What to ask when selecting a rotating assembly

Words: Cindy Bullion

Ask any engine builder their choice for the best combination of rotating parts when building an engine and you will get a wide range of responses. After all, there are a huge number of component choices. Often, the builder’s own personal experiences, along with which parts provide the best profit for them (remember, those guys need to make money too!), will dramatically affect their answers.

If there is one consistent answer across the board, however, it is “matched” systems deliver greater longevity and better performance than selecting individual pieces that may not be completely compatible. In their quest to improve customer service and boost performance, manufacturers of aftermarket performance auto parts have made it much easier to purchase the required parts and ensure nothing is left out of the equation.

So, the question remains; how do you pick the right “system” for your engine build? To get some answers, we spoke with Lunati’s Kirk Peters and Justin Bowers to get some insight into the questions that should be asked when shopping for a rotating assembly. Though they speak about Lunati’s products, most manufacturers have different levels of offerings, so the questions should still be asked regardless of manufacturer. Here are their Top 5:

What is your budget and is that realistic?

Lunati’s Signature Series and I-beam rods are designed with the all-out drag race car in mind. Cars with power adders such as blowers, superchargers, turbochargers, and nitrous especially need added strength in the bottom end.

Bowers: Lunati’s rotating assemblies, which include a crankshaft, rods, pistons, pins, rings, and bearings, range in price from around $2,500 to $4,900. This is the best option when building an engine, since each part has been selected and tuned to achieve a certain amount of power. For this price range, they are getting a heck of a lot of technology along with parts that deliver excellent quality.

Peters: In addition, upgrading only one item in a matched system can deliver a false sense of reality, and a letdown in terms of performance expectation.

What is the desired horsepower expected from your engine?

Peters: Someone building a 550-hp versus 1,300-hp engine is going to have different requirements. In the first case, a Lunati Voodoo assembly rated for up to 1,000 hp would suffice, while the recommendation for the latter is a step up to the premium Signature Series assembly rated for 1,500+ hp. The Voodoo assembly is a great choice for street/strip applications where higher-than-OEM durability and strength is needed, but other engine upgrades have been limited so the car is still streetable. The Voodoo assembly with 4.00-inch stroke for LS engines is Lunati’s biggest seller and a hit among drag racers.

Bowers: The 4340 non-twist forged Voodoo crankshaft is nitride heat-treated and features micro-polished journals with lightening holes to reduce weight for faster acceleration. It’s packaged with Lunati’s H-beam rods — also made from forged 4340 steel — ICON forged pistons, pins, and rings, and King or Clevite premium engine bearings.

Will you be using power adders?

Lunati’s Signature Series crankshaft features gun-drilled mains, lightened and micro-polished rod journals, and windage-reducing, contoured wing counterweights.

Peters: Power adders such as blowers, superchargers, turbochargers, and nitrous put additional stress on an engine’s bottom-end, making a durable rotating assembly essential.

Bowers: Both the Voodoo and Signature Series cranks are forged 4340 steel, but the Signature Series features a beefier forging that is designed to withstand the extra demands. The Signature Series crankshaft features gun-drilled mains, lightened and micro-polished rod journals, and windage-reducing, contoured-wing counterweights. It is also pulsed-plasma nitride heat-treated for even more strength to hold up in all-out racing applications. Included in the Signature Series assembly are premium Diamond or Mahle brand forged pistons, pins, and rings, premium King or Clevite engine bearings, and your choice of Lunati’s H-beam or I-beam rods. The difference between the offered rods is primarily that the I-beam version is CNC-machined and undergoes additional testing for impurities and defects.

What is your application?

Peters: Different types of racing require different components, lightweight versus standard weight. Though all racers look to reduce weight in favor of faster ETs, going the lightweight route in drag racing can be tricky. You could be walking the line between more power to get you down the track and too much power for the bottom end to support.

Bowers: Lunati’s new Voodoo Lightweight Crankshafts, which can be custom-packaged into a balanced assembly, could be a viable option for some heads-up, naturally aspirated classes and bracket racers. Obviously, budget and horsepower requirements will affect that decision.

Are all the parts matched at the same horsepower?

Peters: It is not a good idea to upgrade the bottom end one component at a time. Likewise, they say mismatching components in terms of their horsepower rating, can not only affect performance, but hurt the pocket book down the road. As an example of that concept, we have seen folks use a cast crankshaft upgrade with a set of steel H-beam rods. That would only give you the lesser horsepower rating that matches the crankshaft, not the rods.

Bowers: One thing I could see being an issue is if a guy purchases a good crank then goes cheap on rods and pistons. Well, then he breaks a set of $100 rods and takes out a $1,000 crankshaft. I would suggest it’s better to save up and purchase matching parts.

Source: Lunati, LLC, lunatipower.com