Hot Rod Forum banner

1 - 20 of 22 Posts

·
Registered
Joined
·
6 Posts
Discussion Starter #1
im 17 building my first motor im in canada dont wanna order wrong from states, i dont know alot please help best you can
79 k20 truck motor (3970010).41 gasket, stock deck height??? original heads are 462624, i got 68 vette heads 3917291 that are milled .30 thou and im wondering how big can i go before i hit the piston(flat top with semi circles?), will my intake ports line up aswell????
 

·
Registered
Joined
·
261 Posts
where are you in Canada? You can put a bigger cam in that engine than it can use with either of those (lousey) heads. If you are looking for mid 300 HP we can get you there. If the engine has never been decked chances are you can use shim head gaskets with cast iron heads and have better results. Are you using a solid flat tappet cam or either type of roller. If for any crazy reason you decide to use a hydraulic flat tappet cam then keep it small to give it a better chance to survive.
Details? what intake, fuel management and headers are you using?
 

·
Registered
Joined
·
6 Posts
Discussion Starter #3
I'm doing it for nesatalga I have another 350 I'm taking slow and I'm trading a trans I have no use for that also broken for a set of vortec heads, that's another time....theres been zero engine work done I got it from my neighbor it's been a legit farm truck its whole life.... engine not going back in this truck so I dont need to here that's stoopid engine for vehicle.

Edlebrock 2101
Getting used long tubes tmr dont know brand 2.5 collector
Comp cams k12-206-2 kit
And them vette heads(gonna do light port n polish)
New rings
New cam bearings
No carb or distributor yet
 

·
Registered
Joined
·
261 Posts
well the 2101 is nothing special. Vettes came with lots of head options, none of which are much good. The vortec heads are the best heads GM made. They can get you into the 400 hp range. Where do you want the power band? I dont care if you put the engine in an airplane or boat. It is a bad choice for an airplane imo. You did not mention the "Type" of camshaft you want?
 

·
Registered
Joined
·
1,016 Posts
Wait before you buy it. You will probably get a better cam suggestion. Depending on what heads and everything else you're using.
 

·
Registered
Joined
·
6 Posts
Discussion Starter #8
I listed my build I'm not building a race car guys like seriously answer the question VALVE TO PSITON CLEARANCE, I Have read the biggest cam you can toss in a small block with zero issues has .47x amount of lift so take that lift minus my .30 from my milled heads and theoretically my .440 cam should clear the milled heads correct????
 

·
Registered
Joined
·
261 Posts
this .440 lift max is rediculous. Ive used .6 lift roller cams with no ptv issues and used a .570 lift cam that was too close. Depends on duration and usually icl. The .570 lift I used fit easily after retarding the cam 4º. If you use that .44 lift flat cam ir should fit with acres of room. Doesnt take long to check. You should make 280 + hp,,,
 

·
Registered
Joined
·
1,679 Posts
I listed my build I'm not building a race car guys like seriously answer the question VALVE TO PSITON CLEARANCE, I Have read the biggest cam you can toss in a small block with zero issues has .47x amount of lift so take that lift minus my .30 from my milled heads and theoretically my .440 cam should clear the milled heads correct????
If you're not willing to consider all the variables that affect valve to piston clearance , then no correct answer is available , especially if you want to believe everything you've " heard" . you are asking for free information without providing adequate data , that makes it impossible to provide an accurate answer . Why the attitude ??
 

·
Registered
Joined
·
183 Posts
Ever set of pistons will be different .
Flat tops with "eye brow" valve cut outs come with different sized cuts, same with pistons with d shaped valve cut outs.
Example. My 355 (350 chevy 30 over bore) has LT1type (1970) trw forged pistons, They have the "eye brow" valve releifs cut into the piston, and they are flat tops, My heads are not milled, And the .501 lift 292 cam had more than enough piston to valve clearance after I degree'd in the cam with a degree wheel.

NO MATTER WHAT ANYONE SAYS.
degree the cam of your choice in the block, put modeling clay on the top of the piston, covering the valve cut outs and 1/4" thick above the piston top, put a little oil on the clay part that the valve will hit,(so the clay doesn't stick to the valves with the head gaskets you are going to use, bolt the head down, don't have to torque it , just tight, with a solid lifter in the lifter bore of cyl #1 first the intake and then the exhaust, rocker arm snug, turn the engine by hand if it stops turning don't force it, the clay wont stop it from turning. so if it stops, you stop, and pull the head and check to see if the valve went through the clay to the piston. If it turned fine, do the same to the exhaust for cyl #1.
After you have done this for the intake and exhaust, pull the head and measure the clay where the valve hit it, the thickness of the clay where the valve hit it, to piston top, is your clearance. If the clay is really thin, you will need to use better measuring, but for most mild street engines the clay test will be fine , Mine had 1/16" thickness or more.
This is the DIY method for the guy without all the fancy tools. And back when I built that engine I did not have the fancy tools.
Most times with a cam with ..500 lift, you are fine. but clay is cheap, pistons and valves are not.

The engine I did this too,30 odd years ago. was a 11 to 1 flat top piston(claimed, more like 10.3 to 1 ), and 68cc chamber heads (brodix track 1) and comp magnum 292 hyd flat tappet cam. cam and heads are outdated by todays standards. And both a little on the big side for a 11 to 1 compression street engine. It had quite good power from off idle to 3200 rpm, then at 3500rpm it was like you hit a light switch and it was on like donkey kong. heads,cam, single plane intake were all to big for the cars use 90% of the time. Shoot for an honest 300-350hp and you'll be very happy.
After you get thevehicle to put that 300hp to the ground, you can then worry about (in my tim the tool man voice )MORE POWER..
Or just do like redgreen, add more duct tape. o/p is from canada, he should know who redgreen is.
 

·
Registered
Joined
·
261 Posts
2old. Ill share my experience with a "mechanic".
My nephew is a mechanic, he can do brake jobs and trouble shoot factory issues and he's quite good at it,,,and fast. He wanted to choose a cam for his son's 4x4. He can put it in but has zero concept as to why we should alter cam timing specs from stock as the manufacturers are like gods to mechanics...lol. He refused to upgrade to a roller and used a set of heads from another engine without "blue printing" them as they were fine when on the other engine. The truck runs ok( could be better), has not done a performance tune as the factory tune is all he understands. He has not tuned the carb as out of the box it should be fine in his opinion. He lives out of town so my grand nephew has to wait until I get a chance to teach him what to do in the spring. Dad thinks the truck is just fine as it is,,, etc
 

·
Registered
Joined
·
13,764 Posts
The piston on a stock unmolested block is .025 inch below the gasket, your gasket selection is .041 providing a spacious .061 inch between the mating surfaces.

Piston to valve clearance is an issue through the overlap period where the piston is approaching, at, and leaving TDC while the valves are still open. The piston when the cam is at max lift is nowhere close to the valves. Valve lift does not become a problem unless there is a long duration cam combined with a lot of lift to where the valves are substantially off their seat through the TDC cycle. The Gen II LT4 HOT cam uses 1.6 rockers to achieve .525 inch lift on production pistons, deck clearance, and head gasket.

The big issue with performance engines is when operated close to redline is the valve float may occur. When this happens around the TDC event a valve hanging open due to spring misbehavior might get whacked. So this gets to be a situation where static measures of valve to piston clearance are not very meaningful pieces of information. Therefore having and knowing that you have sufficient static clearance does not mean that there will be no impact.

I’m bringing this detail out so you can see what is going on dynamically and can appreciate that measured clearance in the shop does not necessarily mean your safe from piston and valve collisions.

In general using the the clay or thick solder method of these materials being positioned on the piston with the test assembled engine being hand cranked around to see if upon top end head removal what if any are the thicknesses of the crush marks left by the valves the accepted minimums are .080 inch for the intake valve and .100 inch for the exhaust side. These being based on the exhaust running much hotter than the intake thusly expanding more. Some builders will take these clearances to .060 inch intake and .080 inch exhaust.

Be aware that this is a real PIA process as the at least one assembled head as it will be in the finish build and it’s complete valve train for at least one cylinder needs to be installed with your measuring material on a piston. Then the crank assembly rotated in its normal clockwise direction when looking from the front. Then disassembled to get at the checking medium to measure whatever crush imprint is left. Sometimes you have to do this more than once to get a good measurement.

Keep in mind that if you‘re using an oversized intake especially or offset valve guides that the edges of the relief cut in the piston need to be checked to insure there is sufficient depth at the ends of the relief slot, not just in the center.

Bogie
 

·
Hates: Liver. Loves: Diesel
Joined
·
5,767 Posts
I listed my build I'm not building a race car guys like seriously answer the question VALVE TO PSITON CLEARANCE, I Have read the biggest cam you can toss in a small block with zero issues has .47x amount of lift so take that lift minus my .30 from my milled heads and theoretically my .440 cam should clear the milled heads correct????
Long story short, that is not correct.

Valve lift and deck heights (or whether or not they have been milled) has almost zero impact on valve-piston clearance. The valves operate completely differently from the pistons. I have seen SBCs with .700 valve lift and milled heads AND decks. The important part is not how far the valve opens, but when the valves open and close.

If you think about it, the valve is at peak lift when the piston is about halfway down the cylinder. The real answer is incredibly complex and you can't really guess. Will the valve be closed far enough when the piston comes back up? Hard to guess.... but head decks, head gaskets, and block decks have little to do with it. If the valves were at peak lift when the piston is at TDC, your math would be valid. Since that never happens, it's not a factor.

The real answer is that you have a generous buffer. There are a lot of cams that you can stuff in a stock assembly and know that they'll be fine. If all else fails, you can post here and chances are there are 30 people who have tried your exact combination. I personally had a 383 with 64cc heads and pistons 0.025 out of the hole for an ethanol build and a similar cam, and I had no issues with valve-piston clearance with .553" lift. The reason is, the peak lift happens when the pistons are about half way in its travel. It's more important WHEN they open and close.

The only way to be sure is to assemble it and check.
 

·
Registered
Joined
·
3,611 Posts
the 291 heads also have the valves closer to the deck, so you need to subtract that off the 0.440 lift too.
and the 291 valves are probably 2.02 rather than 1.94 so you have to be concerned with the diameter of the valve hitting the edge of the valve relief (semi circles).
First, locate a good algebra book.....
 

·
Registered
Joined
·
6 Posts
Discussion Starter #18
this .440 lift max is rediculous. Ive used .6 lift roller cams with no ptv issues and used a .570 lift cam that was too close. Depends on duration and usually icl. The .570 lift I used fit easily after retarding the cam 4º. If you use that .44 lift flat cam ir should fit with acres of room. Doesnt take long to check. You should make 280 + hp,,,
How am I spossed to check with only the stock cam available when I dont knwo specs of it either
If you're not willing to consider all the variables that affect valve to piston clearance , then no correct answer is available , especially if you want to believe everything you've " heard" . you are asking for free information without providing adequate data , that makes it impossible to provide an accurate answer . Why the attitude ??
It's
 

·
Registered
Joined
·
6 Posts
Discussion Starter #19
Good day at the shop down to a bare block now tin for clean n then rebuild....I'm not very experienced so thank you for the good explanation, it made a bit more sense as my one buddie says the sorta the same thing he just says watch duration not the lift but I dont get it.... or how do I time the came ti open when the piston is down n closed when the pistons up??
 

·
Rod...from a Chrysler?
Joined
·
5,176 Posts
You need to get on YouTube for some learnin'.
Watch a bunch of videos and read up. All kinds of basic engine operation videos and articles out there.


 
1 - 20 of 22 Posts
Top