[Bill from Hahn RaceCraft]

Hello everyone! I saw some threads here which dealt with questions about the GM Ecotec LE5/LE9 engine in Slingshot, and as I've got many years of experience with the engine in its earlier LE5 form, with many superlative results, I wanted to offer a discussion here in the Hahn RaceCraft forum. I'm happy to share what I know about the engine, so consider this an open discussion. All are welcome to pose questions and/or offer their own insights.

We began to turbocharge the 2.4 liter LE5 in 2006, and immediately struck gold. We were delighted to learn that GM pulled no punches on this, their next chapter of Ecotec. Not only did the engine have a whopping 37 more HP than the 2.2 L61 which preceded it, it also featured a number of impressive internal enhancements.

Variable cam timing was added, giving the engineers a wonderful capability to further broaden the available powerband while ensuring great mileage and drive-ability. The pistons now featured anti-friction coated skirts, another first for Ecotec. Forged connecting rods used the latest in tapered small-end design that simultaneously strengthened the piston while reducing reciprocating weight.

As something which was relatively unprecedented for a normally-aspirated engine of that time, piston-cooling oil jets were added that actually sprayed oil into small cooling passages integral to the underside of the piston dome. Such cooling jets had previously typically only been on forced-induction engines (super or turbocharged), and as we do specialize in forced induction, we were naturally very enthused about this feature.

What the engineers did next continued to surprise us. Now, as we've been in the four-cylinder game since the 1970's, we've seen a number of such revisions from manufacturers over the years, especially such moves to larger displacement versions of existing engines. In every previous instance, such an increase was accompanied by a reduction in RPM redline, for a longer stroke and/or a larger piston exert more force at high RPM, and so the reduced redline was typical for durability. But GM did the exact opposite...when the LE5 was introduced it actually had a HIGHER redline than the earlier 2.2 L61! Now all the enhancements I mention above made even better sense...GM was hedging their bets by enhancing the engine internally to accommodate the higher RPM band.

Right away, we were mighty enthused, and as we'd been the first to turbocharge Ecotec several years earlier, we were chomping at the bit to boost this new player. Soon we had versions making a respectable 390 WHP, which represented over 450 HP at the crank...practically tripling the stock power level! What was most appealing about these high-powered versions was just how stock they still were. Save for valvespring upgrades, and of course our TurboSystem and fuel upgrades, these engines were still 100% stock internally. More on this as we proceed and discuss the subsequent versions of LE5, all the way up to the present time with Slingshot and its LE9!

 

[Turbosling]

What he said ^^ so get those turbo's on and boost away!

 

[Kenneth Miller]

Sounds good Bill!! Appears you are way ahead of the game and may be the first to offer a Turbo for the SS whenever we get them. Your SS turbo will probably be ready for installation before the lst delivery. Please keep us in the loop as your development progresses. Thanks for being a FORUM member. I am already on your email list.

 

[Noah Katz]

Thanks for the rundown on the LE5, Bill.

One thing I don't like about turbos is that they usually entail a lower compression ratio (at least OEM versions), which lowers thermodynamic efficiency.

How much boost can you use, and what HP does that give from an LE5, while w/o lowering CR?

 

[Bill from Hahn RaceCraft]

Thanks for the rundown on the LE5, Bill.

One thing I don't like about turbos is that they usually entail a lower compression ratio (at least OEM versions), which lowers thermodynamic efficiency.

How much boost can you use, and what HP does that give from an LE5, while w/o lowering CR?

You're welcome! The standard LE5/LE9 compression ratio is 10.6:1. With 93 octane fuel and correct tuning, we can coax a maximum of about 13-15 PSI of boost out of that, which gets us to the 300-325 BHP neighborhood.

Today's engines like LE5/LE9 allow higher boost and CR combinations than ever, attributable to sophisticated designs that are very detonation (spark knock) resistant, coupled with very capable engine management systems which allow great latitude with ignition timing tuning. This is further augmented by effective knock sensing systems which will retard timing as needed to accommodate occasional (or even severe) spark knock, thus saving the engine from damage.

 

[Tango]

Is the current Slingshot LE5 the same as the LE5 you were tuning back in 2006?

 

[Noah Katz]

With 93 octane fuel and correct tuning, we can coax a maximum of about 13-15 PSI of boost out of that, which gets us to the 300-325 BHP neighborhood.

Around here the best it gets is 91; what would the numbers be for that?

 

[Bill from Hahn RaceCraft]

Is the current Slingshot LE5 the same as the LE5 you were tuning back in 2006?

Great question, you rather beat me to the punch on this one! Yes, with one exception: today's LE5/LE9 utilizes powdered metal connecting rods, as opposed to the forged steel rods that were in use for two model years, 2006 and 2007.

This change does revise the maximum power we can reasonably and durably expect from an otherwise stock LE5/LE9. Whereas the early forged-rod engines proved supremely durable up to and including 450BHP, for safety's sake we limit the 2008 and up to no more than 300BHP.

Powdered metal rods are a marvel of modern manufacturing. While they're not as capable of ultra-high loads as their forged forebears were, they're also considerably more consistent. Unlike forged or cast rods who will require considerable post-forming machine work to be complete, they are effectively formed to most all final dimensions as they depart the mold, with very little finishing work required to be install-ready. This all adds up to a very consistent, repeatable design, and every rod is just like every other, with very little deviation.

We've done considerable development with such powdered-metal connecting rod engines on many different applications, and have benchmarked the safe ceiling as 75HP per rod, or 300HP for a four-cylinder engine.

On the plus side, since the rest of the LE5/LE9 engine has already proven its mettle at high HP, one can consider upgrading the engine for 300+ HP use simply by swapping out the con rods, with the engine block still in the machine

 

[Bill from Hahn RaceCraft]

Around here the best it gets is 91; what would the numbers be for that?

Usually, for every octane point, we can add/subtract about one PSI of boost, so for your 91 octane fuel, figure 11-13 PSI. Another reasonably approximate benchmark in engines of this size range is approximately 10 HP for every PSI of boost, so you'd look forward to about 300 HP max, which as we just outlined in the last post, is effectively the safe upper limit for today's LE5/LE9.

 

[Noah Katz]

Cool, it's accidentally optimal

Thanks, Bill

 

[Bill from Hahn RaceCraft]

Cool, it's accidentally optimal

Thanks, Bill

Ah yes...serendipity, the most welcome of engineering outcomes

Thank you too, you're welcome.

 

[Bill from Hahn RaceCraft]

As we'd continue to develop LE5 as provided in Solstice-Sky, our very own shop car, a SEMA-award winning machine, would dip in to the high 11-second range in the 1/4 mile. We were justifiably proud to make this happen on a stock 2006 LE5, save for upgraded valve springs. Of course, a Hahn RaceCraft Stage IV TurboSystem provided the motivation to make this roadster sing!

This car would then move on to a new life in the hands of a friend and development partner of ours. Can anyone recognize the car, or name the TV series it would then become featured in?

 

[DKF Texas]

Solstice...right

 

[Bill from Hahn RaceCraft]

Solstice...right

Right you are! This particular Solstice would become well-known on a TV series known as The BullRun Rally. It had been purchased from us by Tony Williams, who then participated in the show with this car, as well as used it in extensive SCCA autocross competition.

The car was thrashed severely, not only by us prior to Tony's purchase of it, but also by him in his racing and television pursuits. After several seasons of this fun, we decided to build an upgraded version of the LE5 engine to suit even higher power levels. Upon removing and dismantling the stock engine, I was delighted to see that in terms of critical areas, the overall amount of wear was no more than that we'd expect from an engine run at stock power levels. Crankshaft main and rod bearings, piston skirts, cylinder bores, all looked excellent, especially in light of the massive power enhancement and continuous harsh duty the car had experienced.

The LE5 had passed its first test, a rather challenging one at that, with flying colors

 

[Otter]

Sounds like you truly know your LE5's Bill, thanks for the inside info on this motor.

Only thing I wonder about is the cast crank. I put auto engines in airplanes and the thing I look for is longevity at medium/high power levels. Almost any decent car engine will work in this application but the really good ones will last 2000 hours in this kind of use. The not so good ones break crankshafts at around 400 hours.

What do you think about the LE5's crank? Seen any failures in hard use?

 

[DKF Texas]

I knew it was Bull something...I knew it wasn't Durham though!!

 

[sloride]

As we'd continue to develop LE5 as provided in Solstice-Sky, our very own shop car, a SEMA-award winning machine, would dip in to the high 11-second range in the 1/4 mile. We were justifiably proud to make this happen on a stock 2006 LE5, save for upgraded valve springs. Of course, a Hahn RaceCraft Stage IV TurboSystem provided the motivation to make this roadster sing!

This car would then move on to a new life in the hands of a friend and development partner of ours. Can anyone recognize the car, or name the TV series it would then become featured in?

Bill, what kind of HP and TQ was this car making?

 

[Bill from Hahn RaceCraft]

Sounds like you truly know your LE5's Bill, thanks for the inside info on this motor.

Only thing I wonder about is the cast crank. I put auto engines in airplanes and the thing I look for is longevity at medium/high power levels. Almost any decent car engine will work in this application but the really good ones will last 2000 hours in this kind of use. The not so good ones break crankshafts at around 400 hours.

What do you think about the LE5's crank? Seen any failures in hard use?

To date, none. Incidentally, I thoroughly enjoy you sharing your aviation observations. While I don't have nearly the experience with aviation applications that you appear to, I'd like to share my thoughts with you and to see how our individual experience sets can interlace. This has the potential to be an exceedingly long discussion, so I'll try to stick to the meat and potatoes to keep it somewhat brief.

In our experience with adding considerable power via turbocharging to engines, we've always been impressed with just how much we can achieve with stock or near-stock engine combinations. This is a formula my family has applied for over 40 years now, across literally dozens of different engine types, everything from V-twins to V-10s, on land, sea and air. Stock, and also stock cast crankshafts, have had superb lifespans over and over. This primarily has to do with how turbocharging increases power, not so much by increasing cylinder pressure during combustion, but by increasing the length of the power cycle so that it performs work upon the piston for many more degrees of crankshaft rotation. The same power cycle characteristics can also be said of supercharging, but because superchargers are direct driven by the crankshaft, there are potential stresses from the conflicting harmonics involved, whereas turbochargers, being driven by exhaust gases, have an inherently "soft" coupling to the engine that is absent any direct drive harmonic issues. This is also one reason why turbochargers have been so popular in aviation engines for, well, just about forever! More on harmonics in a moment.

As one might imagine, these longer power pulses have the additional advantage of reducing crankshaft stress via a more continuous power flow, with the distinct, now longer power pulses able to better adjoin or even overlap one another on multi-cylinder engines, as opposed to shorter power pulses which "feed" power into the crank in a more abrupt fashion. Every time a crankshaft gets "hit" with a power pulse, it winds up slightly, actually slightly twisting, then releasing as the pulse diminishes. So, anything we can do to lengthen the pulses takes some of that torsional stress away, and this can have a very significant effect on crankshaft life.

Now, back to your automotive engine in an airplane comparison. I believe that there are many aspects at play here, but I’ll focus on two: harmonics, and continuity of power flow of different engine types, as well as the interaction of the two. In an automotive application, we see a large variety of RPM ranges, as well as greatly varying loads. Propeller-driven airplanes operate in a much narrower RPM band, with more time spent at continuous loads. To me, this is harder on an engine, especially one that’s not originally designed for the application. The vibration signatures evident from driving a propeller are also very different from automotive to aviation. Compounding the issues are the fact that many automotive engines used in aviation must also utilize a gearcase underdrive so as to slow the output down to propeller-suitable RPM. These gearcases, while certainly well-engineered, add another variable in that they are a potential source of even more harmonics that may, or may not, be well-suited to the engine being used. At the hobbyist level, one does not enjoy the many thousands of hours of airtime development that an OEM supplier of powertrains would implement so as to study and understand, and then correct, all of these subtle but significant issues. As such, it’s my considered opinion that absent such extensive development, you folks ultimately hedge your bets by utilizing forged crankshafts in applications where cast cranks have proven themselves unable to cope with these harmonic challenges over the long haul.

One last thought, and it’s one that an aviation fan can readily agree with: the most effective design for piston-driven general aviation has been the “boxer”, or horizontally opposed engine. This is, by design, one of the strongest possible engine designs from an architecture perspective, and it also has one distinct advantage over V-engines, and that’s the 180-degree crankshaft, which is from an engineering point of view “neutral”, or inherently balanced, not only centrifugally, but also in power pulse flow. The inline-four engine, such as Ecotec LE5/LE9, is also inherently neutral in this regard. Its 180-degree crank and power flow is also perfectly suited to its architecture. Like the boxer, the inline four is also one of the most inherently durable engine designs known to date. Ecotec has also proved to be extremely stable in its “bottom end”, and this is because it combines these naturally strong and neutral characteristics with an exceedingly robust design structure. I’ll show more about this soon as well.

 

[Bill from Hahn RaceCraft]

Bill, what kind of HP and TQ was this car making?

At its peak with the near-stock engine, it was putting down 390 WHP and 370 Wtrq, so figure about 460 engine HP, 435 engine torque.

I’d like to also reiterate that this particular LE5 differed from the Slingshot engine, in that it came equipped with stock forged connecting rods, and also had valvespring and head stud upgrades installed to better accommodate boosted use. We also used higher-octane fuel in it at these power levels to properly accommodate its relatively high stock compression ratio. Nonetheless, the results are valid to our discussion of LE5/LE9’s capability overall, for here was a near-stock LE5 taking a strong licking that just kept on ticking!

Since that time, we have developed a high-boost engine kit that combines a thicker head gasket (to reduce compression ratio) with heavy-duty valve springs/retainers and cylinder head studs, a trifecta of parts that prepares the engine for high-boost operation on standard 93-octane fuel by doing no more than removing and replacing the cylinder head. We’re considering adding a new version with includes connecting rod upgrades, so as to bring up 2008 and newer LE5/LE9 engines to the same capability.

 

[HotRod]

Bill that is fantastic and interesting info. Thx's very much. Reinforces my feeling that Polaris's engine choice for the SS was well considered and speaks to their proven excellent engineering track record.