Does anyone know what the maximum effective compression ratio is for e85? If i'm not mistaken I thought 93 was good for around 11.5-12:1. I have been searching for an exact figure with e85 for a VERY long time but with no definitive results yet. Thank you for your time, knowledge, and help.
Not directly related to your question; As I recall, while studying in the late 80's early 90's, MIT had determined that the compression (knock) limit of 87 octane gasoline was more like 17:1. :shock: This was a single cylinder, variable displacement, variable compression engine in the lab. Also IIRC, how the parameters were modified would not necessarily relate to an actual drive-able vehicle in respect to load, rpm, temp, and other important factors. It could be calculated the effect of tumble and swirl, as well as quench, % of end gasses, surface temps, etc., on knock resistance, as well as what would come out of the tailpipe chemically. Other fuels were covered as well. I tried to approximate a balance point with real world examples of entering load induced knock (as best as a fellow could w/o ridiculous instrumentation) and how far off "ideal lab conditions" were. As far as max ECR with E-85, I think you'll run into limitations to the amount of dome you can physically fit before hampering combustion characteristics. You may diminish returns at the hp peak, but it might hang on longer and have a stronger shift recovery to go more than 14-1. I do know of some @ 15+:1 on race fuel. I do not recall the limitations on alcohol fuels. Ironically, alcohol has likely killed those brain cells...
Unfortunately the real world hardly ever sees what he lab can produce. And in regards to piston size I'll be downsizing the dome for boost on my nailhead. You can only push an asthmatic patient so far before they need extra oxygen :Brow:
If you are thinking of E85 with a blower, I don't think you would need to remove much, if any dome on a Nailhead. I would bet that it helps on a Nail, with the limitation being how much you can stuff through the port with boost. Historically, it's been proven better to use boost over compression to get the same fill (pressure) in the cylinder. It's also known that with better flowing ports, all else equal, the boost gauge might read lower, all the while making more power with less ill effect. The Nail port would have the opposite characteristics. Compression might be your friend here. Nailhead has a timing friendly chamber. You would have one weird looking heavy SOB of a piston to push the compression limits (of alcohol) on the Nail. Not sure if you are starting with a forged slug, if so, I would generously radius off the dome and spend the $$ on some type of knock sensor, rather than new pistons. As you know, re-think your ring gaps.
My point in bringing up the "ideal lab conditions" was to subtly elude to the HUGE gray area between what we read in the Hot Rodding world, and what the real limitations might be or actually are. Exploring that, I've found on my own projects that the numerical comp. ratio is not the limit. It's the entire package and how the ratio fits in there somewhere. Nobody is testing the "compression limit" with their own $$. The projects have to have some usefulness. FYI, I'm talking about using parts I had around and the feasibility of survival between fills of race gas. Once the chamber temps can be managed (hot spots) and incandescence handled, we are left with load induced detonation (meaning load back to the spinning engine across a time period). Understanding that, one should realize that the vehicle itself has more influence to the big picture. I apologize for clouding your question on comp. limits. p These are the questions I had originally when studying this; Once the engine is optimized, what's the effect in a 1500lb vehicle...deep gears...hi flash converter (things that make it rip through the powerband faster or reduce the load back to the engine)? What cam duration (cyl. pressure curve)? For which gear? Obviously top gear is tougher on the engine. At what rpm does det. initiate, given all of the prior? What are safe coolant temps for both engine survival and det. resistance? Light bulb went off at this point, I'm slow... When you radically change some of the above, you can run way more compression than what folks will publicly admit to. Just being honest, I've never pushed that limit on a Buick, nor would I give someone else a compression beast. You'll have to consider more factors of your entire project to get an answer...:grin:
One of the biggest limiting factors is going to be getting the exhaust OUT. For years everyone felt it was the exhaust that was the limiting factor on the "Nail". When in fact in a N/A situation it was in reality the intake. This has been proven over & over again. Now add boost where you have the capability to fill the cylinder to 150% of capacity, it now becomes a problem with the exhaust. With more pressure when the exhaust valve finally opens it HAS to go out, it has no choice. How efficiently it goes out is another matter altogether. Just my thoughts on the subject. Tom T.
Agreed. When that happens, you still can't get any more in. It was fully encompassed in my head, but didn't come out right in the text :Comp:. Thanks for clarifying.:TU: I definitely learn from your Nail experience. That restriction affects any boosted engine at some point. One of the reasons behind less overlap is that blow-down can go either direction. Hopefully you get a bent pushrod warning before the heat related problems come. I'm guessing that was the thought behind the reverse flow boosted Nailhead. 65skylark300, were you thinking about roots, screw, centrifugal, turbo, or chemical? :Brow: The boost or compression limits might be a bit different depending on choice...
For the time being I just wanna screw her and make her drink some juice on occasion. There will be turbos later after I learn more with this setup and from other people who are pushing the limits of the nail in different ways; and have more to give to the project(hopefully a set of aluminum heads to install by that time as well). If we could actually regularly see lab conditions could you imagine the types of numbers we'd be seeing on the street and strip?!:eek2:. As far as vehicle effects upon the engine's limits and characteristics I understand that they are a package and that's about it lol. I do know that for most street and strip cars the cars' setup effect upon engine compression capabilities will be somewhat similar to my application and so I can use their numbers as a rough guideline for my project. I like when people add other questions to my original post because it may be question I never thought to ask or never knew had an effect; especially when coming from someone who may have a very different thought process than myself. I DEFINITELY know that I know very little... which is why I LOVE forums; because there are so many more people out there that have more knowledge and experience that willingly give their opinions and share their knowledge with others(such as Mr. Telesco). Even people who have very little to no knowledge on a subject may point something out that can be useful. As far as exhaust goes... well... it... will... be... a... challenge :laugh:. I foresee many sets of heads in the future on flowbenches of both the cast iron and aluminium kind. I have a goal and I'm in this for the long haul... thankfully I have everyone on here and hopefully can return the favor with whatever data, knowledge, and resources I accrue though this journey.
We're still talking about the car, right? Might have the order mixed up.:eek2: Good plan BTW. The only thing about comparing similar pkg's is that there are SOOO many details that are vital you won't know without complete teardown. Unless one is dedicated and serious, you can't push it. I think most are a long ways off pushing the limits anyways. When you get closer to the planning stages of the build you can hash out the details. Lots of planning into machining specs. Maybe another thread about survival with extreme combo's could be explored. BTW, the gray area between the "monkey see monkey do" crowd and the lab is called "speed secrets". I'm learning all kinds of things about Buicks here, and hopefully can relate my experience with other types to benefit the board. I'm not giving up all my voodoo, though...
I'm talking about the car still and in that order :laughI think :bla. I'm pretty deep into planning stages and trying to get everything worked out in my head and on paper before I start throwing money in directions I didn't need to. Personally I don't like to keep many secrets... but the ones I do/will are either REALLY good or just hard to explain/show to others; and they'll hopefully all be shared some day for the betterment of the car community. :beers2:
For what it's worth, the lab method of testing a fuel's octane number is just that, a test of the fuel in order to give it a rating on a scale based on that piece of equipment. All the lab methods you read about and their results exist simply for the sole purpose of measuring properties against an arbitrarily decided scale (sort of like tornadoes and earthquakes). Don't worry too much about the static compression ratios of the lab tools, their ignition timing, mixtures or what have you. So the idea of throwing those parameters out the window for the sake of relating to cars we drive is exactly what should be done. In the end, in a given driven combination, the higher the number, the more resistance to "knock". That's really all we can take away from the lab. Devon
DaWildcat, what you are saying about motor octane testing is very true. We are talking about two different things. Lots of test papers out there on it. Lots of proven builds since then. OEM's have slowly raised compression since then, although in my opinion conservatively...safely, for good reason. Using what I was attempting to study back then, I put together a few myself, maybe 1989 or '90(?). 1st one was a 7800 rpm sbc @11.8? comp. NA. Big dome, and crappy combustion chamber, and all the expected disadvantages. 92 octane. Several hundred full throttle runs w/ occasional teardowns to verify showed perfect, new looking bearings. Never any trace of det., but I crept up on the tune. I got to block failure (longitudinal valley cracks) on that build before the expected ones. Might have got into det. at that point, but the bottom end didn't show it. Learned something. But who would intentionally try that? Other builds after that were somewhat more extreme. Maybe 10-15 years later, the Hotrod type rags were introducing articles showing the same things I found. I didn't know that was a big deal at the time as they (and everyone else) recommend a more conservative approach to builds. My point in bringing up the textbook gobbledy-gook was that by simply knowing what the lab's limits were and despite what conventional hot rod wisdom suggests, it made me a better builder by altering everything around that one detail. What I'm also saying is that one should have a performance goal first, then hash out the specs. This thread was a curious topic for me as I don't think anyone has really proven the ECR limits of E85, outside a lab. I was trying to provoke Q's I felt more important to ask. There are too many factors besides the ECR. You can radically change one or two simple parameters in the overall paradigm and negate what folks have traditionally felt as limits. But who would hand a beast like that over to an average hot rodder? Being that boosted compression is better than mech. compr., and that alcohol takes the squeeze better than gasoline, and I know what I've personally done, I would bet that one would run out of room for valve reliefs before compression increases would no longer be feasible. Nor would you chase it. I still think that a failure would be caused by something else first. A long time has passed from then to now, maybe absolute limits have been found. Just what I saw then was a ways off what people are believing, even now. I'm not suggesting building a boosted 16:1 powerplant, why risk it? Just do what you have to do to make your goal.
I can share our experience with methanol and hopefully there is some helpful information that is similar to ethanol. We have run turbocharged methanol up to 35 lbs of boost and 6-71 blown methanol at 17lbs of boost. One thing we found with alcohol is detonation is controlled more from air/fuel ratio than compression. The heat of vaporization of a rich alcohol mixture does much to prevent detonation. Both the turbo and blown methanol engines run a static compression ratio of 10:1 with a Dynamic compression ratio in the mid sixes. On a forced induction engine there is little gain in power by increasing static compression ratios as compared to adding boost so anything above 10:1 just reduces the margin of safety. The times we have had detonation was during mid throttle and boost when the mixture went lean. Had the chance to play with E98 for a season in a N/A application. I would say that a Dynamic compression ratio around 9.5:1 would be a good place to start with for N/A E85.
Hi all, After all this time, I had never worked out my dynamic comp ratio. Well here it is Bore 4.5" Stroke 4.36" Rod length 7" Static comp 12.54:1 Inlet valve close 60' ABDC Elevation no more than 100ft Equals 10.32:1 dynamic compression Out of interest the dynamic cranking pressure is calculated at 220psi This is an E85 motor and loves it. The brand of E85 I use is actually 105 octane, but the brand is releasing a race blend at 107 octane. Cant quite remember the initial timing, thinking 10' and 30' total which gave me 832hp @ 6100rpm. It didnt like any more than 30' total on the dyno though. Cheers
I just love the car and engine combination. Beautiful job! Thanks for sharing. I'm interested in the intake valve closing point based on the advertised duration if you don't mind? Thanks
My pleasure. Ya its a bit different, the looks I get driving it around, even from car guys! Its so smooth through the entire rev range straight off idle too. 76' ABDC for the intake valve at adv duration. adv duration 288I and 298E. @ .050 254I and 265E. I will scan my cam card and post it if you like. Cheers
Thanks 76* ABDC intake valve closing would put the intake lobe center at 112* ATDC which seems too retarded unless the cam has a very wide Lobe Separation angle. I would expect the cam to be advanced a few degrees. The cam card would help. The reason I'm checking is I suspect the DCR based on the advertised duration to be around 9.5 Thanks again Paul
You wouldn't happen to have a video of the car's exhaust sound for curious ears would you? :Brow:ray:
