Since you are going to order custom pistons, have them spec'd for an .100 thicker top. This will add some weight but easy to lower the compression later on, just mill .100 off them and check balance. This will also put the top ring land an extra .100 down which is a good thing when using NOS.

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Slant Cecil

You could scrounge up a steel shim gasket for now and then change to a composition gasket later. This will get you about .020" more deck height, give or take, but won't drop 10.5 to 8.5. Maybe you could rework the chambers some at the same time and lower it some more. It would not be a bad time for a valve job to freshen up the top end anyway. I would try building a true compression ratio around 9 or 9.5 to 1 and maybe then you would have a chance at lowering that enough for the blower. Otherwise I don't see it happening with an untouched short block and the same head. If your engines compression ratio is actually blueprinted out at 10.5 to 1, what kind of gas are you going to run? Most engines are nowhere near the compression ratio people think they are, so keep that in mind when guys tell you about running this ratio or that ratio. Unless everything has been measured and the head cc'd you could easily be between a half and a whole number off. 92 octane is not going to cut it with a real 10.5 to 1 cast iron head engine. You would have to run less than optimum timing just to get by. Running more cam won't fix it either, it will just detonate in it's peak torque range under full load. Those high ratios that are actually run with boost also use the highest octane racing fuel or alcohol, not even the 105 octane entry level stuff. Just do allot of research and be careful not to spend your money until you are sure what you want to do and what can actually be done for what you want to spend.

bren: I had the same idea. you can order custom pistons from PAW in any comp ratio you want, so there is a way out.

I still would like to be able to talk one on one with someone who has a higher comp slant like mine that tried a blower, or someone with higher comp with anything that went with a supercharger.

anothersix: I am assuming you are asking me, but yes, the head (and everything else) was cc'd so I know what I am getting. the engine was blueprinted and the head was specifically machined for this particular large cam. ignition will most likely be an MSD at this point.

I am curious about this water/meth injection that was mentioned. can some one explain that? I haven't heard of it before.

I sort of hijacked this post, because it was the same question I had asked many times here but no one could really answer definitively. superchargers can be done with higher compression, it has been done, it just takes more work. I am not falmilair with what it takes, so I was looking for someone to point me in the direction to someone that had done it.

bren, I beleive was just like me, curious to know what it takes.

Water/Meth injection I have done on a supercharged nissan. Didn't work for me, though it was probably not set up right. I spent my hours on it and it should work great but not for me. My was controlled by boost and rpm switches. Above 2700 rpm and 3 lbs boost it switched on and sprayed a fine mist into the charged air stream to cool it. The Meth has fuel and cooling properties greater than water. Isopropenol can be used too. The trick to getting more power out is to advance the timing more, which the cool charge will let you do. My problem was gettting the timing to advance on my 04 nissan. It is factory computer controlled and I was not willing to dig in to the computer. It was still under warranty and would have been voided.

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67Cuda,FAST EZEFI,340cu,CR=10.25,RollerCam&Rocker (XR268HR,#20-810-9)(#1622-16)(EddyRPM#60779,#7576), (MSD6AL,#6425) A904, GearVendorsOD, 8 1/4,3.55:1, ClassicAir

Some of the newer alcohol injections systems really work. What is different about them is they use high pressure pumps, something like a NOS fogger nozzle and electronic controls to regulate the flow based on rpm and boost, not just switches. You can make overall and boost/rpm adjustments with the turn of a knob. The price is new too, $300.00 to $600.00. One of these systems with allot of denatured alcohol sprayed in can really make things happen. Trying to use just water is pretty much a waste of time, it might help detonation some but you won't make much power. You can do things like bolt a supercharger on a high compression engine and then play with it to try to make it get by, but you are just cutting your losses at that point. The real potential for power won't be there. If you are going to go that far, it would be much better to build a low compression engine and have the option to turn up the boost with higher octane or alcohol injection and really make some power. Running less boost with a high compression ratio is not at all the same as running more boost with a low compression ratio. About the real 10.5 to 1, I was not questioning you or anyone in particular. Just making the point that many engines are not verified in any way and it leads to misconceptions about what works with what. I bet you could get even more out of your present 10.5 to 1 setup with higher octane. It's already stepping over the line for the fuel being used (pump gas, I assume?). Denatured alcohol costs about $10.00 or more a gallon, so keep that in mind as well. The advice about getting pistons with thick domes and then cutting them later is probably the least expensive rout that will actually work. Aside from the milling, it's just a ring job and you could look at making a cam change to go with the blower at the same time. It's going to be $$$ to do it right or $$$ to try to fix after it's ruined. I've been there and it's not fun.

I wasn't meaning to ruffle any feathers with this, but I don't think just compression is the limiting factor in going too far for a supercharger (or using pump gas). cam and timing obviously play into it, because a stock intrepid has 10 to 1 compression and runs on 87 octane without any trouble.

in my engines present state, I have been told my cam is "too big" for a supercharger, but no one will tell me what the cut off point is. I am starting to believe there isn't really one, it is more of the combination of all factors considered. thats why I am not letting just compression be a limiting factor. I realize it is a BIG factor, but not the only one.

I am thinking it is a matter of proportions, X compression related to X timing related to X cam specs for optimal (but not the ONLY) performance.

now, if thats true, where would I find that formula? and better yet, isn't it all just the effects of who has been there so far, maybe not even the best way?

Sick6, your not ruffling feathers, but you are rationalizing. It's apples to oranges. If you go back and read my post you will note I stated 10.5 to one was too much with a " cast iron head engine". Don't those Intrepids have aluminum heads with modern (functioning quench areas) chambers? Maybe even reverse cooling, but I have not checked. And they settled on only 10 to 1, even with the latest fuel injection and knock sensor / timing control. At full load most or all of the latest engines will be backing off the timing quite a bit unless it is cold out or they have real good gas in them. And they are not running boost with a 10 to 1 ratio, they are fairly maxed out for what they are. Great for short bursts but you can feel it backing down if you are on a steep hill with your foot to the floor at 70. The EGR is modulated and monitored by the ecm on late engines to control knock at part throttle as well, thinning out the mixture with inert gas. The issue with compression ratio and pump gas comes down to the rate of compression and the heat rise. You can only raise power so much with compression, no matter what octane you have. To make more power you need to burn more fuel, and that means more air. So a few PSI and high compression does not add up compared to say 10 or 15 psi and low compression. With the high boost (15psi) you are taking an engine from maybe 85% VE and pumping it up to near 190%. When you double the pressure of a gas (air) you half the volume / double the density. The benchline psi at sea level is 14.7 psi., thats what we think of as zero. Pumping in this extra air (15 psi on top of 14.7 = 29.7) is what will support burning twice the fuel, and that is where the power is. This is the equation to get a handle on. You are approaching it as though all parts of the equation are equal and interchangable and they are not. Trading a whole bunch of something you need for a little bit of something you already have enough of is not a good trade. What this will leave you with is a combination that is on crutches from the start. Sure you can hobble around, but you won't win races against anything that can really run. And whats the point?

that was my point, I was just stating that just saying "10.5 to one is too much" is too much of a generalization when not taking into consideration all other factors (head, timing, etc.) when I had heard it from other people, not a reference to you. we are stating the same thing just in different terms.
I knew, and I agree with you.
actually, I'm not. I am asking what they are. I am curious to know the hard numbers involved.

Ok. So since you have to start the equation somewhere, here is a well founded generalization. Just build an engine with a blueprinted 8 - 8.5 to 1 ratio ( at least verify what you have) to run a supercharger. Then you can play with all the other parts of the equation to get the most out of it. 8 - 8.5 to 1 will start and idle and run fine without any boost and is probably as much or more than most stock slants actually have anyway. You want this part of the equation as low as is realistic. You could go lower compression for a race setup but will lose low end power when not in boost. The 8.5 to 1 will have good off idle response. The timing can be closer (or the same) to what makes sense and works for all the other normal slant engines since you are not compensating for too high a compression ratio to begin with. You need a normal curve and advance at part throttle or it will run like crap and heat up. Back it off with some sort of boost retard ignition. Get the boost / timing under boost worked out with your normal fuel. You can jet up the secondaries of a 4 barrel somewhat out of proportion to the primaries to help richen it under boost. Then you can play with better octane or alcohol injection and higher boost. As long as it is tuned right your head gasket and bottom end are probably the limiting factor( as far as the engine goes). Plan fuel delivery to exceed your intended horsepower. I have not spent any time looking at cam timing for a slant with a blower, but other engines I have worked on with turbos and superchargers used tighter than normal lobe centers and the timing events, mainly the opening of the intake and closing of the exhaust, became more important. I would be conservative with the cam for two reasons: You will be making much more power anyway without having to rev it and your engine will survive all this extra power much better if you are not making it's life harder by pushing it's rpm limit. A supercharged or turbocharged engine will usually produce power at 300 - 500 rpm more than a normally asperated engine would with the same or similar cam.

thank you AnotherSix, that is more information than I have gotten on those questions in a long time!

I hope I am wording this right, but at what point do you get too much cam overlap? is there a general rule? since you are forcing more in, do you want more exhaust to get it out in a hurry? or do I have that backwards?