Compression ratio, Boost, and E85
I'm going to have to come back and read this when I have time. For what it's worth with no tech or science behind it I run 10.6 to 1 with 16 psi peak on 50% ethanol. It's pretty easy to tune and I never plan on going over 20 psi with this engine and if I did by then I'd have proper sized injectors and a higher ethanol content.
I'm going to have to come back and read this when I have time. For what it's worth with no tech or science behind it I run 10.6 to 1 with 16 psi peak on 50% ethanol. It's pretty easy to tune and I never plan on going over 20 psi with this engine and if I did by then I'd have proper sized injectors and a higher ethanol content.
I'm not saying math is REQUIRED, it would just be very cool to see if the excel agrees with real life or if the math says we should be higher or lower on timing. Everything throws around 14 psi and 14 degrees blablabla. Would be nice to see if math agrees. It's not that it just allows more boost. It also allows for a very forgiving tune up and is less likely to bend rods, lift heads, munch ring lands...etc. All the big issues we see with SBE setups. I get not everyone is running an SBE. But the same forces apply to "built" motors and aren't good for them either. They may not fail immediately...but there is no reason to tax them either.
I'm fairly certain I wasn't detonating when I blew the HG on my 10:1 5.3. It did mange to lift a head and torch the deck of my LC9 though. I feel it was the 25lbs of boost at 4400 rpm that did it. While we know these days that you can get around this issue somewhat with timing and power management at lower RPM, I feel a 9:1 or even lower CR would have saved me there. CYL pressures just get to dang high around PK TQ. And this is magnified with higher SCR. If I'm not towing or pulling a tree's out of the ground I don't care about the big TQ/power at low RPM. I'd prefer to make the majority of my power past PK TQ. And for the guys starting out that don't know how to manage CYL pressure at lower RPM on turbo cars.. 10:1+ SCR seems like a recipe for disaster. Esp. all these 6+ liter baby T4 setups that seem so popular.
I'm fairly certain I wasn't detonating when I blew the HG on my 10:1 5.3. It did mange to lift a head and torch the deck of my LC9 though. I feel it was the 25lbs of boost at 4400 rpm that did it. While we know these days that you can get around this issue somewhat with timing and power management at lower RPM, I feel a 9:1 or even lower CR would have saved me there. CYL pressures just get to dang high around PK TQ. And this is magnified with higher SCR. If I'm not towing or pulling a tree's out of the ground I don't care about the big TQ/power at low RPM. I'd prefer to make the majority of my power past PK TQ. And for the guys starting out that don't know how to manage CYL pressure at lower RPM on turbo cars.. 10:1+ SCR seems like a recipe for disaster. Esp. all these 6+ liter baby T4 setups that seem so popular.
Last edited by Forcefed86; May 7, 2020 at 12:10 PM.
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I definitely agree that low-end torque isn't needed especially in a light weight race car. I would have so many issues and broken parts if my car made any torque below 4k.
There is some math to support the lower CR/higher boost logic.
Cylinder pressure is after all, what produces torque and lifts heads (and can produce detonation).
Effective Compression Ratio target: 22:1 (arbitrary number)
11:1/15 PSI = 22.22:1
9:1/22.6 PSI = 22.22:1
Similar cylinder pressures will produce similar torque at peak, but the overall airflow is different.
Following the 5% per compression point rule, you lose 10% power dropping compression.
But you are increasing absolute pressure from 29.7 PSI to 37.3 PSI, a gain in overall airflow volume of 25.6%
You're looking at about a 15% increase in power, with similar torque/cylinder pressure.
You'll lose part throttle torque, off-boost torque, etc, but you'll be able to make more power while keeping the heads down.
But if keeping the heads down and octane aren't a problem.....
Everything is circumstantial.
There is some math to support the lower CR/higher boost logic.
Cylinder pressure is after all, what produces torque and lifts heads (and can produce detonation).
Effective Compression Ratio target: 22:1 (arbitrary number)
11:1/15 PSI = 22.22:1
9:1/22.6 PSI = 22.22:1
Similar cylinder pressures will produce similar torque at peak, but the overall airflow is different.
Following the 5% per compression point rule, you lose 10% power dropping compression.
But you are increasing absolute pressure from 29.7 PSI to 37.3 PSI, a gain in overall airflow volume of 25.6%
You're looking at about a 15% increase in power, with similar torque/cylinder pressure.
You'll lose part throttle torque, off-boost torque, etc, but you'll be able to make more power while keeping the heads down.
But if keeping the heads down and octane aren't a problem.....
Everything is circumstantial.
There is more to it than that though. Also don’t believe you are calculating the effective CR correctly? Is there even a correct way to do that? I’m not really convinced. I believe you need to take the SQ RT of the final sum and subtract that? Something similar to that I’d have to go look it up. Otherwise you are saying 1 bar of boost on a 8.5:1 motor nets like 16:1 instead of 12:1… even that seems wrong IMO. But more realistic… ,maybe if we are talking 87 octane.
There are too many variables anyway. Dropping even 1 point of comp. allows much more than 3 psi increase. Flame travel, cyl design, VE etc etc… all play a roll.
Even suggesting another engine is wildly off topic, but I'll do it anyway! I turbo’d my 10.2:1 NA 2JZ. I was knock limited around 9-10lbs (91 octane) verified by the knock sensors and AEM EMS. Swapping over to a 2.5mm HG with no other changes allowed me to run 22lbs with no knock. Others have run more. My fuel system/turbo were tapped at that point. I believe I could have run more with a better turbo and fuel system. But again to many variables. But clearly able to run a decent amount of boost over the factory SCR.
There are too many variables anyway. Dropping even 1 point of comp. allows much more than 3 psi increase. Flame travel, cyl design, VE etc etc… all play a roll.
Even suggesting another engine is wildly off topic, but I'll do it anyway! I turbo’d my 10.2:1 NA 2JZ. I was knock limited around 9-10lbs (91 octane) verified by the knock sensors and AEM EMS. Swapping over to a 2.5mm HG with no other changes allowed me to run 22lbs with no knock. Others have run more. My fuel system/turbo were tapped at that point. I believe I could have run more with a better turbo and fuel system. But again to many variables. But clearly able to run a decent amount of boost over the factory SCR.
Last edited by Forcefed86; May 7, 2020 at 04:18 PM.
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There is more to it than that though. Also don’t believe you are calculating the effective CR correctly? Is there even a correct way to do that? I’m not really convinced. I believe you need to take the SQ RT of the final sum and subtract that? Something similar to that I’d have to go look it up. Otherwise you are saying 1 bar of boost on a 8.5:1 motor nets like 16:1 instead of 12:1… even that seems wrong IMO. But more realistic… ,maybe if we are talking 87 octane.
There are too many variables anyway. Dropping even 1 point of comp. allows much more than 3 psi increase. Flame travel, cyl design, VE etc etc… all play a roll.
Even suggesting another engine is wildly off topic, but I'll do it anyway! I turbo’d my 10.2:1 NA 2JZ. I was knock limited around 9-10lbs verified by the knock sensors and AEM EMS. Swapping over to a 2.5mm HG with no other changes allowed me to run 22lbs with no knock. Others have run more. My fuel system/turbo were tapped at that point. I believe I could have run more with a better turbo and fuel system. But again to many variables. But clearly able to run a decent amount of boost over the factory SCR.
There are too many variables anyway. Dropping even 1 point of comp. allows much more than 3 psi increase. Flame travel, cyl design, VE etc etc… all play a roll.
Even suggesting another engine is wildly off topic, but I'll do it anyway! I turbo’d my 10.2:1 NA 2JZ. I was knock limited around 9-10lbs verified by the knock sensors and AEM EMS. Swapping over to a 2.5mm HG with no other changes allowed me to run 22lbs with no knock. Others have run more. My fuel system/turbo were tapped at that point. I believe I could have run more with a better turbo and fuel system. But again to many variables. But clearly able to run a decent amount of boost over the factory SCR.
I fat-fingered the numbers lol.
Last edited by AwesomeAuto; May 7, 2020 at 02:54 PM.
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Thread Starter
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From: Saint Joseph, MO
Wow. Lots of great info here. This is the good stuff I wanted to get into. Maybe it would help if I explain what I am considering. For starters, I am keeping the car a manual 6 speed. Whether I try to keep the t56 or upgrade to a t56 magnum or tr6060 is to be determined. Right now I have a 11 to 1 comp NA motor making 430rwp with 134k miles. Should I tear down the motor, increase ring gap, run a bit thicker head gasket, or while I'm doing all of that work just do it right now forge the internals and run 346 cubes or stroke it out to a 383. The overall goal of the car is to be a fun street car. I want to have a good amount of low end power and have an intense amount of mid to high rpm power. Hence i think twin turbos would be the way to go... Quick spooling that starts around 2500rpm or so and I would still make around 900rwhp in the end. Is this doable? What route do you think makes the most sense? And will be a build that wont blow up in 500 miles, yet doesnt break the bank.
If 900w is your goal, tear it down and replace the pistons/open the ring gap. Stroking or not is up to you but many will recommend not. Turbo(s) can make that power if sized properly and so can a blower.
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I turbo’d my 10.2:1 NA 2JZ. I was knock limited around 9-10lbs verified by the knock sensors and AEM EMS. Swapping over to a 2.5mm HG with no other changes allowed me to run 22lbs with no knock. Others have run more. My fuel system/turbo were tapped at that point. I believe I could have run more with a better turbo and fuel system. But again to many variables. But clearly able to run a decent amount of boost over the factory SCR.
Are you forged? I'm at 15 psi peak on 93 plus windshield washer fluid on a 10.5:1 cast rotating assembly I'm not saying math is REQUIRED, it would just be very cool to see if the excel agrees with real life or if the math says we should be higher or lower on timing. Everything throws around 14 psi and 14 degrees blablabla. Would be nice to see if math agrees.
I'm not saying math is REQUIRED, it would just be very cool to see if the excel agrees with real life or if the math says we should be higher or lower on timing. Everything throws around 14 psi and 14 degrees blablabla. Would be nice to see if math agrees. Wow. Lots of great info here. This is the good stuff I wanted to get into. Maybe it would help if I explain what I am considering. For starters, I am keeping the car a manual 6 speed. Whether I try to keep the t56 or upgrade to a t56 magnum or tr6060 is to be determined. Right now I have a 11 to 1 comp NA motor making 430rwp with 134k miles. Should I tear down the motor, increase ring gap, run a bit thicker head gasket, or while I'm doing all of that work just do it right now forge the internals and run 346 cubes or stroke it out to a 383. The overall goal of the car is to be a fun street car. I want to have a good amount of low end power and have an intense amount of mid to high rpm power. Hence i think twin turbos would be the way to go... Quick spooling that starts around 2500rpm or so and I would still make around 900rwhp in the end. Is this doable? What route do you think makes the most sense? And will be a build that wont blow up in 500 miles, yet doesnt break the bank.
https://oi17.photobucket.com/albums/b100/Hybridgnx/Sc300/SC300%20Video/elkyvslex1.mp4
Yes forged, but does it really matter when we are talking detonation limits of a setup? I'm 4.070 bore with 241 heads ls9 head gaskets piston .007 out of the hole stock stroke. Not even an ideal setup. I didn't do the math just used online calculators and read plugs. I started with 15 degrees peak timing and now at 17 degrees with timing mark in the center of the bend now on #7. On other cylinders the timing mark is closer to the beginning of the bend. 50% ethanol tested with a tester at 90%. I use 4 gallons of 90% mixed with 4 gallons of 93 octane which is 10% E locally. I use this mix consistently to create 50% E. When I get to a 1/4 tank I put the 8 gallon mix in to take me over 3/4 tank. At 16 psi peak my iat's seem to stay very low with the D1x and large air to air. I remember last year with my old motor on a 100 degree day after back to back 3rd gear pulls at 14 psi my iat only went up to barely over 110 if I remember correctly. I haven't seen over 100 degree iat yet with the new motor, but it hasn't been hotter than 70 degrees out so I'll watch it closely at each 10 degree increment as temps get warmer to 80 and 90 degrees. Also running a much larger lower pulley so 16 psi on the 377 feels completely different than 14 psi on my previous 346 sbe. We only get about a week of true 100 degree weather here. With my top end on this motor it certainly isn't the most efficient setup by any means either.
Chamber efficiency matters even at the same CR. I did the same with plug reading I just think it would be cool to see if the math matches. We've been in the 90's outside and no issues so far. I am curious about middle of summer myself. I have to say it was hilarious the other day being in a turbo Fbody with the AC running in stop and go and the coolant temp didn't budge from 181.4 when its so hot out. I haven't seen a FM turbo Fbody do that with all factory accessories.
In this video at about the 1:50 mark you can see the ethanol at even only 40% made more power than 93 plus meth. They kept saying throughout their fuel comparisons E85 and compared everything to it while making small mention that it was actually only 40% ethanol that they were using. You need 50% to realize most of the potential of Ethanol. Another thing to consider is if you start meth at say 4 psi of boost that ethanol is there all the time even at 1 psi so more timing is allowed every where.
I've heard E85 will impact ECTs, that stuff is crazy. If I had it local I probably would have tried it by now. I've always been 93 only, but finally started messing with water/meth and it's been awesome.
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900rwhp with 11:1 on E85 is EASILY DOABLE. NO meth needed just a good air to air intercooler. It will be ultra responsive down low with that compression. You need to talk to LJMS for a cam. It will decide when it lights up.
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When everyone says "ultra responsive" what does that mean exactly? Can you quantify that? I assume you mean horse power. Give an rpm as an example and how much hp would you be picking up by going with 11:1 as opposed to let's say 9.5:1 As it is "down low" I assume that means NA.
Here is a video of the LME build I think they made 1700 at the crank before they lifted heads on stock head bolts. They said they were aiming for 11 to 1 compression on E85. Obviously on an engine dyno with no under hood heat and stop and go real world driving makes a difference though...
