What compression should I run with a turbo? I just bought the HP stage II kit. The machine shop tells me one thing, the dyno tuner another. What I have now is windsor JR iron heads 58cc flat top speed pro forged pistons .040 thick head gasket running 10:1 compression. I am looking at either going with a set of aluminum heads and 64-65cc chambers or o-ring the windsor heads and keep the compression as is. Now the question I have is what head works well with a turbo? Summit says trickflow 205's but I know there are others out there.
The final compression will depend on the amount of boost you plan on producing. The lower the N/A compression the better when adding any sort of air pump. Basically you need to decide what sort of gas you want to use when you fill up. As the compression ratio/boost increases, you will be required to use a higher octane level. As a general rule, the maximum final compression ratio should not exceed 12.4:1 for 92 octane fuel. Octane boosters and higher octane racing fuel will allow you to run a higher final compression ratio. Any high flowing set of heads will work great with a turbo.
shoot for a static cmpression around 9:1 and for FI keep the cam LSA around 113-115* if possible....just my opinion..
What? Why? People drop their compression WAY too much for boost. Ricers run 10+ compression with boost. There are lots of factors. Like mentioned before cam timing is big factor. but so is almuinum vs. steel head, intercooled or not, tune and ignition system. Switching to some alum. heads and 64cc chambers would be a good start and should put you in the 9-9.5 compression area. Which should be fine. Alum. heads are much better for boost cause they dissipate heat so much better and thus are less likely to develop a hot spot on the combustion chamber.
That's funny, I believe people run way too much boost for their compression. Slightly different way of looking at it but it all comes down to a few things which you mentioned. Unfortunately, most people are ignorant of these factors. The compression ratio is simply a contributing factor in the overall event which we are trying to avoid: detonation. Heat is the culprit behind detonation and obviously there are numerous factors which contribute to the addition of heat; primarily this is due to excessive compression/boost combinations. Can you run 13:1 compression with 20 lbs of boost? Of course you can! But... you will need to do some pretty extreme things to offset the increase in temperature experienced if you want to have any sort of chance of avoiding detonation and destroying your engine. So, for the average enthusiast who will be running 13 quarter miles and doesn't plan on spending some major $$, the easiest way to keep an engine running well for the long term is to keep the compression/boost under check. The average person will add aluminum heads because it is the "thing to do" and receive these performance enhancers unknowingly. Sure, we all know about intercooling, but what SORT of intercooling? You might be able to run 12 lbs on air-to-air coolers but run 21 lbs on water-to-air coolers. There are tons of various methods a person can use to defray the offset of detonation. However, STARTING at a low compression is by far the best method available for engine builds because you will have more leeway on the boost portion. Just my two cents.
Yep, boost does not cause detonation. ....... the HEAT from the boost does. but yes you made the right point ..... there is no yes or no answer to this question It's something that has to be determined in the over all engine plan and intended use of the car.
completely depends on what fuel or boost level you're willing to run. You'll be just fine with 10:1 and aluminum heads if you want to keep boost down to at most 6-8psi. The exact amount of boost you can run is completely determined by the detonation threshold of your engine. With lower compression, you can add more boost. Under most circumstances on pump gas, you'll see more power when you trade compression for boost. However, if you're going to make this a race car, you can run compression and boost with race gas. If you want to run E85, you'll be just fine running 10:1 compression and a considerable amount of boost. I'm going to go with the assumption that you want to run pump gas, and this will be a car driven frequently on public roads. If I assume correctly, then my suggestion is to drop your compression by getting another set of aluminum heads with a larger combustion chamber volume. I would not suggest Trick Flow's 205cc heads. That's, in my opinion, way too much head for a 306 cube engine. I think going with no bigger than 185cc heads is appropriate. I've got AFR205 cc heads on my 331, and I believe that they are probably too much head for my combination despite the fact that I'll be revving it to 7k rpm. In your case, they'd be way way overkill. Shoot for a compression ratio of between 8 and 9 to 1. Keep in mind that the lower end of that range will hurt your low-end torque, and anything higher than the high-end of that range will limit the boost you can run on pump gas. I chose to straddle the fence and went with 8.5:1 myself. Interestingly, so did Ford when they produced the '03-'04 Cobra - also 8.5:1. I would recommend an intercooler with any setup you choose, but I feel that it's absolutely mandatory if you stick with your current compression ratio. Also, I highly suggest that you do any further research on this topic at turbomustangs.com where the entire community is devoted to the discussion and there are many experts. I'm no expert but I do have a little experience with a couple of combinations that I've built. Obviously, Superchargers are different than turbos, but the basics are all the same, and in actuality superchargers are less complicated. So people there will be able to answer any questions you have about blowers as well. Chris
I'm an all motor guy, with very little personal experience with forced induction. I'm not going to post a bunch of crap that I've read over the years, either. However, I've known the racer Bryan Hanofee for 20 years, and he has said to run 8:1 with street gas, so that's what I'd do. The guy is very knowledgeable,(even though he's a bowtie fan, heh) especially with forced induction, and he's gone 7.70s in the quarter, so he's gotta be doing something right.
Uugghhh... don't get sucked into the E85 religion. Contrary to popular belief, E85 is not better for your engine nor does it create more power. Quite the opposite actually. Everyone sees the higher-octane levels in E85 and automatically believe it's better. I'm from the Midwest where we've been adding ethanol to our fuel for years. Unless your engine has been modified for use with E85 you will see absolutely no benefit from it. In addition, we have seen innumerable cases of burned up heads caused by the high ethanol content. That said, you can build an engine to run specifically on E85 which will run quite well. E85 is, in essence, an alcohol fuel which means you will need to build your engine similar to an alcohol engine. In a nutshell, this means high fuel flow, high compression, non-corrosive parts, and more timing advance. Since it is 105 octane you can compress it much more than regular gasoline. It also runs cooler since it produces LESS power than gasoline. You make up for it by pumping a bunch more into the engine at higher compression/boost levels. Just be forewarned though... it is highly highly corrosive!
What experience do you have with E85? Clearly not much. Ethanol doesn't make less power, in fact given the same tune and combination, it can make slightly more because it is oygenated. E85 is not corrosive, corrosives eat metal. The concern is about the ethanol eating the rubber components, but cars made from the 80s and onward have seals that are much more tolerante of ethanol. The 15% gasoline makes it much more stable compared to pure ethanol as well. I converted the 88 to run on E85 simply by installing larger injectors to compensate for the increased fuel demand, and I have had no problems with this. The power increase is significant. I'll have track times hopefully tomorrow. I went from being barely able to run 19psi at 10* base timing, to now running 22psi at 18* base timing. If I thought the turbo could be efficient any higher, I would run less timing and more boost. As for desired compression... decide what fuel you want to run and how much boost. You will almost always get more power with higher boost and less compression. You want to avoid having to severly retard the timing because that will kill power and torque. A 10:1 compression ratio is suitable for an alky race car getting boost. I wouldn't want to try to tune and make it work on pump gas. 9:1-9.5:1 compression will work in a low boost pump gas application. You'll want a good intercooler for sure. If you want to run lots of boost, go with 8:1-8.5:1. This is too low if you want to run race gas or alky, but will be perfect for making big power on pump gas.
Experience has no place in the equation. Laboratory experiments are much less biased than opinions and "experience". I would recommend you not take offense to what I have to say and check it out for yourself. A little research goes a long way. Wrong. "E85 has 24.1 percent less energy per gallon than conventional gasoline." - Energy Information Administration "Catastrophic failures of fuel pumps used to transport ethanol have occurred in various facilities. ... Post-failure inspection of the pumps showed corrosive pitting of the metal in the areas of sliding contact." - SAE International "The National Ethanol Vehicle Coalition (NEVC) and the Petroleum Equipment Institute have demonstrated that aluminum is sensitive to corrosion from ethanol. However, the use of corrosive ethanol can be accommodated through the use of appropriate coatings, gasket materials, adhesives, and fuel additives." - Scientific.net Yet you claim it does NOT produce less power? Why in the world would you need more fuel if it produced the same amount of power? You contradicted yourself! As I said, we have been running this junk for years (long before the fad) in the upper mid-west. Not really sure why they liked to run it, I personally believe it was a kick-back to the farmers, but any mechanic worth his mettle will confirm that high ethanol content fuels wreak havoc on the valves. Do yourself and others a favor by doing some research before spouting off unsubstantiated claims.
You are completely misunderstanding my words and taking them out of context and place. The stoic ratio of ethanol is about 30-35% less than gasonline. That means you need 30-35% more to maintain the same air-fuel ratios. That is why I needed to increase the size of the injectors. If your fuel has 24.1% less energy content and you are running 33% more of it, then you are coming out even with gasoline. I am not saying it makes the same power per volume of fuel used! I am saying once you proportionally increase the amount of fuel to keep it stoich, you get the same or slightly more power without otherwise changing the tune Is your SAE source talking about transport and pumping of pure ethanol or E85? I have read papers stating it is much less corrosive once the 15% gasoline is added. I am using ethanol because it is 105 octane and CHEAP. It is 40-50 cents per gallon cheaper than even the crappiest 87 octane you can purchase. I'm not going to pay 6+$ per gallon for race gas on a car I can daily drive on the street, but I like playing around and learning something new.
Not sure how to take that out of context but I apologize if I did. The fact of the matter is that E85 makes LESS power than an equal amount of gasoline. Using more E85 in order to "keep it stoich" is like claiming that wood creates the same amount of energy as coal, you just need to throw more of it in the fireplace. The SAE report is regarding pure ethanol in a production plant. Diluting ethanol with gasoline does reduce the corrosive nature of ethanol. However, it does not change its corrosive nature, simply reduces it. Cheap. That's the word I wanted to hear. Everyone I know who uses E85 eventually comes around to that point. I would be willing to accept that as a viable reason to use it (at least until the tax incentives for E85 production expire and it gets more expensive than gasoline). This is not to say that E85 is worthless. It is entirely possible to create great amounts of power from E85, but I can also create massive amounts of power from peanut oil. Everything has it's advantages and disadvantages, let's try to bring them out into the open and discuss them rather than claim they don't exist.
By same tune, I meant the same Lamda, the same ignition timing, same cam timing, ect. Clearly, if you kept the same air fuel ratio and injector pulse widths, you'd be lucky if the engine even ran on E85. We are talking about engines, which are air pumps. My view is that the amount of power you can make is generally deterimed by the amount of air or more specifically, amount of oxygen you can oxidize. On a fixed amount of air, you will make slightly more power with E85 given the same lamda and timing. I don't see why you are so fixed on energy content. You'd better tell all the racers using methanol they are using the wrong fuel and their fuel has less energy content than 87 octane gasoline. It's worse than even E85! We are talking about making horsepower, not what fuel gives you the best mileage as related to energy content. Your origional assement was that the entire fuel system needs to be replaced to run E85. This is just rediculous and I've never met anyone who actually did it. Maybe it would be 'ideal' but are you really going to keep the car for 50 years and drive it 500,000 miles? It's been proven time and time again by countless numbers of people that cars made from the 80s and onward won't experience fuel system problems on E85. I don't undertsand what you have against it as a cheap alternative to race fuel.
Sorry to bring this back from the dead, but I completely agree with Bhuff30. E85 will make more power with a given tune (same lambda) than gasoline. It's been documented, look it up and you can see for yourself. The biggest advantage with E85 is its motor octane with is 104-105. That means more boost, and/or more compression and that = more power period. However, it has another advantage too. E85 has a lower vaporization point. That means it has an added cooling effect, and as we all know a cooler intake charge is a denser intake charge. That means more power, too. Gimme more boost and more compression any day of the week when it comes to making power. Chris
E85 is good stuff. I'm considering a 10:1 engine with turbos and moderate boost on the street. It seems like more and more people are running higher compresion with turbos these days. I'd lke to know who runs at least 10:1 on the street with turbos and what kind of power/boost they make. The trade-off would be less peak power I would think. But spool up would be faster, off boost power/throttle response would be better and mileage would be better.
I continue to hear plenty of "proof" from people on both sides of this argument but I have yet to see any actual numbers. I wonder if anyone would care to share where they have discovered their "proof" so I can take a look at it? Either side of the discussion.
I'm in the process of gathering a boat-load of data on this subject and will post a new thread with my results. In a nutshell, using E85 without changing anything on your engine is stupid. Using E85 on a motor designed for E85 is smarter.
