI version of the 1112016 points distributors fitted to the 1970 GS455 Stage 1 engines. It has 20-24* of mechanical advance. With 10* of initial advance, full throttle advance is 30-34* where Buick V8's make best power. That full advance does not occur until 4600 RPM though. Realize that at lower RPM like cruising around, mechanical advance is more like 9-13*, so advance with initial advance would be 19-23* PLUS vacuum advance 14-18* for a total around high 30's to low 40's for best gas mileage.

Your vacuum advance may have been replaced at some point because it went bad. To boost low RPM power, many will install lighter springs in the distributor so that full mechanical advance occurs at a much lower RPM. When you do this though, it is important to reduce the vacuum advance to 8-12* to avoid over advance. Because all your mechanical advance is in at cruising RPM's, you need less vacuum advance degrees to get to the low 40's for best economy. At full throttle manifold vacuum will fall to zero, and any advance from the vacuum canister falls out.

So what vacuum canister you want will depend on whether you intend to leave the distributor as stock, or you want the mechanical advance in quicker. The 10* canister will work well if you install springs that get the mechanical advance in by 2500 RPM. If not, get a stock canister with 14-18*.
 
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