Links, links and more links!

I'm new here but getting lost in the links and sub links and their links is time well spent. I've recently replaced the blown 305 in my 85 K-10 with a mystery 383, I say that because I don't know it's history. It's an odd build and I would have liked to tear into it more before dropping it in my truck but she's my daily driver so time was of a limited nature. What I do know is the machine work on the short block seems to be top notch very nice clearancing done with end mill. Scat forged crank, H beam rods, forged pistons. Up top Vortec heads Edelbrock Performer spread bore intake which worked out nicely because I'm a big QuadraJet fan. The mystery aspect is the cam and compression ration. Which makes it harder to fine tune but with all that I've learned from you guys I'm getting there. After dropping it in the first things I went out and bought were a piston stop, timing tape and timing light. Grumpy has made it clear that knowing not guessing TDC and advance curve would be a good place to start.


The Grumpy Grease Monkey mechanical engineer.
Staff member
engine building is about 75% technology and science and 10% art, and 15% skill gained through experience,over time.
doing it successfully mandates the person involved, in the process, can accurately observe, think, and recognize problems,
and if required, stop and think up solutions.

yes it involves knowing how components are intended to function and accurate precision measurement and access to some specific tools and a skilled well equiped machine shop you can trust, is a mandatory factor and skill set.
so many guys seem to be under the absurd impression that any and all solutions,
to any and all problems,
invariably involve, throwing away some component,
and installing some new out of the box part,
instead of acting logically and actually measuring,
thinking and potentially custom clearancing or at least reading the instructions,
and as most experienced engine builders will tell you ,
almost nothing you can buy fits and functions correctly in out-of-the-box, condition
,too near its true potential.after its ,
carefully, inspected, and correctly clearanced, and fitted.
Last edited:


"One test is worth a thousand expert opinions."
Welcome Sam. And of course Grumpy gave you MORE links.
Ultimately, you have to give that engine what IT wants - not what you want to give it.

And you just got a few points for being a Quadrajet fan.
That's very true now it's up to me to really listen to what it's telling me. Now that I have the timing dialed in it's time to start working on the carb. I will post my carb rebuild adventures once I find the right one to start with. Right now it's a little rich at idle and part throttle and lean at WOT so for now I just keep my foot out of it.


Staff member
The mystery aspect is the cam and compression ration.
You could measure cranking pressure by doing a compression test, that would give you an
indication of the compression ratio.

You could back into the CR with this calculator, but remember it's all theoretical. Mine was off
about 20 psi on the cranking pressure.


Welcome to the forum !
Last edited by a moderator:
I will definitely do that. And post my results. Thanks for the tip. I'll also try to get a new set of plugs and make one pull on them so I we can go over "reading" the plugs. I'm a hobbyist photographer so posting good clear pics is one thing I know I can do.


"One test is worth a thousand expert opinions."
Before you touch your carb, make sure EVERYTHING else is correct. The carb is the LAST thing you want to touch.

Have you checked manifold vacuum at idle yet?
19 inches at 800 rpm. 10 degrees advance initial and 32 all in by 3400 vacuum advance hooked up to full manifold. I spent several hours with my HEI and this forum and some graphing paper. Only after verifying TDC. I HAVE to rebuild a carb a previous owner destroyed the chock and the primary throttle shaft is really worn, constant vacuum leak, shows up on the headers with IR temp gun and propane leak test.


The Grumpy Grease Monkey mechanical engineer.
Staff member
BUT your way ahead dealing in verified FACT vs guessing at the cause of problems
That's why I enjoy this forum so much. All your ideas are based on the Scientific Method. Not some stuff your buddies friend's uncle use to do and it always worked for him. I found this place while trying to dial in my timing and I found the information to be invaluable in that endeavor and figured I should join and ask pertinent questions about my new engine and I'll end up learning more and possibly help others like me searching for real information in a sea of b.s. that's found on many other sites.

Anyway I feel at a disadvantage not knowing what cam and compression ration the 383 has. I'll do a compression test soon and post my finding but what else should I look for and check?


The Grumpy Grease Monkey mechanical engineer.
Staff member
you do realize that , if you want to be sure of the cam you have in that new engine you purchased, you need to verify it and not take the sellers word...(if he even remembers)
you could simply pull the water pump and accessories and timing chain cover,
and damper and use a crank socket that allows you to install a degree wheel,
and look at the cam,
I realize that that may seem like a big deal to the guys,
that have not done that hundreds of times,
but even a new guy could get it done in a single days time.

besides its a great excuse to buy a dial indicator, and a stand and degree wheel and damper puller (NEW TOOLS):D:thumbsup:

Damper tool (yes the damper needs to come off and the timing chain and upper gear too look at the end of the cam


most manufacturers IDENTIFY OR mark cams under the timing gear mount surface

KNOWING WHAT YOUR DEALING WITH HELPS, you can use a degree wheel and a crank turning tool and graph out the lift vs degree of rotation, to verify the cam lobe lift/duration if you have the correct tools,

get the smaller 9" version for use in the car , cam degree checking
the 18" versions for checking on the engine stand
the knurled ring, on the damper crank turn tool, below, comes off the damper turn socket so the degree wheel slides on, then its replaced



a crank snout, turning socket,



Last edited:
I didn't think of that and this being my only vehicle I was I a hurry to get it running again. Like all things if I could do things differently in the beginning I would have. I also would have found this place months before the motor swap. I could be under the false impression that measuring valve lift with hydraulic lifters isn't very accurate.


Staff member
I could be under the false impression that measuring valve lift with hydraulic lifters isn't very accurate.
I sure hope it's accurate, I spent several hours plotting the lifter position every 2 degrees. You won't
need every 2°, but I would take a measurement at .050 inches and maximum lift. It would provide
another data point that could be matched to the manufactures numbers.

My thought process in thinking that it wouldn't be too accurate is that there wouldn't be pressurised oil in the system for the hydraulic lifters. But, I'm very new to this and am always willing to learn and try new things. So now I'm thinking I will just continue the timing makers from my timing tape all the way around the harmonic balancer. Then graph my measurements.


The Grumpy Grease Monkey mechanical engineer.
Staff member
If you are concerned with measuring the clearance in the hydraulic lifter seat when selecting and measuring the correct valve train geometry,
so you can order the correct length push rods...
I don,t think you have the correct idea as to how hydraulic lifters work,


yes it is possible for an engine with hydraulic lifters to be pushed too operate at a high enough rpm that the time required for the lifter seat to fully depress and all the oil too be forced up to the push rod/rockers , to be so short that the lifter pumps up and the valves will have less seat time, ( sometimes one of several factors, like the lifter leaving the cam lobes surface as the inertial loads exceed the valve springs ability to maintain lifter too lobe contact, referred too or contributing to what is commonly referred too as valve float) but that has ZERO to do with selecting push rod length or proper valve train geometry, (remember at 6000 rpm the valve is lifted off its seat 50 times PER SECOND)


Proform Pushrod Length Checkers 66789 SBC 3/8" rocker studs

Proform Pushrod Length Checkers 66790 SBC 7/16" rocker studs

Proform Pushrod Length Checkers 66806 BBC 7/16" rocker studs

have you used one of the push-rod length checker tools?

they might be a good cross check, before you order the push-rods.
it would take a bit more time but it would be cheaper in the long term.
to be sure you got it right than it would be to try to return push-rods
remember the tool works when the lifters on the cams base circle
(yes as simple as they are (PICTURE ABOVE) too use they tend to be rather accurate)
yes I use BOTH the push rod checker tools to get the quick check on length, and the adjustable length push-rods and a marker too method verify the correct length with a cross check by looking at the wear/sweep and location, on the valve tip
Proform Pushrod Length Checkers 66789 SBC 3/8" rocker studs

Proform Pushrod Length Checkers 66790 SBC 7/16" rocker studs

heres a bit of useful related push rod length info (POSTED HERE) youll want to select the correct set or SETS for your shop

Big Block Chevy, Standard Length Big Block Intake 3/8" / .080" 8.275"
295-7941-8 Big Block Chevy, Standard Length Big Block Exhaust 3/8" / .080" 9.250"
295-7969-8 Big Block Chevy, Standard Big Block +.100" Long Intake 3/8" / .080" 8.375"
295-7979-8 Big Block Chevy, Standard Big Block +.100" Long Exhaust 3/8" / .080" 9.350"
295-7951-8 Big Block Chevy, Standard Length Big Block Tall Deck Intake 3/8" / .080" 8.675"
295-7961-8 Big Block Chevy, Standard Length Big Block Tall Deck Exhaust 3/8" / .080" 9.650"
295-7800 V8 396-454 Retro Fit Pushrod Set, Intake & Exhaust, 1965-Present
3/8" / .080"
3/8" / .080" 7.725 Int.
8.675 Exh

295-7913-16 Small Block Chevy, Standard Length Small Block Chevy 3/8" / .080" 7.800"
295-7984-16 Small Block Chevy, +.100" Long 3/8" / .080" 7.900"
295-7934-16 Big Block Ford, Standard Length Ford `72-'78 429-460 3/8" / .080" 8.550"
295-7951-16 Big Block Ford, Standard Length Ford `69-'71 429-460 3/8" / .080" 8.675"
295-7582-16 Oldsmobile, Std Length 455 5/16" 9.550"
Last edited:
So, will measuring lift at the valve and subtracting for the rocker ratio while graphing the results get me close enough to get an idea what cam is in the motor and if it's advanced or retarded. It runs well and pulls strong to at least 5000 rpm I've never turned it faster. More than anything I don't like not knowing and it seems like knowing the cam specs not guessing will help me dial in carb when I get to that point. But all this also makes me think I might just want to pull the front cover and take a look and while I'm doing that degree the cam and replace the timing chain, having no idea the brand, condition or any of that good stuff.

And really thank you guys for the time and help! Merry Christmas Eve!


The Grumpy Grease Monkey mechanical engineer.
Staff member
if you plan on graphing the lift vs cam lobe rotation per degree of rotation, you can safely ignore, totally the lifter seat being held up on a running engine, when your using a lifter and push rod too move, and verify a dial indicator reading, (keep in mind the cam rotates at 1/2 the crank rotation speed.)
when checking the cam lobe lift and the cam rotates it compresses the lifter seat as the lobe acceleration ramp, or start of the lifter movement upwards in its lifter bore occurs.
this is how the oil is forced up the push rod to cool the rocker and valve springs and at low rotational rpm's the push-rod lifter seat bottoms out in the lifter well before max lift on the push-rod even gets close,
thus theres a minor delay in the lifter movement as the engine oil is forced up the push rod as the cam lobe rotates under the lifter base but this has very little effect on duration and almost zero on total lift.