HELP! What on earth do I do with 13:1 compression?

[96CamrySport]

Starting a new post on my saga in hopes of attracting some help. So far:

1996 5sfe, 195k miles, head gasket leaked oil, so I bought a replacement head, performed a mild port and polish, ground away some valve shrouding, got the head decked .040", and installed with a 98 5s metal head gasket.

Problems - .040 is acceptable if you grind a LOT out of the combustion chamber. I didn't, due to a time crunch and, well...I was hurrying. Shame on me. Old combustion chamber was 49cc, new volume is 33.

Also, compressed height of factory fiber HG was 1.25mm, height of new gasket is around 1mm. That's probably worth another half compression point, at least.

The car does idle, but I'm not willing to rev it above 2000rpm right now, as the t-belt is slightly loose and I need to modify the tensioner to solve that problem. I did build the head with assembly lube and am running Castrol Syntec 5-30 (the BMW recommended variant)

so- How do I save this? I spent over 20 hours doing this swap, I think the engine will live, as peak cylinder pressures will be similar to 5-6 psi boost, and the fe heads don't breathe very well, which I think will help it live under higher loads. Clearly, I need to drain the tank and fill it with premium gas instead of the 87 octane, but what else? Can I pour some denatured ethanol into the fuel to increase knock resistance? I know I can do something with spark plugs but I'm not really familiar with where to go with them to adjust for a super high compression engine. I also can't really adjust timing, although I did slot out the distributor body in the hopes of making that work. I also intend to cap the vacuum line to the fuel pressure regulator to run a constant 45psi in the rail.


How can I ward off knock in this engine - this car is up for sale, and I need it to be reliable enough to sell. OR - does anyone want to buy a moderately modified 96 coupe?

[Luckynumber5]

You will need a thicker head gasket, the compression is way to high for pump gas. Ethanol is not a good solution, while ethanol is similar to 100+ octane gasoline mixes, it contains less chemical energy. You would need to run straight E85 with much larger injectors in order to get the added knock resistance. Just mixing it with gasoline will likely increase knock.

[96CamrySport]

Where does one get a thicker head gasket for the 5sfe? Can I just put two of them together (kidding, kidding).

Let me guess, mixing about 30% ethanol in would likely just result in less energetic fuel being injected, which would probably result in running leaner than the current fuel mapping unless bigger injectors were used. right? I considered the possibility but have no real numbers to back up any sort of calculations, which is why I asked.

Trouble is, I have no problem telling my customers exactly how much money they'll have to pay for me to fix their very expensive cars, but it's kind of hard for me to swallow the thought of tearing the head off again to fix my own problem on my own cheap car with my own unpaid money and time.
Makes me want to go and .

[96CamrySport]

update: I misread the compression gauge, it's 12:1. Since most bimmers run 185lbs in each cylinder, my coworker has assured me that it'll probably be ok on premium. I cruised around in it earlier, got it up to full operating temp, and it seems to drive ok. I didn't push it though because the torques strut is still off the car.

[96CamrySport]

[Eye8Pussies]

I'd say fill it with premium mixed with some race fuel if you're really paranoid

but for everyday driving, I'd really just click that ol' cap back a couple of notches and retard that timing a bit

[96CamrySport]

Originally Posted by Eye8Pussies

I'd say fill it with premium mixed with some race fuel if you're really paranoid

but for everyday driving, I'd really just click that ol' cap back a couple of notches and retard that timing a bit

computer controlled timing. I twisted the distributor and it didn't make an ounce of difference. Know how to force it to change timing?

in everyday driving it's actually doing ok. I haven't taken a WOT pull on it yet because the top timing cover and torque strut are still off, but I think it'll be ok. I'm just gonna run premium, would still like to be able to adjust timing. any suggestions?

[Eye8Pussies]

ah, forgot that it's an obdII....you're one year too late for obdI and it's simplicity in this situation


and you can pick up a used aem fic for around 200bucks or so if you're lucky and that could solve the problem- otherwise, not much other choice.


Or, if you're paranoid, just pull the knock sensor wire and put the car into limp mode

or maybe you can trick the coolant temp sensor using resistors to make the ecu think that the car is always cold so that it adds fuel...not sure if it also pulls timing then too though

[sc2dave]

good water injection unit with alcohol.

[Eye8Pussies]

Meth injection even better idea