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That's a question that's very difficult to give a good answer on with provided information. Heat is directly related to compression. Depending on how hot it is and the type of supercharger you use will all play a role in that along with the combination effency of your heads. You will gain very little by trying to run a higher compression in a blower motor. You will be better off running a lower compression like 9-1 and let the blower do the work making the hp
 

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On a boosted street engine on E85, there should be no reason why you shouldn't be able to run 11-11.5:1. The engine will be more efficient when not in boost (which will be the majority of drive time on a street car). When you are in boost, it will be for short amounts of time (on the street) and at 7-10 lbs, it will live a long, healthy life.
 

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E85 varies a LOT. Summer blend can be 90+% and Winter can be little more than 50%. If you run E85, you need to check every batch. When you find a GOOD batch, buy it by the drum and store it in SEALED containers filled to the top... and stored out of the heat/direct sunlight.

If you don't do this... especially with a carb... the tune will drive you nuts.
 

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Blower Basics (Part 2): Boost and What You Need to Know - OnAllCylinders "Also, remember that low compression, high boost engines will make more power than high compression, low boost setups."

The above chart is pretty straight forward, but as RCparker said theres other factors too. Add cam and dynamic compression into play and you have even more decisions to make.
 

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My guess - with alum heads (without softening) target dynamic compression no more than 9.5. A street vehicle with correct cam, is NOT going to bleed off much compression. Check web for dynamic compression calculator and plug in your cam numbers. Note - some use adv dur while others use at .050".
 

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Discussion Starter · #8 ·
This is the Camshaft:

Hydraulic Roller

Camshaft Manufacturers Description:
Fair idle, good midrange and strong top-end power, 3,000-6200 rpm powerband. 2,500-3,000 rpm stall converter. Compression: 9.5:1 minimum.
Basic Operating RPM Range:
3,000-6,200
Intake Duration at 050 inch Lift:
236
Exhaust Duration at 050 inch Lift:
242
Duration at 050 inch Lift:
236 int./242 exh.
 

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The shop that tunes my cars typically targets 10:1 static for blower street cars. They told me you are generally safe with their tunes with the variability of ethanol in pump fuel at that level.
 

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This is the Camshaft:

Hydraulic Roller

Camshaft Manufacturers Description:
Fair idle, good midrange and strong top-end power, 3,000-6200 rpm powerband. 2,500-3,000 rpm stall converter. Compression: 9.5:1 minimum.
Basic Operating RPM Range:
3,000-6,200
Intake Duration at 050 inch Lift:
236
Exhaust Duration at 050 inch Lift:
242
Duration at 050 inch Lift:
236 int./242 exh.
With that cam 10:1 would be acceptable with lower boost like you are looking at even running E50. I wouldn’t go any more because you can still run pump gas if you get in a pinch assuming this is a street strip deal.
 

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You can't throw out a number and expect it to be good across the board on every motor. From carb to fuel injection makes a huge difference. Running a piece of shit 6-71 or running a innercooled Whipple would be a huge difference. BBC aren't know for having the best combination chambers though newer heads have addressed that. Trying to compare a factory BBC head to even a factory LS3 head is night and day difference. Every combination has to be looked at as a system. If you target your compression just based off a number and not what you actually have you are about to get to know your piston salesman pretty good
 

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E85 varies a LOT. Summer blend can be 90+% and Winter can be little more than 50%. If you run E85, you need to check every batch. When you find a GOOD batch, buy it by the drum and store it in SEALED containers filled to the top... and stored out of the heat/direct sunlight.

If you don't do this... especially with a carb... the tune will drive you nuts.
I have ran e85 for years and have never seen that much variation. And I would not be chasing the tune for e70-e85.
 

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I have ran e85 for years and have never seen that much variation. And I would not be chasing the tune for e70-e85.
The Sheets stations that sell E85 here say right on the pump... can vary between 51% and 83%.
Some people will buy drums of the summer blend before they switch the the lower percentage winter fuel.
 
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