I was just wondering... If you were to plain your block (not your heads) down, can you increase compression this way? Also, does anyone know how far you can take off your heads or block before you run into valve problems.. I am mostlly interested in EA81, but we can talk EA82 as well.

 

I would love to make my dual carbie EA81 (the real EA81dc, with the vavles the other way round) a higher compresstion. Maybe if I got some new pistons with valve cut outs. Any idea how much compression is possible in one of these engines? 11:1?

The problem with plaining these engines is not the valves coming in contact with the pistons. Instead the holes in the intake manifold will not line up with the holes in the head. You can take it down a bit, but not a lot.

Ahhh, good point... Didn't think of that. So if someone was to make a dual carb setup that went onto each head (like the Alfa 33's have, here is Aus anyway.) it would be possible? If so, anyidea on how much before it breaks something?

Seems there are a few that have gone .020 successfully. Beyond there and I would imagine you would have the manifold alignment problems listed above.

I would imagine that you could run into issues with cylinder liner retention if you started planing the block significantly.

I would be more worried about piston to deck clearance. Can we say 'bent rods' Granted this would be in the extreme, but with decking, less is better.

If you are going to the trouble to dissasemble the engine it's much easier (not to mention more reliable) to just install SPFI pistons (9.5:1 stock), and deck the heads .020. You are looking at very near 10:1 with those two, and that's about as far as you can take it and still get a reliable engine that doesn't ping.

 

GD

have you taken into consideration that if you also do a complete valve job, the valves will sit deeper into the heads thus giving a slightly less compression ratio into the equation

If you are going to the trouble to dissasemble the engine it's much easier (not to mention more reliable) to just install SPFI pistons (9.5:1 stock), and deck the heads .020. You are looking at very near 10:1 with those two, and that's about as far as you can take it and still get a reliable engine that doesn't ping.

 

GD

I didn't say anything about doing a valve job - most times that is not needed, and besides that, if you replace the valve seats, valves, guides, and seals they will not change depth at all. Only a "partial" valve job where the seats are ground, and the valves lapped would cause this. With how cheap new valves and seats are, it would almost be silly to bother. Also the amount of change is very small due to the valve diameter being only a small fraction of the overall cylinder diameter...

 

GD

Excuse my ignorance please.

If honda's can run 12:1 ratio's what is stopping a EA81 from doing it? If the cam were ground right, valve springs upgraded/modified would this help?

I don't want to go to the trouble of importing pistons, or getting custom ones made, nor do I want to spend that much. I was just thinking would it be possible to gain compression this way. Obviouslly you'd need a fair bit of work. So it's a waist of time. But still for a normal EA81. But I still would like to play around with my high flow dual carb'ed EA81.

Excuse my ignorance please.

If honda's can run 12:1 ratio's what is stopping a EA81 from doing it? If the cam were ground right, valve springs upgraded/modified would this help?

I don't want to go to the trouble of importing pistons, or getting custom ones made, nor do I want to spend that much. I was just thinking would it be possible to gain compression this way. Obviouslly you'd need a fair bit of work. So it's a waist of time. But still for a normal EA81. But I still would like to play around with my high flow dual carb'ed EA81.

 

Nothing with the right fuel, but the problem is the EA81 heads have a poor design internally for that much compression. The shape of the cylinder has a lot to do with how much compression you can run. Also those Honda's have EFI, knock sensors, and all sorts of tricks like V-tech that allow them to run high-comp on lesser fuels.

 

GD

Ok.... Although I know honda was using high comp before the weird v-tech stuff.

So do you mean the design of ports for inlet and exhaust on EA81's can't take that much comp? Or the shape of the "bottom" (ummmm) the part where the plug and valves go, what would you call that? hmm.

 

Oh, and BTW I normally use 98octan fuel in my car anyhow... Goes much faster that way.