I'm in the process of assembling the 2.0L. I just purchased a set of Pistons (and cylinders). The pistons are KB pistons flat top. I was told they yield 10:1CR. I blan on using a 0.060 spacer to lower the CR some.

Anyone ever used this combination? What CR did you calculate. I plan on CCing the head etc.. to come up with the actual CR, I just want to compare my results.

I will be using the WebCam 86 grind. Would there be a need to shave the pistons for clearance? Can the push rods be used, or custom ones are needed?

This is my first attemp to assemble a T4 engine.. Any hints will be appreciated....

TIA

Not sure of the answer to your question, but do you know if the KB's ask for cylinder gaskets when mating to the heads? I've heard that no gaskets get used, rather the "lapping" method is used...

You can't calculate the CR until to CC the heads. I'm about to install the same flat top KB pistons with Mahle cylinders I got from Jake. My CR will be 9.2 with a CC of 59.2.

Here is one of several online compression gonkulators.

CR Calculator

The place that sold me the P&C recommended I use the 0.060 shims.. So that's what I intend on doing.

who told you that?


how did you come up with .060"?
are you just picking numbers out of the thin air??

you need to measure the heads and the figure out the CC's of the squish area before deciding which size spacer you "must" have

I highly recommend the last couple of issues (and current) of hot VW's, there is an article by Jake of Aircooled Tech doing an engine build, great info and reading even if building a bone stock motor....

i'd still double check all of the numbers, your heads might not be stock (could have been flycut by a previous owner and have smaller chambers)

[quote]I was told they yield 10:1CR[/quote]
who told you that?

[quote]using a 0.060 spacer to lower the CR some[/quote]
how did you come up with .060"?
are you just picking numbers out of the thin air??

you need to measure the heads and the figure out the CC's of the squish area before deciding which size spacer you "must" have

I highly recommend the last couple of issues (and current) of hot VW's, there is an article by Jake of Aircooled Tech doing an engine build, great info and reading even if building a bone stock motor....
[/quote]


All the information I have regarding the CR and shims is based on the merchant that sold me the parts. I have stock 2.0L heads (which I assume have a well known volume). This is why I'm asking here... As I said in my post, I plan on CCing the heads.

Thank you for recommending the article, I'll take a look at it.. Again, I'm not familiar with the T4 engine, 930 or 951 is a different story.

Good point.

then the place that sold you the P/C obviously doesn't care about your engine. listen to these guys, and do a search on "deck height". good luck.

You must calculate your "deck height" first. That is the distance from the top of the piston to the topedge of the cylinder at TDC. A minimum of .040 is standard cuz the aluminum piston grows bigger than the steel cylinders. You don't want the top of the piston to smash into the head!!!

Then you CC the volume of the head chambers to see exactly what they are. Then you calc the compression ratio and if you need to shim the base of the cylinders to the desired "deck height" to adjust it.

NEVER EVER rely on anybody else!


Do the work yourself so YOU KNOW or you will have problems.

0.040mm or 0.040" ?

helpful tool:
http://www.btinternet.com/~mezporting/header.html

* Good for a static compression calculation.

040" -- generally accepted as the min. for a street engine.

a little lower is probably okay. if it's a race engine and you need to squeeze compression, go as low as you dare. try to knock the carbon off at high revs!

Can you safely go as low as 0.030" ?

i'll let someone who's gone that low answer that question!

i set mine at 042, iirc... flycut the heads to just over 50cc

ended up with 9.65:1 (2056 enginee)

.035 is the minimum with stock rods, they stretch a few thou at high revs.. I run as little as .028 with Carrillos or our Billet rods, but thats risks that only I can take- if I break it I'll fix it..

BTW- a web 86 and 10:1 is not going to be happy on pump gas.. The dynamic compression of that combo spells disaster. The MAX I have safely ran with a Web 86 is 8.3:1.. This is due to it's low duration and valve event timing and the fact that it does NOT feature split duration. The benefits of split duration are HUGE to these engines, in fact I have stopped making all but two of my straight pattern cams, they just don't have the benefits of the split duration variants of them..
Rethink 10:1 on this engine with that cam, 10:1 is fine with the right heads and cam, but the 86 certainly isn't it.

Thank you for the reply. The goal is not to have 10:1CR, We are aiming for 8.5-9:1 and we will be using a modern programmable EFI.

Which modern EFI are you going to use??

I will be installing a DME/modifed harness from a 944. Possible MAF conversion and wasted-spark.. I program the Motronic in-house.. I have full control of it, same as a stand alone. When applicable I'll use the sensors from the 944 or reprogram the DME tables to read the 914 sensors..
I have full access to Stand-Alone systems, but for this project I opted to use the 944 system for ease of install and the inexpensive $.

We talked last week... Cool

9:1 is still very high for a Web 86..

EFI will help things, but at peak torque it'll have a tendency to detonate unless you have a much more efficient chamber shape and mixture motion than stock..