Static Compression Race/Pump.
05-08-2012, 09:42 PM
#21
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Static compression isn't going to tell you much one way or another without evaluating valve events and more specifically, the dynamic compression ratio.
All that aside, there are plenty of people making good power on E85 but there does tend to be a wall of diminishing returns at ~13.5:1 static, where anything beyond that shows little to no gain at all. Not to mention the fact that blend % changes throughout the year, so it's probably better to err on the safe side here.
Start pushing the VE over 100% and things are going to change regardless but your main concern is low rpm cylinder pressures under load, since that's where the chance of detonation is highest.
Just my 2 cents.
All that aside, there are plenty of people making good power on E85 but there does tend to be a wall of diminishing returns at ~13.5:1 static, where anything beyond that shows little to no gain at all. Not to mention the fact that blend % changes throughout the year, so it's probably better to err on the safe side here.
Start pushing the VE over 100% and things are going to change regardless but your main concern is low rpm cylinder pressures under load, since that's where the chance of detonation is highest.
Just my 2 cents.
05-08-2012, 10:36 PM
#23
Static compression isn't going to tell you much one way or another without evaluating valve events and more specifically, the dynamic compression ratio.
All that aside, there are plenty of people making good power on E85 but there does tend to be a wall of diminishing returns at ~13.5:1 static, where anything beyond that shows little to no gain at all. Not to mention the fact that blend % changes throughout the year, so it's probably better to err on the safe side here.
Start pushing the VE over 100% and things are going to change regardless but your main concern is low rpm cylinder pressures under load, since that's where the chance of detonation is highest.
Just my 2 cents.
All that aside, there are plenty of people making good power on E85 but there does tend to be a wall of diminishing returns at ~13.5:1 static, where anything beyond that shows little to no gain at all. Not to mention the fact that blend % changes throughout the year, so it's probably better to err on the safe side here.
Start pushing the VE over 100% and things are going to change regardless but your main concern is low rpm cylinder pressures under load, since that's where the chance of detonation is highest.
Just my 2 cents.
So you personally run E-85, and have built multiple engines below and above 13.5:1 to verify this theory?
05-08-2012, 11:43 PM
#24
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Not an engine builder, I'm an engineer. Just passing along advice I was given by Eric at at Horsepower Innovations when building a maximum effort E85 engine (440 ci SBC) for my 240Z. He builds carbs for E85 and does quite a bit of tuning on E85 builds, so I tend to follow his advice in this area.
As stated earlier, the static compression doesn't get at the root of the issue anyways, since trapped charge is dependent on closing events. 10.5:1 DCR seems to be livable, with enough safety factor to account for % changes (seasonal) and ethanol's hygroscopic nature, which is going to vary octane rating a fair amount dependent on humidity.
Regards
As stated earlier, the static compression doesn't get at the root of the issue anyways, since trapped charge is dependent on closing events. 10.5:1 DCR seems to be livable, with enough safety factor to account for % changes (seasonal) and ethanol's hygroscopic nature, which is going to vary octane rating a fair amount dependent on humidity.
Regards
05-09-2012, 11:15 AM
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I'm not saying there is no validity to the claim that you could run much more than 13.5:1, just that the static number is not as useful as most people might think.
This isn't even as simple as saying, don't run more than xx DCR. If anyone thinks you could sum all of it up as succinctly as a two-three sentence answer then you don't understand the complexity of the issue at all. I'm not attempting to either.
You're going to need ~30% more E85 for best output, stoich is right around 10:1, so we're talking a lot of extra cooling in the combustion chamber and a lot of variables at play. To be fair, there are guys out there running ~17:1 (static) with high boost applications. I run just shy of 14:1 in my 240Z, 440 cid, 4.165 bore, lots of real estate for the flame front and durability being key through a wider rpm range. But then it's a road race car, not a dragster so YMWV.
05-09-2012, 01:15 PM
#28
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Please refrain from pulling what I've said out of context:
Two somewhat mutually exclusive thoughts within one sentence.
That said, I find it interesting that you've determined a stoich value within two decimal place precision for a fuel that varies up to 6% in ethanol content.
I'm currently finding best power at lambda 0.73-0.78 dependent on ethanol content, and using a couple of pre-defined fuel trim tables (MoTec) to compensate. What are your lambda readings at best power?
....going to need ~30% more E85 for best output, stoich is right around 10:1
That said, I find it interesting that you've determined a stoich value within two decimal place precision for a fuel that varies up to 6% in ethanol content.
You realize you run much richer than stoich at wot I hope....
05-09-2012, 01:27 PM
#29
I'm right around .82 but last time at the track I added a little fuel and it did pick up. I have more tuning to do. Still very conservative on the timing as well.
Are you boosted?
And where are these 17:1 high boost motors on E85?
I seriously want to know. I might boost mine.
Are you boosted?
And where are these 17:1 high boost motors on E85?
I seriously want to know. I might boost mine.
05-09-2012, 03:55 PM
#30
As 95 said I'm not interested in this "dynamic compression" theory. I stick to static compression.
I don't know the stoichiometric for E85 but its 14.7 for gas. This does not mean its the best ratio to run. Its just the perfect balance between fuel economy and power.
I don't know the stoichiometric for E85 but its 14.7 for gas. This does not mean its the best ratio to run. Its just the perfect balance between fuel economy and power.
05-09-2012, 06:46 PM
#31
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I'm right around .82 but last time at the track I added a little fuel and it did pick up. I have more tuning to do. Still very conservative on the timing as well.
Are you boosted?
And where are these 17:1 high boost motors on E85?
I seriously want to know. I might boost mine.
Are you boosted?
And where are these 17:1 high boost motors on E85?
I seriously want to know. I might boost mine.
There is an E85 forum, don't have it bookmarked on this computer but I will add the link later. Lots of good information there, and still a great many people learning their way around this fuel.
People using static ratios of 17:1 is just talk through the grapevine, though I'm sure those guys are out there talking about it on the forums 'somewhere'.
Personally, I don't see the point for forced induction. At least not in terms of increasing compression. The charge cooling from latent vaporization and the additional boost that affords you, is in my opinion, where the real gains are to be made. 8-8.5:1, then push a couple of atmospheres through it.
*edit*
http://e85forum.net/forum/index.php
Last edited by Melkor; 05-09-2012 at 08:54 PM. Reason: added link to E85 forums
05-09-2012, 08:28 PM
#33
As 95 said I'm not interested in this "dynamic compression" theory. I stick to static compression.
I don't know the stoichiometric for E85 but its 14.7 for gas. This does not mean its the best ratio to run. Its just the perfect balance between fuel economy and power.
I don't know the stoichiometric for E85 but its 14.7 for gas. This does not mean its the best ratio to run. Its just the perfect balance between fuel economy and power.
It has nothing to with power or the "best balance between fuel economy and power". Every EFI system out therr has an enrichment mode for high load / wot situations in which the AFR will bemuch richer than stoich to produce the most power while also protecting the engine.
05-09-2012, 08:58 PM
#34
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WS,
I have about 65k in the car now, most of which is my own work. If you had a shop do the majority of it, the price tag might be closer to 100. Then again, I'm not running fuel injection at the moment either and that drives things up in a hurry.
FOx,
Sounds like you've already got it all figured out then. Best of luck to ya.
Interesting forum...
I have about 65k in the car now, most of which is my own work. If you had a shop do the majority of it, the price tag might be closer to 100. Then again, I'm not running fuel injection at the moment either and that drives things up in a hurry.
FOx,
Sounds like you've already got it all figured out then. Best of luck to ya.
Interesting forum...
05-10-2012, 02:58 AM
#38
No, not really... 14.67 for gas is stoich, the very definition of stoich is the point of least emissions.
It has nothing to with power or the "best balance between fuel economy and power". Every EFI system out therr has an enrichment mode for high load / wot situations in which the AFR will bemuch richer than stoich to produce the most power while also protecting the engine.
It has nothing to with power or the "best balance between fuel economy and power". Every EFI system out therr has an enrichment mode for high load / wot situations in which the AFR will bemuch richer than stoich to produce the most power while also protecting the engine.
05-10-2012, 03:05 AM
#39
Best mph was .78 for me, .80 not much diff, .82 slower. Timing was also conservative which is curious that more fuel still made more power. Never went richer than .78 but I'd like to step down to see what it does for torque. might like more fuel before peak tq, and leaner as cyl pressure drops off. Wide tuning window for sure! A guy in socal was getting best numbers at .85! LS motor though valve angle may have a play here.
05-10-2012, 03:16 AM
#40
Interesting. I'm cruising around 14.2 - 14.4 on the gas scale, so .97 ish
Even in 6th lugging it with the 6 speed it had plenty of tq and would pick right up without any bog or stumble. It gets progressively richer across the load range in the VE table of course, being OLSD theres not set point it "switches" to WOT.
I would like to get mine on a dyno and spend some time then back my findings up with trap speeds at the track, honestly when they start making a bit of power, tuning on the street and getting good solid data to work with becomes a hand full.
Even in 6th lugging it with the 6 speed it had plenty of tq and would pick right up without any bog or stumble. It gets progressively richer across the load range in the VE table of course, being OLSD theres not set point it "switches" to WOT.
I would like to get mine on a dyno and spend some time then back my findings up with trap speeds at the track, honestly when they start making a bit of power, tuning on the street and getting good solid data to work with becomes a hand full.