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Update 05-09-2019: Available also for 6th Gen Camaro SS and ZL1, for Cadillac CTS-V (2016-present)
There is a much debated problem w/ the throttle response of the C7’s, in all models Stingray, Z51 and Z06, manual or auto, the issue has been described in this and other forums, just to mention a few descriptions:
- Throttle Lag
- Delayed response
- Car feeling heavy or not nimble
- Difficulty climbing hills at low/moderate throttle
- Uncertainty when passing other cars or unpredictable response at low/moderate throttle
- Stumble when shifting on manual transmissions
You name it, this has been my issue w/ this car since test driving at the dealership. I've tried a Throttle controller, AFM disabler, ECM Tuning, and arguably the three most talked about ported throttle bodies (PTB) out there. I have also combined some of the above w/ some success but still not enough. One just needs to hop into almost any other comparable car to feel they respond better.
After spending so much time/money, I decided to take it upon myself to find out, I also have all the equipment needed at work (measuring, testing, simulating, machining etc.)
Long story short; it is the throttle body. Between idle (~5 degree throttle) to ~30 deg throttle angle the amount of mass air flow (which is proportional to power) puts our C7 at a weigh to power ratio similar to that of trucks and SUV’s, both in terms of absolute value and rate of change. Not to be confused w/ the weight to power ratio that is usually published, which is calculated at WOT, above 35 deg throttle angle our C7’s shine. It is on the part throttle range (idle to 30 deg) that the issue exists.
I’m not going to speculate on the reasons, but I can tell you that our throttle body p/n is used in many GM vehicles and that such throttle response helps w/ fuel economy. That helps to keep parts cost low and meet EPA requirements for the fleet. However, I do not think one size fits all and that a sports car needs to sacrifice performance for economy.
The throttle controller and the tune improve response by making the throttle plate move faster between the 5-30 deg range. Faster, but it still needs to go through a tortuous path for the air flow, and the manifold pressure doesn’t recover as fast. It is a transient process, and it is from the intake manifold where the pistons suck the air from. Notice that this is not true throttle response, it is just tricking the ECM into thinking you have pushed the accelerator pedal harder. The actual throttle response is the same, only physical changes to the throttle can make for a true throttle response.
The existing aftermarket ported throttle bodies also helped, they do change the throttle physically, but their effect only starts to take place at about 25 deg in what I thought was the best one of them. Definitely a step in the right direction, but I noticed they were not optimized and that more could be extracted from them, that is a throttle body that can increase the absolute value and rate of change of mass air flow right from idle and up to 35 degrees to achieve the same weight to power ratio (in that range) of similar sports cars that feel nimble and fun to drive at part throttle.
Another long story short, I reversed engineered 10ea C7 OEM throttle bodies, 3ea C7 aftermarket ported throttle bodies, and a benchmark (competing car maker model) OEM throttle body. Optimized/modified the C7 OEM throttle body to meet the benchmark throttle response as well as the goal stated above.
The modified throttle body is made (CNC machined) from a brand new OEM throttle body, flow tested and engine tested. It has been in my C7 since September 2018, works beautifully, no codes, no issues. Driven in different conditions/modes for a few thousand miles now, just waiting for a hard freeze to see how it does on cold weather, it also needs to be tested at high altitude and in different C7 models to make sure it works in all cases, so, still a “Beta” version.
See pics below for more insight into what I’m talking about…and most importantly what do you think? All comments welcome, I’m learning as I go and appreciate your input.
gmtech16450yz, I’d argue that neither of us is looking at the wrong place to fix the problem. I’d rather say that we are taking different approaches, each w/ their corresponding advantages and disadvantages.
Tuning or electronically controlling the throttle plate/blade takes advantage of moving the blade “faster” or “ahead of the foot” to sweep the geometry of the throttle body (TB) in order to increase airflow. What this is doing is simulating a greater pedal travel than the driver is requesting. Many of us have had that type of solution and it does make a difference, but one cannot help but notice that although the throttle responds faster, it does so by following the same path imposed by the geometry of the TB. In other words, it cannot escape the shape of the OEM curve (green) and there is nothing a tune can do about that. Therefore, if the car used to; stumble, hesitate, make abrupt changes of acceleration, etc., it will still do so after the tune only “faster” and in a more abrupt manner. One can certainly move quicker through the issue and pretend it doesn’t exist, but the reality is different, and drivers can and will notice it.
The OEM was designed w/ three very distinct regions, a straight from 0 to 25 degrees, another straight 30-70 deg, then a last curved region after 70 deg (not shown) which is not of importance in this discussion.
The 0 to 25 deg region provides about 1.2 g/s of air per degree of blade travel, while the 30-70 deg region provides about 10 g/s of air per degree. There is a knee (transition) in between those two regimes of the curve. When you transition from one region to another you are changing the airflow rates almost a whole order of magnitude (10X). This is the case described by many drivers trying to pass another car or climbing a hill at 1.2 g/s-deg (not enough) then having to go to 10 g/s-deg (too much) and being at risk of a collision w/ the car in front on the other lane. I’d argue that this is what is dangerous, even more so if enhanced by a tune. Not only dangerous but a persistent nuisance on everyday driving.
On the other hand, the design proposed here takes care of the problem by removing the real/physical barrier to throttle response, that is the geometry of the body itself. The plot (red) speaks for itself. The blade finds an increasingly wider air gap relative to the body earlier in the travel regardless of tune/pedal mapping. The airflow/power at part throttle has been redistributed where needed with a smother transition in between regimes. The driver always knows what the car is going to do, and that predictability makes it safer. The knee of the curve is also wider, and the changes are not abrupt. More importantly, the stumble and the hesitation are eliminated, not swept through with the hope it’s not going to be there. A tune cannot do this.
About the screws and shaft safety concerns:
Fist of all I’d like to reassure you, and more importantly members w/ a genuine interest for this modification, that the main contributors to this design are engineers w/ great academic and empirical backgrounds, also with decades of experience in the fields of aerospace, mechanical, electro-mechanical, design, and materials. I can also tell you that this is not the first butterfly valve we have worked on, neither it is the most critical one.
The screws have been changed to precipitation hardenable stainless steel with 3-4 X picth of engagement (they would fracture under the head rather than stripping the threads), secured at the proper torque value with high temperature aerospace grade thread locking compound, and they are peened as well.
The half-shaft modification has been properly evaluated; metallurgical, static, dynamic, and deflection. In summary; the factor of safety for the half-shaft is greater than 7 (conservatively) with infinite load/life cycles. The weakest point of the assembly happens to be the blade, which is common (for all that matter) to both, the OEM and this design, the factor of safety for the blade is greater than 3. Results follow.
5. Shaft Microstructure. Units in 1/1000 inch. Steel, through hardened and tempered to 100 ksi ultimate strength.
Note: At the risk of giving merit to your speculation, you should know that the ECM will immediately enter limp mode before the car accelerates “to the moon”. In any case we are confident in our design and are able to defend it with data, theoretical and empirical. I have personally tested this design for several months now, members are testing it too. We’ll find out soon enough, stay tuned.
It is also good to remember that half-shaft modifications have been out there for quite a long time and that in that same time period, we have heard in the news about unintended acceleration issues related to software (tune), yes, those have been insane liabilities.
Lastly, if you purchase one of our throttle bodies, you should be able to properly evaluate it and post facts about it. Further speculation will only cloud this thread for the rest of us. You can start a different thread where we can expand on your subject. I’ll try to participate, although I cannot spend much time putting out fires that don’t exist. I’ll do my best based on the merits of your comments, specially if you find more things to “LOL” about.
Long time lurker. Would love to get my hands on something like this. Great job! Hit the nail on the head. This one ups anything I’ve seen on the market and/or forums... impressive indeed...
I started trying to improve my own, and also as a hobby. When I saw it worked and the time/money it took to do it, I started to think it might have potential as a business.
About the motor, there are two different p/n of TB for the C7’s, depending on model year. The older p/n motor was not able to control idle RPM for the modification within (about +/- 30 RPM). In any case, and regardless of model year (TB p/n) the motors need to be the latest T/B p/n, fully compatible GM/Delco motors, and a part modified this way needs to have it.
Backlash; the reason I said minimized is b/c one cannot really get rid of it, at least I have not figured out how, but after having played around w/ several OEM TB’s from different Mfg lots, one can sort the center cluster gears according to tooth thickness and pitch diameter, at the same time, sort the whole gear train of each TB according to shaft center distances, then simply match and swap them.
I’ve also added below a plot of the minimum measured performance of the modified throttle bodies. The fun factor seems to be on the rate of change (slope/gain of curve) from idle (5 deg) to 25 deg. The plots look very similar (a matter of scaling) but the mass air flow gains tell a different story:
OEM: 1.2 grams/sec-Deg (Baseline)
Best Aftermarket: 1.5 grams/sec-Deg (25% Increase)
I'm not an engineer, so please help me understand how your different motor and backlash optimization would flow more air at 20-25% throttle angle than the best PTB on the marketplace.
Have you done other porting or modifications to the flow path that other porters have not?
You know what's even easier? Do not try to drive in 5th or 6th gear at 1300 rpm?
THe only time i have an issue with throttle responsw was trying to ease away from a stop in traffic. If you keep RPM'S above 1700 or so, you never have an issue. (M7)
But it looks like you had fun, so well done... BZ...
I've an '18 LT1 M7 I always run in "Touring" mode. I've 4K miles on it; to date I've seen no untoward issues with throttle response. For some perspective, I'm not a beginner at hipo; I've driven everything from assorted twin-turbos, Vortech, Paxton Novi, Kenne-Bell, even an original Boss 429, among others, on the street and the Salt Flats. Our trottles are computer moderated and I have found others who expect a DBW system to "feel" identical to direct, hard-linkage. That isn't going to happen, to varying degrees for varying reasons under different conditions. But, that said, I see absolutely nothing amiss with my stock Stingray. Now, once one start modding the ballpark changes, of course.
I went with the Katech PTB and noticed a difference in throttle response mainly in cruise. Car would react faster with throttle inputs and actually needed less throttle to make changes to speed or maintain it while climbing a hill. I have an A8 and that's the only change that was noticeable. Very interested to see what you come up with.
I'm not an engineer, so please help me understand how your different motor and backlash optimization would flow more air at 20-25% throttle angle than the best PTB on the marketplace.
Have you done other porting or modifications to the flow path that other porters have not?
I hope you really have something here.
Thanks...
db2xpert, you are right, using the latest TB p/n motor or minimizing backlash does not increase flow at all, it just eliminates a tiny bit of dead band in the system, I hardly believe it is noticeable. The same goes for the half-shaft and the countersunk screws, there are claims that it increases airflow/HP at WOT, but I think it's hardly noticeable/measurable. Nevertheless, they are little steps in the right direction, and they should be included IMO.
The airflow gains (from 5 to 35 deg) are due to the new shape that was given to the active contour of the modified throttle body, that is all the red surfaces in the last picture of post #1. I'm not sure I'd call it porting, as porting usually refers to smoothing corners and improving the surface finish of the flow path. This is a new flow path w/ a matching reworked plate.
The aftermarket PTB's were only ported at the top/upstream active profile, where a corner radius was added. In figure 12 of post #1 you can see the extent of the aftermarket porting, it only works from 25 deg and up, nothing happens between idle and 25 deg (plots overlap w/ OEM contour). The same goes for the bottom/downstream active profile, where nothing was modified (plots overlap w/ OEM).
In this design/mod, the gains start from idle (~5 deg) and both top and lower contour were reshaped. I'm hesitant to disclose more detailed (drawings/graphics) info but I'll post some pictures later to give you a better idea.
Last edited by Mike@SolerEngr; 02-26-2019 at 03:02 PM.
Reason: Added signature
You know what's even easier? Do not try to drive in 5th or 6th gear at 1300 rpm?
THe only time i have an issue with throttle responsw was trying to ease away from a stop in traffic. If you keep RPM'S above 1700 or so, you never have an issue. (M7)
But it looks like you had fun, so well done... BZ...
Exactly, that is what I used to do on my A8, drive in M mode and keep RPM's at about 2000 or higher. But wanted the same effect in D mode and w/o having to get into performance shift mode.
Last edited by Mike@SolerEngr; 02-26-2019 at 03:02 PM.
Reason: Added signature
I've an '18 LT1 M7 I always run in "Touring" mode. I've 4K miles on it; to date I've seen no untoward issues with throttle response. For some perspective, I'm not a beginner at hipo; I've driven everything from assorted twin-turbos, Vortech, Paxton Novi, Kenne-Bell, even an original Boss 429, among others, on the street and the Salt Flats. Our trottles are computer moderated and I have found others who expect a DBW system to "feel" identical to direct, hard-linkage. That isn't going to happen, to varying degrees for varying reasons under different conditions. But, that said, I see absolutely nothing amiss with my stock Stingray. Now, once one start modding the ballpark changes, of course.
True, many feel this way and there is nothing wrong w/ that, it is a matter of feel/taste. I don't have that experience w/ high performance cars. I came from a Subaru BRZ, then a VW GTI and now the Stingray and I felt the difference in throttle response since day one. Both the BRZ and the GTI felt smaller, nimbler. But; how come? The C7 has more than double the HP and it is lighter. I thought it was in my head, until I measured/calculated the weight to power ratio at part throttle of the C7, then went into a 375 HP/ 5700 lb SUV and did the same. The weight to power ratios were the comparable and felt comparable (200-300 lb/HP) at part throttle. Then, I knew it was real.
Last edited by Mike@SolerEngr; 02-26-2019 at 03:03 PM.
Reason: Added signature
I went with the Katech PTB and noticed a difference in throttle response mainly in cruise. Car would react faster with throttle inputs and actually needed less throttle to make changes to speed or maintain it while climbing a hill. I have an A8 and that's the only change that was noticeable. Very interested to see what you come up with.
Had exactly the same experience w/ aftermarket PTB's and decided to find out how much more modification it can support. So far so good. Still needs more testing though.
Last edited by Mike@SolerEngr; 02-26-2019 at 03:04 PM.
Reason: Added signature
I came from a long line of fine, high-revving German automobile (still have it, by the way). The one thing that upon first test drive always bothered me was how sluggish the throttle response was on the C7. Almost like nothing happens at the first 1/2" of pedal travel. Unlike the German with the 6 individual throttle bodies that always seems to jump and pounce straight off the throttle tip-in, the C7 doesn't seem to want to do anything fun until you depress the throttle past 30%. I always just assumed it's the nature of the beast...
Now I know why.
Looks like a ported throttle body is definitely in the books, and here I am thinking that the C7 is good to go to the track bone stock.
db2xpert, you are right, using the latest TB p/n motor or minimizing backlash does not increase flow at all, it just eliminates a tiny bit of dead band in the system, I hardly believe it is noticeable. The same goes for the half-shaft and the countersunk screws, there are claims that it increases airflow/HP at WOT, but I think it's hardly noticeable/measurable. Nevertheless, they are little steps in the right direction, and they should be included IMO.
The airflow gains (from 5 to 35 deg) are due to the new shape that was given to the active contour of the modified throttle body, that is all the red surfaces in the last picture of post #1. I'm not sure I'd call it porting, as porting usually refers to smoothing corners and improving the surface finish of the flow path. This is a new flow path w/ a matching reworked plate.
The aftermarket PTB's were only ported at the top/upstream active profile, where a corner radius was added. In figure 12 of post #1 you can see the extent of the aftermarket porting, it only works from 25 deg and up, nothing happens between idle and 25 deg (plots overlap w/ OEM contour). The same goes for the bottom/downstream active profile, where nothing was modified (plots overlap w/ OEM).
In this design/mod, the gains start from idle (~5 deg) and both top and lower contour were reshaped. I'm hesitant to disclose more detailed (drawings/graphics) info but I'll post some pictures later to give you a better idea.
01-08-2019, 03:35 PM
C7 throttle body response, getting to know it
