I rebuilt a 1974 455 to save my numbers matching 400 engine. I did a stock rebuild. The engine had big valve heads from the factory and the carb had the correct needles and such in it. I already had a factory stage 1 cam so i installed it. Big mistake because the copression level is to low for this cam. I have no bottom end. My question is will just changing the heads to 69 small valve heads be enough to correct this or do i have to do a cam change? ED K
You'd have to check the combustion chamber size to insure raising the compression ratio. You can also use a thinner head gasket. Going from a .040 to a .020 will raise your compression about .65 or so. Not a lot, but every bit helps.
according to the head listing the 69 heads are 69cc and the 74 heads are 71cc. I guess what i need to know is how much this would raise the compression .I could add that to thinner gaskets and get an idea of copression ratio. Does anyone know the least compression someone can run the stage 1 cam with and not loose all the bottom end. ED
cam change in my opinion. its far easier to change aq cam than both cylinder heads-and-ta and poston both have cams just for this situation. i believe its the 413 series cam froem either-keeps the valves closed a little longer to allow the chambers to fill more. thats how i would solve it. in fact that how i did solve it over 10 years ago with one-worked out very well :3gears:
I ran these numbers through my desktop dyno. I used my engine, which is .030 over as a test engine. Assuming your pistons being .050 in the hole and combustion chamber sizes of 69 and 71 cc's, and a 24 cc dish in pistons, here's what I came up with: 71 cc heads, .040 gasket = 9.05 71 cc heads, .020 gasket = 9.43 69 cc heads, .040 gasket = 9.40 69 cc heads, .020 gasket = 9.58 You may be better off getting a cam that is more suited to a lower compression engine. I believe for a cam like you have, you'd need at least 10 to 1 or so to make it work.
I doubt the problem is the cam. The factory stg-1 cam is not a very radical grind. Other problems you may be having, ignition timing, too much lifter preload ( this will cause no low ed power), vac leak. Does it idle rough? By no low end power, describe what you mean. Does it pull good at higher rpm? Just some thoughts. Jim Burek
It has a little bit of a lope but not very much.It is pulling about 16 inches of vacumn.I installed the hei distributor and tried the crane vacumn advance unit with full advance at idle but it didnt really seem to help. Running 12 degrees initial plus the advance plus the weights. If you are going about 60 and floor it that is when it pulls the best.The carb is opening up but i am just not gewtting what i expect out of it. I know from 0 to 60 the 400 would have spanked it. I mechaniced for quite a few years and this is the only motor i havent got to run to potential ED K
What is the total advance, Initial +mechanical?? What RPM is it all in at? The Crane vacuum advance has entirely too much advance in it. It has to be restricted. The HEI's usually have way too much mechanical advance in them. Still guys just install them, set the initial to where they want to, and have no idea what timing the engine is running at going down the road. If you want your BBB to run at it's best, you can't afford, not to know your timing at all RPM's. It's very easy to find out, not so easy to recurve an HEI, but it has to be done. You need 30-34* total (not including vacuum advance) all in at 2500 RPM or less. Then restrict, either the Crane adjustable vacuum advance, or a stock vacuum cannister, to 8-10*, and run it off manifold vacuum. If you get the timing right, you won't believe the difference. Check this thread out: http://www.v8buick.com/showthread.php?t=63475
My initial advance is 12 and with the crane vacumn mod i added another 10 degrees for a total of 22 at idle .I marked the dampner at 13/4 inches and it reaches this mark before 2500 rpm. As the motor revs higher the timing still increases but i dont know how much. I get nopinging at all though and at these rpms the car pulls strong. The 400 had more snap on the bottom end than the 455. On the cars i used to run chevy and Pontiac i never had any problem getting them to run like they should. I was thinking that with the low comp and the Stage cam i was not getting good air flow until rpms built. ED
It can still be overadvancing, even if you don't hear any pinging. Was the cam degreed in? I think you have another problem. Try some lighter springs in the distributor so the mechanical advance maxes out for sure.
Did you degree the cam? It could be that the cam wasn't ground right (would anyone on here be surprised at this?). You may need to advance it more to bring the rpm and torque peaks lower in the rpm range. I'm running a 76 block with a 230/240 - .499/.509 lift cam and it has plenty of bottom end. It idles with 14" of vacuum around 850 rpm. The block is untouched and the heads had only had a cleanup cut to them (73 heads). I have the felpro head gaskets (.038, IIRC). Using Phil's info, I don't think I'm pushing over 9.5:1 compression with the light cut to the heads and the Stage 1 valves in them. No notches in the pistons (stock). My 71 GS455 had plenty of low end torque with a stock motor and previous owner had the cam reground to Stage 1 specs (so says the receipt). With 3.42's and 26" tires, it saw a best 60 ft of 1.855 and 13.42's.
Well its 24 below zero right now so i wont be doing anything for a while. When the motor is reved with the timing light on it the timing mark goes way past the 30 degree mark on the dampner. I did not degree the cam because it is a gm stage one cam with gm timing chain and gears and the lifters are gm for Buick also. I dont understand how it can be over advanced with only 22 degrees at idle. I messed with the different springs and such last summer and nothing helped on the bottom power. Maybe i am expecting to much from this motor. I am used to running 4 speeds but i did have a 67 camaro running just over stock cam with headers and such that would pull the tires in first and second so i would think this 455 should at least roast the tires from a standing start. ED
ED, 24 below 0, Wow :jd: I wouldn't be doing anything either. Wait till it warms up :laugh: It can over advance. Take a 1974 HEI distributor for the 455 Engine. Stock specs call for up to 28* of mechanical advance at 4100 RPM. The stock initial timing on that motor is 4* BTDC. So at 4100 RPM, you have 28 + 4 = 32* total. That's fine. Now you go and get that HEI from a junk yard, and pop it in your engine, and set the initial timing to 12*. Now you have 40* total, definitely too much. The stock vacuum advance on these motors supplied up to 19* additional advance. So lets say you now put in lighter springs, and now your advance is all in at say 2500 RPM. You could be going down the road at 59* of advance. You say you limited the Crane cannister to 10*. Did you do it according to Cranes instructions(with the small black cam). If left untouched the Crane cannister will give about 20* of vacuum advance. Every time you move that little black cam one notch, you advance the base timing 2* There is a better way to limit that cannister, that doesn't advance the timing, it just restricts the distance the pull pin can travel. If you read my post over at the FAQ forum, it has pictures. Hope things warm up for you. You're right, that 455 should turn the tires if you breathe on the gas too hard.
I did the crane unit as described on this board. I really thought getting the advance in early would do the trick because it acts like its late on timing. I have a garage i can work in thats why i would like to do something with it in the winter when i have time.I have a 76 block and some standard higher comp pistons and i also have the 69 heads. Ill have to decide which way to go. Thanks for all ideas and advice ED
Degree the cam Check the cam before you make a bunch of parts changes. They can be off even with "genuine GM" parts. Try advancing it 2 to 4 degrees if it's straight up. As for distributor timing, mechanical advance is limited by the advance stop bushing under the points plate on points style distributors and I think it's the same on HEI. The bushing is plastic and can fall apart from the ozone atmosphere under the cap. I replaced mine with a brass wheel collar from a model airplane - hobby shops will have these. It takes some grinding but you can set the mechanical advance very accurately. You need a dial back light or timing analyzer to check your mechanical advance. Set the mechanical advance to 10-14 degrees with the advance bushing. Use light springs to get it in early (sounds like you have that covered). Then play with the initial and vacuum advance to get best driveability.
I would have to agree with some of the advice from above. If your compression is running a true 9.0 or better, that cam should be working for you. I bought a cam and installed it straight up, only to find out it was off by almost 2.5 degrees. I would recommend dialing in the cam first and really going through your distributor also. You may also want to check your balancer and make sure it's in good shape and hasn't slipped. That will also throw your timing off.
My car really woke up with a correctly curved distributor. What jetting is in the carb? You could be lean.
the dampner on my 400 was slipped when i got the car. Very doggie. Only took about 10 minutes to figure that out. I am thinking about putting my points dist. in just to see if that makes a difference. Sure would be a lot easier than messing with cams and such. I always start with the easy fixes and go from there. The jetting and needles in the carb are what was recommended on this board. I tore the carb down for a rebuild and it was already set up with the right stuff. I guess i should not take for granted the factory cam and such is right . I have never had any trouble with gm stuff before. ED
