Timing on High Compression NA 240

[KA-T_240]

So I built an engine for my 91 and used left over parts from several projects. 90.5mm sohc pistons, I would guess that would make it 11.5-1 give or take. stock thickness cometic with the larger id for the .60 over pistons, arp head studs, stock cams. Intake, header, no cat, 2.5 in exhaust.

Started the car and runs great, took it for a drive and could hear it ping when just srating to accelerate then went away. tweeked the timing back to 22 btdc and then 24 now it rattles like a diesel when accelerating in 2nd from 5mph. reset timing again to 18. sound beter. advanced it 1/8 inch at a time till no ping on 91. I suppose if I would slow the idle down now to 700 and throw a light on it I would be about 12-13 btdc.

So I have about 35 miles intown driving and it runs great had it up around 50-55 and up to around 4500 rpm and even lugged it down in 5th a little.

So what long term or short term problems am I going to run into with the timing set like this? Car is also hella rich and noticed it more and more. Put 33miles on tonight, had some idle time, and went through not quiet a tank of gas, I guess I have not put some in so I do not know how much its sucking.

[infinitexsound]

i guess install a wideband to find out what ur real a/f ratio is at... i dont see anything seriously happening to your engine other then ur valves will turn white, and ur mpg will be really low maybe... are you running a performance cam to really require the necessity to mess with timing?

[S14DB]

He's talking ignition timing not cam timing.

You are prolly gonna need some better gas 93+. Wideband, knock sensor and something to adjust ignition advance not base timing. More than likely standalone.

[gotta240]

Hmmm. i was under the impression that the 91 sohc piston upgrade should run fine without major mods(ie:standalone). The other mods you did shouldn't really affect the way it runs either.

[98s14inaz]

He went from 9.5:1 to 11.5:1, he needs tuning. You can't just dial back the timing and think that is ok. It reminds me of the ka-t guys that retard the timing instead of getting a good tune.

You might be able to get a way with a wideband and safc. I have a friend on another forum that is doing a similar build except he is using 370cc injectors, z32 mafs, and ecu tuning...his car will likely never see the street though. Good luck with your project.

[KA-T_240]

High compression in a KA will not ever need the 370cc injectors or the Z32 maf. People have pulled low 200whp with boost on stock injectors.

Adding to subtracting fuel(AFC) isn't going to make a huge differnce is the fact of the timing. It will make the AF/R better.

I do not have 93 octane available in this area. 91 is what we got.


The gas in the tank is not the best at the moment. mix of OLD nasty gas, 87 octane(my dad put 8 gallons in when we 1st got it going:( ) and 91 onctane

[gotta240]

haha. you just answered your own question. You're trying to run a high comp motor on water sludge.

[crzycav86]

you're gonna have to retard that thing hardcore if you don't want it to ping on shitty gas.

you started out at 22? stock is 20! 18 is getting better, but you might need more.

also, you're probably not running rich if the engine was running fine before the new pistons. you might think it's rich because of misfiring and bogging. it's the timing.

[infinitexsound]

read the fine print.... what kind of cams are u running...? when running a performance cam you need to mess with ignition and cam timing... to get it ti idle nicely.. would help if you listed the cam specs.

[KA-T_240]

you're gonna have to retard that thing hardcore if you don't want it to ping on shitty gas.

you started out at 22? stock is 20! 18 is getting better, but you might need more.

also, you're probably not running rich if the engine was running fine before the new pistons. you might think it's rich because of misfiring and bogging. it's the timing.


If you would have finished reading that sentence. I said we got the pinging to go away at around 15deg. but went a bit more for safety till this nasty gas gets through the car.


read the fine print.... what kind of cams are u running...? when running a performance cam you need to mess with ignition and cam timing... to get it ti idle nicely.. would help if you listed the cam specs.

Re-read my post and then think about what you just asked. I listed that I am running stock cams. So........ I also said it idles just fine and drives just fine.

I am asking about long term affects of having timing like this. And what would cause it to be pretty rich.

[S14DB]

Long term effects are your pistons slowly being eaten away by detonation. You're more then likely "rich" because you are so retarded you aren't getting complete fuel burn. Real way to tell would be to see your EGT's.

Retarding the timing will do nothing but burn your exhaust valves and crack your header. Syphon out that shit gas and dump it in something that runs 87. Fill the tank up with at least 91.

If it was me I would fill up with 100R. Buy a Wideband and EGT. Then get that shit tuned.

[crzycav86]

You won't have any long-term effects if you use good gas.

The timing will have to remain retarded because the higher compression ratio will cause the charge to burn faster. In this case, retarded timing doesn't mean less power, or incomplete burn. That's just what the engine demands, based on the new burn rate.

I still don't understand why you think it's running rich though.

[KA-T_240]

Well, unless when i filled it up with premium it didn't fill up all the way its running rich. I will see what the MPG is after I drive it more. I am working on getting my buddies wideband, but its 70 miles away.

I guess it could be really lean. But, I guess it has not blown up yet.

[crzycav86]

you can check the plugs.

do a hard run, cut off the car, if you see black, then it's rich, if it's white, it's lean. if you see metal flakes, then you're detonating.

[gotta240]

I don't know why this thread is still going. You answered your own question in your second post. DRAIN THE FUCKING GAS... Fill with 91..re-evaluate the situation.

[KA-T_240]

Ya, but having some old gas in is not going to explain why I can not stand to drive the car across my tiny ass little town with out dying.

My dad is going to drive it for a while this weekend. He is not sick to begin with, and will drive it alot nicer then I will. Waiting for his thoughts on the smells of it.

[S14DB]

It's not so much the fact that it's old. But more that it's old 87 in a High Compression motor.