I’ve been casually reading the rally rule books for the major North American sanctioning bodies for well over ten years now. It first started as an exercise in calculating the cost of building a rally car. My teammate and I spent a lot of hours digging through the rules to find all the required hardware and then building spreadsheets to catalog prices. As my participation in rally expanded to volunteering and competing, so did my familiarity with with the rule books.

Through the years, there is one thing in the rules that the sanctioning bodies have never seemed to be able to come together on: maximum allowable displacement. They all seem to have different ideas about what should be allowed and how to go about keeping competition fair. This is something that my teammate and I had not put much thought into. When you’re extremely budget minded like we were back in the day, you just aren’t concerned with whether or not putting a 3-liter Taurus SHO V6 engine into a Ford Festiva is going to bump you into a higher class. What we were concerned about was whether or not our cars would fit within similar classes across multiple sanctioning bodies. We had plans for chasing regional championships in Rally America one season, then a regional championship in Canada another season, then trying for one in NASA later. As long as we stuck with a traditional two liter, twin cam engine, we could go anywhere in our region and compete in the similar classes in AWD or 2WD without modification to the car. There is a lot of overlap among the sanctioning bodies as long as you stay away from the upper limits.

Because I’m going to keep referencing adjusted displacement, I’m going to go over an example for those unfamiliar with how it works. Here are the tables NRS uses for determining adjusted displacement in their Open classes (RA was similar):

NRS tables for maximum allowable displacement [footnote 2] NRS tables for maximum allowable displacement [footnote 2]

Let’s look at that three liter SHO engine I mentioned. It is normally aspirated, has four valves per cylinder and has an absolute displacement of 2986cc. Using factors from the table above:

2986cc x 1.2 ( four valves per cylinder) = 3583cc (adjusted displacement)

That means the SHO powered Festiva would certainly be in the Open 2WD Heavy class. Let’s say we wanted to use a Ford Vulcan engine instead (it's the engine the SHO was based on). It has the same displacement but only has two valves per cylinder that are actuated with pushrods.

2986cc x 1.0 (two valves per cylinder) x 0.8 (pushrods) = 2389cc (adjusted displacement)

The Vulcan equipped Festiva would now be in the Open 2WD Light class where we would prefer to compete since even with a SHO engine, we probably wouldn’t stand a chance against a turbocharged RX7. On the other hand, maybe we would - and that's why these adjusted displacements are used.

Admittedly, I didn’t pay much attention to the American Rally Association rules while they were being drafted and implemented. Up until very recently, none of the events in my region were sanctioned by them. However, after the ARA had completely supplanted Rally America, it was time for me to get up to speed. While I was browsing through their rules, I was slightly surprised to see that they don’t have any adjusted displacements in their class structures. That by itself isn’t really that big of a deal. Rally America had been phasing out adjusted displacements over the last few years and the Canadian Rally Championship doesn’t use them anymore either. The surprise comes from seeing how much displacement the ARA does allow. Three of the five classes in ARA can run 6300cc of real, unadjusted displacement. That’s kind of a big deal.

ARA table for maximum allowable displacement [footnote 3] ARA table for maximum allowable displacement [footnote 3]

For reference, the monster machines of the Group B era that we hold in such high regards (such as the Audi Sport Quattro S1, Lancia Rallye 037, Mini MG Metro 6R4, Ford RS200, and others) were displacing just under 3000cc with normal aspiration and a little over 2100cc with forced induction. Without getting too wrapped up in the Group B specifications, classes were based on adjusted displacement with a 1.4 multiplier for boost. Vehicle weight and tire width were regulated based on that adjusted displacement. Most manufacturers were participating in Class 12 which was limited at 3000cc [footnote 4].

It’s time for a little history: By the early 90’s the Group A cars were faster than the infamous Group B cars despite having much less power. The improvements were mostly due to advancements in suspension, tuning, tires, and other technology. In 1997 the World Rally Car Specifications superseded Group A and further advancements made the cars even faster. In the wake of the global financial crisis around 2009, manufacturers began dropping out of the World Rally Championship, so the FIA tightened the rules to promote more competition and make the series a bit more accommodating to privateer teams. During this time, people began to speculate that American rally cars had become some of the fastest machines due to their more relaxed regulations. However, just a couple years ago, the FIA loosened the restrictions on the WRC cars which resulted in more power, dramatic aero, and even faster stage times.

Without having an opportunity to square off directly or even at similar events, the best we can do is compare available statistics about some of the machines. The Subarus from Vermont Sports Car (2018 US champion) make 330HP and 480lb-ft and weigh 2900lb [footnote 5]. The Ford Fiestas from M-Sport (2018 WRC champion) make 385HP and 332lb-ft and weigh 2624lb [footnote 6]. With all other things being equal, my opinion is that the latest WRC cars are the fastest rally cars ever. Just for kicks, the Peugot 205 Turbo 16 was considered to be the most successful Group B rally car. It made around 500HP and 361lb-ft while weighing under 2200lb in the final E2 spec at the end of the Group B era [footnote 7].

Which one is the fastest? Current WRC M-Sport Fiesta WRC? VSC Subaru WRX STi? Group B Peugot 205 T16? [Sources in footnote 8] Which one is the fastest? Current WRC M-Sport Fiesta WRC? VSC Subaru WRX STi? Group B Peugot 205 T16? [Sources in footnote 8]

All this review of history and numbers is to put into perspective what the Americans have done by allowing such massive engines in competition. Here’s the real kicker: big engines have been allowed in the US for as long as I can remember (and probably longer than that), but no one has been using them! With very few exceptions, most competitors stick to more traditional rally setups like two liter, four cylinder engines with turbos. I have always suspected part of the reason is that most top-tier rally teams prefer to rally a car as it was offered from the manufacturer and thus had obligations (whether implied or explicit) to promote products.

Then why haven't bigger engines been utilized more in US rally? I can only speculate based on my experience and observations. Maybe someone who's been around longer could lend some insight. I think one of the main reasons is weight (and subsequently balance). Take just about any dual cam four cylinder with an iron block, add a turbo, and it can easily make a reliable 300HP. The Mitsubishi Lancer Evolution and the Subaru WRX STi made that power from the factory. However, a traditional 350 V8 with an iron block has twice the cylinders and twice the rotating assembly. It could also make a reliable 300HP but it puts a lot more weight in the front of the car. That could upset the balance of a racing machine that needs to be agile enough to avoid trees while going 100mph.

In the early 90's, Japanese and German car manufacturers began utilizing aluminum V8 engines in their luxury cars. Even though they had similar weights to boosted four cylinders, they didn’t make power as easily and were rather expensive to maintain. On the domestic side, it wasn’t until the mid 2000’s that the all aluminum LS1 started to make a splash in the automotive aftermarket. Even so, there aren’t a lot of rally cars being manufactured by General Motors, so what would you even put it in?

Another issue with large engines is fitment. Even though the options for lightweight, big displacement engines are plentiful now, it still needs to fit into a rally car. All of the Japanese and German V8 engines have dual cam cylinder heads which occupy a lot of real estate under the hood of any car. Additionally, the amount of work required to attach a big engine to an AWD system that can meet the demands of rally is no easy feat. Not many people have the budgets or technical abilities required to build a NASCAR-powered, Sadev-equipped AWD Hoonicorn. [FYI: before it had turbos and methanol, it was legal to run in NRS.]

It's going to be weird seeing this machine go by on stage making LS noises. [Photo source in footnote 9] It's going to be weird seeing this machine go by on stage making LS noises. [Photo source in footnote 9]

Whatever the reasons may have been, at least someone is finally exploring the boundaries of allowable displacement! It is highly unlikely that you have not seen the LS3-powered AWD Chevy Sonic built by PMR Motorsport. Aside from some pictures posted on their website that seem to have appeared on every automotive website on the internet, there haven’t been many details released about the build. One thing that we do know is that the 6.2-liter LS3 crate engine makes 430HP and 425lb-ft straight from the box [footnote 10]. I did have a chance to poke around the car at the Performance Racing Industry trade show in early December where the car was on display, but I didn’t get a chance to talk to anyone about it. I also didn’t take any pictures at the show (which is weird for me) and regret that I did not at least get a couple shots of the Sonic because I thought it was one of the coolest cars there.

As technology has evolved in the thirty-some years since Group B ended, now is as good of a time as any to revive the spirit of that era. I mentioned V8 engines a lot, but there are many amazing engines that can be utilized to push the limits of displacement in most of the open classes in the US (and even Canada with the newly released 2019 rules). This is especially true in the Open 2WD classes. Take a look at the rules and get familiar with them. Get creative and build something that excites people and makes them take notice. Rally is an exciting sport and the cars should be too.

Footnotes and Sources:

[1] Lancia Delta S4 photo source: www.evo.co.uk/rallying/20384/the-anatomy-of-a-group-b-rally-car-history-and-tech-of-rallyings-golden-era

[2] NASA Rally Sport (NRS) rules: www.nasarallysport.com/main/rules

[3] American Rally Association (ARA) rules: www.americanrallyassociation.org/rulesandbulletins

[4] Group B car specifications and rules: rallygroupbshrine.org/

[5] Vermont Sports Car VT15r specs: vtcar.com/projects/srt-usa-2015-open-class-rally-car/

[6] M-Sport Ford Fiesta WRC specs: www.m-sport.co.uk/fiesta-wrc

[7] Peugeot 205 T16 Group B specs: rallygroupbshrine.org/the-group-b-cars/rally-cars/peugeot-205-t16-e1e2/#205t16specs

[8] M-Sport Fiesta photo source: cdn.motor1.com/images/mgl/qvgEL/s1/wrc-rally-australia-2017-sebastien-ogier-julien-ingrassia-ford-fiesta-wrc-m-sport.jpg; VSC WRX STi photo source: secure-akns.subaru.com/content/media/mp_fullscreen_1920/MSX18243_web2.jpg; Peugeot 205 T16 photo source: img.favcars.com/peugeot/205/pictures_peugeot_205_1984_9.jpg

[9] PMR Sonic Engine photo source: www.theblock.com/article/2018/december/ls3-powered-chevy-sonic-rs-is-built-to-rally.html

[10] Chevrolet Performance LS3 specs: www.chevrolet.com/performance/crate-engines/ls3