Valvetrain development enriched with an interesting historical perspective and carburetor tuning highlighted the morning session of the final day at the Advanced Engineering Technology Conference held in Indianapolis. Dan Jesel, founder of Jesel Valvetrain Innovation, spoke on “Tomorrow’s Valvetrain Trends and The Latest Advancements for Performance” followed by Laura Shehan and Johns Sams of Holley Performance Products talking about “How To Setup and Tune Race Carburetors for Optimal Performance.”

Dan Jesel of Jesel Valvetrain Innovations.

Like many veteran racers, Jesel started developing products because nothing was available to fix problems he was encountering on the track. Suffering valve-guide woes, he started by adapting big-block rockers to a small-block head, a move that required relocating the studs.

“I didn’t want to move studs all my life,” quips Jesel. “I made a stand that bolted to the original holes, and then I could move the shaft back.”

The longer pivot length on the rocker made it easier for the valvetrain to cycle at the same spring rate, but he wanted more options. Jesel then developed shaft rockers around 1980 that enabled higher ratios, provided a secure base for offset rocker arms and offered better spring clearance.

In explaining the strategy behind his ball adjusters, Jesel says, “The normal cup adjusters have a 5/16-inch ball, and our ball adjuster is a .280 ball. They ask, ‘why did you go to such a small diameter?’ I had a Pro Mod customer asking for a 3/8 ball and he burned all the pushrods up on the dyno before the race. What happened was the surface speed with the larger diameter. I’ve stuck with the .280 and it’s worked out very well.”

Pro Stock always generates interesting stories, and Jesel’s experience provides a great anecdote!

“When Pro Stock started turning over 10,000 rpm consistently and they started using oil that looked like water, they were burning pushrod tips. They had hardly any oil pressure at idle. I spent close to a year with as many materials I could think of, coatings, finishes…I could never fix it. I knew it was surface speed and friction and they were welding. I took a piece of our lifter bushing material. I got a burnt pushrod, cut it off, machined up a plug, put it in a lathe, and then put it on the Spintron, and that was it.”

Jesel demonstrated the growth of pushrods, starting with 3/8-inch diameter models.

Getting the bends

“When I bent a case-hardened Chevy pushrod, it stayed bent. I knew I had bent it,” he says. “When people started using 3/8 and up, they bend, but you don’t know ’cause they’re not case hardened. Every time I tried to get people to try the heavier pushrod, the engines didn’t run as well, because it changed the cam profile so much.”

Jesel continued with a story of a Pro Stock racer who stepped up to a larger pushrod and didn’t run very well, so he went back to a pushrod that flexed the old-fashioned way.

“It took him a year to realize that he had to shorten the cam down to get it to run right,” says Jesel, noting that episodes like this often get engine builders to run away from a similar proactive solutions because there may be a step backward due to another part of the engine being adversely affected.

“I know why it’s been so long to get where we’re at,” he says, noting that exhaust pushrods now go up to 3/4-inch for some Pro Mod engines. “The problem is, you change one thing and doesn’t work, you run away and tell everyone how bad it is.”

Jesel touched on the development of offset rockers and lifters to improve valvetrain geometry and allow head porters more room to open up the heads. But valve springs have a special place in Jesel’s career.

“Valve springs broke my heart because I’d spent a lot of time on the Spintron trying everything known to mankind…rev kits, pushrods, rocker arms, cam profiles, you name it and pick up a little here and there,” he says. “Then we put in a spring and it picks up a 1,000 rpm.”

Spring pressure changes starting in the late ’60s had around 450 pounds open running just over one-half-inch lift. Now that valve lifts are over 1.1-inch, spring pressures are closing in on 1,400 pounds.

Spring loads quickly outpaced lifter capacity, and Jesel says it took him eight years to develop a suitable 1.062-inch lifter that required offset boring the block. Other advances include keyway lifters and other improved components. Now Jesel offers an 1.220 cartridge lifter and bushing assembly.

As pushrod, lifter, rocker and spring improvements were made, the camshaft had to be addressed to provide the necessary lift.

Johns Sams and Laura Shehan of Holley Performance Products.

“The only reason I started looking at camshafts was lifter location, and then as lifts got higher the base circles got smaller,” recalls Jesel.

When smaller base circles were no longer an option, block designers had to raise the cam location and increase the core size up to 82mm to keep up with the escalating lifts. Except for Top Fuel.

“One of my pet peeves is Top Fuel. We’re so restricted in such a wide-open class. That’s their deal, 54mm,” he sighs, noting that the improvements he’s been able to make now last about 50 to 60 runs per cam compared to 1 to 10 in earlier days.

With the advancement of custom-designed billet blocks, cam sizes have escalated tremendously and Jesel has developed split cam bearings.

“The main problem was moving the tappets without hitting the cam bearings in a situation where you couldn’t move the cam bearings like we did in a billet application,” says Jesel. “You’ll notice the lobe is even with the the top of the bearing, so the lifter doesn’t hang out.

Jesel closed out his presentation by recalling that his famous cam belt drives were developed with some Formula 1 inspiration and following the lead of a Cosworth Vega setup. He then followed up with distributor belt drives that allow larger cap diameters and moved the distributor off the top of the intake to open room for symmetrical runner lengths.

The Holley presenters first stressed proper carb selection before detailing tuning procedures. Factors include type of racing, engine size, expected rpm and induction in addition to using an off-the-shelf or modified carb. Holley says the flow designations are defined by WOT airflow of the entire carb at 20.4 inches of water for a 4V configuration. However, not every 1,250 cfm Holley is the same.

More Holley tuning tips

“Changes in the booster or venturi compared to the original 1,250 will alter wet-flow values,” says Shehan. “The current Holley 1,250 has a straight booster. Using a skirted booster to obtain desired signal strength will sacrifice some WOT airflow.”

For an off-the-shelf carb, Holley has developed calibrations based off data from testing with eight wide-band O2 sensors as well as different fuels, including oxygenated blends.

“We take the flow curve from the flowbench and make it work with the engine and make it tunable by the end user,” says Sams.

Engine tuners use a variety of factors to make carb adjustments, including reading spark plugs, recording EGT, evaluating BSFC numbers off the dyno and watch wideband sensor readings, whether individual cylinders — if so equipped — or averaging each cylinder bank.

“We use 8 wideband sensors to make sure the carb is balanced,” says Sams.

If the overall fuel curve looks good on a dyno run, then adjusting the high-speed bleed in small increments is often one of the best first steps in fine-tuning an off-the-shelf carb.

“When working with the HSB, never move more than .002-inch at a time,” warns Sams. “Once I got the curve smooth, I can add or take away fuel as needed with the jets.

“Also, a lot of people don’t realize how much the idle feed has to do with the entire curve,” he adds.

The idle circuit affects both fuel at idle in addition to the mixture available at the transfer slot. Also, the transfer slot should be visible just beneath the bottom edge of the throttle plate.

Jets should be handled with care and never strung on baling wire. Holley main metering jets are mass flowed and compared to a know standard. The jets are then sorted by flow and stamped accordingly. Since flow is determined by size of the hole and also the shape of the entry, jets should never be drilled.