1101cc vs 1179cc vs 1209cc

[trbig]

Nothing changing except the displacement and maybe some fine tuning of the carbs, what's the HP change expected of these different CC's?



Tod

[81xsproject]

You forgot the 1196

[Crazcnuk]

1101cc 95hp

1179cc 101hp

1209cc 104hp.


Straight displacement calculation. I believe the Wiseco kits also raise compression, not sure what that adds, if any. My
RC Eng 1208cc set raises the compression as well.

Now, if you add free breathing intake, better exhaust, 78-79 cams w/80-81 heads a bit more, I would think.

[trbig]

I believe the Wiseco kits also raise compression,

I was wondering about that. I installed a rod halfway on an old 82 piston, and halfway into the new Wiseco 1179 piston. The Wiseco rings are postioned a little lower on the piston than the 82, but as far as dome height and top edge the pistons, they are the same. I am wondering how it's supposed to bump up compression besides the fact that it will be a new top end?

It was late last night and the 1209 was meant to be 1196. Sorry.


The head will supposedly breathe better, I am staying with stock exhaust (For now) and I will be running the 78 cams in the 82 head.

Thanks.

Tod

[stoked]

Just guessing here but if you increase the volume of something that is being compressed to nearly the same amount as it was before at the smaller volume that increases the overall ratio. It's like if you took a 2 litre bottle of pepsi and tried to compress it into a 1 litre bottle. The ratio would be 2 to 1. Now say you got a bigger 3 litre bottle and tried to get that liquid in a 1 litre bottle. Now your pepsi has a 3 to 1 compression ratio.

It's not exactly this direct with an over bore kit becuse at TDC your volume slightly increases also. But in a system that was 10 to 1 previously, the TDC(which is your 1 reading) will not offset the entire volume of 10 enough to not have an effect. So the compression should definently increase.

[Snow]

Originally posted by stoked
It's like if you took a 2 litre bottle of pepsi and tried to compress it into a 1 litre bottle.

Depending on how much force you applied, you would either end up having a bad day or worse trying to compress liquid

[stoked]

Originally posted by Snow


Depending on how much force you applied, you would either end up having a bad day or worse trying to compress liquid

lol, particularly a carbonated one. It would probaly be a very angry explosion. I guess I should of used the analogy of farting different volumes into the same sized zip lock bag. But I wouldn't want anyone getting any ideas that I had done that before. And then lit it on fire to see the little smelly explosion. And then later got the idea to capture farts in bags and then release them on unsupecting souls watching football on the couch. Nevermind.

[Crazcnuk]

I don't know anything about the Wiseco kits, other than what I have read, and I thought I saw somewhere that those kits raise the compression ratio to 10.25:1. I could be wrong.

My RC pistons have a very definate crown on them that the stock pistons don't.

I used to have some pictures, but I can't find them at the moment.

[trbig]

if you increase the volume of something that is being compressed to nearly the same amount

That's just the deal... IF you increase the bore size, it's compressing it into a bigger space than it was, reducing or negating any increases. The bore doesn't get smaller towards the top.

I think when this thing is quoting a higher compression ratio, it is for the 78/79 motors. These Wiseco pistons and the 80's models have a higher domed piston than they did. So if you put these pistons in one of those engines... yes it would raise compression.

there should be more power due to an increase in CC's, but I really don't think it will increase compression much if at all in the later motors since the pistons are essentially the same... except that the motor will be fresh.


Tod

[Crazcnuk]

Often increasing the bore does increase compression, slightly, because, although the bore is consistent, to the top, the combustion chamber is the same size.

Effectively, you are increasing the volume of the cylinder, and then forcing it into the same size combustion chamber.

[stoked]

Ye, I beleive if you do the volume calculation for BDC vs. TDC for the two different bore sizes you will find the one with the bigger bore will have a higher ratio of BDC to TDC. This is because you are multiplying the increased volume over a much larger distance at BDC than TDC. They do not offset. For a 10 to 1 ratio you're talking 10 times whatever the bore increase is vs. only 1 times the volume increase at TDC. The differences in the increase in volume are not offset, the BDC increase is a larger increase proportionaly.

[79XS11F]

The compression goes up because your compressing a larger volume into the same size combustion chamber space. On the 1979 kit the domes are also taller with deeper valve reliefs in the domes.
Rob

Originally posted by trbig




I was wondering about that. I installed a rod halfway on an old 82 piston, and halfway into the new Wiseco 1179 piston. The Wiseco rings are postioned a little lower on the piston than the 82, but as far as dome height and top edge the pistons, they are the same. I am wondering how it's supposed to bump up compression besides the fact that it will be a new top end?

It was late last night and the 1209 was meant to be 1196. Sorry.


The head will supposedly breathe better, I am staying with stock exhaust (For now) and I will be running the 78 cams in the 82 head.

Thanks.

Tod

[trbig]

On the 1979 kit the domes are also taller with deeper valve reliefs in the domes.

Assuming you meant 1179... There is virtually no difference between the domes and valve reliefs of the Wiseco and 80's model pistons.


If you did mean the kit for your 1979... it's the same kit I have. And yes, it is a taller dome and larger relief than the 78-79 pistons.

As far as compressing into the same space, it isn't. The top of the stroke isn't coming to the very top of the cylinder. So that's why I questioned it.


Tod

[Crazcnuk]

It is squashing more into a smaller space. It has to. The stroke is the same, but the bore has increased.

This could be countered somewhat by raising the piston pin in the piston.


Wiseco claims a 10.25:1 compression ratio on both 1179 and 1196 piston kits, which is an increase from the 9.2 stock ratio. Bore size increase alone can't account for the change, so the piston dome has to be different on the Wiseco pistons.

My RC pistons have a very definate dome to them, which bears no resemblance to stock.

[DiverRay]

The head was changed between '79 and '80, I believe. The big bore kits are listed for use in the '78-'79 engine. The newer head will give a lower compression ratio. Do a search on some of the work that Maximan has done on Zilla...