Lunati small block small base circle cam

[doc396]

Back in 2002 I was putting together a street/strip 327 engine. Long story short, another project came up and 327 went on hold. Now retired I thought I would get back to it. Back then I went through the Jeg's catalog and picked out what was termed a Saturday Night Special. upon assembling the engine I found the lifters dropped to far into the block, and all the valve train geometry was way off. It was listed as a flat tappet solid lifter cam, and appears to be. double checked catalog and only one lifter number listed for chevy small block. Went back to Jegs and told them the problem. They contacted Lunati on the phone while I was there and said that was the correct lifter number. So its just been setting in engine bag on stand since then. Now today with internet I have found that this is a small base circle cam, which nobody seemed to know about back then or at least Me. Has anyone ever used one of these cams and if so what lifter is needed? I already have new lifters and valve train, thinking about replacing with a Lunati Z/28 copy cam and chock it up to lesson learned. Dennis davis

 

[Don Jacks]

I had one in my 408 sb.The lifters were also Lunati.There's no difference as far as lifters go but you will need longer push rods.

 

[doc396]

I am trying to remember, I bought a tool to gauge push rod length and it was something longer than they had a listing for? Also just looking at how far the lifter drops into lifter bore scares me. To much of the lifter is below the bore and oil hole is way off.

 

[scott hall]

You’ll be fine. Used one back in the 80’s. Sounded and run good in a 283 in a 60 Imp 4-speed. Get the correct push rods.

 

[Don Jacks]

The good thing is what's in there now[push rods excluded] is likely of better quality than the new stuff,especially the lifters.

 

[Greg Reimer]

This isn't an unusual situation, neither is it hard to fix. On a small block Chevrolet, valve lift is drastically affected by either too short or too long of a pushrod. You didn't say which rocker arms you planned on using. Install your cam where the degree card says to, install your lifters,push rods, and rocker arms, set up a dial indicator on the valve retainer, adjust the lash accordingly, then rotate the engine through a couple revolutions and note the actual lift at the valve. If the lift is short at the valve, use a longer push rod and repeat the process. If the lift is too high, substitute a shorter push rod and check again. They have adjustable test push rods available for just this purpose of determining proper valve train geometry. In NHRA Stock Eliminator, the maximum allowed valve lift is the OEM spec. Push rods are available for the SBC in increments of OEM length, and in increments of either .050" longer or shorter up to about .300" total. It's not unusual to need different length push rods between intakes and exhausts. In Stock Eliminator, there are minimum deck height specs, it's often necessary to deck a block as much as .050" to get the spec to near the minimum. This adds compression, also, when we CC the combustion chambers, it's often necessary to deck the heads a bunch-sometimes .060-080" to arrive at near the minimum spec. That can make a pushrod as much as .125-.140" too long. You didn't say if your block has been decked, or the heads, but all that has to be taken into account. If the heads were installed and the deck surfaces were already set up, it would be only necessary to establish the proper push rod length, install them, adjust your valves, pre lube everything, fire and warm the engine and then recheck your lash. There is quite a bit of lift and a little duration to be gained by doing all this. Having the tip of the rocker arm properly contacting the tip of the valve stem as close to the center of the stem is the desired goal here. That results in lessening the friction in the valve train, enhancing its longevity as well. There's a lot of little things like this that can really add up in a hurry.

 

[doc396]

Greg Reimer, that's a lot of valuable information and thank you. Here is my situation, I have stock deck and head heights (no milling) along with stock head gasket, I did have screw in studs and guides installed when machine shop did valve job. Even with my adjuster nut bottomed out the valve is barely opened on high side of cam. With the adjuster in the middle of stud threads the gap on low side is very high, 'at least' 1/4 inch (.250). When I go to Lunati web page and book back when I was installing this cam, nothing is even close to long enough. With all that being said, I don't understand why they would sell a cam and not have the correct push rods for a stock chevy small block, knowing they would be required.

 

[Don Jacks]

Because one size does not apply when any thing has been changed.On those old blocks the deck alone can be off as much as .020,same with the thickness of the heads.It's called Production Tolerances.That's why there are tools made to measure the length of the push rod.

 

[Greg Reimer]

Many moons ago,I had a '66 Bel Air 2 door post Stock Eliminator car.It was an old race car from the '70's,but by the late '80's it wasn't even close. I got a 283 standard bore bare block and a set of pistons,decided to build a fresh short block, so after practically sterilizing the block, I had it line honed and bored and honed for my pistons. I didn't deck it the first time to the machine shop,I wanted to mock assemble the short block and measure the deck heights so I could have it machined the way I needed it to be. One deck was parallel and flat with a uniform deck height at true TDC of.050" measured on all four corners of the deck surface, from to rear was consistent. Too much deck height, to be sure, but consistent. The other side was .050" at the front, but the outer side of the deck at the rear was .050", and the inner side, the side closest to the lifter valley, was .025". That meant that during its service life, the right head was twisted .025" on the inner deck surface. They take still warm block castings right out of the foundary,line bore them and bore the cam tunnel, then the block sets in a jig where the deck surfaces are milled, the front and rear faces of the block are surfaced, the cylinders are bored and honed, the oil holes are all drilled, the lifter bores are finished, and all necessary block plugs are installed. After the block cools off, the engine is assembled, started up the first time and run, all that stuff starts to change as the casting shifts and the initial stresses in it relax somewhat.as time progresses, and the car or truck accummulates hours of use and time, the castings quit moving around and assume a final dimension. Even sitting for a month or so from the time that the block and heads were cast until the point of final assembly can stabilize them somewhat. That is why you never buy a brand new block and use it as a precision race car power plant. When I built one of several 68 Chevelles for Stock Eliminator in the 1990's, I pulled a 2 barrel 307 out of one of the cars and noticed that the cast date on the block was around May 12, 1967. The date stamped on the block in front of the right head was around May 15,'67. Don't tell me that was a real seasoned piece! A car engine has got to be one of the most forgiving devices ever made by man. Several percent of them run, and run quite well and they are really no where near right. That's why stuff like short and long push rods and oversize and undersize bearings and all kinds of things like that are on the market. You might try getting an adjustable push rod, not for use in running the engine, but to use as a measuring device to arrive at the correct length push rod. Best wishes on your project! Keep in touch so we can hear how this all evolves.

 

[Greg Reimer]

An older stock racer showed me a trick for determining push rod length using ordinary materials. He used a strip of paper cut from an ordinary brown bag from a grocery store-the brown paper ones, not the plastic. The strip was about 3/4" wide by about three inches long. He would back off the rocker a bit, place the strip between the rocker arm tip, and the tip of the valve stem, then zero lash the rocker with the paper in place. He then would rotate the crank two revolutions in order to open and close the valve completely once. He then would take out the paper and examine the imprint left on the paper. A C shaped imprint on the tip of the valve stem farther away from the push rod end would indicate a push rod that is too long, pushing on the valve stem at an angle. A C shaped imprint caused by contact closest to the rocker stud would indicate too short of a push rod. An oval shaped imprint on the paper strip right in the center of the valve stem indicates correct valve train geometry. Simple, but an effective way to check for proper push rod, rocker arm and valve stem contact.I long have suspected that the extreme valve guide wear noted on some Chevy small blocks could have been from misaligned valve train parts, since forces on the tip of the valve stem would tend to shove it sideways as it cycles through its operation. Roller rockers would be a good thing here with some configurations of engine modifications.

 

[Greg Reimer]

Greg Reimer, that's a lot of valuable information and thank you. Here is my situation, I have stock deck and head heights (no milling) along with stock head gasket, I did have screw in studs and guides installed when machine shop did valve job. Even with my adjuster nut bottomed out the valve is barely opened on high side of cam. With the adjuster in the middle of stud threads the gap on low side is very high, 'at least' 1/4 inch (.250). When I go to Lunati web page and book back when I was installing this cam, nothing is even close to long enough. With all that being said, I don't understand why they would sell a cam and not have the correct push rods for a stock chevy small block, knowing they would be required.

Sometimes, the cam bearing journal overall diameter isn't that awfully big. Using a cam billet with the OEM cam bearing diameter and grinding a cam with the desired lift might result in a camshaft with the lobes being taller than the cam bearing journal's overall diameter. If that was the case, how would you ever install the cam? That would necessitate reducing the diameter of the base circle of the cam lobe so that the taller lobe could be added without it exceeding the cam bearing diameter. A smaller base circle would drop the lifters a bit deeper into the block, facilitating the need for longer pushrods to get the valve train geometry back where it belongs. Push rods are available for the SBC in increments of .050" or so either long or short. It would help if a footnote was included in the camshaft instructions that oversize or undersize push rods might be required. They couldn't just include a set with the cam because they would have no idea what your deck height is, how much the heads have been surfaced, the depth of the valves in the heads, and if the valves have been fly cut, thereby making the valve heads thinner.Lots of variables here.

 

[Greg Reimer]

In the world of NHRA Stock Eliminator, the original concept was that cars had to retain the OEM configuration of the engine and the car's drivetrain. Now. How many of you remember the days of 409's running in A/S ? How much driveline destruction do you remember? A whole cottage industry of aftermarket parts came out to try and beef stuff up without going outside the rules. Even then, the tech guys looking at the cars either before a race or afterwards might not know what they are looking at and would choose to fail a contestant based on faulty knowledge on his part. It used to be that camshafts had to be OEM or factory replaced cams that were approved.Valves had to be OEM, as were valve springs. Push rods, rocker arms, all that had to be exact OEM, as were pistons, ring configurations, rods and cranks and heads. Same with intakes and carburetors. Many cars were rendered practically obsolete when newer model cars came out with better intakes, heads,cams,and carburetors while retaining the same factory rated horsepower. 4 barrel 283's from '57 to '61 had smaller carbs, smaller cams, heads with smaller ports and lower compression, and all kinds of early production idiosyncrasies that were vastly improved by the time the 65-66 283/220 horse engine was reintroduced. One area of improvement came with valve train technology. Valve spring tension was limited to an OEM figure. A valve spring tester was a mandatory addition to any engine builder's shop. That rule was changed. Also, valve material changed from OEM 2 piece valves to stainless one piece. Retainers and locks could be machined steel rather than the OEM material, and cylinder head science took off right along with all that. It used to be that some racers with means and accessibility to a flow bench would gather about 20 to 50 head cores, grab a legal pair of valves, then flow bench all those heads with the same valves and note the results. 2 or more heads would outflow the rest, so those were the best pair of heads for his best engine. He might keep a few pair of heads that were closest to the best, the rest got sold off. Same thing with intake manifolds. The best OEM intake legal on 283's seemed to come from 327 250 horse engines. Later on, the 300 horse 327 intake got added as a legal replacement. You should have seen the improvement! The best two or three of those got retained for use, the rest got sold or scrapped. The NHRA classification guide and engine spec guides had all the listings for the legally accepted heads and intakes, sometimes that was a real advantage if an accepted part was better than the actual OEM part. Some engine blocks were superior than others because some were thicker and stronger than some of the thin stuff that came out later. Same with rods. Steel cranks were usually pretty good, but since steel is heavier than cast iron, some people have utilized cast cranks claiming the lighter weight gives them an advantage. Rules changes come along and it's necessary to review them constantly, some of them actually are an advantage. The summation of all this is simply that in the world of mass production, some parts will always be a bit better than others, and the game plan is to assemble motors with the best parts you can find as you go along. Modifications that optimize the outcome without compromising the whole concept is the balance we try to achieve. Careful attention to detail and being aware of the options available, in this case, the availability of longer push rods to compensate for the cam with the smaller base circle is but one good example of this. Best wishes for the success of your engine build!!!

 

[Greg Reimer]

Another thing that can matter a lot is which casting you get when determining an engine block. My machinist, a racer with a shop behind his house, and a first rate operation at that, located in Vista,97 miles away, had a customer drop off a 350 block for one of his Super Stock engine builds, and the block had the words Hecho en Mexico cast into it. A little skeptically, the engine guy sonic checked it, and it came out as being quite thick. Apparently the foundary down there didn't use the same thin wall casting techniques as the foundries up here that GM uses on domestically produced engines. He did the whole Super Stock treatment to it, assembled it, the customer put it in and raced it, and the result was one of the fastest Super Stock motors he ever built. The cam and the heads weren't that overwhelmingly great, but the block supported the cylinder walls very well and ring seal seemed to be the factor here. I bought a 327 large journal engine about 15 years ago, and the block appeared to have about zero core shift. The lifter bores all looked like they were centered on the lifter bosses, and the camshaft bearing bores looked centered in the cam bearing support area. We had it sonic tested and it came back spot on. I bought pistons, rods,rings and bearings and ran it down to this builder for him to line hone, bore and finish hone, and deck the block. When I picked it up, the machinist, also a Stock and Super Stock racer himself,told me that if I ever wanted to sell that block, he wanted it. He really liked it because the tolerances were so exact. Now, the accepted blocks are Dart castings or Bow Tie blocks which are deliberately made thicker and beefy just for motorsports. As this sport evolves, the vast improvements in horsepower, ET and MPH definitely reflect the advances in technology.

 

[Greg Reimer]

This is getting a bit away from the original topic, with this addition to this discussion I'll stop, but, as with the small block and the Mark lV engine families, there were optimum blocks and other less desirable blocks that you would be wise to stay away from. What is the preferred,best,and optimal casting number 348 and 409 blocks? I used to find 340 horse engines when I first was doing the 409 thing in the mid 1970's,they seemed to be a bit nicer castings than the the earlier blocks, but what would be the optimal casting number to look for while in search of a W motor block to build? Enough time has passed since then that probably a lot of 409 people have certain numbered blocks they prefer while looking for an optimal piece to start with. Any advice?

 

[doc396]

Greg thanks for all your info and help. I just thought of something that looked off but I didn't realize till now. I had the machine shop install screw in studs and guides for the push rods. They did drill out the original guides made in the heads, but I am not sure they machined the boss down enough were the stud and guide screw in head. I am going to pull a old set of heads I have and compare the rocker stud boss.

 

[Greg Reimer]

Usually, screw in studs are longer than OEM replacements in order to facilitate longer adjustment nuts for roller rockers. They might not be too tall, also they allow for the additional thickness of push rod guide plates. Your other set of heads for comparison purposes might not match your good heads you are building in the first place and that might not give you consistent accurate comparisons. On both my 250 horse 327's and my 275 horse Stock Eliminator motors, they all have screw in rocker studs and they can mount OEM stock valve covers without interference with the rockers or the extended poly-locks.