Eventuality of cutting corners... Compression related.

[zandrew]

I started a thread while trying to find some info that would save me some time figuring out compression ratio. After opening it I got a seemingly unanimous reply to simply buy pistons with the corresponding CR. AFter doing more research that seemed like a bad idea considering the manufactures numbers do not match their own math.

This is that thread:

http://www.audizine.com/forum/showth...g-the-AEB-head

My point in starting a new thread is to get away from the negative tone in the other and post what I personally found out. After looking at both Wiseco and JE pistons and their numbers the CR did not make sense nor does the fact they use different chamber volume 43cc and 44cc. I recently got a head from Redline380 (thank you again) and decided to check it. Wow neither was right and neither was even close. The chambers are actually 40cc. I checked 3 chambers 3 seperate times and got the same numbers each time. 40cc, 39.9cc, and 40cc. The 39.9cc could easily been a lil extra build up fugging that one number. My technique is simple and proven. You simply need a piece of plexi-glass with a small 3/32nd hole. A v12cc syringe with needle tip. Vaseline and fluid. I use windshield washer fluid since it is blue and easy to tell if you have any bubbles. (if anyone is interested in the whole process LMK and I will give it to you but it can be done for less then $20)

I was curious as to why there is such a major difference in the chamber volume and called Wiseco. Wiseco explained the numbers posted are not indicative of what the chamber volume is but is simply a model to show what Compression ratio would be if those are the numbers you have. He also (Keith) informed me it was absolutely necessary to do the math so you would know what the CR actually is. I also asked Keith if he could give me a 100% volume of the dish and he informed the number is based off of the CAD drawings and I should also CC the dishes to be 100%.

After I get off the phone with them I call JE to see why they use 43cc and I get the same answer after I inform him my chamber volume is whopping 40cc and their model uses 43cc.

It would appear they model pistons after stock pistons and actually do not check chamber volume or anything like that. This is just JE and Wiseco though.

Knowing what I know now the other Mahle Powerpaks actually look to be right on with their ratios though. Depending on HG thickness the Wiseco are around 9.1:1 to 9.4:1.

I looked at the head and it does not appear to be machined. I did measure deck to intake valve with a depth micrometer and its .0019" and you should be able to shave as much as .0015" and be safe. If you had a true 8.5:1 CR and removed .0015" you would gain about .3:1 CR or about 8.8:1.

[M-Hood]

You do understand JE and Wiseco are the same company? JE already moved their operations to the Wiseco plant.

[zandrew]

JE and Wiseco are owned by the same company but NOT the same company. Kind of like saying an Audi is VW. It is but it isn't.

JE uses 2618 and Wiseco uses 4032. Je uses 43cc and Wiseco uses 44cc (which neither are right). Je and Wiseco have completely different phone numbers as well.

I don't know their long term goals but maybe in the future the may just be the same and contacting one would be the same as contacting both but when I poke to tech's they were completely different people.

Not trying to get in a pissing match. My point is simply that buying pistons and not installing them as per manufactures suggestion is going to give you something completely different then expected. What does piss me off is if this is how it should be done then it should be outlined within the instructions included. Speaking for Wiseco they are not included BUT if you are having the work done at reputable shop this should be standard practice.

[redline380]

I think this is where tuning will play a huge role. You will obviously want to tune the best for whatever your CR is, whether it be low for more boost or high for less.

But, it would be nice to know exactly what the CR is before tuning to take advantage of it. If you think you are at 8.5, and you are actually closer to 9, you would probably be running a tad too much boost. This assumes you are trying to max everything out. Truth be told, for the sake of your engine you should be able to run the same tune on 8.5 and 9 and not have to worry about blowing anything up.