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Highest Dynamic compression ratio with 91 octane and Eldelbrock Head

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Tolemar
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Highest Dynamic compression ratio with 91 octane and Eldelbrock Head

Post by Tolemar » November 9th, 2019, 9:29 am

Hi everyone like to get real world experience of the highest possible Dynamic compression ratio on a stroker with a Eldelbrock aluminum head and 91 octane. I see different DCR examples on other engines but like to know what has been done already. One of the DCR calculator page says that 8.25:1 is a reasonable DCR but has anyone got away with higher without issues? Obviously like to have about .040 quench.

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Re: Highest Dynamic compression ratio with 91 octane and Eldelbrock Head

Post by Tolemar » November 20th, 2019, 11:14 am

Ok so I guess this thread is dead before it started LoL.

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Re: Highest Dynamic compression ratio with 91 octane and Eldelbrock Head

Post by Cummins90 » November 20th, 2019, 1:34 pm

Looks like you will be pioneering the topic. I only have experience with forced induction so unfortunately I cant help you out.

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Re: Highest Dynamic compression ratio with 91 octane and Eldelbrock Head

Post by Cheromaniac » November 20th, 2019, 11:20 pm

There are other factors at play including the state of the cooling system and whether you can get the coolest air possible into your throttle body.
With attention to detail and a tight quench, I'd say even a DCR of 8.5 would be OK as the aluminum head will dissipate more heat than the stock iron unit.
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Tolemar
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Re: Highest Dynamic compression ratio with 91 octane and Eldelbrock Head

Post by Tolemar » November 21st, 2019, 1:26 am

Allready have an all aluminum equivalent to 3 core radiator and a new higher performance flowing waterpump. Not to mention a black magic extreme electric fan that should smoke the factory clutch fan hands down. As far as cold air induction I'll figure something out its a wrangler so I'm sure their are lots of options. Does anybody know what the actual running timing would be under load? I know the LS V8 engines can run a lot higher dynamic compression ratio do to their efficient combustion chamber and conservative timing. Now you say 8.5:1 is doable is this from experience or a guess? Driving down the road and pinging on 91 octane while in overdrive isn't my idea of acceptable. I notice some have slotted their cps in order to get more timing maybe with a higher DCR this is not needed. Unless to reduced map signal from a bigger camshaft is backing timing out a bit but I'm not exactly sure how things work.

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Re: Highest Dynamic compression ratio with 91 octane and Eldelbrock Head

Post by Tolemar » November 21st, 2019, 1:34 am

Cummins90 wrote:
November 20th, 2019, 1:34 pm
Looks like you will be pioneering the topic. I only have experience with forced induction so unfortunately I cant help you out.
I have some experience with building blown big block and smallblock engines also.
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Re: Highest Dynamic compression ratio with 91 octane and Eldelbrock Head

Post by danleym » April 30th, 2020, 1:37 pm

Any chance you've built the engine you were asking about yet? I'm going to be going down the same road, and I'm trying to figure out how high I can push the compression.

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Re: Highest Dynamic compression ratio with 91 octane and Eldelbrock Head

Post by Tolemar » May 1st, 2020, 6:26 am

Not yet just got the engine block from machine shop yesterday but I think the stock timing curve in these Jeeps is really conservative. That with a tight quench , aluminum head and more efficient combustion chamber will allow mine to take more compression. I’m thinking 8.5:1 Dynamic should be fine with an aluminum head. 9:1 dynamic is in race gas territory imo.

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Re: Highest Dynamic compression ratio with 91 octane and Eldelbrock Head

Post by 2jxj » June 9th, 2020, 8:39 pm

Ive gone around 10 to 1 before with standard pistons and also advanced the timing...Was fine no pinging at all with a bunch more torqe...Absolutely reccommend it over a cam swap...

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Re: Highest Dynamic compression ratio with 91 octane and Eldelbrock Head

Post by Bertismyname » June 14th, 2020, 4:16 pm

What year is the jeep. What fuel management are you going to run? Chrysler was fond of using lean burn to reduce emissions. Especially after 1996 or so. The thought was that lean burn was a viable option for e.g.r.
It was for stock engines. Im not saying e.g.r. is the answer for you. But, the lean burn/ cruise kept the engine at the point of detonation. When I worked at the Chrysler dealership pinging was a normal drivability complaint.
The e.g.r. equipped vehicles didn't really have the same issues. Increased cam duration/ overlap helps.

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Re: Highest Dynamic compression ratio with 91 octane and Eldelbrock Head

Post by Tolemar » June 23rd, 2020, 8:26 am

Bertismyname wrote:
June 14th, 2020, 4:16 pm
What year is the jeep. What fuel management are you going to run? Chrysler was fond of using lean burn to reduce emissions. Especially after 1996 or so. The thought was that lean burn was a viable option for e.g.r.
It was for stock engines. Im not saying e.g.r. is the answer for you. But, the lean burn/ cruise kept the engine at the point of detonation. When I worked at the Chrysler dealership pinging was a normal drivability complaint.
The e.g.r. equipped vehicles didn't really have the same issues. Increased cam duration/ overlap helps.
Mine is a 97 tj. Im using a stock computer that im going to be tuning with a hp tuner with larger ford racing 24# 6 hole injectors. being too lean with those injectors shouldn't be an issue if anything I might have to pull some fuel out especially at start up in open loop. Tight quench with an aluminum eldebrock head and bigger cam should keep the detonation at bay but looking at the conservative factory timing map there is a lot of room for improvement. Wot throttle timing in the low 20s is just stupid even on a stock engine. Alsp part throttle timing in the 40s seems excessive to me and is probably why it detonates. I guess they did that for smog reasons but imo its not ideal. im going to be tuneing wit a wide band so everything should go pretty smooth.

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Re: Highest Dynamic compression ratio with 91 octane and Eldelbrock Head

Post by Bertismyname » June 24th, 2020, 7:23 am

40 may be excessive. But the engine will tell you what it wants. When tuning i try to be as consistent with fuel as possible. I will buy fuel from the same station if I end up going through multiple tanks while tuning. I'll also load the vehicle with what ever weight I plan on. Having. Spare tire tools extra fluds that kind of stuff. The weight will affect how the vehicle responds to fuel and timing changes. If you do a Google search of stations near you. You can find which stations have more ethanol in the fuel. Different percentage of ethanol will cause tuning headaches. I look for the stations that use less ethanol.
Near my house the shell stations, 76, and citgo usually have lower ethanol levels and more consistent fuel.

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