What do you guys mean by "corrected" versus Static? Corrected for what?

 

Roughly explains the difference. hth

http://www.dailymotion.com/video/x6xo1j_compression-ratio-corrected-vs-mech_auto

Ride Safe,
Harold

 

Thanks for the effort, Harold, but I don't have the bandwidth to look at teh youtoobes. I did find a reference at http://www.hildrethperformance.com/a...mpression.html . I don't see how you could calculate that accurately without knowing the volumetric efficiency of that particular engine, and that means everything from the air cleaner to the piston over the whole RPM and throttle range, or particularly the area you are looking at. I suppose you could SWAG it a bit, and people who build these things every day might have a good idea of what works well, which is probably your best bet anyway.

My Toyota 20 valve engines run a VE of over 100% on top. Like 110%+ish. That's pretty good for a normally aspirated factory stock 20+ year old head. 5 valves per cylinder, designed by Yamaha, of course. For an 80 inch evo to have a VE like that, it would be putting down like 140-150HP, and I don't see too many street bikes claiming that.

 

9.6:1 corrected is the number that I have found over the years to be the max on 92 octane. any more than that you will need race fuel. some builders claim 9.2 is max and in some cases it is. if you use the 9.6 you need a good programmable aftermarket ignition and you cant use the voes and you will definitely need a professional tuner to dial in the AFR


here is a good book to read might help some of you understand how important corrected compression is.
How to Build a Harley-Davidson Torque Monster

By Bill Rook

chapter 7 compression 101

 

Cranking pressure is an important number to pay attention to and is affected by the cam shaft you choose. To me this is the number that matters most when it is all put together. Ratios are good for planning purposes, especially when selecting new Pistons.

You would do well to buy base gaskets as well as head gaskets in a variety of thicknesses so that you can check clearances, adjust deck height, set squish etc. Gaskets are not very expensive.

I may have missed it but what cam shaft are you going to run?

 

You did miss it. I bought the motor online and found that it had a ev51. Then I removed the front head and found a .010 flat top piston. Then I began searching for info on how to tell head was shaved.
So now I know the head has been shaved down to increase compression, but it's looking like the compression still isn't up to the cam.
My dilemma has been; build the motor to the cam or get a different cam for the motor?
I don't want it to be a dog, but I don't plan on drag racing either.

 

The answer is to be honest about what style of riding you do most often. What is the normal speed you go most of the time? Do you usually ride two up? Do you pull a trailer behind your bike? Do you go up steep grades and high elevations often? Do you spend a lot of time on the interstate or do usually use sweeping side roads? Is most of your riding local?

With those questions honestly answered, determine what cam meets that criteria. Then build the rest of the engine around that cam. To me you end up chasing your tail if you try to do it the other way around.

My Heritage is set up for lots of low end torque at the expense of a little bit of top end horsepower. It runs smoother with less vibration than stock. It needs 91 octane fuel, but can run 87 if needed if run gently. Most people probably make more horsepower than I do. That doesn't matter to me. I never even put it on a dyno, so I don't really know what kind of numbers it makes. I know it makes me smile and runs smoother than it did when stock. I have also surprised some twin cammers that tried to run away from me, although I don't race and and ride slower than most people.

I think a lot of my smoothness is the result of my heads now being equal whereas as the stock heads can sometimes have considerable variation in volume.

 

I found this on Andrews site regarding the EV51. Think about that rpm range carefully.

Easy installation; longer duration for modified street engines with hydraulic lifters and 9.0 or higher com- pression ratio. Power range from 2800-6500 RPM.

 

http://www.nightrider.com/biketech/h...o_byman_ql.htm

never liked the 51 for a stock or stroker for that matter -

your riding buddy has a stroker with 10 to 1 compression - your not going to keep up with him no matter what you do, someone will take a bag full of your money if you keep looking, but in my shop we would send you to someone else, the motor and the starting of it as well as the post ignition stuff that is going to go on, is not worth having that bike around all the time with issues, and the BS that goes with it -

take the pistons out put a set of flat tops in it - take that cam out - install a EV 27 as it is cheaper than the woods by almost a 100 bucks - use cometic .040 head and .020 base tin gaskets - have the heads checked - the springs - the moron who did that to the motor might have sold him drag racing springs and they tend to wipe out the valve guides rocker arm tips and rocker shaft bushings - have that checked not maybe you should - but then again you could just put it all back together again as it was - and ride your other bike this year when this one explodes this spring - then fix it the right way

 

Seems nobody likes this ev51 cam.
This motor has flat tops in it already.
But thanks for the otherwise useless post, feel free to never post again, help like yours is no help at all.