[Fot] TR4 Compression Ratio Calculation Question

[fubog1]

One point which should be emphasized, is that the valve head shape and valve depth have a huge impact on chamber volume.
Different style valves will have different shape on top, ie flat vs dished, and for any given thickness, a head with new valves & seats will have considerably less volume than one with valves that have been faced a few times and deeper re-cut seats.
To really know what the CR is, the head volume has to be measured.
Glen

 

 

 

-----Original Message-----
From: John Hasty <jhasty at mhc-law.com>
To: Steven Belfer <steve at artwithcars.com>
Cc: FOT Triumph <fot at autox.team.net>
Sent: Sat, Sep 24, 2016 10:43 am
Subject: Re: [Fot] TR4 Compression Ratio Calculation Question

Exactly what we did on our 2stroke motorcycle racers

Sent from my iPhone

> On Sep 24, 2016, at 12:39 AM, "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] 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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