Compression ratio

[16v Nova Kev]

1600 bottom end with 1300 head maybe 1400 head what would the compression ratio be

[mowgli]

about 11:1 as a guess

[16v Nova Kev]

Is that way too high

[mowgli]

for normal unleaded, possibly, but for super, it should be ok

[16v Nova Kev]

Bugger that. What could I do to lessen it. I only want to do it because the carbs and manifold came off a 1300/1400

[mowgli]

you can get a dish machined out of the pistons, or get a spacer plate.

or you can measure the cc & work it out exactly. people have done this spec before & made it work very well

[16v Nova Kev]

This is what I have

http://i244.photobucket.com/albums/gg8/16vnovakev/9B7FE81E-214D-484E-BC7D-42D4ED48E78E-193-00000006F18AE565.jpg

[thegingerwhinger]

Port match the se head to suit the penthouse shape manifold. The castings on the se head are quite generous

[meritlover]

for normal unleaded, possibly, but for super, it should be ok

nonsense you cant make that assumption. Motorcycles run in excess of 12.2:1 on unleaded.

i dont know why people get so hung up on CR. its a static figure and one of many factors which make up the burn.
If you calculated the CR based on measured volumes then this is pretty much assuming 100% VE. Most of the time the engine is running in vacuum so its only ever partially filled, so the actual 'dynamic CR' is waay less.

if you have a turbo car running at 10:1 and you double the pressure in the cylinder, you are effectively doubling the compression ratio, as you still have to displace that larger volume into the same size combuston chamber.

in effect, the 10:1 CR engine on 1 bar of boost (gauge pressure) is double the amount of air and would give dynamic CR of 20:1. seems high, but the engine doesnt make the power because the CR is 20:1, it makes it because the charge density is twice what it was off-boost.

compare this to an N/A engine at WOT (max theoretical cylinder pressure of 1bar (atmospheric), the highest it can ever possibly be is 10:1

in principle, it only really matters at full throttle when the engine is breathing 100% of what it possibly can.

Going back to the bike at 12.2:1, generally performance bike engines have terrible VE at half throttle/load, yes they have big valves and wide heads, but they also have wild cams with huge overlap and wide ports that give low air speed, so the charge density is crap. You need to squeeze it to death just to get it to burn. They dont run on unleaded fuels either.

im rambling now, i cant even remember what my point was.... Oh ye, you cant tell by looking at a CR figure whether its ok or not. im sure no ones listening anyway.

[philip]

There is alot of work to just match it and then blend into the rest of the port + the inlet needs tidying up 1st as it looks like its been hacked. Id either get a 1300head (i may know of one) or getting an inlet to suit, another option and i know they do it with superbikes..........epoxy resin/putty the inlet manifold then port it to match head.

[vauxluva]

wait till you try and start it i killed 2 starters running a 1.6 bottom end to a 1.4 head, it did run tho,untill i spun 2 shells on a roundabout. the 1.6 head has a bigger combustion chamber witch sorted the very layzee starts (edit my bad)

[vauxluva]

oh and That was on a 8v smallblock

[philip]

Mate of mine runs 1.4head on a 1600 bottom end, de-shrouds the chamber to get comp to a sensible figure.

[meritlover]

Mate of mine runs 1.4head on a 1600 bottom end, de-shrouds the chamber to get comp to a sensible figure.

so is the net result not similar to running a 1.6 head? what was the advantage running a 1.4 head on a 1.6 block?

[vauxluva]

The only reason i built my engine like that is because i was using my inlet and carb of my sr.,I just wanted more cc

[jimbob-mcgrew]

whats the odds of that resin stuff breaking up phil ?

[jimbob-mcgrew]

i have a compression ratio question aswel, but going the other way.
a friend of mine wants to use 2 headgaskets and a sandwich plate on his 14se, so he can turbo-ready it, any idea on the compression ratio for that ?

[philip]

He does it to get a good gain in compression rather than skim a 1600 head to death. I dont know the cc of the 14 + 16 combustion chambers so couldnt say what comprression it would be.

Ill try and find the bike thread about filling the ports, def worth a read, if done properly it should be ok, but ive never tried it so couldnt say for definate haha

[meritlover]

measure the total thickness of 2 compressed gasket, plus the spacer plate and work out the volume. Add it to the volume of the combustion chamber and do the sums.

[Stuart]

Sell the manifold, buy the right one... Job done and will only cost £20 or so.

[mowgli]

He does it to get a good gain in compression rather than skim a 1600 head to death. I dont know the cc of the 14 + 16 combustion chambers so couldnt say what comprression it would be.

Ill try and find the bike thread about filling the ports, def worth a read, if done properly it should be ok, but ive never tried it so couldnt say for definate haha

i've seen the head on a racing quad with loads of chemical metal in the ports to get the shape right. looks a bit untidy, but it certainly worked.

[turbojolt]

didn't think chemical metal lasted that long it hot areas

[mowgli]

inlet ports aren't that hot

[Stuart]

didn't think chemical metal lasted that long it hot areas

Get the right stuff and you can do almost anything.

[turbojolt]

i supose with all the cold air rushing in there not, but would have thourght they still got fairly hot!

[mowgli]

evaporating petrol is a fantastic coolant

[turbojolt]

I'm just being skeptical as someone used it on my brothers sump and once it got up to temperature it just disintegrated, but as stuart said maybe it was just **** lol

[16v Nova Kev]

Feck it think I will just chuck a red top at it.