Flex fuel build
Thread Starter
Le Mans Master
Joined: Dec 2005
Posts: 6,997
Likes: 1,681
From: Southeast TX
Flex fuel build
How much can you increase the static compression ratio through milling and/or use of thinner head gaskets? Assuming a mid 220's cam with fairly wide LSA (115-117), when do you get into PTV issues? With the heads being good as is, the exhaust being good as is, the intake being good as is, it seems to me that a higher compression LT2 with a mild cam ought to be a pretty good use of funds vs the typical bolt ons. Your thoughts appreciated.
Thread Starter
Le Mans Master
Joined: Dec 2005
Posts: 6,997
Likes: 1,681
From: Southeast TX
You can spend $1500 on a CAI, $6500 on an intake manifold, $8000+ on the exhaust side....and what does that get you?
Thin head gaskets and a little milling....hundreds, not thousands. Flex fuel setup, not sure, new to the platform. Cam swap, not much for parts. Labor will be up there, but not near what you can spend on CAI, intake mani, and exhaust upgrades. What am I missing?
Thin head gaskets and a little milling....hundreds, not thousands. Flex fuel setup, not sure, new to the platform. Cam swap, not much for parts. Labor will be up there, but not near what you can spend on CAI, intake mani, and exhaust upgrades. What am I missing?
Melting Slicks
Joined: Oct 2008
Posts: 2,044
Likes: 1,075
From: Pasadena Texas
You can spend $1500 on a CAI, $6500 on an intake manifold, $8000+ on the exhaust side....and what does that get you?
Thin head gaskets and a little milling....hundreds, not thousands. Flex fuel setup, not sure, new to the platform. Cam swap, not much for parts. Labor will be up there, but not near what you can spend on CAI, intake mani, and exhaust upgrades. What am I missing?
Thin head gaskets and a little milling....hundreds, not thousands. Flex fuel setup, not sure, new to the platform. Cam swap, not much for parts. Labor will be up there, but not near what you can spend on CAI, intake mani, and exhaust upgrades. What am I missing?
Thread Starter
Le Mans Master
Joined: Dec 2005
Posts: 6,997
Likes: 1,681
From: Southeast TX
Hoping that price for a tune will come down over time. Isn't a tune necessary for almost any significant power gain? Maybe I'm looking at this wrong, but I'm thinking that an increase in static compression ratio (12.5:1?) along with E fuels and a mild cam, could result in triple digit power gains. Shouldn't take a really nasty/ill mannered cam either. I've already had my last build with an ill mannered cam. I'll never do that again.
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Racer
Joined: Feb 2020
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From: Philly
I've been down this road. The kinks haven't been worked out in raising the rpm limits, which hurt the effectiveness of a bigger cam. Imo a .040 mill and a .040 Cometic with 7.80 pushrods and an e85 tune is gonna be the cheapest and best bang for the $$...aside from a lighter wheel/drag tire combo.
Thread Starter
Le Mans Master
Joined: Dec 2005
Posts: 6,997
Likes: 1,681
From: Southeast TX
I've been down this road. The kinks haven't been worked out in raising the rpm limits, which hurt the effectiveness of a bigger cam. Imo a .040 mill and a .040 Cometic with 7.80 pushrods and an e85 tune is gonna be the cheapest and best bang for the $$...aside from a lighter wheel/drag tire combo.
Burning Brakes
Joined: Sep 2016
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From: Ohio
If you're doing cam, I think I'd skip the head milling. It wouldn't be worth the risk of PTV issues or being forced to replace the heads if they ever lose flatness and need milled again. It would also be marginal gains compared to the cam. The head gasket change would be fine.
Banned Scam/Spammer
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From: The E-Ray prophet
IMHO, turbos are the ideal solution if you want to run flex-fuel tunes. Supercharger will tie you to the use of whatever pulleys you put on it. Turbos can be adjusted for whatever bar you want...in order to match the fuel supply. Much easier adjusting for knock with turbos than a SC or N/A and adjusting compression ratios.
Burning Brakes
Joined: Sep 2016
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From: Ohio
IMHO, turbos are the ideal solution if you want to run flex-fuel tunes. Supercharger will tie you to the use of whatever pulleys you put on it. Turbos can be adjusted for whatever bar you want...in order to match the fuel supply. Much easier adjusting for knock with turbos than a SC or N/A and adjusting compression ratios.
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From: The E-Ray prophet
Supercharger boost is far more consistent and controllable than turbos. Its not as easy to adjust, but once its set, you can usually forget about it. I don't think turbos are easier to adjust for knock. Boost pressure isn't usually what you adjust when you're trying to tune out knock unless you set it way too high. Even then, you evaluate all of the factors and make your decision from there.
Burning Brakes
Joined: Sep 2016
Posts: 1,133
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From: Ohio
You'll run a little more rich (subjectively) and with less timing on gas, with a better AFR and more timing on E85.
You don't have to swap pulleys. You choose the ratio you want that is survivable on gas and it'll be very happy on E85.
There are even ways to reduce boost below what the pulley combination is setup for depending on the type of supercharger being ran., so you can go with slightly more pulley than needed for gasoline.
Also, in a flex fuel build, there would be zero reason to have to reflash the turbo setup...
Last edited by JoeNova; Oct 14, 2025 at 03:14 PM.
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From: The E-Ray prophet
Odd. Because my experience in the tuner community has it so that you can run 93 octane on the daily, and 110 octane e85 when the time is right. And afaik, the simplest way to handle the additional octane capability--is boost.
That's the main reason why all of the OEM flex-fuel vehicles are maligned as having ****-poor MPG on e85; the engine simply cannot take advantage of the octane. FI is the easy way to fix that.
That's the main reason why all of the OEM flex-fuel vehicles are maligned as having ****-poor MPG on e85; the engine simply cannot take advantage of the octane. FI is the easy way to fix that.
Burning Brakes
Joined: Sep 2016
Posts: 1,133
Likes: 319
From: Ohio
Odd. Because my experience in the tuner community has it so that you can run 93 octane on the daily, and 110 octane e85 when the time is right. And afaik, the simplest way to handle the additional octane capability--is boost.
That's the main reason why all of the OEM flex-fuel vehicles are maligned as having ****-poor MPG on e85; the engine simply cannot take advantage of the octane. FI is the easy way to fix that.
That's the main reason why all of the OEM flex-fuel vehicles are maligned as having ****-poor MPG on e85; the engine simply cannot take advantage of the octane. FI is the easy way to fix that.
I've been speccing, designing, building, fabricating, and tuning for almost 20 years now. I've tuned dozens of different ECU types.
One of my corvettes has a quad-turbo setup on MS3Pro with a flex fuel sensor so I can run any amount of ethanol I want. I can also adjust the boost on the fly and no tuning changes are required.
Changes for E85 and boost don't require retunes or reflashes, and superchargers only need pulley swaps for long term boost changes, which only takes a few minutes once you've done it.
Thread Starter
Le Mans Master
Joined: Dec 2005
Posts: 6,997
Likes: 1,681
From: Southeast TX
Don't think I want to fool with forced induction. I had two C6's that were each TVS2300 blown. Each around 650 at the wheels. They would try to kill me in the first two gears. 3rd gear could get pretty sketchy too. Last Vette was also a C6, but no blower. Everything on top of the short block was ported along with a mild cam upgrade and increased static compression ratio. It had .040 head gaskets and heads that were milled .010. That one made 500 at the wheels and was just more fun than the two beasts that preceded it.
I'd be happy with low to mid 500's at the wheels. Having the transmission last would also make me happy. A mid 220's cam is as big as I'd want to go. No overlap for me. Nasty cam noises don't impress me nowadays. Much rather have smooth with perfect manners.
I'd be happy with low to mid 500's at the wheels. Having the transmission last would also make me happy. A mid 220's cam is as big as I'd want to go. No overlap for me. Nasty cam noises don't impress me nowadays. Much rather have smooth with perfect manners.