8 replies to this topic

[Project_1275_GT]

So ive finally managed to get busy and calculate [best possible] my CR. My concern is so many varied options of numbers i can and have used. I ordered a burette for measuring. I must add a picture at some point as this thing is so big it could never be used... Resorted to syringe used for MTB brakes. Pretty accurate and its all i had. 0-35 ml in 1ml increments. Perspex plate with 2 small holes drilled. 1 to fill through - 1 to let air escape easier. Grease to seal surface. No alcohol or food die. Used my black current an apple juice that was on the side [I truly am an armature]. 

 

So the results - 

 

Head chamber volume - 21cc [checked 3 times and exact every time @ 21cc]

Head gasket - 3.3cc [info taken from MS site for a BK450 compressed gasket]

Deck clearance - 0.93mm = 3.7cc  [measured with a vernier caliper. this could be more accurate]

Piston crown dish - 9.38cc [taken from MS site advised for Mega piston]

Ring land volume - 0.6cc [this info was taken from various other threads and can not be classed as accurate. but is needed i think]

 

Total = 37.98cc

 

Displacement - 327.5cc [this is the standard number used I believe for a 1310 engine] 

 

This gives me a calculated CR of - 9.6/1

 

But im still a little confused. I measured the removed BK450 gasket and although not highly accurate calculated its volume at 3.79cc then on the forum found most people are using 4cc for this gasket. I then also used fluid to check the volume in the piston to deck area and got a value of 14cc across 3 measurements. Also calculated displacement from what i measured and stroke @ 81.28mm. Displacement worked out at 327.26cc

 

so i do the maths again - 

 

Head chamber volume - 21cc 

Head gasket - 3.79cc 

Deck clearance - Piston crown dish - Ring land volume - [now measured using fluid in chamber and syringe] 14cc 

 

Total = 38.79cc

 

Displacement - 327.26cc

 

This gives me a calculated CR of - 9.42/1

 

There is also a reference to the BK450 gasket being calculated at 4cc so if i use this number - 

 

This gives me a calculated CR of - 9.39/1

 

Im hoping by now you see what my problem is... What is the best numbers to use? Mini spares advise no more than 9.4/1 CR to be used.. Im seeing numbers that show between 9.3 and 9.6 dependant on how i do the maths. 

 

Any feed back welcome - This is intended to run on a turbo engine with only standard setup.

Edited by Project_1275_GT, 03 June 2020 - 08:12 AM.

[Steve220]

https://jscalc.io/ca...RNEglVkKLQir11T

 

Just use the calculator.

[Project_1275_GT]

Im liking the calculator. I tried another link that was pinned yesterday and it was no longer active or available. 

 

The calculator gives 9.6

 

So i guess i must do something to reduce this. 

[Project_1275_GT]

Sorry but my heads going to explode with numbers... I Put this info into my build thread and have received a link to a you tube clip from MED saying the BK450 calculates at 4.2cc compressed. Which again brings my CR down to the correct 9.4

 

https://youtu.be/qHoOWEu7IlA

 

The calculator uses 3.2 

 

My measurements got 3.7

 

Mini spares is 3.3

 

Forum info is 4.0

 

I think i must take an average here. if i use 4.0cc my CR is just under or just over the 9.4 dependant on the other measurements used. But all lead me to average 9.4

Edited by Project_1275_GT, 03 June 2020 - 09:15 AM.

[nicklouse]

9.4 or 9.6 don’t worry. Not too high not too low.

[Project_1275_GT]

I must admit this is a complex calculation where the smallest error or difference in figures used can lead to a different final number. I was on the cautious side with fluid measurements to ensure i did not over fill. Plus using a syringe wont be exact or a vernier to measure deck height. My final conclusion is im very close the required 9.4

 

New main bearings arrived this morning so I may well now start the final part of my build. 

 

I have yet another question as the engine will stand for some time now. What oil should be used to lubricate the bores and main bearings on assembly? Standard engine oil??

[GraemeC]

There are two different 'black' head gaskets that commonly get referred to as BK450, where as only one is stamped as such (the other being an AF470). 

The AF470 is slightly thicker and is also considered better (for other reasons, not just thickness).  I suspect that MED supply (and therefore are actually measuring) the AF470.  

 

I have just checked a used AF470 of mine and get 1.0mm thickness. I've also checked a used BK450 and get nearer 0.9mm (giving 3.8cc).

 

I suspect 3.3cc is probably a legacy figure from the original head gasket used 'back in the day' 

[GraemeC]

Lubricate bores with standard engine oil - nothing else otherwise the rings won't bed in properly.

Lubricate main, big end and cam bearings with engine build lube or graphogen.

[Project_1275_GT]

Lubricate bores with standard engine oil - nothing else otherwise the rings won't bed in properly.

Lubricate main, big end and cam bearings with engine build lube or graphogen.

 

Thanks for the info. I have just ordered all other parts from MED to complete the engine build. I think. Final check is to remove pistons and inspect the rings before complete rebuild and finished. 

 

No Doubt i will have some more questions soon :)