Guess my cam
- Thread starter justanotherguy
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Oh, that's a 3/4 race cam!
View attachment 1563361
Your 400 shouldn't be a slug. Maybe the camshaft timing gear is off by one tooth?
Borrow or get yourself a degree wheel and check your camshaft timing. The procedure for using one can be found online and possibly on YouTube.
You guys beat me to it !
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I can guess that cam in... 5 reciprocating assembly rotations !! ( is this a new game show ? )
"Street/race" probably like a280 - 292ish. Too big for that low compression 400,so it's a dog down low. We always picked the "street/race" back then, even if it was a daily driver. Whatever gear you had. How's that for "crystal balling it"?
justanotherguy
Well-Known Member
Good question, most of it is understanding what the car has in it and matching future parts accordingly or changing it out. I neither like nor dislike it. It simply is. Lol.
joew94th
Member
This perked my ears up. I have the same issue only in a 360. Previous owner has no idea what cam it has, but it definitely has one. Of course, I wouldn't know what cam it has if you handed it to me.
has2bmopar
Well-Known Member
Some crazy answers and suggestions here. Just go to the fundamentals.
If it was off a tooth on the timing chain the timing would be way advanced just to make it run. If you don't have a good timing light, put the balancer about 8° BTDC and check the reluctor. If it's not really close to the bar on the pickup coil, it could be off. Doesn't matter if it's on compression stroke for #1, or #6. You can loosen the distributor and line up the reluctor and pickup coil, then obviously snug down the distributor again. The rotor should also be pointed at either #1, or #6.
If it was not close initially on timing, it likely won't even want to run if the timing chain is off a tooth. You can pull the plugs and do a compression test also. I doubt the chain is off, or it would barely be drivable.
To judge your cam put a vacuum gauge on it. If it pulls 10" or less with no vacuum leaks, it's too big for the original 8.2 : 1 compression ratio.
If you insist on numbers, get a set of valve cover gaskets and a dial indicator. At the top of the valve spring retainer will be actual lift. With stamped rockers you could lose some lift, as they are not all that precise. The factory ratio is 1.5, not 1.6. you can check what ratio they are, by checking the lobe lift directly on top of the pushrod bulge on the rocker vs at the retainer. Check a couple of intakes and exhaust valves and you will have actual numbers and not a guessing game.
Also, there are no "small valve" 400 heads. All the open chamber big block heads ran the same size valves... 2.08" intake and 1.74" exhaust.
A friend of mine had a completely unmolested '74 Newport with a 400 and it would roast the tires on the straight away with likely 2.76 gears. Another friend had a bone stock '75 Road Runner with a 400 Thermoquad and he raced a 2wd 1/2 ton square body with a 454 5 times before the Chevy dork went home to kick the dog after 5 losses.
If you want it to run strong, you need to put higher compression pistons in it. Look at the compression height of the pistons and not what anyone claims the compression will be, with an open chamber head. You will need to check the chamber CCs if you want to know the actual compression ratio.
Take your deck height and subtract -
- 1/2 of your stroke
- rod length
- piston compression height
This will give you your deck height/clearance, give or take, without a trusted machinist to square/deck the block.
If it was off a tooth on the timing chain the timing would be way advanced just to make it run. If you don't have a good timing light, put the balancer about 8° BTDC and check the reluctor. If it's not really close to the bar on the pickup coil, it could be off. Doesn't matter if it's on compression stroke for #1, or #6. You can loosen the distributor and line up the reluctor and pickup coil, then obviously snug down the distributor again. The rotor should also be pointed at either #1, or #6.
If it was not close initially on timing, it likely won't even want to run if the timing chain is off a tooth. You can pull the plugs and do a compression test also. I doubt the chain is off, or it would barely be drivable.
To judge your cam put a vacuum gauge on it. If it pulls 10" or less with no vacuum leaks, it's too big for the original 8.2 : 1 compression ratio.
If you insist on numbers, get a set of valve cover gaskets and a dial indicator. At the top of the valve spring retainer will be actual lift. With stamped rockers you could lose some lift, as they are not all that precise. The factory ratio is 1.5, not 1.6. you can check what ratio they are, by checking the lobe lift directly on top of the pushrod bulge on the rocker vs at the retainer. Check a couple of intakes and exhaust valves and you will have actual numbers and not a guessing game.
Also, there are no "small valve" 400 heads. All the open chamber big block heads ran the same size valves... 2.08" intake and 1.74" exhaust.
A friend of mine had a completely unmolested '74 Newport with a 400 and it would roast the tires on the straight away with likely 2.76 gears. Another friend had a bone stock '75 Road Runner with a 400 Thermoquad and he raced a 2wd 1/2 ton square body with a 454 5 times before the Chevy dork went home to kick the dog after 5 losses.
If you want it to run strong, you need to put higher compression pistons in it. Look at the compression height of the pistons and not what anyone claims the compression will be, with an open chamber head. You will need to check the chamber CCs if you want to know the actual compression ratio.
Take your deck height and subtract -
- 1/2 of your stroke
- rod length
- piston compression height
This will give you your deck height/clearance, give or take, without a trusted machinist to square/deck the block.
Last edited:
PsyOps
Well-Known Member
All of the above is useful but is widely wallet dependent. To answer the OP's original question, and if it is a "...Comp Cam "street/race" camshaft installed between 10-15 years ago," I would pull the front cover (& look for any slop in the timing chain itself - did the prior owner simply reuse the old timing chain set?) and follow the recommendation above to remove the timing chain gear to (potentially) get the identification off the cam itself. All other decisions, based on available funds, can come after the cam is IDed.
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