Evo 8 compression ratio! 10.5 vs 9.0
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The GSC S3 cam has a long 238 degree duration @1mm with LCs at 108/116 and a resulting LSA of 112 degrees. This cam timing is excellent for what the cam is designed to do - deliver big power upstairs in drag racing applications. Predictably, it's going to be soft on the bottom, and is not going to spool an 800hp turbo on a 2.0L motor well on the street, particularly not in low gear with an open T3 turbine side. Advancing the intake cam 1 degree and retarding the exhaust cam 1 degree (+1/-1) will make the idle bumpier, but the resulting tighter LSA will shift mechanical efficiency toward the midrange, which should help nominally, albeit at the expense of a few hp on top. On the street however, that is a good trade.
In the interest of not hijacking this fun discussion regarding static compression ratio (SCR), we can reiterate that a higher SCR in this case improves torque nominally at off-boost speeds, where the engine is mechanically inefficient and in a state of a low dynamic compression due to the long cam timing. Raising the SCR however, does not help spool the turbo. If anything, increasing thermal efficiency (the effect of raising the SCR) points to the opposite direction.
In the interest of not hijacking this fun discussion regarding static compression ratio (SCR), we can reiterate that a higher SCR in this case improves torque nominally at off-boost speeds, where the engine is mechanically inefficient and in a state of a low dynamic compression due to the long cam timing. Raising the SCR however, does not help spool the turbo. If anything, increasing thermal efficiency (the effect of raising the SCR) points to the opposite direction.
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Recent studies show that E85 produces 24% more total emissions than Gasoline. That plus the introduction of more EV's says to me that the days of E85 are numbered. It was a bad idea and failed on its main promise of reducing CO2 emissions. We are all driving the modern equivalent of a steam train. So enjoy it while it lasts, its going away.
Mitsuatb
Mitsuatb
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From: usa
Thread Starter
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I was thinking to switch to s2 but car feels so good when at 6k+rpm that I just dont know anymore. From roll I have no problem because I can do brake boost. From dig I can launch with boost so its great too but the biggest pain is when I let say accelerating on first gear from the lights and out of nowhere soccer mom wants to race me with her honda oddysey than when I push full throttle at 3k rpm on 1st gear it take good couple seconds until I hit some boost and than I am hitting rev limiter on 1st heheh.
How much SCR to run is one of those perpetual questions for which there is no one-size-fits-all answer, largely being a matter of available fuel octane with respect to a host of other variables. We should clarify that an engine on boost making 400hp and 400ft/lb @ 5252rpm should benefit from 12-20hp at that point with an equal bump in torque with an increase of one full point of SCR (fuel octane permitting and with appropriate tuning), so it does present nominal improvements in thermal efficiency (and fuel economy) across the board and under all operating conditions. This is why we see newer DI engines being engineered with SCRs that are impractical with our port injected predecessors.
Where fuel octane limitations begin to hamper our ability to achieve MBT (Mean Best Torque) ignition timing however, is the inflection point whereby the ignition retard necessary to avoid knock begins costing more power than is gained by the higher SCR. This isn't really a concern for the drag racing Honda K24s out there running 13:1 SCR and lots of boost on methanol, where there is a fine line between MBT tuning and destruction. More impressive to me were the BMW stock-block 1.5L turbo F1 engines of the 1980s, which had a 7.5:1 SCR and used a ton of boost to get 1200+hp for qualifying and 850hp for the actual race, all achieved on gasoline limited to 102 RON, which is ~97 AKI (US).
Where fuel octane limitations begin to hamper our ability to achieve MBT (Mean Best Torque) ignition timing however, is the inflection point whereby the ignition retard necessary to avoid knock begins costing more power than is gained by the higher SCR. This isn't really a concern for the drag racing Honda K24s out there running 13:1 SCR and lots of boost on methanol, where there is a fine line between MBT tuning and destruction. More impressive to me were the BMW stock-block 1.5L turbo F1 engines of the 1980s, which had a 7.5:1 SCR and used a ton of boost to get 1200+hp for qualifying and 850hp for the actual race, all achieved on gasoline limited to 102 RON, which is ~97 AKI (US).
Yes, but in higher output DI engines, you see lower SCR's. Ford's Gen2 3.5 ecoboost is great example. The standard engine gets 10.5 or 11:1 SCR depending on which vehicle its in. The "HO" version in the raptor, F150 platinum/limited and expedition has a lower compression ratio of 10:1, yet makes more power. And from what I can tell the HO engine has the same cams and turbochargers as the regular variant, they just run more boost.
Yes, but in higher output DI engines, you see lower SCR's. Ford's Gen2 3.5 ecoboost is great example. The standard engine gets 10.5 or 11:1 SCR depending on which vehicle its in. The "HO" version in the raptor, F150 platinum/limited and expedition has a lower compression ratio of 10:1, yet makes more power. And from what I can tell the HO engine has the same cams and turbochargers as the regular variant, they just run more boost.
Originally Posted by RS200
The revised high performance 3.5 EB uses both Direct & Port injection systems; the DI is turned off at low loads to reduce the frictional losses of the engine, which makes it a higher risk for pre-ignition at the higher compression ratio. The DI also can’t supply all the fuel necessary at the max power output, so it makes sense that they prepared the engine for a fuel charge that has poorer atomization from a port fuel setup.
After checking, all 3.5 EB engines are 10.0:1 with the exception of the 2017+ non-HO 3.5L with 10.5:1. I would hazard a guess that it's an efficiency matter on the non-HO version, since it's meant to run on 87 octane and get better fuel economy. More torque at 1,500 RPM from higher static compression off-boost is much more valuable to the average F-150 owner than what it makes at 20 psi. It looks like the sweet spot is 9.5:1 to 11.0:1 on turbo/high performance DI engines whenever they can get away with it; Mercedes upped the compression on the A45 AMG (phenomenal engine) from 8.6:1 to 9.0:1 on the latest generation, with 30.5 psi of boost. Audi went 10.0:1 with the RS3. I'd go 9.5:1 if I was building an E85 car, personally.
Last edited by RS200; Aug 20, 2022 at 11:47 AM.
Looking at the front of the engine (not the car), the cams turn in a clockwise direction. With the outer gear remaining stationary, turning the cam in a clockwise direction is advancing the cam timing, whereas turning the cam in a counterclockwise direction is retarding the cam timing.
Last edited by Ted B; Aug 22, 2022 at 06:31 AM.
Yes, but in higher output DI engines, you see lower SCR's. Ford's Gen2 3.5 ecoboost is great example. The standard engine gets 10.5 or 11:1 SCR depending on which vehicle its in. The "HO" version in the raptor, F150 platinum/limited and expedition has a lower compression ratio of 10:1, yet makes more power. And from what I can tell the HO engine has the same cams and turbochargers as the regular variant, they just run more boost.
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Looking at the front of the engine (not the car), the cams turn in a clockwise direction. With the outer gear remaining stationary, turning the cam in a clockwise direction is advancing the cam timing, whereas turning the cam in a counterclockwise direction is retarding the cam timing.
Last edited by krys88; Aug 22, 2022 at 07:20 PM.
Thank you Ted I really appreciate your help. In you opinion if you had to choose between 9.0:1 vs 10.5:1 on evo engine running only e85 mostly on the street with occasional drag time which compression would you choose? Also which engine would make highest horsepower on boost if everything is the same (turbo, cams ect) but different compression ratio? Thank you!!
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Thank you Ted I really appreciate your help. In you opinion if you had to choose between 9.0:1 vs 10.5:1 on evo engine running only e85 mostly on the street with occasional drag time which compression would you choose? Also which engine would make highest horsepower on boost if everything is the same (turbo, cams ect) but different compression ratio? Thank you!!
Tyler Hassing of Force Engineering has done extensive testing of 4G63 compression ratios and he has done 9:1 and 10.5:1 got within 10-15whp of 10.5:1 with lower 9:1 compression no other mechanical changes still running 55-60psi of boost by only adding 4* of timing. He said spool was no different between the compression ratios.
