[Fot] TR4 Compression Ratio Calculation Question

[Kas Kastner]

Getting down to the less than tenths of a C.C. is fine for really accurate
compression ratios, but in the end you are measuring a ratio of VOLUMES not
pressures so the thing to put in your mind is the effect on the percentage
of volumetric efficiency.

Now for that you have to take a fine pointed thing, aim it at the engine
and ask " How good are you?" Then start at the top of the heap of
volumetric possibilities.  Turbo and/or supercharger 100% plus, overhead
cam, 4 valves, fuel injection around 95%, most triumph engines about 89-91%
at best. Now that 13 to 1 volume ratio does not look so impressive, but
does put a nice crackle in the exhaust note and seems to help a bunch down
the long straights.
As in so many things like this I am just guessing along with everyone else.



*Never be beaten by equipment.*

On Fri, Sep 23, 2016 at 10:33 PM, Bill <ponobill at gmail.com> wrote:

> Yeah, but that’s just step one--after you measure the volume of the
> combustion chamber you still need to know all the stuff Steve Yott
> mentions. At least you do if you want to know the actual compression ratio.
>
>
> On Sep 23, 2016, at 9:19 PM, Steven Belfer <steve at artwithcars.com> wrote:
>
> Get Kas' book. There's a helpful section describing how to CC the head
> using a plate of plexiglass and measuring how much fluid you can fill it
> with.
>
> ~Steve
>
>
> On Sep 23, 2016, at 8:14 PM, Steve Yott <tr4 at wi.rr.com> wrote:
>
> Steve,
> In order to calculate the combustion chamber volume desired you need also
> know the bore, stroke, head gasket diameter and thickness, piston to liner
> clearance, depth of the top ring and deck clearance of the piston (or pop
> up if you are running any).  These all make up the total volume which you
> need to calculate the chamber volume you need for the static compression
> ratio you desire.  Also when doing a chamber volume test don't forget that
> the valve head thickness will affect this measurement.
>
> There are a good number of web sites out there that will do all these
> calculations for you and give you a required chamber volume for the desired
> compression ratio.  There are various head castings out there so I would
> not take the thickness into account except for a rough idea.
>
> This all creates a "static" compression ratio and will not mean much when
> the dynamics of the cam and valve overlap come into play and create the
> "dynamic" compression ratio.... wish there were a good method of
> calculating that!
>
> Steve Yott
>
>
>
> -----Original Message-----
> From: Fot [mailto:fot-bounces at autox.team.net <fot-bounces at autox.team.net>]
> On Behalf Of Stephen Borowski
> Sent: Friday, September 23, 2016 6:45 PM
> To: FOT Triumph <fot at autox.team.net>
> Subject: [Fot] TR4 Compression Ratio Calculation Question
>
> Hello All,
> Does any one know the "chamber volumes" vs "compression ratio” for the TR4
> high port head. What should the head thickness measure?
>
> All comments welcome!
>
> Thxs. Steve
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