E88 Chamber CC reduction after a shave?

[Black Beaut]

Cool, thanks for the extra info there Jon, especially catching the spark plug thread issue, very valid point!

I'm planning on building a stroker block to mate this head to with an 88mm bore so like you say the unshrouding won't matter.

Definitely need to measure the volume property now though!!

Cheers,

Rob

[halz]

L24 cylinder radius: 41.5mm

You logic only works if the chambers are circular and the same radius as the cylinders. As we can see from the pictures, the chambers are not circular so at best, you calculation is a very approximate one.

The best method for accurately determining the chamber ccs is to insert the valves and spark plug, invert the head and lay a sheet of perspex over the chamber. Through a small drilled hole in the perspex use an accurately graduated syringe to fill the chamber space with oil and note how many ccs it takes to do this.

Hopefully this way you will know the actual volume of the combustion chamber with valves closed. I don't mean to sound pedantic but if you are serious about determining compression ratio (and ensuring that it is the same for all cylinders) I think this is the way to do it.

[jmortensen]

Yeah, that's what I did. I got a graduated cylinder from an arts and crafts store, did the plexiglas thing but use Lexan or Lucite - easier to drill. I had to drill a bunch of tiny little air holes to get the air out, and I used a pin drill for that, and I smeared a very very thin surface of grease around the edge of the chamber to seal the lucite to the head. I also found that there was a 4 cc difference -- that's not a misprint 4 cc difference between my old valves which were cut till they had no margin at all and my new valves which had a mostly flat head (originals had a dished head).

A lot of that had to do with REALLY BAD machine work from a previous build, but still it surprised me that there was such a huge difference just by changing the valves.

Jon

[Phred]

Attn. jmortensen,

Your on the right track. A few little tricks will ease the effort required to cc your head. Install the spark plug with a little white grease on the threads, also dab a little of the same stuff on the valve seat area, and then drop the valve onto its seat. The white grease is easy to see and will seal the chamber, no spring is required to hold the valve down. Then seal the plate over the chamber with the same white grease, again because it is highly visible, and creates a good seal that won't wash away, but can be wipped off easily. Then, drill the hole in the plate offset so it is located at the edge of the chamber between the valves. Then set the head up on your bench at a slight angle so the hole is the highest point. Then when filling the chamber, the air will escape out the top leaving no bubbles to contend with. Finally, use cheap rubbing alcohol (99 cents a bottle) and add a little food coloring to aid visibility. The rubbing alcohol has low surface tension, and will flow more easily than other liquids. If you're really into this sort of fun, go down to your local pharmaceutical supply house and buy a cc burett. Zero to 100 cc's works best. I've been doing this for many years, and have found this to be a fairly cheap, painless way to get accurate readings.

Phred

[halz]

Thanks Phred.

As a matter of interest (in your experience) what is the largest deviation in ccs from chamber to chamber that is acceptable? Flipside, what is the smallest deviation from chamber to chamber that its possible to achieve?

Hayden.

[Phred]

halz,

good point to consider! Some race shops will use a +/- .5 ( one half a cc) as a maximun deviation. Which means if all six chambers are within one cc, its good to go. This is usually acceptable, untill compression ratios start to get critical, (12:1 & up) and total compressed volume gets small. Then variance between chambers should be kept to +/- 2 or 3 tenths of a cc, Also, use the smallest chamber to compute compression ratio. It may be helpfull to try this formula for computing compression. Its quicker and less involved than others.

First, compute displacement of one cylinder

bore x bore x stroke x 16.387 x .7854

Then compute total compressed volume:

vol. of one chamber + vol. of head gasket + vol. above piston at TDC ( example- a dished piston, or if a flat top piston is below the deck at TDC)

To find compression ratio:

Divide displacement by total volume and add (1)

Phred

[jmortensen]

Well I wish I had that grease on the valve trick when I was doing this. I just installed the inner valve spring only, and I was using one of those crappy auto parts store compressors. You could have saved me a bunch of time.

Water under the bridge now...

[Black Beaut]

Excellent info guys, much appreciated. Seeing as different valves make such a difference I shall wait until the head has been worked on and the new 280 size valves have been dropped in and the inlet seat has been swapped to steel. Then I can get serious about measuring these suckers!

Cheers,

Rob