Turbo vs. N/A engines - Is CART about  to make a mistake?
by Mark Cipolloni

January 22, 2000

CART is wrestling with the turbo vs. normally aspirated engine formula issue for the next generation CART powerplant.  Here are some thoughts on the issue.

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CARTís turbocharged engines are not common in motorsports today, but they give CART a unique identity from the IRL and F-1. There has been a lot of debate lately as to whether CART should convert to normally aspirated engines or change to a 1.8 liter highly turbocharged engine as proposed by CART's engine manufacturers. NASCAR, the IRL and F-1 are all normally aspirated. Does that mean CART should follow suit? The sound of a turbocharged Champ Car engine at full song is music to the ears of every fan. Everyone loves the sound, and the turbo keeps the noise levels reasonable for the street circuits. Why mess with success?  Why?  Because some folks think CART should give away the farm just to get back to the Indy 500.  This article discusses why a normally aspirated 3.5 liter engine formula for an open-wheel series that races on ovals, including the Indy 500, is a mistake.

Food for thought

The only reason any of the CART engine manufacturers are even considering a normally aspirated engine is to bring CART and the IRL together because Tony George refuses to bend.  However, even today after CART's big-4 were willing to give-in to a normally aspirated engine to bring the series together, there are those within the CART engine manufacturers who think a normally aspirated engine is a mistake.  If CART starts at 3.5 liters and doesn't limit RPM, HP will be through the roof in no time at all (F-1 is a prime example).  Then what?  Change the formula again?  Even with limits on RPM and far stricter engine design limitations than CART, the IRL has already found the need to change from a 4.0 liter to a 3.5 liter engine in just three years.  What's next?  3.0 liters?

On a road course, too much HP is not usually a problem, because the nature of the circuits usually limit terminal velocity.  So if HP creeps up at an alarming rate, as it does in F-1, the engine formula can still remain in place for quite a long time before it needs a major overhaul.  However, on oval tracks, too much HP means high speeds, and bad accidents that kill or injure far too many drivers every year.  Concrete walls are unforgiving.  The point to be made here is that unless you want to place severe restrictions on engine specifications, such as NASCAR does, you must have a way to keep HP in check on oval tracks, and turbos are the best way as we will explain below.

Champ cars are not stock cars.  They are thoroughbred race cars.  They are sophisticated state-of-the-art purpose-built race machines made for one thing and one thing only, to be the best performing automobiles man can build.   That is their mystique, their lure.  They don't look like mom and pops everyday automobile for a reason.

Open wheel race cars from the beginning have always been the best race cars mankind can design and build.  One primary reason the IRL has been rejected by open wheel race fans because the IRL tried their best to make an open-wheel Indy car like a stock car without fenders.  They tried to use stock block engines, place severe limitations on the engine and car design, and race on high-banked oval tracks, just like NASCAR.  Guess what?  It didn't work.  And it won't work in the future.  It is not the heritage of an open-wheel race car.

Then why should CART give in and change to a normally aspirated engine (and give up all its advantages) because that is what the IRL uses, just to get back to Indy?  Maybe it is the IRL that should change, not CART.

What an open wheel cars engine should be

We made our case of why Champ cars should not be stock car copycats, and that goes for the engines too.  An open wheel engine formula should be technically sophisticated.  There should be few limitations on technical development.  Their design should challenge the imagination of our best engineers, just as the entire design of an open wheel race car should challenge our engineers.  When you start telling engine manufacturers where to put the cylinders, how many RPM you can turn, and that it must be a modified production engine, the engine manufacturers say we have NASCAR for that.  They want a training ground for their engineers, to develop technology that can roll down to their production cars someday.  NASCAR stock cars don't provide that opportunity to the manufacturers.  Heck, they still use carburetors.....relics.  NASCAR is a great success, and my hat is off to them.  But we don't need two NASCAR's in this country.  One is quite enough thank you.

If manufacturers have NASCAR to showcase their name, where do they get to showcase their engineering might and ingenuity?  In open wheel racing.....where they always have.  In order to challenge engineers so manufacturers will remain involved in open wheel racing, and keep HP from running out of control, you must first begin with a base engine formula that can keep HP in check yet allow the engineers to think, be imaginative, and push the envelope.

Understand that an internal combustion engine is basically an air pump.  The more air, the more HP it is going to make. Therefore, if your base engine/air pump is too big, you are going to have to place other limitations on development to limit HP.  

If you allow engineers to fully exercise their imaginations
you get awesome engines such as the new Ford-Cosworth XF,
small, light, powerful works of art.

If you agree with the philosophy that an open wheel engine should allow the builders plenty of latitude, then a 3 liter and higher air pump is too big in today's day and age.  Already a 3.0 liter F-1 engine is pushing 900 HP.  Ford, Mercedes and Honda have already produced 3.0 liter normally aspirated engines that make HP at or above current Champ car engines.  However, since F-1 is strictly a road racing series, as we noted above, that is not such a huge problem as it is for a series that competes on oval tracks.  900 HP is a problem for CART and the IRL.  Current oval track designs have not advanced from a safety standpoint to where speeds can be allowed to go unchecked, and with the low weight of a Champ car, 900 HP seems to be about the upper limit we dare to go.  Some think even lower.

Why a small turbocharged engine makes sense

Staying with the assumptions that the engine specifications should not be too limiting, then CART (and the IRL) should start with a small highly pressurized air pump (i.e. turbocharged engine) and let the engineers have at it.  Every time they find a way to reach the so-called 900 HP limit, simply lower the intake pressure produced by the turbocharger, and let the engineers have at it again.

The current 2.65 liter CART turbo engine formula has been a resounding success for three decades.  And remember we still have 10 inhg of boost to play with on the 2.65 liter engine.  If we cut that in half you can bet they could still squeak several more years out of it.  One can expect the same longevity from a small 1.5 to 1.8 liter formula.  We can't say the same thing about the IRL's and F-1's normally aspirated engines.  Before long, they will be changing again....or they will be stifling the engineers who design them.

Turbochargers have become very reliable and not a high expense item. They are a great way to control engine power as speeds continue their annual creep upward.  The engine manufactures proposed the small highly turbocharged engine formula to CART because they know that is the best way to go.   Instead of CART and its engine manufacturers changing, it is the IRL that should be changing if they want to unite the two series.  It's time for common sense to prevail.  Turbocharged engines are the very essence of CART's heritage, and they are the better engine formula. 

Some of our readers had these thoughts.  I think you will find them interesting.

When it comes down to it, turbos main advantage pertains mostly to overall cost savings. The advantages of turbos over NA engines for racing applications:

1. Turbos create higher combustion chamber pressures at the top end (relative to an NA engine) which in turn requires stronger rods, pistons, etc. Consequently, because everything must be built to withstand the pressures at high rpms, engineers can't make the parts as light (as an NA engine) for the lower end of the rpm range (where lightness matters more) and so the extra cost of R&D, as well as the need to make the engine more fragile, is greatly reduced. The result is a less-expensive and stronger engine relative to an NA engine. 

2. Turbo lag has been eliminated (through electronic mgmt and ball-bearing turbo devel) making the cars now traction limited on many road course corners... even more reason that the need for lighter/fragile engine parts to provide quicker acceleration is reduced. (The cost of the turbo is nothing compared to the cost of R&D to make lighter parts).

3. The positive flow into the cylinder during the intake cycle is beneficial to engine parts by reducing the stress of pulling the air in, extending engine life. 

4. The increased chamber pressure does require that compression ratio be reduced... however because Champ cars just happen to use methanol, the higher octane allows them to not have to reduce it as much as a gasoline engine would need.  Also, turbos compress air, which in turn heats it up and could cause engine overheating. However, because of the methanol (which has excellent cooling properties) that problem is eliminated. They don't even need intercoolers.

5. Turbos are much more efficient on oval racing than NA engines... where the speeds tend to be constant near the higher end of the rpm spectrum. Relative to an NA engine, the turbo engine running at top end is getting a *LOT MORE* air pushed into the cylinders with almost no penalty on the engine. (Well, not much now at 40" boost) It's nearly free horsepower... and depending on how much the boost is set... and a lot of it.

6. As cars inevitably get too fast, they can easily be slowed by reducing boost. A constant engine size can be kept over many years (the 2.65L size lasted 30+ years). This means that the pistons, rods, cranks, and blocks will stay essentially the same size for years instead of having to resize and retest if frequent resizing is called for, as has already been the case since F1 and IRL went NA. 

7. An airbox takes away much more air (relative to a turbo car w/o an airbox) from the rear wing whenever a car starts to oversteer on a turn. As the oversteer/wing-air loss increases it eventually causes a breakaway. This has not been a problem in F1 as the turns are relatively slower... but it's been a problem in the IRL when a car is running very fast around turns continuously on ovals.

Three non-tech reasons:

8. They provide muffling for what would otherwise be extremely loud NA engines (and annoying if they use 90 degree cranks) which might require mufflers.

9. Turbos provide a technical differentiation from F1 and NASCAR

10. Most current CART fans prefer the sound of the turbo engines.

I think the current engines are fine except that they are at the end of the line for power reductions, and as revs continue climb power will go through the roof. What is needed is a new smaller formula that will last another 20 years. The engines need to be sized so they will produce the power level desired @ 60 inhg. This will allow revs to rise 50% before this problem reoccurs. They are currently at 16K, and that would make the formula last until 24K is the norm. The current engines make about 330 hp/liter @ 40 inhg. That would put them at 500 hp/liter @ 60 inhg. Taking those numbers, we get 750 hp from 1.5 liters and 900 hp from 1.8 liters. I would go with the 1.5 liter engine, because the power cut will slow the cars on ovals where the real problem is.

My own reasons for turbos are several. Noise reduction, ease of power reductions and the tone of the engine. Another technical advantage is package size. A smaller lighter engine makes it easier to make a good handling car with good aerodynamics.

Any NA engine will make more power than they want a lot sooner than they think. It happened in F1. They went to a 3.5 liter engine to keep power at about 600 bhp. They are now closing on 900 bhp from 3.0 liters only 10 years later. Does 24,000 rpm sound impossible? 18,000 sounded impossible 10 years ago. Turbos are the only way to go.

The author can be contacted at markc@autoracing1.com

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