By Nikolaj (130.161.173.62) on Monday, October 08, 2001 - 07:06 am:

I am now in the process of rebuilding an EN(4) engine with my EB3 exhaust valves. Reason for this is they are flat and look like they create the better flow...(the heads look the same). This engine had a stock CR of 8,4. Different from the normal EN (8,7). Now I am figuring the valves I will use will decrease compression cause they don't stick out as much.. I now figure this must be the only reason for the slight increase in compression, but I am left wondering how an EN1 could have a CR of 8,7??? Are there things I can't see or measure that make that difference?? I am now getting my head shaved for insurance of no compression-loss!

OK, the thing that bugs me is this: When I asked for the valve-guide clearance at the Honda dealer they told me it was 0.20 and 0.25 mm. The cam this engine uses has the same lift, but a longer duration (it says R2, and yes it's a little lumpier). Comparing to the original EB values (0.13 mm) this seems to be counteracting whatever the cam is for, which is longer duration. To my logic my valves will even have less lift now!! But could it be the cam gives longer duration but less lift?? Or are the guides and that whole bridge they are on designed slightly different in the EN?
So what should I do?? Does anyone know the clearance for a RS?? I am suspecting the RS and 1.3S cam are one and the same...
Anyone with anything to say would be greatly appreciated..

By Charles (152.91.9.43) on Monday, October 08, 2001 - 10:45 pm:

The valves will have the same amount of lift no matter how much they stick out, remember lift is how far they rise off the seat, not how far they project into the combustion chamber.

Basically the lighter the valve the better for high revs, and the more tulip shaped the better the flow. Race engines tend to run a bit more clarance than street motors but that is up to you.

If it were me I'd cc the combustion chamber before putting it back together so you know exactly what the static compression is.

By Nikolaj (130.161.173.72) on Tuesday, October 09, 2001 - 03:45 am:

Charles,
They are both the same weight, but the tulip ones stick out into the combustion chamber more... In my mind I picture the incoming fuel kind of being blocked by this, but then again I've heard it may create a better whirl around the outgoing valve. It is not the reason I think the gaps should be different, but I figure since the cam has the same lift but is lumpier, the gap should be the same for any advantage over the stock cam.
It is all very interesting, and this is my first "head-job". I pick up my shaved head tommorow, along with my lighter flywheel. All gaskets and rings are new. I'll have the bigger exhaust (still have to work on it) so I'm kind of stoked to put it all together again. This will probably be my biggest improvement yet...
I'll go for something like .18 and .20 mm first.

By Charles (152.91.9.43) on Tuesday, October 09, 2001 - 08:18 pm:

I would stick to the EN ones. They will flow better even though they look like they take up to much of the port space, they basically guide the air into the combustion chamber through laminar flow, the flatter ones have more turbulence and therefore less air gets in. Look at a nice aerodynamic car or plane cutting through the air compared with a blunt nosed bus or truck. Imagine that the front of the vehicle is the valve which the air must get around. A trick to getting a bit more air in is to give the valves a backcut on the other side to the seat. Valve tricks cn give heaps of gains for little work.

It'll also keep your compression up without messing up the shape of your combustion chambers and throwing out your cam timing (which shaving the head and decking the block will do).

By errol (64.12.107.166) on Thursday, October 11, 2001 - 04:38 am:

AS Charles suggests, the 'tulip' shape is better, but what may throw u off could be the 'margin' or the thickness from the 45deg. seat on the valve to the bottom or what faces the piston. If the valve has been cut several times or just been slapping the seat for 20xx years they tend to get thinner (just slightly) and it appears to be 'sunk' in the head. Like Charles said, CC the head (as close as you can)

By Nikolaj (195.240.207.114) on Thursday, October 11, 2001 - 10:27 am:

I take it I must CC the head with some liquid, hoping it does not leak through the valves...
Thanks for all the valve-info, I will probably go back to using the original (damn, I grinded the EB ones into the head). My flywheel is now 3.88 kg which is almost 50% less than stock. This may seem like too much, but a friend of mine did about the same, and I thought his car's idle is good enough for me!! We'll have to see how she'll run... I shaved my head to those indicators which is max. I have done some reckoning on the subject, and I figure my CR will be around 9, coming from 8.4(EN4).... Now Charles how come the standard EN has a compression of 8.7?? Did they flatten the head less for the EN4, giving it less CR, so the thing would last longer?? And isn't the CC of my chamber the engine's CC's divided by 4 (cilinders) divided by the CR... It makes sense, because the EN 1335/4/8.7 = 38.36cc, while the EB 1238/4/8.1 = 38.21cc, about the same... But for EN4 this goes 1335/4/8.4 = 39.73cc
Charles, where do all these differences come from? Is it simply the hight of the combustion chamber, or are they actually different in shape (I can't see it!). I have always heard that the EB has a better breathing head, but the only difference I can discover is the exhaust valves (this lead me into using the EB3's). The ports seem to be the same diameter as well.
So finally, if the EB3 head breathes better,...why? I figure my next engine will be the EN, with EB3 head, instead of going EN all together... I hate the idea of some jerk being able to tell it's a 1300...
Oh yeah, what is the max CR you can advise for a lasting engine??
Thanks guys...