Mark Duber’s BES Built NMRA Renegade Retrofit 5.8 GT500 Engine Build

Back in January we introduced you to the high-flying adrenaline junky and horsepower addict, Dr. Mark “BirdDoc” Duber, and his record setting 2013 GT500. When we last spoke with Duber he had decided to change venues and prepare his GT500 for NMRA’s Renegade racing format.

Stang TV recently had the opportunity to follow up with Duber and check on the status of his new power source to learn more about his GT500’s transformation to compete in the NMRA’s Renegade racing format.

NMRA Renegade breakdown

For those who aren’t familiar, NMRA Renegade is a heads-up class designed for single power adder small block engines in 1979 or newer Mustangs. Racers have their choice to use a single stage fogger system, dual stage plate nitrous system, 76mm turbocharger, or a specific size supercharger.

Engines are limited in camshaft valve lift and restricted to conventional-style cylinder heads, keeping horsepower ‘’in check’’ to ensure no single combination can dominate the field. Entries are required to race on stock style suspension while using a 28×10.6-inch slick or 275 drag radial tire.

Close-up view of the cylinder sleeves. These sleeves reduce displacement, but Bischoff says they add to the strength of the block.

To prepare his GT500 for a successful run in Renegade, Duber’s first order of business was to fortify the GT500’s powerplant for maximum durability and power while complying with Renegade regulations. And who better to handle the task than the five-time Amsoil Engine Master Champion who built the engine the last time with record setting results?

At the helm, once again, was Tony Bischoff of Bischoff Engine Service in St. Leon, Indiana. Bischoff says, “I’ve been in business for 30 years, since 1985. We build racing engines for Nitrous, N/A, Turbo… you name it, we build it.” With experience like that, and the reputation to match, it’s no wonder Bischoff and his 13-man crew are up to their eyeballs in work.

Inspect and Upgrade

Custom pistons from Ross reduce compression to around 9.3:1. The reduction in compression ratio is due to the change from E85 to VP C16 fuel as required by NMRA rules.

After Duber and Bischoff discussed the game plan, BES was granted temporary custody of Duber’s horsepower lovechild for its Renegade retrofit. Bischoff’s first order of business was to tear down and inspect the engine to see how it handled its first assignment, and to determine whether or not it was up to the new mission.

Bischoff estimates the block could probably endure power levels up to 2,000 hp at the flywheel-horsepower, and their estimated horsepower target for Duber’s engine is around 1,700+ hp at the flywheel.

As luck would have it, Bischoff took precautions during the first overhaul that would continue to pay-off in round two. In an effort to increase the engine’s cylinder strength and durability, Bischoff previously re-sleeved the aluminum block with slightly smaller sleeves.

This technique reduced the engine’s displacement from 358ci (5.8-liter) to 351ci (5.7-liter), trading seven cubic inches for a stronger, more durable block—an excellent characteristic that will prove to be even more important for its next life.

During the inspection, Bischoff was pleased to find the block quite healthy, and the smaller sleeves to be in excellent shape. With a bill of good health, and a displacement in compliance with the NMRA Renegade rules, the green light was given for moving forward with the original GT500 Trinity block.

Cranking up the components

The next component under scrutiny was the factory 5.8-liter forged crank. Upon inspection, Bischoff found the crank had gone from throwing pistons, to throwing in the towel. After its short exposure to 1,200+ hp, and roughly 50 runs; the crank had cracked in three separate places. Catching a problem like this, before bad turned to worse, was a huge bonus.

To correct the weakness, and raise the bar, a billet steel 5.4-liter modular Winberg crank was called in to relieve the stock 5.8 unit. The new Winberg crank features journals modeled after the robust LS engine crank, which Bischoff says added to its strength. The stock stroke, at 4.165-inches, was retained to also comply with Renegade regulations.

Left: Ferrea valves sealing the deal–valve sizes meet Renegade rules, but Bischoff wouldn't give us more than that. Right: Close-up of the combustion chambers.

Complementing the new Winberg crank are a set of custom GRP aluminum rods made specifically for the LS-style journals on the new Winberg crank. The benefits of aluminum rods are numerous, most importantly they are lighter, absorb vibration better, dissipate heat faster, and they encourage faster revving which frees up horsepower within the rotating mass of the engine. Weighing in at 576 grams, with a length of 6.640 inches, these rods are engineered to accelerate.

Putting the squeeze on the supercharged C16 air/fuel mixture are some custom Ross pistons weighing just 431 grams, with a diameter of 3.658 inches, that fill the 3.662-inch cylinder bores. Ensuring the 9.3:1 compression doesn’t escape, is a conventional ring package from Total Seal employing their advance profiling steel top ring design with Napier seconds.

The rings were gapped as follows:

  • Top: 0.022
  • Second: 0.032
  • Oil: 0.032+

Camshaft profiles and earning what you learn

In this industry, an engine’s camshaft profile is an area where engine builders typically withhold information, and rightfully so. With customizable aspects such as lift, lobe separation, and duration, a successful cam profile is earned through knowledge gained over the course of years of experimentation with numerous variations and combinations. If you’ve busted your tail and bank account to learn what works and what doesn’t, you don’t just give that stuff away!

It’s like developing the cure for Loser’s Disease and just handing it over to your opponent—it doesn’t make competitive sense. So when asked about the cam details Bischoff replied, “Yeah, that’s top secret, well, it’s not top secret but you gotta play it like it is! Heh, heh, heh…” Understanding his position there is little we can tell you about the cams in this beast.

What we can tell you is, the old cam profile had a lift of 0.490, and BES increased the lift to an undisclosed height with four new Comp Cams not to exceed the maximum allowable lift of 0.520, as governed by the Renegade rulebook.

Enjoying those proprietary cam profiles are the factory 5.8-liter GT500 Cobra Heads, sporting custom CNC ported combustion chambers modified in-house by BES. The end result was 53cc chambers flowing over 40 cfm better than stock through both the intake and exhaust. Controlling that impressive flow-rate is a complete set of Ferrea valves, including springs and retainers. Holding the rest of the engine together is a complete set of ARP fasteners.

Going with the flow: Before and After CNC porting flow results, expressed in CFM.

Going with the flow: Before and After CNC porting flow results, expressed in CFM.

Call in the reinforcements 

Kenne Bell, front and center

Up front is an insurance package in the form of billet steel primary & secondary timing chains and guides, billet steel crank sprockets, cam gears, and passenger side tensioner. To make sure the tensioner doesn’t jump ship the factory 6mm dowel pin locating the tensioner was replaced with a larger, 8mm pin—everything that could be fortified, was.

Further illustrating that claim is the custom billet hub BES used on the snout of the crank that fit within the ATI Super Damper harmonic balancer. This hub provides extra coverage to the snout of the crank by providing more support and giving it extra strength to cope with the stress that a big supercharger can add. When you’re expecting 1,300-1,400+ lb-ft of torque at the wheels, you need all the support you can get.

Shifting from E85 to C16 fuel

To prepare the engine for the shift from E85 to C16 racing fuel, the compression was dropped from 11:1, down to 9.3:1. This reduction was a multi-faceted mission to balance power with durability while maintaining a decent tuning window for the transition to C16 racing fuel.

Plus, with the addition of more boost, up from 25 to 31 psi, Bischoff felt the compression should be reduced to minimize the potential headaches that running higher cylinder pressures can create. Not one aspect of this engine build was left to chance. Capitalizing on every opportunity, Bischoff and his team at BES built a foundation Duber can count on.

The Man Behind The Curtain

With the Cobra engine back in his custody, Duber and his snake charmer, Chad Epperson of London Chassis Dyno, went to work crowning the Cobra in Kenne Bell fashion. Duber concedes, “Chad is the magic behind the whole build. And really, he’s the Crew Chief, too. He installed the motor, the new TH400 transmission, and completed all the custom fabrication and modifications needed, and he is responsible for all suspension related setup and adjustments.”

Renegade’s first year for Positive Displacement Superchargers

Holley Dominator EFI is taking the place of the factory electronics. That includes upgrading to much hotter coils for the ignition.

Destiny had a hand in Duber’s decision to go Renegade. As luck would have it, 2015 is the first year the NMRA is permitting positive displacement blowers to compete in the Renegade class with 4.7-liters being the largest allowed. Last year Duber  made the jump from a 4.2-liter Kenne Bell supercharger, to their Herculean 4.7-liter, liquid-cooled model.

Dr. Duber explained his reasoning for the shift by outlining the benefits, “Upgrading from the 4.2 to the 4.7 should make the supercharging process more efficient because the twin screws will be turning at a slower speed, reducing heat generation, but maintaining a similar amount of boost thus eliminating the additional heat generated by the smaller 4.2-liter supercharger.”

Further aiding in heat reduction is a Kenne Bell “Bigun” liquid-to-air intercooler discretely stashed away in the factory intercooler location, under the intake manifold. The intercooler upgrade increased the supercharger’s cooling capacity by 30-percent compared to the stock 2013-2014 factory intercooler.

Command and Control

Making the jump from the 4.2 to the 4.7-liter unit increased the engine’s power, in its previous form, from 1,200+ hp to 1,416 hp with no other changes. Putting power like that to the ground proved to be a challenge for the GT500. The OEM computer wasn’t up to the task of managing the kind of power levels the twin-screw 4.7-liter supercharger brought to the equation, and with a new power expectation of  1,700+ hp, changes had to be made.

Duber and Epperson looked to Holley this time around, for the command and control duties. Epperson, in association with Holley personnel, installed a Holley Dominator EFI system for fuel delivery, complemented by a Holley/Davis traction control system. The new Holley combination will help harness the power and control its delivery to the ground while enhancing crucial management capabilities necessary to create power at this level. We’ll be highlighting this install in another article soon.

Delivering  1,700+ horsepower

TH400 in position.

TH400 in position.

Duber’s next hurdle was power delivery. The Tremec Magnum six-speed transmission’s ability to cope with 1,200+ horsepower was impressive, but making the jump to the 1,400+ hp range took the tranny beyond its capabilities. So, when the plans were drawn-up for the GT500’s reincarnation, Duber and Epperson were prepared to ditch the left pedal for an automatic.

Relieving the Tremec Magnum is a JW 3-speed TH400, coupled to the engine by a Neil Chance bolt-together torque converter with approximately a 4500-4800 rpm stall speed. The new combination will handle the GT500’s brawn with more finesse and predictability.

Gearing the GT500 up for entering the world of Renegade racing has officially removed Duber’s GT500 from daily driver status. Duber confessed, “I won’t falsely claim it’s still my daily driver… it’s definitely, officially a race car.”

Additional efforts to relieve the engine of unnecessary responsibilities included removing the alternator and installing a large Lithium Pros lithium ion battery, and ditching the belt-driven water pump for an electric pump. This was no longer a pumped-up street motor, this GT500 has just evolved into a purpose-built Renegade Race Car.

The throttle body will now reside at the back of the supercharger and pointed towards the cowl for cold air and a better air path for incoming air.

“I won’t falsely claim it’s still my daily driver… it’s definitely, officially a race car. -Mark Duber”

Duber is still working the bugs out on his combination, suffering many of the growing pains of heads up racing in a new to you class, with a new engine and new EFI system. Official power numbers and timeslips are still a closely guarded secret, but we’re hoping to see Duber’s car make its track debut some time this year.

In addition to competing in the NMRA’s Renegade division, Duber has plans to compete in some NMCA Extreme Street racing as well—they too will be allowing cars equipped with the 4.7-liter Supercharger in 2015. With new muscle under the hood and excellent sponsors such as London Chassis Dyno, Kenne Bell Superchargers, Van Collier, and Revan Racing behind him; the BirdDoc can’t help but take his GT500 to new heights.

Article Sources

About the author

Ryan MacNeil

Ryan is a freelance writer, ASE Certified Mechanic, Military Veteran, and Hot Rod enthusiast with years of experience in the automotive world. He has a number of builds under his belt including his latest project, a sanitary ’49 Chevy pickup. Ryan’s automotive passion knows no limits—from Hot Rods to VWs to Diesels —he’s resurrected them all.
Read My Articles

Drag Racing in your Inbox.

Build your own custom newsletter with the content you love from Dragzine, directly to your inbox, absolutely FREE!

Free WordPress Themes

We will safeguard your e-mail and only send content you request.

Dragzine - Drag Racing Magazine

We'll send you the most interesting Dragzine articles, news, car features, and videos every week.

Dragzine - Drag Racing Magazine


We will safeguard your e-mail and only send content you request.

Dragzine - Drag Racing Magazine

Thank you for your subscription.

Subscribe to more FREE Online Magazines!

We think you might like...

Street Muscle Magazine
Hot Rods & Muscle Cars
Diesel Army
Diesel Army
Engine Labs
Engine Tech

Dragzine - Drag Racing Magazine

Thank you for your subscription.

Subscribe to more FREE Online Magazines!

We think you might like...

  • Streetmuscle Hot Rods & Muscle Cars
  • Diesel Army Diesel Army
  • Engine Labs Engine Tech

Dragzine - Drag Racing Magazine


Thank you for your subscription.

Thank you for your subscription.

Dragzine - Drag Racing Magazine

Thank you for your subscription.

Thank you for your subscription.