Many of you have asked what we have done with the already great Heffner TT kit to make it even better. While perhaps the first inclination is to say, “that’s none of your business”, but the questions have persisted – primarily coming from let’s call them V1 Heffner TT owners as well as a few fence sitters considering the overall TT system. As we are just completing the #34, Chip asked me to write something up and to try to balance between being informative for existing and prospective TT owners but, without perhaps, revealing what might be considered competitive knowledge. After all, there are choices to be had so some sensitivity is warranted. That said, those that have some fair to medium-level knowledge of turbo charging will likely find nothing new here but maybe some other members will gain a better idea of how improvements can be made.
While the basic principles of turbo charging might be straightforward, as the saying goes, the devil is in the details. The “ideal” turbo set-up is often compromised by physical “packaging” constraints. On the GT , for instance, the way that the motor sits within the frame and the location of the engine mounts, transaxle housing and drive axle placement, all make mounting the turbochargers against the manifolds impossible. So, this is a compromise right out of the box – but every compromise presents opportunity! On the hugely positive side of the GT engine orientation, the intake is on the back of the engine and so getting the charged air from the turbos to the intake is MUCH more ideal than almost any other application that I can think of. Couple this fact with the already integrated intercooler, and you begin to think that maybe Ford had eyeballed turbo charging from the get-go. All in all, it is ideal set-up for turbo charging. One of the things that we really like about the Heffner kit is that the turbochargers sit identically where the factory locates the catalytic converters. As such, all of the OEM heat shielding is retained and leveraged. Consider this and the fact that typically the turbochargers are emitting less heat than the relatively massive OEM cats. Frankly, from an overall packaging perspective, the Heffner TT solution is just about ideal given the packaging layout of the overall car. From a pure turbo-centric perspective, I’d rather have the turbos smack up against the manifolds but that’s virtually impossible in the Ford GT.
One last foundation element. Turbocharging is often a balance between the maximum boost attainment objective and spool-up times. For example, say your target maximum boost (derived from how “beefy” your engine is built and what boost pressures that it can withstand) is 25 psi. You COULD choose a single large turbo that will get you to this target boost level. Alternatively, you could choose (2) turbochargers, essentially splitting the load and each turbo roughly half the size of a single turbo. The advantage of two turbochargers is that being physically smaller and specifically with less mass in the impeller, the turbochargers can spool more quickly. The result is that you can make boost earlier in the RPM range which is most often very desirable. In fact, the lack of available boost in the lower RPMs is probably the single biggest justification of a TT+SC. While an SC DOES help the lower RPMs, another old adage applies here - there's no such thing as a free lunch. In short, while a SC may be helpful on the low-end, in the mid and upper RPMs, the SC is purely a liability. In these RPM ranges the SC is contributing to IATs, adding a heat soak element to the top of the engine, and consuming valuable horsepower off of the front of the crank. Indeed, it is my opinion that the costs far exceed the rewards and so instead of looking for a SC to improve lower RPM performance, we began to look at optimizing the turbo set-up.
OK, with that intro/foundation, coupled with our experience in installing the V1 Heffner TT system several times and having maybe 30 or more hours of combined dyno time, we’ve learned a few things. (Yeah, yeah, I know you can’t teach an old dog new tricks but despite ourselves, we continue to learn.) I should also note that we rent dyno time from some folks that are VERY knowledgeable in forced induction and it was OFTEN beneficial for us to hear their comments and suggestions. Their help and experience has been invaluable. The primary crux of the Heffner V2 system was twofold. First, we wanted to have much better heat management under the clamshell. Although we NEVER experienced any heat-related issues, we know that cooler temps on the exterior elements often meant more heat within the system and more heat IN a turbocharger is BENEFICIAL to power. So, better heat management would yield two benefits. We could lower external heat, improving component longevity, IAT’s, and adjacent component longevity, AND we might be able to increase power. Better heat management was really our primary objective. I also sometimes refer to this as more “OEM-like”. The second objective – and we became more encouraged as we progressed, was to get the system to produce more power EARLIER in the RPM range.
How did we do it? To achieve Objective 1 (improved heat management), we looked into and then accomplished fundamental ways to make a significant reduction in the total surface area of the heated exhaust components. Second, we used the very latest in ceramic heat coating technology to treat ALL exhaust components. Finally, we outfitted the turbochargers with nice little custom blankets to keep the heat in and the outside temps down. The results of all of these changes were very pronounced!
For Objective 2 (power i.e. boost, sooner), we looked at ways to improve the flow of exhaust from the ports on the heads to the not-so-close turbochargers, more efficiently. ANYTHING that we could do to improve flow, accelerate gasses through proper pipe diameters, and reduce turbulence, would be beneficial. Thankfully (and obvious to us at the beginning) there was synergy between Objective 1 and Objective 2. In other words, the steps we took for reduced heated surface area and lessening of emitted heat (Objective 1), also helped us in the power department (Objective 2). Finally, I think we also made some very clever changes – likely smaller contributors overall, but that improved the overall running of the car in both open and closed-loop modes.
Along with all of these changes, we also made changes to allow higher fuel pressures in the car when needed (aka BAP). In another post I presented a graph comparing the Heffner V1 results against the V2 changes that we made. I chose a dyno pull from the V2 set-up that matched the boost level of the highest previous dyno run we had on Terry’s (Apollo) V1 system. I think these were both at 22-23 psi of boost. Both compared pulls were made on Heffner’s “outstanding” TT tune. However, we installed the BAP to allow safer A/F ratios at the high end and to afford us the capability to run a couple of more PSI of boost. To take advantage of the BAP we needed a new custom tune and for this we turned to Torrie. In a 3-hour tuning session (because we broke the dyno at one point), Torrie developed a tune exploiting the higher available fuel pressures and we attained a dyno run of 1017RWHP at ~25psi of boost. Torrie is definitely at the top of the tuning game in my book!!
The net is that all of these changes yielded a car that ran substantially cooler and where the boost would come on MUCH lower in the RPM range. This is what enabled Terry to set the Mojave Mile speed record for a car as well as the highest recorded “stock block” overall speed record for a GT at 238MPH. Frankly (and with the Terry’s concurrence), the car had more in it. The reality is that Terry is very, very considerate of his car and the car’s drivetrain. For those of you that have seen Terry launch – there is never any drama, wheel spin, speed shifting, etc. In comparison to others, Terry’s launches are VERY conservative. (In contrast, the critical fast-shifting to mitigate boost loss in the higher gears has been absolutely mastered by Terry, IMO.) But, the point is that with harder, potentially more drivetrain stressful launches, Terry could have exploited the lower power band even more and gotten to the higher gears sooner with a critical 2-3 seconds of added acceleration time at the top end.
I hope this answers some of the questions we have been asked and sheds some light on what a V2 system is capable of. One of the most telling attributes of this overall system (and the fundamental greatness of the GT and all those who designed her), is that following the Mojave Mile event, TT owners like AlohaGT simply pulled into a gas station in Mojave and filled up with 91 octane. The new boost controllers we installed default to a mere 11-12 psi at start-up and Ryan drove Kelvin’s car 90 miles back to our place with the AC on, stereo playing, and Kelvin catching some needed Z’s – all while the car was getting a gazillion stares on the freeway and averaging ~25mpg. AMAZING!
Note that Skyrex drove his Heffner TT car 4+ hours home following the event. This defies all logic of what any reasonable person would think possible…. drive 4 hours to an event, make numerous 200MPH passes at will, and then drive 4+ hours home after the event. There’s simply not too many cars on the planet that can do this. That’s cool!!
Our latest V2 conversion was Chip’s #34. Mechanically, the car is virtually identical to Terry’s car and the dyno results were literally right on top of each other. Due to minute differences in the cars, as well as the dyno test conditions (air temp. humidity, etc.), Terry’s car had a peak of about 30 more RWHP, whereas Chip’s had a more sustained (broader RPM range) 40 RWTQ advantage.
I hope that this helps to shed some light on the overall system and some of what we have been up to in the last months.
While the basic principles of turbo charging might be straightforward, as the saying goes, the devil is in the details. The “ideal” turbo set-up is often compromised by physical “packaging” constraints. On the GT , for instance, the way that the motor sits within the frame and the location of the engine mounts, transaxle housing and drive axle placement, all make mounting the turbochargers against the manifolds impossible. So, this is a compromise right out of the box – but every compromise presents opportunity! On the hugely positive side of the GT engine orientation, the intake is on the back of the engine and so getting the charged air from the turbos to the intake is MUCH more ideal than almost any other application that I can think of. Couple this fact with the already integrated intercooler, and you begin to think that maybe Ford had eyeballed turbo charging from the get-go. All in all, it is ideal set-up for turbo charging. One of the things that we really like about the Heffner kit is that the turbochargers sit identically where the factory locates the catalytic converters. As such, all of the OEM heat shielding is retained and leveraged. Consider this and the fact that typically the turbochargers are emitting less heat than the relatively massive OEM cats. Frankly, from an overall packaging perspective, the Heffner TT solution is just about ideal given the packaging layout of the overall car. From a pure turbo-centric perspective, I’d rather have the turbos smack up against the manifolds but that’s virtually impossible in the Ford GT.
One last foundation element. Turbocharging is often a balance between the maximum boost attainment objective and spool-up times. For example, say your target maximum boost (derived from how “beefy” your engine is built and what boost pressures that it can withstand) is 25 psi. You COULD choose a single large turbo that will get you to this target boost level. Alternatively, you could choose (2) turbochargers, essentially splitting the load and each turbo roughly half the size of a single turbo. The advantage of two turbochargers is that being physically smaller and specifically with less mass in the impeller, the turbochargers can spool more quickly. The result is that you can make boost earlier in the RPM range which is most often very desirable. In fact, the lack of available boost in the lower RPMs is probably the single biggest justification of a TT+SC. While an SC DOES help the lower RPMs, another old adage applies here - there's no such thing as a free lunch. In short, while a SC may be helpful on the low-end, in the mid and upper RPMs, the SC is purely a liability. In these RPM ranges the SC is contributing to IATs, adding a heat soak element to the top of the engine, and consuming valuable horsepower off of the front of the crank. Indeed, it is my opinion that the costs far exceed the rewards and so instead of looking for a SC to improve lower RPM performance, we began to look at optimizing the turbo set-up.
OK, with that intro/foundation, coupled with our experience in installing the V1 Heffner TT system several times and having maybe 30 or more hours of combined dyno time, we’ve learned a few things. (Yeah, yeah, I know you can’t teach an old dog new tricks but despite ourselves, we continue to learn.) I should also note that we rent dyno time from some folks that are VERY knowledgeable in forced induction and it was OFTEN beneficial for us to hear their comments and suggestions. Their help and experience has been invaluable. The primary crux of the Heffner V2 system was twofold. First, we wanted to have much better heat management under the clamshell. Although we NEVER experienced any heat-related issues, we know that cooler temps on the exterior elements often meant more heat within the system and more heat IN a turbocharger is BENEFICIAL to power. So, better heat management would yield two benefits. We could lower external heat, improving component longevity, IAT’s, and adjacent component longevity, AND we might be able to increase power. Better heat management was really our primary objective. I also sometimes refer to this as more “OEM-like”. The second objective – and we became more encouraged as we progressed, was to get the system to produce more power EARLIER in the RPM range.
How did we do it? To achieve Objective 1 (improved heat management), we looked into and then accomplished fundamental ways to make a significant reduction in the total surface area of the heated exhaust components. Second, we used the very latest in ceramic heat coating technology to treat ALL exhaust components. Finally, we outfitted the turbochargers with nice little custom blankets to keep the heat in and the outside temps down. The results of all of these changes were very pronounced!
For Objective 2 (power i.e. boost, sooner), we looked at ways to improve the flow of exhaust from the ports on the heads to the not-so-close turbochargers, more efficiently. ANYTHING that we could do to improve flow, accelerate gasses through proper pipe diameters, and reduce turbulence, would be beneficial. Thankfully (and obvious to us at the beginning) there was synergy between Objective 1 and Objective 2. In other words, the steps we took for reduced heated surface area and lessening of emitted heat (Objective 1), also helped us in the power department (Objective 2). Finally, I think we also made some very clever changes – likely smaller contributors overall, but that improved the overall running of the car in both open and closed-loop modes.
Along with all of these changes, we also made changes to allow higher fuel pressures in the car when needed (aka BAP). In another post I presented a graph comparing the Heffner V1 results against the V2 changes that we made. I chose a dyno pull from the V2 set-up that matched the boost level of the highest previous dyno run we had on Terry’s (Apollo) V1 system. I think these were both at 22-23 psi of boost. Both compared pulls were made on Heffner’s “outstanding” TT tune. However, we installed the BAP to allow safer A/F ratios at the high end and to afford us the capability to run a couple of more PSI of boost. To take advantage of the BAP we needed a new custom tune and for this we turned to Torrie. In a 3-hour tuning session (because we broke the dyno at one point), Torrie developed a tune exploiting the higher available fuel pressures and we attained a dyno run of 1017RWHP at ~25psi of boost. Torrie is definitely at the top of the tuning game in my book!!
The net is that all of these changes yielded a car that ran substantially cooler and where the boost would come on MUCH lower in the RPM range. This is what enabled Terry to set the Mojave Mile speed record for a car as well as the highest recorded “stock block” overall speed record for a GT at 238MPH. Frankly (and with the Terry’s concurrence), the car had more in it. The reality is that Terry is very, very considerate of his car and the car’s drivetrain. For those of you that have seen Terry launch – there is never any drama, wheel spin, speed shifting, etc. In comparison to others, Terry’s launches are VERY conservative. (In contrast, the critical fast-shifting to mitigate boost loss in the higher gears has been absolutely mastered by Terry, IMO.) But, the point is that with harder, potentially more drivetrain stressful launches, Terry could have exploited the lower power band even more and gotten to the higher gears sooner with a critical 2-3 seconds of added acceleration time at the top end.
I hope this answers some of the questions we have been asked and sheds some light on what a V2 system is capable of. One of the most telling attributes of this overall system (and the fundamental greatness of the GT and all those who designed her), is that following the Mojave Mile event, TT owners like AlohaGT simply pulled into a gas station in Mojave and filled up with 91 octane. The new boost controllers we installed default to a mere 11-12 psi at start-up and Ryan drove Kelvin’s car 90 miles back to our place with the AC on, stereo playing, and Kelvin catching some needed Z’s – all while the car was getting a gazillion stares on the freeway and averaging ~25mpg. AMAZING!
Note that Skyrex drove his Heffner TT car 4+ hours home following the event. This defies all logic of what any reasonable person would think possible…. drive 4 hours to an event, make numerous 200MPH passes at will, and then drive 4+ hours home after the event. There’s simply not too many cars on the planet that can do this. That’s cool!!
Our latest V2 conversion was Chip’s #34. Mechanically, the car is virtually identical to Terry’s car and the dyno results were literally right on top of each other. Due to minute differences in the cars, as well as the dyno test conditions (air temp. humidity, etc.), Terry’s car had a peak of about 30 more RWHP, whereas Chip’s had a more sustained (broader RPM range) 40 RWTQ advantage.
I hope that this helps to shed some light on the overall system and some of what we have been up to in the last months.
