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 aintgotitmusthaveit
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| posted on May 11th, 2009 at 11:41 PM |
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Measuring Compression Ratio - pushrod length impact with 0.080 gasket??
HI Y'all
Nearly finished my supercharger set up and about to try it out .
http://forums.aussieveedubbers.com/viewtopic.php?tid=75111
I am concerned however that the current engine may have too high a compression ratio for boosting.
Has anyone measured compression ratios. If so how does one do it?
Came across this
http://www.discovery-carhire.com.au/widget/compcalc_help.html
But how does one measure things like combustion chambe volume??
Anyway I am assuming my compression is likely to be high. My current 0-100 times are mid to high 7s and the dynoliscious program estimates I have
roughly 100hp on the assumption the replics weighs about 850kgs with me in it.
Specs for the engine are meant to be this :
http://forums.aussieveedubbers.com/viewtopic.php?tid=61971&page=1#pid586478
Except it did not come with electronic ignition or 44 idfs (std points and 40's... don't ask  )
All I have verified is the heads are 044s.
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 vw54
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| posted on May 12th, 2009 at 06:30 AM |
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to measure your compression ratio you will have to pull the engine apart
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 Bizarre
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| posted on May 12th, 2009 at 08:35 AM |
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Engine must be apart to do this - measure the deck height and measure the CC's of the heads and then put the info in here
http://www.aircooled.net/gnrlsite/resource/specgeninfo/calcs.htm
Futue te ipsum!!!
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vw54
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| posted on May 12th, 2009 at 11:38 AM |
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Barry
thats a great size and very useful tool
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trickysimon
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| posted on May 12th, 2009 at 06:35 PM |
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| Quote: | Originally
posted by vw54
Barry
thats a great size and very useful tool
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X2
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aintgotitmusthaveit
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| posted on May 12th, 2009 at 07:22 PM |
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But that is my point. How do you measure the combustion chamber????
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hellbugged
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| posted on May 12th, 2009 at 07:29 PM |
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with the valves in, you will need a CC kit.......
it involves a perspex sheet circular "plug" that sits neatly in the head....lightly greasing the edges to seal off the chamber
....you then fill the combustion chamber with auto matic trans fluid through a small hole (like 2c piece size) in the perspex with the aid of a
syringe........
.....by keeping check of how much fluid goes in and then out of the syringe to fill the chamber, you know the CC's!!
the idea of the trans fluid is that it wont hold bubbles, and the perspex is that you can see when it is full.........any trapped air is manouvered
around till it goes out the "access" hole in the plug
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Craig Torrens
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| posted on May 12th, 2009 at 07:32 PM |
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with a burette...........the head needs to be off the motor, and then setup level on a bench with the combustion chamber facing up..............using
the burette measure how many cc's it takes to fill the combustion chamber.
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hellbugged
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| posted on May 12th, 2009 at 07:33 PM |
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 ...........yeah, mums measuring jug won't cut it
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aintgotitmusthaveit
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| posted on May 12th, 2009 at 07:34 PM |
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CRaig does one use acohol ( worried about surface tension and miniscus?)
How do you block the valves?
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hellbugged
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| posted on May 12th, 2009 at 07:35 PM |
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put the valves in, and use auto trans fluid
use those calcs above and change the cc's by 1......it doesn't effect compression very much at all........there will be varience between each
chamber anyways.
there are good calculators on the CB performance site home page too, gearing and tyre diameter etc
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Craig Torrens
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| posted on May 12th, 2009 at 07:38 PM |
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alcohol evaporates........so no dont use it.
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cb john
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| posted on May 12th, 2009 at 07:40 PM |
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We are using kerosene - less messy than ATF...
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Craig Torrens
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| posted on May 12th, 2009 at 07:46 PM |
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check that you're not getting any leakage via the valves first, by filling the ports with kero and seeing if it leaks past the valve head and
seat...............if you do you will need to lap the valves and seats first.
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aintgotitmusthaveit
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| posted on May 12th, 2009 at 11:45 PM |
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thanks boys. Now just have to find the time to pull the heads off.
If I have to decompres I am guessing spacing under the base of he barrels is preferable.
How hard is this to do?
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aintgotitmusthaveit
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| posted on May 13th, 2009 at 12:14 AM |
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THanks Reub.
On the assumption that I am currently at about 9.5:1 (guessing a combustion chamber 51cc) and when I boost I would probably want to drop to about
8:1
IT means I will need to increase my deck height from about 0.03 to 0.1! Do 0.07" head gaskets make sense??
Are the susceptible to blowng? Thats why I tjhought I would be best off spacing the cylander up particularly when ithecrank case would not seethe
pressures the head would see. Bt I have never done this before! Any advice fropm experience will be much appreciated
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greedy53
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| posted on May 13th, 2009 at 03:50 AM |
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just get a compreson test kit screw it in the plug hole and turn the engine over with foot flat on the go pedal and the coil wire out good luck
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vw54
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| posted on May 13th, 2009 at 07:05 AM |
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yes your better fitting spacers under the barrels to reduce the compression on a blown engine
If you fit inside the head you have more surface area for leaks or blow outs to occur
we have proven this with the vintage drag car by torching cyclinder heads due to the copper casket spacer being eaten away by volatile combustion
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hellbugged
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| posted on May 13th, 2009 at 06:30 PM |
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| Quote: | Originally
posted by vw54
yes your better fitting spacers under the barrels to reduce the compression on a blown engine
If you fit inside the head you have more surface area for leaks or blow outs to occur
we have proven this with the vintage drag car by torching cyclinder heads due to the copper casket spacer being eaten away by volatile combustion
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true that!
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waltermitty
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| posted on May 13th, 2009 at 07:09 PM |
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if you want to lower the compression and get each chamber balanced / cc ed figure out how many ccs volume you need without using a spacer to achieve
your desired compression ratio. then use a die grinder to remove chamber material and achieve the cc you need check by ccing as you go, get all
chambers the same and required cc for the required compression and do away with the bother and complication of spacers and have y76our heads
balanced.M
23 windows ...8 too many!
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hellbugged
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| posted on May 13th, 2009 at 08:03 PM |
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good point Watermitty........not easily done and will depend on what's been done to the chambers already but will keep the deck height nice and low,
which yes, will have many benefits for a blown motor (or any motor)
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Joel
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| posted on May 13th, 2009 at 09:25 PM |
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| Quote: | Originally
posted by aintgotitmusthaveit
thanks boys. Now just have to find the time to pull the heads off.
If I have to decompres I am guessing spacing under the base of he barrels is preferable.
How hard is this to do?
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Nick i ran CB copper head shims
most of the turbo guys on Shoptalk swear by them sayign they give a better seal on boosted engines
no idea if its true but i was happy just with the easy compression drop
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aintgotitmusthaveit
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| posted on May 18th, 2009 at 10:31 PM |
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Have decided to use spacers under the head.
Q. What is the most one can adjust tapets before longer pushrods are required.
Will I get 0.080" out of it?
I know I can adjust it out, I am concerned with any effect on valve position resulting from having a different throw on the rocker arms.
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aintgotitmusthaveit
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| posted on May 19th, 2009 at 08:12 PM |
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Anyone??
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hellbugged
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| posted on May 19th, 2009 at 08:16 PM |
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wait and see..........it one of those things you have to look at when it's all changed
very VERY basically here........at half lift, the tappet adjuster should be "square" to the valve........i'll try to find some good links that i
have seen before..........some pics in my engine build thread
DRY BUILDS ARE YOUR FRIEND!
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