[ANSWERED] Why weren't the C7's E85 compatible in order to combat knock and heat? - CorvetteForum - Chevrolet Corvette Forum Discussion

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[ANSWERED] Why weren't the C7's E85 compatible in order to combat knock and heat?

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[ANSWERED] Why weren't the C7's E85 compatible in order to combat knock and heat?

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Old 11-04-2015, 11:49 AM
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Default [ANSWERED] Why weren't the C7's E85 compatible in order to combat knock and heat?

Original question is here.

RC000E asked:
Allowing the Z06 or C7's the ability to use E85 seems like a fantastic option for track sessions to keep knock retard at bay, reduce EGT's, etc. Was there ever a consideration to make these cars flex fuel compatible and/or why was the decision made not to?
Tadge answered:
RC000E, as you correctly point out, higher octane of E85 is directionally correct in mitigating knock and resulting spark retard. We have recommended the use of racing fuel and octane boost for that very reason in certain situations. The issue with E85 in high performance engines is that there is less total energy per gallon, that is why fuel economy measured in miles per gallon tends to be worse with E85. While it is theoretically possible to build a 650Hp engine that uses E85, The challenge is getting enough fuel into the cylinders. The fuel flow rate to the injectors has to be higher in proportion to the energy content of the fuel. That means over 25% more fuel flow. Direct injection engines require very high fuel pressure to operate. At the time the LT4 engine was designed, there was no pump in existence that could manage the combination of flow and pressure. It is always possible to try to force a supplier into a unique low-volume solution to meet our needs however it would have been larger, heavier and much more expensive. In addition to the pump on the engine, the pump in the fuel tank would have to be up-sized and possibly even need twin pumps. Routing fuel from the tanks at the back of the car to the engine at the front is always a challenge. Higher volume of fuel flowing requires larger lines that are even more difficult to package. So, for a variety of technical reasons, we elected not to design for E85 on Corvette.
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Old 11-04-2015, 12:04 PM
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Fell in line with what was expected I suppose. E85 has a much lower BTU output, so you burn approx 35% more by volume. Scaling up that volume has never proved much of a challenge, but I suppose with DI it became a cost prohibitive option at the time of development.

Off to SEMA...peace Corvette forum...I'll be back with whatever factoids I can dig up.
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Old 11-04-2015, 12:44 PM
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Tadge's points are well made. After all the DI pump is in the block. Any incrase in its size could be prohibitive.

Since E85 is not available to us all, any increase in cost passed on to the consumer in the form of higher MSRP would be suffered by all buyers, but the benefits enjoyed only by a few. It would effectively work as a subsidy. As a Californian I would be subsidizing the use of E85 in the midwest. Not cool haha.

Thanks Tadge and JVP. Great info.
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Old 11-04-2015, 10:06 PM
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It is always a pleasure to read these detailed explanations of the decision process that led to the current Corvette offerings. A heartfelt thanks to Tadge and JVP for making this happen.

Designing a product that is suitable for and desired by a wide audience that is simultaneously profitable (and meets applicable regulations) is certainly not simple as one finds out once you drill down into the process. Years ago when I was teaching an intro to marketing course I found a simple way of getting this across was asking each student to design their own perfect radio station playlist and most of them were shocked when they found that other students didn't share the same idea of the perfect playlist. No product we own or can buy is absolutely perfect for us as an individual but fortunately a lot of products come very close and I am happy to count the C7 in that group.
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Old 11-04-2015, 10:58 PM
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Default Doubtfull call poor decision...

I'm hopeful the aftermarket industry will step up to the challenge and point the way forward for the fuel delivery demands of the DI engine in relation to E85 requirements.

Not throwing my hands up in the air, at $1.59 a gallon for 104 octane cooler running E85 14 to 1 compression or 35 psi boost is sweet feasible fitting very desirable clean burning non stinking high power good for the planet great for Chevrolet or perhaps it's competitors.

In my never to be humble opinion this call by Chevrolet could stand to bite them in the a$$ in the manufactures horse power war in which they so far done well, however the jelly have come to meet it's challenge and perhaps will like to take full advantage of this poor decision and do better.
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Old 11-05-2015, 09:25 PM
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I applaud GM and gadgets for taking the time to answer corvette enthusiasts questions.

We may not always like the answers but the open communication is impressive.

Thank you and the forum for offering us the opportunity to better understand various decisions.
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Old 11-06-2015, 10:32 AM
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There is a very easy solution to the DI pump issue, don't use DI. Use port injection which is the way Chrysler went with the Hellcat engine.
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Old 11-06-2015, 12:28 PM
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Great response. Thanks again to JVP for keeping this channel open!
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Old 11-06-2015, 05:43 PM
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Originally Posted by grcor View Post
There is a very easy solution to the DI pump issue, don't use DI. Use port injection which is the way Chrysler went with the Hellcat engine.
Then they can't hit their MPG goals which was important for them.
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Old 11-06-2015, 06:14 PM
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Originally Posted by 11B250 View Post
Then they can't hit their MPG goals which was important for them.
MPG goals? They add DI, 7 speeds, and cylinder deactivation and get worse gas mileage than the C6 Z06, now that is progress!

Last edited by grcor; 11-06-2015 at 06:19 PM.
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Old 11-06-2015, 11:04 PM
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Originally Posted by grcor View Post
MPG goals? They add DI, 7 speeds, and cylinder deactivation and get worse gas mileage than the C6 Z06, now that is progress!
Never mind the extra 145HP of course.
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Old 11-07-2015, 01:42 AM
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Originally Posted by jvp View Post
Never mind the extra 145HP of course.
The extra 145HP was needed to luge the extra 300 to 350 pounds around. On the track this leads to a huge increase in fuel usage which translation into a lot more heat and it becomes painfully obvious why the car overheats after 4 laps.
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Old 11-07-2015, 08:23 AM
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Originally Posted by grcor View Post
The extra 145HP was needed to luge the extra 300 to 350 pounds around. On the track this leads to a huge increase in fuel usage which translation into a lot more heat and it becomes painfully obvious why the car overheats after 4 laps.
Sure, sure. Because the jump from the C5 Z06 to C6 Z06 was a mere 20HP, right? Oh, wait, no, it wasn't. It was 100HP. So moving from 405HP -> 505HP -> ~525HP would have been acceptable to the market?

Keep swinging. You'll eventually get a hit. It's clear you really don't understand what's at play here.
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Old 11-07-2015, 11:48 AM
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Default Heater on the top...

Lots is at play and supercharging is nice but two small turbos will clean up the heat soak and be more efficient, crank parasitic loses invested in producing heat are showing up at the gas millage charts.

If wasted and available unnecessary heat is employed in producing power combined with DI (a very important and a great step forward) a mountain would be forged too tall to climb for the competition while keeping the head soak at bay loosing at least 100 lbs. and running way cooler with all integral components sparsed rather than piled up, using oversize cold and hot piping will help produce more power with less boost reducing heat compared to minimalist piping.

Racing with a top mounted supercharger is like wearing an artic heated blanket while living at equator.

Hopefully without roughing the big "C", Tadge or any of it's staff on how to do but rather how to position for the game within the free market place of experience.

xBoostx never tbho.
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Old 11-07-2015, 11:59 AM
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Originally Posted by jvp View Post
Sure, sure. Because the jump from the C5 Z06 to C6 Z06 was a mere 20HP, right? Oh, wait, no, it wasn't. It was 100HP. So moving from 405HP -> 505HP -> ~525HP would have been acceptable to the market?

Keep swinging. You'll eventually get a hit. It's clear you really don't understand what's at play here.
I know exactly what is in play here from your point of view. Sell more cars. Appeal to biggest audience that can spend $100,000+. Graying men who are going through a midlife crisis and want the image of driving a high performance sports car to make them feel young again. That image was built on the C5 and C6 Z06 cars that you could take from the showroom to the track with no issues. Unfortunately that image is being destroyed by the C7 Z06 sold as “the most trackable Corvette ever made” and making a convertible Z06’s for “people who want all the performance in an open air experience” even though Corvette convertibles are not allowed on any tracks.

I am sure you have seen all the posts from people who have taken the C7 Z06 to the track and who are disappointed when it overheats and feel that they were misled by Chevrolet. Posts from people who have delayed or canceled their orders until the overheating issues can be resolved (I do not think they will ever be completely resolved). Post from people who want to be “comfortable” in a Z06 when they should have purchased the base model or a GT(Jaguar,etc.). Posts from people who realize that maximum performance tires do not work in the rain and want an all season tire option. Posts from people who have owned a ZR1 and traded for C7 Z06 and now wish they had their old ZR1 back. All these things are destroying what a Z06 is supposed to be. Then you add on the complaints about poor paint quality and Consumer Reports calling the Corvette one of the least reliable cars and sales will be hurt.

Let’s hope that the Corvette engineers are given enough money to fully develop the C8 into a truly great sport car that it is supposed to be.

Last edited by grcor; 11-07-2015 at 12:08 PM.
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Old 11-07-2015, 07:04 PM
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So, help me out here. I know others are putting flex fuel units on their cars and even changing cams with a larger fuel lobe. I have not read that these mods are not beneficial?
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Old 11-09-2015, 07:12 AM
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Originally Posted by jvp View Post
Sure, sure. Because the jump from the C5 Z06 to C6 Z06 was a mere 20HP, right? Oh, wait, no, it wasn't. It was 100HP. So moving from 405HP -> 505HP -> ~525HP would have been acceptable to the market?

Keep swinging. You'll eventually get a hit. It's clear you really don't understand what's at play here.
650 HP is overkill. Sure people make more, but 625 or 600 would have been enough.

BTW for all the tech they put into this car, and the base Stingray in the name of fuel economy they honestly didn't move the needle too much. The C6 got excellent fuel economy for the type of car it was.

Having worked on the program at some point and hearing Tadge talk about it, "Fuel Economy" is his number one go to reason when he does something that most people (even on the program) complained about. It is a very typical corporate stooge type of answer and people are right to question the validity.

As usual, I'm not satisfied with his answers, but then again I've been behind the curtain so for me the magic is gone. Thankfully the value to performance is still there, or else I'd take my dollars elsewhere, and I think most people here are the same way.
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Old 11-09-2015, 07:48 AM
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Originally Posted by LS3 MN6 View Post
650 HP is overkill. Sure people make more, but 625 or 600 would have been enough.
All well and good. The Corvette team and the Power Train team have already said (multiple times) that squeezing much more than 525HP out of an N/A engine wouldn't have worked. They couldn't hit the FE and emissions numbers with it.

So, again: would a 20HP jump from last gen's Z06 been enough? I'll bet it wouldn't.
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Old 11-09-2015, 09:31 AM
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Originally Posted by jvp View Post
All well and good. The Corvette team and the Power Train team have already said (multiple times) that squeezing much more than 525HP out of an N/A engine wouldn't have worked. They couldn't hit the FE and emissions numbers with it.

So, again: would a 20HP jump from last gen's Z06 been enough? I'll bet it wouldn't.
Was I suggesting you needed to go N/A to only have 600?

No, I wasn't.

It is possible to dial back the supercharger size, and power output and both of those things would be more beneficial to fuel economy than many other "complicated" systems they decided to implement.

However you also glazed over the fact that I mentioned the Stingray in my argument as well.

When one picks and chooses points to argue of a larger issue, you can of course make yourself win but this defeats the point of the discussion. So either we have a discussion in all honestly, or we don't.
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Old 11-09-2015, 10:15 AM
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Originally Posted by LS3 MN6 View Post
So either we have a discussion in all honestly, or we don't.
How "in all honesty" do we want to get? Perhaps include why we're (you're)not "behind the curtain" any longer? I bet I know why...

Whoops. I just argued a specific point versus the whole thing. How about I tap out of this and you continue on doing what you're doing.
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