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Alright,
This is rather long and I do apologize for that. I have decided to keep the ’92 head since it has already had some work done to it and the chamber modifications shouldn’t be too hard. Here is what I have so far. It is a bit rough and it is apparently a bit harder to cut a decent groove with a die grinder than I thought. These modifications added about 2cc to the volume of the combustion chamber but I should be able to get that back by taking about 0.017” off the head. Once I have it milled off I will blend it all together a bit better also so that the edges are more rounded.
Does anyone have any recommendations for compression ratio/cranking pressure for this engine? It is just a somewhat boring street driven car that will rarely see WOT and I am mostly concerned with mileage. I was thinking about having the compression be rather high so that part throttle would be better and then maybe have some sort of a throttle stop so that it doesn’t go into WOT. I would like to be able to run 87 octane crap gas but if 89 octane e10 would be better (mostly mileage again) then I would certainly run that. If I did end up needing to run 91 octane that would be OK as well, but I would rather not unless the mileage gain would offset the extra cost. Where I am now I can get e85 also, so a mix of that wouldn’t be out of the question although I am a little worried about it eating up components. I have run about 30% e85 and 70% 87 several times with no problems, not even a check engine light, although I have had the check engine light come on with slightly higher amounts of e85. In other words, I would like to stick with using crap gas unless the benefit from using the higher octane outweighs the extra cost. I was also thinking that the option of using the higher octane would be a good buffer incase it didn’t work with the lower octane fuel or if I did have a throttle stop of some sort then I could remove it if I wanted to run the higher octane for more power. With 9.5:1 compression the cranking pressure was 180psi on a cold cylinder.
Here is some info for the engine:
*Stock replacement camshaft: *Duration at 0.050” lift 214deg intake and exhaust
*120deg lobe separation angle (yes, 120deg and no it’s not a turbo)
*Max lift both intake and exhaust is about 0.4”
Unfortunately I am not sure how it is installed in stock form, I should obviously measure it but I have not.
*Intake valve diam=1.646” (I also have a 1.69” valve, stock ’91, that I am thinking about using)
*Exhaust valve diam.=1.44”
*Bore=3.406”
*Stroke=3.386”
*Rod length=5.6”
*Piston to head clearance=0.038”
*Pretty much everything coated with a thermal barrier coating (chamber, pistons, valves ports)
*Stock TBI
The fire ring in the head gasket didn’t break (unlike the first one I blew on a completely stock engine several years ago), it looked like it just was letting gas go over the top of it. Any thoughts as to why this might happen (improper torque, thin casting, weak bolts, detonation, too high cylinder pressure, over advanced ignition timing……). I don’t think I have much of a problem with engine knock, be it from detonation or pre-ignition, but I do have an automatic (ouch, stop hitting me, I’d rather have a manual) and at low speeds the torque converter locks up and the RPMs drop too low (close to 1500RPM or so) and it will knock under load. If I drive it I make sure that it doesn’t do this by down-shifting but I cannot guarantee that it is always kept out of this condition. This is the only thing out of the ordinary that I can think of that would have caused the failure.
If anyone would like to know anything else feel free to ask.
Thanks again for all the info,
Howard
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