OHC 8V 1300 to 1400 Engine conversion - Looking for info

[jimbob-mcgrew]

i dunno... im stupid

[mowgli]

if a 1300 cc engine has 9:1 compression, then the unswept+swept cc's must be 9 times more than the unswept cc's. 140+325= 465 465/140 is about 3.3

[Royston]

Made a little progress this week, at last the 50 ml burette finally arrived this week, need to knock up a stand for it, hopefully may get some measurements this weekend!!

[mowgli]

woohoo

[Royston]

Been busy today, I have CC'd the following which maybe useful.....

1.2 Cylinder head gasket volume (78.8 mm dia *1.3mm thick) = 6.34cc

1.3 Cylinder head gasket volume (76.0 mm dia *1.3mm thick) = 5.90cc

1.2 Piston Crown volume = 10.4cc

1.3 Piston Crown volume (was a +0.5mm oversize) = 15.3cc

Therefore a 4.9cc difference!

1.2 Cylinder head chamber volume, with valves and spark plug = 18.6cc

1.3 Cylinder head chamber volume, with valves and spark plug = 19.6cc


Therefore a 1cc difference

So now I have the correct volumes

The Compression ratio on a 1.3 engine bored to suit unmodified 1.2 pistons with a 1.3 head will be....

1.3 Head volume = 19.6cc

1.2 Head gasket = 6.34cc

1.2 piston = 10.4cc

which equated to 36.34cc

Swept volume is 348.9cc

Compression ratio equates to 10.6:1 (348.9cc + 36.34cc)/36.34cc

Using the 1.2 head results in a compression ratio of 10.87@1

[garyc]

that assumes your pistons are flush with the top of the block, I have yet to see one that is. our race rules permit 10thou out the top of the block so you may want to take that into concideration.

[Royston]

that assumes your pistons are flush with the top of the block, I have yet to see one that is. our race rules permit 10thou out the top of the block so you may want to take that into concideration.

Yes, you are correct, unfortunately I dont have that info available, I might reassemble the crank and pistons and measure it with some feeler gauges.

Thank you for the pointer, they "felt pretty flush" but will double check

[mowgli]

mine were flush. i guess i was lucky.

i really wish i'd actually kept all my calcs for this conversion, but in the pre internet days, when i devoured CCC mags, as no doubt you did too, i assumed, stuck in my little outpost of the empire (leicestershire) that loads of other people were doing the same as i was....i was wrong

[tothemark]

I know that this is an old thread, but rather than start a new on based on a similar project i thought it best to add to it, so no flaming

I have now sourced some new Mahle 1200ST pistons, (77.8) in standard size and also a set in plus .5 (78.3) and so will probably go down the 1300 block rebore route ignoring my concerns about bore flex.

Working on Roystons figures with my two cylinder heads i have the following, using 1200 pistons, 1300 crank and rods, 1300 block bored out;


Both of these heads have been skimmed previously, hence the low chamber volumes.

1300 head 35/29 inlet outlet
Gasket 6.3mm, chamber 13cc, Piston crown 10.4, swept volume of 1200cc std =348.90/29.7 CR 11.747
Gasket 6.3mm, chamber 13cc, Piston crown 10.92 swept volume of 1200+.5 =366.35/30.22 CR 12.122

C14SE head 38/33 inlet outlet
Gasket 6.3mm, chamber 16cc, Piston crown 10.4, swept volume of 1200cc std =348.90/32.7 CR 10.66
Gasket 6.3mm, chamber 16cc, Piston crown 10.92 swept volume of 1200+.5 =366.35/33.22 CR 11.02


Using my enem Y24, duration 292/107/12.0/2 i am unsure as to whether my clearance tolerances will be ok assuming the block hasnt been decked, can anyone calc that cos i have exhausted my maths capability now.

Dont know if the blocks have been decked, is there a datum point i can use to check ? Cos this will throw a new variable into it.

[Royston]

If the original engine number is present, block wont have been decked.

iirc std 1.3 inlets valves are 33mm, I run 38mm inlets and 31mm exhaust in my 1.3 SR ported head

Will need to have a think about clearances with the cam, are you running solid lifters? I suspect there is enough clearance